Curtiss XP-14

Curtiss XP-14

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Curtiss XP-14

The Curtiss XP-14 was to have been a fighter based around the Curtiss H-1640 Chieftain 12-cylinder air cooled double-row inline engine. Three prototypes of a Curtiss Hawk biplane powered by the Chieftain were ordered as the XP-11, but before they could be built it became clear that the engine had failed. The three XP-11s were completed with different engines, and the XP-14 was cancelled.


Good Morning—Another week of our lives has past and it’s time to talk about airplanes. The Curtiss C-46 Commando is an airplane that was overshadowed by the the DC-3 and has been large ly forgotten however, I have not forgotten and this week I want to reintroduce you to an airplane that made a lot of history and is still making money for commercial operators around the world.

The C-46 Commando – Enjoy………………………

The Curtiss C-46 Commando

The Curtiss Commando began life as a design for a 36-seat commercial airliner with a pressurized cabin, designated the “CW-20”, with development initiated by Curtiss in 1936. The CW-20 was intended to provide a larger, more capable competitor to the Douglas DC-3, which was then entering service. The CW-20 featured a roomy “Double Bubble” fuselage, with a cross-section in the form of two circle segments mated together, top and bottom. This configuration provided large internal volume and the structural strength to support pressurization. The junction between the small segment and the larger top segment was faired over to improve aerodynamics. The CW-20 also featured a low wing with twin radial engines, twin tailfins, and fully retractable tailwheel landing gear — the single-wheel main gear retracting into the engine nacelles. The cockpit windscreen was flush with the fuselage contour, giving the aircraft a whale-like appearance.

Flight tests quickly showed that the twin-fin tail left much to be desired, and it was replaced by a conventional tail arrangement with a single tailfin. The modified aircraft, now known as the “CW-20A”, was demonstrated to airlines, and there were some interest in the type. However, in September 1940 the US Army Air Corps (USAAC), implementing an increasingly frantic program to prepare for war, ordered 200 modified “CW-20Bs” with the military designation of “C-46”. Production began at the Curtiss plant in Buffalo, New York, with the first “Commando” delivered to the US Army Air Forces (which had superseded the Air Corps in the meantime) on 12 July 1942. With a war on, Curtiss focused on military production, and commercial production was out of the question for the duration.

Adapting the CW-20 to military service as the C-46 Commando needed few changes. The first 25 aircraft, designated C-46, were built essentially to the original specifications. The Pratt & Whitney R-2800 engines were replaced by Wright Double Cyclones and plans to provide pressurization were abandoned, as well as a number of minor changes were incorporated.

The Commando initially went into service on the South Atlantic ferry route, and would also participate as a glider tug in the Rhine crossings in March 1945. However, due to its long range, it was primarily used in the Pacific and China-Burma-India (CBI) theaters, becoming the primary cargo lifter for ferrying supplies from India to China over “the Hump”, the Himalaya Mountains, after the Japanese shut down the Burma Road in 1943. Commandos of Colonel Edward H. Alexander’s “India-China Wing” of the USAAF Air Transport Command flew from primitive airstrips in the Indian state of Assam, climbing with overload cargoes to clear ridges from 3.7 to 4.3 kilometers (12,000 to 14,000 feet) high, to land at Chunking and drop off their loads for USAAF General Claire Chennault’s 14th Air Force and Nationalist Chinese forces.

The loss rate of the C-46 was high and it had a mixed reputation with aircrews. Partly the problem was the fact that environment was very harsh, operating conditions were difficult, and Japanese fighters were an occasional threat. However, stories still circulate that the C-46 also suffered from a large number of engineering and manufacturing faults, in particular a leaky hydraulic system. Crews were said to take a barrel of hydraulic fluid along on flights to make sure that the hydraulic systems were topped off before they were used. There was also apparently a fuel leak problem that took a long time to work out, with aircraft being lost in midair explosions at a steady rate until it was.

It doesn’t appear that the C-46 was an inherently bad aircraft, it was just rushed into service without the level of qualification that it would have been run through in peacetime, and it took a lot of work to get the bugs fixed. The aircraft’s detractors called it the “Curtiss Calamity” and the “Leaky Tiki”, though it was also more affectionately named “Dumbo”, after the flying baby elephant in Walt Disney’s 1941 animated movie.

The airlift from India to China, “Flying the Hump,” was the real hour of glory for the Curtiss C-46 Commando. The following is from an article that I found on the web:

In Feb. 1942 President Roosevelt ordered General Arnold to open a supply line across the Himalayas in support of General Chiang Kai-Shek (and his air adviser Claire L. Chennault) at a time when the Japanese offensive was at its peak. Rangoon fell in March 1942 and this cut off the supply via the Burma Road. The initial 26 aircraft for this project were 10 ex-airline DC-3s and some C-53s. The flights were started in late 1942 by the China National Aviation Corporation (CNAC) and the USAAF. By December of that year some 62 DC-3s of various types were involved, but already 15 had been destroyed. Conditions were poor at the airfields serving the China airlift, in September 1942, e.g. fuel was still being pumped by hand from drums.

Chennault, a retired USAAC Colonel who had become special advisor to the Chinese Air Force in 1937, formed the American Volunteer Group (AVG) with 100 US-financed P-40Bs and began operations against the Japanese from bases at Kunming, the first successes recorded on 20 December 1941. In fact, this was the only air defense China had to offer at that time. The AVG ceased to exist on 30 June, 1942. The aircraft were taken over by the 23rd Fighter Group, developing into the China Air Task Force (under Chennault, recalled to active service as a General). Because the Japanese controlled the Chinese coast and the fall of Burma closed off the last remaining supply routes over the ground, all supplies (including aviation fuel!) had to be airlifted in. Existing numbers of aircraft had to be increased to be at all effective.

In early 1943 General Arnold ordered to build up strength to 112 C-47s and 12 C-87s (converted B-24s). Enlarging the effort, they encountered problems of pilot inexperience, weather personnel problems, problems in communications, engineering and maintenance, lack of radio aids and direction finders…. The airfields were not complete and monsoon rains (beginning in June and lasting over 5 months!) played havoc with the facilities. Colonel Alexander, CO of the India-China Wing declared the C-47 unsuitable and requested C-46s. By 15 April 1943, 30 C-46s were delivered, replacing an equal amount of C-47s. More were to follow.

The direct distance between the Assam bases and Kunming was only some 500 miles, but the route is the most rugged imaginable. Chabua, on the banks of the Bhramaputra River, is only 90 ft above sea level but the Valley Walls climb to 10.000 ft. in the Patkai range. A series of ridges rise to a height of 14.000 ft and over, while Kunming itself sits at 6.200 ft. elevation. The icing level is at about 12.000 ft. and the flying was mostly done on instruments in foul weather: constant cloud cover, frequent violent thunderstorms, and tricky wind currents over the mountains…. Men and machines were put through extremes here, pushing the limits!
The service ceiling of the C-46 stood at 16.000 ft., above which it is not completely stable. The Hump was flown at 20.000 or 22.000 ft. eastbound and 21.000 ft. westbound…! As the C-46 cannot climb at 500 ft. per minute, it was necessary to climb near the base to gain sufficient altitude for the crossing.

During the dry season (winter) there was the danger of attacks by the Japanese fighters, but the biggest enemy was the weather. Carburetor icing was encountered, but this was a relatively well understood phenomenon. But there was more… The engines were susceptible to vapor lock at altitude, but as long as fuel was fed from one tank, there was no problem. On attempting to change tanks at altitude, the low atmospheric pressure and the suction of the engine driven pump caused vaporization of the fuel in the line, leading to the engine stopping… The engine could usually be restarted at lower altitude, but over the mountains there was no room to maneuver. The solution proved to be an electrically driven fuel pump inside each tank.

The early C-46s (as flown by Eastern Airlines) were fitted with 3-bladed Hamilton propellers. Fairly early in production these were replaced by the 4-bladed Curtiss electrically operated props. An electric motor was used to alter the angle of the blades. With a little corrosion, the electric contact could be lost, resulting in the prop moving into fine pitch and the engine overspeeding. This was particularly serious on takeoff from high altitude fields. Like Kunming. With gross weights above those initially intended by the designers….! The cumulative effect of the problems encountered was such that by November 1943, some 721 modifications had been ordered. The flow of new C-46s was stopped for a time while a modification program was put into effect. In 1942, when the airlift was first planned, a target of 7.500 tons per month was set, but this proved to be overoptimistic. This goal was not reached till October 1943. A typical payload for a flight consisted of 23 55-gallon steel drums of aviation fuel and 1 1/2 tons of bomb fuses. Other items carried included earth moving equipment aircraft engines and other spares. Little was carried out of China. From 8 February 1944, 25 C-46s were diverted from their original tasks and were seconded to supplement Troop Carrier Command aircraft for a few days of supply droppings in the Arakan region to help British troops to stem a northward Japanese advance the 22.000 troops were down to two days supplies. Assignments like these happened quite often. Sometimes the C-46s played their part in evacuations. While the Hump operation progressed, statistics showed impressive figures: in July 1944 19.050 tons was carried, in December 31.935 tons, by 250 aircraft (daily average availability) in 7.612 trips…. Kunming could not handle all this and Luliang (60 miles East) became an India-China Division terminal in August 1944.

The total number of aircraft assigned to the Hump continued to rise to a maximum of 332 in July 1945, during which 71.042 tons were carried. At present day this would take 536 sorties by C-5 Galaxies…! Personnel involved peaked at 22.359.
By 1945 the tide of war changed and other routes became available thus the C-54 could now could be put to use (it lacked the ceiling of the C-46, but on the routes now available it could carry 1.7 times the payload of the C-46).

The Hump was officially closed on 30 November 1945.

Another interesting article that I found on “Flying the Hump” was located on CNACs web page and is a reprint of an article f rom The Wall Street Journal on Saturday, February 25, 2012. You may have difficulty reading this but if you click on the image itself it will take you to the actual web location.

The web sites that I used are listed below, and if time permits, do some research on your own and let’s see if we can bring history’s forgotten airplane back in to the mainstream.

Have a good weekend and I hope to see you back here next Friday when we will be talking about……………. Take care, fly safe, and be safe.


After the P-40 was successfully introduced in 1940 , Glenn Curtiss tried to design an improved version. The proposal, for which the USAAC was also able to arouse interest , concerned a version of the P-40 with modified laminar wings, reinforced armament and the Continental XIV-1430-3 engine. The project was named XP-53 or Model 88. In October 1940, the order to build two prototypes was received, but development was slow. A short time later the USAAC wanted to test a cell with a Rolls-Royce-Merlin engine , whereupon the second prototype was canceled and a new order was placed for the execution with Merlin as XP-60 or Model 90.

This machine had development priority and so the prototype was able to fly for the first time on September 18, 1941. With the weaker licensed engine Allison V-1710-75 as a specification, Curtiss received the order in October 1941 to build 1,950 series P-60A machines. Curtiss proved, however, that the required performance could not be achieved with the specified engine, whereupon the order was canceled again. Instead, in January 1942, the order was placed to build three prototypes with different engines: XP-60A (Model 95A) with Allison V-1710-75 with General Electric turbocharger, XP-60B (Model 95B) with the same engine, but Wright turbocharged and XP-60C (Model 95C) with Chrysler XIV-2220. Since Curtiss was already aware of the development problems with the Chrysler engine, the company proposed the Pratt & Whitney R-2800 Double Wasp with counter-rotating propellers as an alternative drive, which the USAAF accepted.

Since no engine with a suitable reduction gear was available when the airframe was completed, an R-2800-10 with a four-blade propeller was installed and the resulting machine was called the XP-60E (model 95D) the name XP-60D was given to the first prototype, which has since been re-engineered to a Merlin 61. The planned XP-60 with R-2800-53 and counter-rotating propellers finally flew on January 27, 1943, while the first flight of the XP-60E was further delayed due to problems with the engine installation. At the end of 1943, the XP-53 was unexpectedly requested for troop testing and only completed its maiden flight here however, the performance was so disappointing that the USAAF lost all interest in the pattern. In 1944 there was still a single YP-60E flying with the R-2800-13, but development was abandoned a short time later.

Curtiss H-1640 Chieftain Aircraft Engine

In April 1926 the Curtiss Aeroplane and Motor Company initiated a design study for a 600 hp (447 kW), air-cooled aircraft engine. The engine was to have minimal frontal area while keeping its length as short as possible. Configurations that were considered but discarded were a 9-cylinder single-row radial, a 14-cylinder two-row radial, a 12-cylinder Vee, and a 16-cylinder X. The selected design was a rather unusual 12-cylinder engine that Curtiss referred to as a “hexagon” configuration. This engine was built as the Curtiss H-1640 Chieftain.

The Curtiss H-1640 Chieftain “hexagon” or “inline-radial” engine. The image on the left was taken in 1927 note “Curtiss Hexagon” is written on the valve covers. In front of each cylinder pair is the housing for the vertical shaft that drove the overhead camshafts. The image on the right was taken in 1932 and shows a more refined engine with “Curtiss Chieftain” written on the valve covers. Note the additional cooling fins surrounding the spark plugs. In both images, the baffle at the rear of each exhaust Vee forced cooling air into the intake Vee.

The Curtiss H-1640 was designed by Arthur Leak and Arthur Nutt. The Chieftain’s “hexagon” design was a combination of a radial and Vee engine. The intent was to combine the strengths of both engine configurations: the light and short features of a conventional radial with the narrow and high rpm (for the time) of a conventional Vee engine.

The Chieftain was arranged as if it were a 12-cylinder Vee engine cut into three sections, each being a four-cylinder Vee. The Vee engine sections were then positioned in a radial form 120 degrees apart (each cylinder bank being 60 degrees apart). The end result was a two-row, twelve-cylinder, inline radial engine. The H-1640 resembled a conventional radial engine except that the second cylinder row was directly behind the first.

An engine installation comparison of the air cooled Chieftain-powered XO-18 Falcon at left and a liquid-cooled D-12-powered Falcon at right. Note that while the Chieftain is a wider engine, it blends well with the fuselage and is shorter and not as tall as the Curtiss D-12.

Each four-cylinder Vee section had the cylinder exhaust ports on the inside of the Vee and the intake ports on the outside. Each inline cylinder pair had its own intake runner and dual-overhead camshafts that were enclosed in a common valve cover. The camshafts were driven via a single vertical shaft from the front of the engine. There were four valves per cylinder.

Cooling air was directed through each four-cylinder section’s exhaust Vee here it met a baffle fitted to the rear of the engine and attached to the cowling. This baffle deflected the air and forced it to flow between the inline cylinders and behind the rear cylinder. The air then flowed into the intake Vee that was blocked off at the front. The air exited the cowling via louvers over the intake Vee.

The Curtiss O-1B Falcon that was redesignated XO-18 while it served as the test-bed for the Chieftain engine. Note the exposed valve covers and the exhaust stacks protruding through the engine cowling.

The pistons were aluminum and operated in steel cylinder barrels that were screwed and shrunk into cast aluminum cylinders with integral cooling fins. From U.S. patent 1,962,246 filed by Leak in 1931, it appears that the Chieftain’s connecting rods consisted of two halves that were bolted together. Each half was made up of one master rod and two articulating rods.

The H-1640 Chieftain had a bore of 5.625 in (143 mm) and a stroke of 5.5 in (140 mm), giving a total displacement of 1,640 cu in (26.9 L). The engine’s maximum diameter was 45.25 in (1.15 m). However, a special cowling was used, cut to allow the valve covers and exhaust stacks to protrude through, reducing the diameter of the cowling to 39 in (0.99 m). The engine was 52.3 in (1.33 m) long and weighed 900 lb (408 kg). The Chieftain had a 5.2 to 1 compression ratio and was rated at 600 hp (447 kW) at 2,200 rpm but developed 615 hp (459 kW). When the engine was pressed to 2,330 rpm, it produced 653 hp (487 kW). It was equipped with a centrifugal-type supercharger that allowed the engine to maintain sea-level power up to 12,000 ft (3,658 m). All Chieftain engines built were direct drive but geared versions had been planned. In addition, some design work on a four-row, 24-cylinder version of 1,200 hp (895 kW) had been done.

Side view of the Thomas-Morse XP-13 Viper with the Curtiss Chieftain engine and revised cowl. Not the louvers for the cooling air to exit the cowling.

Because the engine had an even number of cylinders per each row, a unique firing order was developed that alternated between the front and rear rows. When the engine was viewed from the rear, the cylinders were numbered starting with the cylinder bank at the 9 o’clock position and proceeding clockwise around the engine. The rear cylinder row had odd numbers, and the front cylinder row was even so that the rear cylinder of the cylinder bank at 9 o’clock was number 1 and the front was number 2. The firing order was initially 1, 10, 5, 7, 4, 11, 8, 3, 12, 2, 9, 6 but was later changed to 1, 10, 5, 2, 9, 11, 8, 3, 12, 7, 4, 6 in an effort to smooth out the engine.

The H-1640 Chieftain was first run in 1927 and flown in a modified Curtiss O-1B Falcon, redesignated XO-18, in April 1928. The Chieftain-powered test-bed aircraft was found to out-climb and have a higher ceiling than the standard liquid-cooled Curtiss D-12-powered Falcon. In addition, the top-speed of the two aircraft was the same, which was unheard of for that time period when liquid-cooled aircraft were faster than their air-cooled counterparts. However, the engine suffered cooling issues, and the aircraft was modified back to an O-1B in July 1930.

A comparison of the original cowling on the XP-13 at left and the updated cowling at right. The front of the cowling has been extended and angled out. The block-off plates in between the openings have been angled to funnel air into the enlarged openings.

Thomas-Morse also responded to the Army’s interest in using the Curtiss H-1640. The company’s Viper fighter prototype was built to use the Chieftain engine. This aircraft was tested at Wright Field in June 1929 and given the designation XP-13. Engine overheating was encountered, and a revised cowling was tried in an effort to provide adequate cooling for the H-1640. The new cowling had enlarged openings, and the blocked off sections were angled to force more air into the openings. However, over-heating persisted. The XP-13 was tested until September 1930, when a Pratt & Whitney R-1340C engine was installed and the aircraft redesignated XP-13A. Even though this engine was not as powerful, it was lighter and did not suffer the cooling issues present with the Chieftain. The XP-13A was found to be 15 mph (24 km/h) faster than the Chieftain-powered XP-13. Curtiss had planned to produce the Viper under the designation XP-14, but the H-1640 engine was lacking support so no aircraft were built.

Another Chieftain was installed in the Navy’s second Curtiss XF8C-1 prototype in 1930. The H-1640-powered aircraft was known as the Curtiss XOC3. It too suffered from engine over-heating. The Chieftain engine remained installed in the XOC3 until the aircraft was removed from the Navy’s inventory in April 1932.

Detail view of the revised cowling on the Chieftain-powered Thomas-Morse XP-13. The image on the left illustrates the angle of the block-off plates. Note the six, instead of eight, exhaust stacks of the upper cylinders. The last two stacks are combined and exit from a single stack aft of the cowling.

In October 1928, the Army ordered three Curtiss P-6 Hawk aircraft to be powered by the H-1640 engine and designated them XP-11. However, shortly after the order was placed, the engine’s cooling trouble became known and the engine’s development ceased. The aircraft were never built with the Chieftain engine.

A total of eight H-1640 engines were made with six going to the Air Corps and two to the Navy. While the Chieftain’s design may have been problematic, the event that directly led to its lack of support and ultimate abandonment was the merger of Curtiss Aeroplane and Motor Company with Wright Aeronautical in July 1929. After the merger, the liquid-cooled engines were provided by Curtiss and the air-cooled engines from Wright. There was no longer a need for the Chieftain, an air-cooled engine of rather dubious design. However, the concept of a hexagonal engine would be revisited with the Wright H-2120, and other hexagonal engines include the SNCM 137, the Junkers Jumo 222, and the Dobrynin series of aircraft engines..

Reportedly, at least one Curtiss H-1640 Chieftain survives and is in storage at the National Air and Space Museum’s Garber Facility in Silver Hill, Maryland.

The second Curtiss XF8C-1 re-engined with the H-1640 Chieftain and redesignated XOC3.


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Curtiss XP-14 - History

The Last Flying Curtiss Turboelectric Propeller
by Tom Fey
Published 20 Aug 2019 Revised 25 Aug 2019

The Curtiss / Curtiss-Wright Corporation manufactured airplane propellers since the early days of aviation and well into the 1950s. The culmination of their engineering prowess were the 19 foot diameter, 3 blade pusher props on the B-36, the 16 foot contra-rotating propellers that dead-lifted the Lockheed XFY-1 vertically into history, and the subject of this article, the 18 foot diameter 3 blade Turboelectric propeller used predominantly on the Douglas C-133 Loadmaster. The C-133A/B (50 built), YC-121F (2 built), the R7V-2 (2 built), YC-97J (2 built), and YC-124B (1 built) all used the Pratt & Whitney T34 engine. Only the T406 engines in the Osprey, the TP400 engines in the A400M, and Kuznetsov NK-12 engines in the Tu-95 are more powerful than this relic from the 1950s. The majority of T34-powered aircraft used the Curtiss Turboelectric propeller however the YC-121F used the Hamilton-Standard A-3470-5

The Douglas C-133A/B heavy transport is covered in remarkable detail in the 420 page book Remembering and Unsung Giant by Cal Taylor. The book chronicles the testing, the adoption into service in 1956 carrying Titan ICBM missile assemblies, ship propellers and drive shafts, Apollo space capsules, five UH-1 Huey helicopters per load to Vietnam, and other outsize cargo for the US military. The C-133 fleet was retired from military service 15 years later. The book is very highly recommended. I never thought a transport aircraft could be so fascinating (Fig01).

This article will focus on the Curtiss CT735S (Curtiss &ndash Turboprop &ndash SAE #70 spline prop shaft &ndash 3 blade &ndash # 5 blade shank size &ndash Steel) series of turboelectric propellers used on the C-133. Amazingly, the final flight of a Curtiss Turboelectric propeller was in 2008, but more on that later. Since propeller performance and design are intricately linked to the power plant and the performance envelope of the aircraft, some background on the T34 is in order.

Fig01. C-133A, 62014 over San Francisco, April 1959 (Cal Taylor/USAF/Douglas) Fig02. Pratt & Whitney T34 Turboshaft Engine. The engine was 33.75 inches in diameter, 157.4 inches (13 feet) long, and weighed approximately 2,590 lb dry.

The T34 would make fascinating article in and of itself (Fig02). It was a 157.4 inch long, 2,564 lb, single shaft engine with a 13-stage axial flow compressor that achieved a 6 to 1 compression ratio while flowing 100 lb of air per second. The compressor was mated to a 3-stage turbine with shrouded blades, which in turn drove a compound epicyclic gearbox with a reduction ration of 11 to 1. The engine started out at 5,700 ESHP (equivalent shaft horsepower, which is the sum of shaft horsepower plus residual exhaust thrust mathematically converted to power), and eventually 6,500 to 7,500 (wet) ESHP. The engine never quite achieved the power that was expected in the C-133 design, and this produced an avalanche of changes to the airframe that would come back to complicate the working life of the aircraft. The engine, once early reduction gear problems due to aeration of the lubricating oil were partially corrected, was well behaved and quite reliable in service.

While the engineering required to efficiently convert 3200+ hp from a piston R-4360 into thrust are considerable, it is significantly more complex to control the 6500+ hp of the T34. The power characteristics of the turboshaft engine are very different from reciprocating engines. For efficiency and to enable rapid changes in power without delays due to &ldquospooling up&rdquo of the power turbine, turboshaft engines are run at constant speed and within a very narrow rpm window. Fabulously complex fuel controls (Fig03) are integrated with rapid-acting propeller pitch controls to maintain turbine speed within a 3% to 6% range, regardless of power. This was still the age of aneroids, bellcranks, cams, levers, diaphragms, balance tubes, pilot valves, gear trains, lead screws, and analog wizardry.

In flight, the T34 turbine speeds were maintained between 10,670 rpm (97.7%) and 11,000 rpm (100%), resulting in prop speeds of 970 to 1,000 rpm. One thousand one hundred two rpm was considered propeller overspeed. Fuel flow for each engine was between 700 and 4,250 lb/hr (approximately 108 to 654 gallons/hour), and the aircraft held an astonishing 118,534 lb of fuel (18,236 gallons). Oil capacity was 15 gallons per engine, however oil consumption was a paltry 0.5 lb (approximately 9 fluid ounces) per hour per engine.

The narrow rpm range in flight is required because if the turbine speed sags too low, engine power and temperatures can fall outside the desired limits and cause potentially unrecoverable power loss, damage to the engine, and jeopardize flight safety. Allowing the RPM to exceed the upper limits can result in catastrophic failure (thrown blades) of the propeller or power turbine assemblies, both of which operate very near the limits of the metallurgic science of their times.

Flight conditions and the constant-speed nature of the turboshaft engine demands precise, rapid control of the propeller and fuel into the engine. If descending flight caused the prop to start to drive the turbine, a redundant negative torque control (NTC) system would kick in at 102.3% rpm to increase the pitch of the blades, reducing the windmilling effect, and get the rpms back to 100%. Remember, when the prop increases one rpm, the turbine will increase 11 rpm, a ratio that can rapidly put the turbine blades at risk of failure. The permissible exhaust gas temperature range was 400°C (752°F) to 505°C (941°F) for continuous power, not to exceed 760°C (1,400°F).

The NTC signal is generated by the reduction ring gear at the front of the engine. When the engine is driving the propeller, the angled teeth on the ring gear move the gear aft, and this movement is detected and quantified by the torquemeter to measure power output. When the propeller tries to drive the engine, the ring gear slides forward, mechanically driving a plunger rod that activates a switch to energize the Increase Pitch clutch. Once the engine returns to driving the propeller, the plunger rod retracts, and propeller control goes back to the normal governing circuit (Fig 3a).

For the T34 in the C-133, &ldquolow idle&rdquo on the ground was 6,000 rpm (55.5%) to decrease noise, and &ldquohigh idle&rdquo was 10,000 rpm (90.9%) to allow taxiing. The engines actually ran hotter internally at Low Ground Idle than at High Ground Idle, so 2 minutes of the latter was required before shutting down to prevent turbine blade rubbing. Of interest is the diagram from the C-133 pilot&rsquos manual showing the prop/jet blast from the C-133 at Low Ground Idle and full power, as well as the Danger Zones for &ldquoturbine disintegration and propellers&rdquo. Even at Low Ground Idle, a wind of 84 knots at 250° F occurs just aft of the wing. And that doesn&rsquot count the port side Ground Turbine Unit (GTU) exhaust of 175 knots at 350°F! Everything about this plane was big (Fig04).

Fig03. Fuel control for the T34 turboshaft engine used in the Douglas C-133. Fig03a. Negative Torque Control (NTC) actuator on the T34 nose case. When the propeller starts to drive the engine, the ring gear translates forward on the spline, driving the plunger rod forward, which energizes the Increase Pitch clutch. Fig04. Danger Area diagram specifying downstream temperature, wind speed, and component failure threats from the C-133 aircraft during ground operations.

The 3 blade CT735S-B319 Turboelectric propellers were 18 feet in diameter and weighed 1,325 lb per unit (Fig05). The 1060-20C5-12 blades were formed from extruded steel by a proprietary Curtiss process, resulting in a hollow blade with dual span-wise spars and a tip chord of 16.75 inches and a tip thickness of 0.687 inches. Aerodynamic blade root cuffs &ldquoresistant to a sledgehammer&rdquo were bolted to the roots and the blade angles were indexed to +/- 0.5° of each other. The three blades per propeller were &ldquoaerodynamically balanced&rdquo by micro-indexing to equalize thrust due to small manufacturing differences in the shaping of individual blades.

The propeller control and pitch changing system consisted of two main assembles the power section that housed the gearing for changing pitch, and the rear housing, which contained the pitch change clutches, oil filter, and oil pump. The propeller control system was electrical, incorporating reverse pitch, blade angle follow up with system with fuel control for ground operation, negative torque control, manual feathering, synchrophasing, and electrical deicing of the spinner, the leading edges of the blade cuff, and a portion of the leading edge of the blade. The blade angle control system was powered by 28 volt DC current, while deicing of the blades and spinner assembly was powered by a timer assembly and 115/200 volt, 400 cycle alternating current. Electrical power for deicing was transferred to the prop via a 4 lane brush block assembly (Fig06).

Fig05. Curtiss Electric CT735S-B102 Turboelectric Propeller. Fig06. Schematic for electrical deicing of the Curtiss CT735S Turboelectric Propeller.

Curtiss had long experience with electrically-actuated pitch change mechanisms that amplified torque from the modestly-sized electric motors via gear trains with very large reduction gear ratios. Because of these large reduction ratios, pitch change rate was generally slower than hydraulically-actuated propellers.

Before discussing the Turboelectric propeller further, it was my great fortune to make contact with Robert &ldquoBob&rdquo Stegner who spent 13.5 years in the USAF and is an expert on the Curtiss Turboelectric system. Bob kindly shared numerous documents on the C-133 propulsion system, as well as his experiences with the finicky engineering masterpiece. Bob commented that it &ldquotook the average smarty pants&rdquo about 3 years to reach total proficiency on the complex T34/Curtiss Turboelectric propulsion system. After reviewing his remarkable documents, reading about the C-133 and the CT7535S-B102 propeller, I think 3 years to infinity might be a more appropriate answer. As such, I will not delve into the myriad detailed complexities of this propulsion system. I will try instead to explain the basics and hopefully leave a feeling for what Bob&rsquos troubleshooting career must have been like.

The design of the gear train used in the Curtiss Turboelectric propeller goes back perhaps to a patent filed in 1933 by Robert M. Stanley and granted in September of 1935 (Fig07, Fig08, Fig09).The patent describes the use of a worm drive to &ldquore-index&rdquo dual concentric planetary gear trains with mismatches in gear diameters (tooth number) of the pinions that traverse in the gears sets in two places. The result is that one set of planetary gears wants accelerate in speed (advance index compared to prop shaft speed), while the following set of planetary gears wants to decelerate (retard index) compared to the prop shaft speed. When the pitch change worm gear is held stationary, the pinions can be thought to &ldquorun place&rdquo with no net relative movement between the prop shaft drive gear 5 and pitch change gear 24, thus no pitch change. However, when a pitch change signal is transmitted to the annular gear 11, gear 11 changes its index. This change is transferred to pinion gear 6/10, which re-indexes the second annular gear (23/24). The annular gear 23/24 is connected to the base of the blades via a pinion gear-drive shaft-worm gear that turns the blade on its own axis. Once the pitch change input gear becomes stationary, the gears sets go back to &ldquorunning in place&rdquo.

The German Vereinigte Deutsche Metallwerke (VDM) propeller of WWII used the exact same mechanism for pitch change on their propeller however there is no record of licensing between VDM and Robert Stanley. Perhaps it was coincidental invention by Stanley and Dr. Hans Ebert of VDM. I suggest the reader grasp the basics of the conceptual schematic of the VDM propeller (Fig10), and once understood the actuation principles are the same for the Curtiss Turboelectric with one exception: the source of the primary motive power source for pitch change.</sidebar>

The power required to adjust the pitch of an almost 9 foot long Turboelectric propeller blade absorbing 2,200 horsepower is staggering. To execute such a feat, Curtiss chose to tap the motive power for pitch change directly from the propeller shaft. The control and actuation system needed to be able to adjust propeller pitch for positive pitch in flight, neutral thrust for engine starting, reverse thrust (-9° pitch) for reducing the landing roll, and feathering for inflight shut down of an engine. Because of the massive power source available for pitch change, Curtiss could do away with the torque-multiplying reduction gear sets of the WWII props, resulting in a much faster pitch change rate required for turbine applications. The CT735S propeller had a flight pitch change rate of 20° per second while the feathering system could produce 5° of pitch change per second.

The schematic diagram for the Curtiss Turboelectric propeller is complicated (Fig11). In Figure 12, the assemblies in green are &ldquohard&rdquo connected to the propeller shaft and thus spin with the propeller shaft. The components shown in red are assemblies that are not &ldquohard&rdquo connected to the prop shaft and thus may orbit, rotate, or be indexed with respect to each other and/or the prop shaft as pitch signals are executed. An Increase Pitch signal is shown in Figure 12.

Fig11. Operational schematic of the Curtiss CT735S Turboelectric propeller. Note the shaping of the worm gear at the base of the propeller blade. This spool-shaped design maximized tooth contact area and minimized the tooth loading for this highly stressed component. (T.O. 3E3-2-11). Fig12. Operational schematic of the Turboelectric propeller using green to denote assemblies &ldquohard&rdquo linked to the propeller shaft. Assemblies shown in red either rotate or orbit freely around the propeller shaft, or are under active control by the pitch change mechanism. The Increase Pitch clutch is engaged.

Since the input power from the rotating engine/propeller shaft for pitch change was always &ldquoon&rdquo when the engine was turning, there were electronically activated friction clutches geared to the movable ring gear. One clutch for positive pitch change, another geared to spin in the opposite direction for negative pitch change. These clutches were about six inches in diameter, about four inches thick, with multiple interleaved discs, and used a coil to activate a drag clutch ball ramp force multiplier to compress the discs together (Fig13). These clutches ran in oil. The Increase Pitch clutch had to overcome the powerful centrifugal twisting moment and aerodynamic forces that try to force the blade to flat pitch, while the Decrease Pitch clutch had a lesser workload.

When propeller pitch/engine speed was &ldquoonspeed&rdquo, both pitch change clutches were disengaged and a brake circuit, colored blue on Fig12 (8 disc pairs dry type) was activated, holding the Movable Ring Gear, and through the gear train, the Movable Sun Gear in place and allowing the pinions to orbit freely. Upon appropriate electrical command, say for increased pitch, the brake would be deactivated, the Increase Pitch Clutch (only) would be activated, and motive power would be transferred from the propeller shaft though the clutch, to the Moveable Ring Gear to &ldquore-index&rdquo the system and increase the pitch of the propeller blade. To decrease pitch, the brake would be deactivated, the Decrease Pitch clutch would be activated, and the Increase Pitch clutch deactivated (open). There was also a &ldquodead man&rdquo solenoid-operated, mechanical ratchet pitch-locking system in the forward section of the propeller spinner that would lock the blades in place in response to certain system failures. Interestingly, blade pitch could still be increased, but not decreased, when the pitch lock was activated.

The easiest way to get a grip on the Curtiss gear system is to imagine the propeller is at rest and follow the Feathering Motor gear train. Once that is understood, just replace the Feathering Motor drive with the Increase Pitch clutch that harnesses power from the propeller shaft to rotate the moveable ring gear.

Gearing taken off the propeller shaft drove the driving side of the pitch change clutches, the propeller governor input, an oil pump, and a centrifugally driven switch that toggled the propeller into Beta Mode and engaging the feathering motor for control of propeller pitch when prop speed was below 25% of rated speed such as during start up and taxiing. Once prop rpm was greater than 25% of rated speed, the centrifugal switch disengaged Beta Mode and activated the propeller governor control of the propeller. Pitch limit switches were geared to the Moveable Ring Gear.

The Governor Assembly drove the Contactor Assembly that was responsible for opening and closing the circuits to drive the appropriate pitch change clutches, and this operation was modulated by a Differential assembly geared to the Moveable Ring Gear.

So if the propeller pitch change system used power from the rotating propeller shaft, how could a stationary propeller be unfeathered? That is where the feather motor comes into play. When activated by the flyweights that detect low engine speed, the electric feather motor gets clutched in to drive a gear train meshed to the Movable Ring Gear, thus turning the blades.

The propulsion control system consisted of &ldquoa constant speed governor, assembly mounted in the power unit rear housing, a synchronizer assembly mounted in the aircraft, two Beta units (ground operation) coordinator assemblies mounted in the aircraft, a propeller coordinator mounted on the fuel control unit of each turbine, a negative torque switch assembly mounted on each turbine nose section, and the necessary control circuit breakers and switches.&rdquo

Propeller control is effected by two separate control systems that are actuated by the pilot&rsquos power lever. The first system is the flight regime that operates through the propeller synchronizer/governor. The second system is Beta Mode for ground operations when the power lever is below flight idle gate and a coordinated blade angle control system is energized. The &ldquosimplified&rdquo diagram and explanation are shown in Figure 14.

Fig13. Exploded diagram of the Decrease Pitch clutch. When the coil is electrically energized, a ball ramp torque multiplier (xx) pressed the discs together, rotating the pinion and indexing the movable Ring Gear to a decrease pitch via the rotating gear train. Fig14. Simplified control schematic of the propeller and control assemblies. &ldquoSimplified&rdquo should not be confused with &ldquosimple&rdquo.

The propeller governor system is complicated beyond what I can fully understand much less explain (Fig15, Fig16). Suffice it to say that it is exquisitely sensitive to rpm changes and is able to &ldquolead&rsquo changes in pitch setting via sensors, potentiometers, and balance circuits to keep the engine/propeller within the specified rpm range (Fig17).

Bob passed along several interesting bits of information on the Turboelectric propeller. Some of the early troubles were caused by disintegrating Increase Pitch clutches. The torque was so great that a 1/4 inch thick snap ring (# 14 in Fig13) that held the clutch pack together couldn&rsquot withstand the load, disintegrating the clutch and causing an emergency pitch lock response, typically followed by an emergency landing. A 3/8 inch snap ring remedied that issue.

Fig15. Mechanical schematic of the propeller governor assembly. The traditional flyweights and speeder spring are present, but are highly modulated by assemblies that increase the precision and response rate of pitch change. Fig16. The electrical schematic for propeller control. The numerous wires and cannon plugs were adversely affected by the vibration caused by such large propellers, and in the case of the C-133, with fatal consequences. Fig17. Photograph of the case-less Governor. This precision electromechanical clockwork, along with the fuel control, are responsible for safely regulating 6,000+ horsepower.

Late in the career of the C-133, Honeywell and Curtiss Wright developed an onboard analyzer tailored for troubleshooting the T34/Turboelectric propeller propulsion system. The analyzer monitored fourteen parameters on each engine making traces similar to heart rhythm EKGs, on light-sensitive paper (Fig18, Fig19). The analyzer would monitor one engine for one minute, rest for six minutes while crew read the squiggles, then move on to analyze engine #2, etc.

One anomaly detected by the analyzer was that the Increase Pitch clutch circuitry was overly sensitive such that the energize/de-energize cycle was so frequent and of such short duration that very little pitch change was occurring. This caused excessive wear on the clutch, and was eventually remedied with the use of desensitizing circuitry.

Fig18. A Power Plant Analyzer System trace showing normal function during a power reduction and subsequent power increase. Time is along the bottom axis and the Analyzer could be adjusted to expand or compress the tracings. The paper itself was the only record of the Analyzer output. Fig19. A Power Plant Analyzer System trace showing &ldquopending&rdquo failure of the propeller. Even though the contactor was quite active signaling a need to change propeller pitch, little pitch change was achieved. It must have been terrifying to see such a trace over the northern wilderness or Pacific Ocean, far from home.

Exploded diagrams of the propeller hub, front cover, power unit, propeller assembly, and rear housing section are included to once again show the complex nature of these assemblies and the machining skill required to execute the design (Fig20, Fig21, Fig22, Fig23, Fig24).

Fig20. The propeller hub and propeller blade root. The cylindrical housing parallel to the axis of the prop shaft, nestled between the hub sockets, houses the shaft and worm gear from the pitch change gears. The socket insert (1) mates securely with the end of the propeller blade. The peripheral exterior teeth on the insert engage the worm dive. Fig21. Front cover housing with number key for Fig22. Fig22. The Power Unit Assembly. The internally and externally toothed Moveable Ring Gear is shown in the middle with pinion spider assembly (9) to left of the Moveable Ring Gear. The two pitch change clutches seated in the housing and their central output gears will mesh with the outside teeth of the Movable Ring Gear. The Feathering Motor is (1) and Brake Assembly is (9). >Fig23. Propeller Assembly. The Power Unit containing the clutches (49) is at left. The propeller Governor Assembly (11) is at top. Fig24. Rear Housing Assembly showing the clutches (52, 56) and exploded oil pump (37 through 50) that lubricated the propeller pitch change gear trains. The rear housing (70) is a machined work of art.

There were also practical challenges to maintenance of the propulsion system on the C-133. The outboard engines were seventeen feet eight inches off the ground, and the propellers weighed 1,300 lb. A special propeller hoist (Pier ST1641) and work stands were designed for the C-133 by Douglas and allowed an experienced crew to change a propeller in about 4 hours (Fig25, Fig26). The propeller alone required 96 Special Tools and 31 different Technical Order manuals to maintain and repair.

Fig25. The Douglas-designed propeller ST1641 pier and work stand used for propeller maintenance and removal. It appears the propeller stub mount on the pier can be rotated 180°, and then moved off the stub and into place via the overhead crane. The propeller assembly weighed 1,325 lb. (Cal Taylor/USAF) Fig26. The propeller on right reveals the aft end (engine side) of the propeller assembly filled with electromechanical devices. The propeller on the left may be having its propeller nut torqued down with a hydraulic torque wrench. The propeller nut requires at least 2,300, and no more than 2,500 pound-feet of torque to secure. (Cal Taylor/USAF)

The life of the C-133, and the propellers especially, is a history of tragedy. Fifty C-133 aircraft were built, nine aircraft had crashed and one was destroyed on the ground during the 15 years of active duty. Unending electrical problems affecting propeller control, propeller imbalance and synchrophasing issues caused vibration so severe a person or tool boxes would skitter across the cargo floor like electric football players and dangerously fatigue humans as well as the airframe. Underperforming engines required controversial airframe weight reduction to meet performance goals, external fuselage hoop bands to reinforce the lightened airframe, and a myriad of other issues made for a troubled life. Add into that mix the challenging operational environments and the pressing demands of the Cold War summed to wreak havoc on the airplane and the men who flew and maintained her. All of these challenges are well documented in Cal Taylor&rsquos excellent book.

As a side note, Curtiss Wright succeeded in putting their CT634S Turboelectric propellers on the early Lockheed C-130 Hercules aircraft, but the propeller was once again dogged by problems. Curtiss was also in competition for their Turboelectrics to drive the Lockheed L-188 Electra, which first flew in December of 1957. When the President of Eastern Airlines, Eddie Rickenbacker, examined the disassembly of the Curtiss Turboelectric propeller, he infamously quipped &ldquoIt looks like Rube Goldberg lives in there&rdquo. Eastern did not select the Curtiss propellers, choosing instead the Aeroproducts A6441FN-606 propellers.

The Last Flying Curtiss Turboelectric Propellers

Amazingly, Douglas C-133B, serial 56-1999, registered N199AB, continued to fly as a private commercial transport aircraft carrying outsized cargo in Alaska long after the USAF retired their C-133 fleet in August of 1971. Owned by Maurice Carlson, it is N199AB that had the last flying Curtiss Turboelectric propellers, making her final flight from Alaska to Travis Air Force base on August 30, 2008. A gentleman named Ken Kozlowski was responsible for keeping this complex aircraft flying for 37 years beyond its retirement from the military.

The final flight is documented with an excellent photo mosaic with interesting technical detail by Mark M.

Some spectacular documentary video of the final flight and an amateur video of the landing (the sound is incredible) has been made available.

There are several C-133 aircraft preserved in museums: NMUSAF, Dayton, Ohio Pima Air and Space Museum, Tucson, Arizona Air Mobility Museum, Dover AFB, Dover, Maryland Travis AFB Museum near Fairfield, California (Fig27, Fig28). Additionally, the T34/Curtiss Turboelectric propeller YC-97J (52-2693) that was converted to the NASA Turbo Super Guppy survives at the Pima Air and Space Museum Tucson, Arizona (Fig29).

When the AEHS Convention #3 visited the back lot of the New England Air Museum in 2006, I noticed a massive propeller hub moldering in the weeds. There is little doubt this forlorn artifact was one of the Curtiss Turboelectric propellers on C-133B, 59-0529 destroyed by a tornado on 3 Oct 1979 (Fig30).

Fig27. Douglas C-133B, 59-0527, in residence at the Pima Air and Space Museum, Tucson, AZ, USA. (Fey) Fig28. Vertical blade shows the fiberglass reinforcement delaminating from the ageing cuff. Douglas C-133B, 59-0527. (Fey) Fig29. Boeing YC-97J (52-2693) converted to the NASA Turbo Super Guppy rocket component transport that is powered by T34/Curtiss Turboelectric propeller system. Aircraft is shown cocooned in outdoor storage at the Pima Air and Space Museum, October 2017. (Fey) Fig30. The distinctive Curtiss Turboelectric hub, likely off C-133B (59-0529), destroyed by tornado at the New England Air Museum on 3 Oct 1979. Photo taken July 2006. (Fey)

I&rsquod like to thank Bob Stenger for generously sharing his knowledge and treasure trove of technical documents with me, Cal Taylor for writing the masterful, definitive work on the C-133, and AEHS member Bruce Vander Mark for the C-133A/B manual.

Remembering and Unsung Giant by Cal Taylor, First Fleet Publishers, 2005.
C-133A and C-133B Flight Manual, T.O. 1C-133A-1, 15 June 1961.
Handbook Overhaul Instructions, Turboelectric Propeller Model CT735S-B102, T.O. 3E3-2-13, 10 March 1955.
Handbook Operation and Service Instructions, CT735S-B102 Turboelectric Propellers and Propeller Controls, T.O. 3E3-2-11, 15 January 1955.
Power Plant Analyzer System, Technical Manual Part Number ST4235, T.O. 33D4-6-247-1, 1 July 1965.
The Curtiss X-Planes by Francis H. Dean, Schiffer Military History, 2001.

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Curtiss JN-4D Jenny

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Curtiss JN-4D Jenny

Single-engine, two-seat, U.S.-built World War I trainer aircraft 90-horsepower Curtiss OX-5 engine. Tan wings, brown and blue fuselage.

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Curtiss JN-4D Jenny

Single-engine, two-seat, U.S.-built World War I trainer aircraft 90-horsepower Curtiss OX-5 engine. Tan wings, brown and blue fuselage.

CCO - Creative Commons (CC0 1.0)

This media is in the public domain (free of copyright restrictions). You can copy, modify, and distribute this work without contacting the Smithsonian. For more information, visit the Smithsonian's Terms of Use page.

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Curtiss JN-4D Jenny

Single-engine, two-seat, U.S.-built World War I trainer aircraft 90-horsepower Curtiss OX-5 engine. Tan wings, brown and blue fuselage.

CCO - Creative Commons (CC0 1.0)

This media is in the public domain (free of copyright restrictions). You can copy, modify, and distribute this work without contacting the Smithsonian. For more information, visit the Smithsonian's Terms of Use page.

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Curtiss JN-4D Jenny

Single-engine, two-seat, U.S.-built World War I trainer aircraft 90-horsepower Curtiss OX-5 engine. Tan wings, brown and blue fuselage.

CCO - Creative Commons (CC0 1.0)

This media is in the public domain (free of copyright restrictions). You can copy, modify, and distribute this work without contacting the Smithsonian. For more information, visit the Smithsonian's Terms of Use page.

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Curtiss JN-4D Jenny

Single-engine, two-seat, U.S.-built World War I trainer aircraft 90-horsepower Curtiss OX-5 engine. Tan wings, brown and blue fuselage.

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This media is in the public domain (free of copyright restrictions). You can copy, modify, and distribute this work without contacting the Smithsonian. For more information, visit the Smithsonian's Terms of Use page.

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Curtiss JN-4D Jenny

Single-engine, two-seat, U.S.-built World War I trainer aircraft 90-horsepower Curtiss OX-5 engine. Tan wings, brown and blue fuselage.

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This media is in the public domain (free of copyright restrictions). You can copy, modify, and distribute this work without contacting the Smithsonian. For more information, visit the Smithsonian's Terms of Use page.

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Curtiss JN-4D Jenny

Single-engine, two-seat, U.S.-built World War I trainer aircraft 90-horsepower Curtiss OX-5 engine. Tan wings, brown and blue fuselage.

America by Air - Curtiss JN-4D Jenny

Curtiss JN-4 "Jenny"

Curtiss JN-4D Jenny in America by Air

Curtiss JN-4D Jenny - Damage To Tail Fabric

Curtiss JN-4D Jenny - Damage To Wing Fabric

Curtiss JN-4D Jenny at Steven F. Udvar-Hazy Center

Display Status:

This object is on display in the Boeing Aviation Hangar at the Steven F. Udvar-Hazy Center in Chantilly, VA.

The Curtiss JN-4D is almost synonymous with American aviation in the 1920s. The Jenny, as it was affectionately called, appeared in 1917. Heretofore having only produced pusher aircraft, Glenn Curtiss hired an experienced European designer to lead the new project named B. Douglas Thomas, who had worked for Avro and Sopwith in England. The Jenny performed admirably as a trainer for the U.S. Air Service during World War I, but its more significant role in aviation history was as a barnstorming and mail-carrying airplane in the 1920s. Large numbers of relatively inexpensive war surplus Jennys were available in the United States after 1918. Its affordability, ease of operation, and versatility made the Jenny the signature airplane of the barnstorming era. The Smithsonian acquired this Jenny in 1918 directly from the U.S. War Department. It is one of the finest remaining examples of this truly classic airplane.

One of the most famous of all aircraft is the Curtiss JN-4D, popularly known as the Jenny. More than ninety percent of American pilots trained during the First World War received their primary instruction on the Jenny. After the war, thousands of these aircraft were sold at surplus prices on the civilian market.

The Jenny, powered by the equally famous Curtiss OX-5 engine, became the principal aircraft flown by barnstormers during the postwar period. Americans, particularly in rural areas, thrilled to the antics of these pilots performing in the aerial circuses that toured the country during the 1920s. For many, the Jenny would be the first airplane that they would see close-up, and those with a few dollars in hand and their fear in check, typically would make their first flight in a Jenny.

The Curtiss JN series began as a hybrid design in 1914, incorporating the better features of the Model N designed in America by Glenn Curtiss and the Model J designed in England by a young engineer named B. Douglas Thomas. Thomas had been employed as an assistant chief engineer with Sopwith Aviation when Curtiss met him on a trip to England. Impressed with Thomas' aeronautical knowledge, Curtiss hired him and commissioned him to design a two-seat, tractor airplane around the Curtiss-built OX-5 engine.

Thomas' Model J and Curtiss' Model N were both entered in the U.S. Army evaluation trials in September 1914. Curtiss received an order in December 1914 for eight modified Model Js. Curtiss added the letter N to the designation because the modified Model J incorporated significant features of his Model N. The designation officially became the JN-2. In March 1915, Curtiss began construction of a 110,000-square-foot factory in Buffalo, New York. This factory ultimately produced Jennys at the rate of 100 per month.

The First Aero Squadron of the U.S. Air Service, Signal Corps, began receiving JN-2s in early 1915. Some of these aircraft were deployed to Mexico one year later where they performed the first tactical operations for the fledgling U.S. Air Service in the campaign against Pancho Villa.

The JN-2s had equal span wings with four strut-connected ailerons controlled by a shoulder yoke located in the rear cockpit, much like that found on Curtiss' early pusher designs. The performance of the JN-2 was less than satisfactory, so Curtiss improved the design with the substitution of unequal span wings (like the original modified Model J), and ailerons on the upper wings only with a wheel to control them in place of the outmoded yoke system. In addition, a foot bar was installed to control the rudder.

The improved design was designated the JN-3, and this model caught the interest of British authorities who were then seeking primary trainers for the Royal Naval Air Service. In order to meet this and anticipated future British wartime requirements, Curtiss built a production plant in Toronto, Canada. With a few further revisions, the airplane appeared as the JN-4 in mid 1916. JN-4s were acquired by the British as trainers and several were also supplied to the U.S. Air Service, as well as to Curtiss flying schools and private owners. A total of 701 were built.

The JN-4 was quickly followed by the JN-4A, which incorporated several significant changes. It had larger and redesigned tail surfaces to increase directional stability, a revised fuselage introducing significant down thrust to the OX-5 engine, increased dihedral, and ailerons on both wings to improve lateral control. Six hundred and one JN-4As of a total of 781 built were delivered to the U.S. Air Service. The rest went to the Royal Flying Corps, the Royal Naval Air Service, and a few to the U.S. Navy.

Canadian-built Jennys, derived from the earlier JN-3 model, incorporated certain features requested by Canadian authorities. These included a control stick instead of a wheel, a revised tail, and strut-connected ailerons on both wings. This model, which first flew in January 1917, became known as the JN-4(Can), or more popularly, the Canuck. The Curtiss plant in Toronto that had been building JN-3s for the British was taken over by the Canadian government in December 1916, and reformed as Canadian Aeroplanes, Ltd.

Curtiss continued the process of evolutionary design changes to the JN-4. The JN-4B (actually an earlier design than the JN-4A) saw some success in the civilian market, as well as with the U.S. Air Service and the U.S. Navy. The JN-4C was fitted with experimental wings, but only one was built.

The JN-4D, the definitive design of the JN series, was introduced in June 1917, just one month after the United States entered the First World War. Principal design changes for this model included a control stick substituted for the control wheel, ailerons only on the upper wing, and curved cut-outs on the inner trailing edges of all four wing panels. This last change provided easier cockpit entry and egress.

Wartime demand for the JN-4D quickly outstripped Curtiss' production capacity and the U.S. Air Service let contracts with six other American manufacturers: Fowler Airplane Corporation, Liberty Iron Works, Springfield Aircraft Corporation, St. Louis Aircraft Corporation, U.S. Aircraft Corporation, and Howell & Lesser. Canadian Aeroplanes, Ltd., was also called upon to deliver JN-4 Canucks under an existing contract for JN-4Ds, in order to meet the dramatic increase in wartime demand.

The U.S. Air Service found more applications for the JN-4 and this resulted in another JN variant with a more powerful engine. A requirement for an advanced trainer led to the development of the JN-4H, with a 150-horsepower Wright-Martin-built, Hispano-Suiza engine in place of the 90-horsepower Curtiss OX-5. The JN-4H, with a strengthened structure and increased fuel capacity, spawned a number of purpose-built variants, including the JN-4HT, a dual-control trainer, the JN-4HB, a bomber trainer fitted with bomb racks, and the JN-4HG, a single-control gunnery trainer. Further minor improvements in the JN-4H series led to the JN-6H, the principal change being a reversion to strut-connected ailerons on both wings.

The U.S. Navy procured 201 JN series aircraft during the period 1917 to 1923. Most of these aircraft were JN-4Hs received from U.S. Air Service stocks, and they were used by the U.S. Navy and Marine Corps as landplane trainers. The Navy also adopted a modified Jenny, designated the N-9, for primary seaplane training. These aircraft, fitted with a pontoon and wingtip floats, were powered by Hispano-Suiza or Curtiss OXX engines. Five hundred and ten N-9s were purchased from the Curtiss and Burgess companies, although Naval air cadets disliked the under-performing N-9.

The final iteration of the JN series was the JNS, or Standard Jenny. This designation, appearing in 1923, was used to identify obsolescent JN-4H and JN-6H models that were rebuilt and modified, with a reversion, once again, to ailerons on the top wing only. This model was powered by either the 150- or 180-horsepower Hispano-Suiza engine built by Wright Martin.

During the war, Curtiss and six other American companies delivered 6,070 JN series aircraft to the U.S. Air Service, with Curtiss supplying 4,895 of the total. In 1919, the U.S. Air Service still had 3,285 Jennys and the Navy 76. Some of the

Standard Jennies would remain in limited service until finally withdrawn in 1927.

In November 1918, contracts for war material were abruptly terminated and the U.S. government began to dispose of surplus stocks to the civilian market. There was a substantial demand for the surplus aircraft and the government invited bids from the manufacturers and others with overhaul and repair facilities. Curtiss bought back $20 million worth of equipment, mostly Jennys and OX-5 engines, at a cost of 13 cents on the dollar. Curtiss quickly began refurbishing and aggressively marketing these aircraft. The British, in the meantime, were moving even more quickly to dispose of their surplus inventory, and hundreds of Canadian JN-4 Canucks began to flood the American market.

In mid 1919, Curtiss began offering new Jennys to the public at a cost of $4,000, and new OX-5 engines for $1,000. At the same time, Curtiss began an extensive marketing campaign highlighting the many civilian applications of the Jenny, which included commuting, photo-mapping, policing, medical use, forest patrol, real estate

work, and pleasure flying, proclaiming that "the JN is a good machine for the sportsman. It stunts well and develops great speed as compared with land conveyances. It has been used in all the exhibitions by the U.S. Army flyers, and by most of the flyers who have exhibited since the close of the war." It was this last application that would make the Jenny an enduring legend. The Jenny, and to a lesser extent, the Standard J-1, would be the principal aerial mounts for those gypsy fliers called barnstormers.

During the 1920s, civilian pilots roamed the countryside, giving passenger rides and putting on aerial circuses that drew hundreds of people, making as much as $300 a day. The slow flying Jenny was perfect for wing-walkers who clung to the Jenny's maze of struts, the straight wheel axle, or the king posts above the wings while performing death-defying stunts for the crowds below.

Pilots found a myriad of ways to improve the performance of their Jennys, which included clipping wings or adding high-lift monoplane wings, using more efficient propellers, and replacing the 90-horsepower Curtiss OX-5 engine with a 150-horsepower Hispano-Suiza, or any one of a number of other widely available surplus engines. Pilots could also enhance the performance of their OX-5 engines by installing conversion kits that included silver-bronze bearings three-ring, high-compression pistons perfect circle piston rings new magnetos replaceable valve guides and seats new valves and intake controls roller rocker arms and grease-tight and fail-proof intake rocker arms and pins. Thirty-eight hundred of these Miller conversion kits, named after their developer, were sold.

Jenny prices continued to drop as the air services began selling surplus stocks directly to the public and used Jennys would eventually change hands among private owners for as little as $50. Unused OX-5 engines sold for $250.

By 1925, new and more efficient designs were being offered to a more affluent and demanding public, and interest in the Jenny began to wane. Two years later, newly instituted Federal airworthiness requirements for both airplanes and pilots brought the Jenny and Barnstorming Era to a close, for the venerable Jenny could not meet the requirements. By 1930, Jenny hulks and components could be found all over the country.

Duesenberg W-24 Marine Engine

Although his father was a co-founder of the Dodge Brothers Company, progenitor to today’s Dodge automobile company, Horace Elgin Dodge Jr. did not follow his father into the automobile business. But like his father, he was very interested in watercraft. In 1923, after his father had passed, he founded Dodge Boat Works in Detroit, Michigan. This venture was backed by a $2 million investment from his mother, Anna Thompson Dodge.

Side view of the J. Paul Miller-developed Duesenberg W-24 engine.

Dodge was very involved in boat racing, and he wanted to create a boat that would be unbeatable. In 1925, Dodge approached Duesenberg Brothers Racing to build an engine to propel him to victory in the Gold Cup race. An agreement was made, and a contact was signed on 27 January 1926—$32,500 for the construction of two complete engines with enough spare parts to build a third. The first engine was to be delivered on 15 June 1926, with the second following on 6 July 1926. Although Fred Duesenberg was involved with the engine project, it was most likely Augie Duesenberg who did the majority of the work.

The contracted engine was essentially three straight-eight engines on a common aluminum crankcase, creating a W-24. Why a “W” engine configuration was chosen is not known, but it does provide for a powerful engine in a fairly compact space. At this same time in history, the Napier Lion W-12 engine was powering record-setting air, land, and marine speed machines, and it is easy to see how the Lion could have served as inspiration.

View of the Duesenberg W-24 under construction.

The engine’s bore was 2.875 in (73 mm) and stroke was 4.0 in (102 mm), giving a total displacement of 623 cu in (10.2 L). The two side banks were angled 60 degrees from the center vertical bank. Each of the W-24’s engine banks was made up of two four-cylinder blocks with integral heads. The first four-cylinder blocks were supposedly made of cast iron, but later cylinder blocks were cast aluminum with steel cylinder liners. The engine’s single crankshaft was supported by five main bearings. The connecting rods were of the tubular type, with the master rod in the center bank and an articulated rod for each outer bank.

Four valves per cylinder operated in a pentroof combustion chamber. All together, the engine’s 96 valves took about a week of labor to adjust. The valves were actuated in each engine bank by dual overhead camshafts that extended the length of the engine. The camshafts were geared to the crankshaft via idler gears. Each block of four cylinders had five exhaust ports. The three middle exhaust ports each shared two exhaust valves. Exhaust from each bank was collect in a single water jacketed manifold. One spark plug was installed in each cylinder and fired by a camshaft-driven Delco distributor mounted at the rear of each cylinder bank.

The complex gear-drive arrangement for the camshafts at the rear of the 24-cylinder Duesenberg. The pinion on the crankshaft had 17 teeth, the intermediate gears had 74 teeth, and the camshaft gears had 34 teeth. The center intermediate gear engaged an idler gear that had 45 teeth. The gearing drove the camshafts at half engine speed.

Initially, one updraft carburetor fed air to each of the six four-cylinder blocks. Poor fuel distribution resulted, and the engine never ran well. The updraft carburetors were replaced with downdraft carburetors, and the W-24’s running improved, but it was still not perfect. The six downdraft carburetors were replaced by 12 Zenith downdraft carburetors, improving performance yet again. Finally, 12 Holley downdraft carburetors replaced the Zeniths, and the engine began to run smoothly. Although running better than ever, the W-24 only produced a disappointing 475 hp (354 kW).

The first engine was delivered to Dodge in 1927. Earlier that year, J. Paul Miller began working at the Duesenberg factory and was involved with W-24 engine for many years. Some of Miller’s first changes were installing I-beam connecting rods in place of the tubular ones and replacing the Delco distributors with Bosch magnetos. From 1929 to 1935, Miller worked for Dodge and continued to develop the engine. Unfortunately for Dodge, the 24-cylinder engines brought nothing but frustration. As a result, he never paid Duesenberg the last $2,000 for the engines.

Rear of the 24-cylinder Duesenberg showing two two-barrel carburetors feeding the supercharger. Note the camshaft-driven Bosch magnetos.

The 1931 Gold Cup race was held on Lake Montauk in New York, and the W-24 engine was installed in Dodge’s Miss Syndicate III boat. Miss Syndicate III failed to finish the first heat. In 1932, Miss Syndicate III had been renamed Delphine V. Dodge Sr. had named a yacht after his daughter, and Dodge Jr. continued the “Delphine tradition,” naming numerous boats after his sister. Again, the Gold Cup race was held on Lake Montauk in New York. During the first heat race, the W-24-powered Delphine V dropped out after three laps. Dodge entered five boats for the 1933 Gold Cup race held on the Detroit River. A 24-cylinder Duesenberg was installed in two of the entries: the new Delphine VIII and the new Delphine IX. That year, Delphine VIII failed to start, and Delphine IX did not finish a single heat. In 1934, in disgust, Dodge sold one (but probably both) W-24 engine to Herb Mendelson.

Before the sale, Dodge was inspired by the performance of the supercharged Packard engine in one of this other boats, Delphine IV. Since a rule change allowed superchargers to be used starting in 1935, Dodge had commissioned Miller to design a supercharger for the W-24. This unfinished project was sold to Mendelson, and Miller was retained by Mendelson to continue the work on the engine. It was Miller’s refinements of the supercharged engine that really brought the W-24 to life. The supercharger used an 8 in (203 mm) impeller and spun at 6.5 times crankshaft speed (32,500 rpm at 5,000 rpm engine speed), creating 15 psi (1.03 bar) of boost. Initially, two two-barrel carburetors were used on the supercharged engine, but these were replaced by a single four-barrel Stromberg carburetor. Along with new Miller-designed intake manifolds, the fuel distribution problems were finally solved. The exhaust manifolds were discarded and replaced by 30 vertical exhaust stacks extending into the air. With the changes, the engine weighed 1,400 lb (635 kg) and was referred to as the “Mendelson-Duesenberg W-24.” The engine began to run like a champion and now produced over 850 hp (634 kW) at 5,000 rpm. Reportedly, at full song the engine produced a sound like nothing else on earth.

The W-24 being installed in in the Arena-designed Notre Dame by Gene Arena, Walter Schmid, and Bert MacKenzie.

Mendelson installed the W-24 into his boat, the Clell Perry-designed rear-engined Notre Dame (the first). Its first competition was the 1935 President’s Cup race on the Potomac River. Perry was the driver and won the race. In 1937, Perry was again at the controls when the W-24-powered Notre Dame won the Gold Cup race, held on the Detroit River, averaging 63.68 mph (102.48 km/h) over the 90 mile (145 km) course.

While making a high speed run on the Detroit River in preparation for the 1938 Gold Cup race, Perry was injured when the new Notre Dame (the second) boat went out of control and flipped over. (This accident possibly destroyed one of the W-24 engines.) The new Notre Dame was repaired, and Dan Arena took over the driving duties. He finished second in the President’s Cup race but did not like the boat’s stability. Mendelson asked Arena what he thought was needed to cure the stability issues, and Arena said, “Build another boat.” Mendelson agreed, and Arena designed a new 22 ft (6.7 m) boat, again named Notre Dame (the third), with the W-24 engine placed in front of the driver.

Dan Arena (standing) preparing to run the W-24-powered Notre Dame with his brother Gene as the riding mechanic, as Bert MacKenzie makes final preparations.

After a bit of a rough start, Arena won the 1939 and 1940 President’s Cup races in the new Notre Dame. In 1940 on the Detroit River, the W-24 powered the Notre Dame to a new class speed record of 100.987 mph (162.523 km/h). The boat was placed in storage during World War II but was taken out in 1947 and won the Silver Cup race on the Detroit River and finished second in the President’s Cup race. By this time, competitors were installing WWII surplus Allison engines in their boats, and the Duesenberg W-24 could no longer compete. The engine was removed and placed in storage.

At least one Duesenberg W-24 engine survives along with many spare parts. As of 2013, the engine is owned by Gerard Raney and has been rebuilt for installation in a Notre Dame (the third) replica that is under construction. In the mid-1990s, Miller and Arena were both involved in the project, which is based out of the San Francisco Bay Area. Undoubtedly, the engine and boat combination will be quite a sight when the project is finished.

The surviving Duesenberg W-24 engine owned by Gerard Raney as seen in 1996. Note that each cylinder bank is made up of two four-cylinder blocks the gap between the blocks is visible on the bank nearest the camera. The camshaft housings extend the length of the engine. (Pat O’Connor image)


In the years before the outbreak of World War II, a number of countries became intrigued by the idea of developing a very light fighter aircraft, [2] with these proposals often being derived from the design of racing aircraft. Following the consideration of a modified French Caudron racer by the U.S. Army Air Corps, a proposition that was considered uneconomical, [2] Douglas Aircraft made an unsolicited proposal to the Army Air Corps of their Model 312 design in 1939. [2]

World War II, also known as the Second World War, was a global war that lasted from 1939 to 1945. The vast majority of the world's countries—including all the great powers—eventually formed two opposing military alliances: the Allies and the Axis. A state of total war emerged, directly involving more than 100 million people from over 30 countries. The major participants threw their entire economic, industrial, and scientific capabilities behind the war effort, blurring the distinction between civilian and military resources. World War II was the deadliest conflict in human history, marked by 50 to 85 million fatalities, most of whom were civilians in the Soviet Union and China. It included massacres, the genocide of the Holocaust, strategic bombing, premeditated death from starvation and disease, and the only use of nuclear weapons in war.

Air racing is a highly specialised type of motorsport that involves airplanes or other types of aircraft that compete over a fixed course, with the winner either returning the shortest time, the one to complete it with the most points, or to come closest to a previously estimated time.

The Caudron C.450 and C.460 were French racing aircraft built to participate in the Coupe Deutsch de la Meurthe race of 1934.


The Curtiss Model 75 was a private venture by the company, designed by former Northrop engineer Donovan Berlin. The first prototype constructed in 1934 featured all-metal construction with fabric-covered control surfaces, a Wright XR-1670-5 radial engine developing 900 hp (671 kW), and typical U.S. Army Air Corps armament of one 0.3 in (7.62 mm) and one 0.5 in (12.7 mm) machine guns firing through the propeller arc. Also typical of the time was the total absence of armor or self-sealing fuel tanks. The distinctive landing gear which rotated 90° to fold the main wheels flat into the thin trailing portion of the wing was actually a Boeing-patented design for which Curtiss had to pay royalties.

The prototype first flew on 6 May 1935, reaching 281 mph (452 km/h) at 10,000 ft (3,050 m) during early test flights. On 27 May 1935, the prototype was flown to Wright Field, Ohio, to compete in the USAAC fly-off for a new single-seat fighter but the contest was delayed because the Seversky entry crashed on the way to the contest. Curtiss took advantage of the delay to replace the unreliable engine with a Wright XR-1820-39 Cyclone producing 950 hp (709 kW) and to rework the fuselage, adding the distinctive scalloped rear windows to improve rear visibility. The new prototype was designated Model 75B with the R-1670 version retroactively designated Model 75D. The fly-off finally took place in April 1936. Unfortunately, the new engine failed to deliver its rated power and the aircraft attained only 285 mph (460 km/h).

Although its competitor, the Seversky P-35, also underperformed and was more expensive, it was still declared the winner and awarded a contract for 77 aircraft. Then, on 16 June 1936, Curtiss received an order from USAAC for three prototypes designated Y1P-36. The USAAC was concerned about political turmoil in Europe and about Seversky's ability to deliver P-35s in a reasonable timeframe and therefore wanted a backup fighter. The Y1P-36 (Model 75E) was powered by a Pratt & Whitney R-1830-13 Twin Wasp engine producing 900 hp (671 kW) and further enlarged scalloped rear canopy. The new aircraft performed so well that it won the 1937 USAAC competition with an order for 210 P-36A fighters.

Curtiss YP-37

In early 1937, the USAAC ordered Curtiss to adapt one P-36 to the new liquid-cooled turbo-supercharged Allison V-1710 engine with 1,150 hp (858 kW). Designated XP-37, the aircraft used the original Model 75 airframe with radiators mounted on the sides of the fuselage around the engine. The cockpit was moved far to the rear to make room for the radiators and to balance the aircraft. The aircraft flew in April 1937, reaching 340 mph (547 km/h) at 20,000 ft (6,100 m). Although the turbo-supercharger was extremely unreliable and visibility from the cockpit on takeoff and landing was virtually nonexistent, the USAAC was sufficiently intrigued by the promised performance to order 13 service test YP-37s. Featuring improved aerodynamics and a more reliable turbo-supercharger, the aircraft first flew in June 1939. However, the powerplant remained unreliable and the project was cancelled in favor of another Curtiss design, the P-40.

Curtiss XP-42

In an attempt to improve the aerodynamics of the air-cooled piston engines, the fourth production P-36A (serial 38-004), designated the XP-42, was equipped with a long streamlined cowling resembling that of a liquid-cooled engine. Twelve different designs were tried with little success - although the aircraft was faster than a standard P-36A, engine cooling problems were never resolved. Since the new P-40 was faster, the project was cancelled. Late in its service life, the sole XP-42 was fitted with an all-moving tailplane and used to study that control configuration.

Babe Ruth Sues to Name His Own Candy𠅊nd Loses

Candy wrapper for Ruth&aposs Home Run candy bar, c. 1926

Transcendental Graphics/Getty Images

In 1926, Ruth decided to enter the candy business himself and licensed his name to the George H. Ruth Candy Company, which sought to register “Ruth’s Home Run Candy” with the U.S. Patent and Trademark Office. Wrappers showed a head shot of a smiling Ruth in his uniform along with the note � Ruth’s Own Candy.” The Curtiss Candy Company sued for copyright infringement and claimed that the candy bar had not been named after the baseball star, but Ruth Cleveland, eldest daughter of President Grover Cleveland. 

The explanation seemed odd given that the girl nicknamed �y Ruth” by the press had been born in 1891, three decades before the introduction of the candy bar. By 1921, not only was she not a baby—she wasn’t even alive, having died of diphtheria in 1904. Newspapers and the American public paid close attention to �y Ruth” after her father returned to the White House in 1893 for his second presidential term, but the Clevelands fiercely protected their daughter’s privacy and refused repeated requests by American newspapers to take her photograph. Few Americans ever knew what �y Ruth” looked like. By 1921, Babe Ruth was a household name while �y Ruth,” who died 17 years beforehand, was a historical footnote.

Watch the video: Curtiss-Wright XP-55 Ascender