Curtiss HA - Dunkirk Fighter

[Dynoman]

I didn't see the Curtiss HA aircraft in the forums. This aircraft was a little unique in that it was designed by a notable US Marine aviator (Bernard Smith) and constructed by Curtiss Aircraft Company, to become the first naval fighter aircraft.

The Curtiss H.A. (believed to stand for the Curtiss Hydro Aeroplane) was designed by Marine aviator Bernard L. Smith (the second licensed Marine Aviator in US history), who graduated with honors in mechanical engineering from Virginia Polytechnic Institute in 1909. He trained with the Navy at the 'Curtiss Camp' and held the most amount of flight time in the Navy's A-1 training aircraft. During WWI he was sent to Paris as an Assistant Naval Attaché, touring French aircraft factories and returning to the US with ideas for the it's burgeoning aircraft industry. He designed a seaplane fighter for the Navy, who contracted with the Curtiss aircraft company to construct the design. The fighter was originally called the Smith Gun Scout. It was later designated as the Curtiss HA and nicknamed the Dunkirk Fighter (as hopeful harbinger of gaining air supremacy over the region held by Germans in Belgium).

The aircraft was test flown by famed Curtiss test pilot Roland Rohlfs with Bernard Smith occupying the rear seat. The design was a little unique in that the upper biplane wing had dihedral and the lower wing anhedral. The aircraft also suffered from stability issues and a rearward CG. A redesign of the aircraft resulted in the HA-1 and HA-2 designs. The last being a candidate for a land-based mail plane.

 

[Dynoman]

Photos of Capt. Bernard Smith and Curtiss's Roland Rohlfs in 1918 and 1919, respectively. The Dunkirk Fighter first flew on March 21, 1918. Smith was affiliated with the design of the NC-4 flying boat for the Navy (I don't have any details on his participation) and Rohls recounts the flight of the Dunkirk Fighter in the article Plane Luck American Aviation History Society Journal, Vol 17., 1973. Rohlfs describes the first flight of the aircraft as one of the most dangerous flights he had ever flown. The aircraft longitudinal instability was so severe that he nearly crashed while flying and eventually had to time the oscillations to impact the water in a horizontal attitude, which destroyed the aircraft, but saved the crew.

 

[Silencer1]

Thanks for sharing this drawing and photos!
Curious to see, how aesthetically elegant, aerodynamically sleek and compact "Smith Gun Scout" was on the sketches - and what eventually became realized in the real HA-1.

 

[riggerrob]

That sort of aft Center of Gravity was a common problem with pre-1920s airplanes. They eventually figured out that they needed to keep the C. of G. at 25 percent of mean aerodynamic chord to allow mere mortal military pilots to fly them without crashing.

If you look at any of the modern 1960s or later replicas of WW1 airplanes, (Redfern, Graham Lee Robert Baslee) most of them have unusually long engine mounts to improve balance and stability.

 

[Dynoman]

The original sketch (in blue) looks as if the radiator was a conformal wing mounted design. There were a number of designs that operated with this arrangement, however a bullet to the radiator resulted in the pilot splashed with steaming hot radiator water (Prestone wasn't used until circa 1928-29). The large diameter engine cowling was the result of encasing the Liberty in order to streamline it and include the front radiator.

Aircraft instability was a problem for early designers well into WWI. If you look at the Sopwith Camel, for example, the fuel tank was positioned behind the pilot. The aircraft could not fly without pitching up dramatically on takeoff, requiring the pilot to keep the stick forward on takeoff until he had adequate speed.

RAF aircraft had such directional instability problems during WWI that they resisted enclosed cockpits long afterward, because they felt that the wind on their face would provide them with a better sense of the sideslip angles.

 

[robunos]

The original sketch (in blue) looks as if the radiator was a conformal wing mounted design. There were a number of designs that operated with this arrangement, however a bullet to the radiator resulted in the pilot splashed with steaming hot radiator water

The Germans used this type of radiator a lot, and they found the answer was to offset the radiator to either port or starboard, rather than on the centreline.

cheers,
Robin.

 

[Dynoman]

From the article the radiator may have been undersized. The Dunkirk Fighter suffered from overheating according to the article. The Liberty engine was enclosed with a small aperture for the radiator to minimize drag, however these design points worked to overheat the engine. The later HA's had a larger radiator.

To add to the answer to the question about the size of the cowling, there were also four .30 caliber machine guns mounted on top of the engine under the cowling. The carburetor intake and the oil cooler inlets would also increase the frontal area of the aircraft, which would likely be under the cowling. A cutaway of the aircraft would be great to have. I added a picture of its radiator.

 

[Dynoman]

Wrecked Dunkirk Fighter after first flight.

 

[Kant1983]

arhiv 1

 

[Kant1983]

arhiv 2

 

[Dynoman]

Land based version that was used as a mailplane and nicknamed the Bulldog. I modified the profile of the Dunkirk Fighter to the Bulldog.

 

[riggerrob]

Wrecked Dunkirk Fighter after first flight.

that broken back suggests a rapid rate of descent when she hit the water.

 

[riggerrob]

arhiv 1

From a structural and aerodynamic perspective, it would have made more sense to simply bolt the upper wings directly to the top corners of the fuselage.

 

[Dynoman]

Both men survived the impact, however, I can imagine that they must have had some injuries. The visibility from the cockpit was horrible for taxing as demonstrated in the picture provided by Kant1983 below. Aerodynamically the configuration you mentioned was better (as seen in the Curtiss Battleplane, R3C racer, DFW Floh and the Aeromarine PG-1), unfortunately the increased performance was at the expense of pilot visibility.