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Curtiss XP-55 Ascender
Posted on November 2, 2021 by atcDave
A prototype that was never really considered for a production order, Let's look at a design meant to tackle difficult aerodynamic issues as new areas of speed and performance were dealt with at the end of the piston-engine fighter era.
In the late 1930s it seemed aircraft were approaching absolute aerodynamic limits. As airfoils approached the speed of sound they literally couldn't get out of their own way fast enough to move any faster. The Army Air Corp suggested to several manufacturers that they would entertain very unusual designs to get a next step forward in performance. The military did not have a program for pure experimental, research types at this time so these were to be considered next (or next next) generation fighters.
Three designs would be approved for construction (I expect eventually to offer all three at this site) including one by Curtiss that the company tagged "CW24". It featured a swept wing which was already known to offer some advantages at high speed and was a "canard" design (literally "duck-like", but in aviation usually translated as "tail first"). Significantly it was a "pusher", propeller in back. This was seen as a hugely important, it let all the turbulence coming off the propeller dissipate in the aircraft's wake instead of interacting with and causing turbulent airflow all along the length of the airframe. In the days before computer aided design and flight management systems it also led to stability issues, not unlike driving a rear wheel drive car on ice. But this isn't an impossible problem, just another trick to deal with. The propeller could be jettisoned in case the pilot needed to bail out. A Curtiss engineer suggested the name "Ascender" as a naughty pun, that apparently caught on and became official.
Due to concerns about the configuration a 1:1 scale model; steel frame covered by fabric with a 275 hp engine, was ordered for flight tests. The tests were considered a limited success and three prototypes were ordered. Among the features settled on was a new Pratt & Whitney X-1800 engine. This would have entered production as the H-2600 to match the engine block and displacement. It was projected to generate between 1800 – 2200 hp. However the engine failed to live up to expectations. With demand for actual production increasing the engine was discontinued in 1940 with only a single example, so Pratt & Whitney could focus on their radial engines. The P-55 switched to the tried and true Alison V-1710.
That switch may represent the point at which the AAF gave up on the project as an actual production aircraft. Certainly by the time the first XP-55 prototype flew on July 13, 1943 it was expected to be a pure experimental type. Data was sought for the swept wing, the configuration overall. It could be directly compared with other aircraft using the same powerplant (especially early P-51).
The wingtips do have a sort of tacked on look to them!
Usually the performance is described as unremarkable. The numbers aren't bad, but aren't great either. Its top speed was 390 mph at 19000 ft. That actually seems fast to me for a single-engine Alison powered aircraft. Although not fast enough to compete with the latest Mustang or Thunderbolt; or of course, new jets in development.
Other aspects of its performance clearly were remarkable, just not in a good way. The type's roll stability was particularly bad. The first prototype was destroyed in a November 1943 crash when the pilot found himself in an inverted flat spin he couldn't recover from. After loosing 16000 feet altitude he successfully bailed out.
The second prototype was modified with a larger horizontal stabilizer and elevators to improve take-off performance. It also had wingtips extended out past the vertical tail surfaces to improve roll stability. One of my sources claims test pilots were broadly scared of the type (Weapons and Warfare. Years ago, I'm sure I read a test pilot report that said it was the "most terrifying machine he ever flew". But I can't locate that source now, so take it for what its worth…)
The third prototype was delivered armed with four M2 .50 machine guns. Its extended wingtips were further modified with "trailerons", this was basically a repeater for the ailerons on the main part of the wing to further improve roll performance. It was thought this may have finally fixed the roll stability, and the second prototype was modified along similar lines. On May 27, 1945 the third prototype crashed at an air show at Wright Field in Dayton, Ohio. It happened during a low pass with a P-38 Lightning and P-51 Mustang. The pilot, William C Glasgow decided to try a slow roll during the low pass. He, along with four civilians on the ground were killed.
The program was terminated with only the second prototype remaining. Today it can be seen at the Air Zoo in Kalamazoo, Michigan.
This is the second prototype. I had to do some extra research as this type is much less well documented than most of what I build. In particular, I wanted to do the second aircraft because I've seen that one. I know right where its sitting! The kit included decals for it. But the kit also has the final form of the wingtips, and I couldn't find it in writing if it was ever modified that way (I did in fact find that information much later). I wound up using the very helpful post and photo albums at Jeff Groves excellent Inch High Guy website. The pictures of the actual aircraft settled all questions that the aircraft did indeed have the enlarged wingtips with trailerons.
The XP-55 had a similar V-1710 to any of the early Mustangs, so this P-51A could provide meaningful data. The Mustang was about the same speed, but handled far better.
This build represents a victory of sorts for me. Its the first true "limited run" kit I've successfully built. I have also built kits by Mirage, Fine Molds and early Eduard; which all kind of straddle the line between main stream and limited run. Years ago (25?) I attempted a Commonwealth Boomerang by LTD. What an awful experience that was. The incomplete model made an unscheduled flight into the basement wall. So I've been cautious ever since. I've bought a small number as the technology seemed to improve; companies like Special Hobby and Classic Airframes often offer the minor types that no main stream kit maker will ever touch. So I've acquired a small number of them.
In the last couple years there has been an explosion of little companies making these kits in Eastern Europe. The quality clearly keeps getting better, and dang if they don't offer some irresistible subject matter! So I decided this was a good time to see if could handle one of these modern, limited run kits. This was by the Ukrainian company Modelsvit. It was definitely still tricky, a lot of test fitting and trimming. Followed by filling and sanding. Certainly far more than we would expect from a modern main line kit. But in a way, I felt like growing up with 1960s Monogram, Revell, Airfix really prepared me pretty well for this! I really skimp on the photo-etch (I dislike it, and use the bare minimum); but the plastic is only difficult to work with. I'd comment that I will do more of these, but of course the Yak-9 "on my workbench" now is also a Modelsvit kit. Hopefully that will be done in a week or so! The real test will be when I try an older kit in a few months (I have a few candidates for what that will be!).
Japan performed similar research. The J7W however actually had a more modern engine (Mitsubishi Ha-43 with 2100 hp). It is funny to see the "comparable" American type looking so much smaller; unlike, well, absolutely every other such comparison we could make!
The main display area of the Air Zoo. See anything familiar?
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10 Responses to Curtiss XP-55 Ascender
jfwknifton says:
Thanks for that comprehensive account. I hadn't realised that "Ascender" was a pun because the word "ass" is just the old fashioned word for a donkey. It's a very clever pun, and surely the only one associated with aircraft names?
The world's only flying donkey. I love it! Too bad it never won the race at Donegal…
There are definitely a few other oddly named types, but Ascender may be the champ.
I didn't get the pun until I read John's comment.
Great post Plane Dave.
Reblogged this on My Forgotten Hobby IV and commented:
To know more about the real meaning of an Ascender…
Designed to appeal to the adolescent in all of us.
Aviationtrails says:
A very interesting write up Dave. It certainly looked a challenging aircraft to build and fly but I guess that's the way aircraft development goes. Learning by failure.
Yeah, especially before Computers were so involved. It made flight testing a very dangerous process!
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panzerman1944 says:
Your comment on the growing number of small kit companies coming onto the modeling scene from eastern Europe resonated with me. I use my models in illustrating WWII military subjects I lecture at a local university here in south-central PA. As you do, I too look for unusual aircraft types to add to my collection and use in my classes. The one I was hoping to find to build for a class on strategic bombers was the never completed Junkers Ju-488. I finally found a kit from one of these new companies and was terribly disappointed. It was cast in yellow resin and almost lacking in surface detail and many of the parts were molded in a single mass. I quickly realized this was beyond my model-making abilities and put the parts back in the box and regretfully put it aside.
Hah! Yeah I've seen some pretty scary stuff too! I have a couple that scare the daylights out of me. But I think the current state of the art looks pretty good. Modelsvit was buildable. I'll be trying a Dora Wings kit soon that looks pretty good. And it does mean some minor types are getting kitted.
But I bet it will be a while before the Ju 488 ever shows up! Maybe, in another decade, with more extensive 3-D printing… Well, never say never…
I think I would have enjoyed your History class! What an awesome way to bring things to life.