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Aerospace Pictures and Art Thread


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A bunch of Berkut/Firkin goodness has dropped, courtesy of Paralay on the Key Publishing forums:     Model of a further-developed Berkut with rectangular nozzles.  Sukhoi actually test-flew a rec

AEROGAVIN  

The Curtis XP-55 Ascender was an ill-starred, and unconventional fighter design.

2SVA7xh.jpg

 

Ascender was designed by Don R. Berlin, who also designed the combat-proven Curtis Hawk series of fighters.  Given such an excellent mind, it should have been a good design.  But its pedigree was the end of the good luck for the design.

Don R. Berlin left Curtis immediately after he designed the Ascender to work for the Fisher division of General Motors.  This meant that his expertise was not available to de-bug the XP-55, which would hurt the design badly during the prototyping phase.

The next disaster to befall the XP-55 program is that the engine originally intended for it was cancelled.  The plane was originally designed around a Pratt and Whitney X-1800, a technologically advanced and ambitious liquid-cooled sleeve-valve engine similar in general concept to the Napier Sabre that powered the Hawker Typhoon.  All development work on this engine was cancelled just prior to the outbreak of World War Two when Pratt and Whitney consolidated all production and development work on to the Wasp family of air-cooled radial engines.  By 1940 all development effort was used exclusively on the R-1830, R-2000, R-2800 and R-3460.  Legacy engine designs were kept in production, but no further development energy was to be squandered upon them.

While this was a fine decision in terms of wartime production rationalization, and in particular allowed Pratt and Whitney to produce vast numbers of war-winning R-1830s for Wildcats and Fortresses, as well as large numbers of the godlike R-2800, it did leave the XP-55 short on power.  The Allison V-1710-95 was substituted, but this was a much smaller engine that produced almost 1000 less horsepower than was envisioned for the X-1800.

The final nail in the coffin was the plane's handling.  The wings were swept, not to reduce transonic wave drag (which was basically not understood at the time), but to place the wingtip rudders at a greater moment length and move the center of lift rearward in order to offset the destabilizing effect of the canards.  The stall characteristics of swept wings were similarly unknown at the time, and this led to some hair-raising surprises for test pilots.  Test pilot Brig. Gen. Benjamin S. Kelsey had this to say about the Ascender:

"The slow, steady stall was quite satisfactory, and the plane behaved normally in the usual intentional maneuvers.  Because some aircraft have different characteristics when a stall is initiated abruptly, I tried a sharp pullup.  The nose came up rapidly to a very high angle, and forward nose-down control was ineffective in checking the pitch-up.  What happened next was a series of of completely confusing out-of-control gyrations.  Essentially a wobbly sort of spin developed from which recover was possible.

After trying a few more violent stalls, all of which went through the same sort of out-of-control contortions, I thought I knew what happend[sic], but I am still not sure.  Initially the plane, without the damping of a conventional tail to slow the ray of pitch, came up to such a steep angle that the forward elevator could not be moved enough to get any down force on the nose.  What must have followed was a stall with the nose pointed nearly straight up.  This much and the beginning of a rolling motion was fairly clear.

Assuming that with the swept wing, one side or the other stalled first, the plane did a sort of twisting cartwheel, first rotating about the fuselage and then pivoting on one wingtip.  As it went over the top in something like a hammerhead stall, the top advancing wing seemed to roll the plane partially onto its back.  This rotation of the aircraft about its fuselage axis and in the plane of the wing was like an autorotation spin except that the axis of the spiral was falling through the horizontal so that it was probably more nearly a very wobbly snap roll.  With the rudder surfaces located on the wingtips and the fin surface close to the center of gravity over the engine, these surfaces weren't effective in slowing the spinning.

All of this occurred in very rapid sequence, and noting was effective until a recognizable spin had developed.  If one visualizes the movements of the outside references-- the horizon, sky, and earth-- it will be readily apparent that the pilot was in no position to provide a precise description of what went on."

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