Came across some info in the Cobra I and Cobra II.
Mira Slovak said that he ran a P-51H propeller on a P-39 and almost could not control it. When he tried to turn right, it wanted to do an outside snap roll to the left. After several atttempts, he wound up turning left and landing as quickly as possible. Seems the 4-bladed P-51H prop had a lot more blade area than the 3-blade stock prop, and the increase in surface area forward of the CL could not be handled by the P-39 tail. He is pretty sure that's what killed Mike Carol ... the extra area forward of the CL simply overpowered the tail surfaces of the P-39. If he had used a P-63, he'd have been OK since it was designed for a lot more power and HAD it in late models.
Cobra I and II used very similar propellers to the P-51H from the P-63E. They were very successful and these top test pilots set top speeds and won races. The airplane is controllable and it takes proper handling to do so.
Our shop has a 100-series Allison in the CAF P-63 at San Marcos and it is running and flying just fine. We COULD install an aux blower (we have two), but they aren't wanting one.
The old Cobra II was flown by Lefty Gardner before it crashed and he had this to say to Joe Yancey (they were good friends).
Lefty did not fly Cobra II before it crashed. No one did until the first test flight after the restoration when Mike Carroll took off and was killed bailing out. Tex Johnston (then vice president of Aero Space Lines based in SoCal), Darryl Greenamyer (several time world speed record, multi-time Reno Champion, and Lockheed and Air force test pilot), and Lyle Shelton (Naval Aviator, Naval test pilot, inter-service jet instructor and multi time air racer, at the time) all offered to due the initial test flights on Cobra II and they were declined by Mike on advice from his mentor E.D. Weiner.
When Lefty flew it at Reno, he said the Allison G-6 horsepower was awesome, and the driveshaft bowed over a foot and half under his seat! It was not designed for the power being used (the P-69 driveshaft WAS). He said it was far and away the fastest-accelerating aircaft he had ever flown until a mag let go and he decided to land on the remnaining mag rather than risk losing both. He said it flew "OK but not great due to limited control surface authority" but was very torquey and needed careful handling when at full rattle with the G-6 engine of about 2,850 HP+. When he landed, he was fast enough to have been a half lap ahead of the eventual winner that year.
This Lefty Gardner story is about flying John Sandberg's P-63 King Cobra "Tipsy Miss". It is anecdotal and the airplane was never very successful due to Sandberg endless fiddling.
That data from Joe Yancey after the nice article in a warbird magazine about the Cobra I and II this month. In fact, Joe will be missing from the shop tomorrow due to having to be in Palm Springs to work on THEIR Kingcobra that has issues with either simply a mag or something more serious. We hope it is just a mag. If not, it could be an easily fix or overhaul time ... we won't know until we get there. Mostly, their eninge seemed healthy last time was saw it, so Joe's thinking it could be a mag only at this time. More data after the visit ...
Thanks to Joe we have some very good Allison work going on in the warbird community.