Thanks F4UDOA, it's the same report I quoted some time ago, actually all USAF comparisons I have seen state pretty clearly that the P-51 had better dive acceleration than the P-38. Maybe at low altitude and if dive angle is very low the P-38 might have a initial advantage but so far I have not seen real world test which support this.
bolillo_loco,
The dive capability comparison in the AHT appears to be based on the calculations just like level flight accelerations (exhaust thrust and propeller efficiency are not counted nor drag at given Cl/speed/weight combination).
The fabric covered elevator was not a big problem if the plane was trimmed nose heavy and correct control techniques were used (see The Mustang Story p. 116 and AHT p.345), Borsodi did his dive tests with fabric covered elevators. BTW I have told this before...
No one has claimed that full throttle vertical dive with 400mph TAS starting speed from 30-40k all way down would have been safe with the P-51. Borsodi made 32 dives and reached mach 0.86. In that mach 0.86 dive radiator damaged but the plane was under control all the time. What I have stated is that the P-51 could start dive from high altitude at high speed and enter compressebility speeds (above mach 0.75) and recover safely if correct control techniques were used (please consult those references).
The Wright field test claimed in the AHT is a good example about phenomena I described above ie it was not recommended to pull out from dive if the plane was allready in the compressebility speeds because buffeting would increase when g load increases and might damage plane. And again it should be noted that during this test many dives were made and the plane stayed under control all the time.
And it was certainly possible to broke wings of the P-51 during the pull out if correct control techniques (nose down trim) and fuel management (not too much fuel in the fuselage tank) were not used. But it was same with pretty much all other planes too.
HoHun,
I believe that Kelly Johnson and his team did best they can with the aerodynamics of the P-38. There just was not enough knowledge when the P-38 was designed and it appears that there was a bit plain bad luck.
This graph explains pretty well what went wrong. The wing itself without fuselage does pretty well at Cl 0.1; up to about mach 0.75 there is no tuck under and at Cl 0.2 tuck under starts at about mach 0.72. But everything changes with standard fuselage ie tuck under starts around mach 0.67 depending on Cl. With revised fuselage tuck under starts at low Cl values around mach 0,7 and this was confirmed with a modified plane which did safely more than Mach 0.7. So with a different fuselage the P-38 might have been much safer in dive but there would have been still problems under higher g loads.
The Clmax qualities of the wing is another story but I don't know how much of the drop is caused by the fuselage and wing center section. Probably Johnson and his team were aware about Clmax drop but they were designing a interceptor after all, not a dog fighter.
gripen
