Takeoff distance comparisons

[F4UDOA]

Pyro,

I have done some limited flight testing of three A/C that I have solid takeoff run data.
Those three A/C are the P38L, P51D and F4U-1D. The results were as follows measued in seconds at 75% fuel load no external stores. I use the second intersecting runway as my point of reference for when the A/C leaves the ground then count the time to cross it in seconds since I can't measure feet. All A/C are in the clean condition(Especially since flaps do not yet produce lift in AH).

P-51D leaves the ground approx. 3sec. before
second runway crossing
P-38L lifts off at approx. 2 sec. before  F4U-1D lifts off at approx 1.5 sec before

This is backward from the AHT reference of actual performance in which takeoffs are as follows.
P-51D 10176LBS 1185FT
P-38J 17699LBS 1080FT
F4U-1D 12289LBS 840FT

Is it possible that the lift and acceleration calculation does not take into consideration the performance of the larger airscrew on the F4U? It does displace more air and pressure?
Anyway that's my small wine for the day.

F4UDOA

[Dinger]

I'm no expert on these things, but shouldn't you be testing these birds with 100% fuel and in the manual-specified takeoff configuration?
Besides, measuring the takeoff in "seconds before hitting the crossing" seems inherently flawed unless the takeoff speeds are identical.
What you could do would be to run the recorder, set everything up according to hoyle, and at the moment the vsi goes positive ROC, freeze frame, go outside top-down view and get a screenshot of the plane's shadow on the RW, then compare results.

[This message has been edited by Dinger (edited 03-16-2000).]