RRAM:
Thanks for the data on the alt variation on BHP. Here's some recalcs based on the Engine BHP figures you provided. Again bear in mind that these are approximations.
(1) Drag = Thrust approximations
@ SL with BHP 1775, .8 Prop Eff..
If max level speed = 335 mph, D= 1590 lbs
If max level speed = 351 mph, D= 1517 lbs
@21K with BHP 1425, .8 prop eff...
if max level speed = 407 mph, D= 1050 lbs
(2) Parasite Drag Coefficient Approximations
Using the above estimates:
SL max level speed 335 mph, CD0=.026
SL max level speed 351 mph, CD0=.022
21k max level speed 407 mph, CD0=.021
[EDIT: just to be clear, Di was factored in and I applied the CD = CDi + CD0 equation to derive CD0]
(3) Expected Max Speed at 21k using CD0=.022
Assuming 1050 lbs drag, max level speed at 21k = 406mph
(4) Expected Max Speed at 21k using CD0=.026
Assuming 1050 lbs drag, max level speed at 21k = 379mph
CONCLUSION:
Very interesting indeed. First it would appear with the modified BHP #'s that CD0~.021, .022 is more accurate. 2nd with a CD0=.022, the resulting max level speed at 21k gets you the appropriate max level speed of 406 mph.
You guys asking for an increase of the A-5's speed to 351 mph at sea level may be on to something here. The approximations based on the engine data assumptions, resulting drag, and max level speed at 21k estimates appear to be in line with what you are indicating.
Of course I'm missing details such as thrust calculations aren't as straightforward as the T = BHP*PE * 550 / V that I was using nor are PE figures constant. However if the gets us with 85% of an accurate approximation then something may be amiss.
Pyro, HT- any comment?
Tango, XO
412th FS Braunco Mustangs
