Thought this might be of interest to a few of you:
Ju88 flight testing, fuel weight determination, note on drag.
Method: autotakeoff from a sea-level airfield, timed climb to 10,000ft. Stopwatch started as soon as the manifold pressure gauge starts registering pressure.
Fuel load time(secs)
25% 398
50% 418
75% 440
100% 460
Same test, but with 25% fuel and internal bomb loads (so that there is no change in drag*):
bombs time (secs)
500kg 432
1000kg 472
Inspecting the above, the time for 25% fuel plus 500kg bombs falls between the data for 50% and 75% fuel with no bombload. Interpolating between the two values, 432 is 14/22 of the way between 418 and 440, therefore the equivalent total weight of fuel is 50% + (14/22*25%) = 50+15.9 = 65.9% fuel. Subtracting the 25% fuel actually carried, it can be seen that 500kg of bombs carried internally appear to have the same effect on climb performance as about 41% of maximum fuel load.
From this the actual maximum fuel load can be calculated; (100/41)*500 beng the mass, in kg, of fuel carried, which works out to about 1220kgs. Assuming a density for aviation fuel of .7 (water = 1.0), this equates to
1220/0.7 = 1743litres of fuel. At 4.546 litres to the UK gallon and 3.785 litres to a US gallon that equates to 383.4 or 460.5 gallons respectively, the latter being easily within reasonable error bounds of the 463 gallons stated as being carried by HTC. Therefore 1% of a full fuel load for the Ju88 in AH masses about 12.2kgs, and 25% fuel masses about 305kgs.
Further tests were done to gain some idea of the extent to which drag is modelled and affects things, using 25% fuel and the stated bomb loads:
2x250kgs external 439s
4x250kgs external 487s
2x500kgs external 484s
2x250kgs exteral plus 10x50kgs internal 479s
These figures demonstrate clearly that the drag of external stores IS modelled, and the relative amounts of drag produced by various loadouts is consistent with expectations (whether the actual amount of drag produced is consistent with reailty is another matter which I am as yet unable to test; I have no reason to doubt that it isn't however).
*to what extent the effect on the CG (centre of gravity) of having different loadouts aboard affects the angle of attack of the flying surfaces and thus the amount of drag generated I do not know and have had to assume that it is negligible.
Esme
CO, Kampfgeschwader 2 "Holzhammer"
