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Hi Greybeard and Bletchley,
I found same problems with a comparison between Ni.11 and Caproni Ca.20 performances.
The “lose” of 25 Hp maybe is due to a fitting of different kind of propeller (with different efficiency) in the two versions of Camel.
If I understand it right at Vmax Drag = Trusth, with the
Drag Coefficient as = (550*nu*P)/(0,5*ro*S*(1,47*Vmax)^3), with
nu = propeller efficiency
P = available power
ro = air density
S = wing surface
And 550 and 1,47 constant valid only for UK system
By this (if I understand it right) you can see that for a unit increase of Vmax you need to give ^3 more power to the system.
In my comparison I use a nu=0,68. With this value (that feels a little bit low) my ceiling rates calculations match with test datas.
So if you have the ceiling times of Camel with both engines is possible to verify my hypothesis of two different spinners……. Maybe.
Paolo
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