Quote:
Originally Posted by Ironflight
Engineering school was a long time ago, but the formula I always use for Rate of Climb (ROC) is:
ROC - 33,000 x (Excess HP/Weight) with ROC in fpm and weight in lbs. A little algebra can be used with the formula to compare the ROC's for two different weights. While you should know the HP(required and available) from your Phase 1 flight testing, the actual values of Excess HP and the constant drop out when you are looking for Delta ROC.
As my professors used to say, "The derivation is left as an exercise for the student."
Paul
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I would modify your formula a bit:
ROC = 33,000 x (Excess HP/Weight) x eta
where eta is the propulsive efficiency of the propeller. For a propellor at optimum efficiency, eta is typically about 85%. But if you are climbing at an off-design speed (i.e, climbing with a cruise prop), efficiency can be significantly lower.