Quote:
Originally Posted by drgondog
Given that it doesn't work at zero velocity, what do YOU use to yield the Thrust/Total Thrust/Total Force (all interchangeable) at max power on the ground, chocks or brakes in place? There IS a Force at work but no acceleration as it is in equilibrium. Demonstrate your knowledge of Physics.
In other words, given your vast knowledge of Aero Engineering, based on the easy to understand explanations by Harri, could you calculate take off run, distance to clear`50 ft obstacle and what would your velocity be over the 50 ft obstacle if;
a.) you knew Bhp, or in case of jet - static thrust
b.) wing Aspect ratio,
c.) gross weight,
d.) CL and CDp,
e.) wing area.
Before you start what do you need to know about Cdp that we have not yet discussed?
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The specific problem to be solved was the effect of the weight to the max speed at constant power. What I did was that I calculated Cd0 ie Cdp backwards from the flight test data, using estimated but good enough values of n, e and exhaust thrust. Because the assumed weight change was rather small and speed rather high, the small errors in these estimated parameters can't cause large error; less than 1km/h in that specific case.
Note that accuracy of the Cd0 is not that critical for this specific problem because we are dealing with the same plane at different weights; using Cd0 from say Lednicer's works would have resulted very similar change of the speed due to weight change.
Other point of the analysis was to show why the parametric analysis can't be used to solve this specific problem. There is no constant key parameter needed for the parametric study ie the speed, Cl, drag and thrust are not constant. Therefore polar approach using iteration process is the right way.
However, calculating static thrust, take of distances etc. are other kind of problems which need different approach and indeed out of topic of this thread.