No, it doesn't. Not necessarily.Originally posted by WTE_Galway:
The apparent division by zero just means mathematically it needs to be approached as a limit case.
thrust hp = engine hp * prop efficiency
For all situations where neither engine hp or prop efficiency (so basically all situations where engine is on and prop is mounted) thrust hp > 0.
So,
T = P/v with P > 0 and v = 0, so
T = n.d. or, if you want to use a limit case,
T -> infinite
That's basically all there is to it, but I'll be going on ranting a bit.
No, acceleration may or may not take place. That's not part of the equation.First note that:
T =P/v
is a simplified case assuming a stable system where no acceleration takes place.
Yes, and no matter how large the thrust is, your P from that equation will always be 0 (i.e. T from P/v = n.d.).now, rearranging and solving for P:
P = Tv
If v=0, then the propulsive POWER of the propeller/engine as a system is ZERO.
So, basically you're calculating:Getting back to T =P/v.
Given P = 0 it can be easily shown that for
the limit case as v->0 then T=0
(in non mathematical terms - regardless of how small v gets P = 0 and hence P/v is zero and THRUST remains ZERO)
T = P/v, P = Tv so T = T*v/v so T = T. That's all you've done, and it leads nowhere.
Excess thrust was not the point. Total thrust was.HOWEVER even from commonsense, if its a stable system where v is constant at zero their can be no EXCESS thrust and the total EXCESS thrust vector must be zero.
I'm used to seeing physics getting raped on this board, but now not even math is spared any longer. That hurts.![]()
WTE_Galway got it right.thrust hp = engine hp * prop efficiency
Power by definition is force x velocity. If our velocity is zero then our power is zero.
Its just basic physics.
http://www.ajdesigner.com/phpp...n_velocity_force.php
The rest is a clown fest.
For example, Thrust Horsepower by definition is:And the proper form of it is actually:
T = P*n/V
Shaft Horsepower x n and the 325 is a conversion factor for using Knots in the BGS system. It is not what some were taught to parrot and without understanding the definition of Thrust Horsepower it does not fit their mold.
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Actually, I started the thread after a question was asked about whether, and how accurately, IL-2 modelled ground effect. This involved attempting to answer two questions: (a) how IL-2 models GE, and (b) what are the effects of GE in real life. Without measurement, mathematical models tell us precisely nothing - they can only be a statement about how reality is expected to behave if the maths and the underlying assumptions are correct. It is noticeable that this thread contains (a) some data gathered from attempts at measuring IL-2 GE, and NO verifiable data about real-world GE. On this basis, almost anything IL-2 does might be right, wrong, or just plain irrelevant. In order to simulate something, you need to know what it is that is being simulated. On the evidence presented so far, I could argue that real-world ground effect was caused by proximity to earthworms...
Originally posted by Kettenhunde:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">NO verifiable data about real-world GE.
That is not true.
I gave you a simple method to estimate the effect that agrees with real world results very well in the first few posting on the subject. </div></BLOCKQUOTE>
A 'method to estimate the effect' isn't the same thing as 'verifiable data' though, is it? Given the contradictory explanations of GE I've seen, I see little reason to attach any particular credence to estimates.
I think that the IL-2 GE model is wrong. I've still not got much idea about what it would look like if it was right.