Customizable engine thrust uneffected by RPM, blade count or blade length

[hrobertson]

Using the either of the customizable engines it is possible to customize the number of blades, the blade length, and the max RPM. None of these variables effect the thrust produced by the engine.

This can be seen in these screenshots showing a plane with highly asymmetric engines flying without any issue: http://imgur.com/a/biAz7

Relevant forum posts: http://forum.kerbalspaceprogram.com/index.php?/topic/22583-firespitter-propeller-plane-and-helicopter-parts-v71-may-5th-for-ksp-10/&do=findComment&comment=2101470 http://forum.kerbalspaceprogram.com/index.php?/topic/22583-firespitter-propeller-plane-and-helicopter-parts-v71-may-5th-for-ksp-10/&do=findComment&comment=2462942

[Ruedii]

Honestly, Max RPM blade count and blade length should change the behavior of the engine at different altitudes, and at different speeds. It should also change the behavior of how the plane throttles.

Average thrust should be unaffected, just at what speed and altitude the thrust is strongest, and what speed and altitude the plane flies most efficiently.

I'm not sure exactly how this all would work, you'd need to ask an expert. Most of the documentation on the matter is over my head.

[hrobertson]

For any given RPM, increasing blade length/number of blades will increase power at all atmospheric densities.

For any given RPM, as blade length is increased the speed of the tips of the blades increases. Tip speed needs to be limited as problematic shock waves will form at high speeds.

There are obviously many other factors that can effect the thrust produced for example the optimal blade geometry and pitch angle varies with atmospheric density.

Useful resources: http://www.aerospaceweb.org/question/propulsion/q0039.shtml http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.17.8601&rep=rep1&type=pdf http://www.airspacemag.com/need-to-know/are-more-propeller-blades-better-108981404/?no-ist

[Ruedii]

That is what I heard longer blades, and more blades improves transmission of power, but limits the speed at which that power can be delivered. If I recall the altitude comes in with the fact that it uses air speed not ground speed.

[hrobertson]

but limits the speed at which that power can be delivered

What do you mean by this?

For any given propeller at a set RPM, there is a finite amount of thrust that can be produced for a given atmospheric density. Thrust vs drag of the vehicle results in a top speed. At higher altitudes there is less drag but the prop will produce less thrust. If you add another blade or make the blades longer, you increase the amount of thrust produced (and increase drag but not as much) and thus increase the top speed and thus the max maintainable altitude.

The primary limitation is running out of space to add additional blades.

My comment on blade tip speed is a separate issue and can probably be ignored for KSP.

[Ruedii]

A propeller's thrust also varies with the speed it's going in a forward velocity. As it reaches faster speeds high pressure builds up on the front, and low pressure on the back, canceling out it's thrust.

[LastStarDust]

Sorry to bump an old thread but was this issue ever addressed? Because I am still experiencing the same problem as the OP.