Lower tip speed with larger blades? I'm pretty sure it's the...

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al-pbs

489 Posts.

31/08/16

06:19

Post #: 18809151
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Originally posted by nihilism ↑

This was my original concern and you're completely correct (about if not 90 degrees it is highly inefficient) and if you look back, you'll actually find me stating this was a major concern.

However I did some calculations based on specific rpm's and I found that the centrifugal force at most rpms above 2000 gets the blade to over 88degrees (i.e. almost perpindicular to the body).

This would still be an efficient loss, and having it on a dual access would also mean you would need to lock pitch somehow, however it is definitely doable to have a 'weak lock' mechanism involving something which would add just enough force to overcome the drag (i.e. has to be a force applier like a magnet or spring or else it would never get into locked position) which then also locks the blade and pitch.

This sort of system would then fold back as soon as any larger force (than the weak-lock force) is applied to the front of the blade.

However, with all this said, there is always going to be some impact based purely on momentum, however with larger blades they should have a lower tip speed also. it's really one of those things you'd need to test to see how much the fold-away blades would reduce the impact.

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Lower tip speed with larger blades?
I'm pretty sure it's the other way around.
Thats the problem with helocopter blades as their tip speed reaches supersonic speed hence the noise
A lot of momentum right there - potentially very hazardous design.

Good theory though

Last edited by al-pbs: 31/08/16

IOT Price at posting: 2.7¢ Sentiment: None Disclosure: Held
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0 Great analysis

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