Blade wrapping.

diadave

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I have a set of metal bensen/Brock blades on my kb2.These are the ones with the air gaps between sections.would wrapping with vinyl be possible.I mean the stuff car fans cover their cars with.just a thought I'd like to throw out to all you experts.thank you.
 

C. Beaty

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Some individuals have tried sealing the gaps with sticky tape but the pressure near the tips is fairly high which blows out the tape.
 

kolibri282

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Dave, I have tried to get some ball park figures. If I got the math right then for a 10 ft rotor at 400rpm the tip pressure would be something like 1.3 psi (88.8 mBar). To test the seal you could place the blade upright and fill the end with about 36 inches of water, that would give you the 1.3 psi. You might want to make that 54 inches to have a margin of safety of 1.5. After sealing the ends you will probably have to rebalance your blades. Please note that these figures come without any warranty whatsoever!


Please check my calculation all ye experts, just in case I messed up something.



Rotor_Tip_Pressure.jpg
 

CLS447

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One piece of vinyl, root to tip, with seam meeting at trailing edge ?
 

C. Beaty

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kolibri282;n1131900 said:
Please check my calculation all ye experts, just in case I messed up something.
I get 1.4 psi for calculation of dynamic pressure.
Close enough for government work.
 

kolibri282

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Thanks for checking,Chuck!
Close enough for government work.
to me sounds a bit like "I'm not too happy with my government" which definitely is true in Germany these days...;-)
 
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C. Beaty

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kolibri282;n1131951 said:
Thanks for checking,Chuck!
to me sounds a bit like "I'm not too happy with my government" which definitely is true in Germany these days...;-)
But isn’t Frauke Petry out to fix things?

But the expression; “Close enough for government work” doesn’t reflect discontent, it means simply that when dealing with government bureaucracy, paperwork is more important than content. Forms must be filled out correctly with all the tees crossed and all the eyes dotted.
 
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diadave

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Thanks you guys ,I know you lot would have the answer.I was only really thinking aloud sort of thing.I would not tty it, what if vinyl came off one blade ,bye bye gyro.
 

kolibri282

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But isn’t Frauke Petry out to fix things?
Actually since she left the AfD she has somewhat vanished into thin air, though she is not the kind to disappear for very long. My guess: she'll do the jack in the box thingy and pop right up again one of these days...;-)
 

Jean Claude

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kolibri282;n1131900 said:
Please check my calculation all ye experts, just in case I messed up something.

In my opinion, your calculation is false, Juergen. You have assumed that the density of the air inside is constant, while it increases with the distribution of the internal pressure.
 
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diadave

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What would be the result of doing this,(vinyl wrapping), successfully. ie ,effect on lift/drag, flare on landing and anything else such as is it a good idea(pros and cons).Thanks again for all your input on this and your continuing input on this forum.
 

Jean Claude

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After taking into account the density gradient of the indoor air, the calculation of Juergen is underestimated only about 10%
17300 N / m2 instead of 15800 N / m2 for a diameter of 8.5 m at 360rpm
Seal the cuts on the underside and root with a tape. Drill a small hole to the tip should put the inside in depression and the tape could not be blown. Just my two cents.
 
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diadave

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Good idea,(the little hole to relieve the pressure).This stuff sticks like the proverbial sh+t to a shovel. I bought some to put some stripes on my motorhome and gots loads left so might just give it a wirl. If I do will let you know the result. Thanks Claude for that idea.
 

kolibri282

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Juergen is underestimated only about 10%
It's them negligent engineers, you know JC. They simply simplify whenever they deem things negligible......
(and then these scaramouchs add a margin of safety to make up for their sloppiness.......;-)
 

C. Beaty

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Stagnation or ram pressure is identical to centrifugal pressure: ½ pV[SUP]2[/SUP]. In Imperial units, p (air density) = 0.0023 slugs/ft[SUP]3, [/SUP], V (velocity) ft/second and pressure = lbs/ft[SUP]2[/SUP].

But doing it the easy way spoils all the fun; everyone enjoys a lovely page of differential equations.
 

diadave

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Sorry Claude ,but my days of differential equations ended about 50 years ago,but I see the point(I think). A hole drilled in the end of a blade creates adrop in pressure which would remove, or help to,get rid of pressure built up in the blade.
 

kolibri282

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Stagnation or ram pressure is identical to centrifugal pressure
The (omega*R)^2 in my formula is the tip speed squared, but is this really obvious before you integrated along the blade to get that result, Chuck? To me it rather looks like one of those results where, after you arrived at it, you go: ups, that's funny, isn't it?
 

C. Beaty

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The rationale Juergen, is that if the blade was a uniform tube without friction, the velocity of air leaving the tip would be identical to free stream velocity.

Cap it off and you have a pitot tube.
 

Jean Claude

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kolibri282;n1132241 said:
It's them negligent engineers, you know JC. They simply simplify whenever they deem things negligible......
(and then these scaramouchs add a margin of safety to make up for their sloppiness.......;-)
I agree, Juergen. I just need to roughly quantify the errors before assuming it to be negligible.
500 "Gs" at the tip deserved more attention
 
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