Pod & Boom ; the folding prop integrated Around the boom

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Bille Floyd

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Sep 26, 2019
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And HERE is the deal breaker ; no real suitable way around it :

...
There's also the possibility of exciting flutter in the tail control surfaces with vibrations from the prop, which is never "perfectly" balanced.

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Thanks Guys ; it was a fun thought experiment !!

Bille
 

Derswede

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If you need a large dia bearing, get an old sock knitting machine, pull the cylinder out. Most have a 4" to 5" diameter bearing under the cylinder. Those are designed for 500 RPM for days on end. Just a sourcing idea.

Derswede
 

Derswede

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2300 rpm. If you can't buy one, let me know, I sell knitting machines and can probably find you a couple of bearings out of a scrapped machine. Will have several machines going to Scrap in Kentucky early next month. Will trade for bourbon!

Derswede
 

proppastie

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2300 rpm. If you can't buy one, let me know, I sell knitting machines and can probably find you a couple of bearings out of a scrapped machine. Will have several machines going to Scrap in Kentucky early next month. Will trade for bourbon!

Derswede
so my boom is out of round about .015, .....has rivets at the first and last tube transitions ..... not sure about the out of round though. I think i would need a split inner bolted together, with the out of round jig-ground in.....custom all the way, and would be difficult to find someone who would build it. ....sort of why I did not think too long about this.
 

AdrianS

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IIRC the issue is the rotating speed of the balls: as the surface speed goes up with the bearing diameter, the limiting rpm drops.
 

proppastie

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IIRC the issue is the rotating speed of the balls: as the surface speed goes up with the bearing diameter, the limiting rpm drops.
yes surface speed is the limiting factor of that specification.....not being a bearing designer the thought occurs as to at what load and if there is wiggle room on a lightly loaded design.....and is 20 or 30 hp a light load?....probably not...I would think a tapered roller bearing rather than a ball bearing might be a better fit.
 

wsimpso1

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Has anyone ever built a prop hub , that was integrated around the
outside of a 10" tube ; with a belt drive from an engine below ?

I see a 10" minimalist , SS bearing race , that's backed up with carbon
for the bearings to ride on, and wouldn't weigh a Huge amount ; with
the hub and prop flanges using the same type construction. The folding
prop blades would be like a flapping rotor blade ; changes in pitch and
yaw, would not stress the hub. The bearings would need a race to ride
in ; then the bearing count could be kept low.

Just an idea ; don't really know, how Dumb it is ----------- yet ?

Bille

See where i'm going with this ? :View attachment 96960
Yes. It really isn't a good idea. By the time the boom is stiff enough and strong enough (having to go through the hub of the prop) it is complicated and heavy and greatly complicates service work.

Billski
 

Riggerrob

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If your PSRU braces close to the bearing, the propeller drive train will impart few additional forces on the tail boom. Try to think of it as bolting the PSRU solidly to the rear bulkhead of the nacelle, then the tail boom just floats in the middle of the bearing.

Then you only have to worry about vibration. The simplest way to damp vibration is to over-build your tail boom so stiff that it will not vibrate at propeller rpm. If you cannot build your tail boom stiff enough, there are a dozen forms of vibration dampeners, starting with simple weights bolted solidly to the boom.
For that, you will need a vibration analyst engineer ... way above my pay grade.
 

plncraze

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Find Rivers Stone and ask him. Does anyone here know him or any of his friends? He had Len Niemi as an employee and provided a place for A.J. Smith to build his race plane.
 
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