Pod & Boom ; the folding prop integrated Around the boom

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

Bille Floyd

Well-Known Member
Joined
Sep 26, 2019
Messages
223
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.

...
Thanks Guys ; it was a fun thought experiment !!

Bille
 

Derswede

Well-Known Member
Joined
Jan 6, 2016
Messages
924
Location
Central North Carolina
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

Well-Known Member
Joined
Jan 6, 2016
Messages
924
Location
Central North Carolina
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

Well-Known Member
Log Member
Joined
Feb 19, 2012
Messages
4,536
Location
NJ
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

Well-Known Member
Joined
Jul 5, 2014
Messages
516
Location
Australia
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

Well-Known Member
Log Member
Joined
Feb 19, 2012
Messages
4,536
Location
NJ
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

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
6,730
Location
Saline Michigan
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

Well-Known Member
Joined
Sep 9, 2014
Messages
1,410
Location
Canada
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

Well-Known Member
HBA Supporter
Joined
May 11, 2006
Messages
1,799
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.
 

Victor Bravo

Well-Known Member
Joined
Jul 30, 2014
Messages
7,291
Location
KWHP, Los Angeles CA, USA
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.
Wow, I haven't heard Len Neimi's name in a while. He built the fabulous Sisu gliders, which were world class competition gliders once upon a time.
 

plncraze

Well-Known Member
HBA Supporter
Joined
May 11, 2006
Messages
1,799
If you include the AJ-2 Niemi has two planes in the Smithsonian.
 
Last edited:

simflyer

Well-Known Member
Joined
Sep 24, 2015
Messages
179
Location
Moravia
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 ?
Bille, I saw few designs of this kind - mostly gliders, even not exactly American Eaglet. One is french Sirius II. Interresting could be to get look on Bailey Tempest - Am looking for wing inner photos and drawings (was for sale with one Tempest glider). Also interresting could be photos of inner wing structure of Super Floater.
 

Attachments

Top