Tail boom propeller

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flyndude

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There was an article several years ago in Sustainable Skies about 3 projects to place a propeller that rotated around the tail boom on a glider.

Ring Around the Tail Boom › Sustainable Skies

This seems like a good solution to the problem of prop clearance and would also give you minimum drag with a folding prop. This article was from 2014 and I haven't been able to find any updates or other projects using this idea. I want to power an ultralight glider and something like this I think would work very well for me. Is anyone aware of others using this idea, or reasons why this might not be a good idea?
 

Riggerrob

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Dozens of designers have sketched "around the fuselage propellers", but only a few have made it as far as flying prototypes. Many proposals looked like GFW-4 with the propeller rotating around a large diameter aft fuselage.
Is it really that difficult to build a propeller hub with a large diameter hole up the middle???????????????
How stiff does the circular prop hub have to be????????
Stemme has already proven that you don't need to rigidly mount prop blades to the hub as centrifugal force is enough to hold them in thrust position. Stemme has also proven that you can conceal a significant portion of the prop hub because the inner portions of prop blades produce little thrust.
During World War 2, thousands of American, French, German and Soviet fighters flew with motor-cannons firing through the centers or their PSRUs and propellers. American Bell P-39 Airacobra and P-63 King Cobra. French Moraine and Dewoitine, German Me.109 and Soviet Yaks. Mind you, they only fired 20 mm or 35 mm bullets, so were tiny in comparison with an entire fuselage.

The only production ATFP was the Austrian Brdistchka HB-3, with a small diameter upper prop-boom, but it also has a second lower boom to stabilizer the tail surfaces.

Looking at the problem from the other end ... what is the structural minimum fuselage diameter?????????
I ask about minimum diameter because of the hassle of streamlining pusher props immediately behind the wing (ala. Seabee amphibian). A larger diameter aft fuselage would simplify streamlining.
 

Martin W

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There is a nicely built enclosed gyrocopter that has the tail boom mounted on a 4or5 inch tube which passes thru the prop bearing .... dont have the link .... sorry .

.
 

flyndude

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Looking at the problem from the other end ... what is the structural minimum fuselage diameter?????????
I ask about minimum diameter because of the hassle of streamlining pusher props immediately behind the wing (ala. Seabee amphibian). A larger diameter aft fuselage would simplify streamlining.

Something that would go around about a 8 or 9 inch fuselage would be about ideal for my current glider.
 

pylon500

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The Rivers plane was very interesting, But that was an awful lot of complexity just to hold a fin and rudder behind the prop, when tip rudders would have been easier and more effective?
I am one of the people that was doing the folding prop around a boom on a Tempest glider.
Project is on hold until I can find the right electric motor.
Boom_bearing.png
 

Riggerrob

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The Rivers plane was very interesting, But that was an awful lot of complexity just to hold a fin and rudder behind the prop, when tip rudders would have been easier and more effective?
I am one of the people that was doing the folding prop around a boom on a Tempest glider.
Project is on hold until I can find the right electric motor.
View attachment 120910

Dear Pylon 500,
What is the inside diameter of that prop bearing?
Where did you beg, borrow or steal the bearing?
How many horsepower?
What prop diameter?
How much does your reduction gear weight?
 

pylon500

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You probably want to go and read through this thread;
I now have the glider, which I was only going to use as a glider, then dabbled with the idea of fitting a small 2 stroke to the drive system, but in doing some calculations realised these guys were looking to turn the prop a bit too slow to be effective, as well as having a diameter that was too big to run on the ground.
I intend to go down to a smaller diameter, about 42", but I need an electric motor that will put out about 10~12hp at around 10,000 rpm.
I'm currently looking at some of those motors for 'electric surfboards', when I'm not snowed under my other projects...
 

Martin W

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Dear Pylon 500,
What is the inside diameter of that prop bearing?
Where did you beg, borrow or steal the bearing?
How many horsepower?
What prop diameter?
How much does your reduction gear weight?
Apologies again for not supplying a link (still looking for it)
It was a nicely built gyrocopter prototype that mounted the tailboom thru the prop

--Did not use a large bearing ... inside diameter was only 3-4 inches
--Power was Rotax with a gates belt reduction drive
--The large pulley was also the typical prop mount
--The pulley was built using a hollow shaft with 2 typical bearings except about 3-4 inches dia instead of normal 2 inch bearing
-- this allowed the tailboom (tube) to pass thru the assembly with tail and rudder on the end
-- rudder cables passed thru the inside of the tube
-- very clean design and flew OK
-- designer said the un-braced boom was a bit too flexible during hard rudder
-- concerns about harmonic flutter in certain circumstances
-- thus did not go into manufacture.

.
 

Island_flyer

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I remember that Gyrocopter. It was built in Bulgaria. NIKI Club Sport or something like it.
The Kallithea is one of their complete gyroplanes for sale. I don't think they offer kits. Obviously great visibility. A few years ago a company in Switzerland modified one for VTOL (using 16 motors and props for lift). They called it the passenger drone. That project was sold and became the Elroy, presumably still under development. Here's the original.
 

Vigilant1

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The Kallithea is one of their complete gyroplanes for sale. I don't think they offer kits. .... Here's the original.
Well, some truth in advertising? From the linked web page:

... great proportions and the specious cockpit lend the gyroplane...
 

Martin W

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Not a very good example .... (It is from a Cox powered model) .... but gives the general idea.

.
tailboom thru the prop.JPG tailboom thru prop.JPG
 

Eddie Clark

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I am the person that built the Rivers R-1. It was designed by E.B Gibby Gibson who was the Chief engineer on the Lockeed C-5A. It was an idea he had played around with for a long time. It was financed by River Stone of Greenville SC. It had a Cyuna 2 stroke engine mounted inverted under the boom. It was mounted pretty much the same as Cox model Shown. Because of the spar design, Which I didn't agree on, I was overruled for I'm not an engineer, was way too heavy. also, it had the wrong prop with too much pitch. I flew it in ground effect at around 20 ft. up and down the runway at the old Donaldson Air Base. Because of cost and lose of interest from the owner, the project was abandoned. I had built production molds for most of the parts. And no, I don't know if they still exist as I have no interest. Len Niemi and I used the fuse. mold when we built the Junco motor glider and returned it to Rivers. The good thing about the system was there was not vibration in the vert. tail. But, I personally wound not recommend the system simply due to the complexity if you need to service the thing. Major pain in the rear. Eddie Clark.
 

Vigilant1

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But, I personally would not recommend the system simply due to the complexity if you need to service the thing. Major pain in the rear. Eddie Clark.
Hmmm, and thought up by the Chief Engineer of the C-5A. I'm seeing a trend here.
The Galaxy was an amazing plane in many ways but simplicity/reliability/maintainability was not its strong suit.
When flying very far from USAF maintenance (e.g most places in Africa etc), it was a very poor idea to "kneel" the aircraft's landing gear if there was ANY alternative. The chances of getting the plane and crew stuck there were not insignificant. Bring out a loader, build up some ramps or just dump the stuff off the back ramp, but think hard before kneeling the plane and make sure there's (acceptable) billeting nearby before you do it.
 
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rotax618

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The idea is without merit on a number of areas, first the tail boom has to be light and stiff in torsion and bending, this require a reasonable diameter thin walled tube. To have sufficient section modulus to resist the fatigue of having a vibrating propellor rotating around and I assume driven by belts which are applying a large lateral load to the boom is counter intuitive.
To my mind and perceived advantage is negated by the many disadvantages and complexity.
This is the autogyro you referred to, note that the prop shaft is quite small in diameter, probably a high strength steel tube with the short tail attached to it.97D0C902-1BF1-4EB6-99F7-19EBB442B430.jpeg
 
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