Tail boom propeller

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Aesquire

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Jul 28, 2014
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Rochester, NY, USA
On another thread I recommend Not using long prop shaft extensions and prop around boom in your designs.

Got some flack, deserved, and both ideas have been executed nicely.

I still consider them to be "expert" items that can stall progress and lead to abandoned projects.

But if there's any place to figure them out, here is good. :)
 

Riggerrob

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Sep 9, 2014
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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.View attachment 120975

Dear rotax618,

Which brings us back to the question: what is the largest inside diameter prop hub that you can built with semi-production prop blades, reduction belts, etc.?
I am thinking of installing a bracing bearing immediately forward of the PSRU belt to minimize shaft bending. Then custom machine a pulley and combined prop hub to accept production prop blades (say Whirlwind).
The tail boom/center shaft could also have internal reinforcements (press-fit sleeves) to better withstand vibration and bending loads.
Outside diameter of the fuselage will be 2 feet (single-seater) or 4 feet (two-seater side-by-side) to minimize drag caused by too rapid a neck-down aft of the cockpit.
It would also help to know how much the prop blade roots contribute to thrust .... and at what diameter do they start to contribute to thrust ....
Many innovators have tried to build around the fuselage props. A few have flown prototypes, but only a handful have reached production. What is the limitation????????????
 

Eddie Clark

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Aug 16, 2015
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Fouintain SC
In defense of Gibby, on the C-5A, I remember him telling me that the problem was with what the gov. wanted. The airplane was built on the margin of safety. this led to the wing mods. I remember Gibby talking with Joe Cornish, his boss at Lockheed, (after Gibby's retirement) Do I get a big bonus for Lockheed getting the contract to fix the problem. Joe said, it doesn't work that way. I heard that phone call. I loved working with the people that I have learned from in my life. trough them. I have been able to gain a lot of knowledge. Too much to list here.
 

Vigilant1

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Jan 24, 2011
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In defense of Gibby, on the C-5A, I remember him telling me that the problem was with what the gov. wanted.
I can believe that. It is a great plane in many respects, but, in retrospect the requirements it was built to meet were not well thought out. For example, the plane was built to operate off unimproved strips. Sounds really great, but in 50 years of operation we've never done that. It is hard to imagine a case where it would be done >in real life< except in the most extreme set of unlikely circumstances. Yet, that requirement caused all kinds of reduced capability in other areas.
Still, a tremendous plane and it remains very important today.
 
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