Vought V173

The V173 was the first flying concept of the circular wing STOL plane designed by Charles H Zimmerman first flown in 1942.
 
It still exists in the Frontier of Flight museum in Texas.
It uses two 80hp Continental A80 flat 4 geared to drive early Corsair propellers. Quite logical as it was built by Vought! It flew until 1947 making 191 flights.
Zimmerman's concept was that the spiral flow from outward rotating props positioned at the tips of the circular wing would counter the significant wing tip losses from such a low aspect ratio wing. 
 
Following my tradition of building "challenging" designs my idea is to build a Depron light weight version using 10x5 CW & CCW 3 blade as scale props to give a span of 23.5". At that size a 28mm Out runner will be the exact diameter of the prop nacelles. It will definitely also use a gyro!
We shall see.  . .    
 

That beast would be challenging to fly if one engine quit! 
I suspect that rudder/fn blanking at high AOA would be the main problem. Differential throttle steering?

I have ordered a CC & CCW 10x5 three blade prop but of course they are coming from China so could be some weeks before they get here.
 
They are apparently for a model of a B17. When did a B17 ever have counter rotating props!
As I already have a suitable 28mm out runner the intention is make up a "test" nacelle for the V173 to see how it looks and how much thrust it can deliver before starting to make the airframe.
An in flight photo of the V173.
 
Although both the fuselage elevator and the tail plane elevator are absolutely neutral the "trim" position of the all moving tail plane does look a bit of a worry!
Does it need that much decalage to achieve any sort of longitudinal stability?
It wouldn't surprise me if it does.
Although a full size version the XF5U with 2x1350 hp P&W radials was built it was never flown.
Surprisingly  the XF5U did not use counter rotating props like the V173 but each prop had cyclic pitch control like a helicopter to alter the effective centre of thrust. Ground test showed it suffered from serious vibration.
The project was cancelled in 1947 when the US Navy decided longer carriers with steam catapults was a far more practical way to operate high performance fighters.

As I suspected - assymetric thrust for steering.
-
You can see - with those huge props - where they got the idea for the Osprey helicoptery thing that keeps breaking!

It looks as though the engines must have been inboard with some kind of long drive system.

I can find no layout of the engines in the V 173. I presume the flat 4s were mounted under the inboard hatches with 4 air intakes each side.  I presume the drive line was similar to the much larger XF5U with two right angle gear boxes each side. .
 
What is surprising is they managed to actually fly it on a total on just 160hp.
A rather grainy video of it flying.

Also showing contra rotating props. The drive losses must have been quite high.

Found this on the tube as well - - ignore the silly intro -

or this one -

Interesting, given the advances in electric propulsion I think it would prove to be a nice flyer.

Just musing but this is my first attempt at a 28mm diameter nacelle.
 
The motor bell, motor mount and the nacelle are all the same diameter. The motor wires run inside the nacelle.
I don't have the props yet but hopefully I will be able to print a suitable spinner..
Printed in nacelle even printed in single wall PLA will be plenty strong enough but with the motor stuck right on the end it will take some careful design to mount it into a light foam body.

The test nacelle with its full spinner. There is actually a prop driver inside! 
 
I still don't have the props so the spinner body will need to have 3 cut outs programmed in.

That looks rude! 

Just wait till it starts going round!  

OOH Matron!

A short video of the test nacelle running. Not exactly exciting but it does run pretty smoothly.