Vought V173

The outboard servo installed with the tail planes fitted.
 
There are a couple of videos of model RC V173 flying and although they appear to have rear elevators it is not possible to determine if it is used or are just relying on the tail planes as elevons.
I also note that the models although fitted with scale  "show" 3 blade props actually fly with much smaller ones suggesting they are not really using the aerodynamic principles that Zimmerman proposed but are flying at a speed where the tail planes are in a more conventional airflow.

We shall see what happens when full diameter props are used.

The "no elevator" conversion is complete.
 
It is in effect a tissue covered extension of the existing body so it will rely on solely on the elevons for pitch and roll control.

The other aspect that I have mentioned is the flying RC versions use much small props.
 
I suspect it is flying as a very low aspect ratio wing rather than demonstrating any effect of the prop wash countering the big wing tip losses.
This very detailed XF5U has even smaller props!
 
Both fly well enough but likely due to the power of electrics rather any aerodynamic efficiency.
What I want to achieve is the very slow flying speed that the V-123 actually could achieve without using  a "hovering" thrust to weight ratio.
With its tiny motors I certainly won't have it!
 
But then it likely won't fly either! 

It moves!
A very short video of the V173 taxiing along a bed.

The object was to see if it could taxi on a soft surface and not tip over.
So far so good but the RH motor generates more thrust ten the LH. With such limited a limited rudder moment this is a serious problem.
The ESCs have been calibrated. I suspect the ESC is at fault as it has trouble starting to rotate the prop whereas the RH one does not.
I fear a bit more tissue will have to be cut away to change the ESC.
It is running on a rather old 1800mAh 2s.
 

Was it a test bed - or a bed test? 

The motor problem seems a bit more involved than I thought.
They both start and run to full power much more reliably when driven via a servo tester rather than the Rx. At some power levels you can even hear the prop "beat" suggesting they must be close to being "in sync".
Not sure why a servo tester should do a better job than an Rx.

Just for info with both motors at full power it only draws 9.02A  70.4W. High power it is not!  

After much though the only way to overcome the asymmetric thrust is to use differential thrust.
First had to open up a bit of the V173 tissue to arrange individual Rx leads from the ESCs. I then discovered that the channel order on the Rx is not the same as used by the HK Tx6i. Makes selecting the channels for a mix a bit odd - throttle is channel 3. It appears the Tx channel order has been set by Mode1 not Mode 2.
I then arranged a mix such that one throttle had about 8% less travel. This hopefully would compensate for the thrust difference between the motors.
I then arranged for two more mixes that the rudder in both directions had a modest 20% input to the throttle.
The intention is to have a very gentle rudder effect on the throttle differential.
So far it has demonstrated that it can now more or less turn left and right using the rudder/differential thrust but it is incredibly sensitive. Its a bit "all or nothing" at the moment.
Once I get it under some sort of repeatable control a video will follow.

A video of my first stumbling attempts at maneuvering the V173 on a reasonable surface using the rudder controlled differential throttles.

The throttle mix is offset by 7% to account for the weaker LH motor. With no rudder input it does more or less taxi in a straight line
The rudder input to the throttle differential is set to 30% but with the props at the tip of the very short span of the airframe it does make any maneuvering very sensitive.
The V173 is not short of thrust. Full power gives a near 1:1 thrust to weight and was not used at any time in the video.
The big problem for the future is I have no suitable surface to take off from and I just can't imagine a maiden hand launch. 

Ooops!
It looks to me as though the motor speeds are different, are you sure it's not a difference in Prop pitch?

If you can - swap sides with the props, reverse the motors, and see if it swerves the same way, or t'other.

Reversing requires opening up.

Again! 

The props are both marked 12x3.8 SF but possibly different manufacturers so there could be a difference in their effective pitch but the way the motors start convinces me the LH motor is weaker than the RH.
With tits extreme tail down attitude the weight on the tail skid is high which means quite a bit of power is required to make it move.at all so slow speed maneuvering is difficult. To help remedy this I have added a fixed tail wheel.
 
It certainly reduces the forces required to make it move which hopefully will allow a much less aggressive rudder induced differential thrust. The fact the wheel is fixed should help keep it initially straight straight although the weight on the tail reduces almost instantly with any sort of prop wash.
Will video the next taxi attempt.    

 

A video of tonight's taxi test with the tail wheel.

Everything has a red tint as the video was shot under artificial light.
It moves with less thrust but is still tricky to maneuver in a small space.
I expect for actual flight the rudder/differential thrust mix will have to be significantly reduced.