Vectored Thrust

[Deskpilot]

I've been following a thread called 'Ring Tail' on HBA in the states and have added my comments and design mods. Just as a point of interest, what do you think, would it work. I've modified my original DeMansfield Bolt design. If you're not sure what I'm getting at, the whole ring-tail assy pivots in 2 degree of freedom, and yes, the prop is in there, also pivoting.

 

 

 

[facthunter]

Probably a concept thing. You would need a CV joint in the drive and there would be some "funny" gyroscopics, I imagine. Nev

 

 

[Deskpilot]

Probably a concept thing. You would need a CV joint in the drive and there would be some "funny" gyroscopics, I imagine. Nev

Yes and yes. Originally I had the CV or UJ at the mid prop position to eliminate as much gyroscopic effects as possible but later had to move it in front of the prop to facilitate a swash plate. Still, it intrigues me.

 

 

[fly_tornado]

have a look @ the vector thrust RC planes. they are fixed fans and the nozzle moves on 2 axis. the problem with your design is if the CV joint fails that will leave the aircraft really unstable.

 

 

[facthunter]

I see a problem with tip clearance. The efficiency would diminish significantly if the gap was excessive. Having relative motion of the prop or the "ring" would require a fair amount , would it not? Nev

 

 

[Deskpilot]

The idea is that the prop and duct move as one assembly. Therefore there's no change in tip clearances except any from duct distortion should it be too flexible. As to the whole assembly breaking free of the aircraft and the resulting dive into the unknown, I'm working on a double, but 'hinging', connection, to be sure, to be sure as the Irish might say. It will probably end up being too heavy but the journey is keeping me off the streets. Stay tuned and remember, think outside the box.

 

 

[Guest aussie carl]

What about when the fan stops. 2deg isn't going to give much control surface over the fan shroud/tail fin.

 

 

[Deskpilot]

Carl, 2 degrees of freedom means movement in 2 axis, ie, yaw and pitch. As to how many degrees of movement in each axis, I don't don't know but would probably be about half of normal control planes.

 

I think I'm right in saying a standard plane will have 6 degrees of freedom, yaw left, yaw right, pitch up, pitch down, roll left and roll right. A helicopter or VTOL plane will have 8 as they can go straight up and down as well.

 

 

[Guest aussie carl]

Disclaimer. I am no engineer but I will try to explain it as I see it.

 

With the fan pushing, the airspeed through the tail control surface will be higher than the the aircrafts airspeed so will make the ring tail quit efficent.

 

With the fan spinning slowly, ie the pitch speed of the prop is slower than the airspeed of the aircraft.

 

I see this acting as an air brake causing an air dam in the ring tail. This of course will seriously reduce the tails ability to stabilise and control the airframe.

 

The air dam will cause drag, enough to drop the nose, applying up elevator will be ineffective as the ring tail is no longer efficient etc etc etc. until power is reapplied.

 

With the fan stopped. The air through the ring tail will be same as the aircraft's speed but will be slightly obstruced by the fan making it less effecient.

 

It would be relatively easy to build a scale RC model of the concept to do some testing.

 

I believe with larger external control surfaces (outside the ring tail) and with the prop at low speeds spinning enough not to cause an air dam effect. I think it would fly.

 

Just my thoughts.

 

 

[Deskpilot]

Thanks Carl, I agree with some of your observations, but first lets get it right. It's a ducted prop, not fan. The surface area of each are so different the cause and effects will be very different. Yes, there will be a 'breaking effect' when the throttle is closed but not as much as you seem to think. The only real problem I see is that one would have to do 'carrier landings' to be sure of full control. ie, power on until touch-down. The Duct does actually act as a normal fin and stab set-up but not quite so efficiently.

 

 

[Guest aussie carl]

The only real problem I see is that one would have to do 'carrier landings' to be sure of full control. ie, power on until touch-down. .

This is exactly what I was refering to above. What if you have no power.

Fan is a slang term I use for propeller. Sorry for the confusion.

 

I feel you may underestimate the breaking affect of a spinning propeller. when spinning slow enough the pitch speed is slower than the actual airspeed. This is exaderated by the duct which is on the tail.

 

Also the duct is in turbelent air from the fuse/cockpit making it very innefficent when there is no power.

 

 

[Deskpilot]

OK Carl, I'll bow to your obviously more informed knowledge. Guess an R/C model is needed for further evaluation. Any takers?

 

 

[fly_tornado]

try bananahobby.com they have some nice videos showing vectored thrust planes

 

 

[Guest aussie carl]

What you want to build in RC is relativly easy.

 

An electric version should be built so motor can be cut and flight charecteristics observed at height.

 

I happen to own a RC hobby store www.revmaxhobbies.com.au

 

The fuse and wing are easy. I have a spare wing 1200mm Clark Y section. The tips taper a bit but that wont affect much.

 

I see your wing is constant chord with semisymetrical section. Your wing would be more stable and penetrate gusty conditions better. I have a wing that would reprosent your wing better but it is much larger and the cost of running gear would be higher BUT I see the larger model giving better flight test results.

 

For the fuse/tail boom a RC helicopter Tail boom could be used with the torc tube normaly used to drive the tail rotor, this would drive the propeller.

 

Motor would be mid mounted and battery up front to simulate pilot weight.

 

I am keen to build something for your experementation but need to fininsh of some other projects before taking on another.

 

If you can scale down your drawings so the wing span is 1480mm and provide some other basic dimentions and weights I may be able to knock something up using the collection of stuff I have accumulated over the years.

 

The model I am basing my ideas is in the video below. One I done an electric conversion on. It weighed about 2.8kg and produced ALOT more power than a nitro powered engine.

 

 

 

[Deskpilot]

Thanks Carl, that would be very interesting for all of us. My one request is that you don't over power it as that doesn't represent reality at all. I'll get back to you with some dimensions a bit later.

 

 

[Guest aussie carl]

Yer no probs. Detuning poower is easy.

 

 

[Deskpilot]

OK Carl, attached a a few images and dimensions that you might be able to use. The boom tube length was just a guess when I swapped the conventional tail with the VT unit. This was originally a design I put aside due to it being 'slated by the yanks' as being useless and too expensive to produce (the prop revolved around the boom just aft of the wings)

 

Hope you can do something with this info. BTW, I've no idea as to what the airfoil section is as I stretched it somewhat. I'd go with the Clark Y at this stage.

 

 

 

 

 

 

[Guest aussie carl]

Thanks.

 

What diameter is the duct

 

I am going to struggle with the boom on the same centerline as the wing spar, a full size job would have similar manufacturing problems.

 

It would be much simpler to manufacture if the prop was fixed and the duct could move the desired amount for elev and rud control. the clearance on the duct would have to be increased slightly, this I see as a good thing.

 

1. less noise

 

2. less diffence in control responce between differnt power settings and motor off.

 

Just throwing some thoughs in the air.

 

 

[Deskpilot]

Carl, the main thing is to see if the plane is controllable without power so the actual sizing isn't all that important. That said, see attached image. Let me say that a plain ring tail is now flying successfully in the states using a tractor configuration. With this design, we have to move the prop as well so there might be gyroscopic effects as well. I fully understand that a fixed prop would easier but I want a more instant response so that we can perform the Cobra? that the ruskies do with their fighter. Remember, this is only for the fun of it.

 

 

 

[Guest aussie carl]

yer cool I'll put some thought into it.

 

 

[Deskpilot]

Hi Carl, it's been a while so any movement on the r/c model?

 

 

[Guest aussie carl]

I have done a little but have to make the propeller vectored had put it in the to hard basket. It needs some sort of universal to handle the movement, for a RC model this will add weight and complexity to the rear.

 

Sorry I no longer have time for this project.

 

 

[Deskpilot]

Fair enough mate. I'll give it a go although I'm not r/c competent. I'm sure I'll find some-one local who's into it.

 

 

[Guest aussie carl]

I am happy to help out if you share your project on the forum. I can send you what I have started if is of any use to you, althoug the wing may be to long to post.

 

OH and make sure you find someone local to you who can actual fly RC planes and not some who does alot of talking about it. Go to a local field and sus them out first. They should be able to aero a model with ease and there equipment should be well presented and operates without fuss.

 

If they have "gold wings" or instructors rating all the better.

 

 

[Deskpilot]

Thanks for the offer Carl, but let's not waste the postage. I will do some simple tests and if they work out and prove my theory, I will build a cheap, half size, non flying model of the tail assemble. With this I should be able to refine my design ready for a full size one......maybe.

 

In the mean time, I'm up-dating the pod and wing design so stay tuned. This 'project' aint dead yet.