Tailless/ Windfreak

[Tom Wilson]

Is there anyone out there with experience of building a "Windfreak"of RCModeller of November 1978. Would like to speak to them regarding washout and their thoughts on it. The original plans and build instructions make no mention of washout but in an article in BARCS "Soarer" mgagazine in March 1982 by a Ken Lees, he appears to have built in some washout but gives no details .

[Erfolg]

I have the article I believe in a RCM, I think, not sure where.

 

The main issue is that it had an elliptical dihedral wing. There was no washout, the planform being a plank, albeit with a wavy trailing edge. The wing section was very thin, from what I remember, based on taking a Aquila? aerofoil then tagging on a reflex trailing edge to the max. camber line of the Aquila wing section.

 

The model had a massive rudder, as the turning moment was very short, pitch was controlled by inboard elevators, driven from a torque rod system from a model boat.

 

There was one in the club back in the Barcs league days, it flew very well. It was modified to tip dihedral, straight trailing edge.. It certainly could move, which many wings from that era could not.

 

 

I Have considered building one myself, for electric, but using tip elevons, with no dihedral, or slight simple dihedral

[Erfolg]

I cannot find the magazine, I assume it was thrown out, when my wife made me rationalize my old magazines.

 

However I have a reduced scale drawing, a photocopy of the drawing in the magazine. It was designed by Roger Sanders, drawn by Pail Plecan.

[Erfolg]

Ah! A Eureka moment.

 

I was so near commitment to building the model, I have cut the part two pages out of the magazine, and then placed them in my files. So I have some information, i not everything.

[Tom Wilson]

Yes you are absolutely correct, but what I am trying to establish is whether it might be better with a bit of washout and how much. As you say, there was one in the BARCs league, and I would like to contact the builder if he is still around. I am building it with elliptical dihedral ( no joints) and am making a board at present. Ken Lees, who wrote the article for "Soarer" said that he used fibre board like the type estate agents use, and I can only assume from that, that he means what we now call hardboard. He also mentions washout as he said that you have to pack up the board on one side and then remember to transfer the packing for the opposite wing.
Fuselage is built as is the rudder and elevators. Spars are all made and attached to the sheeting which is all cut (takes 12 sheets of 1/16")and all wing ribs are cut. All I have to do is stick it all together.

Tom.

[Tom Wilson]

I have the magazine, the full size plans and a copy of the build instructions which are exactly the same as the magazine.

[Erfolg]

From Memory either Jim Radcliffe or Peter Coles, they both had a flying wing, which I think either was or were based on the Windfreak, which were flown in the BARCs leauge.

 

Jim Radcliffe is still around.

 

I have seen one proper Windfreak, that is per plan, no washout I am sure. The model was flat spun around its centre, like a sycamore leaf, no hint of a tip stall. But as the root and tip are essentially the same chord, I would not expect an issue.

[Former Member]

[This posting has been removed]

[Erfolg]

Eric

 

The Windfreak was a thermal glider, no acrobatic pretensions.

 

 

I was thinking that there are a lot of slope fliers of wings, whose knowledge would be directly relevant, with respect to stalling wings, or flying near the stall.

 

In my case I have flown 4 tailless thermal type gliders, none had a tendency to drop a wing, the stall being a mush. In my case, getting to the stall could be an issue, as the drag increased disproportionally with up elevator, so much so, that the speed needed keeping up to prevent rapid sink. But then again my experiences are limited, particularly compared to many slope fliers.

[Tom Wilson]

My preference is thermal. I have never flown from a slope and I don't have any inclination to do so, it just doesn't appeal to me. So from that point of view, I'm not really interested in flying inverted except perhaps to get me down out of a thermal or down quickly. the designer claims almost instant stall recovery , and excellent pitch control. Thanks for your input.

[Erfolg]

Tom

 

For getting out of a thermal, the flat spin as demonstrated to me works. Better still are air brakes.

 

Crow braking is now fashionable on conventional gliders and works really well, but not sure how easy it would be to mix into a wing. Brakes are needed for hitting the spot, there is no substitute, IMHO.

Edited By Erfolg on 30/04/2011 12:40:24

[Tom Wilson]

Crow brakes would not be possible with this wing without re-designing completely.

I do intend however to install scissor brakes behind the mainspar. Designer reckons that the model will pitch severely with top brakes only and either bottom brakes or better stil top and bottom should be used. The problem is that the wing section is only 23mm thick so I am trying to make up brakes on the lines of the "Schemp-Hirth" brakes which would be ideal except for the fact that they are only manufactured at a minimum of 30 mm when closed.If you know of any others ,I'd like to here about them.

[Brian Rapier]

Just found this conversation and signed up. I built a Windfreak with my then 17 year son in the late 70s, and built another one as a slope soarer last year. It is now finally trimmed and a sorted and I was flying it at Ivinghoe last Thursday.

 

The original flew very well, being a very fast thermal soarer for the time. We used straight dihedral. I was flying in the BARCS league at the time but we never used this glider in competition. It did however have two weaknesses - the large downswept tip plates were easily damaged in anything less than a perfect landing, and more importantly the huge rudder would flutter at high speed and detach itself. There are reports out there from the time of this happening, and the wing then coming down safely inverted.

 

In our case my son was high in a big thermal, the rudder fluttered and detached and presumably the wing pitched foward with such violence one wing exploded in mid air. The other did descend undamaged and fuselage buried itself six inches in the ground. We decided not to re-build and bought a Centiphase kit instead.

 

My slope soaring version is the same planform and wing section (I am actually used the original ply templates ! ) but has very little dihedral, tip plates reduced in size and held on with magnets and tape, and ailerons. So the original elevator is used with the trailing edges beyond that as ailerons.

 

Trimming it has been an adventure to say the least, but it now flies well. To get the controls balanced all four flaps are used as ailerons with big movements, but the elevator only is used for pitch with very little movement. Each outing so far I have reduced it further. To get the precision needed I switched to Savox digital metal geared servos

 

It does not appear to stall at all, and most landings are smooth and no problem. The boldest thing is that I do have crow braking. Needless to say setting that up was done at altitude - the first try it performed a half loop, next time after adjustment a sharp dive, but the third time spot on which was lucky. It just slows right down and hovers like a big bird of prey. . .

 

So Tom I will attempt to attach a picture, and anything else you want to know just get in touch

[Brian Rapier]

Trying to attach a picture again

 

Can't see how to get it to browse my picture album - it is much simpler on RCgroups !

 

Anyone got any suggestions as to how this works

[Erfolg]

Brian

 

I have considered seriously building one myself, along the same lines as yourself. If I do get round to building one, I would do something very similar to yourselves.

 

It would have a very small amount of dihedral, fixed fin/rudder and use aileron for roll control and pitch. Of course it would be electric powered, I cannot be fussed with bungies these days

 

The real issue then becomes one of braking. I built ,some +15 years ago, a plank of 120" span using Eppler 186, which had letter box airbrakes. I found the brakes worked fine other than pitch up, requiring down elevator, the added drag reducing airspeed and steepened the glide. In this era the pitch up could be dialed into combining down elevator with airbrake opening. It is probably better to make the inboard trailing edge a crow type brake, as you have done.

 

The thin wing section, with low camber, is defiantly better than the thick E186 for thermal flying.

 

The present wing I fly, resorted to the same approach that seems the method that WW2 German jet wings proposed, that is a sweep back, the inner wing being E205, the outer 1/3rd span being E205 reflexed as the Windfreak. Although the concept does work, the performance is generally a long way short of pretty basic conventional thermal gliders. The plus side, like the plank it does not really stall. Get the CG to far back, it spins with no provocation.

 

After experimenting a lot with this model over the years, I think planks are probably better.

 

 

A few pictures of your model would be nice

[Brian Rapier]

Hi Erfolg - have just worked out how to put photos online

[Brian Rapier]

You will notice it does have a rudder, but I found it had no great effect. When the gears stripped on the servo through accidentally knocking the rudder I just removed the servo and taped it up. It gives more room in fuz for the leads as well

 

It needed a lot of lead in the nose to balance so I would make an electric version with a longer nose, and obviously a wider fus to take a battery. With experience of this one I would reduce the width of the flaps as it is so sensitive to minute trim changes

 

So far it has flown in winds up to 15 mph and coped fine with that. The main trimming and fine CG adjustment was done in a 10 mph westerly at Ivinghoe which was perfect conditions for it - every landing that morning was perfect and right by me (rather better than my usual standard)

 

An electric version is an interesting idea as I would only need to make a second fuz and I do have suitable motor + ESC in stock. Maybe next winter . . .

 

Another pic alonside my FVK Rival

You can see this is a BIG glider

[Erfolg]

Brian, it looks really good.

 

The nose seems short, compared to how I think the plan looked.

 

I do feel it would make a good thermal model, for a wing.

 

I assume that you have just bulged the underside of the wing panels to enclose the servos? How susceptible are the control horns to damage in landing, as the wings are almost on the ground?

 

 

[Tom Wilson]

Some very interesting posts here. I want to try the eliptical dihedral which rules out crow brakes. Do the lower brakes not get damaged on landing, or do you close them before it hits the ground ?, in which case it sort of defeats the object of brakes. I have now manged to design a scissor brake that will come down to the required 23mm wing thickness but am worried of the same problem of the lower brakes catching on landing.

The only thing holding me up at present is the building board I managed to get a 50" x 20" x 3/4" plywood for the base board, but need to fit 2 pieces of angle iron to the underside as there is slight buckling over the length. I have cut the curved pieces for the elliptical dihedral to be fixed to the upperside, but now need something to go on top that is rigid enough not to twist but flexible enough to bend to the curve and preferably soft enough to stick pins in. Has anyone built one with elliptical dihedral?

[Brian Rapier]

I think I built the fus as the plan, widened slightly to fit the Futaba 617 Rx. A longer nose would have been better, as the volume of lead required was difficult to fit in the ballast box.

 

Concerning the servos I originally fitted JR ES 375 servos as I usually use them in small gliders, and they would fit within the the wing. The operated OK in flight, but I stripped the gears on 2 of them just handling the model.

They were replaced with Savox metal geared digital 0257 2.2 kg servos of about the same size which have been fine so far.

 

They are glued onto servo covers from Phoenix Models, using 2 mm rods inside 2 mm i.d. carbon tube to stop them flexing

 

Trust this helps

[Erfolg]

Brian, I am aware that others have had similar issues with stripping gears on landing, where the under surface is at the bottom of the fuz., where there is no undercarriage, ie glider, Spitfire and landing on grass. I now drive via the upper surface in these instances, not as pretty, but does save servos.

 

What are using for the push rods?

 

Tom, there are many foamie gliders with elliptical dihedral, such as the Multiplex Easy Glider, Parkzone Radican. It certainly works well, on them, although I know of at least two, where ailerons have been built in, inboard of the curved bit. The reason, ailerons are defiantly better than rudder dihedral for precision control.

 

I think we have to remember why we all tended to use rudder control for turning! Servos were expensive, even at standard sizes, they weighed a tonne and that was the convention. Today the same constraints no longer exist.

 

As for air brakes, with a computer radio, it is simple to set up a letter box airbrake to provide a save steep descent.

 

At the end of the day, all are personal views, but it can be advantageous, to question what we intend doing and why.

[Tom Wilson]

Yes Brian, I like the idea of fitting carbon tube over the rods. I have just modified my Hi-Phase which had a bicycle spoke type rod inside the fin for elevator control. The problem was the flex in the rod more especially as it had a kink in it for clearance. I used 2mm carbon rod but made up aluminium end adaptors which were araldited to the rod and threaded to take a small piece of the threaded spoke to allow standard clevises to be screwed on , but your idea is much simpler.

You have a point erfolg , When this model was originally designed and built in 1982 they wouldn't have had computer txs, so maybe I should just go with letter box spoilers and see how it reacts. It would certainly make life easier.

[Brian Rapier]

Had some good flying with the Windfreak Friday before last and managed to get some inflight pics showing the crow braking in action - just click on my library.

 

It flew well in a 12-15 mph westerly and handled some fast passes perfectly - no control surface flutter and flexing nicely through the edge turbulence

[Brian Rapier]

I see it is 5 years since my last post ! The Windfreak has been flown many times, and was re-furbished last year with a fuselage re-spray and a new 2000 Eneloop fitted. However my slope activities are now limited due to age and infirmity so I am disposing of my larger soarers.

So the Windfreak is for sale for around £100 which included the 4 Savox digital metal geared servos, new Eneloop etc. I have details of all the control throws recorded. Just needs a 7 ch Rx and Tx with sufficient mixes. I am located in Harpenden, Herts and would deliver within 50 or 60 miles