Electric powered gliders

[KEN D]

I am building a scratch build electric powered 1.5 metre wingspan glider with a moving tailplane.

Can anyone help me with dimensions etc.

Thanks.

Ken D

[Robin Colbourne]

Ken, about 59 inches would be a good distance wingtip to wingtip...

Seriously though, find an existing successful design of the general proportions that you like, e.g. on Outerzone, and use the approximate areas and dimensions. You can change the outlines to give it a unique shape, and scale it up or down, by creating a multiplication factor for each linear dimension. The Goldberg Electra, which in turn is based on their Gentle Lady design, would be a good place to start: Outerzone - Goldberg Electra

If you want a more scientific approach, have a read of Model Aircraft Aerodynamics by Martin Simons.
Radio Control Thermal Soaring by George Stringwell is also very helpful and covers construction techniques as well.

[Piers Bowlan]

Many designs on the Aerofred site too Ken. Just out of interest, why are you going for an all-moving tailplane?

Welcome to the forum by the way.

Edited By Piers Bowlan on 20/04/2020 14:29:30

[Cuban8]

1.5 metres or around 60 inches in old terms is a bit on the small side. Why not go a bit bigger up to 2 metres? The model will perform better, give you improved duration in marginal conditions and will be easier to handle over all.

[Simon Chaddock]

KEN D

All moving tail planes can be a bit tricky simply because the control movement used in normal flight is very small indeed, just a few degrees.

The linkage has to be arranged that the full servo travel creates only a small tail plane movement and there must be absolutely no 'slop'.

Too much tail plane travel particularly in the nose down sense and something is likely to break.

Edited By Simon Chaddock on 20/04/2020 15:46:41

[Cuban8]

My old Balsa Cabin Sonata E had a half elevator (as designed). Simple and made no difference to the handling. Agree about AMTs. Need to be very well engineered so might be a challenge on a smallish model.

[Andy J]

Ken

I would scale down a Bird of Time, the pdf plan for which is easily obtainable on the web for free. Currently my 1:1 build for that glider is three quarters complete, built as a test for a new laser cutter. Think it would have been cheaper to buy the kit though as certainly consumed a lot of balsa doing test cuts.

[PatMc]

I agree that 1.5m is a tad small for a glider, if it's intended for thermal soaring, my choice would be 2m min.
I disagree with the opinion that AMT is difficult to make for a 1.5m or any other size glider, just requires care & a little forethought when designing & building. IMO is often worth the effort in order to make a model easier to store, transport & assemble/dis-assemble.

Any reason for the 1.5m span limit ?

Edited By PatMc on 20/04/2020 16:59:38

[David perry 1]

I dont agree with 2m minimum. Even my venerable old Easy Pigeon will give thermal flights of over an hour in decent condx. It flies well. I ha e had many many flights with 1.5m glidersthat do me proud.

2m, in my opinion, IS a better span but become unwieldy on the ground and a pain in the car.

These things need considering. As a first pass of second the 59 or 60 inch decision. I'd also countenance against an all flying stab, but if he wants it he wants it. Nice n easy movement rules the day.

D

[Piers Bowlan]

Ken didn't say if it was a thermal or slope soarer but a 60in slope soarer is a nice size. I asked why Ken was keen on an AMT, as opposed to a separate tailplane and elevators. By this I didn't infer a criticism of AMTs, I have both types of glider and I can't really see the advantage one way or the other with either set up. Perhaps PatMc can help here as I know he is an experienced glider guilder. The smallest model I built with an AMT was a DLG called a Lift Worx Seeker at just 100g. It was rudder and all moving T-tail, it flew beautifully in light airs and would thermal in a tiny puff of lift.

[Robin Colbourne]

Posted by Piers Bowlan on 21/04/2020 11:54:29:

Ken didn't say if it was a thermal or slope soarer but a 60in slope soarer is a nice size.

Piers, Ken did say 'electric', so I made the assumption is the model will be thermal soarer-ish.

Whilst I would agree that a large thermal soarer has its advantages, maybe the idea is something to keep in the car or take on holiday, which would make a removable tail surfaces and the compact size an advantage?

[Erfolg]

I think the issue that Patmac is discussing is the limitations of small gliders.

In the past I used to compete in the 2m events, always a disappointment compared to the performance of a 100s, model, get to bigger sizes such as 144", again better still.

I essence almost anything will thermal, from an old flying barge, a chuck glider.

There is an additional issue with a small model, when you thermal it, it soon specks out. The problem soon becomes one, of a cold sweat or a hot flush, of how do I get it down. At altitude, you have no clue at all what it is doing. Many will tell you, fly it inverted, spin it down, if only you actually could see what is happening. Sometimes a deluge of bits, preceded by a scream, that is at some distance tells you the body has tent pegged.

these are a selection of small 2m types models. If I had not built them, they would be much bigger. All electrified gliders, sadly bereft of air brakes, or spoilers. about 20-30 years old in their original forms.

From about 30-40 years back, this is nearer the size minimum needed.

Yet for performance a model glass ship beats anything I have ever built hands down, leagues away in all aspects of performance, if I only had the money.

[David perry 1]

All good points Erfolg,all good points. But convenience of a 60" is superb.

I have never had a 144" glider and I'd love one maybe knows the time. I have just bought the plans for the original, 60", super sinbad FF glider which I shall radio-fy. I'm tempted with the 90 inch kit too... it did occur to me that two versions of the same model make n excellent comparison!

I once built a Dave Hughes Sorcerer, of which model I built many in fact, with a double span wing. That flew like it was glued to a cloud..

D

[PatMc]

Posted by Piers Bowlan on 21/04/2020 11:54:29:

Ken didn't say if it was a thermal or slope soarer but a 60in slope soarer is a nice size. I asked why Ken was keen on an AMT, as opposed to a separate tailplane and elevators. By this I didn't infer a criticism of AMTs, I have both types of glider and I can't really see the advantage one way or the other with either set up. Perhaps PatMc can help here as I know he is an experienced glider guilder. The smallest model I built with an AMT was a DLG called a Lift Worx Seeker at just 100g. It was rudder and all moving T-tail, it flew beautifully in light airs and would thermal in a tiny puff of lift.

Piers, I don't think an AMT has any aerodynamic advantage over a separate tailplane & elevator.
However I find having a removeable tailplane convenient from the POV of model storage & transport. Also they're less likely to suffer hanger damage than permanently fixed tailplanes.
AMT's are generally easier to rig & de-rig than conventional tailplanes and don't require any tools when doing so.

Be interesting to have some further input from the OP.

Edited By PatMc on 21/04/2020 14:49:52

[David Hall 9]

Posted by Erfolg on 21/04/2020 13:59:01:

.............................

Yet for performance a model glass ship beats anything I have ever built hands down, leagues away in all aspects of performance, if I only had the money.

 

Apologies, not directly related to the OP, but this comment from Erfolg stirred my enthusiasm.....

Last year, I became a bit more serious about competing in F5J and decided to move into open class. I had completed with 2m models and had enjoyed it, but noted that even my 2.5m ship would seem to handle better and (apparently) outperform the 2m. I am building a 3m balsa glider (nearly finished) but in the meantime, I bought a competitive, well used CF 3.8M ship. I have begun to regret my purchase (buying into this a bit too heavily) and have thought that I should stay with my smaller models...

I've heard one or two others mention the performance levels of the CF moulded ships, Erfolg's comment reminded me of these... Perhaps, if I am lucky enough to survive the virus, I should at least have a go with it.. If I don't survive it, my wife might sell it for half of what I told her I paid for it.

Edited By David Hall 9 on 21/04/2020 16:53:00

[Piers Bowlan]

Robin most of my slope gliders seem to have acquired a motor at some stage as I also fly them from the flat on occasion. Yes. I wondered if Ken was planning to build something to keep in the car too. Some time ago I built an Auriga glider, a 'Silent Flight' plan I think? It had a v-tail which I modified to close flat like a butterfly's wings for transport. I built the wing with a wire joiner so that it could break down and fit into a lightweight transport box. A simple 60 inch model that flew in many different locations thanks in part to the tiny BL motor I installed up front. I am not a purist!

Good point about losing sight of a small glider Erf, been there, done that. The 42in span Liftworx Seeker I mentioned earlier was definitely best flown close-in for that reason.

I thought that was probably the case PatMc, I think Boeing would be using AMTs if they were more efficient but they all use separate elevators and the stab is just moved for trim. I say just but a pretty important function!

[David perry 1]

Piper did the same with the cub...elevators and move the stab for trim. One big disadvantage of an all flying surface, well two in fact, is that they can be tricky for pilots to handle (cf ww1 fighters with poor stability but a rather exciting maneouverability) and they are extremely powerful...a runaway is uncontrollable. I accept that a trim.runaeay can also be but a full stab runaway would really spoil my day .

Of course, using a horizontal stab as trim does allow the whole surface to stream which is efficient. But whether that would be worth a heap of ants in a model I wouldnt say .

[PatMc]

Posted by David perry 1 on 21/04/2020 17:58:37:

Piper did the same with the cub...elevators and move the stab for trim. One big disadvantage of an all flying surface, well two in fact, is that they can be tricky for pilots to handle (cf ww1 fighters with poor stability but a rather exciting maneouverability) and they are extremely powerful...a runaway is uncontrollable. I accept that a trim.runaeay can also be but a full stab runaway would really spoil my day .

Of course, using a horizontal stab as trim does allow the whole surface to stream which is efficient. But whether that would be worth a heap of ants in a model I wouldnt say .

So long as the pivot is at or forward of the 25% area line, models with AMT's are not tricky (because of the AMT) to fly. AMT's are not extremely powerful in fact a hinged elevator is more powerful. Dunno what you mean by "runaway".

[Robin Colbourne]

Quite a few full-size sailplanes use all moving tails. The Schempp-Hirth Standard Cirrus and Nimbus designs are probably the best known. They are also well known for inexperienced pilots getting into PIOs (Pilot Induced Oscillations). One was even written off by a pilot getting into a PIO on the take off run!

The Morane L' Parasol' also had all flying tail surfaces. This is what Cecil Lewis had to say about it in 'Sagittarius Rising':

"I had a look over her, and the more I saw of her the less I liked her. It was certainly not love at first sight . . . the elevator was as sensitive as a gold balance; the least movement stood you on your head or on your tail. You couldn't leave the machine to its own devices for a moment . . . the Morane really was a death trap . . . Subsequently I flew every machine used by the Air Force during the war. They were all child's play after the Morane . . . but I did come to love the Morane as I loved no other aeroplane."

[David perry 1]

Runaway: uncontrolled surface movement to extreme travel.

[PatMc]

Posted by Robin Colbourne on 21/04/2020 22:09:16:

Quite a few full-size sailplanes use all moving tails. The Schempp-Hirth Standard Cirrus and Nimbus designs are probably the best known. They are also well known for inexperienced pilots getting into PIOs (Pilot Induced Oscillations). One was even written off by a pilot getting into a PIO on the take off run!

The Morane L' Parasol' also had all flying tail surfaces. This is what Cecil Lewis had to say about it in 'Sagittarius Rising':

"I had a look over her, and the more I saw of her the less I liked her. It was certainly not love at first sight . . . the elevator was as sensitive as a gold balance; the least movement stood you on your head or on your tail. You couldn't leave the machine to its own devices for a moment . . . the Morane really was a death trap . . . Subsequently I flew every machine used by the Air Force during the war. They were all child's play after the Morane . . . but I did come to love the Morane as I loved no other aeroplane."

If the tailplane has a fully symmetrical section & pivots at the 25% area line there is little or no pitching moment so little if any feedback is felt on the control column. I can only hazard a guess that such a situation in a full size glider could easily lead to PIO's. OTOH this wouldn't apply to an RC glider where the "feedback" is supplied by the Tx stick centering springs.
A friend of mine had a share in a Schleicher glider (IIRC a K6) for many years. It had an AMT but I can't remember him ever mentioning any PIO type problems with it, I'm sure he would have if there had been any.

The Morane L's elevator sensitivity was probably simply due more to the extremely small tail area than any other factor. There were several other WW1 aircraft with AMT's but I've never heard similar comments of oversensitive elevator control being applied to them.

Regarding RC models with AMT I've had many stretching back over around 40 years but never found the elevator control to be oversensitive on any. The ASK 14 in my avatar is one, the glider in the photo below another.

Now used as a hack slope soarer the Diamond is at least 30 years old.

[PatMc]

Posted by David perry 1 on 21/04/2020 22:09:54:

Runaway: uncontrolled surface movement to extreme travel.

Runaway would cause the same problem to a tailplane with hinged elevators as it would to an AMT.

[David perry 1]

Maybe. The forces available though can be huge and feedback low. Never mind. All the airliners I've flown and most of the light aircraft do not use all flying stabs. The stab is often uses as a trim device to lessen drag.

The piper Cherokee series use all flying stabs of course, and they're fitted with anti-servo tabs to help add some feel.

Our models are made for a variety of reasons...one is looks, another is "because I want to". Bottom line is if one fancies all flying, all flying it is! As has been said, since we fly through sprung sticks via a powerful servo many full size issues do not appear. I suspect hinges cut from a lemonade bottle are easier to administer than all flying surfaces. Certainly I've fitted probably 99 percent elevator types over the years. Just easier I guess .

[Erfolg]

The vast majority of my gliders (types) had or have AMT. As Patmac has written the pivot needs to be well forward, that 25% mentioned works well.

You may notice that many of the older AMT had swept back tailplanes, that was part of getting to the 25%, and producing a stable arrangement.

I always arranged my own AMT to pull the front of the tailplane down, this puts the linkage always in tension, be it a snake or pushrod, or even closed loop.

The problem with AMT, is that the pivot in the fin is invariably short in length, after some time the tube more often than not wears, the Tailplane flops about a bit. Yet the pivot benefits from being large in diameter, as the loads when the model is at speed are higher than i thought. I have had and seen TP wires/rods bent at large angles from these loads.

I imagine that modern moulded models have non of these problems, Probably both better engineered with better/stronger materials than my old models.

I have found that conventional arrangements easier to engineer, but require accurate setting up for traveling at speed with minimum drag. They are always applying some corrective pitching load.

[David perry 1]

I was fortunate once in that I did NOT have a floppy stab in an A320, but several of my friends and colleagues did. They reported that it was terrifying. . Airbus eventually told us it was exactly as we get on models...wear and slop. Much heavy maintenance later that plane was repaired.