New lightweight wing.

[Neil Spooner]

For my last restoration I made carbon fibre cowlings. The result of vacuum bagging created superb light weight cowlings which I was extremely pleased with.
My thoughts turn towards the constant quest for improvements to the a/c which cost weight.
The wing spar is almost solid wood at its root and hence very heavy (I can only just lift it.)
So the question is: Who would be prepared to pay for a new wing with a superior airfoil (better inverted performance) & probably half the weight?
Is there anyone in this group who has the design ability to create a build plan for such a wing? I may be prepared to build such a wing.
And of course the next question is how much would you be willing to pay?

[JimCrawford]

Hi Neil,

Is it the spar or the whole wing that you can only just lift - which would make it ~ 50lbs?

I ask because I am engaged in the same exercise, although with a different aircraft, a Flitzer variant 'K' Goblin. Weight is of course the primary driver. If the spar is 50lbs (which seems a lot) then you could expect to save 30lbs by going to carbon, a rather significant weight reduction on such a light aircraft.

I started my exercise because of the possibility of building a Goblin under SSDR rules but with a VW engine that's just not feasible. A Briggs & Stratton conversion might make it or the three cylinder radial but I have my Revmaster VW waiting for an airframe. A consequence of this study was that it appeared both considerably cheaper and easier to source the carbon materials than to build in spruce or Douglas fir for the spar. When you have eight spars, albeit small, it makes a difference! A French group investigated carbon ribs but they couldn't match the efficiency of traditional stick and biscuit construction. Similarly the leading edge ply for the Nipper is probably best retained as ply but extended to meet the spar on the undersurface.
A new wing opens the possibility of using push/pull rods or torque tubes for the ailerons to get rid of the cables, also perhaps a more conventional method of attaching the wing to the fuselage.

Do you have moulds for your cowlings? I should be flying soon, LAA engineering willing, but I could consider making a new set.

Jim

[Neil Spooner]

Sorry for any confusion, I refer to the complete wing regards to weight. Even so a carbon spar would be substantially lighter and potentially stronger.
I would think that a carbon sheet leading edge would be much lighter and stronger, bonded to the top and bottom of the spar would certainly create more strength.
I am not sure that the complexity of carbon ribs would make a huge difference.
Push/pull rods would certainly make the aileron control circuit much nicer, but need a lot of work to get it past certification.
I borrowed Barry Smiths cowling moulds a long time ago and made my own moulds from them. The cowlings are a massive advance in the drag profile and look of the a/c.

[Paul1954]

I can't attach PDF files, so this will take three posts...

A Nipper is a very affordable aircraft that is capable of basic aerobatics. With a competent pilot and an inverted fuel and oil system, it is able to compete in Intermediate Level competitions. Mine once flew Inverted down the 26-mile length of Loch Ness.

A plastic wing would (in my opinion) be a complete waste of time and money. But hey, whatever floats your boat.

If you want a lighter wing, why not replicate the existing planform and section in metal? Or perhaps try replicating the Gusty wing in metal? However, a new wing plan is no minor mod and will invalidate the existing LAA approval. You would be required to have your aircraft approved as a new design.

[Paul1954]

As promised.

[Paul1954]

And finally... PS, I think the Gusty was put up for sale a while back but didn't sell (?). Somewhere near Oshkosh...

[Neil Spooner]

Thank you for posting that Paul, I have tried and tried to find more information on the Gusty, so that is really interesting. Currently I am away from home so I will save those files later.
Getting rid of the nose wheel is an excellent way of loosing drag and weight, however I am sure that many Nipper owners would shy away from a short coupled tailwheel aircraft. I have a spare fuselage which has a bent nose leg which would make an excellent donor for a Gusty project….I will probably do it when I have less time!

[JimCrawford]

Paul, thanks for posting that Gusty article, very interesting.
I agree that getting rid of the nosewheel is probably the single most effective weight reduction path for a Nipper. I also believe a tailwheel Nipper wouldn't be any more of a problem than a Taylor monoplane, Turbulent or Jodel, all of which have about the same short coupled geometry. If I was starting from a fuselage frame to be refurbished I'd certainly look at the tailwheel conversion - even with the work involved in getting it through the LAA. That shouldn't be too difficult as the Acro Advanced could possibly be copied.

Covering the aircraft in Oratex may also result in a significant weight reduction.

A new wing would certainly have to go through a rigorous assessment but again, if you've done the sums to the LAA's satisfaction and appropriate handling flights performed, it's not an impossible project.
I'd caution against replacing the ply on the carbon wing. I did some work on an 1930s replica for a SSDR, possibly electric project. The problem I came up against was that the carbon alternative was so thin to react the flight loads that I became worried that it would be susceptible to ground handling and hangar rash. The thicker ply isn't significantly heavier but is much more durable.

Jim

[Neil Spooner]

Good input and discussion…thanks to contributors.
For the same weight a carbon leading edge is going to be much stronger. Foam leading and trailing ribs made of light weight foam would provide plenty of support, but I would be pleased of any suggestions on what other techniques are available.
As per the Gusty full length ailerons would make a useful increase to the roll rate.
A standard wing with a tailwheel would not be a good combination I think.
Torque links to the ailerons is a nice concept, but how to find room in the cockpit is an interesting conundrum…the trailing edge step is a problem. There is no room in the cockpit forward of the seat for them. Flaperons would be good, but keep it KISS?

[Paul1954]

Other than my comments earlier, posting the Gusty articles, and pointing out that the Gusty ailerons are standard Nipper ailerons, this is not a subject of interest to me.

[JimCrawford]

Hi Neil,

Well that's a hell of a rabbit hole you've set for me to fall down! I should be doing other stuff but this is much more interesting!

To summarise; you would like to investigate a carbon wing to get the benefit of reduced weight and the possibility of incorporating a section better suited to aerobatics. There is also the option of going for a tailwheel configuration to get rid of some more weight, I won't comment any more on that.

So to the wing:

The spar isn't really a problem, just a matter of doing schemes and sums until the design stabilises. My concern would be with replacing the ply covering with carbon. There are two issues to consider. For the leading edge I'm not sure if the simplest method would be to lay up a flat sheet of twill of suitable dimensions and then form this around the wing ribs to the spar. It might not go around the leading edge radius although it would probably be possible to add a wood leading edge for the tight radius and then fair in top and bottom carbon skins. This would also have the desirable effect of making the leading edge much more durable for ground handling. The spar web is going to be quite thin with carbon caps and the top to bottom leading edge skins are now stabilising the spar against lateral buckling. The carbon skins between the spars could also be laid up flat - vacuum bagged on a sheet of glass for efficiency - they may need some sort of internal rib to take the drag loads but that is easily sorted.

Your choice of airfoil section will be driven by your requirement for a 'Gusty' type with it's abrupt stall or something gentler. Either way you will probably scheme a zero incidence, zero dihedral, symmetric section wing plan. Here is a cunning plan. This wing will require stick back pitch to fly erect and stick forward pitch to fly inverted. So the horizontal datum will change with attitude meaning points lost in competition. How about fitting flaps with limited deflection, say 10 degrees, such that when deflected down for erect flight and reflexed up for inverted flight the aircraft datum remains horizontal. This could be mixed in with the ailerons to produce a sympathetic deflection if that would be useful.

The concentric torque tubes for the ailerons and flaps would have to run along the rear spar and that will do away with the drop down step, so how do you get in the damn thing? The solution is already half fitted. Make the step down stop the first step, it may need enlarging and strengthening, and strengthen the top skin so it can be stood on.

The above ramblings of a feeble mind are for your amusement as you see fit.
Relieved of mental turmoil I can now get back to do some work!

Cheers

Jim

[Neil Spooner]

This is the first time I have seen this article, and thought that I had read the Gusty had longer ailerons.
With a greater symmetrical deflection I would think the roll rate may be better, but increased span ailerons may be a good thing for future development. The Nipper is so small that judging it in competition is difficult.

The beauty of a symmetrical airfoil section is its ease of manufacture. I would propose making a simple mould for the LE, but glued to & braced by foam ribs at the same points.

What about a foot hole in the side of the fuselage to make it possible to step on to the wing which is stressed for a “step”?

The current design of aileron control system is ok & would be improved by the use of pulleys with a ball race rather than the bushed ones currently used. KISS!

The write up on the handling of the Gusty suggested a predictable benign stall, so I am not worried about that, so I would prefer not to get involved in flaps.

I would use the same tail group mod as I have used before.

More information on how the Gustys fuselage was modified to accept the main & tailwheel loads would be useful.

I would also prefer to stay with the VW, but use the 2.2L. Although many people would like an electric starter I would prefer to save the weight.

[JimCrawford]

Hi Neil,

The flaps I suggested aren't for stall modification but for pitch attitude control during aerobatics to keep the aircraft datum horizontal whether erect or inverted for aerobatic competition scoring.

The Gusty and the Acro Advanced both use a beam type of undercarriage. I wonder if it would be possible to just move the existing legs forward to new tabs welded on to the lower longerons. Perhaps reversing the legs to give the suspension rubbers a better geometry. I don't think there would be much to do to add a tailwheel. The fuselage longerons are the same diameter along their whole length to must be well over strength at the tail cluster.

I agree with your comment about an electric starter - completely unnecessary weight, and you would need a battery capable of starting. Perhaps any desire for a starter is generated by experience with poorly adjusted or condition of magnetos, particularly the Lucas type without impulse. My electronic ignition set up starts first or second swing.

I would still go with torque tubes or push rods for controls. I find pulleys and cables the work of the devil even though I've had to make up plenty!

Jim

[Paul1954]

… but if I can help you avoid errors in your logic?

“The flaps I suggested aren't for stall modification but for pitch attitude control during aerobatics to keep the aircraft datum horizontal whether erect or inverted for aerobatic competition scoring.” The judging criteria is FLIGHT PATH.

The Acro Advanced u/c is heavy. I think the first one cracked or was found to be cracked after delivery. The second one had to be made thicker. It came from the USA. If you want ‘light’ what about Wittman style gear?

The first Acro tail gear had an issue with shimmy. I don’t recall the why.

[Neil Spooner]

As you say, flight path is the criteria, not attitude….so as much as your suggestion is interesting I think the complexity of the system is going to muddy the waters. If it were so important I am sure that manufactures of extreme aerobatic aircraft would have embraced this concept. I don’t know of any aircraft that have used this idea. It sounds like a good recipe for an oscillating environment.

A symmetrical wing with a D box provides great ridgity and strength.