Piper Super Cub Wing Tips

[Mr Ficky]

I'm building a Ben Buckle design of a Piper Supercub; I believe it goes back to 1983. May I ask you Super Cub builders whether the wing tips should be as picture A, B or C?

[Paul De Tourtoulon]

Not Ben Buckle ones but I have an old 3 channel one and a later one both "C"

[Mr Ficky]

Oh right! Do you get any tip stall?

[Paul De Tourtoulon]

No, only on my warbirds, ie Spitfire and the likes, but then again I don't land at 5 Mph,,,

[cymaz]

 

Building in some washout will help

Edited December 27, 2022 by cymaz

[Paul De Tourtoulon]

I don't, if it needs it you can always put a bit of up ailerons on both sides of the wing.

[Martin Harris - Moderator]

It’s a useful work around to tame a “tip staller” but only assuming it has scale-ish ailerons and not the strip ailerons found on semi-scale or many sports designs. 
 

If you’re building a model that needs some it’s much better to build in any required washout.  I don’t know the Ben Buckle design but my 1/4 scale (Premier/Aerotech) Cub has functional struts and these control the wing twist in the same way as the full size. 
 

The downside of washout is that it can introduce a lot of aerodynamic twist at high speed and works the wrong way in inverted flight - neither of which should be too much of a problem for a Cub being flown in a scale manner!

[PatMc]

1 hour ago, Paul De Tourtoulon said:

I don't, if it needs it you can always put a bit of up ailerons on both sides of the wing.

Up ailerons each wing doesn't work as washout when wing is very close to stall (i.e. just when it's needed)

[Martin Harris - Moderator]

I understand why it shouldn’t as although the theoretical chord line is at a reduced angle of attack only the aileron portion actually changes and the critical part of the aerofoil presents at the same angle of attack but practical experience suggests that it does have a significant effect. Maybe  we need to consider the flow effects of the whole air mass but that’s way above my pay grade!

[Denis Watkins]

Raising the ailerons a little results in adding an amount of dihedral and just delays that particular wings Stall a little longer.

The old fellas taught this when I was a lad, and now I am the old fella improving stability of flat wingers with the Reflex method.

[Mr Ficky]

Many good comments - thank you! From your comments I'm thinking of putting in a small amount of wash out using functional wing struts. So, with that in mind, how do I create this?

Martin Harris  - would you be so kind enough as to explain how the struts are made and attached on your Premier  / Aerotech cub?

Is it possible to make the struts so they can be adjusted to get the right amount of wash out?

[Simon Chaddock]

This drawing would suggest the 'normal' Super Cub has a B type wing tip, however a scan through the Google images suggest some are modified to A or even simply cut off square.

If you can find a picture of a full size Super Cub whatever tip it has must be "right". 

.

[J D 8]

Using the struts to create washout along the whoul wing, not what is needed.

Washout should only be at the wing tip. With a built up wing on the building board you prop the trailing edge of the end ribs. The last 2 or 3 with the outermost one highest. When the glue sets the washout is now built into the tip and the tip block or structure will follow the end rib adding a tad more washout. The difference between the trailing edge of the root rib and tip rib need be no more than three degrees.

[Martin Harris - Moderator]

That's fine if you have a wing with good torsional rigidity but my Cub follows full size construction with front and rear spars located by a strut each and no D box. The washout on both full size and model is controlled by twist along the whole wing structure.

 

The original model design specified 2mm clevises on threaded studs attached to plywood struts.  I used 3mm fittings but after a clevis failed in flight, followed by an extremely gently flown return to earth with a ridiculous amount of dihedral on one wing as the struts are anything but decorative, I redesigned the struts to use internally reinforced aluminium streamlined struts and custom fittings but this is a 17 lb model so Mr. F's Ben Buckle would probably not need anything like these complications.  I don't know the model but it may not have the flexibility to use the struts to set/control washout.

[Mr Ficky]

I'm still constructing the wings and I am having a D box. I haven't as yet put the lower and upper sheeting on as yet, but I have put the webbing in and the wing is quite stiff; I've also put 1mm carbon strips down the length of each spar contributing to the stiffness.

So I'm thinking too, of using the struts to create washout, as it's a little too late to build it in the wing - I could give it a go when gluing on the sheeting. I'll only put in a max of 2%.

Martin - is it possible to post a photo of your redesigned struts? (I was thinking of using spruce and shaping it).

[David Ovenden]

On 26/12/2022 at 20:33, Mr Ficky said:

Oh right! Do you get any tip stall?

I don't have the Ben Buckle version, but I have had several cubs over the years. RM plan version 1970s ( 72") ThunderTiger J3 cub ARTF (80"), E -FLITE (67") and the big H9 ARTF 9 (108"). None of these had washout and none of them were prone to tip stalling. So it may not be much of a problem with the BB version as long as the model isn't too heavy?

[Don Fry]

I’ve flown a Goldberg Cub, and the 26% Toni Clarke PA 18 Cub. Both are benign flyers. Neither had washout.

I reckon you are making work if you want to alter the aerodynamics of an established kit/plan. And don’t think it’s an easy fix. A wing designed to be warped is made floppy. A wing designed not to be warped is built to have resistance to the warp.
Anything will tip stall, bank it, reduce power, keep raising the nose, or trying to raise the nose with the elevator, and nothing will fail to tip stall. 
Try it at night, and don’t go there thereafter.

 

[Paul De Tourtoulon]

The piper cub wing is a lot like the Baron, the same section etc,,, I have never stalled a wing that shape.

 

If you want a plane that will tip stall build a Spitfire with it's beautiful elliptique wing and over power

it with a big 4 stroke and an oversized APC prop,,,

 

 

[Piers Bowlan]

For scale fidelity ‘B’ would get my vote although ‘C’ is probably most common with Cub model designs, - easier to build with a flat bottomed section. 👍
Full size practice is often to design a wingtip to minimise drag and maximise efficiency. 
Its shape will not have an effect on adverse stalling charactistics. If a designer is concerned about that he might include a little washout, amongst other things.

A properly constructed parallel chord wing on a lightly loaded Ben Buckle Super Cub should have a totally benign stall - unless severely provoked!

Just build it to the plan, don’t agonise about it. 😉

Edited December 28, 2022 by Piers Bowlan

[kc]

Mr Ficky - see the message I sent you about the Radio Modeller copy with the article for this model.

[Martin Harris - Moderator]

18 hours ago, Mr Ficky said:

I'm still constructing the wings and I am having a D box. I haven't as yet put the lower and upper sheeting on as yet, but I have put the webbing in and the wing is quite stiff; I've also put 1mm carbon strips down the length of each spar contributing to the stiffness.

So I'm thinking too, of using the struts to create washout, as it's a little too late to build it in the wing - I could give it a go when gluing on the sheeting. I'll only put in a max of 2%.

Martin - is it possible to post a photo of your redesigned struts? (I was thinking of using spruce and shaping it).

Yours is of very different construction and your struts aren’t likely to be more than decorative. It sounds unlikely that they would be able to exert enough influence on a stiff construction.  If you want washout and the model uses a (non-scale) D box then jig the wing before sheeting it. 

 

For what it’s worth, here are a few details as requested. 

 

 

[Ian Lennox]

It seems like I'm perhaps over thinking it! Thanks for the pictures Martin! Much appreciated. It does seem though that the struts are not simply decorative. KC put me on to the Jan 1984 issue of Radio Modeller where there's an article on this model. Thanks kc! The struts create the dihedral by locking it in place. The article also mentions washout. Unfortunately though, the build was covered over 2 issues, and so I've only got half the information. I'm now on the hunt for the Jan 1984 issue of Radio Modeller too!

[kc]

Just to correct this for anyone else and for future reference - the Cub construction article by Ben Buckle is In Radio Modeller Dec 1983.    That article was Ben Buckles reworking of the J A Drake plan RM84.   It was not a Ben Buckle kit.     The Jan 84 issue does not have any of the construction article but does have an article on full size Grasshopper Cubs by Peter Cooksley.