The one wing to rule them all... - RC Groups
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Nov 10, 2017, 08:00 AM
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miniphase's Avatar

The one wing to rule them all...

I have a gap in my quiver- a heavy weight sloper for those windier days and big hills.

Game plan is-

5 metre span

very little washout

maybe 15 to 20lbs auw?

Here's a photo of the initial mock-up. I'm running through the build in my mind with an aim to
keep things as quick, simple and heavy as possible. Let the build commence with a flurry of
productivity, and then move on at my usual sporadic snail's pace....
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Nov 10, 2017, 11:18 AM
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Knoll53's Avatar
Yes ! it.

Even at 20lbs auw, it would only be 18oz/sf wing loading which is very common for scale planes and they fly fine, even somewhat floaty at that loading. The 325mm wing chord is really going to be your friend. That coupled with a high cruise speed will make for some nice performance not to mention interesting hand launches. Bigger does fly better.

Let me guess..............solid foam wing, dual carbon spars, full carbon skins.

Will you be offering kits?
Nov 10, 2017, 03:54 PM
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miniphase's Avatar
If I can hit 18oz/ft that would be great. I'll be using the EH 2/12 again and that moves along quite respectfully at 11 oz/ft. As for launches, if it's 15mph plus, I don't think I'll have too much of a problem. Anything less than that might need a bit of bungee assist followed by some interesting scratching around!...we shall see when it comes to light conditions!

Yes to the foam wing Kent. I was thinking of 1/32nd ply skins with glass underneath, but then I came across some 3.6mm ply (9/64ths?) in the local diy store. A fraction of the price of the 1/32 ply, and an easy way to add weight too.

I've done a little test piece to make sure it will conform, it comes up very stiff indeed when epoxied on to the foam.

Initially I was thinking ply shear web with carbon caps, but with the thicker skins I might get away with just 1/2 inch thick, full depth timber...once again it's cheap, stiff and heavy. I'm not sure there will even be anything to be gained by capping it with carbon....but I'm open to suggestions!

Kit market might be limited to a few deranged individuals for this one!
Last edited by miniphase; Nov 10, 2017 at 04:04 PM.
Nov 10, 2017, 06:18 PM
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Knoll53's Avatar
Wow, you were serious about building heavy. Thick plywood should do it. The TE is brilliant. That big meaty wood spar would be a lot stiffer with carbon caps. Stiffness is the game for high speed passes. Here in the states I found maple veneer with paper backing at the ever popular 1/42" thickness for a reasonable price for a 4'x8' sheet. That, plus glass would also make a killer skin as well, plus it would be flexible to form. Test your mock up for torsional stiffness as well. You saw my video of my wing exploding so you know the demons at play here. Who knew a wing could flex that much. Full depth dual spars creates multiple torsion cells and thus adds torsional stiffness as the sketch suggests............................. did you say that you were open to suggestions?

What sort of LE do you have in mind?

I feel sorry for any model that gets in your way.
Nov 11, 2017, 03:03 AM
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mhodgson's Avatar
Criss cross pattern of carbon tows, disser style, under the sheeting?
Nov 11, 2017, 03:21 AM
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miniphase's Avatar
I did consider the disser approach, but introducing the aerofoil curve into the ply does make it very stiff, however Kent raises the nub of the issue....the skin needs to be a closed unit in order to maximise its rigidity. I think you might be swaying me towards the introduction of a secondary, lesser swept spar for the first wing panel, ie the first 1.5 metres of semi-span.

Good to hear you can get veneers easily Kent, I researched a lot of veneers and plys, but they were all coming out at several times the price of the 3.6mm diy ply, plus postage and with minimum orders. In terms of stiffness to cost ratio, I don't think the 3.6mm diy ply can be beat! I have got to source some new foam though. The Knauf Space Board that I love is no longer available, so I think I'll have to source some blue foam and recalibrate my hotwire accordingly.

Just for the record, the ply skin for each panel (this will be a four piece wing) weighs about 2 kilos (around 4 1/2lbs) and the spar for each panel weighs around 300g, so I'm already nearing 10kg with no effort what so ever Maybe the carbon spar caps would be a sensible insurance policy!!

Leading edge would just be hard balsa btw.
Last edited by miniphase; Nov 11, 2017 at 03:32 AM.
Nov 11, 2017, 04:09 AM
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mhodgson's Avatar
It sounds impressive and heavy.
Have you checked the rules on weights and insurance coverage?
Nov 11, 2017, 05:05 AM
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miniphase's Avatar
This model will be pretty small and light compared to some of my flying comrades' beasts!

But if I keep her below 20kg it's pretty simple; I have to stay outside of controlled airspace and stay below 400ft. However if ESSA have their wicked way in the coming year or so it'll be nothing more than a hanger queen, so it'll be good to get a flight or two in with it before then!
Nov 11, 2017, 08:04 AM
Registered User
Your heading made me stop and look in.

Surely you meant "one wing to wule them all"?

With my apologies to Fudd and Tolkien.

Serious build, btw!
Nov 11, 2017, 08:21 AM
Red Merle ALES VI
Curtis Suter's Avatar
There is no doubt in my mind that you know this but I'd concentrate the extra weight in the center and keep the outer extremities light to aid in roll control as well as balance.
Very neat project.
Nov 11, 2017, 08:23 AM
HerkS's Avatar
Not really a suggestion Paul, but considering the very high AR on these big models, you could seriously consider using a bit less sweep.
Nov 11, 2017, 10:24 AM
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Knoll53's Avatar
Originally Posted by Curtis Suter
concentrate the extra weight in the center and keep the outer extremities light to aid in roll control
The DS builders will sometimes add lead out in the wings for the express purpose of smoothing out the roll rate. Go figure. Keeping the wing tips light has many advantages, until you catch a wing tip on landing. With a 20lb. plane behind it, that wingtip had better be up to the task. I vote for titanium LE and TE with unobtanium dual spars.

There is a discussion in the Slope PSS forum regarding the merits of oak LE over bass wood LE. Amazingly the oak wasn't strong enough, at 3/4" thick! There is magic to the resilience of that bass wood. Apparently, PSS is Latin for "spectacular crash".

I am beginning to see the charm in the DIY ply. I AM a little concerned that the force needed to make it conform to the airfoil curve might result in some airfoil distortion. I guess the mock up will settle that question.

Are you going to go back to your earlier post where to welcomed suggestions? (note to self: start all threads with phrase" stop bothering me, it just a build log !)
Nov 11, 2017, 10:33 AM
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Knoll53's Avatar
Originally Posted by HerkS
Not really a suggestion Paul, but considering the very high AR on these big models, you could seriously consider using a bit less sweep.
We are going to need to see a white paper on that, preferably by the end the day.
Nov 11, 2017, 11:44 AM
HerkS's Avatar
Originally Posted by Knoll53
We are going to need to see a white paper on that, preferably by the end the day.
No treatise on this one Kent. There are only a couple of plus factors for less sweep that I can think of.
One is that there is less spanwise flow during higher AOA flight. So stability margin is more stable and lift distribution is a bit more efficient.
The other is that all else being equal the flutter speed will be higher. Whereas highly swept wings are negatively affected by both of those factors.

Just something else to think about when you are putting together a new design.
Nov 11, 2017, 12:17 PM
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Knoll53's Avatar
Thanks for keeping it simple Herk. I get that.

Interesting fact. Rigidity matters. If you design a beam, for example, and you laminate a very rigid material next to a flexible material, the rigid material will take most (all) of the stress. In order for the flexible material to actually contribute it's strength, it must deflect, but the rigid material won't let it. So the materials do not work together, they work sequentially. First the rigid material fails, then lots of deflection occurs, then the flexible material fails. If you add carbon spar caps to the 1/2" timber, design the spar caps for all of the tension and compression on those extreme faces of the beam. The timber that was originally acting as a complete beam is now acting as only a shear web for the carbon caps.

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