I am currently flying a scratchbuilt eSupra that I built last winter. (see first photo) It flies wonderfully! When I built this model last winter I wanted a wing that would also withstand a winch launch, thus the wing is much, much stronger than needed for ALES competition. The overall weight of this model is 76oz for a wing loading of 10.8oz sq/ft.

This winter I am building eSupra that is designed for ALES competition.

The design goals are:
- Simple to build; no complex spar making
- Inexpensive
- Accurate planform and airfoils
- Withstand ALES style landings
- Have a wing loading under 9oz sq/ft thus an all up weight of 64oz or less, ready to fly

Now that I have the design goals I needed to figure out what composite materials to use for the layup for the wing and fuselages.
I am using a spreadsheet that was accomplished by Vincent in the Netherlands, his RCGroups name is Prop-er.
Here is a link to his excellent work:
https://www.rcgroups.com/forums/show....php?t=1213427
I couldn't figure out how to input the shear webs that increase the strength of this wing by close to 70% as per some tests that Phil Barnes completed about half a decade ago. I'll post more about that later. However, this does give me a good idea of the weights I hope to achieve.

I wanted to use Dow Square edge 25psi foam as it’s inexpensive and readily available.
The wing planform and airfoils have already been set by Dr. Drela’s Supra. The plans are available here:
http://www.charlesriverrc.org/articles/supra/supra.htm

I reduced the wingspan by 4” to 130” as it’s easier to transport in my vehicle.
I will build a flat 60” panel that will have two 35” outer panels with angled joiners to obtain an equivalent dihedral angle of six degrees.

Now that I know what I want in a model I needed to determine the estimated speed and Lift Coefficient. Dr. Drela lists a Cl of 1.2 on the plans. I chose to use that figure and a max speed of 35mph for the stress calculations.
Since I’m not zooming off the hi-start or making any F3B speed runs I chose to use 35mph as a max design speed. This is still too fast for a thermalling speed but if the pilot were to lose sight of his/her model and end up in a diving spiral that they would have some extra load capability in the wing to safely recover the model in a flyable condition.

I started playing with layups and spars in Prop-er spreadsheet and this is what I’ve come up with.

The Wing:
No Spar, It will be a stressed wing construction.
I'll use Style 716 or 80/20 uni-carbon fiber for the forward part of the wing and 1.7oz bias kevlar for the back of the wing with a finishing layer of 1.19oz fiberglass.
I'll insert two shear webs of unidirectional carbon fiber laminate (.014" thick x 3/16" deep) into the wings top surface only. This will be inserted into the foam, it's easy to do and will attach to the top skin only to prevent the wing from buckling on top, the most common failure point.
See post# 72

To join the wings I’ll be using a 5/16” hollow round aluminum joiner inside a brass tube. The wall thickness is .049”
I’ll add 1.7oz Kevlar to the leading edges for impact resistance and also have a live Kevlar hinge.

The Fuselage:
The tailboom will be rolled 4.7oz carbon fiber on a pool cue
I haven't quite decided on the forward pod but it'll most likely be fiberglass with carbon fiber reinforcements and perhaps some kevlar, but doubtful. I'll have carbon fiber where the tailboom will join the forward pod and carbon where the motor mounts. I’ll run some carbon fiber along the sides of the rest of the pod to reinforce the the hatch opening. The canopy/hatch will be fiberglass. This should be a 2.4G compliant fuselage.

To this day I still use the instructional videos I produced. Available at www.TailwindGliders.com

Curtis

September 2014 Update:
A new build is starting. Please see this thread for the changes:
https://www.rcgroups.com/forums/show...8#post29558828

April 2017 Carboline Layup.
https://www.rcgroups.com/forums/show...postcount=1429

Red Merle VII Build Begins here using Gerald Taylor (GT) Synergy Airfoils Design stage late 2017
https://www.rcgroups.com/forums/show...0#post38649170

Red Merle VIII Build Begins here using Gerald Taylor (GT) Synergy Airfoils Design stage late 2018
https://www.rcgroups.com/forums/show...3#post40647921

Red Merle IX Build Begins here using Gerald Taylor (GT) Synergy Airfoils Design stage late 2019
https://www.rcgroups.com/forums/show...4#post43058277

Wanna build a wing using a Spar instead of Stressed Skin....
See Bennetbr's build thread. He did a super job and ended up with a flying weight of 60oz on his first build!
https://www.rcgroups.com/forums/show...pra-Wing-Build

A four piece wing:
https://www.rcgroups.com/forums/show...1#post44179673

Here is a comparison of the current eSupra I have and the proposed wing layup for the ALES eSupra.

The current eSupra I built had 25psi foam, 5.7 oz carbon fiber from behind the high point of the wing forward to the leading edge top and bottom. Then 1.7oz Kevlar for the aft part of the wing. The spar was a carbon fiber tube of .56” diameter with a wall thickness of .050. I also used this as the outer panels wing joiner tube.
The first photo shows the calculations from Prop-er spreadsheet for my current eSupra. The spreadsheet gives a weight of 36.6oz.
The current wing came out ready to fly at 40.4oz with servos, full chord plywood rib joiners and a center plywood rib for the wing bolts.
So that’s pretty close for me!

Photo two shows the layup as explained in post #1. Notice the weight difference!

The ALES eSupra is designed for 35mph and Cl of 1.2 which results in a Max G load of 6G’s. The max wing deflection is right on target with the current eSupra I’m flying!

This gives me great confidence that Prop-er spreadsheet is very accurate and I'll be able to achieve my ALES eSupra goals!

Now that I have the planform, airfoils, layups and required materials I’ll get to cutting foam airfoils and ordering some materials I don’t have on hand.

Curtis
Montana

Your design goal 6G is far too low for an RC sailplane. The expected loads from turbulence are much higher on airplanes with low stall speeds compared to full size ({max speed/stall speed}^2 = G load). It is very easy to pull 10G when you aren't in the airplane.

Kevin

Very interesting approach, I was thinkign ont hose same lines. My problem is the size :P I was working on a smaller wing and I really run out of time :P I know is a bad excuse but is difficult to work alone :P

I would also go with a higher max speed, just in case of the need of a high g manuver, you really never know when the worst case scenario will come.


Good luck with the build and keep us posted

Regards

EZ

Kevin,

I certainly appreciate your opinion.
But there is something wrong with some calculations then.
The spreadsheet for my current eSupra shows max stresses for the layup/spar at 76oz and 40mph is 7G's.
I'll dive this model straight to the ground and accomplish hard pullups and/or a stand it up on a wingtip as I'm passing in front of me and pulling a very hard tight turn. It shows no signs of any bending or stress breaks.

There are no plans to ever dive the ALES eSupra like this.

For the proposed ALES eSupra the max stresses for the layup I've chosen are at 65oz and 35mph 6G's.

So it seems that I'm either good to go as designed, or the spreadsheets/calc's I use are in error or I'm not using them properly. Hmm.

I do know the spreadsheets are for a two piece wing and this is a three piece wing.

I'll think it through more, thanks for the kind thoughts and review of my project.

Curtis
Montana

The spreadsheet outputs have to be wrong. A Supra will certainly exceed 40mph by a large margin, and sharp pull-ups will be far more than 7Gs.

Kevin

Originally Posted by kcaldwel

The spreadsheet outputs have to be wrong. A Supra will certainly exceed 40mph by a large margin, and sharp pull-ups will be far more than 7Gs.

Kevin

Kevin,

The Supra when input in the spreadsheet is 95mph at 50oz and a Cl of 1.2 give 64G's and a max wing deflection of 18.5 inches.
You can download the spreadsheet with data already entered for the Supra here:
https://www.rcgroups.com/forums/show...9&postcount=20

I believe the spreadsheet is quite accurate. I'll be able to tell you more in the Spring.

I am NOT building a hand towed, winched or even hi-started eSupra. But one that has a motor in the nose for electric launch to 200m in 30 seconds then nice gradual smooth landings as there is a motor in the nose.

The only reason for additional structure is if/when a pilot where to lose sight of his/her model and end up in an unusual attitude and needs some G forces to recover. There are procedures to reduce G's during unusual attitudes. Don't recover while in a bank! Level the wings then apply smooth elevator control.

The example I'm giving is with the eSupra I already have flying that was over built for electric flight purposes and what data the spreadsheet is giving me as results. I have proven those this summer.

So with the data for the F3J Supra, my eSupra and the proposed ALES only wing I came up with layup. I've flown a WACO Magic years ago that had a spruce spar and fiberglass layup off of a winch. It made people cringe when the say the wing become a U shape on the winch. But I never broke it and I even launched it in England's high winds.

Make sense? Or am I totally lost in Montana?

Curtis

Are you sure you want to proceed until you resolve it?

Kevin

Originally Posted by kcaldwel

Are you sure you want to proceed until you resolve it?

Kevin

Help! What's your solution for my design goals back on post #1?

Thanks
Curtis

1. Measure with a micrometer
2. Mark it with chalk
3. Cut with an axe

tk

Here is an ALES model that is a two piece wing. Obviously the stresses where the wing join are the highest. They use a 8x130mm fiberglass wing joiner. It's also an 80oz model!

http://www.espritmodel.com/grafas-31e-f5jales-arf.aspx

Would my design one piece 60" center panel wing be stronger?

Thoughts? Lessons? Help? References? Tutorials?

Curtis
Montana

What lay-up output do you get for 15G and 60mph? Can you cross check it with Joe Wurt's spreadsheet?

Kevin

Sorry, I grabbed the wrong model.

It's the Prelude:
http://www.espritmodel.com/prelude-25e-f5jales-arf.aspx
Carbon wing joiner of 10x180mm

This is a two piece wing!

A friend of mine is building one of these and I was looking over it the other day.

Curtis

Originally Posted by kcaldwel

What lay-up output do you get for 15G and 60mph? Can you cross check it with Joe Wurt's spreadsheet?

Kevin

I can't because Joe W. spreadsheet doesn't allow for a lower density foam than 60psi or Spyder foam. That makes a huge difference! See my Design Goals as I am using 25psi foam.

Curtis

Originally Posted by kcaldwel

Your design goal 4G is far too low for an RC sailplane. The expected loads from turbulence are much higher on airplanes with low stall speeds compared to full size ({max speed/stall speed}^2 = G load). It is very easy to pull 10G when you aren't in the airplane.

Kevin

At what Lift Coefficient (Cl)?

I don't think I'll achieve a Cl = 1.2.
If I go with the original layup I've chosen and a Cl = 1.0 then max G = 11. This is with a 65 ounce model weight and 1017sq inches of wing area.

Still thinking.....

Curtis
Montana