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Oct 26, 2011, 02:17 PM
solastagia
kcaldwel's Avatar
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Last edited by kcaldwel; Jan 25, 2012 at 11:27 PM.
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Oct 26, 2011, 03:20 PM
solastagia
kcaldwel's Avatar
Why don't you think you'll achieve a Cl of 1.2? Dr. Drela thought that was the design point, so that is what I would use.

Do you want the 2 layers of 1.4oz glass for handling? It doesn't add much to the strength. 1 layer of 1.4oz. glass, and 3 tapering carbon darts gets a 23oz wing weight prediction, and 60mph and 20G strength. I can send the details if you want. Of course this spreadsheet doesn't calculate the torsional loads, so perhaps a 1 layer skin wouldn't be torsionally strong/stiff enough.

Kevin

Edit: Kevlar may not be a great choice for a tail boom material. It has very low compression strength and stiffness, so the tail boom will flex a lot, and fold rather easily. A carbon/glass combination is much better.
Last edited by kcaldwel; Feb 01, 2013 at 07:38 PM.
Oct 26, 2011, 04:04 PM
Dark Side of the Red Merle
Curtis Suter's Avatar
Thread OP
Quote:
Originally Posted by kcaldwel
Why don't you think you'll achieve a Cl of 1.2? Dr. Drela thought that was the design point, so that is what I would use.

Do you want the 2 layers of 1.4oz glass for handling? It doesn't add much to the strength. 1 layer of 1.4oz. glass, and 3 tapering carbon darts gets a 23oz wing weight prediction, and 60mph and 20G strength. I can send the details if you want. Of course this spreadsheet doesn't calculate the torsional loads, so perhaps a 1 layer skin wouldn't be torsionally strong/stiff enough.

Kevin

Edit: Kevlar may not be a great choice for a tail boom material. It has very low compression strength and stiffness, so the tail boom will flex a lot, and fold rather easily. A carbon/glass combination is much better.
If the max speed is reduced doesn't Cl decrease? I'm just not ever going to fly it fast. It's a thermal glider with slide in gliding landings. ALES contest format.
I wish I had a model of the Supra for XFLR5. Perhaps I'll sit down one snowy day and make one.
Yes two layers 1.4oz of fiberglass for torsional stiffness and strength and finger dents etc...

I agree about what you say with the Kevlar boom. But for an ALES model it'd work great.

I have a TD plane of 120" that has a Kevlar boom, three wraps of 1.7oz Kevlar. It's a WACO Millenium. I've also had a WACO Magic with the same boom and they work great.
I also have a carbon boom on my eSupra.

So the question I have is:
Which boom would be lighter?
3 layers of 1.7oz Kevlar or 2 layers 4.7oz carbon?
Either would work for an ALES model.

Gotta run, work called.

Curtis
Last edited by Curtis Suter; Oct 26, 2011 at 04:21 PM.
Oct 26, 2011, 04:29 PM
Launchpad McQuack
Prop-er's Avatar
Time to step in.

First: A VNE (@CL1,2) of 35mph seems indeed a bit risky.
9 Oz/sqft = 27 gr/dmē
Max. airspeed [m/s] = 4 * √(27*1.635/1.2) = 24 m/s = 54mph

Then about the trigger of the discussion: the design strength of your current "heavy" Supra. I replicated your calculation and noticed a problem with the tube spar. Currently the calculation of the tube shares it's material properties with the capped spar. Of course, the tube should have it's own material selection. I will fix this.

The workaround is to specify a very, very, very small capped spar.

If I start increasing the VNE (@CL1,2), the design fails at 65mph @ 19G's.
See enclosed sheet.
Last edited by Prop-er; Oct 27, 2011 at 02:53 AM.
Oct 26, 2011, 04:42 PM
solastagia
kcaldwel's Avatar
...
Last edited by kcaldwel; Jan 25, 2012 at 11:26 PM.
Oct 26, 2011, 11:11 PM
Registered User
hornet_dave's Avatar
Please dont forget that for wing bending calculations, you can ignore the weight of the wing itself. The wing structure only needs to carry the weight of the fuselage multiplied by your design load factor.
Oct 27, 2011, 08:32 AM
Dark Side of the Red Merle
Curtis Suter's Avatar
Thread OP

Thanks!


First off I'd like to say thanks so much for the quick and immediate responses from everyone. I so much appreciate the help and the lessons.

As I'm sure you can tell I'm not educated enough to fully correlate some of the aerodynamic principles, but it's not from lack of trying.

Now that I know I was viewing incorrect data on my current eSupra I do think I could add a carbon dart as suggested and this will increase the breaking point to 53mph and 15G at a Cl = 1.2 and 65oz model weight.

Vincent, is your spreadsheet assuming a two piece wing?
The eSupra will be a three piece wing thus some of these calculations don't exactly follow accordingly as the one piece center section will be stronger than a two piece wing. Right?

Okay, that's all the ramblings I have time for.

I have to work again this morning so I can afford the extra carbon fiber for the wing.

Curtis
Montana
Oct 27, 2011, 08:33 AM
Dark Side of the Red Merle
Curtis Suter's Avatar
Thread OP
Quote:
Originally Posted by hornet_dave
Please don't forget that for wing bending calculations, you can ignore the weight of the wing itself. The wing structure only needs to carry the weight of the fuselage multiplied by your design load factor.
I was chatting on the phone with a brilliant fellow modeler here in town and he posed this exact question and wanted me to ask if he was correct.

You must have been eavesdropping on our conversation as you answered this for us perfectly!

Thanks
Curtis
Oct 27, 2011, 10:52 AM
solastagia
kcaldwel's Avatar
...
Last edited by kcaldwel; Jan 25, 2012 at 11:25 PM.
Oct 27, 2011, 01:03 PM
Registered User
Kevin,
Those "Booms" made to Weston's specs were 3 layers of 1.7os
Kevlar rolled onto a 3 mil acetate form, 2" to 1". No carbon!!! They were stiff!
Don't know how the weight compared to carbon booms. The fuse was made
on a plug, then pealed off by slitting the fuse and joining again. Crude
by todays methods, but it worked.
This is great, I plan on building one or two of these. ALES is a fun format.
John
Oct 27, 2011, 01:14 PM
solastagia
kcaldwel's Avatar
I'd love an eSupra for ALES too, but it is a bit daunting as a build project.

Kevin
Last edited by kcaldwel; Feb 01, 2013 at 07:44 PM.
Oct 27, 2011, 07:04 PM
Dark Side of the Red Merle
Curtis Suter's Avatar
Thread OP
Quote:
Originally Posted by kcaldwel

I'd love an eSupra for ALES too, but it is a bit daunting as a build project.

Kevin
Kevin,

This is exactly what I'm trying to do, make it less of a daunting task, as you will see in my build. The wing can be the most complex but an ALES plane makes this real easy without any complex spar making or wing joiners. I'll show the joiners later, piece of cake to do!

The rolled boom is easy and the forward pod is easy too. Hardest part of the forward pod is carving the male mold, but a good friend here turned one on a lather for me, which is what I'm currently using on the "heavy" eSupra. So I'll just reuse that male mold.

There really isn't much that I haven't already shown in my instructional DVD's at www.TailwindGliders/Sales.html
But I'll show my progress here.
It'd be cool if someone were to build along! Hint hint.

I'm also excited about proving the accuracy of Vincents spreadsheet. Well perhaps I shouldn't say "prove" as it's already known to be accurate with other models. But I guess prove it from the stand point that I can build a simple ALES plane with the results from using it.

None of these building procedures are new, they are actually stone age simple but very accurate. The proof will be in the pudding of the final weight and if she holds together in flight, but that we won't know till Spring in the Northern Hemisphere.

Curtis
Montana
Last edited by Curtis Suter; Oct 28, 2011 at 05:27 AM. Reason: I had more to say.
Oct 27, 2011, 11:09 PM
working to the closest cm
jirvin_4505's Avatar
Quote:
Originally Posted by CloudyIFR
Kevin,
.....

There really isn't much that I haven't already shown in my instructional DVD's at www.TailwindGliders.com
......

Curtis
Montana

Hi Curtis - are missing links on your web page?

I couldn't get to the actual videos.

cheers jeff
Oct 28, 2011, 05:27 AM
Dark Side of the Red Merle
Curtis Suter's Avatar
Thread OP
Quote:
Originally Posted by jirvin_4505
Hi Curtis - are missing links on your web page?

I couldn't get to the actual videos.

cheers jeff
Jeff,

This is a direct link to the "sales" page of the website:
http://tailwindgliders.com/Sales.html

As I sit here just past 4am the website isn't working! That's not good!

I'll try and look at it later but I'm working a 16 hour day today.

Curtis
Montana
Oct 28, 2011, 05:44 AM
working to the closest cm
jirvin_4505's Avatar
Quote:
Originally Posted by CloudyIFR
Jeff,

This is a direct link to the "sales" page of the website:
http://tailwindgliders.com/Sales.html

As I sit here just past 4am the website isn't working! That's not good!

I'll try and look at it later but I'm working a 16 hour day today.

Curtis
Montana
looks to be working - thanks curtis


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