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Old Aug 18, 2014, 12:56 AM
Tony Audsley Retired Locksmith
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Airfoils from Depron

I have seen the “Armin” wing construction videos, and it is very good if you simply want a “Airfoil” … don't get me wrong, I have used this method lots of times with very good success.

Apart from the fact dollar tree foam reacts quite different to Depron when bending, if you want a more controlled or defined airfoil from Depron, it isn’t quite so easy to do

I have played with various methods of scoring and bending Depron and each one gives a different leading edge shape / radius but non give a consistent shape throughout the length of the wing ... and thats just a straight wing, different story again when its a tapered wing

Even if you use ribs of Depron or Balsa, it is not easy to get a consistent wing airfoil shape because the ribs crush parts of the Depron on the curve

I will be trying various methods and simple tests and will be very happy for any comments, suggestions, help or recommendations you might have

As you will see from the pics, where the rib is, you can get a very defined shape, BUT (and remember this is only a very short piece of Depron) if you look at the other side where there is no rib, it is quite different …

What is the answer ? is it better to use a constant balsa shaped inside the leading edge, to help keep its shape ? add more ribs ?

Food for thought

Lockey
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Old Aug 18, 2014, 01:28 AM
Tony Audsley Retired Locksmith
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Say we want to make a Clark Y airfoil shape ....

1 st one is to bend the leading edge and hope that the foil stays consistent all the way through

2nd one is to make the foil in 2 sections and make the leading edge from Balsa, this way it would be easier to keep the foil consistent all the way through

3rd would be to bend the leading edge and use some sort of fillet (maybe balsa) to control the shape of the leading edge

Thoughts ?

Lockey
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Old Aug 18, 2014, 02:00 AM
Tony Audsley Retired Locksmith
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Other ways to maybe control the shape of the foil

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Old Aug 18, 2014, 05:02 AM
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I am also a firm believer in the use of Depron foam, as I find it is the nearest material to balsa, and can be used very similarly for construction, even for some fairly big models.

I like to use some balsa for additional strength at the leading edge, spars, and trailing edge where ailerons are fitted.
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Old Aug 18, 2014, 05:06 AM
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Originally Posted by Lockey View Post
Other ways to maybe control the shape of the foil

Lockey
I think it's a no-brainer that the last option (multiple ribs) is going to lead to the most "uniform" cross section. The most pressing concern, with respect to this issue, is asymmetry between the wings.
I think the real question is: What does your particular design require in terms of precision?
For a "typical" floater flying at jogging/walking speed, a lot of asymmetry between left and right wings can be acceptable (compensated with trim or simply by pilot skill). For a swept flying wing with high aspect ratio, much less asymmetry can be tolerated (I've got one high AR flying wing that is so badly asymmetrical that it is almost guaranteed to spin at stall no matter how skilled the pilot and no matter how its trimmed). Even if it's not a flying wing, but it is simply something you're going to fly at fairly high speed - asymmetry is going to really be uncomfortable at high speed.
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Old Aug 18, 2014, 05:11 AM
Tony Audsley Retired Locksmith
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Quote:
Originally Posted by eflightray View Post
I am also a firm believer in the use of Depron foam, as I find it is the nearest material to balsa, and can be used very similarly for construction, even for some fairly big models.

I like to use some balsa for additional strength at the leading edge, spars, and trailing edge where ailerons are fitted.
Very NICE work there eflightray, love your work and thanks for sharing

I am however, not a great fan of 3 mm Depron, I find it too soft and weak, I prefer to use 6mm Depron or for rolling I use MPF (Model Plane Foam) which is brought in from the USA at great expense

Luckily, we are able to get all the various thicknesses and types of Depron locally here in Perth, but I believe we pay a lot more than you guys in the UK

Thanks for popping in Nuteman and as always, glad to hear your comments ... you are so right of course, it is quite important for both wings to be symmetrical or as identical as possible and I have found that by using the "Armin" type of build for the wings, it is a little hit and miss ... ribs are important, its just a matter of "how many is enough"

As I said to eflightray, I am not a big fan of 3 mm Depron (for most builds) so it is probably not necessary to have as many ribs as you would if you were using 3 mm ... for 6 mm Depron, I would guess around 4 to 6" (100 to 150 mm) centers would suffice

Lockey

EDIT .... Of course, weight and ease of building comes into it somewhere there too
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Old Aug 18, 2014, 05:25 PM
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Originally Posted by Lockey View Post
I am however, not a great fan of 3 mm Depron, I find it too soft and weak, I prefer to use 6mm Depron wings, it is a little hit and miss ... ribs are important, its just a matter of "how many is enough"
There is a way constructing shape consistent and tough wings with 3mm Depron using no ribs at all.
Don't believe it? Try this one:

Cut the following pieces of 3mm Depron:
800mm x 305mm
800mm x 130mm

Cut the following piece of 6mm Depron:
800mm x 8mm

Now take a pen and draw a line on the bigger Depron part at 150mm (lengthwise).
On the other side put some packing tape (prime with spray adhesive if necessary).
Now score the depron deeply along the line ont he side which is not taped (an old CD is perfect for that purpose).
This is gonna be your LE.

Now glue the smaller Depron part on the side of the score that has 150mm. Glue it with a 5mm distance to it.
If you want a more solid wing put some mesh tape in between. I use the one which is used for drywall spackling.
Then glue the 6mm Depron spar on the lamination approx. 50mm from the LE.
Now you carefully fold the upper part over the wing along the score until you're able to match upper and lowe TE on each other.

Give the lower part of the TE a 5mm wide application of glue (use some masking tape) , then put some glue on top of the spar and fold the upper part over again.
Match the TEs again and weight down the wing on a flat surface using phone books or similar.
Done.

This example gives you the wing for an scale Bronco OV10, 800mm wingspan.

Building method can be adapted in various ways:
- use some 3mm balsa instead of the 6mm Depron spar
- do the lamination just until the TE and sand it down (for more glueing surface)
- do a laminated spar (3 layers of 3mm Depron with a 3mm CF tube laminated in between)

just to name some...

Yeah, you might say this is the Armin style wing building.
Yes, it's similar.
But as Lockey already said Depron reacts quite different when it comes to bending and this method considers the special characteristics of Depron.
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Last edited by mysticranger; Aug 18, 2014 at 05:46 PM.
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Old Aug 18, 2014, 08:09 PM
Tony Audsley Retired Locksmith
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mysticranger .... WOW mate, this would have to be the best explanation I have ever read (without pictures) that explains exactly how to do it ... THANK YOU

I do like the idea of laminating 2 x 3 mm Depron on the bottom surface

The thing I have against 3 mm Depron is not that it is thinner, but the consistency is different ... seems a lot softer, marks easier and doesn't sand as good

Its like the black / gray Depron, this is also a lot softer, great for making canopy's but wouldn't use it for structural building

By the way, where are you putting the mesh tape ? .... all the way between the 2 pieces?

Cheers

Lockey
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Old Aug 18, 2014, 09:07 PM
Tony Audsley Retired Locksmith
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The problem I have found, is that when you score the leading edge and simply fold it (with tape on the outside of course) it tends to give a … too sharp a leading edge for most airfoil shapes

By experimenting, I have found that the leading edge radius can be controlled (somewhat) by using different thicknesses of material to bend it around …

Unfortunately, it does not keep square and uniform without some kind of support … ie: formers / ribs or leading edge support and / or spars

This wing was very strong without a CF spar but one could be easily added if needed
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Old Aug 18, 2014, 09:27 PM
Tony Audsley Retired Locksmith
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This is another wing I built with a lot thinner foil

As I said at the beginning of this thread, it is not too difficult to make "an airfoil shape" but more difficult to make a "real" aifoil shape ... just how important this is with foam models I guess is debatable, does it make them fly better ?

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Old Aug 18, 2014, 10:13 PM
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How about using CF tow on the inside of the wing skin , top and bottom and lightweight 1/4 oz fiberglass cloth on the outside using the 3mm foam?
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Old Aug 18, 2014, 10:24 PM
Tony Audsley Retired Locksmith
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Originally Posted by A320 GSB View Post
How about using CF tow on the inside of the wing skin , top and bottom and lightweight 1/4 oz fiberglass cloth on the outside using the 3mm foam?
Hey, GSB ... good to see you here mate ... that sounds like an awful lot of work mate, easier to just glue in a CF spar

By the way, whats a CF tow ? ... did I tell you, I don't like 3 mm Depron much ... oh by the way ... did I also tell you "I hate hand launching planes" ... you're a pilot so you should know ... thats not how you fly a plane eh I guess this is the one you fly ? (see pic) the orange one

I do hope you build one of these GBS, I am sure you will love it ... the Tiny Fokker I mean, not the A320

Hey, maybe I should d a pusher prop version of one of the A320's eh !! ... Oh dear, here we go again ... derailing the thread, must stop it

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Old Aug 19, 2014, 01:06 AM
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Originally Posted by Lockey View Post
As I said at the beginning of this thread, it is not too difficult to make "an airfoil shape" but more difficult to make a "real" aifoil shape ... just how important this is with foam models I guess is debatable, does it make them fly better ?
I think it's been pretty well established that for model scale, variations in airfoil shape for spans up till 60" or so have very minimal impact in comparison to basic factors like aspect ratio and wing loading (at model Reynolds number, this seems to be borne out).

I think people spend tons of time tweaking airfoils to eek out tiny improvements when their efforts could be better spent elsewhere. At low Reynolds numbers of model planes, it's much harder to get large improvement with this.
I remember a long thread (I think it was in the "Flying Wings" section) where there was tons of discussion about changing airfoil parameters (like twist, airfoil selection for various sections of the wing, etc.). Somebody finally asked the guy how much was gained by all that. He answered 3% "improvement" (whatever areas of improvement were involved). To me, that's just not worth the effort.
Then there was another thread about this university that claimed some bizarre/huge improvement percentage with sophisticated wing twist, etc. It turned out it was really much less than that (like 10%) - and that was for a fairly large model - go down to 60" or less, and I suspect you'll find much less than 10% gained.
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Old Aug 19, 2014, 02:18 AM
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See you got issues getting an accurate LE when folding.
K, ways to solve this:
- after scoring the LE with the CD score once again with a more round shaped device (i always used the bottom edge of a lighter)
or
- fold the wing on the outside first, then bevel the score carefully.

Both will give your LE some direction during the folding.

You can also cut the wing panel at the LE without scoring, then bevel the inside edges and join them again on a strip of packing tape. Join them edge to edge or put them with 1 or 2 mm distance in order to influence airfoil shape. You can also try some different bevels on lower and upper part...

Lots of choices...

btw I was putting two strips of mesh tape on the front and back edge of the lamination doubler.
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Old Aug 19, 2014, 05:32 AM
Tony Audsley Retired Locksmith
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As you can see from some of the pics, I have tried various bevels, spacers, etc but haven't found one that I am completely happy with ... the fork one came the closest, but the radius is a little bit on the big side, maybe need to cut off one of the prongs

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