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Author Topic: Flap design.  (Read 6564 times)

Offline Perry Rose

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Flap design.
« on: August 27, 2018, 11:55:30 AM »
Without using carbon fiber which is the best design for flaps that are  roughly 3" at the big end 1.5" at the tip and 28 inches long? The leading edge is 1/2 inch thick. Lightness is needed too.  They are for a .60 size profile stunter. Maybe 65 ounces when finished.
I may be wrong but I doubt it.
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Offline Matt Brown

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Re: Flap design.
« Reply #1 on: August 27, 2018, 12:57:06 PM »
Conventional built up construction but fully sheeted with 1/32” on a 45 degree bias. Top and bottom 45s opposite directions.
That’s my two cents worth and you get what you pay for.  ;D

Matt

Online Ken Culbertson

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Re: Flap design.
« Reply #2 on: August 27, 2018, 01:01:46 PM »
Without using carbon fiber which is the best design for flaps that are  roughly 3" at the big end 1.5" at the tip and 28 inches long? The leading edge is 1/2 inch thick. Lightness is needed too.  They are for a .60 size profile stunter. Maybe 65 ounces when finished.
I would use a built up sheeted arrangement.  I build the frame using stiff light 3/8 square for the LE and 3/8 x 1/4 for the TE with the 3/8 being the tall dimension. Draw a center line on both on the outside.  Full depth light 1/16 ribs every 1" followed by zig zag ribs inbetween.  End rib is 1/8 bass.  Epoxy brass tube for flap horn to inside recessed 1/4" and add a 2nd 1/8 bass rib. ( sandwich the tubing)  While still on the board, block sand the top to the line on the TE then fill the space over the horn tube with more epoxy and sheet the top with soft straight grained 1/16.  It will be stiff enough to flip it over and do the same to the other side and still maintain the double taper.  The 1/4 TE will all but disappear leaving you a 1/8" thick TE and 1/2" LE.  Gobs lighter and stiffer and warp resistant than solid.

I am sure that some others will have some even better ways.  If they do, I will use theirs next time! y1

Ken
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Online Ken Culbertson

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Re: Flap design.
« Reply #3 on: August 27, 2018, 01:13:29 PM »
Conventional built up construction but fully sheeted with 1/32” on a 45 degree bias. Top and bottom 45s opposite directions.
That’s my two cents worth and you get what you pay for.  ;D

Matt
That cross grain is a good idea but I wouldn't use 1/32.  Warps too easy with the glue and CA will make sanding difficult.  1/16 and sand like hell.

Ken
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Offline Tim Wescott

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Re: Flap design.
« Reply #4 on: August 27, 2018, 02:05:34 PM »
Maybe 65 ounces when finished.

Well, if your weight budget is 65 ounces for the flaps, just machine them out of 2024 -- you'll come in much lower than your target, and they should be plenty stiff.
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Offline Tim Wescott

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Re: Flap design.
« Reply #5 on: August 27, 2018, 02:07:35 PM »
Well, if your weight budget is 65 ounces for the flaps, just machine them out of 2024 -- you'll come in much lower than your target, and they should be plenty stiff.

Oh you meant 65 ounces for the whole plane!  Silly me.  Here -- read this.  Just search for the first occurrence of the word 'flap' and go from there.
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Offline Lauri Malila

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Re: Flap design.
« Reply #6 on: August 27, 2018, 02:44:55 PM »
Conventional built up construction but fully sheeted with 1/32” on a 45 degree bias. Top and bottom 45s opposite directions.
That’s my two cents worth and you get what you pay for.  ;D

Matt

That would not be a good idea as the stifness would not be same in both directions in torsion.
The structure must be symmetrical.
Fully sheeted with +/-45 degree glassfiber (I would use at least 50g/m2, not the lightest 25g stuff) helps a little, but carbon would be better.
With balsa only, best way to get stiffness is to make flap thicker. L

Online Ken Culbertson

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Re: Flap design.
« Reply #7 on: August 27, 2018, 03:29:54 PM »
That would not be a good idea as the stifness would not be same in both directions in torsion.
The structure must be symmetrical.
Fully sheeted with +/-45 degree glassfiber (I would use at least 50g/m2, not the lightest 25g stuff) helps a little, but carbon would be better.
With balsa only, best way to get stiffness is to make flap thicker. L
I am not sure why having the grain "X" pattern is any different from having the glass in an "X".  With a 1/2" tapered flap you are not going to get much torsion.  I use the cross grain on things like rudders with good results.  With sheeting you get a triangle shape that resists torsion twisting.

Ken
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Online Ken Culbertson

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Re: Flap design.
« Reply #8 on: August 27, 2018, 03:56:16 PM »
The difference is wood grain goes one way on top the other way on the bottom. Fiberglass grain goes both ways top and bottom.
That was a brain fart on my part.  Sorry, but I still do not get how putting the sheeting on the same way is going to produce uneven torsion. 

Ken
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Offline Chris Wilson

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Re: Flap design.
« Reply #9 on: August 27, 2018, 06:35:41 PM »
Have seen blue board foam that is sheeted with balsa work quite well.
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Offline Gerald Arana

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Re: Flap design.
« Reply #10 on: August 27, 2018, 06:55:30 PM »
Personally, I use 3.2 OZ. deck cloth. Very close weave and when cut on the bias, it's very strong. Haven't used it on flaps but suffice it to say, I'd bet it'd be very resistant to tortion and when using the toilet paper method, it'd be fairly light too.

Just my two cents worth. (It's worth what you paid for it!)

Jerry

Offline Matt Brown

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Re: Flap design.
« Reply #11 on: August 28, 2018, 04:25:49 AM »
If you're going to put the sheeting on at 45 degrees, you would want to put the grain the same direction both top and bottom since the flap is being driven from one end. Otherwise the side with the right grain would take the load in compression or tension and the other side would just get folded. You want the grain going from front inboard to rear outboard on both sides, right?


Motorman 8)


I was going to post exactly this, this morning. I was thinking about it last night laying in bed and came to the same conclusion. Since this thread popped up, I keep thinking about building several flaps with different construction and compare them torsionally and weight. Also only considering construction, no glassing or covering. I think the sheeted blue foam would be stiffest especially if the sheeting is done on a 45 but it will likely also be the heaviest.

Matt

Online Ken Culbertson

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Re: Flap design.
« Reply #12 on: August 28, 2018, 07:11:46 AM »

I was going to post exactly this, this morning. I was thinking about it last night laying in bed and came to the same conclusion. Since this thread popped up, I keep thinking about building several flaps with different construction and compare them torsionally and weight. Also only considering construction, no glassing or covering. I think the sheeted blue foam would be stiffest especially if the sheeting is done on a 45 but it will likely also be the heaviest.

Matt
I think what we are finding here is that there is no one best way to skin this cat.  I have just finished a set using the method I added above so I checked them for torsional twist and there is virtually none.  Maybe a 1/16th of an inch. They are 3/8, 1/2 would be even stiffer.  I can get that much twist in a solid sheet of 3/8.  Neither have covering yet but one has 2 coats of sanding sealer and the other one is still naked.  The sealer cuts the twist in half.  Maybe the direction of the grain on the sheeting doesn't make that much difference (mine is parallel to the flap span) but I am willing to bet that the covering does.

This one kept me thinking last night too - do we need help?

Ken
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Offline Dave_Trible

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Re: Flap design.
« Reply #13 on: August 28, 2018, 07:18:55 AM »
I’ve had a lot of aggravation in recent years trying to keep built up- sheet covered flaps straight for very long due to shrinkage of the covering and dope.  I’ve replaced the flaps more than once on several airplanes.  I’m now back to solid carved 3/8 medium balsa with a 3/32” bass trailing edge and NO covering material- just non- tautening dope.  So far so good.  I even had the issues with carbon covering though not as bad or soon.

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Online Ken Culbertson

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Re: Flap design.
« Reply #14 on: August 28, 2018, 07:34:20 AM »
I’ve had a lot of aggravation in recent years trying to keep built up- sheet covered flaps straight for very long due to shrinkage of the covering and dope.  I’ve replaced the flaps more than once on several airplanes.  I’m now back to solid carved 3/8 medium balsa with a 3/32” bass trailing edge and NO covering material- just non- tautening dope.  So far so good.  I even had the issues with carbon covering though not as bad or soon.

Dave
I flew a lot of hand launch glider back when my arm was not so ancient.  We never covered the wings but we did put a glass like finish on them using lacquer sanding sealer followed by a thin coat of lacquer when you could no longer see the grain then rubbed out.  Incredibly durable, didn't warp like dope and very light. Vibration would tear that apart on an IC but with electric these types of finishes are possible again.  Curious, why brass vs carbon on the TE?  Good idea though and I am going to shamelessly steal it on the set I have on the bench. Do you round out the TE to "embed" the tubing or just glue it on and fill in the trough?

Ken
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Offline Dave_Trible

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Re: Flap design.
« Reply #15 on: August 28, 2018, 07:39:32 AM »
The basswood is easy to work with,  cheap and the LHS has it.  A carbon strip would be OK too.  Never thought about that application.  Sorry if I made it unclear.

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Online Ken Culbertson

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Re: Flap design.
« Reply #16 on: August 28, 2018, 08:07:30 AM »
The basswood is easy to work with,  cheap and the LHS has it.  A carbon strip would be OK too.  Never thought about that application.  Sorry if I made it unclear.

Dave
I have a 3/32 carbon tube in the shop.  I will try it and let you know how it works.  I find myself using more basswood.  Our LHS's carry it too, more than balsa and it is not that bad.  1/16 bass weighs about the same as 1/8 medium balsa.  I have used it in fuselages and I don't see much wrong with it.

Ken
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Offline Lauri Malila

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Re: Flap design.
« Reply #17 on: August 28, 2018, 10:29:28 AM »
Ok, back to the first post, how to get best results without help of composites.
Two kind of unwanted deformation has been mentioned; deformation under stress, meaning torsional stifness and deformation during test of time, meaning warping.
The dilemma with balsa(or any)wood is that regardless of density, the individual wood cells are allways more or less the same. This means that in denser, heavier, wood there is more wood cells per volume unit.
Because of that, denser wood is more prone to warping, so that's the price you pay for using heavier wood to increase stifness.
And the other way, lighter wood is more stable but with lower stifness.
So the best way would be to use light, quarter grain cut wood and to keep thickness as thick as possible.
Reinforcing the trailing edge with something harder, carbon or hardwood, is nice especially against handling damage but as it is located at the central axis of flap, it won't do much to increase stifness.
If you really want to do it right, the best way is to use skin with modulus of elasticity higher than balsa's, kept solidly apart from each others with a lightweight core. The core can be dense ribs or some lightweight foam, like Rohacell, or if you want to go a step further, honeycomb.
The skin could be of thin balsa/glassfiber laminate, thin plywood or thin carbon sheet. There are really nice thin carbon products easily available, starting from under 50g/m2 for a nice biaxial product. Please don't confuse them with carbon veil, the veil has nothing to do with correct use of carbon fiber. L

Offline Gerald Arana

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Re: Flap design.
« Reply #18 on: August 28, 2018, 11:34:15 AM »
Ok, back to the first post, how to get best results without help of composites.
Two kind of unwanted deformation has been mentioned; deformation under stress, meaning torsional stifness and deformation during test of time, meaning warping.
The dilemma with balsa(or any)wood is that regardless of density, the individual wood cells are allways more or less the same. This means that in denser, heavier, wood there is more wood cells per volume unit.
Because of that, denser wood is more prone to warping, so that's the price you pay for using heavier wood to increase stifness.
And the other way, lighter wood is more stable but with lower stifness.
So the best way would be to use light, quarter grain cut wood and to keep thickness as thick as possible.
Reinforcing the trailing edge with something harder, carbon or hardwood, is nice especially against handling damage but as it is located at the central axis of flap, it won't do much to increase stifness.
If you really want to do it right, the best way is to use skin with modulus of elasticity higher than balsa's, kept solidly apart from each others with a lightweight core. The core can be dense ribs or some lightweight foam, like Rohacell, or if you want to go a step further, honeycomb.
The skin could be of thin balsa/glassfiber laminate, thin plywood or thin carbon sheet. There are really nice thin carbon products easily available, starting from under 50g/m2 for a nice biaxial product. Please don't confuse them with carbon veil, the veil has nothing to do with correct use of carbon fiber. L

Perfect! Plus one. Why wouldn't you want to use the newest, bestest, lightest (yeah, I now that's not a word) material available for your next super world beater?!  ???

Just my 2 cents worth.  y1

Jerry

Offline Lauri Malila

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Re: Flap design.
« Reply #19 on: August 28, 2018, 12:04:12 PM »
Good question, Jerry.
I mean, in so many other categories of aeromodelling it's more like natural evolution, and has caused many revolutions. Basically new technology comes and walks over old, no matter how well the old has been made.
Of course, especially in free flight we go quite deep into the newest technology, cnc'd metal molds etc, in things like stunt flaps it does not have to be so complex for excellent results. L

Offline Gerald Arana

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Re: Flap design.
« Reply #20 on: August 28, 2018, 05:03:18 PM »
Good question, Jerry.
I mean, in so many other categories of aeromodelling it's more like natural evolution, and has caused many revolutions. Basically new technology comes and walks over old, no matter how well the old has been made.
Of course, especially in free flight we go quite deep into the newest technology, cnc'd metal molds etc, in things like stunt flaps it does not have to be so complex for excellent results. L

Lauri, My good friend and RC glider competitor Fred W. showed me a CF glider stab (full flying) that was made in a CNC mold of CF and I was really impressed! Extremely stiff and so light I had to hold it down to keep it from floating away...........well almost!
The only draw back was the cost was pretty high.

I enjoy your posts, Jerry

Offline phil c

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Re: Flap design.
« Reply #21 on: August 28, 2018, 07:51:14 PM »
Without using carbon fiber which is the best design for flaps that are  roughly 3" at the big end 1.5" at the tip and 28 inches long? The leading edge is 1/2 inch thick. Lightness is needed too.  They are for a .60 size profile stunter. Maybe 65 ounces when finished.

If you want the stiffest, lightest flap don't taper it.  Make it constant thickness, and glass it top and bottom with bias fiberglass.
Rectangular sections are stiffer than triangular sections.
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Offline Randy Cuberly

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Re: Flap design.
« Reply #22 on: August 29, 2018, 01:03:01 AM »
If you want the stiffest, lightest flap don't taper it.  Make it constant thickness, and glass it top and bottom with bias fiberglass.
Rectangular sections are stiffer than triangular sections.

This is the method that I have adopted also because I've had the same issues as Dave with warping and twisting when covering flaps.  However it seems that covering solid flaps with fiberglass cloth, cut on the bias, and epoxy finishing resin eliminates this tendency.  And Boy are they stiff.  Yeah they are a bit heavier but it's weight well spent in my opinion.  Nothing is worse than trying to trim an airplane with wimpy or twisted flaps...  I have a colossus that I desperately need to replace the flaps on just for this reason! 

I've also had significant problems with foam flaps covered with balsa in this regard!  Haven't yet come up with a viable solution for this situation!

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Offline Steve Helmick

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Re: Flap design.
« Reply #23 on: August 29, 2018, 05:01:04 PM »
"The skin could be of thin balsa/glassfiber laminate, thin plywood or thin carbon sheet. There are really nice thin carbon products easily available, starting from under 50g/m2 for a nice biaxial product. Please don't confuse them with carbon veil, the veil has nothing to do with correct use of carbon fiber. L"


How is "veil" different than "mat"? I wouldn't mess with .2 oz or .3 oz/sq.meter on flaps, but would think a few layers of .5 oz (which I have in stock), or perhaps could get something more like 1 or 2 oz. per sq. meter would be good? Actual fabric would cost a lot, and putting it on a bias isn't very cost effective. It would be nice if 4" wide tape was made on the bias. I looked at "Tap Plastics" website and didn't find any carbon anything, and tried to find CST, but just got crap about Central Standard Time and some MicroSoft acronym for their latest & (cough) greatest.  :P  Steve

Edit: I have been wondering about wrapping a flap in a hunk of that "CF braided sleeve" stuff. I guess the angle of the weave would depend on the size of the sleeve and taper of the flap, so maybe not so wonderful. 
« Last Edit: August 29, 2018, 05:22:33 PM by Steve Helmick »
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Offline John Watson

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Re: Flap design.
« Reply #24 on: August 29, 2018, 07:21:34 PM »
What effect does more flap area create?

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Re: Flap design.
« Reply #25 on: August 29, 2018, 10:24:52 PM »
What effect does more flap area create?

More pitching moment that needs to be counteracted by the elevator, more hinge moment that needs to be overcome by differential line tension, and more drag that needs to be overcome by thrust.  More flaps usually, depending on the airfoil, give more lift capability, hence you can turn tighter corners more predictably unless the mass you gotta add to counteract the detrimental effects exceeds the added lift capability.  More flap also affects the pitch dynamics.  It can make it easier to fly level and fly round loops.
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Offline Tim Wescott

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Re: Flap design.
« Reply #26 on: August 30, 2018, 09:00:56 AM »
How is "veil" different than "mat"?

AFAIK, veil has really long fibers and mat has short fibers -- basically feet as opposed to inches.  I think that the idea of veil is that it adds more strength than mat because of the long fibers, but doesn't print through the way that cloth does, because the fibers are randomly oriented.

Quote
Edit: I have been wondering about wrapping a flap in a hunk of that "CF braided sleeve" stuff. I guess the angle of the weave would depend on the size of the sleeve and taper of the flap, so maybe not so wonderful.

I suspect that even with a tapered flap you could get a reasonable compromise.  Particularly if you figure that you don't need as much torsional stiffness out at the end of the flap than you do at the root -- use the diameter of sleeve that's optimal for the flap root or just a few inches out, and accept the fact that the angle will be shallower at the end.

Quote
It would be nice if 4" wide tape was made on the bias.

Take some sleeve, slit it lengthwise, get it on the flap before it all unravels -- poof, you're done.
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Offline Lauri Malila

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Re: Flap design.
« Reply #27 on: August 30, 2018, 11:03:11 AM »
[quote
How is "veil" different than "mat"?
[/quote]

Like day and night, Steve.
Here is a couple of pictures. First is veil, and as you see it has very little short (up to about an inch) fibers with random orientation. So the mechanical strenght is very low, even the thinnest gf cloth gives better results when applied correctly.
Second is a typical woven flat tow Textreme cloth, 76g/m2. These flat tow cloths like Textreme are the best performing woven carbon products as fibers run very straight, and they are also very easy to handle compared to classic woven carbon cloths. The lightest we use at the moment is 44g/m2 if I remember right.
Another good option would be the Carboline material (check www.carboline.info  ). L

Online Paul Walker

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Re: Flap design.
« Reply #28 on: September 01, 2018, 06:15:34 PM »
OR  you could build your flaps like Howard.

Home made +/- 45 degree carbon tube LE. Very rigid in torsion. Very wimpy in bending, which is exactly what you want.

Maybe he will elaborate on his construction process.....

Offline Chris Wilson

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Re: Flap design.
« Reply #29 on: September 01, 2018, 07:12:33 PM »
Another rather obvious way to prevent twist is to drive the flaps from both ends - haven't seen this done but it is possible.
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Offline Perry Rose

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Re: Flap design.
« Reply #30 on: September 02, 2018, 07:56:49 AM »
After reading all the posts and dividing by 2 I came up with this.  The first picture shows the rabit joints turned into a dado by laminating two layers of 1/4 x 5/8 balsa for the leading edge. The hinge slots are sanded into each piece before gluing. A piece of 1/8 balsa glued into the dado with 3/16 sq. ribs sanded to shape. Now do I cover with doctor paper, silk span, new silk span or poly span and paint or use iron on covering? The way this is going I'll never get it done.
I may be wrong but I doubt it.
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Offline Lauri Malila

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Re: Flap design.
« Reply #31 on: September 02, 2018, 08:15:25 AM »
If I understand right, you have a balsa sheet in the centerline of flap, and then ribs on both side to give a desired cross section.
As mentioned earlier, the material in middle does practically nothing for stifness.
It would be better with balsa skins and ribs inbetween.
L

Offline Steve Helmick

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Re: Flap design.
« Reply #32 on: September 02, 2018, 01:39:36 PM »
Googled for both Textreme and Carboline. From Sweden and Russia, respectively, and I didn't see a way to order a couple of square meters of anything on either's website. I noticed that Textreme makes a version of their product in a 45+/- fabric, which would be splendid, but obtaining this stuff might be expensive or nearly impossible.

I'll have to check US sources for composite materials and see if I can find them here, or something similar. I've only dealt with CST in the past, and don't know the name of the one in the LA area. If anybody can post the links for those two, please do. My old tower has those links, but apparently needs a new power supply, so until I can get that fixed, I'm having to use DuckDuckGo or Google search engines. Wondering why they are not called "search motors", since they're friggin' electric?   ;) Steve
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Offline pmackenzie

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Re: Flap design.
« Reply #33 on: September 02, 2018, 02:18:05 PM »
You can order both from RG in Germany:

https://shop1.r-g.de/en/list/Fibre-reinforcements/Carbon-fibre

email them for a shipping quote.

AFAIK, there is no US source for the really light carbon stuff.

Two most common US sources for composite stuff are CST sales

http://www.cstsales.com/

and

Aerospace composite products

https://store.acpsales.com/categories/1799/dry-fabrics-reinforcements


(Also Carboline is made in the Ukraine, not Russia. Still two different countries :) )
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Online Ken Culbertson

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Re: Flap design.
« Reply #34 on: September 02, 2018, 03:29:50 PM »
Another rather obvious way to prevent twist is to drive the flaps from both ends - haven't seen this done but it is possible.
Then we would have to start another thread to deal with "Center Sag" LL~

Ken
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Offline Lauri Malila

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Re: Flap design.
« Reply #35 on: September 04, 2018, 01:24:32 AM »
OR  you could build your flaps like Howard.

Home made +/- 45 degree carbon tube LE. Very rigid in torsion. Very wimpy in bending, which is exactly what you want.

Maybe he will elaborate on his construction process.....

I understand what you mean, but that sounds like you want the wing to flex:)

Offline jfv

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Re: Flap design.
« Reply #36 on: September 04, 2018, 07:34:55 AM »
Googled for both Textreme and Carboline. From Sweden and Russia, respectively, and I didn't see a way to order a couple of square meters of anything on either's website. I noticed that Textreme makes a version of their product in a 45+/- fabric, which would be splendid, but obtaining this stuff might be expensive or nearly impossible.

I'll have to check US sources for composite materials and see if I can find them here, or something similar. I've only dealt with CST in the past, and don't know the name of the one in the LA area. If anybody can post the links for those two, please do. My old tower has those links, but apparently needs a new power supply, so until I can get that fixed, I'm having to use DuckDuckGo or Google search engines. Wondering why they are not called "search motors", since they're friggin' electric?   ;) Steve

Here's what you might try.  2 layers of unidirectional CF at opposite 45 degrees bias.  Expensive but light and strong.

https://shop1.r-g.de/en/art/192029060-CBA310
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Offline Avaiojet

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Re: Flap design.
« Reply #37 on: September 04, 2018, 10:15:01 AM »
Here's what you might try.  2 layers of unidirectional CF at opposite 45 degrees bias.  Expensive but light and strong.

https://shop1.r-g.de/en/art/192029060-CBA310

This Post caught my interest.

An examination of other products may shine some light.

Tennis racquets.

For those that don't know, I have over a 40 year history of tennis instruction. I still teach tennis.

"Equipment," as also technique is extremely important.

I've seen equipment change as well as style techniques.

Style, well, there's no interest there.  LL~

Equipment? Well, that's another thing entirely.

Not to waste time or to bore people to death, I'll cut to the chase.

Stiffness in a tennis racket is extremely important at the higher level of play. So is weight.

ALL, manufactures results/conclusions, with hours of testing over many years, improvements over improvements, with the production of tennis rackets where their goal is to create stiffness while reducing weight, they seem to agree on the materials they use.

Layers/strips of CF placed at the diagonal and soaked with Epoxy resin.

They heat cure at 150 degrees.

If there was a better material than CF, tennis racket manufactures would be using it.

They do compete with each other in the market place.

Trump Derangement Syndrome. TDS. 
Avaiojet Derangement Syndrome. ADS.
Amazing how ignorance can get in the way of the learning process.
If you're Trolled, you know you're doing something right.  Alpha Mike Foxtrot. "No one has ever made a difference by being like everyone else."  Marcus Cordeiro, The "Mark of Excellence," you will not be forgotten. "No amount of evidence will ever persuade an idiot."- Mark Twain. I look at the Forum as a place to contribute and make friends, some view it as a Realm where they could be King.   Proverb 11.9  "With his mouth the Godless destroys his neighbor..."  "Perhaps the greatest challenge in modeling is to build a competitive control line stunter that looks like a real airplane." David McCellan, 1980.

Offline Lauri Malila

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Re: Flap design.
« Reply #38 on: September 04, 2018, 02:06:15 PM »
Here's what you might try.  2 layers of unidirectional CF at opposite 45 degrees bias.  Expensive but light and strong.

https://shop1.r-g.de/en/art/192029060-CBA310

That seems to be the Ukrainian product, from V. Gavrilko. Propably the second best option.
Slightly better would be the ThinSkin from creativecompositetechnologies.com.
With such non-woven products ans parts like flaps, with thin cross section, it's important to use (and buy:() products with  +/- and -/+ 45 degree fiber orientation on opposite sides, otherwise you end up with asymmetrick behaviour under stress. In this sense woven products are better. L

Online Brett Buck

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Re: Flap design.
« Reply #39 on: September 04, 2018, 04:34:16 PM »
I understand what you mean, but that sounds like you want the wing to flex:)

    Given that Paul was an industry-leading structural engineer, I am pretty sure he knows that no matter what you want, it *is* going to flex, so you had better accommodate that flex.

      Brett

Offline Dan Berry

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Re: Flap design.
« Reply #40 on: September 04, 2018, 05:58:48 PM »
I am absolutely fascinated by all of the responses that indicate that the first four words in the original post have no meaning.

Online Ken Culbertson

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Re: Flap design.
« Reply #41 on: September 04, 2018, 07:14:21 PM »
I am absolutely fascinated by all of the responses that indicate that the first four words in the original post have no meaning.
Maybe Perry knew that if you get 10 of us in a room you will have 12 different opinions and just wanted a good laugh.

Just out of curiosity, has anybody done a serious video observation of flaps at work? 

Ken
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Online Paul Walker

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Re: Flap design.
« Reply #42 on: September 04, 2018, 09:03:45 PM »
I understand what you mean, but that sounds like you want the wing to flex:)

Not what I meant. Fact is the wing will flex. If you build an infinitely rigid flap it will keep the wing trailing edge from deflecting. The hinges that connect the two will attempt to transmit the forces necessary to make the wing comply to the flap. Hinge loads increase as does the friction in those hinges and it will increase the moment required at the bellcrank to move the control surfaces. None of this is what you want.

Instead, make the flaps wimpy in bending and rigid as heck in torsion, and the hinge loads are minimized, and the flaps don't twist the wing.

One way to do that is with a  Howard torque tube, or....WITHOUT carbon, make the flaps out of 1/4" flat sheet (no chordwise taper) made with "perfect" "C" grain balsa. The last Predator had those and they are more rigid than a 3/8" tapered sheet or built up tapered flaps. With the 1/4" wood, they are not very rigid in bending also. Good wood is hard to beat.

Online Ken Culbertson

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Re: Flap design.
« Reply #43 on: September 05, 2018, 08:15:33 AM »
Not what I meant. Fact is the wing will flex. If you build an infinitely rigid flap it will keep the wing trailing edge from deflecting. The hinges that connect the two will attempt to transmit the forces necessary to make the wing comply to the flap. Hinge loads increase as does the friction in those hinges and it will increase the moment required at the bellcrank to move the control surfaces. None of this is what you want.

Instead, make the flaps wimpy in bending and rigid as heck in torsion, and the hinge loads are minimized, and the flaps don't twist the wing.

One way to do that is with a  Howard torque tube, or....WITHOUT carbon, make the flaps out of 1/4" flat sheet (no chord wise taper) made with "perfect" "C" grain balsa. The last Predator had those and they are more rigid than a 3/8" tapered sheet or built up tapered flaps. With the 1/4" wood, they are not very rigid in bending also. Good wood is hard to beat.
If I understand your argument, you are saying that flaps should be chord wise stiff and span wise flexible with as little torsion twisting as possible.  This all but eliminates carbon and makes any form of angled rib (like I currently build) built up problematic.  As far as I can see, only a moderately thick flat solid flap with a traditional covering fits that definition.  Sometimes the easiest to build is actually the best. 

I am all in on the argument for chord wise stiffness but am also curious why torsional twisting is bad if it is consistent and balanced?  It seems to me that the effort to eliminate it is greater than the effort to trim for it.

Ken
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Offline phil c

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Re: Flap design.
« Reply #44 on: September 05, 2018, 08:50:14 AM »
" Actual fabric would cost a lot, and putting it on a bias isn't very cost effective."

Steve H- the cheapest way to biased narrow widths is to cut a rectangular strip about 1.5x wider than needed.  Pull on the opposite corners until the warp and woof threads are at ~45 deg.

I find the biggest problem with CF cloth is keeping it together.  I've sprayed it both with laundry spray starch or light coats of clear laquer.  When it's dry cut to shape.  Either will stick the threads together enough to cut the fabric.
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Online Paul Walker

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Re: Flap design.
« Reply #45 on: September 05, 2018, 11:09:37 AM »
  This all but eliminates carbon and makes any form of angled rib (like I currently build) built up problematic. 

Ken

Quite the opposite. Carbon IS the answer. I was trying to answer the question he asked about not using carbon.

A carbon tube with only +/-  45 plies is very rigid in torsion, but quite wimpy in bending. That IS the perfect solution.  Making them is the problem!

Online Ken Culbertson

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Re: Flap design.
« Reply #46 on: September 05, 2018, 02:25:41 PM »
.... I was trying to answer the question he asked .....

I didn't think we did that anymore!  LL~

 Sorry to have taken the wrong conclusion.  I am still perplexed why lack of torsional twist is any better than even torsional twist or is "even" the goal and making them rigid is one way of achieving it?

I have another issue with Carbon that may be totally incorrect but I have always wondered about it.  If we assume that the wing TE flexes in a turn it must be putting tremendous pressure on the hinges since the deflected flap will have to twist chord wise (span wise lengthening of the TE) to follow the wing flex.  With a carbon skin this flexibility would be nearly impossible, eventually lead to hinge failure and probably add a lot to the control pressure.  Since I don't see this happening, I wonder just how much our wings actually do flex.  Can't be much.

Perhaps this is why cloth hinges work so well.  They have just enough give to not suffer from the pressure in the hinge, they just look like crap.

Ken
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Offline frank williams

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Re: Flap design.
« Reply #47 on: September 05, 2018, 03:40:07 PM »
This site looks like the material that Dorian and Mark were using for the all carbon plane at this years Nats.
creativecompositetechnologies.com

Offline Perry Rose

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Re: Flap design.
« Reply #48 on: September 06, 2018, 05:15:34 AM »
After reading all the responses I figured the best way for "me" to make the flaps. I went to Michael's and got some Revel balsa which is very firm and cut two pieces of 1/4" balsa 3/4 x 29 for the leading edges. I cut a 1/8 wide rabbet joint in each then sanded the hinge slots in each and glued two together to form the leading edge with a dado joint centered, just like the previous photo. I cut the flaps out of the firm whttps://stunthanger.com/smf/Smileys/classic/hatsoff.gifood and glued them into the dado joints. The reason for the leading edge is that the wing trailing edge is 1/2" wide. Now the covering will taper almost matching the airfoil.
  A big thank you to all who answered and a hearty handclasp.
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Offline frank williams

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Re: Flap design.
« Reply #49 on: September 11, 2018, 07:12:34 PM »
I understand you already built your flaps, but I finally got around to finding the drawing of what I have used for torsion resistant flaps.  The box at the leading edge of the flap is a torque box that works quite well to prevent twisting of the flap.  You can cover the completed sheeted flap with carbon vail.


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