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Old Nov 12, 2012, 03:27 PM
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Knoll53's Avatar
United States, CA, Marina
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Cool design, nice modeling.

Are you concerned about torsional flex on the long torque tube controlling the entire tip? It will certainly be good for low speeds but possible flutter at high speed.

You could try the prototype with the tip acting as both aileron and elevator and if some how too weak for elevator, then cut in elevator flaps elsewhere, but my money is on them providing adequate elevator control. This is a plank. They are quite pitch sensitive. It doesn't take much to throw them around.

Think of them as rudders at the tips. Imagine if they were both kicked up 1 1/2" at the TE. Wouldn't that produce lots torque to affect the pitch? It may not be "clean" but should be effective. Your 3rd image would produce nose down.

As always, I may be missing something here. Hope you build this one....very interesting.

Kent
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Old Nov 12, 2012, 04:38 PM
Just call me crash for short
Quick61's Avatar
United States, OH, The Plains
Joined Jan 2011
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Quote:
Originally Posted by Knoll53 View Post
Cool design, nice modeling.

Are you concerned about torsional flex on the long torque tube controlling the entire tip? It will certainly be good for low speeds but possible flutter at high speed.

You could try the prototype with the tip acting as both aileron and elevator and if some how too weak for elevator, then cut in elevator flaps elsewhere, but my money is on them providing adequate elevator control. This is a plank. They are quite pitch sensitive. It doesn't take much to throw them around.

Think of them as rudders at the tips. Imagine if they were both kicked up 1 1/2" at the TE. Wouldn't that produce lots torque to affect the pitch? It may not be "clean" but should be effective. Your 3rd image would produce nose down.

As always, I may be missing something here. Hope you build this one....very interesting.

Kent
Yes, I want to lean real hard along with your thinking of the pitch sensitive traits of a plank wing, but to be on the safe side, and given this is a prototype, maybe I should just go ahead and add in the elevators (only 1 more servo needed) and fly it both ways. Like money, guns and lawyers, better to have and not need, than to need and not have.

Anyway, here is what I am thinking for elevators. Looks about right. Note that not all the ribs and such are drawn in yet - just for visual reference. Thanks for the kind comments. I do try with the CAD, being self taught and all, it's good to hear when others think I'm dong OK.

Oh, and I have been thinking about the twisting in the CF tube. At these lengths (~12") and weight, I don't think it will be much of an issue. Now going bigger and heavier, I will be looking at drill rod or custom CF / FG tubes built for torsional loading.

Mark
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Last edited by Quick61; Nov 12, 2012 at 04:48 PM.
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Old Nov 12, 2012, 05:19 PM
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Knoll53's Avatar
United States, CA, Marina
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Sweet !....(and safe)

If that elevator was acting alone, it would probably be just big enough to get the job done. Assuming the CG is pushed way back.

If you happen to suffer from a need to know (as I do) you could program the tips to act as elevons and then add a program to drive the inboard elevator flap as a slave to the elevator function. Put that program on a switch and test fly with everything working. Once at a safe altitude, turn off the inboard elevator program and try to fly with just the tips as elevons.

This will be one cool little plane.

Kent
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Old Nov 12, 2012, 06:03 PM
Just call me crash for short
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United States, OH, The Plains
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Quote:
Originally Posted by Knoll53 View Post
Sweet !....(and safe)

If that elevator was acting alone, it would probably be just big enough to get the job done. Assuming the CG is pushed way back.

If you happen to suffer from a need to know (as I do) you could program the tips to act as elevons and then add a program to drive the inboard elevator flap as a slave to the elevator function. Put that program on a switch and test fly with everything working. Once at a safe altitude, turn off the inboard elevator program and try to fly with just the tips as elevons.

This will be one cool little plane.

Kent
Shiny, I'll get the rest of the parts drawn up, mod the ribs on the cut sheets and make a run at it.

Mark
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Old Nov 23, 2012, 03:08 AM
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
3,199 Posts
Central fin on a plank.Is there a way to come up with an optimum size of fin area:wing area.Lots of variables I can see,profile,shape,position etc.The only figures I've found are "between .015 and .025"
Any thoughts?
Stuart
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Old Nov 23, 2012, 07:40 AM
the answer 42 is
Switzerland, AG, Lenzburg
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stuart the articles from Peter Wick on RCSD explain all what you ask and bring some small formulas how to calculate them

EZ
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Old Nov 23, 2012, 11:05 AM
I don't like your altitude
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Originally Posted by Edwinzea View Post
stuart the articles from Peter Wick on RCSD explain all what you ask and bring some small formulas how to calculate them

EZ
Thanks EZ,took some interesting reading to find it but got there.As I expected,a lot of ifs and buts,but a quick run of the formula gives a close result to the above figures.
Regards Stuart
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Old Nov 25, 2012, 05:31 PM
I don't like your altitude
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First try at a fin.I'm going to have a go at a split air brake.Most of the examples I've looked at comment on a pitch up when they are deployed,so lowering the hinged area may help reduce this.
Bit more triangulation will let me get a good idea of the surface area.
Stuart
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Old Dec 16, 2012, 04:48 AM
I don't like your altitude
Stupot46's Avatar
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After a bad dose of something or other,done a bit of fin and fuselage.Waiting for wings to arrive,so no final shaping till then.
I'm using Kents method,glassed foam plug,but I'm going to try dissolving the foam with acetone.
To fit some formers I was considering slicing the plug at the required positions,taking the former shapes and then tack glueing it back together.
If I did this,but took a 2mm slice out,then replaced it with a section of foam of the same thickness but 2mm smaller on the outer dimension,this would leave a groove in the reassembled plug.
Fill the groove(push the first layer of cloth in/ strip of cloth/carbon tow/ micro balloons,whatever's best)
When the foam is dissolved an internal flange will be left,adding stiffness and a fixing point for the formers.
The pic is a template I used to cut out the plug,the lines are positions for a hatch and battery bay.
Do you guys think this is a workable idea?
Regards Stuart
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Old Dec 21, 2012, 10:39 AM
I don't like your altitude
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Did a trial.First pic.is the foam cut in 3places;horizontal for a hatch,depron spacer;l/h for a former position,depron spacer,r/h a former set in.Next is the grooves filled with tow,and then a couple of layers of light cloth spray glued on.
Last two are after the foam dissolved out.Very messy.
The fixed former worked well,the tow flange is a qualified success,a couple of places I didn't fill the groove quite enough and it hasn't adhered well.
With a bit of refinement I think formers and wing seat etc can be set into the plug this way
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Old Dec 21, 2012, 12:17 PM
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I see that you have the loose tow fibers in a groove. I wonder if the tow could be better attached with spray adhesive? I haven't tried it yet, but thinking something along the lines of:
  • light spray of adhesive on the foam core
  • stretch the tow tight and press it into the adhesive
  • press with waxed paper, cure and remove paper
  • repeat for glass cloth

just a thought from the guy with miles of tow and who is looking for ways to use it.

Kent
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Old Dec 21, 2012, 12:20 PM
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Knoll53's Avatar
United States, CA, Marina
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Quote:
Originally Posted by Stupot46 View Post
First try at a fin.I'm going to have a go at a split air brake.Most of the examples I've looked at comment on a pitch up when they are deployed,so lowering the hinged area may help reduce this.
Stuart
the reason for the pitch up during split rudder deployment is because those gliders have an inclined hinge line. As in backward leaning hinge line. If there was a forward leaning hinge line, there would be a nose pitch. A vertical hinge line will produce a neutral pitch response.

Kent
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Old Dec 21, 2012, 12:46 PM
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Quote:
Originally Posted by Knoll53 View Post
the reason for the pitch up during split rudder deployment is because those gliders have an inclined hinge line. As in backward leaning hinge line. If there was a forward leaning hinge line, there would be a nose pitch. A vertical hinge line will produce a neutral pitch response.

Kent
I vote for the height of the drag from the split rudder above the CG:

http://www.rcgroups.com/forums/showp...43&postcount=6

Kevin
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Old Dec 21, 2012, 01:23 PM
I don't like your altitude
Stupot46's Avatar
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Originally Posted by kcaldwel View Post
I vote for the height of the drag from the split rudder above the CG:

http://www.rcgroups.com/forums/showp...43&postcount=6

Kevin
I was toying with the idea of drawing an arc from the cog to the line of the hinge,but I still can't figure out the optimum angle.
Stuart
Ill have to study the Drela link
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Old Dec 21, 2012, 01:39 PM
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
3,199 Posts
Quote:
Originally Posted by Knoll53 View Post
I see that you have the loose tow fibers in a groove. I wonder if the tow could be better attached with spray adhesive? I haven't tried it yet, but thinking something along the lines of:
  • light spray of adhesive on the foam core
  • stretch the tow tight and press it into the adhesive
  • press with waxed paper, cure and remove paper
  • repeat for glass cloth

just a thought from the guy with miles of tow and who is looking for ways to use it.

Kent
The idea was to make an internal flange as a stiffener,hence the groove.Not sure if I'll go that route,the ply former worked really well.With a bit of planning it should be possible to pre-install all the formers into the fuse plug before glassing.
I'm still waiting for the wing cores,so can't go much further.
Stuart
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