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Author Topic: New coupe  (Read 823 times)
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Richard Ewing
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« on: July 07, 2017, 09:27:02 PM »

Not quit ready for a test glide but getting close.  This is the replacement for my 1st coupe that I lost last year in Oregon.  It has the same plan form as my 1st coupe, but with BE airfoils in the wing.  Functionally it incorporates a wing DT, and colored mylar for improved chances of recovery.  At 77grams its not light, but it's got 220 square inches of wing.
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Richard Ewing
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« Reply #1 on: July 07, 2017, 09:28:16 PM »

more photos...
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DerekMc
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« Reply #2 on: July 07, 2017, 09:41:13 PM »

Nice!
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They fly better when you smile!
Derek
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« Reply #3 on: July 08, 2017, 02:34:20 AM »

Damn!  I hope you make it to Oregon this year, I'd really like to see this.
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« Reply #4 on: July 08, 2017, 07:25:54 AM »

Rick;

Great looking F1G!  Will you be able to get away without a turbulator?

Any idea of weight added with pop-up wing; would like to see detail shot. Is it similar to Blake/Tiffany system?

Louis

PS: Neat adjustable-height sawhorse---source?
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Richard Ewing
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« Reply #5 on: July 09, 2017, 01:44:01 AM »

Louis,

I think the last thing I read about using these shapes was that Tmat still used a turbulator, but about half the typical height.  I'll probably use one layer of chart tape at the end of the flat zone.

The wing DT is inpired by Blake's, but I had to work around a mechanical timer, and mine is probably not as good. More photos to fallow.

The table on saw horses is IKEA.
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OZPAF
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« Reply #6 on: July 09, 2017, 05:31:51 AM »

I'm interested to see how it performs with it's BE foils. Very nice Richard.

John
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« Reply #7 on: July 09, 2017, 05:33:16 AM »

Richard,

Thanks for the info. DTing to wing seems to be the best way to go for small models---I've seen too many stay in thermals with stab popped up.

Have you considered intermittent turbulators? There was a paper in 2003 Sympo that was based on wind tunnel tests in Germany. I've been using scale plastic rivets made for model railroad use. Tichy Train Group makes & sells the rivets in a lot of different sizes. For F1B I'm using .050" (1.27mm) diameter round-head rivets. This gives a height of .025" (.635mm). Spacing is 10mm center-to-center, spaced back about 10mm from leading edge. I'm using the rivets on conventional AA-airfoiled wings and on a 6-panel Stefanchuk wing with the BE6156an root airfoil (page 187 in 2011 Sympo). I've not tried the bumps on a true LDA airfoil with the flat area on top.

The rivets come with a narrow shaft (i.e. they look like real rivets). I've found the easiest way to cut the head off is to use a single-edge razor blade; do this inside a shoe box--the heads fly off and are impossible to find if they go on floor, workbench, etc.

You could glue rivet heads on an adhesive strip to allow for adjustment. I just glued them straight onto D-box using slow epoxy. Best way I've found to handle the rivets is with a gum massager---it looks like a dental tool but has a rubber tip. I touch tip to my tongue, then pick up rivet and position on pre-applied drop of epoxy on D-box. Then I use a #11 X-Acto blade to get in exact position. For spacing, I run a strip of masking tape along D-box, then mark 10mm intervals. I've ended up using DP-460 epoxy because it is slow-setting and has just the right amount of tack---doesn't take but a very small drop. Gluing on the 180 rivets for a long F1B wing takes a couple of hours.

A pack of 96 #8076 .050" rivets was $3.00 last I ordered. www.tichytraingroup.com
P.O. Box 220, Adamance, NC 27201; (336)217-8523

Louis
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Tmat
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« Reply #8 on: July 14, 2017, 05:06:34 PM »

I think the last thing I read about using these shapes was that Tmat still used a turbulator, but about half the typical height.  I'll probably use one layer of chart tape at the end of the flat zone.

Richard,
You are correct, I'm using a turbulator roughly 0,3 to 0,4 mm high located at the back edge of the flat section.
My latest Coupe uses the BE5547 airfoil which is not LDA. Very nice glide and climb with no vices.

Tmat
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Richard Ewing
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« Reply #9 on: July 16, 2017, 11:16:14 AM »

Tony,

Thanks for the turbulator dimension.  That's two layers of the tape I have.  Some hand glides in the local school yard with that looked nice this morning.

Here are a few more pictures showing the wing rotation DT function.  The little plywood cradles under the wing joiner rod were added in an attempt to improve the roll stiffness of the wing to fuselage in the flight configuration.  It only help a little, so I added a layer of +/- 45 carbon to the "spine" or the dog bone shaped element, and that feels much better.
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Richard Ewing
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« Reply #10 on: July 16, 2017, 11:18:49 AM »

a picture of the wing DT line turn around post with it's edge to reduce tension on the timer side
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Richard Ewing
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« Reply #11 on: July 16, 2017, 11:34:21 AM »

Back to the topic of turbulators on LDA airfoils on a coupe:

  Last year, my 1st plane with a sorta LDA airfoil did want to stall as the day warmed up and the conditions became less calm.  I had some discussion with Blake Jensen and Tiffany O'dell on the topic since their coupes also use an airfoil with some LDA like shape at the front.  Blake told me that they have to be very careful to speed up the glide in the bumpy afternoon rounds and think the Ukrainian airfoils do better in those conditions.

I only have the one model, and I'll be flying it a the contest in Tangent this August.  I'm expecting warm "bumpy" conditions as the day progresses.  Do you think a higher turbulator is called for, and/or additional roughness or trips strips of some kind, ("invigurators")?

Tony,
Where shall I look for the coordinates of the BE airfoils on you current coupe?
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« Reply #12 on: July 16, 2017, 03:38:30 PM »

Richard;

Thanks for the detail shots of the wing dt.  Looks a bit lighter than the system Blake & Tiffany use. Do you also DT stab? 

Louis
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FF Bruce
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« Reply #13 on: July 16, 2017, 05:30:36 PM »

Richard,did you know that the two FAI contests at Tangent in Aug. have been moved to Sept. because of the World Champs?We still fly coupe but combine it with A-1 and three flights not in rounds.
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Hepcat
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« Reply #14 on: July 16, 2017, 06:00:01 PM »

Response to #11
Richard,
I have neither a wind runnel nor one of the computer programmes that might compute the airflow around an aerofoil but I think the tendency to stall in the afternoons is to be expected.  We have spent over half a century trying to improve the sinking speed of aeroplanes at our Reynolds numbers and have done pretty well at it. We found we needed a good amount of camber for a high lift coefficient but had to maintain a smooth airflow over the top surface.  This usually required quite a high entry angle for the camber line and usually a certain amount of turbulation of the flow over the upper surface.  The results have been excellent.  However of recent years glider flyers have found that the height gained on the tow is more important to them than the minimum sinking speed so for the climb part of the flight they are looking for aerofoils with low camber, low entry angle and presumably no turbulators.  The pseudonym of LDA (low drag aerofoil) has been quickly adopted without the relationship to speed always being clear.  I realize that there can be an argument that they can speed up the climb of a rubber model but the energy to climb a rubber model faster still has to come from the permitted amount of rubber whereas the extra climb speed of a glider comes from the energy of the launcher. 
So back to the original matter of a rubber model with an LDA stalling in turbulent air. If the model is trimmed for minimum sinking speed I think this is inevitable.  The smaller entry angle and lower camber will cause a breakaway of flow that I don’t think turbulators would prevent.  I suppose that really I have said no more than ‘horses for courses’!
Looks a great coupe.
John
   
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Richard Ewing
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« Reply #15 on: July 17, 2017, 01:24:08 AM »

John,

Thanks for the comments on airfoils.  I hadn't thought about it in terms of entry angle, but that is easy for me to visualize now that you've mentioned it. 

When I started this plane several years ago, my inspiration came from reports of LDA F1B models with very exciting (fast) initial climbs.   That just sounded like fun for a coupe.  So I stared one with the same size , (220 square inches) as my first coupe.  But having launched into the same air with Tiffany O'dell last year, seeing her smaller area plane race away from mine, I think I agree with your "horsed for courses" comment as it applies to more than just airfoil choice.  Of course, her plane was perfectly trimmed, and expertly flown.   But it still confirmed what lots of others have written about regarding smaller coupes for rough conditions.  If I hadn't lost my only plane at that contest, I might have started a different , (smaller) design, with a more traditional, (more camber, larger entry angle) airfoil.  But I already had some the work completed for the big LDA wing and have still only just gotten the plane completed for the contest next month. 

Bruce,
Rob Lane and I are planning to be there in August, and he'll be flying glider.  Combining events may complicate our plans to time and retrieve , but fewer flights should help that.  Last years 2 contests on the same day, (10 official flights) was fun but busy.  Will that be the format for the Sept 8,9,10 event?
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« Reply #16 on: July 17, 2017, 10:31:22 AM »

Richard, the Aug. contest is the 18,19 & 20 any event,any day and you don't need to finish on the day you start.On Fri. we also fly Vintage FAI power and Pro P-30 in rounds,we also have night  flying & ROW.On Mon. the eclipse is happening around 9:30  or so and some will try and fly during it. If you don't have a room by now you won't there are hundred thousand people coming for the eclipse and all rooms are gone (at double the price).   
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« Reply #17 on: July 17, 2017, 10:32:16 AM »

Oh yes the Sept. contest is as you say.
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Tmat
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« Reply #18 on: July 17, 2017, 01:15:49 PM »

Do you think a higher turbulator is called for, and/or additional roughness or trips strips of some kind, ("invigurators")?
Tony,
Where shall I look for the coordinates of the BE airfoils on you current coupe?
Richard,
I can send you the co-ordinates. PM or email me.
Yes, a more aggressive (read higher) turbulator and a slight forward CG shift will do the trick.

Tmat
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F1B guy...
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