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Author Topic: My Couper "S" traditional/hitech build  (Read 5454 times)
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DerekMc
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« on: March 02, 2009, 06:19:03 PM »

Howdy folks,

I finally got started on a new coupe this past weekend. It is the Couper "S" designed by Andrew Longhurst and published in Free Flight quarterly #28. I think it is #28. I will check when I get home. I like Andrews design philosophy and this is a plane I can build pretty much all by myself with stuff from the Local Hobbyshop (LHS). The one exception so far is the kite spar tailboom. It is not from my LHS. I bought it at the LKS (local Kite shop). I will post some pictures as I proceed. This will be a slow build because I am quite busy at the moment. I do find that I get to the building board a bit more when I take pictures and share them so we shall how it all comes together.

Andrew says to use whatever airfoil you want so I am going to try the one from Jack Emery's Coupe. I am intrigued by its thick trailing edge. I hope to install a RDT system which will allow test flying on some local fields. The plan is to place a small servo at the end of the motor tube which will release the leading edge of the wing along with the stab to around a 70 degree angle.

Derek
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schnellwilli
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« Reply #1 on: March 02, 2009, 06:30:52 PM »

I just checked it out and it is Issue #28. Nice traditional model! Simple, fuctional home made front end. I liked what he said,"Nothing to buy from Russia".
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DerekMc
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« Reply #2 on: March 02, 2009, 06:49:45 PM »

Thanks Bill for the FFQ information. The "Nothing to buy from Russia" is part of Andrew's design philosophy that I liked!

Derek
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applehoney
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« Reply #3 on: March 02, 2009, 07:02:39 PM »

...part of Andrew's design philosophy that I liked!

And probably the last competition flyer extant in Britain who doesn't use a blast tube!
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DerekMc
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« Reply #4 on: March 02, 2009, 07:43:33 PM »


And probably the last competition flyer extant in Britain who doesn't use a blast tube!

The motor tube is very simple and can take blown motors. Andrew uses something called 'dressmakers tape' to wrap his motor tube. I have no idea what that is and neither did the fabric stores that I checked so I am going to use envelope tyvek in its place. One avenue i wish to explore in the future is to use 1/32" sheet wood instead of 1/16". I wind my motors outside the model so the motor will break when I am adding hand turns. Spiral wound 1/32" sheet might be able to take the bulge of a busted motor. At some point we shall see.

Derek
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Randy Reynolds
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« Reply #5 on: March 02, 2009, 08:40:38 PM »

Hi Derek,

I am interested in the Couper "S" as well. Especially the tip up wing which will save an airplane from those big thermals. I've twice had 15-20 minute flights on my Burdov Candy after the DT went off!

I wonder why you would want to use 1/32" for the fuse when the airplane comes in at 68 grams as is?

I'm trying to sort out how to use a conventional tapered CF tailboom and fitting it up to the square fuse end. Have you sorted that out? It would be good if it broke down into two pieces for transportation as well.

Randy
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« Reply #6 on: March 02, 2009, 09:16:36 PM »

The motor tube is very simple and can take blown motors.

Possibly so.. but my tongue-in-cheek comment was due to he not using a blast tube in any sort of fuselage .... he is a fast builder, though .... Wink
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DerekMc
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« Reply #7 on: March 02, 2009, 10:32:13 PM »


I wonder why you would want to use 1/32" for the fuse when the airplane comes in at 68 grams as is?

I'm trying to sort out how to use a conventional tapered CF tailboom and fitting it up to the square fuse end. Have you sorted that out? It would be good if it broke down into two pieces for transportation as well.

Hi Randy,
We shall see how close to weight my first Couper "S" will be. I plan to put some electronics in it in the form of a radio dt and transmitting bug. My bugs are 3 grams and the RDT is dependent on the weight of the servo you use. So if using 1/32" on the fuse gets me closer to the 70 grams and it will take a motor failure due to hand turns and be stiff enough to not twist then why not? Not asking for much am I!

I considered making the plane break down into a two piece fuselage and two piece wings but i am concerned about the weight it would add. I drive to the flying fields so a bigger box works fine for me. As to how to do it I thought of using the plan method but fitting the tailboom into a box that would slide into the back of the motor tube and connect them with a hook of some kind. If you give it a shot make sure you post how you do it!

Derek
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DerekMc
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« Reply #8 on: March 02, 2009, 10:33:53 PM »

Possibly so.. but my tongue-in-cheek comment was due to he not using a blast tube in any sort of fuselage .... he is a fast builder, though .... Wink

That takes more guts than I have! I am an incredibly slow builder so i want my planes to hang around as long as possible!
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DerekMc
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« Reply #9 on: March 03, 2009, 01:18:19 AM »

Here is the unfinished motor tube. 3/32 stringers of 11 pound wood. 1/16 vertical grain 6 pound sheet sides. 5 grams ready to be doped inside and out, then wrapped with 5 mm Tyvek strip on 12 mm centers attached with more dope. After that dries I will cover it all with good old esaki japanese tissue. it's good to be building again!

Derek
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Couper "S" Build: The Motor Tube er square
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« Reply #10 on: March 03, 2009, 01:37:10 PM »

Great stuff Derek, I'm sure Andrew will be delighted to learn that someone is building another Couper S. We have a coupe competition coming up the weekend after next, at Middle Wallop & I'm sure Andrew will be there.

Andrew & I have gone along slightly different paths, but both using the SOC coupe as the base. For mine, I make a 22mm dia 1/16th rolled balsa motor tube with Tyvek on the inside (as per the Don Ross book). One of the benefits of having it inside is that it stops rubber lube soaking in. Like you I use a kite boom (Aviasport Skinny) which I glue on top of the fus wirh a low (1/2") pylon. I've now built 4 or 5 over the past few years for myself & my son, including a couple with Jedelsky wings (one was a bit of a heavyweight, so I named it 'Enry Couper - after the British boxer).

 Andrew is right that a square fus makes wing mounting simple & gives you somewhere to put the tomy DT timer, as I have to mount mine out in the wind!

Enjoy the build, and keep us posted on progress.

Regards
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Me with F1B - epic retrieval (flew 10km after DT)


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« Reply #11 on: March 03, 2009, 03:21:09 PM »

Hi All,
I am in the hunt for a coupe design and I was wondering if anyone has a picture of a completed Couper S to show?? Right now I am leaning towards Bob Whites Beau Coupe.

Thanks
Bernard
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« Reply #12 on: March 03, 2009, 04:28:45 PM »

Bernard

It featured in Free Flight Quarterly a few issues ago, and I'd offer to scan the 3 view for you except that I have yet to fathom out how to scan a full page (I end up with 10% or less). If you really want to see what's available, you couldn't do better than buying a copy of the FFQ coupe book - nay bible! Dozens of models, most of which have sufficient information to enable full size plans to be drawn. I've read mine so frequently that the pages are starting to fall out. Much of the contents was contained in two issues of FFQ which may be available as downloads. Just Google Free Flight Quarterly!

Peter
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DerekMc
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« Reply #13 on: March 03, 2009, 06:43:16 PM »

Andrew L. emailed me and gave the dressmakers ribbon another name. It is also known as organza and Michaels Craft carries it in a quarter inch wide variety. I will be next to a Michaels tomorrow and will pick some up and give it a try.

PeeTee, I will use the same boom as you (Aviasport Skinny). Which end do you use? The thicker end for greater stiffness or the smaller end for lighter weight. Or does it not make that big a difference. Just wondering!

Derek
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DerekMc
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« Reply #14 on: March 04, 2009, 12:25:12 PM »

I received good news from Sergio Montes, Free Flight Quarterly's editor. There will be a new edition of FFQ Coupe book in a larger format and it will include two full size plans. And one of them is the Couper "S"! How cool is that.

Sergio gave me permission to post a copy of the Couper "S" drawing from FFQ #28. If you would like a full size copy please send me your email in a personal message and I will send you one. Please remember to say where the scan come from (Free Flight Quarterly #28, Andre Longhurst) if you share it with somebody else.

Derek
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Re: My Couper "S" traditional/hitech build
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« Reply #15 on: March 04, 2009, 11:23:41 PM »

Derek, thanks for posting that plan....I ordered a Beau Coupe short kit so I guess I will be building that instead of the couper s but the couper might be next.....looks like a nice straight forward design.
Bernard
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DerekMc
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« Reply #16 on: March 06, 2009, 06:09:13 PM »

Today I cut out the blanks to make another motor tube. I decided to go ahead and build two planes.

I was able to find 7mm organza ribbon at Michaels Crafts. At a dollar for 5 yards you really can't for wrong. It is the "Sheerly Yours" ribbon by Offray. I wound the ribbon around the fuselage on 15mm centers. Every two winds i anchored it with a drop of CA which made the job easier to manage. I slid the fuselage onto a wood dowel wrapped with a paper towel. This allowed the fuselage to spin on the dowel as i wound the ribbon on. I found it hard to keep the ribbon exactly on center. I did not try to hard because it will be under tissue. One of the pictures shows the set up I used and the other is the final result ready for tissue. The brown bag was my attempt to provide contrast. My work top is white and it all blended in.

Next is the tissue and attaching the kite spar tailboom.

Derek
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Re: My Couper "S" Motor tube
Re: My Couper "S" Motor tube
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DerekMc
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« Reply #17 on: March 06, 2009, 09:56:40 PM »

Somehow i quoted my self unintentionally. O I thought I was clicking modify and I clicked Quote. So modify does not last very long on this forum. I will need to pay more attention to my spelling!
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DerekMc
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« Reply #18 on: March 07, 2009, 03:36:57 AM »

A couple more pictures to share:

1. Tissue covered motor tube and tailboom on alignment jig. My jig is a 36" piece of L shaped aluminum. Very easy to use when your motor tube is a square. Used shims to make sure the tailboom was straight. I cut tailboom to length with my dremel cut off tool. Ligned it up and glued it in.

2. Top two tailboom support glued in. This process was pretty fussy. Lot's of hand fitting and sanding to get a decent fit on the motor tube and tailboom. Lots of crazy angles and a curved surface to deal with.

3. Completed tailboom support pieces in place and wrapped with aramid thread. I am going to add a small box for my transmitter bug on the back of the motor tube. I will cover the tailboom supports with doped tissue. Hopefully it will come out okay. Weight so far is just under 14 grams.
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Re: My Couper "S" Motor tube and Tailboom
Re: My Couper "S" Motor tube and Tailboom
Re: My Couper "S" Motor tube and Tailboom
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« Reply #19 on: March 07, 2009, 11:03:28 AM »

Derek, Good pictures showing the alignment method. I wondered about using a round tailboom versus the one Andrew uses. I had thought also about using a regular connector from an F1G supplier and cutting a bore into the rear bulkhead for it. However your method looks very good thus far and I'm sure it will be sturdy enough.

If you have any contact with Andrew L. I wonder about a couple of items on the Couper "S". One is the purpose of the underslung fin.......is there an advantage there in trimming without the gadgetry? Secondly I flew in a contest last week-end where a flyer was using a DPR and that seemed to me to be a significant advantage with a free 25' altitude gain before the prop comes on. While I certainly don't want to go that route under the heading of simplicity, can the Couper "S" be launched aggressively?? Lastly are there any suggestions on setting up the angles for the DT? The concept of a tip-up wing is pure genius I think.

Continued good luck in your construction of the Couper "S".

Randy
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DerekMc
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« Reply #20 on: March 07, 2009, 12:50:17 PM »

Hi Randy,

Underslung fin. I am not completely sure but in the myst of my memory there was something about the advantage of getting the fin out of the wingwash, making it more effective. The negative side is that it is more easily damaged. Any aerodynamisists out there with a proper answer?

DPR: There is some controversy about its effectiveness. I remember reading in a NFFS symposium or Free Flight forum (maybe Peter King?) that it is effective if you can throw the model very hard with the prop starting at a specific point. If it starts too late then the plane basically stops and you lose any height gain. When I flew F1B I used DPR and found that about half of my launches had the plane almost come to a stop before the prop started. Part of that is skill but it is hard to make an accurate throw every time. Andruikov and Jensen do not seem to have many problems with it. Practice makes perfect!

Instant Prop start alleviates most of these concerns and the prop starts at the point of greatest acceleration (right at release) so those with weeny arms like me can concentrate on the proper launch angle rather than throw velocity. I am going to try IPR on my Couper S using an idea that I first heard about from Hepcat John Barker. You use a wire that slides through a tube on the bottom of the nose of the fuselage. It engages the prop arm wire and keeps it from spinning. The wire is attached to your throwing wrist with a lanyard of some type. When you throw the airplane the lanyard pulls the wire out of the tube releasing the prop: instant prop start! Will the couper S wing be able to handle it? I will find out!

As to the DT, the write up says that Andrew pops the leading edge of the wing up to a 70 degree angle. I have seen other coupes DT this way and it works. Andrew also pops the stab up 70 degrees. With both the wing and stab up the plane should come down with authority.

Anybody want to fill in or correct the above information? Please feel free to do so!

Derek
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DerekMc
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« Reply #21 on: March 07, 2009, 06:58:08 PM »

DPR: There is some controversy about its effectiveness.

That is an overstatement by me! The last 9 F1B world champions all used DPR so it obviously has something going for it!

Derek
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« Reply #22 on: March 07, 2009, 09:57:17 PM »

I'll be interested to see how IPR can be accomplished with the wire in tube idea. Offhand I would think that the lanyard pull from the wrist needs to be fairly straight or it would rip out the tube. Of course that's a failure that wouldn't hurt the flight as long as the trajectory of the model isn't upset. Got me thinking though!

I suppose that if the wire exiting the tube was fairly long and limber enough that it could certainly work.
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« Reply #23 on: March 08, 2009, 02:57:06 PM »

Randy
I first devised the ‘tube and pin’ system as a bench test to see what the forces on a propeller release were like before doing something more complicated. It all worked with so little trouble that I just used it as is. (I said ‘devised’ because I thought that I was doing something original but found out long afterwards that TW Clarke had been using it on his Clarke Flyers in about 1910!)

I don’t remember the tube and pin system itself ever letting me down but I have been embarrassed several times because of forgetting to put the ‘Montreal’ stop in the correct position for flight. What happens then is that after a mighty vertical launch the pin releases, the propeller does not start, because the Montreal is on stop, and the model stalls mightily and hits the ground nose first!

For my Coupes, on 12 strands of 1/8, I use an 18swg(0.048) pin in a 16swg(0.064) brass tube (I guess that would be 0.047 in 0.062 in the US). The tube is 0.5 inches long and is mounted as near to the propeller as is practical. I have just realized I have a picture - it is attached.

John
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DerekMc
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« Reply #24 on: March 08, 2009, 07:48:43 PM »

Thank you John for the picture of your instant prop release. Makes your set up quite clear. I am going to give it a try for sure.

I finished the motor tube to tailboom transition. It turned out surprisingly strong. I decided to hold off on building a little box for holding the transmitter bug till later.
On the table next is full size drawings of the fin, stab and wing. The stab is a flat plate so it will be quick to build. Onward!
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