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Old 12-06-2013, 04:43 AM   #1
Abuelo
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Default $75.00 Build Contest: Pou du Ciel

When the contest was announced I thought, 'What an opportunity.' Been intending to build something in foam, maybe with an EDF, neither of which I had used before, and had a plane in mind. The North American F-108 Rapier from the 1950s seemed the ideal project.

The Rapier looked like a scaled down B-70 Valkyrie with a fuselage similar to the Vigilante, also a North American design. Intended to be a Mach 3 interceptor and an escort fighter for the Valk, it had its mission all spelled out. The military wanted 450 of them.

However, the contest discussion comments clarified that it had to be an aircraft that had actually flown and the Rapier never made it past the mock-up stage. After the B-70 fatal crash and project cancellation it was also cancelled, plus ICBMs and Mutual Assured Destruction (MAD) were cheaper.

So, my emphasis shifted and will go with the 1920s Pou du Ciel, aka "Flying Flea." There are several plans, three-views, and photos on the web showing different builder's variations on the theme. Will go with a period typical paint scheme, to be decided later.

The build will be balsa, bass, and ply with a silk and nitrate dope covering. Will use mainly Titebond glue with some epoxy and may glass in the nose area. The main wing span is around 45 inches so it will be close to 1/6 scale. No idea yet on weight but it should be light and either a 300 or 400 motor, both of which I have awaiting planes. Photos will follow. Ribs are cut, spars glued up, and the full flying rudder built (5 grams).

Six out of seven dwarves are not Happy.
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Old 12-06-2013, 05:37 AM   #2
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Photos of progress so far.

Rib blanks are sandwiched between two 1/8 baltic birch masters and clamped in a vise, block sanded with 80 grit to shape and fine sanded down to the ply. Spar slots are cut slightly under size and filed for a snug fit on the spars.

The rudder outline is four laminations of 1/32 x 3/16 balsa dry wrapped and glued around the cardboard form. Left overnight then rough sanded down so the lams don't show and close to 1/8. The ribs are 1/8 and when dry, all is sanded level. The cap ribs, also 1/8, overlap and are block sanded to shape.


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Old 12-06-2013, 07:44 AM   #3
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Default A Flea to Fly

Reads like an interesting project. I have given up on silk and dope a long time ago. Just too smelly and dangerous from what I have read over the years. Following your progress and process.
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Old 12-06-2013, 01:26 PM   #4
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Abuelo
An interesting plane - particularly with the original control system!
It gained huge interest in the 1930's as it was particularly simple to build but the UK Civil Aviation Authority eventually refused a CofA on the grounds it was aerodynamically unsafe (unrecoverable spin) without significant modifications.
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Old 12-06-2013, 06:15 PM   #5
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Leave it to the government to ruin the fun! Great choice for a model Abuelo. Good luck in the contest!
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Old 12-18-2013, 10:48 AM   #6
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Looking good so far

I may be getting Older, But I Refuse to grow Up I am Having to much Fun to Grow Up LOL
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Old 12-22-2013, 12:33 AM   #7
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Managed some building time this week; originally had a trip scheduled that got postponed until after Christmas. So laid out and scroll sawed interior structural components using 1/8" Baltic birch ply and 1/8" balsa.

I elected not to use doublers in the nose area, rather to use a ply framework. The photos show these, which include a support for the firewall, support for a battery and ESC shelf, and the cabane. A fun project, fitting the pieces as I want to be sure they fit before glueing them in. The outer bottom fuselage will be 1/16" ply from the nose as far back as the 12" piece will go, with the top and remaining bottom of 1/16" balsa. The fuselage sides are 3/32" balsa sheet with 1/8" square basswood strips along the top to serve as a support for the rear wing hold-down blind nuts.

The sides are cut from three edge glued 3/32" x 36" balsa. Due to their odd size, a majority of the wood was left for a future project; the two sides with the bass strips weigh 27 gr / 1 oz. The ply and balsa framework and bulkheads weigh 76 gr / 2 3/4 oz.

I intend to use an E-flight 400 920 kv motor with a 22 amp ESC and a three cell 1300 mAh/30c battery. Weight for these is 210 gr / 7 3/8 oz. Would welcome suggestions on what low speed high thrust pitch prop to use.

The original control system will be followed as closely as possible, with some decisions to be made. Looking at the photos on Google, the cabane usually terminates at a single point where the wing pivots, and the control rod activates two pushrods from the fuse to near the trailing edge of the main wing. With one on each side there should be adequate resistance to the wing rotating but still allow pivoting, but the photos usually also show landing and flying wires. I'm leaning towards each cabane being separate, for a four point support, and no wires. What I haven't decided on is where the control rods will mount, either just aft of the wheels or just aft of the seat. Either should work. One photo showed a single centered rod just in front of the rear wing.

Have two 14 gr metal gear servos on order. I suspect the load on the gears may be pretty high since pitch control will be from moving the entire main wing. I also think mounting that servo on its side is a good idea as then the plane of the servo output shaft and the control shaft, which will be close to each other, will be the same. Thoughts?

One issue that will need flight testing to resolve, and in addition to their tendency to spin, is the wash down from the main wing over the rear wing. On the early Flying Fleas moving the trailing edge down (equivalent to applying up elevator) would increase the airflow over the top of the rear wing. Thus, the rear wing's lift would increase forcing the nose down and often flying the Flea into the ground. The rib pattern I'm following is reflexed so I'm thinking this issue is resolved. Will see.

Photos of a Flying Flea in the Air and Space Museum (Dulles) also attached to show where my build is generally heading.


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Six out of seven dwarves are not Happy.
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Old 12-22-2013, 12:57 AM   #8
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That looks cool signed up and good luck

Happy flying may your crashes be limited and if they are not limited let them be cool.
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Old 12-22-2013, 01:02 AM   #9
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Very nice work.....impressed...
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Old 12-22-2013, 02:31 AM   #10
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Beautiful work!
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Old 12-22-2013, 12:59 PM   #11
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Abuelo
In some respects the original single point mounting of the front wing has a lot to be said for it. The cabane strut is simple and strong. Note the flying wires carry no load other than to prevent the wing moving around the central pivot. In addition the wires (on both the wings) have generous angles down to the fuselage to keep the loads low.

As you point out the reflex trailing edge (on both wings) was essential and was eventually made mandatory.
The wing incidence control was another issue. On the original they were just wires which relied on the centre of pressure always being behind the wing pivot point. At some angle of attack thus proved not to be the case so the control wires would go slack leaving no elevator control.
In all current Fleas the wing control wires have been replaced by rods so the wing incidence is always under the pilots control.

Nice build. Keep going.
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Old 12-22-2013, 03:59 PM   #12
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Thank you for the kind comments and suggestion. You've got me thinking that maybe the single point mount might be the better way to go. Would be easy enough to do right now, before assembly.

Plus adding functional flying wires, per your description, would enhance the appearance and just might work to keep the wing from rotating on the mount. I like the idea of using dressmaker hooks and loops for the wire attachment. Leaning towards the control shaft being behind the seat with rods to the wing, and built-in differential. The plan calls for moving the wing a 1/2" up and 1" for down, with up on the wing equal to down on an elevator.

Will be away until early January so have time to decide. Will post when I return.

Have a great holiday.

Abuelo

Six out of seven dwarves are not Happy.
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Old 12-22-2013, 10:44 PM   #13
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I like your choice of subject,Abuelo.I built a 1/4 scale flea from the RCM plans some 20 years ago.That had a servo in the cockpit,controlling axle,which led to arms outside the fuselage,connected with pushrods to the wing.This worked very well.It was 66" span,powered by a .26 fourstroke.I sold it to an antique shop owner,who had it hanging outside his shop for years.
One of the english magazines had a free plan included some time ago for an electric flea,I will build that one sometime.
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Old 12-24-2013, 06:41 PM   #14
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Default Point well taken

Appreciate your comments and after giving the mount some thought decided the single point pivot was the way to go. The photo shows my first attempt, 3/32" music wire and doubled brass tubing, wire wrapped and soldered.

Will probably install a few of the flying wires, will see. Have plenty of time to decide. That RCM 66" version would be really impressive, maybe next time.

Abuelo Bill


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Old 01-22-2014, 09:02 PM   #15
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Unhappy Pou du Ciel now on the shelf

Going to bug out of the contest.

Tried three versions of the cabanes and didn't really like how any turned out. Then, once back from all the holiday activities and could start building went to work on the fuselage. With the balsa bending around the bulkheads coupled with ply skeleton resistance there was some ominous crackling followed by some splitting. Kinda lost enthusiasm at that point.

May get back and try again, do some rethinking first, and see if any of my other projects truly have lower priority. At least I have the materials to finish by the end of February. If not, well, there is always next time.

Abuelo Bill

PS: Have really enjoyed the other contest postings, the imaginative techniques and choices of aircraft. About time to try my hand with a scratch foamy, the Magnum Reloaded and Slowly particularly.

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Old 01-22-2014, 09:20 PM   #16
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Originally Posted by Abuelo View Post
Going to bug out of the contest.

Tried three versions of the cabanas and didn't really like how any turned out. Then, once back from all the holiday activities and could start building went to work on the fuselage. With the balsa bending around the bulkheads coupled with ply skeleton resistance there was some ominous crackling followed by some splitting. Kinda lost enthusiasm at that point.

May get back and try again, do some rethinking first, and see if any of my other projects truly have lower priority. At least I have the materials to finish by the end of February. If not, well, there is always next time.

Abuelo Bill

PS: Have really enjoyed the other contest postings, the imaginative techniques and choices of aircraft. About time to try my hand with a scratch foamy, the Magnum Reloaded and Slowly particularly.
Dont Throw in the towel Yet Use some Bamboo Skewer Sticks for the cabanas, epoxy them together, use small CF rod for the wires, it will be a lot stronger with CF rods, in high stress areas, use epoxy to prevent splitting and cracking, wrap areas with sewing thread then coat with a thin layer of epoxy if needed in high stress areas.hope that helps, Chellie

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Old 01-22-2014, 10:40 PM   #17
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Please don't give up,Bill.To bend balsa or ply,it helps a lot if you wet the wood first,either with water or thinned ammonia.With ply,fix it around a coffee can or W-H-Y with strong rubber bands.
Your first cabane bracket looked very similar to the one used on the rcm version.What was the problem with it?Too sloppy?It will be a lot tighter once you have flying wires attached.The wing actuating rod helps too.
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