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  1. #1
    MJD's Avatar
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    Kit sacrelige.. Bad Baby Birdie mutant

    ..but don't worry I am drawing up the model as I go. And I plan to pull a mold or at leasy a plug from the canopy. So the 1/2A version can be repro'ed.

    I had it set up in the front end for a CX-11, but I'm putting that in the Goldberg Chipmunk instead. And I needed a quick & fun test bed to fly the MDS .15. So I'll fully sheet the wing, firm up as necessary here and there, shorten the aileron and use dual servos, battery and servos in rear of fuselage.

    Shortened the nose 1" too, that will help the CG. Bet it still comes in at a decent weight, kit spec is 22oz. Engine and pipe is 7.3 oz.

    Click image for larger version. 

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    Marine GOOP = magic faerie boogers in a tube, sticks everything.

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  2. #2
    Tony A.'s Avatar
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    Looks like it will be a fun rocket to fly!
    \"I love the smell of Cox Engines in the morning!\"

  3. #3
    Pond Skipper's Avatar
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    What is the pipe length from the start of the stinger to the center of the piston?
    Big fat convergent / divergent volume should be less peaky on the NV. What
    prop and rpm are you expecting.

  4. #4
    MJD's Avatar
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    It's the same pipe that ran 30.5k on the bench prop. The stock MDS pipe was 2.5-3k below that. This is a used Profi F2A pipe, I froze water in the header section and tweaked it to clear the fuse. There is also a repair over the weld. I'll cowl it to hide the ugliness.

    Props in 5.5" diameter range, 5"-6" pitch. Likely a clipped Graupner 6x5.5 to start.
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  5. #5
    Pond Skipper's Avatar
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    Frozen ice water sure is a faster way to remove then packing sand in the pipe, bend looks good.
    If 33.3k unloaded with a 6P / 189 mph should be hard to see at 170

  6. #6
    MJD's Avatar
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    The bend worked fine, I'll bench run it soon as it's hospitable enough. However - tech tip: don't fill the pipe all the way. I got this technique from brass instrument making techniques, but those are either constant diameter or tapered bore tubes. In the case of the pipe, with the fat center section and tiny stinger outlet.. hmm, tough to expand. I split the weld, soon as I took it out of the freezer I thought "dumbass, why didn't I just fill the header..?".

    The ugly bits are my JB Weld/glass repair. The pipe still weighs 29 grams which is the same as the new Profi pipe, so I'll live with it. It's a test bed..
    Marine GOOP = magic faerie boogers in a tube, sticks everything.

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  7. #7
    MJD's Avatar
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    p.s. Missed your question, I'll measure up the pipe and let you know.

    The airfoil looks funky in the pic, but the paper is a bit mangled in that area. The airfoil thickness is definitely not conducive to top speed, but I figure there is enough power on tap to move briskly enough. Don't want to make a total project out of it, simple conversion and some giggles is the goal.
    Last edited by MJD; 02-01-2016 at 06:35 AM.
    Marine GOOP = magic faerie boogers in a tube, sticks everything.

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  8. #8
    skaliwag's Avatar
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    The airfoil / span / root and tip cords on this "Birdie" are close to the Ace Tapered foam core.
    Real Airplanes have Round Engines and Two Wings.

  9. #9
    Pond Skipper's Avatar
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    I used an ACE tapper balsa sheet core with a OS FP 25 it was peppy with a APC 8x6
    Enough wing for easy landings in a slight breeze.

  10. #10

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    Quote Originally Posted by MJD View Post
    ..but don't worry I am drawing up the model as I go. And I plan to pull a mold or at leasy a plug from the canopy. So the 1/2A version can be repro'ed.

    I had it set up in the front end for a CX-11, but I'm putting that in the Goldberg Chipmunk instead. And I needed a quick & fun test bed to fly the MDS .15. So I'll fully sheet the wing, firm up as necessary here and there, shorten the aileron and use dual servos, battery and servos in rear of fuselage.

    Shortened the nose 1" too, that will help the CG. Bet it still comes in at a decent weight, kit spec is 22oz. Engine and pipe is 7.3 oz.

    Click image for larger version. 

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    Did you stretch out the tail? the fuse looks longer than the plans to me.
    Content, but not Complacent.

  11. #11
    MJD's Avatar
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    No it is stock from the firewall back - just an optical illusion. What may be fooling you is the 1 inch I lopped off the nose last night, the parallax error holding my iPhone up in the air, and the plans are all ripply from abusive fondling and poor rolling over the years.

    I know the airfoil is fat, but I don't want to get mired down in modifications. I've seen an ACE wing do 120mph on 300 watts, which I think is roundabout the power of a reasonable sport .15. So this should do at least that..

    200 squares, even at 24-25 ounces, will be a reasonable wing loading. Safe enough to land more than once anyways. In theory.
    Marine GOOP = magic faerie boogers in a tube, sticks everything.

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  12. #12
    MJD's Avatar
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    Quote Originally Posted by skaliwag View Post
    The airfoil / span / root and tip cords on this "Birdie" are close to the Ace Tapered foam core.
    Yeah, quite close. I get 16%.. chances are it's a NACA 2416. Not too thin is it.. oh well.

    UPDATE: no it's not a NACA 2416, might be a Staedtler-Mars special based on one, dunno. I smoothed out the plans and looked more closely at the ribs - the lower surface has been flattened from the rear of the spar to the TE. Definitely more camber than it needs in this incarnation.

    I can't see any use for a working rudder on this, but I might need the servo weight in the rear. The Simple 400 used to do fun things when I pulled the sticks to the bottom corners at full speed.
    Last edited by MJD; 02-01-2016 at 08:31 PM.
    Marine GOOP = magic faerie boogers in a tube, sticks everything.

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  13. #13
    combatpigg's Avatar
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    The G2 5.5 x 5.5 prop is a good one to try.

    I remember having a great time with this kit and with the plane that came out of it.
    That's not an Indian movie man, that's a test pattern....

  14. #14
    skaliwag's Avatar
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    My all time Fave.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Real Airplanes have Round Engines and Two Wings.

  15. #15
    MJD's Avatar
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    Nice!

    Hard to say if all the qualities that make this an old favorite are really going to be allowed to showcase themselves with this gross mutation.
    Marine GOOP = magic faerie boogers in a tube, sticks everything.

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  16. #16
    Mr Cox's Avatar
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    It seems a bit drastic to go from a .049 engine to a .15 engine with a tuned pipe...
    Wasn't there a Birdie 10 as well, it might be better suited?

    The few planes with a thick wing profiles that I have put more power into, didn't really shine. Perhaps it's just me but a low weight and modest power, seems to make for a better overall performance.

  17. #17
    MJD's Avatar
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    I agree, but I am not going for an optimum solution, nor do I expect this thing to have good manners. This is a quick and dirty conversion only. I am not sure the .10 size would perform on the tiny props needed for this engine. It could be a snarling screaming disaster waiting to happen. Sounds like fun to me.
    Marine GOOP = magic faerie boogers in a tube, sticks everything.

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  18. #18
    Mr Cox's Avatar
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    Yes, it is all part of the fun.
    Sure beats RTF stuff...

  19. #19
    MJD's Avatar
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    Quote Originally Posted by combatpigg View Post
    The G2 5.5 x 5.5 prop is a good one to try.

    I remember having a great time with this kit and with the plane that came out of it.
    The F2A speed trainer article you can find through NASS mentions that best speeds on that model were with around a 5.5 x 5 with some blade area:


    1. Propeller. The best speed was achieved with a Master Airscrew 7x5 S-2 G/F Nylon Gray Propeller cut to 140 mm (5.5 inches) diameter. With this prop the engine was turning about 30,000 rpm in the air. I suggest starting with 6 inch diameter and cutting the prop until the engine pipes up. Too small propeller will turn a lot of rpm with no thrust. We also tried more pitch (up to 6.5 inches) but this did not result in faster speed.
    2. With these modifications and settings the system performed quite well. The fastest time achieved in a practice session was just over 200 kph, which is excellent considering the exposed lines, landing gear and no engine cowling. The airplane routinely did around 160-180 kph with a Rossi pipe and slowed down to 150 kph on the stock pipe (on FAI 80/20 fuel).


    Even though this is just a sport 1/2A model by design, with no lines there is every possibility it will leave the ukie trainer in the dust. As mentioned ad nauseum, I clocked 126 mph on a Simple 400 - similar wing - with about 300W electric.
    Marine GOOP = magic faerie boogers in a tube, sticks everything.

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  20. #20
    MJD's Avatar
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    I suited up against some cool winds today, had to bench run the MDS .15 with the mangled bent pipe. Responding to taunts from fellow RCU members to run it with a flight prop, I made a 5.5x5 from an APC 7x5. It staged without much trouble (hmm, more prop load) and recorded 27,800 without trying to squeeze it to death.

    Made a new stab today, also fixtured the fuselage between two Al extrusions and tacked the tail together nice and straight. I am moving the vertical stab back stab stays in stock position, but internal linkage. 1/64 ply caps cover the joiner pockets in the middle photo.

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    Marine GOOP = magic faerie boogers in a tube, sticks everything.

    Revver Bro #231

  21. #21
    combatpigg's Avatar
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    Quote Originally Posted by MJD View Post
    I suited up against some cool winds today, had to bench run the MDS .15 with the mangled bent pipe. Responding to taunts from fellow RCU members to run it with a flight prop, I made a 5.5x5 from an APC 7x5. It staged without much trouble (hmm, more prop load) and recorded 27,800 without trying to squeeze it to death.

    Made a new stab today, also fixtured the fuselage between two Al extrusions and tacked the tail together nice and straight. I am moving the vertical stab back stab stays in stock position, but internal linkage. 1/64 ply caps cover the joiner pockets in the middle photo.

    Click image for larger version. 

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    I like that Norwegian Log Cabin wood work..!
    That's not an Indian movie man, that's a test pattern....

  22. #22
    MJD's Avatar
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    I was debating between stiff 1/8" or 3/16" for the tail group. I went 1/8".. once it is anchored to the fuse it should reveal if more torsional stiffness is needed.

    So far I have only used the kits fuselage, we'll see what is left. My intent is to build the kit wing and sheet it. I will try to avoid the urge to redesign the wing and start from scratch with a 10-12% airfoil.. no-o-o-o just get it done and move on..
    Marine GOOP = magic faerie boogers in a tube, sticks everything.

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  23. #23
    MJD's Avatar
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    I am not sure of the spread on the pipe response. It staged on the ground run yesterday without distress, needled easily, and ran cool enough. But it recorded 30.5k on the pitchless bench prop and 27,800 on this. So.. I am thinking launched rich it should unload and sing away a couple of k rpm higher. May take a bit more shaft load based on the easy staging.
    Marine GOOP = magic faerie boogers in a tube, sticks everything.

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  24. #24
    MJD's Avatar
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    Double post
    Last edited by MJD; 02-12-2016 at 07:15 PM.
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  25. #25
    MJD's Avatar
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    Weighs in at 11.0 oz as you see it. With care I wonder where it could end up:

    Blind guess time:

    Wing 5oz
    Battery .8oz
    Servos: 1.4oz
    Rx: 0.2oz
    finish the cowl area, glass/prime/finish and film: 3 oz?
    Tank: 1.5oz
    Linkages and other crap: 1.5oz..????????

    13.4oz + 11.0oz = 24.4oz.

    So if I'm real lucky should end up around 16oz/sqft wing loading, more likely 17-18oz/sqft. Won't be a floater but should return to earth safely enough.

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    Don't need a rudder and esp. don't want to deal with two concealed linkages. Don't need a sub-fin either. The wing is so simple, I may just take the extra couple of hours and cut replacement ribs and leave the kit wing alone. That way I just have to replicate the fuselage (it's really simple) and voila have all the bits again. I'll get it all CAD drawn first, then build a new fuse and old flying surfaces and make a 1/2A version. I already made the plug for a glass/epoxy canopy mold.
    Last edited by MJD; 02-12-2016 at 07:16 PM.
    Marine GOOP = magic faerie boogers in a tube, sticks everything.

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