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Old Oct 25, 2004, 11:47 PM
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Depron J3 Cub "Park Trainer" - Part 3

Part 3 of Scott Alford's popular cub build.

Thread 1:http://www.rcgroups.com/forums/showt...1&page=1&pp=15

Thread 2:http://www.rcgroups.com/forums/showt...4&page=1&pp=15
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Old Oct 26, 2004, 12:05 AM
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Mike: I measure 2.25 inches at each wingtip. I believe Scott's original plan called for 5 degrees each side or an included angle of 170 degrees. I drew the angle out and then bent the joiner with the spars in place to match. I'm not sure if my finished wing is exactly right b/c I sometimes change the dihedral when I tape them. So, I would trust the 170 degrees more than my measured 2.25 if you want to build to the plan.

The last two wings I built had the dihedral set by bending a piece of music wire and epoxying it inside the carbon tube. I did it that way b/c I didn't have the right size brass tube to put over the carbon I was using. However, once I did it, I prefer it over the brass tube b/c it's lighter and gives a smooth LE.
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Old Oct 26, 2004, 12:39 AM
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I am getting a little off-schedule in my builds, but still should be able to maiden one, if not both, on Tuesday. (Weather permitting.) Seems I still spend too much time on the Internet!

I used a "toy" protractor and drew out a base line with a second line comming off at a 5* angle. At the lenght of a wing half, that measured 1 3/4 inches above the base line. Your 2.25 inch measurement looks a lot more reasonable, to me.

I haven't gotten an CF in, so I'll probably use a brass tube that the bamboo skewers fit in. That's worked well for me in the past, and I can let it into the LE and get a reasonably smooth finish.

We're up to part III !!!

Who'd a thunk it?

Mike S.
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Old Oct 26, 2004, 05:47 AM
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Cary,

Thanks for starting the new thread! I would have never have thought it would have gone so far. See what can happen when you inocently show some pics and put a few drawings on the net. Thanks guys this has been a great thread. How many more people have got this great little plane in the air??

Mike,

Dihedral, now you are stretching the memory but 5 degrees a side sound right. The more dihedral the more stable so anywhere between 3 - 5 degrees should be Ok.

Scott
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Old Oct 26, 2004, 12:52 PM
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Hello!!
What size CUB can i build for an IPS A gear??
I would like to use this gear..
IPS A on 1047 (129gr of thrust)
KAN 250 6cell pack ( no lipo for me till I can solo.. )
CC 20 ( I know its heavy at 8grams)
GWS R6N
GWS pico servos
Thanks!
Ashwin
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Old Oct 26, 2004, 01:45 PM
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I did some thinking about the hinges I've used in the past on foam models and came up with an idea that I just tested and it worked like a charm!

I just "over-explained" this invisible hinge, HERE.

You might find it useful. (You may have already done this, yourself, for all I know.)

Mike S.
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Old Oct 26, 2004, 04:27 PM
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Diameter of wire to join the elevator halves together

My build is progressing, not as fast as Cary or Mike, I'm only stealing 30mins or so a day so far ! What size of piano wire are people using to joining the elevator halves together, I used 2mm, but that seems a little big?

I will try and post some pictures of my build so far tomorrow.

Mike, have you tried the Gobrushless custom single can motors, I think they will swing a 8 inch prop from my tests so far ( current static around 5 - 6 amps ). Good tip on the hinging!

Paul C.
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Old Oct 26, 2004, 05:44 PM
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Paul,

Yes, I do have a GBx single. I'd have to look around and see just what the numbers were on it, though. It's a good motor, but I really want to get my Strong Motors RC double flying.

Me, fast? No way. I'm way behind again, as I'm so easily distracted. I putzed about too long play with that hinge idea, so no maiden flights today.

Still looking good for tomorrow, though!

I did tape the wings together and mount them on the fuses, just to see what difference there might be between the two different foams. I'm talking totally bare airframes here, bamboo skewers taped onto the wing-halves, nothing else but foam.

I was kind of surprised, but in retrospect, I really shouldn't have been. Both the deSP and the FFF model balanced at *exactly* the same point! My little "cheapie" scale isn't really meant to weigh things this light, but it does give me a relative idea of the weights.

Both were weighed as they are in the picture and for the balance comparison. That is, a pair of bamboo skewers taped to the underside of the wings, and nothing else but foam. No batts, motors, servos, nothing else, at all.

The dpSB Cub weighed approx. 80 grams, with the FFF Cub a little heavier, perhaps 85 grams.

So, unless the dpSB turns out to have a much greater "crash-resistance" after finishing, or other clear advantage, I'll be sticking with the FFF as it's much less of a PITA from the get-go.

If the dpSB Cub wins out, then I'll consider ordering some depron for future builds. On the other hand, if FFF comes out on top, I'll use my current stock of SturdyBoard to use "paper on," (one side or both,) as a foam-substitute for light ply where needed.

The extra day will be put to good use. If I have to stay up all night, I'll be flying one or both, Tuesday. I may have enough time to slap a coat of paint on them, too. I want to give both at least a single coat of the Minwax PolyA, mostly to prevent "hangar rash." I think I'll try mixing in some "craft" acrylic paint to the Minwax while I'm at it. I don't plan on using any fg cloth on either at this time.

Oh yes, the second picture. . .

Never turn your back on a cat!

Mike S.
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Old Oct 26, 2004, 08:33 PM
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Quote:
Originally Posted by mad mike
Paul,
The extra day will be put to good use. If I have to stay up all night, I'll be flying one or both, Tuesday.
lol . . . er, Mike, today is Tuesday. You really should take a break. Go for a walk with the wife, play catch with the kids, meditate, . . . but no more glue fumes for 24 hours.
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Old Oct 26, 2004, 09:24 PM
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Here kitty kitty... Mike. Cubs are look'n good. Shame about the dpsb being a pia as she does look good in white.
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Old Oct 26, 2004, 09:26 PM
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Quote:
Originally Posted by Spy king
Hello!!
What size CUB can i build for an IPS A gear??
I would like to use this gear..
IPS A on 1047 (129gr of thrust)
KAN 250 6cell pack ( no lipo for me till I can solo.. )
CC 20 ( I know its heavy at 8grams)
GWS R6N
GWS pico servos
Thanks!
Ashwin
Hi, Ashwin.

You don't seem to have much luck getting answers to this question on the forums. You might try an 80% size, using some thinner (lighter) material in some places to save weight. That would come out to about a 30 inch wingspan (the original is 38", isn't it?). Lighten it as much as you can without compromising the structural integrity, and you should be okay.

Hope this helps,

Barry
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Old Oct 26, 2004, 09:32 PM
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"lol . . . er, Mike, today is Tuesday. "

Sometimes, I just don't know when I am!

Mike S.
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Old Oct 26, 2004, 09:43 PM
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Ashwin,

I would agree with blowentw. About an 80% size would be ok. Cary is currently building one at 60% size by simply scaling down the drawings. 5mm material scaled 60% gives the correct key sizes for 3mm material. If you do one in between then just adjust the slot sizes to suit the thinner material.

As usual it will all come down to grams (or oz's).

Scott
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Old Oct 27, 2004, 04:25 AM
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Hi Guys,

A few pictures of my build so far. The tailplane isn't glued in yet, before anyone says it's crooked

BR.......Paul C.
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Old Oct 27, 2004, 06:24 AM
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Looking good there, Paul!

Looks like your wheels are as large as mine. A bit large, but if your flying field is anything like mine, you'll be glad you didn't try for more scale-looking wheels. Guess were both building "Brush Cubs."

I printed out two full sheets of the transparency film hinges, one small and one medium. Next time I print some, I'll just use a simple line drawing with out the color! You can see the dark blue thru the white foam. Not so much on the FFF one, though.

These hinges work great!

Well, back to work for me. I'm gluing up the tail feathers and installing the control system.

Mike S.
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