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Author Topic: 15" Gee Bee Model Z  (Read 777 times)
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vtdiy
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« on: December 21, 2018, 04:24:42 PM »

This is a Gee Bee Model Z I started a couple years ago. It is 15" span and built of 2mm Depron. To get a design, I started looking at a Fiddler's Green paper version, but it wasn't proportioned well for a flying model. The wing incidence was wrong, tail hinge rake was wrong, and the huge canopy and cockpit gave it a cartoonish look. Nevertheless I pasted the models paper pieces to some scrap depron, and built a non flying version.

I marked that practice fuselage then cut it up, added pieces where I thought necessary, and changed others. I checked the prototype periodically by temporarily taping it back back together and disassembling and trimming until it suited what I thought would look and fly well. Finally I cut it apart again, and made patterns from those pieces.

I also opted not to go the printed tissue overlay route, often done for paper model conversions I didn't like the orange blocky graphics.  Instead, I painted my model by hand. Only the big letters and numbers were applied separately -- For them, I just painted some thin tracing paper black with the same paint I used on the model, and cut them out and applied. I pressed my own canopy from clear salad container plastic. The R/C gear Is an inexpensive WLToys helicopter brick and the motor is a geared F939 coreless unit from Banggood.

http://www.sredmond.com/Models/GeeBee/Canopy.JPG

The model flew well, other than needing greatly reduced rates to 35%! AUW was 33 grams. Here's one of the first test flights -- apologies for the fog over snow in the beginning, and the small size of the model in view. But it is only fifteen inches, and moves along pretty well! Especially at 1:16 when I give it full throttle rather than half! My daughter did the best she could keeping the yellow dot in view as the cameraman.

http://www.dailymotion.com/video/x5d2vyg

15" Gee Bee Model Z
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Don McLellan
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« Reply #1 on: December 21, 2018, 05:20:30 PM »

Very nice model and very nice flight!  How did you do the 'City of Springfield' and 'Powered by PW Wasp Jr' on the cowl?

Don
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vtdiy
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« Reply #2 on: December 21, 2018, 05:59:36 PM »

Thanks Don!

I should have said -- the cowl was the only part I did use stock from the original paper model prototype I built. I simply carefully painted gloss black around the logo, which had been printed on tissue adhered to the depron, with a fine brush.
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Mefot
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« Reply #3 on: December 21, 2018, 06:20:31 PM »

Very nice looking and flying model !!! I suspect that Peter Fardell would be interested in a plan of this model ( apart from me !!! ). Any chance of publishing your patterns ?  Cheesy
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Crabby
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« Reply #4 on: December 21, 2018, 06:20:59 PM »

VT I guess you opted out on the landing gear? The thing about those 30's planes with the big faired in landing is you now have essentially 3 rudders! Great looking flight!
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vtdiy
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« Reply #5 on: December 21, 2018, 07:27:21 PM »

Well, Crabby, not yet! I started to install ailerons last year and planned to add the landing gear last, as I knew it would be de-satabilizing, and I wanted to have the plane wrung out as much as possible beforehand.

The aileron installation was decided on because I flew it indoors and found that tricky.

The plane rolls beautifully and quickly with only an RET setup, but rolling back to level is slower. Not a problem outside, but inside I had to really anticipate what I was doing with the walls seeming awfully close doing figure 8's.

Maybe I should have added more dihedral, but it already has a fair amount, and with such short wings and wide body that would cut lift probably, plus too much dihedral wouldn't look very good on this model.

The reason I had to reduce rates to 35% originally was because the model was actually very slow to respond to rudder. I figured out that this was due to the rudder stalling. As soon as I reduced rates, turn and roll rates went up, which was the opposite of what usually happens. At 35% the roll rate was great. This is a pylon racer after all.

But for the return to level, I think what happens with this very short and squat body is when you roll it into a bank, and then give opposite rudder to bring it back, the top rudder is partly blanketed by the fuselage. So the return is slower than the initial roll.

Anyway, long story short, the plane now has a partially installed aileron setup (I had to change out receivers, and also add a servo and tiny cables) and I'm not real satisfied with it --too much backlash and binding. Actually wish I'd left well enough alone and just flown outdoors.

I'll fix it, or return it to the original RET state, and then I hope to add in the missing landing gear. Not that it will do much good outdoors in even mown grass that reaches above the wings  on something this small! But it will look right anyway.
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vtdiy
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« Reply #6 on: December 21, 2018, 07:30:40 PM »

I've been thinking lately that I should do maybe a 20" or 24" version as a more reasonable backyard flyer, with ailerons built in from the start.
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OZPAF
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« Reply #7 on: December 22, 2018, 06:23:47 PM »

What a neat looking little model VT. Do you have much structure under the fuse skins? I guess you wouldn't need much on a 15" WS model.
I think ailerons/elevator/throttle works much better for these small faster flying models and would for a slightly larger version use separate tiny 3gm or less, servos buried in the wing. I had a great flying little MPX Fox of 20"WS using this approach and it was great - fast, aerobatic and a decent glide even at 10oz/ft2 wing loading. I miss the little hooligan - lost in marshes when it ran out of battery!

John
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vtdiy
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« Reply #8 on: December 22, 2018, 10:19:11 PM »

Hi John, thanks Kindly!

It's just a shell, and I added an equipment tray slid in through the nose. Here's a pic with just a color basecoat on. I had to do this because there are no hatches, so pushrods were set up in place in advance. Old timers will note the retro style balsa and wire pushrods. They still work. High stiffness, low mass.

http://www.sredmond.com/Models/GeeBee/RCGear.JPG


Yours sounds like a fun plane! I had a 20" Cox Warbird P-47 that I added ailerons to (and a brushless motor) and same thing as you -- loved that plane, wonderful for the resricted tree lined field space I have adjacent to the house. I was very comfortable doing low altitude maneuvers below tree level. The only thing I didn't like about it was I hadn't designed and built it from scratch! I'd like to get that kind of performance out of something I came up with myself. My P40 is pretty close, but a little heavier and faster, so not quite the same low level ease. Well also, no ailerons.

I think I'm narrowing in on what will do it for me performance wise that I can claim as my own. I love the golden age racers, Unfortunately, as mentioned earlier with Crabby, they usually had big honkin landing gear, and that a 15" or 20" scale it just tangles them up on the grass I have. Non functional. There's a few of interest with retracts, though, naturally, my favorites all had long legs and pants.

I did a much bigger Brown B-2 36" span, and even then I couldn't take off in grass with scale gear. Liked that plane, though. I still have it.
15" Gee Bee Model Z
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OZPAF
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« Reply #9 on: December 24, 2018, 02:14:28 AM »

That's a good solution for the equipment installation. The tray approach is very practical.
Here are the pics of my Fox.
Merry Christmas.

John
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