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Old Oct 12, 2003, 06:17 PM
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Pitts Special from 2" foam...Photos

This is my latest creation from 2" foam, cut using a hot wire. It's a semi-scale Pitts Special, created from plans and photos I could scavenge from the web.

Wingspan: 28"
Motor: IPS twin B
Prop: 10-8
Battery: ETec 700 3S1P
AUW: 8.5 oz
Weight without batteries: 6.8 oz
Airfoil: Eppler 472 (fully symetrical)

I flew it for the first time today in high winds. It handled the wind quite well. On the first few flights, I didn't like the way it handled in loops, but I later discovered that I had the CG way too far back. After moving my batteries forward, it handled quite well. Inside loop and outside loops are easy. I rolls nicely, but I wish I had made the ailerons a little larger so that it rolled more quickly. One thing that is a little odd is that if I give it a lot of rudder, it turns, but it also wants to dive at the same time (anyone have any ideas?).

I can't wait to try it without the wind!

Here are some photos:
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Old Oct 12, 2003, 06:18 PM
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Old Oct 12, 2003, 06:20 PM
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Old Oct 12, 2003, 06:38 PM
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man, that is sweet !!!!! How does it fly?
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Old Oct 12, 2003, 07:10 PM
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It flies great! I forgot to mention that on a fresh charge it pulls staight up with ease. It flies just as well up side down as right side up. it requires a little throttle to keep it flying when landing, but it slows down reasonably well. it flies well at half throttle, but like I said, if I start on the runway and give it full throttle, it will roll about 10 feet, lift off the ground, then fly straight up to over 100 feet (or higher if I care to do it.)

- Brad
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Old Oct 12, 2003, 07:42 PM
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Australia, NSW, Sydney
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BQuick,

That's a very nice plane. It's great to see people working in foam but getting away from simple profile fuselages.

I think the answer to your question about diving in turns is that the rudder input is putting the plane into a big skid, ie. the turn is not co-ordinated, and the plane is yawing too much into the turn. The lack of dihedral and small sweepback (on the top wing only) require large rudder deflection to get the plane to roll, but when it does roll, the resultant skid working with the generous side area produces a lateral force which slides the plane downwards.


This past weekend I too had the first flight of a similar plane, and also in high winds! Mine is a 90% Ultimate Bipe, built with a 3mm Depron "box" fuselage with curved top pieces and rounded corners. It has an IPS Dual A, E-Tec 700 2S, flying weight 225grams. It handled the high wind remarkably well, but was no fun to fly in these conditions.

This morning (Monday) I got up early and flew it in dead calm conditions and got a glimpse of how well this design performs. I will post some pictures here as soon as my friend comes round with his camera.

How did you make the wing on your Pitts? Is it double skinned over ribs or profile cut and solid? What thickness is that Airfoil?

Graham.
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Old Oct 12, 2003, 09:24 PM
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Graham,

The wings are solid. I cut two templates out of wood and used them with the hot wire to cut the cores. They are 9/16" thick.

I understand how skidding might make it want to roll, but I can't figure out why it would want to dive. I was trying to do knife edge, but when I got it rolled on it's side and applied rudder, it acted as if I had applied down elevator. It may be that my tail section is too small since I think it's actually to scale. I'll have to try it in less wind.

- Brad
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Old Oct 13, 2003, 06:34 AM
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Brad,

That's interesting. So, maybe you didn't have enough rudder movement or side area to get it to knife edge, and it just sunk towards the ground? Stupid question, but are you sure you applied rudder in the correct direction?

My Ultmate Bipe seems to have the rudder power/side area to achieve knife edge, but my brain can't quite get all the co-ordination right just yet! Like all new flying challenges I have found knife edge to be a whole new parallel universe set of control inputs that I haven't got my head around yet, but now with the Ultimate Bipe I should soon be able to speak more authoritatively.

Did you weigh the wing cores? Did you cover them with anything?

Graham.
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Old Oct 13, 2003, 07:32 AM
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Graham,

I think it has enough rudder. I can see it swing around quite a bit when full rudder is applied. My latest theory is that I have the CG too low. I currently have my battery strapped to the bottom. If I get a chance, I'm going to try moving the battery up toward the top of the fuselage to see what that does for me.

No, I didn't weigh the wing cores, but they are quite light. I didn't cover them or strenghten them either. I've found that with these lightweight planes, as long as the wings are thick enough, the foam itself is strong enough to hand the forces. I experimented with covering some wings recently with Solarfilm Lite. They looked nicer, but they were quite a bit heavier. I plan on painting this plane.

- Brad
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Old Oct 13, 2003, 06:51 PM
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Well, I got a chance to run two packs through it today with very little wind. I must say that it flies great. It will take off and fly quite easily at half throttle and it's quite docile at low throttle, which suprised me a little. I was expecting to have to keep the speed up more.

I got to try some more knife edge. I'm not that good at it, but it still requires me to hold in up elevator to maintain the knife edge. It will stay on edge as long as I want and will even gain altitude!

It has been a while since I've flown an aerobatic biplane and I fogot how much fun they were. I was expecting it to feel more like my low wing that I recently built with similar size and construction, but it's got a different feel.

Now, I just have to figure out how I'm going to paint it.

- Brad
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