Rubber Flight

[Bark65]

I recently built a Frog Redwing and had a chance to fly it today. Test flights in the backyard have been smooth and successful. I took it to a field tonight and put about 250 turns into the rubber and let it loose. The first flight (launched into a 5 mph wind) the plane climbed steeply and quickly and ended in a quick nose dive into the ground. The next flight (launched with the wind) was smooth with the plane gaining about 10-12 feet of altitude and flying about 50 yards with a nice smooth landing. The next two flights were a repeat of the first with the last flight resulting in a broken nose block. I figure the plane is not properly balanced. Any thoughts?

[Dave Robelen]

Hello Bark,
Does the bird have some turn while it is climbing? It is fairly common for a model climbing straight ahead to stall and drop. If the low power flights look good, and the problem comes with more turns in the rubber, adding downthrust will help. If a low powered glide looks OK, I would make the remaining adjustments by tilting the thrustline. Down to break a stall, some turn to help keep the climb smooth. It may want to turn one way beter than the other, If that is the case, go with the natural turn. If, after you set a turn, the bird wants to start diving in the turn, the wing on the inside of the turn needs to be twisted a bit LE up to keep the model level.
Regards, Dave

[Bark65]

Dave,
Thanks for the reply. I think I corrected the problem by adding a bit of down, right thrust. Test flights with up to 130 turns produced a smoother climb without the severe nose dive. My prop broke during test flights so I never got past 130 turns. The plane still wants to fly left. I've noticed the fuselage has a slight warp that curves to the left. This might be why the plane is turning in that direction. I'll have to wait till the new props come in before I know more.
Good flying,
Bark

[Bark65]

The new props arrived today. I made 2 quick test flights in the back yard and things are looking better. The downthrust seemed to have worked. The plane is not turning to the left as quickly as before. Soon as this tropical depression clears out of NC I'll be able to take it to the field. Until then construction on the Raven is keeping me busy. Construction is slower than the Redwing but I seem to be getting better results this time around. Will post some construction pics in a week or two.
Good flying,
Bark

[Dave Robelen]

Hi Bark,
Somewhere along the line, you may want to increase the flight time still more. A longer rubber motor is the next step. It is common in this type of model to use a motor 1.5X the distance between anchors. Combine this with stretching the motor out to wind it with a winder, and you will start getting some impressive flights. Interestingly, the longer motor has a "softer" burst, so the climb adjustments are more reasonable.
Enjoy, Dave

[Bark65]

Dave,
Went to the field today and put 300 turns on the rubber. The plane gained about 10 feet of altitude, flew level for about 10 seconds and gradually decended to the ground. There are still plenty of winds in the rubber at the end of the flight. The length of the rubber motor is about 2 inches longer than the distance between both anchor points. I'm using 3/16th inch rubber. I'm starting to wonder if the plane is just too heavy. I calculated the wing loading after I built it and it came in at 0.71 grams/ sq inch. I have a book on Rubber Powered Models by Don Ross. He recommends a wing loading no higher than 0.50 grams/ sq. inch. Any thoughts on this? I've thought about removing the covering and recovering with the Japense tissue paper I ordered to try and bring the weight down. I know I sprayed the clear coat too heavy on it as well.
Bark

[Dave Robelen]

Hello Bark,
Trying to reduce the weight of an existing model can be very frustrating, and potentially destructive before you finish. My approach was to treat every model as a learning experience, and go from there. Sure enough, they got progressively lighter and fly longer.
Matching the rubber size to the model can improve matters as well. If a loop of 3/16" is not quite enough, I would move to two loops of 1/8" runbber, and make the motor a bit longer. Again, stretch winding will also add flight time if the motor has enough power to climb decently at the start of the flight.
Cheers, Dave

[Bark65]

Dave,
Thanks again for the advice. I think I'll enlarge the 3/16th rubber to 1.5 times the length of the fuselage and stretch wind it. I built a crude device to hold the airplane so I can stretch wind. I don't have a winder at present so I've been just using my finger. Need to add a winder to the "to buy list". I'm going to try and wind it up within 80% of breaking point (Ross book says close to 83 turns per inch of rubber) and see what happens. If that does not work I'll try using the 2 strands of 1/8 inch as you suggested.

[Bark65]

Dave,
I made up a 14 inch motor this morning from the 3/16 inch rubber. Took it to the field and stretch winded 1000 turns. The plane flew about 80 yards at a maximum altitude of about 15 feet, ade a nice gentle left turn,and crashed into a fence. No damage to the plane. I think your right about going to 1/8 inch rubber. I think this might provide enough power to get the bird to climb higher. I don't think the 3/16 is supplying enough power. I'll post a flight report when the new rubber comes in.
Thanks again,
Bark