I have a P-40 Warhawk that I am almost finished with. I recently installed the rubber band and the propeller, and after widing it about 250 times, I noticed the propeller wasn’t spinning fast, I mean it was slow. I went to my local hobby shop and bought a small ball bearing thingy for the prop, so that it doesn’t rub against the nose bearing, but still no luck. I don’t know what the problem is. The length of the rubber band is two times the distance from the pegs to the front of the plane. When I wind the rubberband, I make sure to strech it out while I’m winding it. I have even wound the propeller about 450 times, but still the propeller spins too slow. I mean there is now way it would fly with that speed. Does anybody know what’s causing this, any help please!
Sounds like the rubber-band might be old and weak ,or of poor quality, or too long. If this is a Guillow’s kit, they give you “extra”.
So you might try shortening it to where it is a taught simple double strand, but not tight, or replacing it or both. In any case, you do not want any slack/sagging in the rubber-band motor.
Have you considered installing an electric motor set-up in this bird?
They are a heck of a lot easier to wind-up.
Tom T [C):-)]
Hey Thanks Tom. You know, it seems like the advancement in motors and batteries seems like a great alternative to free flight. Do you know of any website that I could do some more research in looking at motors, e.g. the size of motor I might need, battery size, weight issues, etc. Thanks
for example: http://www.slowfly.com
very active forum on electrics: http://www.rcgroups.com/forums/
Thanks Tom. I did some research and had a question for you. In general, is there some sort of equation/calculation for the amount of grams of thrust you should have in an electric motor for your airplane to fly well? For example, I read in one of those links that if you had a 70 gram airplane, you would need a motor that would provide 25-30% of grams of thrust for the plane. So you would need a motor that had around 20 grams of thrust. Is that true? Have you heard of anything like this?
I have not heard of anything like this specifically, but it looks as though you have a simple formula already, and it sounds about right, except I would believe that the “grams-thrust” would be not just the motor, but the motor/propeller/power pack airframe combination.
This is because without the propeller, you got no thrust.
A motor alone is usually rated in horsepower (obviously these would be fractional), which is a function of torque and speed.
I would lean closer to the 30% value as well, since not only do you have the weignt of the airframe, but the added motor, switch, wiring and battery pack,etc.
I would see if I could get an accurate weight of the plane plus the motor drive equipment (in grams)and then do the 30%, or 0.3 x total weight(in grams).
If the specifics are not available, you try SWAG’ing it by going to your LHS and simply seeing what size motor/propeller combination is usually provided with which size/weight airframe.
I hope this helps.
Tom T [C):-)]