Friday, September 26, 2014

Pushing Simple Planes to Greater Duration

It would sure be nice to have a very large open area to fly free flight model airplanes but more commonly only smaller areas like a schoolyard or a soccer field are available. Flying from the somewhat risky flying site, I normally fly the simpler rubber powered models that would not be a big financial or building time investment  loss if the model could not be recovered from a flight.  Last evening I grabbed several simple rubber powered models and headed to a small field because the wind was almost still.

Collection of Simple Rubber Powered Free Flight Airplanes

The first model into the air was an AMA Racer which is a really simple flat wing design with triangle shaped flying surfaces. Normally this plane is built on the plan material but I covered with tissue paper instead to save weight and because I think it looks better. For a simple plane it really flies pretty well and achieved a fair altitude. Next in the air was an Easy Built IMP which is a ROG type plane with a single surface curved airfoil. This provides good lift but the glide is really steep into the ground, after the rubber winds down the airplane is on the ground within a few seconds.  Most the small simple planes do not glide very well when the propeller starts freewheeling.

AMA Racer 

Easy Built IMP

Flew the original plane I had designed that has the tail surfaces of a Denny Dart and a flat wing with winglets; vertical fins on the wing for stability. I had curved the ribs while wet to give an airfoil with a small amount of curve but not too much that it caused excessive drag. This airplane flies well but seems to require a proper launch or it can crash right after launching. Last plane to be flown is plane with an airfoil covered on both sides that normally will climb slightly higher than the other airplanes I brought out.

Plane of My Design

Two Surface Covered Wing Airplane

The longest duration of any of these planes without much thermal help appears to be one minute at the very best. This makes for a nice flight over a small field but I was thinking about how more duration could be obtained using this size of airplane with a 6” diameter plastic propeller. I think the key is to reduce weight more by lighter covering or structure so that the airplane can fly with thinner rubber strip that will accept more winds without breaking.  Using 1/8” wide rubber strip 97 turns per inch is considered maximum but if the airplane can climb on 3/32” rubber turns per inch is 129. 

Anyway this has me wanting to try to get a flight of at least 1 ½ minutes outdoors without thermal help. 

Bill Kuhl

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