Tuesday, May 23, 2017

Behavior of Free Flight Airplanes & Little Girl With a Curl Syndrome

The more I build and fly free flight model airplanes, the more it appears that the models may have personalities like humans or animals do, that is characteristics that make each one somewhat unique.  Ultimately there has to be reasons based on design, trim adjustments, and accuracy in construction for the flight characteristics.   Some models appear to have a preference to turn one direction over the other in flight, trying to change that may not be easy.  With the smaller models it appears that the freewheeling propeller can change the direction of the glide either right or left. On my electric Sniffer model which has always had a preference to glide to the left I did some glides from a small hill with the propeller removed and the plane repeatedly glided straight.

Sniffer Electric Powered

This year my objectives are to build more accurate models, use methods to ensure nothing shifts in flight, and learn to adjust the models to perform in a consistent manner. I am guilty of wanting to get the airplane flying before finished with all of the little details such as keying the wing and stab so it cannot shift in flight.  I have also learned that changes in the thrust can make big differences in the flight pattern, example is with electric, some of the battery is used up rather quickly and the rpm drops, this could have a big effect on the flight power pattern if you keep flying without changing out the battery.

Sniffer Flying Well 

Recently I worked with adjusting my electric powered Sniffer free flight and think I made some real progress. To start with in the flying session I tried to force the plane to glide right and climb right with rudder tab. Too much right and it was not climbing, backed off on right rudder and the glide was too straight. 

With Proper Trim it Lands Almost Perfect

In desperation I put the rudder tab left, I was afraid the glide would be too much left but that appeared to be not the case. Now it climbed very consistent to the left and the glide was consistent left also. Flight after flight was darn near the same. I could let it get fairly high for the flying site and it would land close most of the time. 

Stab Keyed on Sky Demon e20 Electric

Ending this blog posts with some quotes about quirks of free flight models from people with a whole lot more knowledge and experience than myself: 

“I have built three 32 inch Brooklyn dodgers over the years.  The first one flew right-right, and was a great model. The second flew left- left and was also a great model. The third one flew right-left and no matter what I tried (including the directions) , it would not fly well on anything more than two 
thirds power. I threw it away.”

“--FF models of all types suffer from the little girl with the curl syndrome. When they are good, they are very very good, but when they are bad they are horrid. You do what you have to do to make them fly--although the universal advice is make just one change at a time. Some models never survive the trimming process, and other models soldier on for years of flying.”

“Cabin sport models-of which the Sniffer is a typical example- frequently seem to prefer L-L trim. Personally I fly them the way they want to fly naturally-which is usually L-L.....occasionally I've had a cabin model that preferred going R-and very rarely-one that was happy turning either way without any particular preference.....some were even the same design! [Vic Smeed 'Tomboy' , 40" simplex and Modelair 'Hummingbird']......I think in practice it results from the subtle interaction of thrustline, cabin height and fin area....”

Bill Kuhl

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