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Bob Wilson

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Tech Talk - Blow'n In the Wind

by Bob 'Commodore' Wilson, President, Macon Aero Modelers

  The fact is, the model does not know there is a wind blowing...

            "For many of our formative years in RC, the magazines printed letters to the editor about whether or not an RC model aircraft speeded up or slowed down in downwind turns/upwind turns. They finally quit printing stuff like that since it dragged on and on and flyers were just unwilling to accept the facts and the subject simply wore itself out.

            All newcomers, it seemed, fully believed that wind had an effect on a models speed when it turned down wind.

            The argument really got a foothold when we started flying pylon racers. Modelers swore that they saw their model dive during a downwind turn and felt it was because the model had been flying upwind and suddenly turned downwind and lost airspeed and thus altitude, apparently rushing to catch up with the wind. Rocket scientists offered numerous explanations but through all of this, there was a very simple test that could confirm or deny the existance of the problem. Simply rent a full scale airplane and make some turns upwind and downwind, noting airspeed changes, if any. Of course, there weren't any airspeed changes and any full scale pilot will tell you that. But, mythology and old wives tales die hard and the argument, even though not in print anymore, persists today.

            I'm am a Throne Reader. Many men are, by the way. We like to pick something up to read while on the Throne and while I don't know the statistcal breakdown of how many men read while on the Throne, I seriously doubt women read to the extent that men do. And, no, I am not going to do any research on the matter, you'll just have to take my word for it.

            Anyway, in the May 1997 issue of "Aviation Modeller International" a British publication, there is an article that settles the matter once and for all. A Brit by the name of Dennis Allen built a telemetry system for reading airspeed while the model is flying. He apparently is quite a guru with electronic stuff and a notable pilot in merry old England and the article printed pictures of his electronics along with the resulting graphs.

            Flying in a 15 mph wind, Dennis, and a partner who is a British aerobatic champion, took turns flying circles and making all sorts of heading changes and while the article is 4 pages long, I won't bore you with the details except to tell you that they flew upwind and downwind, steep banks, shallow banks, high speed and low speed and need I tell you that there was no recorded change in airspeed of the model. Try as they may, they could not get the model to pick up speed on a downwind turn and there was no change when the model turned upwind.

            The fact is, the model does not know there is a wind blowing, in spite of what you see and interpret as the wind affecting the model. (Sorry, Greg, but them thar's the facts)

            What does happen, is turbulence is effecting the model. If the model is still on the ground, because the landing gear is still touching the ground, wind can pick up a wing and flip the model over, but only when it is still on the ground.

            In the air, however, it's a different story. What you see there is the effect of turbulence. And when you turn the model downwind, it does not pick up speed. But, depending on the altitude, it may pick up turbulence, updrafts, downdrafts, micro bursts, wind gusts, and all sort of disturbed air which the novice will usually confuse with the wind blowing on or against the model.

            Is any of this information important to flying an RC model? Well, yes and no. Personally, I enjoy aerodynamics and knowing how my airplane operates under different conditions. For the most part, however, RC pilots can attribute anything to what their airplane is doing and it won't make much difference. You can even blame the Devil for some of your woopsidoopsies. And most folks will agree that your model is being "pushed" by the wind. As long as you learn to compensate for air flow, or the Devil, it won't matter. Just enjoy."

 

           Bob Wilson

President, Macon Aero Modelers, Inc.

 

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