Radio Control: Sport & Aerobatics
Ron Van Putte
Wind Aloft
When I read John Preston's August 1984 "Safety Comes First" column, I enjoyed the description of what it would be like to fly an RC airplane from an aircraft carrier moving downwind at the same speed as the wind. It was a perfect example of how an aircraft is "unaware" of a steady wind, and I mentioned it in my November 1984 column. The description had appeared in a club newsletter, but I had the vague feeling I'd read it before, several years earlier.
Sometime after the November issue of Model Aviation appeared, I copied a portion of a Frank & Ernest comic from a Sunday newspaper and sent it off to South Africa. The comic had one character saying, "Why is there a difference between ground speed and air speed?" and the other replying, "That's easy. It's because the earth is round and the air is flat!" I sent it to Len Salter, who has written extensively about the effects of wind on aircraft flight and lives in Cape Town; I thought he'd enjoy it. I also sent along a copy of my November column, which contained figures showing the ground track of an airplane performing 180° turns in varying wind conditions.
A few days later I received a letter from Len Salter. He wrote that he was pleased to receive my letter and the article, and that he would be quoting the first part of my article in Flysheet (the newsletter of the Cape Radio Fliers, Cape Town) and publishing the cartoon. He also enclosed copies of two of his articles, including one titled "All You Need is an Aircraft Carrier," which had been published in RCM&E (Radio Control Models and Electronics) and Wings Over Africa.
Len Salter — background
Len noted that, although he has resided in South Africa since 1966, he remains a British citizen and an ex-RAF pilot who served during the war. During his 4½ years in the RAF he flew Tiger Moths, Fleet Finches, Avro Ansons and Avro Lancasters.
He also recalled the 1979 World FAI RC Aerobatics Championships staged in South Africa, where he met some AMA officials (including John Worth) and members of the U.S. team (Dave Brown, Mark Radcliff and Dean Koger). Through reciprocal arrangements with John Worth, Len sent Flysheet and received copies of Model Aviation.
Len's letter and the enclosed articles generated a stack of responses, mostly from correspondents who misunderstood the relation of aircraft kinetics to the ground. In his writing he has a unique way of taunting those who disagree with him, and I enjoyed his pieces. Below are excerpts and ideas drawn from what he sent.
Excerpts from Len Salter
"Wind has no effect whatsoever on the reactions of an aircraft in flight. If turbulence and wind shear spring up they will, of course, upset the machine, but the reactions of the aeroplane are only in relation to the airmass. I acknowledge their existence, but when I refer to wind in this article I am referring to a constant-moving airmass. Wind will only affect your aircraft relative to the ground, as it will drift 100% with the wind.
"There it is, gentlemen, quite simple, really, except to the diehards who perpetuate fallacies."
Len goes on to debunk the myth that the kinetic energy of an aircraft (subject to an equal thrust force) will vary between into-wind flight and downwind flight, or flight in any other direction. He offers a simple experiment to demonstrate the point.
- Attend your flying field equipped with a stopwatch, pen and paper, and enlist a colleague to act as timekeeper and recorder.
- Fly to a safe height and go well out downwind, then come in at full bore at maximum airspeed.
- When ready, call "Now" to your timekeeper and fully close the throttle at the same time. On the command "Now," your timekeeper starts the watch.
- Fly straight and level for as long as possible. Ignoring the idling prop (which affects nothing in this experiment), kinetic energy is now the model's only energy source. Drag will dissipate this energy, causing the airspeed to reduce progressively. Eventually the aircraft will stall. On seeing the nose (or a wing) drop, the watch is stopped and the duration of level flight is recorded.
- Repeat this procedure into the wind and across the wind in both directions. The sequence of directions is unimportant. Compare the recorded times.
Len reports that the recorded times are equal, plus or minus human error. A little error will creep in (for example, not maintaining absolutely level flight), and for greater accuracy the procedure can be repeated.
He also relates a personal anecdote: "I have flown a full-size Tiger Moth in a strong headwind backwards relative to the earth. Now let's apply the (kinetic energy) myth to that situation. It implies that my aircraft had no kinetic energy (or a minus quantity) and should have fallen out of the sky!"
If anyone would like a complete set of the material Len sent, he suggested mailing a self-addressed stamped envelope (SASE) to obtain copies.
Commentary and clarification
Len's style is provocative, but his basic point is essentially correct: the aircraft's reactions are determined relative to the airmass, not the ground. The most important references for the pilot are indicated/true airspeed and attitude, not ground speed. If you fly by ground references you will be continually correcting for drift and will be out of position for your maneuvers. In aerobatics this is critical: plan for the wind, allow for drift, practice heading corrections, and get the model back to the same place in the airmass for each figure. Fly to the airmass and forget the ground.
Pattern Poker
This column concludes with an idea sent to me by Bill Kite of Kingsport, TN. Bill's club, Tri Cities Aeromodelers, Inc., wanted a change for their annual club dinner or picnic and came up with "Pattern Poker." It worked like this:
- Take playing cards from a deck and give them to the contestant.
- The contestant draws six cards; depending on what he draws, he is assigned maneuvers from the classification he flies. For example, in the Novice classification: one equals takeoff, two is straight flight out, five is stall turn.
- The contestant then draws three additional cards; what they represent will be selected from the next higher Pattern classification.
- There are a total of nine maneuvers to be scored.
The idea was to allow equal competition when there were only a few fliers of different levels. Bill noted that with two rounds and the same flight schedule, luck played a part—some drew maneuvers they liked, others did not. They needed two or three decks of cards and extra help in processing. They invited a club from 20 miles away and had 16 contestants; a Novice won first place, a Sportsman was second and an Advanced flier third. The whole event took about 2½ hours, then they started eating.
I think it sounds like fun. If there are any more good ideas out there, send them along. How about some good pictures, too?
Ron Van Putte 111 Sleepy Oaks Rd. Ft. Walton Beach, FL 32548
Transcribed from original scans by AI. Minor OCR errors may remain.
