Radio Control
SPORT/AEROBATICS Ron Van Putte
Last month, I promised to include descriptions on how to perform maneuvers from the Novice/Sportsman class on a monthly basis. This month's maneuver will be the Stall Turn.
The Stall Turn is an upwind maneuver, meaning that it is initiated from an upwind heading. It is strongly affected by the wind. By that I mean that the appearance of the maneuver is affected. (We all know that, except for gusts, the airplane doesn't know that the wind is blowing.)
The wind has an effect on the airplane only in that we are trying to make the maneuver look the same, whether the wind is blowing or not. What a good flier does is recognize this and then compensate for the effects of the wind on the appearance of the maneuver. However, a beginning Pattern flier is only concerned with doing the maneuver well enough so that it is recognizable and still have his airplane intact after the maneuver is completed. So, let's treat the Stall Turn from that aspect and worry about the effects of the wind later.
A good running engine with sufficient power to permit vertical flight for a short time is mandatory. You can't expect to be able to perform a good Stall Turn if the engine is too puny to sustain the airplane in vertical flight for several aircraft lengths.
The maneuver must be started with the wings level. If one wing is down at the start, the vertical portion of the maneuver will be canted off to that side. If you discover that the airplane is consistently canted off to one side in vertical flight, it is probably rolled in that direction at the start.
A short, wings-level entry should be followed by a smooth rotation to vertical flight. The excess power available will determine the radius of rotation. Lower-powered aircraft need to be rotated faster, because the rotation bleeds off speed quicker with them. However, be cautious not to pitch the airplane up too quickly, because that will slow the airplane down, too. You have to find what's right for the airplane.
Stop the pitch rotation when the airplane is vertical. For some reason, many newcomers to Pattern flying can't seem to recognize when the airplane is vertical. If it isn't pitched up enough, the airplane probably won't stall cleanly, and it will tend to "steer around" the turn rather than stall. This causes the downward flight path to be offset more than the maximum of two wingspans from the upward path, and the rule book calls for a downgrade for this. On the other hand, pitching the airplane up too much usually ends in a "flop." Make certain that the airplane is really traveling vertically before trying to initiate the stall. If you get it vertical and it tries to crank off to one side of its own accord, you didn't trim it properly. Ensure that the ailerons and rudder are properly trimmed. (Refer to my December 1982 column for suggestions on how to trim the airplane.)
Most airplanes yaw better to the left because of engine effects, but engine right thrust may cause particular airplanes to prefer yaws to the right. So, yaws in both directions should be tried to see which way is better. The rudder command should be put in following the vertical segment of the maneuver and a reduction of power. Most Pattern airplanes yaw better and stall more cleanly if the engine speed is reduced to idle. However, sport/Pattern airplanes, particularly the low-powered ones, will do a better job at higher throttle settings.
Kick in the rudder just before the airplane comes to a stop. If it gets too slow, the rudder won't have the power to take it around. Many people put in a "blip" of throttle to get additional airflow over the rudder to help yaw the airplane.
Hold in the rudder control until the airplane stalls cleanly and rotates in yaw past 90°. I usually let go of the rudder stick just after the airplane yaws 90°. This keeps the airplane from wobbling in yaw on the way down. If the airplane wobbles, you held in the rudder command too long. Some judges insist on seeing the airplane wobble exiting a stall turn. I think these are bad judges. Good judges know what to look for and reward a pilot who is skillful enough to execute a wobble-less Stall Turn.
Don't touch the elevator or throttle control until the airplane performs a downward vertical leg just like the upward one, then ease in the elevator to pitch the airplane back to horizontal flight. Only after the airplane is horizontal should the throttle be advanced.
Now, what about the effects of wind? Obviously, the effect of a direct headwind is to blow the airplane back. The way to counter a headwind is to pitch the airplane up just short of vertical so that the wind will blow the airplane path back to vertical. The effect of a crosswind is far more complicated.
The maneuver is partly judged on how well a vertical flight path is achieved. However, if the airplane is traveling vertically in a crosswind, the airplane will actually be in a yawed flight condition. The directional stability of the airplane tends to yaw the airplane into the crosswind. As the airplane slows down, the yaw effect becomes greater. Consequently, it is usually easier to perform a Stall Turn if the airplane is yawed into the wind at the top. In fact, if the crosswind is strong, it may be nearly impossible to perform the yaw away from the wind.
I suggest trying the first few Stall Turn maneuvers in near-calm wind conditions and learning how to handle the effects of wind only after the basic technique for performing the maneuver is achieved.
In the September 1982 column I published the escapades of Dewey Godditt (AKA David P. Anderson) in his attempts to get a show-quality finish by using a badger hair brush. Dewey wrote me the following letter after his "adventures" appeared in the magazine.
"Thank you for printing my warning about the hazards of using badger hair brushes. I'm sorry you fell on the floor after reading it. I hope you weren't hurt. But this just goes to show how dangerous this hobby can be.
"Keep reading Flare-Out for I am a regular contributor. Last month's column was about how I was asked to paint the outhouse at the flying field. When I brought the completed canvas to the club meeting, the members were speechless. Next month's column details my experiences flying in the nats. What a mess those pesky insects make when they get stuck in castor oil!
"Now I'm working on an article explaining why a plane loses altitude in a down-wind turn. It's very simple. You see, if the wind is blowing down . . ."
Way back in the December 1977 issue of Model Aviation, I published information on a servo tester which had originally (I think) been published by Hugh Shoemaker in the DCRC Newsletter (Washington, DC). I got a flock of requests for the schematic when the column was first published. However, I still get requests; I got one just last week. The tester has several virtues: it is inexpensive, easy to assemble, small, and parts are not difficult to locate. If you'd like a copy of the original article, send me a self-addressed and stamped envelope, and I'll get it to you by return mail.
I just received a letter from Gene Somebody. Gene's real last name was on the envelope, but it was misplaced. Regardless, here's a slightly edited version of Gene's letter.
"As a B-47 operator stationed at Topeka, KS circa 1960, I was a member of the RC club there. I read about the Knox gelatin routine in our literature of that day and tried it on the wing and tail of a Stormer. One coat of water/gelatin mixture sealed the silk so well that three coats of butyrate dope gave it a gorgeous, translucent finish. I took it to the club meeting, basked in the boys' admiration, and gave them a lecture on how it was done.
"At the next club meeting a chap, in a high state of dudgeon, displayed a silk-covered wing that was pitiful to behold. It looked as if he had finished it with stucco. 'You $!@#,' he said, pointing to me, 'Look what you caused me to do to my wing.' Post mortem revealed that he had mixed the gelatin into his dope! Egad.
"For me, the perfect finishing method for balsa-sheeted surfaces, especially compound curves, is this: brush on two or three coats of butyrate dope, sanding the fuzz off each time. Drape 3/4-oz. glass cloth over the surface, one piece for the whole fuselage. Brush the dope through the glass cloth, pushing out the wrinkles and folds ahead of the brush and making a ragged overlapped seam on the bottom. Brush on two or three coats of talcum/dope mixture or Sig Superfill, and give it a good sanding. Shoot on the color. This gives a durable, good and lightweight finish.
"My old flattop Stormer (Vintage 1960–1962 for you younger readers, RV?) is still the best 'hot dogging' aircraft there is without any mods to the original design except a bolt-on wing and landing gear, plus a fixed horizontal stab."
Since the Stall Turn took more than half of this month's column and the Three Axial Rolls took a similar amount of last month's column, I plan to skip a month before resuming with descriptions of how to perform Novice/Sportsman class maneuvers. Maybe every other month is a more appropriate mix.
Ron Van Putte 111 Sleepy Oaks Rd. Ft. Walton Beach, FL 32548
Transcribed from original scans by AI. Minor OCR errors may remain.
