Control Line: Aerobatics
Wynn Paul
Last month we flew the new airplane in level flight to examine the characteristics of a high or low outboard wing; we also watched inverted flight, inside and outside round loops, the inside square, the gliding traits after the engine cuts, and the landing features. After observing these items, you should get a very good idea of whether this new plane is going to fly pretty good or be a fixture on the wall.
Keep in mind the variables that you have to work with, and there are quite a number: tip weight, nose weight, tail weight, engine offset, prop selection, engine shims, leadout variance, flying-line length and handle adjustment. More drastic moves involve tweaking the flaps, cutting on the flaps, cutting on the elevators, changing the flap horn alignment by cutting into the fuselage, changing the landing gear, or bending the initial L.G. wires.
Let's assume that you have gotten the plane to have the wing straight in level and inverted flight, there seems to be sufficient pull on the lines most of the time including inside and outside round loops, the inside square seems to pull pretty good, the outside wing panel doesn't drop during the corners, and the glide is pretty balanced between groovy and sensitive. You now have a plane that is actually in pretty good trim.
Rolling in level flight — causes and fixes
A couple of things that could crop up during these maneuvers: on some windy days the plane tends to rock about the roll axis in level flight. There are a couple of theories about why this happens, including heavy tips on a foam wing, rudder effect of wheel spats or pants, sharp leading edge on the wing, and stalling action caused by unequal panels. Since these trimming articles are supposed to be long on practical solutions and short on theory, let's see what we can do for this malady.
First, you might try removing the wheel spats or pants or using different L.G. wire entirely. If this seems to have no effect, you might try adding tip weight in 1/4 oz. increments until the wing starts to dip badly in the inside squares. This may solve the rolling in level flight. Of course, this rolling doesn't really hurt anything, it just looks bad after takeoff and during the interim between maneuvers.
Plane goes loose at the tops of loops or squares
If the plane seems to go loose on the lines at the tops of the inside or outside round loops, and also at the tops of the inside and outside squares, then the first thing to try here is more tip weight. You might also try moving the leadouts forward to increase line tension here; at the same time (on a different flight — remember this) you may have to decrease the amount of tip weight.
Let me say right here that I firmly believe in adjusting tip weight and nose weight as primary trimming items. Some people really like to try prop changes, some like to try leadout and engine offset changes, and some like to spend a lot of time with the flaps — bending, cutting, trimming the trailing edges, etc. Each flier will have to try to keep an open mind and not get into a rut trying the same thing over and over to trim out a recalcitrant airplane. Don't be afraid to cut on the plane if all else fails. Better to have a good flying airplane with some minor repairs showing than an 18-pointer that can't fly.
The triangle
One of everyone's most difficult maneuvers is the triangle. The first corner isn't bad, but getting the top angle just right is difficult and, of course, deadman's corner is always a thrill. If the top angle is too big then that third corner is less than 60 degrees, and will very often tend to stall out the plane that is overweight or that has a low tail volume coefficient relative to the wing area. You will need your spotter to watch and keep you informed as to the size of the top angle of the triangle. Better to have it too small than too large.
To help make that third corner a good one and eliminate stalling or sinking, you might try adding nose weight and/or changing the prop by going to less blade area (helps in turning) or more prop diameter. Obviously, if you get a big bobble on that third corner and it can't be chalked up to nerves or inexperience, then try more nose weight by all means. Another way to smooth out the turning is to try a smaller line spacing on the handle. The popular E-Z-Just is about 4½ in. If you try a Martine Custom Master adjustable handle you can get closer line separation which acts like adding nose weight by slowing down the turning.
Prop selection
Don't forget that changing props can make some big differences. More blade area will help line tension and slow down the engine. Larger diameter will give more line tension. Larger blade area will soften the turning ability. Try at least two flights with each prop to get the feel of what it does to the pattern and see which one helps.
Yaw, leadouts and offsets
So far, I have conveniently stayed away from mentioning "yaw," the outward or inward turning of the plane about the vertical axis. I have a few theories about the confusion of some stunt fliers who intermix excessive yaw with good line tension, with optimal engine offset, and with proper leadout rake. I have seen very few planes in the air that looked, or appeared, to be flying with the nose pointed out too far—or at least far enough out so that it detracted from the appearance of the flight. However, I'll keep these to myself and get on with trimming out the stunt plane.
Leadout position is, of course, the prime variable in adjusting the yaw of a plane. Engine offset is a second and rudder offset (if applicable) is a third. Experimentation is the best way I know of to find the best leadout setting. Funny thing, one of the most important items of flying (leadout sweep) is one of the most mysterious parts of building and design. Perhaps mysterious is not the word; let's try completely "left out" in the directions. For instance, of the hundred or so airplane articles that have appeared in print, I can remember only a few who actually gave a dimension for a starting point in setting the leadouts: Gialdini said 5 degrees aft of the bellcrank in the Olympic article, and only a couple of others even mentioned it, including Bill Netzeband who advised a seven-degree starting point. Of course, with adjustable leadouts this is not too critical, but it is something the beginner often wonders about when starting a plane from scratch.
Some people don't recommend engine offset as they feel we are wasting engine power and creating too much yaw. I personally have always found that I can fly better when the engine is pointing out about 2–4 degrees. I never worry too much about line tension, because there is always the tug by the engine wasting horsepower, helping to keep the airplane tight on the lines.
If you don't think that a rudder will help with line tension, or adversely create excessive yaw, try watching a movable-rudder plane from the downwind side when it's doing those outside square loops or the inside square loops. Watch the plane jerk outwards when that movable rudder moves out. If you have a movable or adjustable rudder, try several different settings until you get the right balance between line tension and excessive yaw.
Positioning tips for maneuvers (from Jim Young)
Some tips straight from an old article by Jim Young (Bellanca, MAM, October, 1969, p. 11) regarding the proper positioning for maneuvers to maintain uniform line tension and constant speed. This is for counter-clockwise fliers:
- Inside loops, inside squares and triangles — 15 degrees left of downwind.
- Outside loops, outside squares — 15 degrees right of downwind.
- Horizontal round and square eights — inside loop 15 degrees right of downwind and outside loop 15 degrees left of downwind, with the intersection directly downwind.
- Vertical eights and hourglass — from straight downwind to 15 degrees to the right of downwind (experimentation is necessary here especially).
- Cloverleaf — first and fourth loop 15 degrees right of downwind, second and third loops 15 degrees left of downwind, and the vertical intersection directly downwind.
- Wingover and overhead eight — start maneuver directly upwind and complete the maneuver directly downwind.
The square eight
The square eight is such a tough figure to get looking decent, especially for the novice. First of all, make certain that you have thought it out ahead enough so that you put the center intersection exactly downwind. Make the inside square big enough so that, when you get to the outside part, you can make the outside square big also, and avoid the tiny round "squares" that we often see in the beginners' patterns. I firmly feel that a novice should make the figure bigger than normal so that he can work on the overall shape and the intersections, then try to get it down to legal size.
Don't become alarmed if, in the transition climbing intersection from the outside square bottom up into the second inside square, the plane feels as if it's going to fall out of the air. This is one of the most demanding parts of the pattern on the engine. This particular part of the square-eight maneuver is a very good way to see just how much "guts" the engine has. If the lines go limp as the plane starts its climb, then pull in, and you may have to step backward.
The vertical eight
The vertical eight can be performed without too much trouble if the first inside round is done as small as possible, allowing the top loop to have plenty of room. Try to get your spotter to see if you are letting the plane go behind your head, a major no-no. There is a prominent Nats finalist for many years who always gets away with the plane going behind his head on the vertical eight but no one seems to want to call it. I think that's called reputation.
The hourglass
The hourglass has probably put as many planes out to pasture as has the New Jersey Turnpike caused motorists to give up driving. In the first place this is a very hard maneuver to visualize from inside the circle. It almost looks like a vertical eight and of course comes out looking like it a lot of the time. I really feel that the first corner sets up the maneuver, both for size and placement. If I can start the maneuver in the right spot just left of downwind and have the proper angle as I start the climb I am well on the way to a good maneuver.
Again, I can't stress too much the value of a good spotter here in helping you to decide where to put this maneuver. If you go too far to the left to start, then you will immediately get over on the plane's back as it starts to ascend. By then, the maneuver is lost and you have to again get the plane on its back on the descent to get back to the far right side to make the maneuver look symmetrical. I feel that it is better to have a high, narrow hourglass than a stretched out one with the plane spending a lot of time over on its backside.
The cloverleaf
The cloverleaf on many days with the wind over 10 mph must be whipped into the first loop. If you don't whip it and step back to get enough line tension, it's a gooey maneuver and you can get one of those "McDonald-7/8" over-the-top clovers that brings chills and gray hairs. Be certain to fly far enough after the first loop before starting the second loop so that, by the time you start your vertical climb up to the third loop, you are not running directly through the center of the first loop's path! This is the most common mistake of beginners, and novices, and advanced, and experts.
Final tips and contact
Let's hope these two columns have helped you in trimming out your plane and experimenting with some of the maneuvers. Try to get someone to spot for you and don't be afraid to try several types of changes in trimming, but always try to change just one item per flight.
For information on stunt or PAMPA, contact Wynn Paul, 1640 Maywick Drive, Lexington, KY 40504.
Transcribed from original scans by AI. Minor OCR errors may remain.
