An Inside Loop
Chances are that you performed a single loop at least once in your student period. Probably when you were cruising along at a nice safe altitude, and not expecting it, your instructor casually told you to pull the elevator stick straight back to see what happens. To your amazement, you did a loop. "Wow!" you thought. "I'm doing tricks already." Your confidence went up and you became a better student.What we are going to practice now is called the 3 inside loops. One loop is easy, as you proved when you were still a fledgling student. Three loops is another matter. The problem with three loops is that by the third loop, things can get awfully cockeyed. I once completed my third loop heading exactly away from me, or 90 degrees from my entry heading! To complete my embarrassment, it was during a contest with the judges intently trying to figure out what I was up to. This is definitely not a maneuver to practice during a crosswind. In addition to the exit heading problem I just mentioned, three loops can blow way in or out during a crosswind. This is because it is a relatively long maneuver in terms of time, and during that time the air mass in which the plane is flying will have moved quite a bit by the end of the third loop.
Initially you may have to start by practicing only one loop, building up to three loops as you develop the knack for keeping the wings level and the figure nice and round.Keeping the wings level, you ask? Yes. No trainer or sport model aircraft will fly a loop with the wings level unless you introduce some aileron or rudder correction during the loop.
This is because under the added g forces present in the loop, the heaviest wing is going to be forced farther outward-downward than the lighter side. Failure to correct for this condition results in the loops corkscrewing the entire plane in the direction of the low wing. You could start the maneuver 300 feet from yourself and end it a considerable distance closer or farther out, even in a dead calm wind.
In all probability, your right wing panel will act like the heavy side because that is the side most engine mufflers hang over. That muffler hanging off to one side under the heavier g loadings of aerobatics will make the aircraft fly as if the the whole right wing panel weighs more than the left panel, even though both wing halves may be of equal weight.
In pattern aircraft, weights are typically added to the left wing panel tips to cancel out the muffler/tuned pipe factor. This allows the plane to fly through three loops with much less aileron correction.
If your wing has been crashed repaired, one side may be heavier from this cause, and if it happens to be the muffler side, you'll get the g force effect all more noticeably. Since you now know your wings are not likely to remain level, you can be watchful to apply aileron or rudder correction as soon as you notice "wing walk" taking place.
With experience you'll be able to see the heavy wing effect anywhere in the loop, and to apply correction anywhere, perhaps even constantly, so that observers think your wings are remaining level naturally. But initially you may only be able to see, or at least react, at the very top and bottom of the loop. If you can start out making corrections at both the top and the bottom, you'll not have as drastic a correction to make at the bottom. Making that leveling correction while the plane is inverted at the top is easier than you might suppose. This is because the rule of "pushing the aileron/rudder control stick under the low wing" works upside down as well as right side up.
Of course you'll have to prove that your plane always drops its right wing because of the muffler effect, you can be ready with constant left correction.
SIZE OF LOOPS AND ROUNDNESS
How large a loop is right for you model is dependent upon how much engine power you have. Some low powered full scale aircraft actually have to dive first to build up enough airspeed before pulling up into a tight loop, then falling through the back half into what ends up being an egg-shaped maneuver. These days most modelers are flying with excess power.
Models that were designed for .29 and .35 sized engines are powered with .40s, and the .40s are super powerful on top of that. Therefore you can perform rather large loops, and have power to make them perfectly round. A very large loop has the disadvantage that you are exposed for a longer period of time to destabilizing influence.
Keeping your loop just a tad in the tight side will help it "groove" a little better. The tighter loop will will accentuate the heavy wing, but if you are ready for that effect, it need not be a problem.
Applying a constant amount of up elevator will not produce a round loop. This is because you are fighting gravity on the way up, and have it helping you on the way down. Headwinds are also a factor. Across the top of the loop, they can blow you horizontally so that you produce an elongated shape. To get a round loop in light winds, ease off the elevator coming over the top, and then apply more again as you are coming to level and starting back up again.
If you have a powerful engine for your model size, throttling it down on the backside of the loops may be helpful.
In high winds, elevator procedure may need to be reversed from the light wind procedure. In the initial climb, lighter application of of elevator will be useful, and coming over the top both throttling back and tightening the elevator control quite soon will help to stop the elongation that takes place in strong winds. Except in almost calm conditions, loops are very hard to perform downwind because of the cumulative effects described above. For this reason, rule books designate this an "upwind" maneuver.
SMOOTH & LEVEL EXIT
One of the graceful and satisfying parts of the inside loops is the achievement of a smooth transition from looping to level flight at the exit without getting a dip or rise, searching for level.
The trick in getting a smooth exit is to completely get off elevator just before dead bottom center of the last loop. If you stay on the elevator right down to the bottom, and then release, the combination of your delayed reaction time and the momentum of the plane will result in the plane starting another loop and then dipping back to level or even below level.
Also, as you transition to a level exit, don't forget to release that aileron or rudder correction you have been holding in the loop to correct for the heavy wing effect.