A 3 Turn Spin
I would suggest your carburetor be capable of holding an idle for 20 seconds or more, and then be able to rapidly change to full throttle without causing the engine to cut out (too lean), or to sputter out (too rich). Furthermore, the carburetor must be able to do this both with a full tank of fuel, and with a tank near empty.
Without question you should be utilizing muffler pressure as the only return air supply to the fuel tank. Such air under pressure will help to minimize the fuel flow differences between a full and low tank. Once you gain this reliable carburetor setting, don't tamper with it. A click or two of adjustment on the top end (full throttle) may be appropriate as humidity and temperature fluctuate from day to day, but the idle setting should not require readjusting, even with a more substantial weather change.
This maneuver is particularly good to learn if you plan to do some teaching. Like the three horizontal rolles, the plane is set into a spin aboutits longitudinal axis, testing your ability to keep track of its position. Thus, if you can learn to deal with a spinning plane and handle its recovery, you will be that much more skilled and that much more comfortable with rescuing students from their errors.
As with so many of the maneuvers we have discussed so far, this one is a classic in full scale aviation. For years full scale military training involved learning how to get into and out of spins, perhaps they still do. But a word of caution. Model airplanes handle and fly a lot like their full scale counterparts, but not exactly. The relative size of our models to air molecules compared to full scale is such that our models control and behave somewhat differently. This whole area of ratio of aircraft size to the size of air molecules is dealt with in the concept of "Reynolds Numbers" if you want to read more about it.
The Spins are one of the maneuvers where your full scale experience won't apply exactly to the model. For example, some fully symmetrical model wings don't spin well without using ailerons along with the usual rudder and elevator. In full scale the stress is on the rudder only.
Also in full scale the stopping of the spins requires more careful action than with a model. Simply neutralizing the controls will invariably stop a model from spinning within 1/2 revolution.
My own experience in spinning a model is based upon fully symmetrical wings, arranged in the advanced trainer or pattern configurations. The three-channel flat bottom wing is also capable of this maneuver, according to other modelers I have consulted.
The Three-Turn Spin is the only maneuver we will be discussing for sport fliers that has an entry position totally out of the flight corridor, though if you do it well, you should be exiting into the standard flight corridor, of 100-200 feet of altitude, 300 feet out from yourself. During practice, of course, starting extra high is suggested.
To practice this maneuver, fly level into the wind, at 300 feet or more of altitude. Throttle back to idle to a point where the plane will coast to a full stall just in front of you. During the coasting period apply increasing amounts of up elevator so that you maintain level flight and so that by the time the plane comes to a full stall, with its nose slightly high, you will be applying full up elevator.
It obviously takes practice to time all this so you stall in front of yourself. Differing wind speed will affect when you should throttle back.
With the plane hovering in full stall, it will fall off on one wing or the other. Keep applying full elevator, and add full rudder, as well as full ailerons if you have them, to the side the plane falls. A spin should result. Count three spins, release all controls, either at 2 1/2 spins or whatever it takes for your plane to stop at three spins, allow the plane to descend a bit farther, and then apply full throttle as you pull out into a level exit upwind.
With many planes you can determine which wing will drop by applying rudder and aileron to that side just as the plane is hesitating in its stall. However, once in a while such "coaxing" has no effect, and the plane will fall off on the other wing anyway. Then you have to quickly change your rudder and aileron application to that side. If you are not quick enough, you may just get a spiral dive.
If the spins are too fast for you, ease off on ailerons and rudder after the first spin has started, and the spins should proceed at a slower rate. Experiment to see if you plane can do the spins without application of the aileron.
The biggest challenge of the three spins is to avoid a spiral dive. In a spiral dive, the plane is "flying" toward the ground while doing an axial barrel roll, rather than falling toward the ground, and spinning tightly about its longitudinal axis.
Spiral dives can occur when the plane is forced over into its dive before a true stall has occurred. Spiral dives can also result when you have inadequate elevator or rudder throw, or the center of gravity is too far off.