Inverted Flight
The aerobatic maneuver called straight inverted flight is deceptively simple: The model is rolled onto its back, flown in that inverted position for four seconds or more, and then rolled back to upright flight.
But in that simple description lie two more skills to be mastered that you have not encountered in the maneuvers practiced in previous lessons. These skills are:
o slow rolling
o smoothly attaining and holding sustained
inverted flight
So far your use of aileron in rolling has always been to apply the control it its maximum -- the Split 3 Turn, Immelmann, Reverse Cuban Eight, and 3 Horizontal Rolls have all been accomplished with full ailerons which produces a fast roll rate.
While rolling to inverted flight can also be done with application of full aileron, the resultant quick roll is ungraceful. Instead of looking like an aerobatic maneuver, it looks like the quick flipping of a pancake flapjack. Therefore slow rolling into inverted is the preferred approach.
To achieve a slower roll rate, you simply move the aileron control stick to less than its full position, utilizing instead about 1/3 to 1/2 of full stick.
The reason untutored modelers flip quickly over to inverted is to minimize getting a "dip" in their flight path as they press forward on elevator to establish level inverted flight. In case you have not experimented with inverted flight, you will find that even though the model may be trimmed for level flight while upright, once inverted it wants to sink. To prevent that sink, you must apply and hold some down elevator, which when you are upside down is equivalent to giving up elevator. The amount depends upon your wing airfoil, and center of gravity location.
A flat bottom airfoil lies poorly upside down. Even with full down elevator such airfoils are hard to hold level. Semi-symetrical are easier to fly upside down, though they require substantial down elevatgor. Full symmetrical airfoils are easiest to fly upside down, requiring usually only moderate down elevator. Holding the inverted flight level in the roll axis is much easier with ailerons, rather than operating only with rudder.
An advantage of slow rolling to inverted flight is that you get some time to deal with the transition on elevator to forward stick pressure while rolling is still taking place. To achieve a level flight path throughout the roll to inverted position without getting a dip, start sliding forward onto down elevator as the plane's wing passes the first 90 degrees of roll, gradually reaching the required amount of down elevator for level inverted flight just as the wings complete their roll to fully inverted. Slide quickly off of aileron, while holding your down elevator, to stop the roll exactly at 180 degrees, parallel to the ground. Hold inverted for four to six seconds, and time your roll to inverted so that the center of the inverted flight is in front of you. This means you must start the process of slow rolling to inverted well off to one side.
The process of rolling upright consists of continuing to hold down elevator, and resmikng your prior 1/3 to 1/2 aileron stick position, so you can get the same roll rate as before. As the wing passes 45 degrees, begin releasing down elevator. Release it fast enough that just as you pass 90 degrees you are off down elevator. As your wings are near 45 degrees to upright, give a small bump of up elevator. That bump of up will ensure a perfectly level trajectory as the wings reach level, at which time you release both aileron and elevator.
While labeled a downwind maneuver for purposes of competition sequencing, this maneuver can be practiced and slow either up or down wind.