# Doing the Roll

If you have been to the flying field just a few times, you have seen plenty of rolls. A roll is the maneuver where the aircraft rotates its wings 360 degrees while flying in a level, straight line. The roll starts and ends with the aircraft headed in the same direction, and at the same altitude, as before the roll began. Well, that’s the theory anyway.

But that is not often the practice. You can see all types of rolls. Some rolls end with the airplane headed down 45 degrees or more. Others end with the airplane one hundred feet or more higher than the maneuver’s start. Still others start out all right but soon have the airplane heading off at a ninety-degree angle from the line of flight.

Many RC pilots perform rolls seemingly whenever and however the whim grabs them. Rolls are performed in the corners heading away at a forty five-degree angle. Sometimes the airplane is flying diagonally across the flying area. Sometimes the roll is so fast it is hard to see. Consecutive rolls vary in speed and direction. It seems there is no pattern to how the maneuver can be performed.

But then, suddenly rising above all the din of wildly rolling aircraft scattered all over the flying area, there approaches a sport plane that is flying parallel to the flight line, about seventy five feet out. About two hundred feet before reaching the point opposite its pilot, it begins to slowly roll. The wing continues to rotate but direction and altitude never change and the airplane covers four hundred feet before the wing returns to level flight.

When this happens, you can almost hear the field noise disappear as all eyes are on this airplane. When performed well, the simple slow roll is truly a joy to watch. It is deceptively simple in appearance but is performed so rarely that it must be difficult to do. It seems impossible to most new RC pilots that they can ever learn to fly that way. But any RC pilot willing to take the time to learn the right way can master great slow rolls, or consecutive straight rolls.

After all, when all is said and done, the roll is really simple. Apply full aileron deflection and stop when you are upright once again. It can’t be that hard, can it? Sounds a bit too easy, doesn’t it?

Well no, it isn’t that easy. Properly learning to roll well requires learning the roll in stages. This is a maneuver that will require a lot of interaction with your instructor.

In my club, the roll is a required maneuver to pass the solo test. So instructors teach it before the student can solo. Other clubs may be different. If your club is one of them, I urge you to talk to your favorite instructor before trying this maneuver—or any advanced maneuver for that matter.

Now on to the first stage:

Establish a straight line parallel to the runway and a few mistakes high. Yes, I know you have heard this all before. This straight line is the entry for all good maneuvers. Performing any maneuver exactly where you want while flying in a straight line puts the pilot in charge of the aircraft. Doing a maneuver only when the pilot feels “comfortable” with the aircraft’s position puts the airplane in charge of the pilot. Not the best way to fly.

If you can’t fly a straight line, you can’t very well enter any maneuver. This is the first thing to practice. It may be and look boring, but this is the maneuver every pilot needs to learn first. (I know, we have said this before, but it is even truer for the roll than for any other maneuver. So practice flying those straight lines first.)

Photo 1    Photo 2

OK so you’re flying a nice straight line, parallel to the runway and not too low. The aircraft is flying at ½ to ¾ throttle in level flight. Go to full throttle then point the nose slightly up (photo 1). Just raise the nose about twenty degrees and then neutralize the elevator. You want a slight climb. NOW, apply full aileron deflection (photo 2). Try rolling to the left at first. As the airplane becomes inverted (photo 3), PUSH down elevator. Don’t worry, the airplane will go up. Remember when you’re inverted up is down and down is up. The “down elevator is up” part when inverted is what you need to remember and do.

Photo 3        Photo 4

As the aircraft rolls to inverted, the wing becomes less efficient and loses lift. Most sport aircraft have slightly positive wing incidences set for upright flight. Once inverted, the positive wing incidence becomes negative further reducing the wing’s lifting force. Therefore, the aircraft starts to head earthward. Applying down elevator increases the wing’s positive angle of attack increasing lift back to normal. The aircraft remains at a constant, or slightly higher, altitude.

OK, back to the roll. As the airplane continues to roll and approaches knife-edge flight (photo 4) you want to let go of the down elevator. If down elevator is maintained, the airplane will start to turn away from the line of flight. While in knife-edge flight, the nose will start to drop, as there is very little lift in this attitude. For now, don’t worry about it. Raising the nose 20 degrees before beginning the roll compensates for this attitude and altitude loss.

Continue to hold full aileron deflection and soon the airplane will be in a normal, upright attitude. Then let go of the aileron. Add some up elevator to return to level flight and then neutralize all controls. Establish a straight flight path again and go back to part throttle operation. Done! Doesn’t that feel good? With the average aerobatic trainer, like the Hangar 9 Arrow pictured here, this maneuver should take about two seconds and cover about 100-150 feet.

When viewed from the side, your airplane’s flight path will resemble the crude drawing in Fig. 1.

Figure 1

I know that this is not the perfect slow roll you want to learn. Not yet anyway. It is also not a good way to perform consecutive fast rolls. But it is the way to start to learn them. Continue flying these single rolls until you can perform them in either direction, in a straight line and always just where you want them to be.

The most common question about this maneuver is ‘How much down elevator do I use when inverted?” I can’t give you an exact answer to that question as it is aircraft dependent.. Flat bottom trainers usually require about half of all available down elevator to remain in level flight. Aerobatic trainers require less.

I could easily say” Enough to stay in level flight”, but you would probably just get mad at me for saying that. This is where your instructor comes in. He will show you a roll and will know how much is enough. A good way is for the instructor to fly the roll and have you watch the sticks. If for some reason you can’t get to an instructor, try giving full down when inverted. Then vary the amount of down on subsequent rolls.

A hint for instructors: I had a student who just couldn’t give down when inverted. He always ended up doing a split “S”. That’s a nice maneuver but, it isn’t a roll. Finally; I took over and rolled the airplane inverted, held it there with enough down to keep it level, made sure he was holding the same amount of down and no aileron, and gave him control through the buddy box. Now he was flying inverted and was able to complete the roll to get out of inverted.  With several try’s he ‘got it’ and was able to do a pretty decent roll.

As you get better doing the roll, you will start easing in the down elevator and then easing out the down elevator. You will also find that less up elevator is needed at the start as you get better with the down elevator part of the maneuver. As you progress, you’ll find that the arc in the flight path, so pronounced at the start of your learning, becomes almost flat. Once the arc flattens, try doing two consecutive rolls. Master that and then try three rolls.

What about roll rate, or speed? For basic and aerobatic trainers, the best consecutive roll rate is usually around two seconds per full roll. More aerobatic aircraft should be set so that full aileron deflection produces three rolls in five seconds. These are good starting points and can then be adjusted to the pilot’s preferences.

But now, try doing the roll slower and slower. Ease in the down elevator and then as the airplane slowly returns to upright ease out the down elevator. Nice! Slower rolls are impressive. As you get to more advanced airplanes, you will find that they need less and less down elevator. When flying either the Arrow pictured above, or the Hobbico AviStar in the following photos, inverted flight uses less down elevator.

At some point you will be flying a fairly advanced aerobatic airplane and will need almost no down elevator. But, regardless of the aircraft, as you reduce the roll rate, you will start seeing the need to add top rudder to your rolls. When the airplane is sideways or ‘knife-edge, the only lift is provided by the fuselage side area. In order to keep the airplane going in a straight line the pilot will need to give rudder toward the sky, or top. A roll to the left will need first right rudder then left when the airplane has rolled to the other side. This is pretty advanced stuff. But it is something your trainer is capable of flying so it is time to at least look at the slow roll in theory.

Photo 5     Photo 6

Fly a straight line and then apply very slight up elevator and one-quarter left aileron. As soon as the aircraft starts to roll, release the up elevator. When the aircraft reaches the bank attitude shown in photo 5, slowly begin to apply right rudder. By the time the aircraft reaches knife-edge, photo 6, you will be holding full right rudder. Notice how the fuselage in photo 6 is at a positive angle of attack; the nose is pointing upwards. This helps to maintain altitude and is caused by the full right rudder.

Photo 7   Photo 8

As soon as the aircraft rolls past knife-edge, slowly begin to release the right rudder. By the time the airplane rolls to the position shown in photo 7, all rudder should be gone and you start applying down elevator. By the time the airplane is inverted (photo 8), all the down elevator you will need should be in there.

Photo 9   Photo 10

As the aircraft continues the slow roll, begin to release the down elevator until it is all gone as the aircraft reaches the attitude shown in photo 9. Slowly start to input left rudder now. As the airplane rolls to the subsequent knife-edge in photo 10, full left rudder should be there.

Now here is where something different happens. The roll rate changes dramatically. It starts to increase. You probably did not notice much difference in the roll rate when right rudder was applied in the first knife-edge. The full-span ailerons in most of today’s trainers are so powerful, they easily overcome opposite rudder. The airplane just kept rolling around at about the same rate.

But all trainers, basic or aerobatic, possess a demon known as “roll coupling”. This strange term just means that the aircraft will roll with just rudder input; no ailerons. Applying rudder opposite the turn direction doesn’t mean much. But applying it in the same direction as the already powerful ailerons results in a much faster roll rate.

You want to maintain a constant roll rate so what to do? Simple to say and hard to do is that you need to decrease aileron input. As the airplane approaches the second knife-edge, reduce aileron input by half the amount you were initially holding. That should do it and keep the roll rate constant.

Photo 11   Photo 12

Again, once knife-edge is past, begin to release the left rudder. Again, here is a catch. As you slowly release left rudder, you need to slowly increase left aileron. By the time the position in photo 11 is reached, all left rudder should be gone and aileron input should be back to original levels. This keeps the roll rate constant. The aircraft should recover as in photo 12, with a slightly nose-high attitude just as it started the maneuver.

One other thing about high-wing trainers, they tend to have pitch coupling when in full knife-edge. This means that the aircraft leaves the straight flight path and starts to turn towards the wing. This is called “pulling towards the canopy” and is hard to adjust. For now, forget about this nasty habit. If the roll is otherwise done correctly, the two “canopy pulls” are in opposite and equal directions and should cancel out by maneuver’s end.

Now you know why aerobatic airplane designers do all they can to eliminate both roll and pitch coupling. Such couplings make it harder to fly those pretty maneuvers. Now, you also know two important flying qualities to check before you buy your first aerobatic model aircraft. Make sure the one you get has little or no coupling. Your flying will be easier and you will smile a lot more if you do.

The slow roll takes practice and careful attention to detail. Many sport pilots never even try to master its intricacies. But for those who do, a new world of attractive rolling maneuvers awaits them. Rolling circles and rolling loops require first mastering the straight slow roll. Then there is the four-point roll, also eight and sixteen point ones, that are really just a slow roll with hesitations. And don’t forget rolling squares and triangle loops either.

And then there are… well you get the picture. The slow and consecutive rolls form the foundation of many of the maneuvers you will want to do later on. So learn the single, two-second roll first. Then once you have that mastered, start slowing it down a little at a time. By the time you get your first aerobatic airplane, it will be you everyone at your field is watching as your airplane slow rolls the entire length of the flight line.

Q

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Posted by Bob Karasiewicz on Filed under Flight Maneuvers. You can follow any responses to this entry through the RSS 2.0. You can leave a response or trackback to this entry