What makes an airplane turn. This question was asked to me a couple of years ago at an aerobatics school. Originally i fumbled through ailerons and then thought of my gliders with none of these just a rudder and elevator of course, then mentioning the rudder. He replied yeah in a disbelieving tone. I asked why do you ask and he replied , not to disturb my trainig path." I heard of an article by a proclaimed aircraft expert called Mr propeller head and he went along those lines", as i did. This is regarding the use of rudder or aileron to roll and elevator to pull it around. A few months later i chased around the school looking for this advanced aerobatics pilot with my new answer. He then said " congradulations Mr propeller head you understand now". So lets see what everyone has to offer.If this should start WW3 just remember i`m on your side!
Dave

Shouldn't ...

The wing turns the aircraft. The ailerons, elevator, rudder control the bank, yaw, rate of turn, etc., but the turning forces are exerted on the wing in the form of the vector sum of horizontal forces on the banked wing.

Bedford

Very true, however, a turn can be completed with no use of a banked wing, hence the stated use of ailerons, rudder or both with the push of the elevator is technically correct, IMHO.

Ken

Ken

If you use the "push" of elevator then the wing is doing the work.

The only way you can turn the aircraft without using the lift provided by the wing is if you use a bunch of rudder to yaw the thing around. Then you're using the "lift" provided by the fuselage. F=ma.

BeePee is absolutely right. In a coordinated turn, the wing turns the airplane. Of course it is possible to yaw an airplane around keeping the wings level and pushing the back end around with the rudder. This is akin to knife-edge flight where the fuselage is yawed nose upward and a combination of fuselage lift and power is used to keep the airplane in the air. However that maneuver is not confused with normal flight where the wings are the source of lift.

The wings can be banked by several means. Ailerons are by far the most common means and a combination of rudder and dihedral is the second most popular method for models. Spoilers and wing warping have been used in some full-scale airplanes, to bank and unbank the wing. Whatever means is used, the purpose is to bank the wing to turn and level the wing to stop the turn.

To turn, nothing else is required. However when the wing is banked to turn the airplane, the lift being produced by the wing is now tilted toward the side and the force available to support the weight is reduced, and the airplane will begin to descend. To make a level (or climbing) turn, the total lift force must be increased. This is usually done by adding elevator control to increase angle of attack, or increasing power (or a combination of both).

When ailerons are used to bank and unbank the wing, the airplane tends to yaw opposite the direction of bank. For this reason, to bank the wings with a pure rolling motion it is usually necessary to apply a little rudder control in the direction of the turn at the same time as ailerons are moved in order to counteract this “adverse yaw”. When the ailerons are no longer deflected, the rudder is moved to neutral also. When the turn is complete, the wing is rolled back level with simultaneous aileron and rudder control.

Yep, that was my point exactly. It isn't "always" necessary, technically, to use the wings to produce the "turn". In a rudder turn the tail section is "yawed" to change direction. The majority of lift is still provided by the original forces, wing and fuse, however in this instance the turn has occured by the yaw of the tail which was produced by the rudder movement.
BeePee is correct, in a coordinated turn, my point was only that there is another way which does not use the wing, you know, for arguments sake.

Just trying to show all avenues, you know, that WW3 thing.

Ken

The Pilot

These are the 180 degree-turn procedures:


1-Ailerons bank the aircraft

2-Up elevator is applied after neutralizing the aileron sitck. Then, holding the up elevator in a turn makes the airplane turn.

3-Elevator stick is neutralized when the turn is over

4- Opposite aileron is applied to stay on course.


That's simple!

This is almost right. If the turn is to be level, elevator must begin to be applied as soon as the wings begin to bank and increase until the maximum bank angle is reached. Up elevator is held as long as the airplane is turning. When rolling the wings level, up elevator is reduced as the bank is reduced so that when the wings reach level, up elevator is no longer required.

Up elevator doesn’t turn the airplane, it is only necessary to maintain altitude for a level (or climbing) turn. The airplane will turn anytime the wings are banked, however if up elevator is not applied the airplane will also descend.

So a related question.

What goes on when I see a pylon racer make a turn. It almost looks like they approach the turn in a knife edge and make the turn with the elevator (w/conventional tail). I'm not sure what goes on with a v-tail. Is that really what is going on? Why would this be a good way to make a quick turn?

Carl

You'll note that they don't stay in that knife edge for long. Ever whatched a swallow fly? They flit their wings a few times then fold them and "coast" for a second in a nice little arc before flitting again. LIke the swallows the pylon models coast for a moment with some help from the fuselage side area. And they don't turn only because they are typically set very close to neutral stability so they don't "lift" around in a turn until they add the up elevator. But if they went to knife edge a 1/ or 1/2 second earlier the model would side slip and loose more altitude most likely.

Having only seen about 1/2 a dozen pylon models fly ever this was my impression. I think the "hang time" looks longer only because they cover so much ground in that moment

How do any of the above responses apply to a flying wing-type aircraft, such as the B-2? No rudder, no fuselage.

Lachlan

"Up elevator doesn’t turn the airplane" This is absolutely true when you use a bumping method to keep the aircraft on course. However, to make a U shape turn or constant altitude turn, up elevator is held in throughout the turn. That aerodynamically means that the up elevator turns the aircraft while making a 180 degree-turn.

all factual large/full scale aircraft aside. I would like to see you land/ control, turn, a model airplane, no aeilerons, with out a rudder. you may be experts on fullsize aircraft, but we are in models talking to modelers. this not an egineering school. dick

A flying wing turns the same way a more conventional aircraft turns. The wing is banked and for a level (or climbing) turn its angle of attack is increased, using whatever control passes for an elevator. There isn’t much information publicly available regarding the control system of the B-2 bomber, but it’s probably safe to assume that it is computer controlled and doesn’t necessarily depend on aerodynamic surfaces for stability. From the pictures it appears that the things that looks like split ailerons provide yaw control (the equivalent of a rudder). The flap like things near the rear of the wing are the angle of attack control (the equivalent of an elevator).

To fly a turn, the roll control is used to bank the wing, and the yaw damper (or computer) uses the yaw control to eliminate any adverse yaw. Simultaneously the pitch control increases the angle of attack enough to maintain level flight.

Like most things in life there's no simple answer. While I agree with Lou about the turn being "built in" for most aircraft there are always exceptions. Pattern and hardcore aerobatic sport models or the hot pylon racers mentioned above that are trimed to dead on neutral stability do not have even the most basic decalage or longitudinal dihedral (as in up trim) to produce the basic turn once banked. Without that built in pitch stability or application of up elevator the model will side slip right into the ground. But in reality that is a very special case that applies to a very small percentage of aircraft be they models or full sized. For the rest there's enough built in decalage to provide at least a minimum of the up elevator trim to "climb" around the turn even if that turn is a spiral dive.

I say there's no one single control that turns the plane. The aileron or rudder plus dihedral is neccesary to bank the craft and then the positive pitch stability or elevator input is used to make the airplane pitch up around the turn. So it takes TWO controls or factors to provide even a basic spiral dive type turn.

Hey, thanks! That sure made sense. Isn't that plane beautiful? And utterly amazing! To see one actually fly is inspiring, to say the least.

LM

Full size aircraft and models all work the same way. The wing must be banked to fly a coordinated turn. If there are no ailerons the model must have some dihedral effect so that the yaw introduced by the rudder will roll the wing into a bank. I flew rudder only R/C models for years before I ever had the luxury of elevator and throttle control. The rudder was used to bank the wings (due to the dihedral) which caused the aircraft to turn.

Turns were quite well done without elevator control as well. All that is necessary to turn an airplane is to bank the wing. Of course, since in a banked condition some of the lift is tilted sideways the airplane will not maintain altitude unless elevator is also applied. But the purpose of up elevator is to maintain altitude, not turn the airplane.

To understand steep turns like the pylon racer, it’s necessary to understand that the force that pulls the aircraft around a turn always comes from the wing. The steeper the bank, the more force the wing must provide. In fact to maintain altitude in a sixty-degree bank it must provide twice the force required in straight and level flight. This additional force is produced by increasing the angle of attack with the elevator. An airplane can’t maintain altitude in a coordinated turn with a vertical bank.

The pylon racer will often enter the turn a little high, roll into a vertical bank, pull as much additional lift as possible without stalling the wing and accept the inevitable loss of altitude during the tightest part of the turn. As BMatthews said they “coast” in this vertical bank condition momentarily before rolling out of the turn. They would not intentionally fly actual knife-edge, as the resulting sideslip would add drag that would eliminate the advantage of a tighter turn.

The original question asked was, “what makes an airplane turn?” It didn’t ask what controls were used. Obviously, several controls are used to fly a turn but it’s the bank that turns the airplane.

Well all answers are good.As far as dihedral needed for a rudder turn to bank the wings imagine this. Left rudder input causes the right wing to go faster than the left and produce more lift and produce a roll. In level flight a aircraft must prduce 1g of lift anymore or less will cause it to climb or descend. So in aturn this 1g is vectored into the turn direction even without control input to maintain height the aircraft will do a descending tun. Remembering that the primary effect of rudder is yaw and the secondary effect is roll. A 60 degree banked turn requires 2g to maintain level flight. To work out a planes stalling speed at 2g you get the square root of the g(2) wich is 1.4 times the planes clean stall speed, no flaps.At 55kts times 1.4 gives a stalling speed of 77 kts, under this speed the aircraft will stall and drop. This is true with models and full size. So when pulling massive g`s out of adive with a big heavy model watch out for the high speed stall on high rates. By the way this stick position will be the same at any speed and if your ever there dont pull more ease of up the gass or again your wings wont save your tail! B-2 is awesome

I know the pylon racers at our field spend a lot of time trimming to get very little drop or rise at turn 1.

Sorry, my question on the Pylon racers was phrased poorly. I realize that a racer is not in an actual knife-edge and was really trying to describe the relatively "vertical bank" that seems to start early in the turn. I've called "cuts" at turn 1 at a couple of events and (from the side of the field) it sure looks like the planes are flying with banked wings but straight as an arrow. Thinking on this, if the pylon racer is going 150 mph it would take several seconds and several football fields to turn in a 1 or 2 g bank. So Bruce must be correct the entry and exit from the turn look really stretched out because of the velocity of the planes. Clearly the appearance of straight flight is enhanced by a side view, also.

I'm still wondering if the final quick and violent change in direction, in this case, is done by elevator input (to maximize AOA and force a very high-g turn) or is it just banked to nearly vertical?

At the speeds they are going you would not expect much of a vertical drop in the fraction of a second that it takes to do the sharpest part of the turn, even if you lost all vertical lift.

Carl

That is absolutely correct. A turn requires the coordination of all flight controls. However that wasn’t the question asked. The question was “What makes an airplane turn?” The answer is that the force produced by the wing when tilted to one side makes the airplane turn. A coordinated turn is only possible with a banked wing. To bank and unbank a wing and control altitude, requires several control inputs as described throughout this thread.

In the case of an aerobatic model balanced to neutral (or even negative) stability, if the wing is producing lift due to control input or trim, it will turn if banked. The thing that turns an airplane is the tilted force produced by a lifting wing. It really is that simple.

Well said. I think you have described the pylon turn quite well.

When the rudder is used to bank an aircraft, the slight differential in speed between the advancing wing panel and the retreating one is not enough to produce the difference in lift needed to bank the aircraft...unless the wings are extraordinarily long. The reason the plane will bank is because of the dihedral in the wing panels. When the plane is yawed, say to the left, the right wing is advanced ahead of the left wing. The wing's dihedral then causes an increase in the angle of attack vis-a-vis the relative wind. The left wing will
"see" a reduction in AOA to the relative wind. This causes the bank.

A swept-wing aircraft will experience a similar effect because when the aircraft is yawed, one wing now has "more" span exposed to the relative wind, and one wing has "less" span exposed. This also causes a differential in lift, which causes the bank.

If the speed of the advancing/retreating wing panels was the main reason, then low-wing models with zero dihedral, such as the Top Flite Contender would still have positive roll couple with yaw. They do not. They act just the opposite, with right yaw producing zero or left bank. The adverse roll couple is caused by the same reason as above, except the advancing wing now "sees" less of an AOA to the relative wind, and the retreating wing "sees" more.

All of the above can be easily seen visually if you use a high-wing model with dihedral and a fixed point from which to view. Set the model dead-on and the viewpoint ahead of the model such that both wings have an equal appearance. Now yaw the wing a few degrees one way. From that same viewpoint you'll see more of the underside of one wing that the other. The wind "sees" this as if the entire wing panel pivoted its leading edge upward. The increased AOA causes more lift on that side. You'll see more of the upper side of the opposite wing panel. That means that the apparent AOA to the relative wind has decreased, and the lift produced is reduced.

Wolfgang Langeweische's book, "Stick and Rudder", presents a very clear picture of how an airplane flies, and how the pilot controls it. as any book I've ever read. Please be advised that he presents all of this in a phenomenological manner, and not in a truly scientific way. His book is concerned about having clear mental pictures of what's going on so that the pilot can do a better job of controlling the aircraft. "True" aerodynamics he leaves up to the designers and scientists. An invaluable book for full-size as well as model pilots.

Pylon turns (the RC type) – Sooner or later in every pylon racer’s career, this subject is discussed and dissected. And there are basically two types of pylon turns, the theoretical perfect turn, and then what most people actually do. First off, the airplanes in the fast classes of racing (428 Quickie), (422 Q-40), and (FAI) are very fast airplanes by modeling standards. The 428 can do around 170 mph, while the other two fill in the gaps to 200. So they are covering around 250-270 feet per second and would need very little top rudder to knife edge the length of the race course.

BUT, testing with radar shows that flying the entire race while in knife edge results in about a 5 mph penalty in top speed. While this might also result in the shortest distance, it is not typically the course flown by the top competitors. A faster path results in the airplane flying with a bank angle of around 45 –60 degrees, and then rolling to near vertical at the turns. Now any airplane that is trimmed for level flight when the wings are level will require a slight amount of up elevator when banked to this angle, resulting in a very large radius turn (around 1800 feet) while the airplane is loaded at about 1 ½ g’s. What this looks like in the air is the airplane come out of the tight turn at the pylon with the wings near vertical, and rolls out to the 50 degree bank. Because of the release point of the elevator and the big radius flown to the other end of the course, the airplane will move about 25 feet wide of a straight line path before returning to the next turn entry point. The pilot then rolls up to the vertical and does the next turn. Do this 20 times in about 1 minute, and you have just finished a heat.

WHY? When the airplane is in the vertical, pulling g’s, it is pulling around 30 to 40 g’s which causes a great deal of drag. To lower this drag, high aspect wings are now used within the limits of the rules. But another method of reducing this drag is to cut the turn short. So an event that looks to the causal observer to be 20 turns of 180 degrees is really 20 turns of about 166 degrees interspersed with 20 turns of about 14 degrees. Since less time is spent slowing down in the high g turns, the model is able to maintain a higher average speed. Now it is true that the airplane is flying a longer path, but the difference in length is rather small.

As far as the actual bank angle in the high g turns, is it 90 degrees? I use the turns to gain or lose altitude by banking less than 90 to gain, while overbanking to lose it. One must also remember that the course is very dynamic with three other airplanes trying to fly a similar path, with corrections for them as well as cross winds included.

High plains & Bax- you guys are right on. Well said.