FF Cordinated Right Turns

[TuDogs]

Fast flight coordinated right turns are giving me a problem. All out left turns seem to be no problem. Could one of you pro guys explain this to me. My solution right now is to try not to make many high speed left turns because I have them down pretty well.

Now I have noticed that a high speed turn to the left seems very natural, but correct me if I am wrong, altitude management becomes a real issue banking and yanking to the right. I do not have a problem flying the tail. I suspect that when the blades are turning into the direction of the turn, at high forward speed, there are some blade flapping, rotational or blade lag physics coming into play. My head probably thinks a right turn is the same as a left, and I need to do them differently.

Practice
Practice
Practice
CRASH
Rebuild
Practice etc. etc. etc.

[Skarn]

This is natural....everyone has a turn direction that is more difficult that others. Mine is right turns as well. This carries over to almost everything....when skiing, I can carve incredible left turns, but to the right is not as natural. Same with my motorcycle.....hard leaning lefts are nothing, but the rights are more difficult.

But with heli's, due to the tail rotor direction, right turns are harder anyway.....

Skarn

[Aussie_G]

Interesting..

I have problems with left turns, I can do both, but left always looks uncoordinated and just doesnt feel natural to me.

[Skiddz]

In reality, the right turn (from the heli's perspective, not yours) takes a little more power. The reason is the TR has to yaw the heli to the right to maintain a coordinated turn. Pushing the nose to the right requires the TR to not only just counteract the torque of the main rotor, but provide even more thrust to over come that torque.

You ARE adding a bit of power when you roll into the turn and removning it when you exit, right? In order to maintain speed and altitude, you'll have to do so.

[vera]

"the TR has to yaw the heli to the right to maintain a coordinated turn."

Actually, the tail will weathervane if not for a gyro. In full size helis there is no gyro trying to hold heading or oppose heading changes, and so no rudder is applied to help the turn. Of course the same is true for a RC heli that has no gyro. Whatever amount of rudder is required to counter torque, it stays the same if the forward speed stays the same regardless of turns. In the RC world almost everybody uses a gyro nowdays and of course that thing trys to block heading changes, and so rudder input is required. But that rudder input isn't changing the pitch on the tail blades (if the turn is coordinated, no slip or skid), it's just preventing the gyro from changing the pitch to fight the turn.

[Skiddz]

"the TR has to yaw the heli to the right to maintain a coordinated turn."

Actually, the tail will weathervane if not for a gyro. In full size helis there is no gyro trying to hold heading or oppose heading changes, and so no rudder is applied to help the turn.

Well, that's good because (most) full scale helis don't have a "rudder" (BTW: I'm a commercial heli pilot IRL) Virtually all pod 'n boom helis have vertical fins that help the weathervaning you speak of. Crank a heli over in an aggressive turn and you'll certainly use some TR control to stay coordinated.

Of course the same is true for a RC heli that has no gyro. Whatever amount of rudder is required to counter torque, it stays the same if the forward speed stays the same regardless of turns. In the RC world almost everybody uses a gyro nowdays and of course that thing trys to block heading changes, and so rudder input is required. But that rudder input isn't changing the pitch on the tail blades (if the turn is coordinated, no slip or skid), it's just preventing the gyro from changing the pitch to fight the turn.

And that stick input "preventing" the change most certainly would change the pitch of the blades. You don't think a gyro in rate mote changes the pitch of the TR to keep the tail more or less "behind" the heli in a turn?? The power change to maintain airspeed and altitude will most certainly require some TR pitch change..

[vera]

"(most) full scale helis don't have a "rudder"

Yeah, but we call those things on the floor "rudder pedals" anyway. (ATP MEL fixed wing, commercial rotorcraft, cfi, ifi) Many heli pilots start out on airplanes cuz it's a cheaper way to go, so they're used to rudder pedals and it's easier to say than "anti torque pedals", and the RC control box calls that stick the rudder control. But unlike airplanes, where the rudder is used to correct for adverse yaw caused by differential drag resulting from aileron deflection, the heli contraption doesn't suffer that anomoly.

"You don't think a gyro in rate mote changes the pitch of the TR to keep the tail more or less "behind" the heli in a turn?? "

No, I don't. The gyro attempts to prevent changes on the vertical axis, regardless of rate or HH mode. In HH mode the gyro "remembers" what heading it's supposed to be on so as to be able to return to it, rather than simply trying to stop any change of heading which tends to accumulate errors rather than undoing them.

"The power change to maintain airspeed and altitude will most certainly require some TR pitch change.."

Agreed. A change of torque or rpm or forward speed changes the required tail pitch.

[Skiddz]

Yeah, but we call those things on the floor "rudder pedals" anyway. (ATP MEL fixed wing, commercial rotorcraft, cfi, ifi) Many heli pilots start out on airplanes cuz it's a cheaper way to go, so they're used to rudder pedals and it's easier to say than "anti torque pedals", and the RC control box calls that stick the rudder control. But unlike airplanes, where the rudder is used to correct for adverse yaw caused by differential drag resulting from aileron deflection, the heli contraption doesn't suffer that anomoly.

hehe, I must be the odd man out 'cuz I've never called 'em rudder pedals. I just call it a "pedal input".. I sorta cringe here when I tell someone to add a "rudder" input...

No, I don't. The gyro attempts to prevent changes on the vertical axis, regardless of rate or HH mode. In HH mode the gyro "remembers" what heading it's supposed to be on so as to be able to return to it, rather than simply trying to stop any change of heading which tends to accumulate errors rather than undoing them.

It'd be interesting to put a logger on the TR servo and the Tx's stick to see exactly what's going on. Next time I go flying (full scale) I'm gonna leave my feet on the floor in both right and left turns with no power changes and watch the turn coordinator and see what happens. I don't know if I apply a pedal input in turns or not. I've gotten to the point where flying is sort of an "unconscious" effort and I don't think about what I'm doing, it just sorta happens..

[vera]

"I must be the odd man out 'cuz I've never called 'em rudder pedals."

Yeah, it feels kinda cringey... but the TX box and even the RX refers to "rudder". When I was teaching full scale rotors all my students came from airplanes and although they knew the right terminology we all referred to "rudder".

"It'd be interesting to put a logger on the TR servo and the Tx's stick to see exactly what's going on."

Wouldn't it be cool to have telemetry. We could have a heads-up display on sunglasses, eyeball the heli and see the gauges. What a rush that would be. RC ILS contest?

"watch the turn coordinator and see what happens"

Cool. Then, leave the collective alone also, else the torque will change. Keep this in mind. The ball of the TBI is not on the longitudinal axis (most likely anyway). Let's say you're in the right seat, so your TBI is on the right side of the axis. Roll right swings the ball to the outside of that circle, which is to the right. During the roll this off-center ball is due to the roll itself... centrifugal force ... or is it centripetal ... working on the ball. Anyway a rapid right roll will swing the ball (on the right side TBI) to the right. The ball in the TBI on the other side will swing out to the left in the right roll. In short, the ball gives erroneous reading DURING the roll unless it's located on the centerline. Also you're gonna need to coordinate back stick right away because you're trying to accelerate the rate of heading change from zero to something. If you just lay it over without back stick it surely will slip, but rudder is the wrong gadget to fix that even if it makes the ball happy. The acceleration that brings on the turn will have to come out of altitude. Roll into the turn coordinating back stick and check the ball when the roll is stopped. Ignore the ball while the roll is going on.

[Skiddz]

Yeah, it feels kinda cringey... but the TX box and even the RX refers to "rudder". When I was teaching full scale rotors all my students came from airplanes and although they knew the right terminology we all referred to "rudder".

I still hear the new students call it "aileron and elevator" too. I want to yell across the hangar and correct 'em, but don't want to step on their instructor's toes. I'm sure the DPE will zing 'em on it should they go for a check ride. :)

Wouldn't it be cool to have telemetry. We could have a heads-up display on sunglasses, eyeball the heli and see the gauges. What a rush that would be. RC ILS contest?

You mean like this: http://eagletreesystems.com/press/spektrum.pdf ?? 3D in heavy fog.. Now that'd be a trip. hehehe


Cool. Then, leave the collective alone also, else the torque will change. Keep this in mind. The ball of the TBI is not on the longitudinal axis (most likely anyway). Let's say you're in the right seat, so your TBI is on the right side of the axis. Roll right swings the ball to the outside of that circle, which is to the right. During the roll this off-center ball is due to the roll itself... centrifugal force ... or is it centripetal ... working on the ball. Anyway a rapid right roll will swing the ball (on the right side TBI) to the right. The ball in the TBI on the other side will swing out to the left in the right roll. In short, the ball gives erroneous reading DURING the roll unless it's located on the centerline. Also you're gonna need to coordinate back stick right away because you're trying to accelerate the rate of heading change from zero to something. If you just lay it over without back stick it surely will slip, but rudder is the wrong gadget to fix that even if it makes the ball happy. The acceleration that brings on the turn will have to come out of altitude. Roll into the turn coordinating back stick and check the ball when the roll is stopped. Ignore the ball while the roll is going on.

Most definitely. I'd have to get established in a constant rate/altitude turn at various bank angles and do at least one full 360 to see what's going on. I'm sure wind will have some effect as well, so I'll have to try and enter the turns from the same position, heading and airpseed each time to minimize any "errors" caused by the wind. I'm gonna head over the FBO in a minute and see if I can get a heli for tomorrow or Sunday...

[vera]

"I'm sure wind will have some effect..."

Only in relation to ground track, which is a thing the aircraft doesn't know about. If you hold a steady rate of turn then of course you'll fly a perfect circle through the air. If there's any wind it won't be a circle over the ground, but the aircraft doesn't know about that.

One of the things that trips up airplane pilots is making a turn towards a downwind direction. As the ground speed increases the pilot reacts by pulling up, thinking he must be diving on account of the gained ground speed... which has lead to more than one fatal stall. Ground speed doesn't mean a thing to the aircraft.

Think of a boat in a river. If it's anchored then it experiences the current of the river. If the anchor is pulled then it drifts with the river and there is no longer any current as far as the boat is concerned.