Transient TQ when turning left
Thread Starter
Joined: Apr 2000
Posts: 196
Likes: 1
From: UK
407: Nice idea, an increase in rotor profile drag (is it still called that?).
Simon: Finish at CFS as B2, 6 months (army) later upgrade to B1. For those that wish to, there are A2 and A1 upgrades should they wish to 'improve'.
Simon: Finish at CFS as B2, 6 months (army) later upgrade to B1. For those that wish to, there are A2 and A1 upgrades should they wish to 'improve'.
Joined: Apr 2000
Aviation Qualifications: ATP+Mil
Posts: 10,959
Likes: 1,814
From: EGDC
Jeep, long time no hear - I don't remember this happening in the hover in the Gazelle but I agree about the rate of roll - you remember we used to demo it going from a left turn into a right turn to show the greatest Tq spike. We also taught that it was due to the nature of the governor ie a reset one with no static droop.
Joined: Jan 2003
Posts: 365
Likes: 15
From: CYPG
Now this is purely uneducated drivel, but could it not have anything to do with the way the shaft spins? (Direction of rotation). (roll against direction of rotation, as opposed to with the direction of rotation?)
Just like the increase in hover height in a turbine with pedal turns (As explaind by Shawn Coyle).
Just a thought...
Just like the increase in hover height in a turbine with pedal turns (As explaind by Shawn Coyle).
Just a thought...
Thread Starter
Joined: Apr 2000
Posts: 196
Likes: 1
From: UK
Crab,
Still alive and kicking matey. I remember the demos well. Static droop allowed in the gem hmg, no static droop in the astazou. The 701 series in the Apache has an impressive tq sqike if you arent careful. The digital control unit, not a full fadec, controls the tq spike when over the 100% mark but its rather easy to get a 30% tq swing when happily winging it around in roll and pitch (for other reasons of course). Hence the questioning of why does it do that. I have heard a few different reasons over the years and thought the experts would give me a defining answer. Of course to your normal 'student' it is easy enough to prove any of the answers to their satisfaction, but to the more enlightened the awkward question can always upset the board work.
Winnie,
I am inclined to think spinning objects/gyroscopic effects are something to do with it. I am waiting for someone to prove it to me
Still alive and kicking matey. I remember the demos well. Static droop allowed in the gem hmg, no static droop in the astazou. The 701 series in the Apache has an impressive tq sqike if you arent careful. The digital control unit, not a full fadec, controls the tq spike when over the 100% mark but its rather easy to get a 30% tq swing when happily winging it around in roll and pitch (for other reasons of course). Hence the questioning of why does it do that. I have heard a few different reasons over the years and thought the experts would give me a defining answer. Of course to your normal 'student' it is easy enough to prove any of the answers to their satisfaction, but to the more enlightened the awkward question can always upset the board work.
Winnie,
I am inclined to think spinning objects/gyroscopic effects are something to do with it. I am waiting for someone to prove it to me
Joined: Nov 2003
Posts: 90
Likes: 0
From: Scandinavia
Just a thought
Does this happen to all helicopters?
If it does, then shouldn't it be noticeable in autorotation as well? Of course the rotor will spin faster in the turn, but it should wind up faster when rolling right than left if there is some sort of resistance in the rotor-system, gyroscopic or mecanic. Or will it be too small difference to notice?
If there's no difference maybe that shows that the reason for the spike is on the engine-side of the freewheel and not the rotor-side?
Or probably I'm way off, it's known to happen
/2beers
If it does, then shouldn't it be noticeable in autorotation as well? Of course the rotor will spin faster in the turn, but it should wind up faster when rolling right than left if there is some sort of resistance in the rotor-system, gyroscopic or mecanic. Or will it be too small difference to notice?
If there's no difference maybe that shows that the reason for the spike is on the engine-side of the freewheel and not the rotor-side?
Or probably I'm way off, it's known to happen
/2beers
Thread Starter
Joined: Apr 2000
Posts: 196
Likes: 1
From: UK
2beers,
I am sure it is happening in auto, should you put a roll input in, but as your NR is allowed to fluctuate in autorotation, the transient rise or fall is masked - the nr moves instead of tq change.
Have another one.
I am sure it is happening in auto, should you put a roll input in, but as your NR is allowed to fluctuate in autorotation, the transient rise or fall is masked - the nr moves instead of tq change.
Have another one.
) 
Joined: Apr 2000
Aviation Qualifications: ATP+Mil
Posts: 10,959
Likes: 1,814
From: EGDC
It is the stated fact that this happens in a zero wind hover that is perplexing - the occurence in fwd flight is easily explained by the changes in drag on the advancing and retreating sides as mentioned earlier.
To produce an increase in tq when rolling left (US rotation) the aerodynamic load must increase as drag rises and the Nr tries to decay - therefore the opposite must occur when rolling right.
Any gyroscopic theorists have any data about precession rates with and against the direction of rotation - does a gyro speed up if it precesses against the direction of rotation (spin axis)?
As soon as you remove the advancing and retreating side inequalities from this argument it becomes very confusing - any yaw due to sideslip that might have the effect of increasing or decreasing the Nr would be very small and short-lived in the hover, unless you were prepared to let it sideslip into the ground for the sake of science.
To produce an increase in tq when rolling left (US rotation) the aerodynamic load must increase as drag rises and the Nr tries to decay - therefore the opposite must occur when rolling right.
Any gyroscopic theorists have any data about precession rates with and against the direction of rotation - does a gyro speed up if it precesses against the direction of rotation (spin axis)?
As soon as you remove the advancing and retreating side inequalities from this argument it becomes very confusing - any yaw due to sideslip that might have the effect of increasing or decreasing the Nr would be very small and short-lived in the hover, unless you were prepared to let it sideslip into the ground for the sake of science.
Joined: Jul 1999
Posts: 3,931
Likes: 142
From: Warrington, UK
Not sure if this will help. Just been flying, EC 135 with full FADEC, 80kts S&L, fairly vigorous left turn to about 30 deg of bank gave a Tq increase of between 3 - 5%. Corresponding drop in Tq for right turns.
Don't ask me what it means. That's why I never got past B1!
Don't ask me what it means. That's why I never got past B1!
Joined: Apr 2003
Posts: 3,012
Likes: 1
From: USA
crab,
It was me who asserted that it is there at all speeds. I did hundreds of maneuvers in 'Hawks and S-76 to understand the nature of maneuverability once upon a time, work that lead to an AGARD tech report and several AHS papers, and that helped lay out the Comanche's main and tail rotor systems. When next in the cockpit, (next week) I will repeat same to confirm.
My speculation then and now is that the engine/drivetrain system, including tail shafting, is all rotating the same way, and the delta torque of that system is a contributer, perhaps via a conservation of angular momentum. The effect is not in pitch in a hover, telling me it is not purely a main rotor effect (not H force, for example) and it follows roll acceleration and rate, even into rearward flight.
I will do some calculations based on inertias and velocities in a few days (when my ears stop ringing from having been boxed!)
It was me who asserted that it is there at all speeds. I did hundreds of maneuvers in 'Hawks and S-76 to understand the nature of maneuverability once upon a time, work that lead to an AGARD tech report and several AHS papers, and that helped lay out the Comanche's main and tail rotor systems. When next in the cockpit, (next week) I will repeat same to confirm.
My speculation then and now is that the engine/drivetrain system, including tail shafting, is all rotating the same way, and the delta torque of that system is a contributer, perhaps via a conservation of angular momentum. The effect is not in pitch in a hover, telling me it is not purely a main rotor effect (not H force, for example) and it follows roll acceleration and rate, even into rearward flight.
I will do some calculations based on inertias and velocities in a few days (when my ears stop ringing from having been boxed!)
Joined: Sep 2001
Posts: 1,051
Likes: 0
From: CA
Its been a long time since I studied the aerodynamics; so patience with the lay terms and my ignorance.
Is it possible that the inc. in TQ turning into the advancing blade is correlated to the coupling through the main rotor and the thrust from the tail rotor.
You could also ask the question "why do helicopters turn more easily in one direction, than the other"
Two forces to the right (USA) assisting the turn, only one through the mast for a left hand turn.
Thus it takes more "effort" for the aircraft to change its attitude left as opposed to right. Effort = Torque.
Has anyone noticed at the start of the reality TV show "The Apprentice" when the S76 does the break to the left that the tail "tucks" into the turn? Sloppy flying or something else?
Is it possible that the inc. in TQ turning into the advancing blade is correlated to the coupling through the main rotor and the thrust from the tail rotor.
You could also ask the question "why do helicopters turn more easily in one direction, than the other"
Two forces to the right (USA) assisting the turn, only one through the mast for a left hand turn.
Thus it takes more "effort" for the aircraft to change its attitude left as opposed to right. Effort = Torque.
Has anyone noticed at the start of the reality TV show "The Apprentice" when the S76 does the break to the left that the tail "tucks" into the turn? Sloppy flying or something else?
Joined: Apr 2000
Aviation Qualifications: ATP+Mil
Posts: 10,959
Likes: 1,814
From: EGDC
Nick, if it is not noticeable in pitch then that must add weight to your drive-train theory since pitch attitude changes are in line with the drivetrain and the Tq spikes are only caused by attitude changes perpendicular to the drive-train.
Steve76 - you have hit on a question that has long been unanswered 'why does the helo turn more easily one way than the other'. I have always found wingovers easier to the right on a US rotation and to the left on a French rotation which correlates to the reduction in Tq when you roll against the direction of rotation. Has TR thrust got anything to do with it? I'm sure it has but not as the major cause.
Steve76 - you have hit on a question that has long been unanswered 'why does the helo turn more easily one way than the other'. I have always found wingovers easier to the right on a US rotation and to the left on a French rotation which correlates to the reduction in Tq when you roll against the direction of rotation. Has TR thrust got anything to do with it? I'm sure it has but not as the major cause.
