Torquing helicopters

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Cacophonix
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Torquing helicopters

#1 Post by Cacophonix » Thu Dec 13, 2018 3:42 pm

Polite question for the rotary cognoscenti here who feel inclined to answer.

I am doing a spot turn, to the right, in an R44 (anticlockwise rotor) and putting in right pedal, am I right (no pun intended) in saying that TRPM (tail rotor RPM) will decrease thus increasing RRPM (main rotor RPM) and increasing main rotor torque.

If I am correct in the statement above, then what is the best measure or indicator to be looking at to ensure that I don't over torque the engine. I guess I am asking, what is the relationship between torque and RPM? I guess it is clear that torque is proportional RRPM but is it so in all cases in a helicopter...?

Am I, as usual overthinking this?


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Re: Torquing helicopters

#2 Post by G~Man » Thu Dec 13, 2018 5:56 pm

You are correct but yes you are over thinking it. The RPM will only increase if you make a violent maneuver. As long as you make mellow controlled inputs you will not notice a difference. Having said that, it is 25 years since I flew an R-44, (serial #7).
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Re: Torquing helicopters

#3 Post by CharlieOneSix » Thu Dec 13, 2018 6:32 pm

Caco - as G~Man says, you are overthinking it. Tail rotor rpm can't change unless the main rotor rpm changes. In an R44, putting in right pedal reduces the angle of attack of those blades, and therefore the drag. There is therefore less power demanded by the tail rotor. Imperceptibly the main rotor rpm would tend to increase, this would be sensed by the governor (or the pilot in a non-governed machine) which would reduce fuel flow to the engine so that the datum rotor rpm are maintained. As a result the torque would reduce.

As you know, the aim in powered helicopter flight is to keep the rotor rpm constant - whether that be measured as a percentage (usually 100%) or as a defined numerical rpm. Torque will only change by the power required to keep the rotor rpm constant, so torque is proportional to power required to maintain RRPM rather than RRPM itself.

Left pedal = increased torque; Right pedal = Reduced torque......unless you're flying one of those froggie or russkie machines and then it's reversed. Throw in a bit of w/v during your spot turn and you'll be working so much like a one armed paperhanger that you won't notice the subtleties I describe! :D

Tip. In a strongish wind always do your R44 spot turn to the left first of all. If you haven't got enough power to turn 90 degrees to the left then you can always come back into wind. If you did it to the right first and it runs away with you then you possibly might not have enough left pedal/torque to stop it.
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Re: Torquing helicopters

#4 Post by Cacophonix » Thu Dec 13, 2018 7:52 pm

Thank you to G~Man and C16 for the advice. Great thing to be able to ask the pro's and get the real gen on these matters.

Much appreciated.

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Re: Torquing helicopters

#5 Post by G~Man » Thu Dec 13, 2018 11:38 pm

Incidentally, this is the last R-44 I flew...... It had made a hard landing on a pinnacle in the Shasta mountains and the insurance company paid us to go fetch it.
100_1438.jpg
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Re: Torquing helicopters

#6 Post by Seenenough » Fri Dec 14, 2018 3:42 am

I was taught that you should not have to think about which pedal to push.It does not matter which way the disk turns as they all need a bit of counter pedal on lift off.Your feet should naturally react to the movement of the nose.

One side pedal absorbs power and the other reduces power requirement.

Get over the square and square bash.I found it the best way to develop feel.

We all went though thinking about it but in the end it becomes a feel.

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Re: Torquing helicopters

#7 Post by Cacophonix » Fri Dec 14, 2018 4:34 am

Seenenough wrote:
Fri Dec 14, 2018 3:42 am
I was taught that you should not have to think about which pedal to push.It does not matter which way the disk turns as they all need a bit of counter pedal on lift off.Your feet should naturally react to the movement of the nose.

One side pedal absorbs power and the other reduces power requirement.

Get over the square and square bash.I found it the best way to develop feel.

We all went though thinking about it but in the end it becomes a feel.
Many thanks for the good advice. Much appreciated.

I am in the square bashing phase at the moment but have developed a "thing" about the idea of over torquing an engine after my instructor told me of a student who had done exactly that at another flying school in a Bell 206, and about the concomitant expense. While it is true that I do overthink, I am happy to say I am now slowly beginning to develop "happy feet" but always like to know why I am doing something and take comfort from your words of experience and wisdom.

C16's timely advice about turning left first in a spot turn in a strong wind being the kind of advice my addled noodle might not have appreciated intuitively at this stage.


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Re: Torquing helicopters

#8 Post by CharlieOneSix » Fri Dec 14, 2018 9:01 am

Seenenough wrote:
Fri Dec 14, 2018 3:42 am
I was taught that you should not have to think about which pedal to push.It does not matter which way the disk turns as they all need a bit of counter pedal on lift off.Your feet should naturally react to the movement of the nose.....
Absolutely! Just like learning to drive where the interaction of clutch, accelerator, gear lever etc all seemed a black art initially but soon evolved into one smooth coordinated movement.
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Re: Torquing helicopters

#9 Post by Seenenough » Fri Dec 14, 2018 12:56 pm

When in a ground effect hover make small changes to the collective without any pedal input and get used to the nose moving left and right as this will become important later on for emergecy training when learning to land without tail authority.Throttle changes are another way to to move the nose.

Also learn to listen to the machine as the changes in the sound it makes also tells you things.You can very clearly hear a machine that is laboring close to its limits.It is particularly evident with piston powered machines.

Every time I did a type conversion first thing I did to feel the machine was to go and square bash with it.

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Re: Torquing helicopters

#10 Post by G~Man » Fri Dec 14, 2018 5:37 pm

Forgive my ignorance, but what is "square bashing"?
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Re: Torquing helicopters

#11 Post by Seenenough » Fri Dec 14, 2018 7:38 pm

Most training facilies have a square helicopter landing pad or two on the on the air field out of the way of traffic.

For hover training we were taught to move the helicopter while hovering in ground effect moving around the perimeter of the square with the nose staying pointed on a heading both clockwise and then anti clockwise then move around the perimeter of the square keeping the nose pointed to the center of the pad also in both directions.Into wind,wind on the sides and also wind on the tail.

There are lots of things you can do but they all develop coordination between the hands and the feet.You also get to learn how to feel what the helicopter does and how it reacts to control inputs.It especially develops fine hover control which is necessary particularly later on when doing underslung work.

It is also very good to learn how to avoid getting white knuckles and leg cramps and staying relaxed with the machine.

The other exercise that teaches hand and feet coordination is doing quick stops.

I found it much more fun to do than circuits and landings which in a helicopter are quite boring.

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Re: Torquing helicopters

#12 Post by G~Man » Fri Dec 14, 2018 8:18 pm

Thanx
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