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Tail Rotor


TimW68
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"With the antitorque pedals in the neutral position, the tail rotor has a medium positive pitch angle. In medium positive pitch, the tail rotor thrust approximately equals the torque of the main rotor during cruise flight, so the helicopter maintains a constant heading in level flight."

 

- Rotorcraft Flying Handbook, Chapter 3

 

Otherwise, we'd get tired left feet! :)

 

Full left pedal -- strong positive pitch

Neutral - medium positive pitch

Right - slight negative pitch (for autorotations)

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"With the antitorque pedals in the neutral position, the tail rotor has a medium positive pitch angle. In medium positive pitch, the tail rotor thrust approximately equals the torque of the main rotor during cruise flight, so the helicopter maintains a constant heading in level flight."

 

- Rotorcraft Flying Handbook, Chapter 3

 

Otherwise, we'd get tired left feet! :)

 

Full left pedal -- strong positive pitch

Neutral - medium positive pitch

Right - slight negative pitch (for autorotations)

 

do they say what type helicopter ?

 

I'm wondering what kind of "assist" they use to hold a positive pitch. The old 269 hi-speed T/R's used a spring in the control system, but the LTS (LowTurningSpeed) newer style used nothing. Remember that a spinning airfoil will find the "path of least resistance" as in no pitch/thrust. Then there is the aerodynamic twisting moment of the blade design, that could add some pitch,,,,,interesting is the study of aerodynamics, huh? :o

 

Maybe that is why the LTS T/R of the 269 has such a forward sweep to the blade? could be the centrifugal twisting moment ?

Edited by pokey
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I wonder if anyone has exparimented with useing an electric motor to drive the tail rotor. The advantages would be numerous and with a small amount of technolongy could make pilotage easier...

Thought's?

 

i dont think it would make it "easier" but could make the drive system simpler. Friend of mine stopped by the other day w/ a tiny remote control electric helicopter, it had what you are talking about The tail rotor motor was about the size of a small pea ! i couldnt believe it was an electric motor ! Now, if that technology can be eventually brought to full size helicopters? who knows !!

 

 

BTW 1bad, that 32 has impressive 1/4 mile times

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i dont think it would make it "easier"!!

The motor would be controlled by a voltage regulator of sorts, if a very small amount of technology were to be biult in, the heli could easily, automaticly maintain a given heading whether it be cruzing or hovering, or even during take off.

 

BTW 1bad, that 32 has impressive 1/4 mile times

 

Thanks,

Im under the impression that you think i have a hotrod of a 1932 vintage??

My SN reference's the car in my sig.. incase there is any confusion.

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Thanks,

Im under the impression that you think i have a hotrod of a 1932 vintage??

My SN reference's the car in my sig.. incase there is any confusion.

 

there is no confusing that "sled" in front of the junkpile was made in 1932. B)

 

back to the electric tail rotor tho: would eliminate the T/R drive system, the pitch change mechanism, the gearbox, and ALL the associated control systems.....would add a bit of wire & a "tiny" electric motor. I hope we see it in the future !

 

(along w/ a 3600 pound z32) ~~~ are ya sure it is that heavy?

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"With the antitorque pedals in the neutral position, the tail rotor has a medium positive pitch angle. In medium positive pitch, the tail rotor thrust approximately equals the torque of the main rotor during cruise flight, so the helicopter maintains a constant heading in level flight."

 

- Rotorcraft Flying Handbook, Chapter 3

 

Otherwise, we'd get tired left feet! :)

 

Full left pedal -- strong positive pitch

Neutral - medium positive pitch

Right - slight negative pitch (for autorotations)

 

While this may be true in most cases it is not in all cases. The RFH likes to keep things simple. When it comes to flying the EC130 while in cruise flight you will have a lot of left pedal input. Just under half depending on the speed you are going. (left pedal since it's a clockwise system)

 

Obviously the faster we go the more left pedal I have to put in to stay in trim. The Fenestron tail rotor is very effective in cruise flight.

 

This is my biggest negitive about the EC130. It takes more effort to fly in cruise flight than any other helicopter I have flown before. I also notice my legs are quite tired after a long days of flying. This could also be in part to the fact that the Fenestron is not hydrualicly boosted so it does take more effort.

 

Just thought I'd point out there is an exception to the rule when it comes to "neutral pedals" in cruise flight.

 

JD

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I'm kinda suprised we dont already have electric driven tail rotor's. Every gear box and drive shaft coupler draw's extra hp from the engine. And when does a heli need the TR most? probebly durning a hover or taking off, would be my guess?

No more need to change pitch to change the effect of the TR, just give the motor more or less voltage, or reverse the voltage polarity to spin the TR in reverse.... if that is ever needed? (auto-rotation?? or spin into the wind?)

 

My Z wieghs 3350, but when i hop in and bolt on the stickies it wieghs 3570. This is with many wieght reductions. Most Z32's curb wieght ~3550-3650lbs

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I don't think y'all are thinking this through. The pitch has to be changed, and changed constantly, to maintain a heading at low speeds, especially at a hover. You have to be able to put in a lot of pitch in both directions, to be able to turn in both directions and to maintain heading in winds from all directions. You never want to slow the rotation speed, and certainly never reverse the direction of rotation. Tiny electric motors are fine for models, but won't do the job for a full-size helicopter. What are you going to use for electrical power? A battery? Charging it takes power, and it's not reliable. Generators and alternators are among the least reliable components on any aircraft, or car for that matter. The tail rotor is too important to be driven by those. If a model crashes, it's just a loss of a little money. With a real helicopter, people can die. Reliability is important, and response time is critical. Mechanical connections will continue to be used.

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I don't think y'all are thinking this through. The pitch has to be changed, and changed constantly, to maintain a heading at low speeds, especially at a hover.

 

With conventional technoligy yes, the fact that the TR is connected to the drive train means it's speed can not be changed, thus the pitch has to be, in order to change its effect.

With an eletric motor the roational speed can be changed, so a fixed pitch would have more or less effect per its speed.

And with a system like fuzzy logic or a simular technology, a control modual could easly vary the voltage for you to mantain the last heading input it was given through the use of the rudder pedal's.

 

You never want to slow the rotation speed, and certainly never reverse the direction of rotation.

In the case of the main rotor blade yes, but if you didnt have a way to change the pitch of the wings the only way to create lift would be to change the speed of the wing.

 

Tiny electric motors are fine for models, but won't do the job for a full-size helicopter. What are you going to use for electrical power? A battery? Charging it takes power, and it's not reliable. Generators and alternators are among the least reliable components on any aircraft, or car for that matter. The tail rotor is too important to be driven by those. If a model crashes, it's just a loss of a little money. With a real helicopter, people can die. Reliability is important, and response time is critical. Mechanical connections will continue to be used.

 

Obviously the motor size would have to be calculated by how much power it would need to make, both peak and sustained.

The charging system would have to be beefed up to handle the extra load from the motor.

Me not being a real pilot (yet), i have to ask.. when you lose an altinator or a charging system, do you just say "oh well" and keep flying??

Or do you start looking for a place to land?

 

I agree its not fair to compair "toy's" to the real thing, but most technology is first tested on smaller less important application's.

 

This disscution is a "fart in the wind" and will have no impact on any aircraft design in the future, but sometimes its fun to colaberate with other people.

And who know's 10 years from now when i finally have the $ to get my PPL, we might have a motor driven TR aircraft, you might fly it and say.... "crap i wish i had this 10 years ago".

Edited by 1badz32
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It's simply not possible to vary only the speed, and not the pitch, of the tail rotor and still provide adequate control. You have to be able to put in pitch in both directions to ensure adequate control under all conditions. The tail rotor has to be able to pitch in both directions.

 

Electrical failure, especially with a turbine engine, is not an emergency, just an inconvenience, unless you're in IMC. I would continue to my destination, as I have before. If the tail rotor is controlled by an electric motor, and you lose electricity, you have an immediate emergency.

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<br />It's simply not possible to vary only the speed, and not the pitch, of the tail rotor and still provide adequate control.

How can you say that with any certainty. Has it ever been tested on a full size air craft? it obviously works with small scale aircraft, so in theory, a larger motor "should" have the same effect on a larger aircraft.

 

Now i dont pretend to be any sort of engineer, or have any of the logistic's figured out, I was just kicking idea's around.

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How can you say that with any certainty. Has it ever been tested on a full size air craft? it obviously works with small scale aircraft, so in theory, a larger motor "should" have the same effect on a larger aircraft.

 

Now i dont pretend to be any sort of engineer, or have any of the logistic's figured out, I was just kicking idea's around.

 

I seem to recall hearing - years ago - about some experiments along this line of thinking. But think about it for a minute: what happens when you want to make a pedal turn against a stiff crosswind, and engine torque isn't enough to give you a positive turn rate? If the tail rotor is only making pitch in one direction, you'd basically have to wait for the wind to die down to make the turn.

 

Unless, of course, the helicopter is on a treadmill... then all bets are off :D

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'1badz32' asked-

"I wonder if anyone has exparimented with useing an electric motor to drive the tail rotor."

Electric anything is another failure mode. Sure, driveshafts, bearings, gearboxes fail. Put that whole list together, and I've had exponentially more generator failures in 40 years than the total. Add starters, the number increases dramatically if not exponentially. Against: 1 drive shaft issue; 1 gearbox issue; 1 control run issue- wait, no 2 control run failures- a bearing and a control cable; all in conventional mechanical systems and successful if stressful. Control failures are another complication that adds even more substance to my NO electric T/R vote- Remember when Blackhawk stabilator control issues caused "Sikorsky lawn darts"? A stabilator is much simpler than your proposal.

 

"The advantages would be numerous and with a small amount of technolongy could make pilotage easier..."

How, exactly, would electric T/R drive " make pilotage easier"? An autopilot in yaw? Learning yaw control AND an autopilot complicates the learning process and the emergency process. Autopilots kill people, too.

 

When the world goes to crap in helicopter flight, the ability to autorotate to a survivable landing is your ace in the hole. Simple sound reliable control runs and the main rotor driving everything makes that a solo maneuver. Don't 'fix' what ain't broke.

 

You want to make helos easier and safer? Eliminate the requirement for control boost while making the aircraft dynamically stable, with a high inertia rotor system that's simpler, lighter, more durable than state of the art designs- less to fail, less to do in the meantime and more options when 'it' happens.

Edited by Wally
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The motor would be controlled by a voltage regulator of sorts, if a very small amount of technology were to be biult in, the heli could easily, automaticly maintain a given heading whether it be cruzing or hovering, or even during take off.

 

Until a wire comes loose or you get a dirty connection.

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I've had an alternator/low voltage light come on four times in seven days. All during steep approaches to confined areas. Had that been a tail rotor drive motor whatsit, I'd be dead, and there would have been quite a bit of wreckage to clean up.

 

I'm all for innovation, especially in helicopters. But mechanical TR gearboxes work. They work well. Not that I ever do, but if I had to do a "the building is on fire and I have to get the heck out of here" preflight, I'm looking at the Main Rotor and the TR.

 

Anyway, that's my story and I'm stickin to it.

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