My '74 helicopter

Jens

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Really - how much and how often do a tail rotor push in the wrong direction...!

Really - how much and how often do a tail rotor push in the wrong direction...!

You sure don't listen to any of us who have!
I can listen to 'tons' of explanations, here on the forum, why a tail rotor is needed for counter acting the torque from the rotor.
To my knowledge, there are no explanations to listen to, how often and when we need a tail rotor to help the frame the wrong way around.
 

brett s

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I already listed a couple, remember? Do you plan on always descending using a lot of power, or never autorotating?

It doesn't matter how often you need the capability, if you don't have it when you need it you're screwed - and those times aren't unusual to encounter in everyday flying.

Most tail rotors have a few more degrees of pitch available in the direction for countering rotor torque, they also still have a significant amount in the other direction.

But you've already made up your mind that it's not required, all those other helicopter designers must be crazy & experienced pilots don't know what they're talking about :lalala:
 

Jens

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Brett, I don't think we disagree a lot.
It is surprising to me, that the need of opposite push from a tail rotor, aren't unusual to encounter in everyday flying.
That is not instantly self evident to me, so I will pay attention to this, and maybe one day I will get what this is all about.

Until then, I think one could fly safely with a prop as tail rotor – even driven by a hyd.

A statement similar to: “You can drive a car with 2 wheel brakes”.

But I might be wrong - has happen before :D
 

C. Beaty

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Jens, even torqueless helicopters more often than not have tail rotors.

The Hiller Hornet ramjet helicopter had a small, 1 blade tail rotor. Canted vanes have sometimes been used in torqueless helicopters but yaw control is marginal in many situations.

In a standard torque driven helicopter, the disconnect (over running clutch) between engine and rotor is normally between 1st and 2nd reduction stages. The drag of the gearbox tends to rotate the fuselage in a direction opposite to power on condition, requiring opposite thrust from the tail rotor.

In an autorotative landing, positive yaw control is essential.
 

Vance

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Part of the take off sequence that I was taught in a helicopter was to do a 360 degree turn to look for traffic.

I trained to fly a helicopter in Augusta Kansas and there was always a wind.

As you rotate slowly around with the wind at your tail suddenly the helicopter will go “over center” and you have to quickly apply opposite peddle to arrest the rotation.

When you hover taxi the helicopter wants to weathervane into the wind and you need both pedals to keep it pointed in the proper direction.

Thank you, Vance
 
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brett s

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In 3 older helicopters designs I've hit the pedal stops in both directions.

Can't say the same for cyclic, at least not unintentionally.

In newer designs there's usually more tail rotor control margin, but it's there for a reason. I can't recall ever getting really close to the stops in the R22 but it's been a long time since I've flown one.
 

earthbnd misfit

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I have only had one lesson in a 5 seater jet ranger, [long time ago, not sure of the model] and i found the rudder pedals really heavy to control, hard to get the feel of it. So is the tail rotor always proportional speed to the main rotor? Also, if you had a large enough vertical tail on a heli, and you had a high enough forward speed, and you lost all drive to the tail rotor, could it still be flown?
 

birdy

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could it still be flown?
Yes.
I know of a bloke had an eagle take out his R22 tail rotor wen he was cruisen along, and while he was at speed, it stayed streight. Things start to rotate quick tho wen you slow.
He had to setup for a full PO auto wen he landed, coz he knew he had no tail rotor.
The tail rotor is hard linked to the main, and is driven by it wen the noise stops.
 

brett s

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Yep - some types can continue flight after losing tail rotor thrust, at least in some situations (when light); others pretty much can't at all.
 

Jens

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Jens, even torqueless helicopters more often than not have tail rotors.
That's a different situation.
Sounds contradiction that you need push from tail rotor in both directions in autorotation – as you could land with a dead engine??
Never mind for my part. I will remember there is an issue here with ‘real’ helicopters.

I am rather collecting information for hovercopters with 1 rotor as well as for the better solution with 2 counter rotating rotors.
And for this kind of rotor craft, there is almost constant power on the main rotor.
So for a one rotor hovercopter a (hyd driven) prop would definitely be fine – I think.

But your C-74, with the very visibly shaft drive, have also inspired me for another ‘tail rotor’ solution – the NOTAR tail.
http://www.aerospaceweb.org/question/helicopters/q0034.shtml
http://www.livevideo.com/video/D269B24E3E8D4D85A82414780576D84C/farnborough-demo-for-notar-hel.aspx

Maybe it should be made longer and even more shaped like a wing.
Advantage would be one less (visible) spinning item, that scares people.
A big disadvantage in side wind etc. – so not a way to go for 'real' helicopters.
 

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C. Beaty

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There have been many attempts to eliminate tail rotors.

The first I’m aware of was the Cierva W-9 with air ducted through the tail cone to a nozzle at the tip.

Another was the Piasecki helicopter with a ducted propeller at the end of the tail with vanes to control exit angle.

Even if these things had worked, both seem more complex to me than an ordinary tail rotor.

Photos lifted from the Aviastar site.
 

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Alan_Cheatham

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But your C-74, with the very visibly shaft drive, have also inspired me for another ‘tail rotor’ solution – the NOTAR tail.
If you study the details of the NOTAR you will find that it is very complex mechanically, not just a fan blowing air through a tube.
.
 

earthbnd misfit

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If you wanted to rotate from one direction to another quickly, trying to rotate the duct from one side to the other must be slower then pitching a tail rotor? Or would the duct never have to face the opposite direction? And as the duct faces down, wouldn't that pitch the nose down as well?
 

C. Beaty

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The Cierva W-9 dates from the end of WWII when much was yet to be learned about helicopters. The designers may have thought they didn't need tail rotor thrust from both directions.

The W-9 also had tilt hub cyclic control which required hydraulic servos.
 

LGoodhind

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Gessow & Meyers (fig 2-7) also shows what amounts to a rudder mounted diagonally in the down wash- was anything like that ever used? In the spirit of a horizontal stab that has different AOA or airfoils as a way to deal with p-factor, has a helicopter ever used asymetrical elements on the airframe as a way to cancel rotor torque?
 

C. Beaty

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Sure, some of the very early helicopter experiments used the tail boom as a wing to try to balance main rotor torque but I suppose it didn’t work very well. Unlike the fat pig, none made it to market.

Some tip jet helicopters have used canted tail vanes to catch the rotor downwash. But tip jet helicopters only need a little thrust to provide heading control.

There have been some attempts to use offset propeller thrust to provide torque compensation in compound helicopters where forward propeller thrust was desired to increase forward speed. But with engine and propeller on a stub wing, the moment arm was so short that hovering required an extreme nose up attitude.
 

C. Beaty

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David, 1974 was 45 years ago if my arithmetic is correct; and my memory isn’t perfect. However, my ‘74 helicopter wasn’t totally by guess and by gosh; I ran through the calculations for both main and tail rotor rpm, probably based on a top speed of ~50 mph. The required main rotor rpm would have been quite low as a result low disc loading and very low blade loading. With only 30 or so hp available, you don’t run rotor tip speed at anything approaching mach1.

I do recall the tail rotor running at 2400 rpm and having a diameter of 4 feet.
 
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