Helicopters with no tail rotors..?

[siko]

erdnase said:

That's the one!

I've read up a little on Wiki about these, and it's pretty fascinating. If I understood it correctly, as well as having a "fan" pushing air out the tail, the actual boom/shaft is like a wing on its side? This way, the downwash from the main rotor flows over the wing design and creates "lift", albeit at 90 degrees to how a normal wing would work, creating a force in the opposite direction to counter the torque?

I'd never heard about this, and spent a good hour on Wiki reading about helicopter designs today. Awesome

Spot on mate - I seem to remember the practical demonstration of this 'coanda' effect is to put two candles next to each other and the flames should merge into one. I think it's something to do with 'entrainment of the boundary layer'....but this was info from a long time ago and I could never get the damn 'candles' to work when I was trying to 'prove' it!!

I remember the tail boom is shaped like a wing (when looked at from behind the aircraft) and the air from the fan is blown over the 'top' of the wing (like a fixed-wing), this airflow effectively 'captures' the down wash from the main rotor and accelerates it down, creating lift due to the higher speed, and hence pressure differential. Clear as mud?!

[anonymous-user]

This gives a much clearer idea of how it's actually working.

[Eric Mc]

Here's a British attempt at using jet efflux instead of a tail rotor - the Cierva W9

[erdnase]

So I assume the shaft/wing creates the majority of the counter-torque, and the fan is used for minor adjustments, etc? I'm just wondering why you'd need both.

If there was no wing shaped boom (excuse my awful terminology!), would all that downwash from the main rotor be going to waste - or is there a trade off between vertical lift when using the NOTAR design?

Helicopters are amazing things. I've had a few radio controlled ones. Just the cheap little electric designs with 2 coutner rotating blades, but they never cease to amaze me. You can understand a bit of the science behind them.. but when you see them just hovering - it's not science, it's voodoo!

[dr_gn]

Eric Mc said:

dr_gn said:

Eric Mc said:

The Defender is single rotor and uses what is called the Coanda Effect instead of a tail rotor to counteract torque. Air is bled from the engine through a rotatable slot in the tail boom. The airflow from the slot creates differing levels of pressure on one side opf the boom. Varying the slot angle allows the helicopter to rotate.
The main advantages are that it is quieter than a tail rotor and is claimed to be safer as there is less mechanical complexity in the design.

It's not air bled from the engine, it's from a seperate fan at the front of the boom.

I presume the fan is driven off the engine by a shaft of some sort?

Bulldog's diagram pretty much sums it up. It's a fan driven by the rotor transmission.

Some time ago I was looking into the NOTAR system for a UAV type model, Initially I assumed it was exhaust gas being expelled out of movable duct at the end of the boom, but the obvious question was what happens if the engine stops? With the gearbox driven fan, at least if the engine disintigrates the fan hopefully still works in conjunction with the main rotor.

[-Pete-]

Sounds about right, but the torque provided by the shaft/wing isn't controllable by the pilot, so the fan driven ducts allow him/her to fine tune rotation using the footpedals.

Helicopters, like humming birds, are definitely impossible. That's why I love them!

[dr_gn]

erdnase said:

So I assume the shaft/wing creates the majority of the counter-torque, and the fan is used for minor adjustments, etc? I'm just wondering why you'd need both.

The boom counteracts the torque reaction, the duct at the end is used for yaw control.

The fan does two things - controls the boundary layer via bleed vents along the boom, and provides the air for the movable yaw contrl duct at the rear.

At least that's the way I understand it.

[Eric Mc]

I would assume that it is an overall safer system than the conventional tail rotor. A lot of helicoptyers have been lost due to tail rotor or tail rotor drive-shaft failure.

[dr_gn]

Eric Mc said:

I would assume that it is an overall safer system than the conventional tail rotor. A lot of helicoptyers have been lost due to tail rotor or tail rotor drive-shaft failure.

No idea, but it's a neat solution I think.

[Dirty Frank]

Eric Mc said:

Quite a lot of helicopter designs do not use tail rotars. The bulk of these alternative methods of neutralising torque depend on two rotors rotating in opposite direction. These can be mounted seprately or together. If together, they can be intermeshing or in a biplane configuration, Here are some examples of twin rotor styles -

They have one of those at the Manchester Museum Of Science and Industry. Assuming it is actually a Bristol Belvedere

http://en.wikipedia.org/wiki/File:Bristol_Belevder...

[-Pete-]

And the tail rotor has a habit of chopping people up or hitting things in an urban environment. Having said that, I've never seen a NOTAR heli for real, in fact the air ambulance around here uses a Eurocopter with an enclosed rotor - is it possible you saw something like this? http://www.tvacaa.org/

[Eric Mc]

Haing said that -

= http://www.youtube.com/watch?v=MvMcsJTOYI0&fea...

[dr_gn]

-Pete- said:

And the tail rotor has a habit of chopping people up or hitting things in an urban environment. Having said that, I've never seen a NOTAR heli for real, in fact the air ambulance around here uses a Eurocopter with an enclosed rotor - is it possible you saw something like this? http://www.tvacaa.org/

I see this one nearly every day:

[-Pete-]

dr_gn said:

I see this one nearly every day:

Are you a criminal?

[mrloudly]

-Pete- said:

dr_gn said:

I see this one nearly every day:

Are you a criminal?

Northant's one lives next door, they regularly give me a flypast down my runway ;-) Tis very quiet, although I believe it's design was driven forwards on it's safety aspect more than anything else.

[Zad]

I think it makes sense that any helicopter that regularly has to land in confined spaces, and keep the rotors running while they load up via the rear clamshells, should have a shrouded tail rotor or similar torque / yaw control.

The Sud/Eurocopter tail fenestron was a good idea, but is rather noisy and has bigger losses than the conventional tail rotor system. There have also been quite a few crashes which were blamed on lack of tail rotor authority.

[louiebaby]

Eric Mc said:

Quite a lot of helicopter designs do not use tail rotars. The bulk of these alternative methods of neutralising torque depend on two rotors rotating in opposite direction. These can be mounted seprately or together. If together, they can be intermeshing or in a biplane configuration, Here are some examples of twin rotor styles -

At the risk of looking like a complete plum, what the hell is this, and how does it work? Does it have two main rotors a foot or two apart?

[dr_gn]

louiebaby said:

Eric Mc said:

Quite a lot of helicopter designs do not use tail rotars. The bulk of these alternative methods of neutralising torque depend on two rotors rotating in opposite direction. These can be mounted seprately or together. If together, they can be intermeshing or in a biplane configuration, Here are some examples of twin rotor styles -

At the risk of looking like a complete plum, what the hell is this, and how does it work? Does it have two main rotors a foot or two apart?

Fourth type down:

http://www.helis.com/howflies/rotconf2.php

[angry jock]

It's a Kaman HH-43 Husky. Contra-rotating blades one at a different angle and pitch.
Here's a picture of one in flight.

[louiebaby]

dr_gn said:

Fourth type down:

http://www.helis.com/howflies/rotconf2.php

Thank you. So it's fine until the gears or differential or whatever keeps the rotors in sync misses a couple of teeth, they chop each other to bits, and you just drop out of the sky?

I wonder why it was never a popular design?