Why hasn't notar 'taken off'

[Wigglyamps]

As a non flying helicopter enthusiast (apart from 30 minutes in Schweizer), I was wondering why there aren't more helicopters using the notar system. Presumably there are less moving parts and weight saving advantages over conventional tail rotor systems. Are there copyright issues? Is it less responsive than conventional systems?
Any feedback gratefully received

Wigglyamps

[Frenchrotorhead]

From this website :


NOTAR

Advantages

• Reduced noise

Benefits of the NOTAR system include greatly reduced external noise (NOTAR-equipped helicopters are among the quietest certified helicopters). This is because up to 60% of the noise from conventional helicopters is produced by the interaction of the tip vortices of the main and tail rotor.[1]

• Increased safety and reliability

Helicopter accidents may be caused by the tail rotor striking tree branches, power lines, the ground or other obstructions. Eliminating the tail rotor removes this hazard and enables NOTAR helicopters to go where tail rotor layout helicopters cannot i.e. close to trees or buildings.[verification needed] They are also safer for ground crews to work near as there is no danger posed from a spinning tail rotor.

• Reduced vibration

Since there is no interaction between tip vortices of the main and tail rotor, the operational vibration is reduced.

• Reduced Pilot Workload

The thrust force of the coandă effect caters to the need of antitorque force. As the torque effect requires more antitorque, the Coandă effect provides more lift to provide that antitorque.[citation needed]
Disadvantages

• Efficiency

The NOTAR system is not as efficient as the tail rotor, and NOTAR helicopters sacrifice some power as a result.[citation needed]

• Maneuverability

Although generally agile and stable, at high forward airspeeds the properties of the airflow over the tail boom change, and the Coandă effect fails. The 'H'-shaped tail characteristic of NOTAR helicopters is used to provide anti-torque at speed using conventional moving control surfaces. As a result, the helicopter can be difficult to turn when traveling at speed, and the large control surfaces of the tail inhibit maximum sideways velocity.[citation needed]

• Aerodynamics

The translating tendency and the tail rotor roll forces continue to exist.[citation needed]

[Pandalet]

I've not flown one myself, but I seem to remember pilots who had saying the tail controls were a little laggy and could be 'mush'. Then there's the fact that the design comes with license and royalty fees payable to Boeing, plus MD (who make all the NOTAR helicopters currently) having some management issues.

[Bravo73]

Originally Posted by Wigglyamps

Presumably there are less moving parts and weight saving advantages over conventional tail rotor systems.

Unfortunately, you've got the wrong end of the stick. If anything, there are probably more moving parts and the weight is probably greater than a traditional tail rotor assembly.

A notar still needs a 'fan' to work. It's just that the fan is at the base of the tailboom, rather than at the far end. And the weight of the vertical tailplanes (needed because the fan doesn't provide enough directional control in the cruise) is generally more than a traditional tailplane.

The advantages, however, are quieter operation and better safety on the ground.

HTH

[ReverseFlight]

I have heard they are quite "twitchy" to control esp in a hover. Can someone either confirm or rebut this ?

[Hughes500]

Not twitchy at all. The best way of describing the pedals is as follows. For those that drive manual cars think of it like this. The clutch on your car will need adjusting just before a service so the pedal travels a long way before the effect, thats your notar. After service clutch is adjusted so the clutch pedal now like an on off switch thats your tail rotor.
Basically it doesnt react as quick but it will then over react as you put too much input in. Once you are used to it it is easier to do spot turns. Best fun with a new pilot is to put one in the hover and take your feet off the pedals, she will sit in the hover and if you are gentle you can transition a way fly a circuit and back to the hover without using the pedals !!!! A very surprised new pilot:

[md 600 driver]

i think the best way to describe it is

not a tail rotor ,or a fenestrom its a notar and the pedals feel different but still control the helicopter in the accepted way

hughes 500

she will sit in the hover and if you are gentle you can transition a way fly a circuit and back to the hover without using the pedals !!!! A very surprised new pilot:

are you are refering to a 520 because not all 600 have ysas it was an extra on the first 70 ships or so

[newfieboy]

I got aprox 2000hrs in the 520 about 10 yrs ago......fun machine to fly, but not much of a people carrier, and the limited range made ferries across Canada interesting, to say we visited airports we would never normally visit for fuel is rather an understatement. The 6 machines the company had all had YSAS but IIRC all the a/c had circuit breaker pulled and tiewrapped inop, apparently the system was always going u/s so company stopped repairing it. Due to nature of our work, mostly moving drills, we spent a fair bit of time practicing zero airspeed autos from 100ft and if my memory is all it was, scary to say the least, the first time I had it demonstrated, I was pretty horrifyed at the way the nose dropped straight down,literally.... Qiute a suprise as it took 3 people to wheel out the hangar being very tail heavy, 2xpushing and one guy standing on front of skids as a dead weight to keep tail off ground.....like I said fun machine and always generated lots of interset amongst other crews, but I think these days I;ll stick to Eurocopter and Bell mediums thank you very much. Now the 500D, that was a blast.........

Newfie.

[500e]

How right you are newfie 3 strong men

[Hughes500]

MD 600

Sorry I forgot about the 600 not having ysas, yes was refering to 520

[Wigglyamps]

Thankyou for all your replies, notar obviously isn't as good as I thought it was.

[md 600 driver]

wiggleamps

?? why i dont think any of the pilots that have time on them that replied on this thread said that. my vote notar good

[PotentialPilot]

Is there anything special about notar's that allows people to do silly things like this?

Run with no one occupying the helicopter?

Also, don't the safety risks about a tail rotor still apply as hot exhuast fumes still flow? Except for the risk of being hit by blades of a tail rotor.

[md 600 driver]

potential pilot

in some countrys pilots are allowed to have all types of helicopters left with engine and blades turning

your comment as to the exhuast gases were you meaning coming out of the exhuast or out of the end of the tailboom
FYI on md notars its just cold air that comes out of the end of the tail boom from a fan connected to the gearbox

[PotentialPilot]

MD
I was referring to hot air from both outlets, although you say it's cold air that comes from the boom, wouldn't the air still be hot enough to "cook" from a distance up to the end of the boom from the main engine?

Curiousity only

[mfriskel]

The air that comes from the tailboom (slots or thruster) is the same temperature at the air around the helicopter. The air that operates the NOTAR system is drawn in from above (large opening behind main rotor) via a fan driven by the output shaft of the transmission. The air is accelerated down the tailboom (not a compressor as the pressure in the tailboom is not much of an increase) and some exits the slots, the rest exits the thruster- at the same temp (differences as in any increased velocity like you home cooling fans) as it entered. I don't understand how after 20 years people still think engine exhaust is used in teh NOTAR system.

[elro]

To the best of my knowledge the only NOTAR system that utilised 'hot' engine exhaust gases was a redesigned alouette III called Cirstel - Combined Infra Red Suppression and Tailrotor Elimination

Initial research and development workbegan in 1987 and construction of the prototype started in 1993. The demonstrator is due to make its maiden flight "in the next few months," according to project engineer Nols Fonternel. The workwas conducted by Denel under an SAAF technology contract. It was administered by Armscor. While Cirstel has some similarities to the McDonnell Douglas NOTAR (NOTail Rotor) system, it is a different design, Fonternel said. Although, like NOTAR, it uses the Coanda effect of the engine bleed-air to eliminate the need for a tail rotor while also incorporating suppression of the exhaust's infrared signature. The Cirstel principle splits the high pressure air from the enginefor use in the Coanda slots, while the low pressure air is bled-off for the tail thruster and to mix and cool the engine exhaust. The thruster nozzle is a Denel-patented clamshell design, unlike McDonnell Douglas' `rotating can' concept. Denel intends "to apply the Cirstel to a new helicopter design, to be developed - hopefully - with a new partner," Fonternel said.

[rotorfossil]

When the 520 first came out, I ran a comparison with the equivalent 500E. The 520 was heavier, slower & used more fuel. However it was quieter & you could back it into a tree without too much damage.
What people tend to forget is that the Coanda bit doesn't work in forward flight and all the anti torque has to be provided by the fins at a cost in drag.

[elro]

Here's a simple Notar explanation

[Shawn Coyle]

The Commanche used exhaust gas down the tail boom for IR shielding, but it also has a ducted tail rotor.