Why hasn't notar 'taken off'
 

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

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]

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.

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

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

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:

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

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

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.... :eek: Qiute a suprise as it took 3 people to wheel out the hanger 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.........:ok:

Newfie.

How right you are newfie 3 strong men :ok:

MD 600

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

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

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

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.

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

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

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.

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
https://lh6.googleusercontent.com/_m...totype_138.jpg

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.

Here's a simple Notar explanation :ok:
https://lh4.googleusercontent.com/_m...anation_lg.gif

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

You are talking about NOTAR popularity. I believe, in this case, one needs to look at the environment within which NOTAR is produced - a firm which has battled with some fairly fundamental challenges for the better part of the past 20 years and which struggles to attain steady growth in terms of sales.

Had this not been the case, and say the NOTAR patent sold to a manufacturer with a significantly higher product throughput, one might have witnessed the progressive refinement of the technology resulting in improvements in its operational effectiveness and further boosting its popularity.

Because early publicity surrounding NOTAR technology intimated that exhaust gases would be integrated with accelerated ambient air to pressure the boom. When this option was not selected the corresponding publicity was considerably less (.. one can understand how a front page heading in the Herald Tribune "Hughes Backs Down From Integrating Exhaust Gases in Newfangled Helicopter Technology" might have limited readership appeal) .. and, consequently, those lacking proximity to NOTAR development and operations did not appreciate that this strategy had been altered.

PPRuNe's Rotorheads and other mediums are doing a great job of educating (well, most of the time ;)) those who are interested in these things.

S.

The mythology of Notar has grown, and continues to grow, due to the excellent public relations campaign that was conducted 25 years ago. Here is some factual info:
1) Notar works, is effective, flies well and is quieter and generally immune to tail strikes. People who fly them like them.
2) Notar has considerably more critical parts than a tail rotor. It has a tail rotor inside its tail cone, with all the tail rotor stuff, and it has a Coanda slot, and it has the rotating nozzle at the tail, and it has the sas and sometimes a rudder. It costs more, weighs more, has mor maintenance and more critical failure potential.
3) The Coanda slot has limited use as anti-torque. Only in very low wind does the main rotor wash fall squarely on the tail cone, allowing the Coanda magic to work. Every other time the Coanda effect is small, and Notar uses its tail tip thruster, which is fairly inefficient.
4) The power losses of the Notar are fairly large, relative to an open tail rotor, so the payload of a Notar is lower, or the installed power is higher.
5) Why fewer Notars? Less payload, more fuel flow in cruise,(but also quieter, less likely to have a tail strike.)

The customers choose.

If you do a lot of landings, particularly ad hoc urban and rural, a notar feels good, from a safety perspective.

We've just logged 100hr and 600 landings in our new 902.

NOTAR
 

I must rely on the experience of others who have actually flown them but I'm told that the weight of the fan mechanism takes some getting used to. It's situated immediately behind the cabin and not easily balanced.

For military uses it might prove advantageous to be able to back into a dark notch in the woods and either land or observe from the hover. However, it will take some practice to perfect. I've also been told that the reaction time is notably reduced.

sgt major
i have not heard that one yet but its not true anyway

sgt major
i have not heard that one yet but its not true anyway

Yep sadly, I think when NOTAR came out a lot of the heli industry looked and went ooooo thats a big contender, and then slagged it hugely. Then it came out, in small dribs and drabs, and true it was not well supported in parts support then ( ten yrs ago now). Nor was the B747 went that went out and commercial companies said its too big!!!
Times move on and it has still found its place ( among all the slagging) as always it is customers choice. I am not a pilot to slag EC/Bell/Augusta/ or who ever. They all have their merits and bad points! However in my limited time doing the occasional HEMS work in UK I find them...... bloody brilliant for that work. I have not flown an EC135 so can't say, mates of mine have and they like erm , so there you go. As to the question as why has NOTAR not taken off, I think who has the licence for it!!! always wondered why there was not smaller versions of a Chinny about, there is I know a HELIX but who has the licence!!!:ok:

BT.

You have a "NEW" 902?....

1st time I'd ever flown a helicopter with just 15 hours on the clock.

That's new for me.