PRO's and Con's of NOTAR

[TIMTS]

Hi!

I am currently in CFI groundschool, and I have to research the pro's and cons' of the NOTAR system.
I have heard that it doesn't like wind from the right, is sluggish, quiet and all that....
I was hoping anyone in here could help me...

Thanks :p

[HeliMark]

You should do a search on this forum and the usenet (Rec.Aviation.Rotorcraft) on NOTAR's. You will find plenty of info on them, both the good, and plenty of the bad.

The only real difference of wind from the right (over the "E" model), other then the tail being bigger and catching more wind, is the increase demand of TOT/Torque over the tail rotor version. The NOTAR generally does not have a very big excess of TOT/Torque available.

Dang, and today I have to trade my "E" model in for a BlowTar so that I keep everyone happy that I am current in them. At least it is only for a day.....

[john du'pruyting]

Pro's
1. You wouldn't want to back into a bush with anything else rivetted to your fuselage (no tittering at the back of the class, by bush I mean green sticky up thing that grows in the ground. By fuselage I mean the compartment that passengers and crew are carried in. Don't be so vulgar! ;) )

2. It is exceptionally quiet, and the noise that it does make seems, (to my uneducated ear) to be of a far more comfortable pitch than any other tail rotor system
3. The 'anti-torque drivetrain is far shorter than any other system so one feels (maybe mistakenly) a loss of anti-torque drive is far less likely than in a conventional or fenestron system
Cons
1. Said to use more power (although once you fly it regularly you don't seem to notice.)
2. At cruise speed Notar has little / no effect therefore further system needed for yaw control / damping (VSCS in our 902).
3. There is a limitation on hovering in winds > 17 kts from 80 -190 degree band above 5000 ft DA (again 902 can't speak for 520 / 600). Although I get a nose bleed and vertigo if I go that high!

PS. anti-torque failure in this are at least as interesting as tail rotor failures in anything else you care to think of!!;

[Vfrpilotpb]

JDp,

Long time no converse, nice to see your still active, many people have been after your pin, but still in my lapel.

Many regards
PeterB

(Sunny Brum?????)

[john du'pruyting]

Hello there PB. Make the most of the pin. Due to the Powers that Be in our (their?)finance department, insisting that we must have proper accounting procedures, issue receipts and generally make the workload of selling pin badges for charity far too onerous (At the moment anyway!). We have had to hold any more orders. :mad: I suppose there was a risk that we might all have been corrupted by the 'huge sums of money we were making;)

Oh yes, and its sunnier than up your neck of the woods (although you wouldn't know that today!).

And to keep on message with this topic, I refer the honourable gentleman to the answer I gave earlier.:p

[Nick Lappos]

NOTAR facts and the hype are sometimes a bit far apart. One attempt at fair assessment:

1) Protection - A++ all the way. The parts that are exposed (rudder, rotating can) are robust and can take a smack, unlike a tail rotor.

2) Safety - A++ Passengers are not exposed to danger at all.

3) Noise - A - Tail rotors are generally much noisier.

4) Simplicity, C Notar has more critical parts than a typical tail rotor, they are out of sight, so they seem fewer. A full variable pitch tail rotor is buried inside the tail cone, as well as a full control system for the can, loss of either is a big deal. Also, a mandatory rudder sas is required in some models.

5) Power - C Notar consumes much more power than a tail rotor. The comments above are a tad nieve in expecting that the TOT might be higher. As long as the flight manual weights are flown, performance is quite nice. However, the Notar's flight manual weights are quite a bit lower than an equivilent tail rotor helicopter with the same engine power, about 1 passenger less. This also means that Notar is made more marginal in yaw than a tail rotor, because a bigger Notar eats even more power, so it purposely has less yaw control power, thus the flight manual limitations at altitude.

6) Handling - C The Notar does not help act as a tail fin, unlike a tail rotor, which behaves like a fin to help damp yaw oscillations. The weaker yaw stability is noticable, but not much of a problem.

Nick

[TIMTS]

I was wondering about this "stick the tail in the bushes" thing you can do with the NOTAR, how will this affect the Coanda effect?
Also heard rumors of a tail tuck (or something) on the last part of an auto....could someone explain this (if it exists)

Thanks again for all the help...appreciate it:D

[Capn Notarious]

From what we read in the Forum, you dont work for the folks that make Notar: however do you believe it likely that tail rotors might become redundant? For without wishing to be offensive to other manafacturers. 1) How many rotorheads would like to fly Notar.
2)How many helicopter companies would want to have been the folks that invented it.
3) Do we think that environmental/safety concerns may demand the farewell of the T/R.
4)Given that turbines are improving year on year, is power into the fan and thus greater tail control: really an issue?

Guess what I would fly, but here in Merry England two motors please.

Happy Saturdays and safe landings

[john du'pruyting]

This tail in the bush scenario is a bit pointess in reality. I really only use it to illustrate a safety point. The rear end, as Nick L says, is pretty benign to the outsider be it passenger, yapping dog or marauding yak. There is only the swivelling bucket on the rear to cause damage to a third party, pretty tame compared to the circular saw on other types. If you were to reverse the rear end into some horticulture with the sort of hamfistedness a pilot of my skills might display, although you are not going to lose your tail rotor as you may in a T/R or fenestron equipped aircraft, you may still manage to jam enough branches into the nozzle to restrict / deprive you of any low speed directional control. The end result of this could of course be just as spectacular!
I feel that its biggest plus, especially in the urban area I have the good fortune to be working over, it the comfortable noise level.
Capt N, I don't feel that the fact Nick L works for another manufacturer is relevant here, his views are always worth reading.

[Thomas coupling]

Ok, so it's:

more complicated to build.
heavier than its equivalent.
restricted in its hover envelope.
in need of additional assistance to maintain stable forward flight.
much more expensive than its competitors....

why did someone manufacture the damn thing......
dare I say it...buy one...
:D :eek:

[HeliMark]

john du'pruyting, there are no restrictions as to hovering in winds on the 520 at altitude, unlike to 600 or 902. As I understand it, the restriction is due to the power required to hover with the winds can exceed the available power.

TIMITS, I think that by the time the Coanda does not work due to the bush or tree you have backed into, you will have one heck of a lot more problems then that. Also the tail tuck is on normal approaches. Somewhere in the 15 kt. speed area, the tail likes to tuck in on you a little. It is not a dramatic tuck though. A simple solution is just adding a little power just as it is starting and that will stop it. After several flights, you do it without even thinking about it. During auto's, at least I do not notice it and it would be just about the time you are starting your flare anyway.

The main reason a lot of the police departments here has bought them is that they are quiet. With the noise enviroment around here, and everywhere, it is a big factor in buying.

All of our 520N's have their mist eliminators removed inorder to recover as much power as we can get. We still have the particle seperators in them, but as weak as they are the extra power is a must.

[john du'pruyting]

TC..Cheap shot. Maybe the salesmen of the opposition put people off?:p

[Cyclic Hotline]

One of the most endearing features of the 500 tail rotor, is the ability to stick in one notch of pedal, at idle, and bask in the cooling breeze (which will keep even the most ferocious bugs at bay) for the remainder of the day whilst the geologists, biologists, or whatever, are doing their thing. ;) This is a very important feature in the bug ridden areas of the world.

I don't know how long a tank of gas might last, a long time indeed?

How does the Notar fare in this capability? :)

[Nick Lappos]

Capn Notarious,

Let me answer each of your points:

Capn:
"From what we read in the Forum, you dont work for the folks that make Notar: however do you believe it likely that tail rotors might become redundant? "

Nick sez: The facts should speak for themselves, and who we work for is (if we stick to facts) of little consequence. Were the flight performance and handling of a helicopter based on opinion, I'd have us all vote for a really spiffy one, but the metal only behaves real, natural laws, far more stringent than opinion.

Capn: "For without wishing to be offensive to other manafacturers. 1) How many rotorheads would like to fly Notar."

Nick sez: Now we're on to something, Capn. Let the marketplace decide, with hard cash and real sales. That is the only true test.

Capn: "2)How many helicopter companies would want to have been the folks that invented it. "

Nick sez: Tip Nozzel helos have been around a long time (first flown in 1947), and even back then they ate too much power, handled poorly and did not succeed. If you think hard engineering decisions are made on jealous motives and envy, think again. Sales count, that is how you vote, and what we really listen to.

Capn: "3) Do we think that environmental/safety concerns may demand the farewell of the T/R. "

Nick sez: It is not safer to bring one less survivor off a mountaintop, it is not safer to have twice the critical parts to fail. The US Army modified several OH-6's to NOTAR, tried them for a long while, then paid to remove the NOTAR and go back to tail rotors. Too little performance, too much yaw workload, and not enough control. All things are a compromise, NOTAR is no exception.

Capn: "4)Given that turbines are improving year on year, is power into the fan and thus greater tail control: really an issue? "

Nick sez: So with a larger engine NOTAR can carry what today's smaller-engined helos can carry. The helo can carry even more with the larger engine. Your point is flawed - no matter what the engine size, NOTAR eats more power, carries less.

Capn: "Guess what I would fly, but here in Merry England two motors please. "

Nick sez: We could have figured that out, after all you chose to call yourself after the rear end of a helicopter! ;) Seriously, the power penalty of the NOTAR are even more horrendous as the size increases. The NOTAR LHX proposed by MD and Bell had two fans, variable slots, movable rudders and everything but the kitcheon sink to try and make it work. The fan on Comanche has twice the yaw control, less weight and lower power consumption, and it won.

Capn: "Happy Saturdays and safe landings"

Nick sez: Thanks, and to you too!!



:cool:

[Buitenzorg]

Capn Notarious

Now that Nick has had his say, let me answer your questionnaire.

1) How many rotorheads would like to fly Notar.

Hey, I’d like to fly them, see what they handle like etc. But the only type I’d like to fly professionally is the 902 model Explorer, with the PW207E engines. All others are badly underpowered, and the singles auto like a lead safe should the engine quit.

2) How many helicopter companies would want to have been the folks that invented it.

Any of them! A patent on file is like money in the bank. But your question isn’t the right one to ask, it should have been: 2) How many helicopter companies would want to have been the folks that had to pay the development costs for it as well as reap the benefits of it. To answer that question, ask yourself: Which helicopter company has been passed around corporate parents like a hot potato these last 20 years? The only one I can think of happened to invent the NOTAR system.

3) Do we think that environmental/safety concerns may demand the farewell of the T/R.

Safety concerns: no. Look at the T/R setup on the BK117, even Shaquille O’Neal can’t get hit by that rotor. Environmental concerns: maybe. It’s a trade-off anyway, since a NOTAR will burn more fuel to do the same work than a T/R-equipped helicopter. Less noise but more emissions. Anyway, environmental/safety concerns may demand, but economical concerns will decide.

4) Given that turbines are improving year on year, is power into the fan and thus greater tail control: really an issue?

You’d better believe it. If I, as an operator, have to pay for extra engine power I want that power to lift things that’ll pay me a return, not just push a tail to the side.

I could explain how I personally arrived at these viewpoints (and they are only my own), but it would become a very long and probably boring post. Let me just say that analysis of pros and cons of the NOTAR system will limit its uses unless required by regulation.


Cyclic Hotline

An Allison 250–C20 should burn about 10 gals per hour at idle, turbine engines are awfully inefficient at low power settings.

[Capn Notarious]

So Nick here then is another question.
In order to do without the drive train along the tail boom.
Has anyone thought of using a mini turbine directly coupled
into the fenestron or open tail rotor. I realise now that everyone is saying "Centre of Gravity."
For as my non engineering mind would believe( and probably incorrectly It is the extra gearbox bearings coupling failures, that cause designer/operator/mechanic/pilot :WORRY

Right thats my lot now pull it apart and help us all learn:confused: Im not confused just interested

[What Limits]

There has been little made of the safety aspect in that if you are doing HEMS then bushy-topped trees do come into play and if I was foolish enough to try to back into a bush, I would rather do it in a 902 than a Bolkow!

Someone tried that in England in a Bolkow recently and the bush won!

Don't forget that with a thruster comes thrust and if you do a quality conversion course onto type, then you will be shown the effects of the vast amount of air coming out of the back. IMHO it could cause some damage or injury.

Having said that, the NOTAR is far more powerful than any other conventional tail rotor and in my opinion uses far less power.

For fellow PPruners, remember that Thomas Coupling is a rabid disciple of the EC135 and will not have anything bad said about his baby, and also will not have anything good said about the MD902!:D

[Nick Lappos]

Capn Notarious,

Lots of ways exist to drive a tail rotor, a small engine might be about 100 times more likely to fail than the drive shafting we now use. Various schemes such as hydraulic motors and such have been discussed, none are as reliable as the shafting we use.

Our worry is always tied to our beliefs, maybe not to the actual failure probability. The stats for drive failure is so remote, it does not even show up in the data, while the stats for CFIT account for 35% of all crashes, and 50% of the fatal ones. I wish we could all start a thread wishing for EGPWS instead of mechanical improvements to non-problems!

The Notar has lots of good points, and a few poor ones and no bad ones. It belongs in the playing field, but it is not a savior, IMHO. Customers will determine if it is the way to go. So far, the vote is a resounding no, otherwise Boeing would have held on to the Notar line when they sold the light McD helos off. The sales of the Notar family are far less than the competing conventional helos, I believe, probably due to the reduced payload and increased complexity, ie, less value for money.

"What Limits", while you believe that the NOTAR has more thrust than a tail rotor, you are quite wrong. The advantages of NOTAR are many, but strong yaw control is not one of them. Beliefs are nice though, they comfort you at night. Do not be shaken by facts.

[Capn Notarious]

Nick.

Thank you for taking the time and effort, to explain all the stuff that you do.

[Thomas coupling]

Now what is the name of the helo that has the lowest noise signature (light twin class) in Europe, to date??

Probably the same one that has sold more light twins than any other helo company in the world.



WAT limits: I only quote fact not fiction unlike your latest quote: notar produces more thrust...more efficient than normal tail rotor????????
If you wish to denigrate the situation to a personal level lets stick to the facts. Most of which are embedded within this current thread. ;)

[Flight Safety]

In the thread "What about helicopters needs fixing" that Nick started, one of the areas of helo improvement being discussed has been lower noise levels.

In my opinion, the NOTAR is a good "urban" helicopter because of its low noise signature and its safety around people and other obstacles. I think the MD902 for example, is a good machine for work in and around the "city" environment precisely because it's a NOTAR (and also a Cat A helo). The lower altitiude "urban" environments generally plays to the NOTAR's strengths.

[Grey Area]

I was evaluating an MD900 Explorer 2 months ago and found a few gotchas. Nothing new.

During the side step we managed to find some undesirable pitch / yaw couples and a peak torque spike of +40% (that is 70% to 110% while maintaining heading at 25 kts in a translation to the left.

The NR / TQ display gives no decent trend cues to the pilot due to its digital display (very flash but I'd prefer an analog gauge).

Due to the VSCS and heading hold / turn co-ordination mode change-over during decelerations, a quickstop and turn to the right is a recipe for disaster unless you really know the aircraft or like to live close to the edge!

[HeliMark]

The MD600N is well known to have a very interesting tuck in a right turn. Do a right orbit and slow it down, it will tuck in on you and twist to the right even faster. The main reason for this is that the tail loses a lot of its air as being blanketed by the fuselage. It does not do this in a left turn.

[md 600 driver]

yes helimark the 600 does have a interesting tuck ,but when you know when it can happen it does not cause a problem

as a owner and a pilot of a md 600 i make the following comments

power
i find the 600 has more than enough power in all modes of flight i dont think i have ever run out of power in a pedal turn

safety

safer for passengers also when flying tail rotor helis landing in private sites i dont get that suck up hairs on the back of my neck with the 600 [any body approaching from the rear is not going to walk into the t/r. ]

fun
i find the 600 a joy to fly fast, responsive,pure grunt power.

cost to run

not bad either

ysas

now there is a thing the 600 does not have a ysas like the 520 but there is a retro fit mine is being done 29/7
apparntly it will let me lift off without pedals ,land without pedals , and make autos easier ,

any way i like the 600 but there is one helicopter i would like more than the 600 and that is a 900 but now i am dreaming
i test flew one a couple of months ago it was pure sex.[i also had a go in a 135 it was not a patch on the 900

regards all

[WhatLimits]

Perhaps it is time for someone to give us the benefit of their experience and knowledge by offering an objective assessment of the two types of tail rotor.

Another good thing would be for someone to define the terms, power, thrust, efficiency.


With my little brain, I just make comparisons with my feet,

Conventional tail rotor = large pedal movement
NOTAR = small pedal movement.

[Thomas coupling]

WAT limits: isn't that what N Lappos did on page one:confused: :confused: :confused:

[chopperdr]

on the issue of notar technology, it is my understanding that the boeing co. still retains the rights / pattens to this technology. IMHO, i would say that notar technology needs more development to achieve its potential. remember the fenestron on todays 135, 130 and 120 is a much different animal than on the gazelle or dauphin.

[FLIR]

Hi All,
as a 902 convert (previous on a BO 105) I feel that the Bite of the Assymetric blades of the anti-tank tail rotor mod on the 105 was the best response one could expect of a conventional tail rotor, but with experience on the 902 (207E) explorer I find that tweaking the controls during apparent pedal run out can and will solve the problem of lack of torque control. All you need to do is raise or lower the collective to counter any excess torque requirement whilst keeping the pedal on the stop! You may get a few comments on the up and down antics - but the aircraft WILL stay in the same place!!!!!!! Even at all up mass the 902 will handle the torque with ease (I have done this at +20 C and it managed with heaps in hand) as far as the NOTAR is concerned it can and will perform, you just need to adapt your handling to take account of the differing aerodynamic systems. The "TUCK" the everone seems to talk about is a non starter - once you have handled the machine it is overcome automatically during flight.

Be safe out there.

FLIR:cool: :cool: :cool: :cool: :cool:

[Nick Lappos]

FLIR is right about the collective pumps, which vary the main rotor torque and thus make the tail thrust become comparitively higher when the collective is reduced.

The reduction of collective will restore yaw margin, but that unfriendly scraping sound of the earth on the belly is also caused by collective reduction. Like finding yourself between a rock and a hard place.

This is actually the reason for most LTE events - the pilot comes into a hover and pulls somewhat more than hover power during that last part of the decel. This extra main torque can completely wash out the antitorque, especially of the marginal systems that experience LTE. While spinning at low altitude, one temptation is to reduce the collective, and a hard landing results.

[FLIR]

Nick,
The one thing I would not countenance is running into a low or marginal power situation whilst at low level - even with a notar!!!! You know only too well that the accident that causes the 'scraping sounds' you mention, has begun with the decision to start the approach and not taking full account of the limited power situation the pilot is facing. During my training as a military pilot we went through a great deal of limited power situations, both piston and turbine machines, without full and complete knowledge of what is happening, going to happen or might happen the limited power margin (be it tail rotor, notar or main rotor) will bite HARD, being low level only gives you one thing more to consider!! Pumping the collective to offset low or poor torque yaw control can only be done at altitude, then if it all goes pear shaped you can fly away - even if you are only at 300 ft on police ops!!

regards

FLIR :cool: :cool: :cool: :cool: :cool:

[Thomas coupling]

Why do you need to 'pump the collective' at all in a modern state of the art helo???

[Barannfin]

Because "Real men fly Helicopters"

[HeliMark]

The big reason for the need to pump the collective in the NOTAR is that it just takes a little more time for the tail to react. It has the same authority as the tail version, just slower.

Going into a high/hot place, if you do a correct approach to a hover, should not require any pumping of the collective. It should not be any different from the rotor version. The only thing that may occure is if you are in gusty wind conditions (winds varying say 20-30 degrees in direction) with marginal power, you may need to plan your approach to the ground to avoid exceeding the engine limits in a hover due to the pedal work.

[Thomas coupling]

Mmmm, interesting:eek: