Notar helicopters and autorotation?

[bolkow]

Can anyone tell me whether or not the Notar can autorotate? I am unfamiliar with this type of machine but my understanding is that the tail function functions when it gets power from the down draft draft from the main rotors under power. Are there issues with regards to auto's when power is off or reduced? If the question sounds silly then my apologies, I know little about notars or their operation.

[chopjock]

If the internal fan is engine driven, and if it stops when the engine stops, then auto is still possible by weather cocking the fusalage on the way down. However if the fan is gearbox driven it should continue to supply low pressure air flow to the slots and auto normally.:ok:

[md 600 driver]

the fan is gearbox driven
in auto it turns with the main blades not the engine

[nodrama]

A Notar helicopter uses the Coandă effect to counter torque effect of the main rotor, which does utilise down-wash from the rotors.

The low-pressure air through the slots and for the directional control 'bucket' is, however, produced by a main transmission driven fan.....so still works during autos. I don't know if the anti-torque effects of the notar system are reduced during autos, but there will still be directional control.

[md 600 driver]

no drama A Notar helicopter uses the Coandă effect to counter torque

you wouldnt get coanda effect without the fan

[nodrama]

I know...I was just comfirming the point in the original question that downwash from the main rotor does play it's part in how the notar works.

[rotorfossil]

As I understand it, the downwash and coanda effect on the boom is mainly effective in the hover and low speed flight, hence the large angled fins for cruise flight. In autorotation, the airflow over the boom is the wrong way round and presumably yaw control is from the can at the back and the fins. I can remember the yaw effects on entering auto in the 520N feeling a bit strange at first.

[Bertie Thruster]

I don't know if the anti-torque effects of the notar system are reduced during autos,

Is anti torque required in autorotation?

[RVDT]

Wikipedia is your friend -Notar (http://en.wikipedia.org/wiki/NOTAR) How it works (http://en.wikipedia.org/wiki/File:NOTAR_System.svg)

It should really be called No Visible Tail Rotor. Contrary to popular belief there is still a tail rotor and tail rotor gearbox and driveshaft etc. and in addition a composite tailboom with slots in it and a controllable thruster and controllable vertical fins and control cables and bellcranks and sector gears and bearings and.....................................................blah blah blah.

In autorotation the "autorotative driving section" of the disk which is making the blades rotate is in the inner part of the disk. The section of the disk that is providing "lift" (although not enough to sustain level flight but more than no lift at all i.e. glide) is in the outer part. Therefore the inner and outer part of the blade being connected there are no forces going through the transmission so there is very little torque reaction. The torque reaction that remains is in the opposite direction to powered flight as it is required to overcome friction in the main and tail rotor transmission, freewheel drag, swashplate bearing, mast bearing, still rotating fan etc etc. These items are all still using energy which is now only available from the main rotor.

A little quirk of the Notar is when you increase collective pitch on touchdown during autoration you will get antitorque from the Coanda effect when you don't really need it. This is a little different from "conventional" helicopters.

[Bertie Thruster]

just had a look.............found a 'driveshaft' and a 'tail rotor' but couldn't find a 'tail rotor gearbox'.

[jayteeto]

I hope you are all joking. Is there no torque to counteract in auturotation? Thats why you autorotate with a tail rotor failure. Thought it was April 1st for a moment.........

[Bertie Thruster]

except that for a "notar fan drive failure":

CAUTION: Do not attempt an autorotation from forward flight unless an actual double engine failure occurs.

[RVDT]

BT,

500N5400 NOTAR FAN GEARBOX

900D1400522-101 NOTAR FAN DRIVE ASSY

Conveniently missing from the marketing blurb.

To be clear, there IS torque reaction during autorotation.

[Shawn Coyle]

My spies tell me that while there is no problem with controlling yaw in autorotation, in the part between powered level flight and autorotation, i.e. a low power descent, yaw control is less than sparkling - some even report difficulty in turning right. Anyone confirm this?

[Bertie Thruster]

RVDT: Can't find a 'NOTAR FAN DRIVE ASSY' on mine, just a 'Fan Assembly, NOTAR' ! No gearbox there.

Shawn..what sort of airspeed , when you say 'low power descent'?

[Hughes500]

Shawn
Think your spies are wrong. Take a 520 put it in the hover with ysas turned on. You can then fly a circuit with feet off the pedals as long as you do a low powered descent and a gentle pull in power at the bottom
Interesting to watch non 520 pilots faces when you do it though. I cant say I have ever experienced yaw problems, dont know about 600 or 902 perhaps they are different

[chopjock]

Bertie Thruster
CAUTION: Do not attempt an autorotation from forward flight unless an actual double engine failure occurs.

Could someone explain ?

[Bertie Thruster]

sorry chop,

jayteetoo said; Thats why you autorotate with a tail rotor failure.

I, next post, said; except that for a "notar fan drive failure":

what i meant to say was; except you don't autorotate for a notar fan drive failure

I followed it with the RFM warning given for notar fan drive failure;

CAUTION: Do not attempt an autorotation from forward flight unless an actual double engine failure occurs.

I hope that is a bit clearer!

[md 600 driver]

hughes 500

600 is the same [as long as it has ysas on ysas was a extra on the 600 ]

[chopjock]

Well it's a little clearer, but I still do not understand why you should not autorotate after a fan failure and why you can not auto rotate unless you have a double engine failure?

[SkyyL4]

Here is how NOT to do it :eek:


jUVwFItH0I0

[Bertie Thruster]

Well it's a little clearer, but I still do not understand why you should not autorotate after a fan failure and why you can not auto rotate unless you have a double engine failure?

2 questions there i think. unless you are having me on!

1) 'conventional' autorotation does not work for a notar failure.

2) after a notar failure, if both engines happened to fail (for whatever reason) then not entering autorotation would be rather final!

[RVDT]

It's the softer option. Power on run-on landing at **knots?

Not possible without at least one engine of course.

The auto without the fan has probably never been proven nor does it have to be. The power on option can probably be demonstrated with a "zero anti-torque" setting.

Read this download (http://www.mlit.go.jp/jtsb/eng-air_report/JA6757.pdf) about a 900 in Japan.

[Stan Switek]

Good example here:

qTFVQOkAneM

[Ian Corrigible]

Here is how NOT to do it
The unfortunate irony here being that this training flight, flown with a factory pilot on board, was actually being filmed by other CBP pilots who had concerns over the 600N's autorotational characteristics (esp. in light of the loss of an aircraft during a post-IFSD auto in Februrary) and who were hoping to have their fears assuaged.

This fleet, the largest NOTAR fleet in the U.S. and the second largest worldwide, has now reportedly been grounded due to safety concerns.

I/C

[SkyyL4]

Ian,

It looks to me like this accident was pilot error and had nothing to do with the aircraft capabilities.

[Sulley]

Shawn -upon initial auto entry (902) the rotor rpm is or can be a little feisty to begin with.So what happens often is that the 'auto' is now effectively a low power descent not a true auto (15-20% torque) under these conditions turning right can be interesting. :ooh:

[DeltaNg]

Seems like a NOTAR is a lot of extra hassle for a dummy-proof helicopter.

[HueyLoach]

My spies tell me that while there is no problem with controlling yaw in autorotation, in the part between powered level flight and autorotation, i.e. a low power descent, yaw control is less than sparkling - some even report difficulty in turning right. Anyone confirm this?

Yes, yaw control is not as good as a conventional helicopter but once you get used to it (some tap dancing), is not a major issue. Difficulties doing right turns? I don't think so, if you maintain some airspeed and aircraft in trim. I am talking about the 600N. I don't know the 520 or 900.

[HueyLoach]

It looks to me like this accident was pilot error and had nothing to do with the aircraft capabilities.
It may have something to do with it; I don't know. In addition the 600N has one the highest disc loading figures in its weight class. What it means is that unless the pilot executes an almost flawless autorotation from entry to touchdown, his/her chances of not damaging the aircraft are slim. Very little margin for error in my opinion.

[rotorfossil]

Delta ng. I agree. When the 520 first came out, it was possible to compare it directly with the 500E. The 520 was slower, used more fuel and lifted less. I agree it was quieter, you could back it into a tree and idiots couldn't walk into the tail rotor. Didn't seem a particularly good deal overall.

[DeltaNg]

lol...

Lots of people go on about the backing it into a tree or whatever - does that mean it is like a dodgem car so that it just bounces off whatever it hits and you just carry on ? :}

Surely the next step is to get rid of the pesky rotor blades too, they can catch on things as well. NOTAR/NOBLA is the future......:ok:

[Bertie Thruster]

Why are you fretting so much about the 902, Craig?

Are you thinking of moving across the road?

[DeltaNg]

Thought about it, but no. I need to get really good at surfing - and quick ! :ok:

[jim63]

Seems alittle fast for practice autos.
Police Helicopter Pilot - Police Helicopter Journal - Video Of Border Patrol MD600 Helicopter Auto-HardLanding. (http://www.policehelicopterpilot.com/police-helicopter-journal/2009/10/30/video-of-border-patrol-md600-helicopter-auto-hard-landing.html)

[Nigel Osborn]

I'm sorry but from that video that simply looks like a bad auto. I'm quite sure FAA would have certified the 500 for autos, so unless there was a mechanical problem, what is left other than human error which unfortunately can happen to anyone.:confused:

[Trans Lift]

Looks like a crap auto to me too. Tried to flare but it was way too late...

[mfriskel]

I believe there were several successful autos prior to that one.

[SilsoeSid]

I love the comment;

Also, as I stated in the original post, I have personally received emergency procedures training from the same CFI on several occassions and can attest to his professionalism, outstanding skill level, and expert knowledge of all things helicopters. You be the judge.
:ugh:

psst...no-one mention Dennis!:E

[Hell Man]

Yes there was a Brit who's last name rhymed with the Grand Canyon who suffered a similar problem of fast approaching ground :ooh: in an HU269!

Perhaps lite helos should be fitted with a basic rad alt!

[helimutt]

Hell man surely you jest?? You really think doing aerobatics would give you time to be looking inside at the rad alt to see that you're 20' off the ground? What would you suggest you set the bug to as a warning when doing aerobatics then? :hmm:

[Ian Corrigible]

Confirmation of the fate of CBP's MD600Ns: CBP puts MD600 fleet into desert storage (http://www.helihub.com/2010/10/29/us-customs-border-protection-puts-md600-fleet-into-desert-storage/).

I/C

[Vertical Freedom]

Hmmmmmmm seems by that article the NOTAR does not auto so good, more like a greased anvil. Actually there is no such thing as a NOTAR, its just that the anti-torque control system is hidden from view, with some major disadvantages; does not work at altitude & gobbles more power than a Fenestron. But wow damn quiet :):) VF

[mfriskel]

I wouldn't say that NOTAR doesn't auto so good, but I would probably say that the USBP 600's and maybe even all 600's don't auto so good. I did not find them unpleasant at all to autorotate (to touchdown and up to max internal gross weight) in. One thing that has changed in recent years is the MR blades. There is signifigant differences in the lift capability and the autorotation charachteristics of a 369, 500N or 600N with blades produced by HTC (current factory blade) and the blades that were produced by Boeing (and before that MDHI or Hughes).
The 600 was an eye-opener the first time you did an auto, but once you learned the techniques was not a problem. You definatly did not want to doze off while flying though- you have to stay on your game.

Remember, in true autorotation you are not using anti-torque, only at most a little anti-friction. Guys that bitch about yaw at the bottom are landing with the engine driving the rotor (maybe the technique needs improved) or doing a power recovery (probably from a lower than 100% NR) If the NR is above 100% when you join the needles, you won't get a yaw. If you touchdown without the engine driving the rotor you will not get an uncontrollable yaw either.

The USBP disliked the 600 for more than just autorotation charachteristics. The biggest problem was trying to replace the beloved OH-6A with the 600. Too different of animal to compare. After you get a firm dislike for something, anything is better and it is hard to change minds that are made up.

There is such a thing as NOTAR, it is even trademarked! You are correct, NOTAR does not work at altitude, I have never landed or hovered above 12,500 Hd feet in a NOTAR (MD902 and MD600). But up to 12,500 I can say it worked every bit as well as tail-rotor machines I have flown at comperable weights.

[md 600 driver]

after spending a few hours throwing the 600 at the ground at mesa with mfriskel i didnt have any problems

i survived and so did the helicopter when i had a engine stop at cranfield [its a real quiet helicopter when the donkey stops ]

[Hughes500]

Just looked at the video, auto was crap, flying at what looks like down wind at less than 500 ft when entered, the " wings" werent even level when the ac flared and the flare was way way too late. Mind you impressed with the undercarriage !
Mark are htc blades with the new erosion strip( eliminating that " valley" behind the smaller strip) back to the level of the old MD blades ? Certainly having filled and faired my 101 htc blades put about 8 kts on the speed of a D model.

[mfriskel]

I can't answer to the "new" abrasion strip as I haven't flown them. If it fixes the problems it is a good thing that has been a long time comeing. Filling and fareing was a good "mod" to the abrasion strip, but by no means a fix to get back to the performance of the Boeing blades.
The other odd thing about those blades was the honeycomb patch that slightly deformed the outer portion of the blade. It had to have some aerodynamic effects on the blade.
If the "new" abrasion strips get you back to no more than 2 or 3 degrees of down tab in the major sections of the blades I would say they are better, but if you are still having to use nearly 5 degrees of down tab I would say no.

[handysnaks]

Actually there is no such thing as a NOTAR

It has a fan, not a tail rotor! so NOTAR is more than apt!:rolleyes:

[md 600 driver]

VFreedom

Total disagree

Yes it has a fan, but no where near the tail, so it's a NO tail rotor

[PANews]

There is background to this.

The USBP never selected the MD600 - it was decided from the start that it was unsuitable for their mission.

They selected the AS350. Unfortunately at that time the European manufacturer had been involved in what US Authorities thought to be shady trading [I am not sure of the exact circumnstances without more research] and they were forbidden to buy the EC product.

As soon as the period of prohibition finished the USBP were back at Eurocopter's door.

So it was not really the fault of the 600 it did not meet the spec., it was never selected against that specification, it was second best, and will have had its enemies from the start.

[AdamFrisch]

Does this mean I can get my hands on one of those laid-off BP 600's for small change?;)

[mfriskel]

PANEWS, you know that for FACT, or just what you would like to think? I am curious about the "prohibition" period. Never heard of that one. The USBP did select the MD600, that is why they were ordered and paid for. It was not a suitable replacement for the OH-6, but it was not marketed nor sold as a replacement, it was to suppliment in a different mission. Unfortunatly, the one that is in the air, or out of the hangar is the one that is used. What happens then is trying to compare apples to oranges, and the guys who liked apples didn't like what they had- they were also very vocal. The guys who liked oranges just kept doing their jobs.
USBP did not have good luck with the AS350 from the early 90s, well before delivery of the first MD600. I remember one rolling down a mountain in Arizona that was trying to do a job that an OH-6 would do just fine.
I also believe they have suffered fatal accident(s) in their AS350 fleet, but not in the MD600 fleet.

[mfriskel]

"It's the softer option. Power on run-on landing at **knots?

Not possible without at least one engine of course.

The auto without the fan has probably never been proven nor does it have to be. The power on option can probably be demonstrated with a "zero anti-torque" setting.

Read this download (http://www.mlit.go.jp/jtsb/eng-air_report/JA6757.pdf) about a 900 in Japan."

RVDT- It is really not possible to truely demonstrate a fan failure as minimum fan pitch in all three models is still a signifigant amount of airflow. The the thruster is open straight down or up to give you no thrust from the thruster. This will give you good COANDA effect and some anti-tq when the acft slows. The other control, the VSCS or vertical stabilizers will have some angle of incidence. With a true fan failure you would be able to hold full left pedal in a 500/600 and have anti-tq to quite a low airspeed. If I was an engineer, I would have a switch in the 902 that would allow a pilot to set any of three set angles on the VSCS for emergency. Could be nice for either stuck thruster or failed fan.
The Japan accident was very interesting. The pilot flew that acft for over an hour before attempting to land. He had good control until he performed a fairly tight turn to final and slowed the airspeed to a very slow forward speed and a slight climb. At that point the acft started to spin and it was "Mister Toad's Wild Ride" from 200 feet AGL. If you ever get a chance to see that video, it will open your eyes for sure. The structure of the acft saved those two guys bacon for sure.