Zero speed auto > Hover (without gaining airspeed)

[rudestuff]

My Roommate (who's recently got his CFI and therefore knows everything about flying there is to know) Was telling me his theory of how you could be in a zero airspeed auto, then recover to a hover just by pulling enough power fast enough.

He thinks that it is possible to 'power' his way out of it. I told him it seems to me he doesn't really understand the concept of SWP if he thinks that. I'm sure more experienced people than me can help convince him...

As I understand it, in autorotation the blade roots are stalled - any additon of power neccesitates up-collective (to prevent overspeed) which increases the stall/tip vortices etc and at zero A/S would send you straight into SWP.

[Matthew Parsons]

SWP...This could be entertaining.

Can you bring in power at the bottom of a zero airspeed autorotation to arrive at a hover?

Best answer: it depends. Depends on Nr droop, engine governing characteristics, rate of descent, and power available. (might have missed something)

Settling with power implies you don't have sufficient power to maintain level. If that is true then you will not be able to arrest your descent. If you have plenty of excess power and the Nr doesn't droop too much you might be able to get away with this.

Vortex ring state would be my biggest concern. You have zero forward airspeed, rate of descent, and then you bring in power, giving the three conditions that are required. Whether you get into VRS depends on characteristics of the helicopter, your rate of descent, and the power that you apply. This would be a very bad thing to encounter.

I do not recommend trying this.

Matthew.

[cl12pv2s]

Matthew,

Without wanting to start a debate on this, I think rudestuff was actually refering to SWP due to Vortex Ring State.

Rudestuff, you are saying,

Imagine you drop vertically in autorotation, aiming to pull collective really aggressively to reduce your rate of descent to a survivable rate...

I guess it could be possible to do given the right equipment and pilot...

I don't think that VRS would develop fast enough in this short timespan to be of consequence

...the deceleration required to reduce the decent rate to a survivable one is quite a lot. This would sup a great deal of Nr, so could only realistly be done with a high-inertia rotor system or with absolutely split second timing and a sharp yank on the collective.

Well, in practice the timing would need to be so perfect that it's not a method to count on as a means of surviving an engine failure...As Nick posts below, an experienced pilot with 'split' second accuracy in timing and the right helicopter could pull this one off

So no, I'm not going to try that any time soon!

cl12pv2s

[malabo]

Been there done that, only to landing, not hover. B206, H300 etc. You'd better have the throttle off, otherwise you'll overtorque at the bottom. Takes a fine eye to gauge the exact millisecond for that one sharp collective pull at the bottom. Clever instructor trick if you do it all the time. Wasted as a training technique to the unwashed that do a full on auto every 10 years or so.

[NickLappos]

The idea that it is "impossible" to go vertically upward from a vertically downward autorotation because you will somehow slip into unrecoverable vortex ring state is simply not true. The myths of vortex ring state are legend, and hardly worth repeating, so let me state the opposite:

The real rules of Vortex Ring State:

1) If you have lots of excess power, you can lift collective and fly vertically out of VRS. VRS is not a Black Hole, it is a place where the rotor has greatly increased power required, because it is wasting so much power recirculating air. If you have enough excess power (about twice the power needed to HOGE) you can simply apply collective and smoothly go from descent to climb, a vertical climb.

2) In a zero knot auto, you can recover with engine power and climb vertically, without gobs of excess power (but certainly with more than HOGE power) just do not dwell at VRS state descent rates (about 1500 to 2000 fpm for most helos, 1000 or so for light pistons) but rather climb smartly trhu the descent into a climb.

3) If you have enough rotor inertia, you can land from a zero knot autorotation without rolling up the engine throttles, simply lift collective and time it right. You will NOT experience VRS as you stop the descent, not even a burble. The flow for VRS has to establish, it does not automatically present itself when you get a momentary combination of ROD and speed. I have done these by the dozens in Bells, and VRS is not a consideration.

[rotorrookie]

My Roommate (who's recently got his CFI and therefore knows everything about flying there is to know)

and he really thought this was possible ?????
was he sleeping in principles of flight classes????

and he's CFI now.... omg

[MightyGem]

(who's recently got his CFI and therefore knows everything about flying there is to know)

Hmmm...I don't think there's anyone who knows all there is about flying. Or will somebody prove me wrong...

[212man]

rotorookie, you obviously didn't read the post above yours!

[WSPS]

R22 / R44

Hi there,

any of you chaps out there tried it with an R22 or R44?

We do quite a lot of no-flare auto's where you come in at 40-50 KIAS, bring your rotor-rpm up to maximum and do a full touch-down. This works quite well even in a light piston.

But trying a no-speed in an R22 would seem very hairy at best to me.

So anyone out there who gave it a try?

Keep the rotor in the green

[oldpinger]

I'm pretty sure it is impossible to get into vortex ring in any kind of auto (except a botched power recovery) as you need an induced flow through the disk to get into vortex ring, therefore in auto, no induced flow and not possible. A low speed auto only gives you two of the requirements for VRS, ie low speed and a rate of descent. I imagine if you are pulling power to overshoot from an auto and still descending with low speed on, could be exciting, but from experience, some helos are difficult to get into vortex ring even if you try.
Back in the days of gazelles and 705sqn we used to do zero speed autos by plummetting down at about 40kts indicated, with the engine at idle, wait until the requisite moment and cushion like a b#stard running along the ground at about 30kts. VERY sporting and I'm sure the instructors didn't get paid enough.
Never hit VRS in that case anyway.


Oops, just read Mr Lappos' reply above, all covered...

[cl12pv2s]

we used to do zero speed autos by plummetting down at about 40kts indicated

Hold on...are we talking two different things here?

I read the original question to mean, vertical descent with 0 indicated airspeed. That to me is a 'zero speed auto'.

Oldpinger, you are describing what I would call a 'constant attitude / no flare' auto.

Nick, which were you refering to?

cl12pv2s

[Aesir]

I have done these by the dozens in Bells,

This is the key here! Donīt try this in any other product

[BlenderPilot]

I attended Bell 206 training at a large GOM operator, (my company paid for me to go there, I didn't work for them) and when I got there I was shown the helicopter that I was going to begin training in, a 206 with fixed floats, I inquired as to why we were going to do autos in a float equipped helicopter since I never flew over water?

They said that from they have been told by my boss I spent a lot of time flying low and slow and that they were going to teach me vertical autos from the within the "dead man's curve".

So off we went, hover at say 250 feet, chop the throttle, vertical descent and as the world came up to us fastest than I have ever seen before, a sharp collective pull stopped the descent, lots of water splashing everywhere, chin bubbles partially submerged for a second or two (reason for a float equipped helicopter) and I even got to see a Crawfish sliding down the windshield once!, helicopter and passengers in one piece.

And there you go, almost vertical autorotation with no flare, just a collective pull to stop the descent, on a side note, the collective pull had to be extremely well timed, sharp without being abrupt, and I remember the collective almost touching the roof! I would never try this in skid helicopter since the chances of messing it up seem astronomical to me.

[170']

More in context with zero speed auto's than SWP...

I had a chance to go thru CHC's mountain flying course in Penticton...

This was a long time ago (JR was the CFI,maybe still is, anyone know?)...During the course we were taught 100' hovering auto's in the Short leg 206's used for training...

Pretty spooky stuff at first, but by the time you get to do it yourself, you were pretty happy that the IP's there are (were?) helo God's, and would keep you out of trouble.

These weren't power recoveries, but to the ground...

It was the first and last time I ever got to practise the manouevre and wouldn't want to try it solo as a training exercise. But life gave me an opportunity for real, with a busted short shaft in a UH1H .

Basically just went 210 feet straight down, did a partial pitch pull(and lever down again) around 80-100' and then waited 'til I couldn't stand it any more and pulled it all in....wrecked the machine due hostile terrain. Can't really say how it would've worked out on flat clear ground. but I think SWP or VRS is the last of your worries in this type of scenario, no time for anything to develop....more a case of lucking out with the timing...

I think the average pilot(me) is pretty lucky to land undamaged from a vertical auto above the normal hover auto height,plus or minus a few feet...simply because we don't get a chance to practice!

In regards to flying out of SWP/VRS (hard to find a difference while it's happening) with Power, I have to agree with Nick Lappos...Done it many times with 214B's which leads me to agree with Aesir on Bell products...

Merry Christmas to all...

[KikoLobo]

Blender!

Where did you do this?

Its a nice idea... The floats i mean


I did some OGE Hovering autos at bell school, we where about 200-250 feet and the 206B, gladly stopped the descent rate with an abrupt collective pull at the right time (at the bottom )...

The only thing to notice, is that it was me, the pilot and 40 minutes worth of fuel on board on a very low altitude place (alliance airport, in Dallas), the only thing that was not on our favor was low winds (almost zero wind) and hot day. Not humid though. But very low on weight... Certainly teached me what i should try to avoid flying in....

QUESTION (NO DEBATE PLEASE!): SWP or VRT, requires POWER... So how can one enter one in an auto rotation??? (Not possible). Also some concerns grew that you could enter one on the recovery process, well if you pull collective at the last moment, arrest descend and the open the throttle, you can't get in there, cause ur descent rate its going to be slower than 300fpm, or you are dead.

A word though... I would never attempt to recover from this, i would go to land, and attempt it with a good instructor that knows what he is doing... If on a robbie, try it with a factory instructor or someone with vast experience, if on a bell try it with a good bell instructor.

170\'

How did the UH1H bahaves on autos, compared to a 206B?

That was a job well done man!
Congrats. Do you have any pics?

What cause the shaft brakage?

[happyhamster]

Blender - was that the recommeded procedure for landing a 206 with floats onto the water ?

[diethelm]

I thought in autorotation that the rotor system was, in "Autorotative State"?

[170']

KikoLobo

It was intergranular cracking due to corrosion on the inner surface according to the Feds, Which I think is fairly unusual.

Normally the unmodified S/S fails with too many high cycle counts on 35 year old grease...This was way back when and we were using pretty old machines and original shafts and exmil grease..The K-flex solved the problem...

The UH1H is a sweetheart in an auto, but I prefer the 206 if we're playing Auto's as it's more manouverable close to the ground if you really want to make that spot... and I'll try to dig up the photos after the break, not very good as they were taken by our POI with a Fed camera...supplied by the lowest bidder ;-)

Feliz Navidad

[Matthew Parsons]

Just to clear a few things up because unlike any other topic, this one has expanded from the orginal question.


1. Landing a zero speed auto without an engine is possible. Many of us have done it, but it is a technique requiring timing, the right machine, the right conditions (DA, weight mostly).

2. Power recovery from a zero speed auto is a very different thing from #1. With power recovery you can get into other problems.

3. If you had enough power you can avoid spending too much time at a possible VRS condition. If you had enough power you can fly out of VRS (I've never tried it, but theory seems valid). However...everyone who has complained about not having enough power in your helicopter, raise your hand. Thought so.

Unless you can be convinced that you have enough power to try this before entering, there is no way you should even consider it. If it's not in your flight manual don't do it. If you have better options, use them.

[BlenderPilot]

These pictures were taken on precisely the day of my vertical autotraining.

This was some of the best training I have ever recieved, out of the box, real world oriented, to say the least.

Compared to factory training I have found that going to real operators for training is very useful, for example last year I went for training in Oregon with an operator, now that was an eye opening experience! Real world, not routine, the other guys at my company have recently been to Canadian H for AS350 training and say it has been the best training ever had, better than factory. Same in my case for Bell training, the training recieved from real operators has been better than factory training, MUCH CHEAPER TOO.

IMHO Factory is good for ground training, but in my experience flight training has always been better with operators, their instructors are usually not political about training, they will keep you safe and everything else comes second, could it have to do anything with lawsuits?

That's me in both pictures.