Downwind Autorotations?

[HCU]

We all know should you suffer an engine failure downwind you would perform a 180 degree auto to finish flaring into wind.

However there are apparently 4 defined reasons why it's bad to auto downwind - any ideas?

- Fast ground run on speed?
- Larger glide distance?
- poor IAS in relation to ground speed?
- ?

[Arm out the window]

If going for zero ground speed, you'll experience zero and then a little bit of negative airspeed in the latter stages of the flare, therefore crunching on harder than normal (eg. into a 10 kt breeze).
Directional control in the last stages would also be harder with the wind up the choof.

[SASless]

I am confused....what does "a slight bit of negative airspeed" have to do with "crunching down harder"?

[griffothefog]

Nowt, if you drive a chinook

[Arm out the window]

Maybe I didn't put that quite right - if a 'normal' auto had 10 kts on the nose when you got zero ground speed, you'd have a decent amount of cushioning power.
If there's some tailwind, somewhere in the latter part of the flare you'll have zero airspeed - if that's the time you're levelling and cushioning on, it'll be like doing a zero speeder in nil wind, so not so much spare collective for the cushion.
Going through that point and getting some negative airspeed might help you out from the cushioning point of view, I suppose, but the weathercocking effect would probably be a pain for directional control.

[DennisK]

Autorotations with tail wind.

My two pennorth.

Inadvisable ... final flare has reduced cyclic responsiveness and quite likely to result in a higher speed 'run on' with increased risk of roll over.

However, when teaching advanced emergency handling, there is a school of thought that says 'providing there is a reserve of height ... and particularly where the surface offers minimum landing site options ... following the failure, it can be preferable to initially 'Turn downwind.'

The procedure allows the heli to cover more of the surface and provides greater selection of suitable landing sites. Always providing the heli is returned to an 'into wind' position for the actaul touch down.

I teach the method when offering mutual advanced continuation training to interested pilots.

Happy and safe flying out there.

DRK

[A.Agincourt]

HCU
Downwind Autorotations?
We all know should you suffer an engine failure downwind you would perform a 180 degree auto to finish flaring into wind.

Really? To be honest I cannot think of a single set of circumstances other than as a demonstration why not, when I would even contemplate such a manoeuvre.

Best Wishes

[Bertie Thruster]

Really? To be honest I cannot think Mr Agincourt has flown a military Gazelle low level.

[A.Agincourt]

So please explain the technique Bertie - in a Gazelle. Lets say 100 knots downwind at 50' over a set of ploughed fields. W/V - say 270/20 heading on entry 090.

Curiosity here

Best Wishes

[3top]

Hi all,

a short while ago I had a discussion about a similar subject with a "Safety Counselor".

The subject was "Downwind take off - loss of engine"

a) I do not generally promote downwind take offs.

b) In this case though it is (in my opinion...) preferable to a take-off into the general wind direction.

The hangar to take off from is at the up-wind end of the runway. Directly after the runway there is a village/town.

Downwind is all open fields, mostly level.

Downwind take off can be done over a blacktop runway or a hard grass area beside the runway.

So far I was always able to creep slightly into the wind (quartering tailwind),
obtain recommended climbout speed (60-65 IAS) before leaving the boundaries of the airport. In case of an engine failure, my selection would be in this case to run it on straight ahead (AS350B3, other aircraft may be less forgiving when putting them down at 30-40 kts....).

c) It was suggested and asked, why I would not hover downwind and then take off into the wind.

To hover downwind in the usual conditions, seems (to me...) no less dangerous than "let the bird run". Especially if it behaves well - no overly itchy tail, good power, good acceleration....

Further, even if I hover all the way to end of the runway (keep in mind downwind...) I still would have to do at least a 120 degree turn (quartering tailwind again) to avoid going over the town at less than 500 ft, although this would be at an altitude of around 500 ft.
Never the less, an engine failure at 500 ft at 70 kts IAS and I still have to go downwind before I can turn into the wind again, is not my choice if can avoid it!
The town is arranged in such a manner, that even from a 1000 ft it would be hard to find a place to go if an auto should become necessary.....

Back to the downwind hover: Obviously it would be a rather high torque, low speed situation. If a power failure occurs in this situation I would not consider it any less challenging than a run-on at 30-40 kts Groundspeed.

I had a sudden engine stoppage in a R-22 in a hover (my fault/stupidity) and was not prepared for the violent fast turn to the left!! It is quite a difference from practising a soft (or even snappy) engine failure in a hover (you are prepared for it and counting on it!), to the real thing. This "occurance" happened into the wind. Don't want to know what it looks like downwind!

My preference would be with the downwind run-on in my specific case.


d) Again! I do not promote downwind autos as a general maneuver!

Off course one has to take into account all factors in a specific case:

1 - Straight downwind versus slightly quartering downwind
2 - Engine power available for take-off (useless when the engine is gone, but struggling to stay in the air while trying to run for take-off is not good enough...)
3 - Aircraft - familiarity, tendency to run well on the ground, roll-over tendency, weight/power
4 - Terrain in case of emergency
5 - Above all, pilot proficieny


In this specific case I prefer the down wind take-off, because:

1 - Enough Power to get going fast
2 - Aircraft is very well behaved on the ground (running on situation)
3 - Aircraft has a very strong landing gear
4 - Complete avoidance of over flight of the town
5 - Fraction of time spent in adverse (tailwind) situation versus prolonged downwind hover (see my rational about hover power failures above)
6 - Terrain favorable for run-on landing


My personal choice in this specific case is to limit the exposed time as much as possible.


Of course before going towards "advanced maneuvers", one has to analyze the specific situation and if possible, practice simulated situations with a proficient instructor.
Remember, there is no old heroes!

If you are "working" with your helicopter, a lot of times you would have no choice but downwind (or any wind), because it is the only option.
No matter what, keep flying the aircraft until everything has stopped moving.
If the engine fails you really just care to be able to walk away, no matter if the airframe ever flies again - if it does, it is a bonus...


Back to lurking!

Fire away!

3top

[Fly_For_Fun]

A.Agincourt

So please explain the technique Bertie - in a Gazelle. Lets say 100 knots downwind at 50' over a set of ploughed fields. W/V - say 270/20 heading on entry 090.

What are you doing at 50ft agl. Another reason for the 500ft rule perhaps.

Bertie you are my hero.

[Bertie Thruster]

500ft? Our mil auths often used to read "transit not above 150ft agl."


A. Agincourt.....I don't think I'd be happy cruising downwind (or even into wind) at 100kt/50ft, so lets say Intermediate Pitch Setting with a 125 kt IAS approx (some cabs would give you 130kt)

1.Dowwind you had always just flown over and observed and had just behind you the terrain you would have for a forced landing if the donk stopped.

2. If the terrain just behind was ok when the donk stops;you're laughing;

3. Bang!..... Coordinated zoom climb to what height you can get at 60-70 kt (up to 300ft, if you got it going pronto,)

4. 180' turn or a/r into w/v.

5.Land, aiming for min fwd ground speed.

If, due to the nature of the terrain just passed you elected to continue and land downwind then a flare to height was still required to get the airspeed off before hitting the ground.

All this needed practice. We were given plenty. (one of our QHI's would initiate this exercise at max chat, 20-30ft downwind by chopping the throttle!! That was on a large grass airfield however and you knew it was coming......good fun though!)

I only had 1 engine failure in a Gazelle. Luckily it was into wind. (and conveniently at a 5 ft hover!)


Chuteless; spot on! I presume "GOG" is some reference to grey hair? (very little actually) Abbreviation search gave me;

"GOG: Gift of God"

[HELOFAN]

So avoiding settling with power is an answer then?

but wait there is more.

HF

[Rotorbee]

So avoiding settling with power is an answer then?

You can't get into settling with power in an autorotation. No power, no settling with it. And as we are on the subject, no ring state vortex either.

[Bertie Thruster]

PS oh to be working an aircraft that could gain 300 feet from engine failure

It made Gazelle 'quickstops' a really good coordination exercise; a twitch too much on the cyclic and you went up like a rocket.

[HELOFAN]

Oh I thought we were PRACTICING auto's downwind meant recovering with power, not sitting it down as not everyone likes to teach full downs to al students at every stage.


Course now I dont see the word practice in the ORIGINAL post so that would make me assuming and we all know what that makes us.

So then I guess I would rather the into wind auto over the with wind auto so that I still have some lift available for the nice cusioned flare rather than the crunching, heavy run on landing with wind auto.

A little more lift is better than a little less isnt it.
Doesnt VRS = SWP?



HF

[A.Agincourt]

Fly_For_Fun
A.Agincourt

Quote:
So please explain the technique Bertie - in a Gazelle. Lets say 100 knots downwind at 50' over a set of ploughed fields. W/V - say 270/20 heading on entry 090.
What are you doing at 50ft agl. Another reason for the 500ft rule perhaps.

Bertie you are my hero.

You might have missed Bertie's point - "military" Gazelle was specified. Military aircrew frequently fly at 50 feet AGL or to be more precise 50' above obstacles en-route when engaged on tactical operations or practising for such.

The 500' rule is not always mandatory, under certain circumstances.

You nominate hero's rather to soon methinks.

Best Wishes

[[email protected]]

We use flare effect to stop the aircraft during a normal EoL - the airflow is presented to the underside of the disc by selecting a nose up attitude which increases rotor thrust, reduces RoD and forward speed. Now try this with a 20 kt tailwind - as you pass zero airspeed you still have 20 kts groundspeed to get rid of so you pull the nose up further but nothing happens. Why? because the air is approaching the disc from behind so all the nose up in the world won't generate any flare effect. You will still hit the ground at 20 kts but with the tail striking first because you have so much nose up attitude. Or worse - you will start to raise the lever when the nose up doesn't work and hit even harder with rapidly decaying Nr.

Try a downwind approach to the hover in 20 kts of wind if you don't believe me - it takes more nose up to slow the aircraft down and more power which is the reason we teach slow walking pace for downwind approaches - flaring hard at the end because you are coming in hot will lead to embarassment.

[A.Agincourt]

Bertie:

I don't think I'd be happy cruising downwind (or even into wind) at 100kt/50ft,

Hell's teeth old boy, neither would I but I never specified that it was in a cruise profile. You'll agree I am sure, that these things always seem to occur at the least opportune moment. I have no doubt's that you have indeed carried out the above profile - at some point in time. Tell me clearly that you have not please.

so lets say Intermediate Pitch Setting with a 125 kt IAS approx (some cabs would give you 130kt)

Ok....

1.Dowwind you had always just flown over and observed and had just behind you the terrain you would have for a forced landing if the donk stopped.

As always.......

2. If the terrain just behind was ok when the donk stops;you're laughing;
3. Bang!..... Coordinated zoom climb to what height you can get at 60-70 kt (up to 300ft, if you got it going pronto,)
4. 180' turn or a/r into w/v.
5.Land, aiming for min fwd ground speed.

Agreed.........but you left off the end the following techniques available following the zoom and 180. You also are aware of course, that the manoeuvre you describe whilst usable, does have a very clear danger in terms of cyclic control and the old issue of cyclic against gut, nose down and no airspeed. Which is why a full 180 in this event is not completely without danger. But it does depend upon the W/V value. The lower the velocity the less of a problem and vice versa.

All this needed practice. We were given plenty. (one of our QHI's would initiate this exercise at max chat, 20-30ft downwind by chopping the throttle!! That was on a large grass airfield however and you knew it was coming......good fun though!)

Indeed.

I only had 1 engine failure in a Gazelle. Luckily it was into wind. (and conveniently at a 5 ft hover!)

In the scenario you proposition above, I'd recommend that following the zoom to 300 feet [or whatever is achievable] you ensure you have 20 knots plus the wind speed indicated and do not turn more than 100 degrees until you have positively identified and selected the point to go to. The turn should be a low angle [less than 15 degrees of bank] without attitude correction. Once into wind you can then adjust accordingly and as you mention, minimum TD velocity in both directions is preferable.

Best Wishes

[A.Agincourt]

chuteless : A.Agincourt must own a huge amount of teddies

when he throws one away it seems to get replaced awful quick

I am not too sure to what you are referring. If you could post a reference or something.

Best Wishes