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Entering autos: discussion split from Glasgow crash thread

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Entering autos: discussion split from Glasgow crash thread

Old 14th Dec 2013, 08:40
  #101 (permalink)  
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Goolie's rotor-tipped in-flight-autorotaion-restart-system:

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Old 14th Dec 2013, 08:44
  #102 (permalink)  
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As a former fixed wing pilot, my real worry is a bunch of helo pilots arguing about how to fly a helo after an ehgine failure.
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Old 14th Dec 2013, 09:01
  #103 (permalink)  
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Originally Posted by SLFool View Post

Been done.
Quite so.

Indeed since the days of the Catherine Wheel!
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Old 14th Dec 2013, 09:30
  #104 (permalink)  
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Why run on?

Vertical speed and horizontal speed each have v-squared energy terms.
Rotor speed has an rpm-squared energy term, and a drag/work-done-moving-air v-squared dissipation term. Potential energy has a height dependence.

These components of energy all have to sum to zero at the end of the process, and the key goal is low vertical speed at zero height.

Having lots of energy dissipated in drag from the rotor is good, but there's only one solution to the energy sum with horizontal and vertical speed both zero on touchdown. That might not be achievable.

The potential energy in a 200 feet drop is about equal to the kinetic energies of a 70 knot speed and a ~200rpm rotor speed. There's also the initial groundspeed, and the energy lost beating up the air to be considered.
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Old 14th Dec 2013, 09:44
  #105 (permalink)  
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Firstly, may I add to the many messages of condolence to the families of the people on the ground, the helicopter flight crew, and the Police Force involved.

We have the best people in the World investigating the accident; the AAIB. Please let them do their job.

I had the pleasure of meeting Pete and his lovely wife in October this year.
Pete may be new to PPRuNe but he is most certainly not new to flying helicopters; he would most likely put a reasonable number of you 'experts' to shame, a true professional.

Pete (and he will correct me if I am mistaken) is referring to the use of available stored energy that the pilot can call upon to prevent Low RPM Rotor Stall should they find themselves in a situation where their single engine has failed.

Cruise Flight:
With a low inertia rotor system, the least amount of energy stored in the helicopter and which is immediately available to the pilot, is that stored in the main rotor (kinetic). Hence the rotor RPM decays quickly.
However, the most amount of stored energy available is stored in the forward airspeed and this is available to the pilot instantly. The pilot can call on this energy to prevent rotor rpm decay during the entry into autorotation by applying aft cyclic.
In fact if I take an R22 at a 90kt IAS cruise flight condition I have some 8 seconds of stored kinetic energy that would allow me plenty of time to lower the collective (Note: it does not change the intervention time). It is there…. so use it.
For those that say 'well I might need it for range' then range is of no use to you if you are a brick! The primary task is to establish autorotation. If you fly defensively you will reduce the requirement for range autos (I am talking single engine operation).

In the hover the pilot should lower the collective lever and allow the helicopter to descend and regain the RRPM before applying fwd cyclic for airspeed; the positive effect of increasing the airspeed is an increase in RRPM.
However there is a negative first, and that is a reduction of RRPM. So if the pilot should apply fwd cyclic before the RRPM has recovered this will add to their problems.

There is more but I am due out to dinner.

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Old 14th Dec 2013, 09:51
  #106 (permalink)  
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one might end up in IMC conditions at some important part of the rocket assisted autorotation? perhaps better with compressed air..
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Old 14th Dec 2013, 11:41
  #107 (permalink)  
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To SLFool

I think the answer is - it depends.

Can your helicopter descend vertically without power at a steady speed?
Is that speed slow enough that it can be exchanged for rotor speed by increasing collective pitch just before touchdown?

If not - higher weight? smaller rotor? - then some forward speed is inevitable, to give more lift at lower collective pitch, so that the vertical speed is slow enough that it can be pulled away on touchdown.

In the video it looks like - from those heights/speeds and in that helicopter - forward speed is required. It never looks like a stable state of descent is reached in the time available (although the ground is out of shot), and so there's a juggling of rotor speed, forward and vertical speed throughout the descent.

A lot of relevant issues seem to be be raised in the text with
Height?velocity diagram - Wikipedia, the free encyclopedia

In steady vertical descent at speed v_d, potential energy is being exchanged for kinetic energy of the air beaten down through the rotor disk at v_f, and a little into turbulent motion too. From energy conservation M.g.v_d ~ A.rho.v_f.v_f.v_f/2, and from momentum/Newton-II M.g ~ A.rho.v_f.v_f. This gives v_f scaling with the square root of M/(A.rho), making it easier in dense air, with low weight and a big rotor, and gives a simplistic vertical speed of v_d ~ v_f/2. That's not comfortably distant from a vortex ring state - as v_f ~ v_d, rather than v_f >> v_d.

For the R44, A~75 sq-m, M~1000kg, so v_f ~ 10 m/s, v_d~5 m/s: I'd say that 5 m/s makes sense from the video.
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Old 14th Dec 2013, 12:24
  #108 (permalink)  
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Watching the video of the R22 doing HOGE autorotations reminds me of Shooting Craps with Loaded Dice.....it works so long as the Dice are your own and you know what numbers they will show when rolled.

As we have pointed out in the past....knowing the engine is going to quit and being prepared for it does not happen in the real World.

I wonder....what would the Video look like if you added in a mere 1.0 Second delay to the Pilot moving any controls? Better yet add a 2.0 second delay which would still be a pretty quick response by a Pilot who experiences an engine failure for real.....reckon the end would be as pretty?

Ask Nick Lappos, Shawn Coyle, and John Dixson about that.....as they have all done it in their Test Work.

Last edited by SASless; 14th Dec 2013 at 12:40.
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Old 14th Dec 2013, 12:43
  #109 (permalink)  
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I wonder....what would the Video look like if you added in a mere 1.0 Second delay to the Pilot moving any controls? Better yet add a 2.0 second delay which would still be a pretty quick response by a Pilot who experiences an engine failure for real.....
But any pilot HOGE would be primed and waiting for that yaw and change in engine noise. Unlikely just freezing on the controls...
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Old 14th Dec 2013, 13:00
  #110 (permalink)  
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Unless your job involves long periods of OGE hovering when you are usually concentrating on performing a task or mission.

There is no ONE way of entering autorotation that will optimise your chances in every given situation but the basic idea that lowering the collective fully WILL prevent any further Nr decay and flaring with the cyclic WILL (if you have any forward speed) help recover the Nr - is what we should be highlighting to all and sundry, especially the low timers.

One exception maybe - the Germans used to teach, on the Huey at nap of the earth flying heights, to raise the lever first to get the tail clear of the ground before flaring so you didn't add a tail rotor strike to your list of woes. But of course the Huey had massive rotor inertia - try that in a Robbie and it would go very wrong very quickly
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Old 14th Dec 2013, 13:13
  #111 (permalink)  
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The aft cyclic also loads the head a bit in opposition to the unload that lowering the collective may induce, depending upon rate of control movement. HC raised that point early on in this discussion, and given how rotor blades get their autorotational qualities, his early point on "don't unload the head!" remains sound advice ... and is consistent with various posts on energy management, Nr maintenance, and control manipulation.

I guess Pete has seen this as an instructor, but Savoia talks to what I have observed. Lowering the collective does not/should not happen in isolation. When flying a helicopter, one typically has to move the cyclic (and pedals) in compensation when the collective is moved depending upon the maneuver and probably on the amount of automatic/stabilization features that a given helicopter has, and has on at the time. For example, if you have an "altitude hold" feature engaged when the engines quit, you either have to override is with force or disengage it while lowering the collective and adjusting attitude at the same time.

Without a bit of practice at that, the reaction won't be instinctive, and one could indeed get a bit behind the aircraft. The Real Life experiences shared in the last few pages are most instructive, and I thank the gentlemen for taking the time to share with us their actual experiences. The only engine failures or rollback I ever had were on two engined machines, so a precautionary landing was done: hooray for two engines!

I am not sure why Pete made the case about a deep dark secret. What he may be reflecting is what he's seen people actually do, which means, he may be pointing out what reflexes and instincts seem to happen in aircraft, rather than what someone may or may not have been taught.

From the Australian teaching manual: LEARNING OUTCOMES:
The student will be able to follow the PFL drill and satisfactorily enter autorotation, glide towards a selected area, make a distress call and secure the aircraft for a landing. For the practice situation, the student will be able to overshoot safely by 500ft AGL.
An unpowered helicopter does not so much glide as plummet.
(With a nod to Monty Python and the flying sheep sketch )

Last edited by Lonewolf_50; 14th Dec 2013 at 13:25.
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Old 14th Dec 2013, 13:26
  #112 (permalink)  
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But any pilot HOGE would be primed and waiting for that yaw and change in engine noise. Unlikely just freezing on the controls...
Done any long lining....Forest Fire fighting....fertilizing with a bucket....fish hauling....construction work.....Cherry Drying?

Pilots do not go about their business day after day....hour after hour....sat up on their seat with their mind alert and focused upon responding to an engine failure....that just doesn't happen unless something alerts them to a problem beforehand.

You focus your attention on the immediate tasks at hand and hopefully your training and experience is such that you react properly when the time comes and you do so in a very timely manner which requires that initial response to be instinctual and correct for the situation.


The US Army did the same as the Germans on that.....as when flying very close to the Surface at or above 90 Knots....you did have to "Pop" the Collective first....then apply a large amount of Aft Cyclic to Climb to about 300 feet before reaching 60 Knots and initiating a "normal" autorotation.

Yes....the old Huey has lots of Inertia in the Rotor system....which has saved a lot of lives over the years. The transition to the Huey from Low Inertia Rotor Systems takes some understanding and acceptance, in the past I have found some reluctance to that when doing Conversion training.

Usually it takes doing a Hovering Autorotation....landing to the ground....then picking the aircraft up and repeating the maneuver while turning the aircraft 180 degrees without using any throttle, to get the point across.

Don't be trying that with your Gazelle.
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Old 14th Dec 2013, 13:36
  #113 (permalink)  
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My point entirely SAS

Personally I have always taught a co-ordinated entry to auto such that the rate of lever lowering or the rate of application of aft cyclic are variables based on the situation. The only real exception is the high hover although, as has been said before, the nose will drop as the lever is lowered so some aft cyclic will be required unless you want to gain airspeed.
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Old 14th Dec 2013, 13:40
  #114 (permalink)  
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Chop Jock

Someone who doesn't fly much OGE hovering might be primed I agree,and they should be! But by far; most slingloads percentage wise are performed by people who do it all day everyday and it becomes just a standard flight regime.When I'm assembling something with a 150-200 foot line, I'm mostly focused on not screwing up and hurting someone on the ground/tower or whatever. That and not looking like a schmuck if I do screw up!
The actual flying is just automatic.

In my experience and speaking only for myself. I do not respond in 1.6 seconds (I read somewhere I should) It takes me longer than that to think
F*** what is it now!

As I said earlier, it's impossible to stay primed and ready for immediate action all day long (very long days in utility work). It's such a normal procedure you can compare it to taking off from a runway for an airplane. yes a degree of alertness is always there, but fatigue and sometimes boredom take their toll.
We as a species are just unable to function in a constant state of super heightened alert.

Just an opinion, with no math or stats to back it up ;-)

Last edited by 170'; 14th Dec 2013 at 13:58.
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Old 14th Dec 2013, 13:44
  #115 (permalink)  
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Takes us back to a discussion about Mode White, Green, Yellow, and Red Modes of Piloting!

The transition from each is pretty quick....but to jump a Mode does not go quickly or well and to jump two Modes scares the Bejeesus out you.

Pilots should stay in the Green Mode....and never the White! Occasional visits to the Yellow Mode are normal, expected, and consistent with good Piloting.

Forays into the Red Mode suggest unexpected mechanical problems with the aircraft or sudden abnormal events occurring from outside sources not under the Pilot's control or having been caught smack dab in the middle of a White Mode Experience.

The White Mode is that warm, fuzzy, feel good, thinking about Dinner, cuddling with your Girl Friend before going home for Dinner with the Wife sort of mental state....where you are miles away from where you are sitting.

The Green Mode is you are paying attention to what is going on....are attuned to the situation so you are anticipating any actions you might have to take, still relaxed and comfortable.

The Yellow Mode is when you tweak to the need to pay attention to a specific issue that may require distinct action in either maneuvering the aircraft or taking some unique action to correct a problem or situation.

The Red Mode is triggered by something that grabs our attention which unattended to will result in much worse things happening. That is when the Adrenalin flows...the Heart Beat turns into a Snare Drum Tattoo....and your focus turns to exactly what is the threat.

Last edited by SASless; 14th Dec 2013 at 13:57.
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Old 14th Dec 2013, 13:50
  #116 (permalink)  
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Exactly..Couldn't find the succinct words...Well done lad!
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Old 14th Dec 2013, 16:33
  #117 (permalink)  
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Some general thoughts on the topic of recovery from OGE Hover engine failure:

1) The Dead Man's Curve is a decent guide to how much trouble you are in. If below 250 to 300 feet AGL when the engine quits at a hover, you WILL crash. The operative issue is the stored energy in the rotor (high for a Bell, low for a Robbie), and the quickness of the pilot in getting the collective down.
2) The maneuver from low altitude is hardly an autorotation, it is more related to a controlled drop and a race to gain enough forward speed to help create a cyclic flare at the bottom. The trick is to fall while gaining forward speed by lowering the nose sharply (25 degrees, which is like pointing at the ground). Lower the lever a bunch and try to keep the rotor in the green. As the earth looms up, sharply pull the nose up to flare, and pull the collective to your armpits to use all the rotor energy left to cushion the blow.
3) If you are at 500 feet AGL or more, the forward speed you gain will be enough to get you to normal autorotation speed, so bottom of the maneuver will look like a normal autorotation, and the success is virtually assured.
4) any helicopter can establish a zero knot autorotation, with the rotor rpm stabilized in the green, and no forward speed, in a true auto state (windmill brake state). The rate of descent, however, will be horrendous, and no safe landing can be made from this condition. It is likely to be 4,000 feet per minute descent rate or higher.

OGE hover at lower altitude is a crap shoot. From anywhere near the top of the dead man's curve downward, it is very likely that an engine failure will be a real mess.
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Old 14th Dec 2013, 17:08
  #118 (permalink)  
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If you visit Penticton BC. You will find hovering autos from 100 to 150' performed all day long in Bell 206's.Zero forward airspeed, just a vertical hovering auto.
A check or two on the collective on the way down.

Very spooky the first time the IP demonstrates it and then easy peasy- Once those guys show you how! and are sitting alongside in case you muff it

I am definitely not the only guy who went through the CHC mountain flying course so corroboration should be forthcoming...

Racing to get forward airspeed is the last thing I'd want to do in the bush!
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Old 14th Dec 2013, 17:36
  #119 (permalink)  
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This will be interesting...................
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Old 14th Dec 2013, 17:45
  #120 (permalink)  
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Chest-beating and youtube videos of light helos flown by experts is one way to determine how to fly your aircraft. Its approved flight manual is another. You get to pick which one you want, but your passengers, should they be foolish enough to climb into your aircraft, trust you to use the right procedures. Here is a copy of the Dead Man's Curves for two helos. As a pro, I made a living producing these curves, with the help of a local fire department standing by, and with the full knowledge that little extra exists when we make these charts. Several times I bounced off the ground, saved by the toughness of the machine I was in and a little blind luck.

If you make your living from flying, you will find yourself driving a taxi should a government inspector see you "youtubing it." For your own fun flying, use 170 feet as a safe hover altitude if you wish, but should the engine quit, don't expect a warm welcome from the ground when you reach it.

Bell 206B:

Robinson R22:
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