Technique for Auto's Outside HV Curve?

[rjtjrt]

I know - best technique is not to be there in the first place!

But, if for some reason engine fails at 50 ft and 10 knots what is the best technique to minimise impact effect on crew other than close eyes and pray?

JR

[Fun Police]

i've never done it but i saw it written like this once: "bend the pole twice, once at the top and once at the bottom"

[212man]

I assume you mean INSIDE the HV curve?

[Um... lifting...]

Originally Posted by 212man

I assume you mean INSIDE the HV curve?

50' and 10 knots I think covers that... I've probably done about 800 autos to touchdown over time and I think I've got the maneuver to the point that if I keep at it, pretty soon I might just get it down. Most of those autos are in single-engine Bells and were it me, in a relatively high-inertia system (in a low inertia system with only one motor, I'd figure out a way to not be at 50' and 10 knots or get another machine except maybe doing a really tight confined area landing if I absolutely had to...), I KNOW I wouldn't get any rpm back... I'd try to keep what I had and only spend altitude and preserve or possibly add just a touch of speed, no more than maybe a degree or two of nose down. Smoothly (but quickly) full down and simultaneous pedal, level and pull (in general, the more rotor speed I got, the higher and smoother the pull, the less, the later and harder... probably going to yank about 5' off the deck in this case). You'll feel when there's no point in pulling anymore... try to make that moment match exactly when you've got no more to pull. Unlike a normal profile, a flare's out of the question, and there's no need anyway at that speed... landing attitude in say a 206 may mean the difference between a couple cracked vertebrae or a severed spine, so you want to make best use of the skid geometry (it's not a collective only maneuver). That means you want to touch down right about 6" forward of where the skid begins to turn upward from the flat (if that sounds anal, it is... and it works too)... when the aircraft touches, depending upon forward speed, the attitude will rock back (it dissipates energy to rotate that fuselage back those few degrees, and that's what an auto is all about... controlling the dissipation of energy...) and THEN the skids will spread. At this point, bending any skids or striking the tail is the least of your worries... this is a controlled (we hope) crash. It's sort of like landing on the balls of your feet vice flatfooted. Makes a significant difference. Land square on the flats of the skids, you're probably leaving on a backboard. And like Mom told you... sit up straight and try to live right and for heaven's sake... no yaw or drift.
If for some reason you're in a single engine with wheels... the same holds true, but land smack on the mains for a tricycle gear, maybe slightly nose up for a tailwheel.

[paco]

That's about where you are inspecting 11 kv power lines a lot of the time, and as lifting says, you don't want to be there in anything that doesn't have a high-inertia rotor.

So, assuming a 206, you wouldn't want to be doing anything with the cyclic, aside from a small correction for the nose down tendency (the 500 seems to do this more than other machines) - you certainly wouldn't try to slow down either, just accept what speed you have. Otherwise, dump the collective straight away, keep the attitude and at the right moment HEAVE UP ON THE COLLECTIVE progressively and smoothly, co-ordinating the pedals, keeping the fuselage and skids flat, as mentioned. The 206 for a very short time will produce more than it should in such a situation (see Dennis Venturi's article in Helicopters magazine - a Canadian one - many moons ago), and it works best in a vertical auto.

It is important to use all the collective you have available in a rapid, smooth movement. As fun police says - bend the pole at the top and at the bottom!

Phil

PS - this is an advanced technique and not to be tried while solo or by the inexperienced!

[Project Pilot FH1100]

One day, years and years ago when I was young and stupid, I got to wondering about the hovering auto capabilities of the 206B I was flying (on popouts). I could never get it to land and then takeoff again and do a 360 pedal turn, like the OH-6 drivers use to brag that they could do.

I was working for a company carrying cargo out of a large airport. Parked adjacent to our helicopter was a Boeing 727. The mechanic of the jet had related that the horizontal stab of the 727 when empty was 33 feet off the ground. I said, "Hmm."

So I started doing hovering autos. Lightly loaded, straight down. First from three feet, then higher and higher. Got to where I had to lower the collective to maintain some semblance of rpm. Finally, I was up so high that I was just looking down on the top of the 727's horizontal stab. I figured the skids were right about 30 feet. At that point I could no longer cushion the fall and the touchdowns were as firm as I'd accept (not much firmer than my normal touchdowns, actually). Higher altitude than that, I would have had to lower the nose slightly and accept a little ground-run (not that I tried but it had once been demonstrated to me). Like I said, I was young and stupid.

Fifty feet and 10 knots? Doable without damage, I suppose, if you're using Um...Lifting's techniques...and if you're ready for it...and if you have a smooth area to run-on...and if you're in a 206. Too many "if's" for me, thank you.

[maxeemum]

It all Depends

All good responses from previous posters. I guess like all things in aviation the answer is it all depends. This usually doesn't sit well with those that want a formula type answer, but the truth is it all depends:

1. How heavy are you?
2. Is the wind on the nose, X/W or are you D/W? How strong is the wind?
3. Are you in a single eng or twin eng machine?
4. If all power plants fail, does the rotor store energy (high inertia blade system) eg Bell or lose energy rapidly eg Sikorsky?-This is my experience with Black Hawk.
5. How current/recent are you with the recovery procedure? ie when was the last time you practiced the emergency
6. Do you have a place to land? Can you accept a run on or zero speed
7. Does the machine have skids vs wheels-oleos and wheels make a huge difference when it comes to absorbing impact
8. What is the DA/Temp-Hot, high and humid means less bernoulis for lift
9. What are the visibility and conditions like?-Ever tried doing an auto in horizontal rain where you can only see slant range down, not straight ahead (this is typically 800 m vis which is still VFR in most ICAO countries)
10. How are you feeling on the day, tired & fatigued, rested and fresh-This will alter your reaction times to the emergency.

These are not the only top 10, however concepts worth working through.

As you can see there is no absolute answer. General concepts are the key and you would already be aware of these. Lower the lever, small amount of FWD cyclic, set the attitude for LDG, if you can run on then do so (more inflow will delay the RRPM decay) if you can't run on then zero spd. Cushion with collective when your arse starts to suck up the seat cushion.

Point is if you can walk away with crew + pax and a salvageable machine you have done a stirling job. If you walk away with with crew + pax all in a service able state and the machine in tatters then you have done everything that has been asked of you. Life and limb first, machine second.

Hope this helps.

Max

[topendtorque]

Low level autos and I guess also have done several hundred LL autos as has Lifting with a few real ones thrown in. I believe that these maneuvres are not for ab initio, rather operational training after at least three hundred hours.

Five things to remember.
1) Airspeed always takes the P out of pain, get the cyclic forward pronto and don’t try to flare off airspeed at the ground, just level the skids.
Remember it takes a heck of a lot less energy to fly a helicopter at translation or above than anywhere below translation, keep that energy for your preservation. (Less Pain)
2) Always try to arrive with RPM. Collective down straight away.
3) One big pull at the bottom, if you’re lucky that lift will take effect at just the same time that your skids reach bounce point, if it has been that critical - as Lifting says above.
4) That low, it is hard to pick an easy spot, you are usually committed to what is in front of your feet, but do try to get the skids into a hole, so that you can put them down level, forget the aircraft, just worry about yourself. You should be tabbing spots and your position references every thirty seconds regardless until it is automatic. (Your instructor did teach you that, eh what?)
5) Mayday straight away as the collective goes down

An easy rule of thumb is, just damm well point both levers at where you want to go, and do it now! Include in that your anti-torque pedal, to the floor.

If you sit there fat, happy, dumb, flat footed and leave the cyclic central at ten knots then you will lose quite some RPM by the time you get down. Cyclic forward unloads the disk and allows the aircraft to sink and maintain the energy in the RPM, still without too high a rate of descent. Where-as if you are losing RPM the ROD will be on a sharply increasing curve. (Pain)

You can do the same thing in fixed wings if you are a bit high on finals, solution, just dump the pole forward and then backwards and the net effect is that you haven’t gained airspeed or ROD but you have chopped anything up to fifty feet of altitude which puts you into a strip instead of over the end.

Note also that with cyclic forward airspeed will increase and it then takes less energy to fly the aircraft which translates into less ROD, easy!

You should have been taught that power requirements lessen from the hover, to 10 knots, to 20 knots and so on until you go past minimum power speed where power required will then increase.

In training I never went below fifteen knots as a minimum for any height in a high inertia system and would taper off as height increases above 100 feet or decreases below thirty feet. That sort of training saved quite some aircraft in both high and low incerta systems in our outfit, some with total power loss at a seventy feet hover and not a scratch.

It is imperative that before that sort of training and at all times that the auto RPM is rigged correctly. Too high auto RPM will absolutely destroy your day as the basic action is - you must be able to go right down with the collective without having to think – which also gives you the best advantage at the bottom, to have the full lever to go all the way up.

Never do that training without currency in either yourself or your instructor.

However WRT the low inertia R22 system and the H269, IMHO that you only have to breathe forward on the cyclic and translation happens much quicker than say the hillier or Bell 47. The heavier aircraft have a higher overall mass which takes some energy to just get accelerating forwards.

The trick is to get familiar with your aircraft somewhere well above the ground and experiment with the different factors that Maxeemum has highlighted. I have no idea of the disk loading comparisons between say a Blackhawk and a R22; I guess the R22 would be better. Experiment also with your aircrafts ability to skid either way with just a touch of side cyclic and more or less pedal, remember to wash it off before ground contact.

Of the several low ones that I have had for real, the only one that I didn’t fly away from after engine repairs or whatever was in a R22 from fifty feet and the spot was 90 degrees left amongst 35 foot high timber. I was first looking at a spot ahead which I knew I would easily get to with in a ’47, but no way with the small machine. I was at max AUW and WX was lousy, stinking hot with rain showers all round. I did not walk easily away from it even though the machine was still very much in one piece; in fact for a while I crawled. In hindsight we found that the the auto RPM was set up way too high, proved by the fact that the ELT went off before the low warning RPM horn. So I still wonder whether I might have pulled it off had the auto RPM been right.

The best survival technique is to scan, plan, and again, all day.
and plan again tet.

[rudestuff]

So what you're saying is - you had too much rpm?!!!
And I always thought you could never have too much of that stuff if you lose an engine....

If your ELT went off before the Low RPM horn - it just means you hit the ground with plenty of RPM - meaning YOU didn't pull enough collective.

[Um... lifting...]

Yep, keep in mind that from about 700fpm ROD or higher on touchdown it's going to smart a bit and you ARE going to lose some rotor energy on entry unless you're clairvoyant or are doing it for practice and entry is self-inflicted.

From 50' AGL you're going to have maybe (and I do mean maybe) 8-10s to pull this whole thing off from "Oh sh*t..." to "Sweet mama... stop!"... not a lot of opportunities to fix any problems if you manage to hesitate. That's why I don't like the idea of doing much with the fuselage attitude other than setting it up for touchdown or just a whisker nose low. The initial situation was starting from 50' and all your focus needs to go into not making things worse, not getting too clever.

[topendtorque]

Originally Posted by rudestuff

So what you're saying is - you had too much rpm?!!!
And I always thought you could never have too much of that stuff if you lose an engine....

If your ELT went off before the Low RPM horn - it just means you hit the ground with plenty of RPM - meaning YOU didn't pull enough collective.

No fear pulled the whole lot sunshine.

Perhaps I could explain it again. if the auto rpm is set too high, then when you throw the lifesaver down what happens is that negative pitch is set on the rotor blades which will give you two definite things.

1) high RPM

2) astrominically high ROD.

excess RPM repuires energy to build up. fact one.

That also contributes to high ROD because that energy has been stolen from the only energy available, good old mother gravity.

Excess high ROD is the first killer.

Unfortunately for me I could have made things a whole lot worse by going straight ahead into several very solid 35 feet high trees, absolutely no way says I who just happened to remember something that I had spied with my little eye out to the left and clear, a fence line in fact. so we arrived level and flat with no strikes on anything major. That's the way it goes.

The ONLY way to do any autorotation is to first set up your aircraft as per the manufacturers book.

in my case I had a machine delivered to me in the field, test flown by someone else who later told me, Oh yeah the auto RPM was a bit high. I guess now about two full turns on the pitch links, at least.

Sorry Lifting, I must digress on one point, decision time must be within TWO seconds after the engine goes silent, or find another job.
count it down, one hundred and one - one hundred ------ etc. my ab-initio instructor sorted me on that point, for sure.
all others cop it from there.

[Um... lifting...]

Originally Posted by topendtorque

Sorry Lifting, I must digress on one point, decision time must be within TWO seconds after the engine goes silent, or find another job.
count it down, one hundred and one - one hundred ------ etc. my ab-initio instructor sorted me on that point, for sure.
all others cop it from there.

You're quite right... the way I wrote it was open to a lot of misinterpretation though I didn't intend that. What I meant was that from the time the engine quits at 50' until the time you are on the ground will be 8-10s. I should have been clearer.
No matter how quick you are, your reaction time won't be any faster than 1s, 2s is what you need to have, so not a lot of margin for error.

[rudestuff]

Ok, I agree that auto RPM can be 'set' - however it is still controlled by the pilot. one of the things you are taught is rpm control with the collective -especially during turns, flares etc. I don't think "the RPM was set wrong!" is a valid excuse.

Anyway, from 50' unless you are some kind of Jedi you are going to lose a lot of rpm if you wait 1 second, and in the 5 seconds or so it takes to reach the ground you'd be lucky to get it back to 100% let alone overspeed it.

Excess rpm can always be reduced to decrease ROD - of course you have to pull collective before you hit the ground!

Almost forgot - R22 doesn't have negative pitch. There is flat pitch, but in autorotation airflow is from below so AOA is positive.

[Arm out the window]

Jeez, rudestuff, I don't think it's a case of valid excuses or not - sounds like he was faced with a split-second decision, the kind none of us want to have to make, and did very well.
Bottoming the collective is hopefully an ingrained response, and I wouldn't think that from 50 ft with an engine failure there'd be heaps of time to go 'hmm, that rotor rpm is pretty high for my collective position, best get that checked after landing'!

[rudestuff]

I agree, slam it down - he absolutely did the right thing.

I was merely expressing my oppinion that you can't have too much rpm in that situation, and that if you lose the engine in a hover/high power setting, you are more likely to have low rpm than too-high rpm. Apologies for being rude.

[Shawn Coyle]

I was going to try to stay out of this one, but one comment regarding topendtorque's points -

Going for airspeed isn't always the answer. A very good article some time ago by Pete Gilles showed that pushing forward and getting airspeed will result in loss of rotor RPM, and hence control, etc. He had at least two examples where the pilots instinctively pushed forward (because that's what they'd been taught), and both rolled over following a very hard landing with very low rotor RPM.

There is no 100%, always right technique for engine failures, either inside or outside the HV diagram. Good training and experience can build judgment as to what to do when the engine stops. Memorizing procedures in the blind belief that one size will fit all situations is not the way to do it.

[Devil 49]

A big AMEN to Mr Coyle's reminder that there isn't any single reliable solution to all the problems you might encounter. Lots of good information.

One quibble, regarding managing NR in this scenario- Do what you can to ensure survival and minimise injury. You can't ignore NR, but not having to work against the aircraft's rigging gives you time to devote your attention to maximising the success of what's happening- you are landing, NOW!
Voice of experience- You'll have very, very little time and a lot to do. My only complete actual complete power loss came at hover, and the difference was astounding. A real power failure in a turbine loses NR due not only to a delay in reaction, you also lose substantially more NR than you're used to seeing in training scenarios due to lack of residual energy the working engine delivers in practice. The aircraft comes down quicker and one has less energy to deal with it than you're accustomed to.

Scan, plan- continuously- and accept the fact that sometimes survival is all you'll get from a successful emergency procedure. If that's not enough, you shouldn't be there.

[Hiro Protagonist]

Originally Posted by Devil 49

The aircraft comes down quicker and one has less energy to deal with it than you're accustomed to.

This reminds me of a conversation I was having the other day about practice autos and aircraft weights. How many of us spend the day at max. gross weight (minus fuel burn) but train for autos with a nice light empty helicopter (two pilots, half fuel).

Anyone out there regularly load the aircraft up with sandbags to make for more realistic training?

[yellowbird135]

Initial flight control rigging according manuals will give you a more or less desired RPM with a full down collective (power off). some finetuning is required after this initial set-up. This is done to test fly straight auto's; depending on manufacturer, graphs correcting for weight, temp and DA will lead to a certain desired RPM region. (done it lots of times, and almost all of them needed additional adjustments to get it right.)
Ofcourse a real one never occurs with the conditions (Weight , temp etc) at which the final rigging was made.
However the whole idea is that when adjustments according the manuals are made, that RPM control is possible under all conditions.
Ofcourse it's easier to correct for over RRPM's (pull the lever a bit) than for under RRPM (manouvering) During the first seconds of a power off situation the first thing is to bottom the collective and at the same time minimizing the pilots effort to control RRPM. (minimize the already sky-high workload)
So I think there is such a thing as a wrongly set auto RPM.

cheers YB

[topendtorque]

Originally Posted by Shawn Coyle

Going for airspeed isn't always the answer. A very good article some time ago by Pete Gilles showed that pushing forward and getting airspeed will result in loss of rotor RPM, and hence control, etc. He had at least two examples where the pilots instinctively pushed forward (because that's what they'd been taught), and both rolled over following a very hard landing with very low rotor RPM.

Thanks for that Shawn Coyle, any chance of getting a reference to source the article? thanks in advance. Never too late to pick up new tricks.

There is no doubt that if one attempts to get airspeed without first the collective down then that will mean lots of lost RPM, if that was to be interpreted from the article you quote????

i guess I have always advocated as follows- if you have to hover just above the trees, well make it as low as you can and always with any likely spots immediately in front of you. i.e. looking down through your feet.

This comes from lots of practice in making touchdowns softer as a result of just a tad of airspeed, i.e. translation if possible. this can be experimented with during hovering autos by introducing a bit of forward cyclic. One note of caution - do not introduce too much forward cyclic, unless you want a blood nose.

The difference when doing hover autos from as high as you feel comfortable in a vertical hovering auto should be quite noticeable.

Of course if you are climbing vertically out of a small hole when things go silent, then its straight back down, no question.
cheers tet