RVDT

Looks like the ladies have put the handbags away!

As to the why's and wherefores -

I have a soft spot for Ray Prouty always making sense of these matters and managing to put it into terms for the average Joe to understand.

His articles have been around for years and have thankfully been resurrected into modern digital format from multiple sources. Even available or the "i" fraternity as well I think thanks to Shawn Coyle.

Read Ray's sensible articles and you may find that there is a little bit more to it than the hissy fit demonstrated previously on this thread!

I have met him a couple of times and he is a true gentleman.

He is even a "go to" guy for Pete Gillies.

G0ULI

When reading the report it is also necessary to remember that the Vietnam War was in full swing at the time and that obviously influenced the mindset at the time. An extra couple of hundred yards flight in a battle damaged helicopter might make the difference between escape and capture by the enemy, or quite literally, life and death. Given the choices facing a pilot in that situation, they may well have considered the risk worth taking at that time. This experiment was clearly undertaken due to stories that some pilots had managed to stretch the autorotation range under combat conditions, but I suspect that there were many more who didn't and paid the ultimate price. A very interesting historical document, but not the basis for ignoring the figures in your helicopter manual.

SASless

GOULI,

Having spent a bit of time there....if you think there are variables in autorotations.....the variables in determining one's fate flying helicopters in combat are far more varied and much less susceptible to codification than the matter of helicopter aerodynamics.

Might I ask you how you arrived at the opinion the NASA Testing was predicated upon such a notion?

That it was done on an Aircraft that did not make it into the inventory and not on the Huey would suggest otherwise.

The OH-58A was late in the War and in much fewer numbers than the Huey....as the OH-6A was the primary light helicopter in service.

Each aircraft in use had the standard Autorotation Airspeeds identified and established procedures for doing such kinds of descents and landings.

Lord knows we did enough of them in practice and for real over the years.

If you are interested....this web site is an interesting place to take a wander through.....it is not a complete data base but does have a wealth of information about US Army Helicopter Losses over the years.


http://www.armyaircrews.com/index.html

G0ULI

SASless
Apart from the Vietnam War, this was also the height of the Cold War. NASA and the US military would naturally investigate anything that might allow an aircraft to perform that little bit better. The helicopter used was probably just what NASA had in its inventory for use at that time as being representative of a general purpose helicopter. As the report implies, it was the first time anyone had explored helicopter performance right at the edge of it falling out of the sky. During and after any war there are numerous tales of pilots achieving the impossible. It was probably only in 1969 that the expertise and equipment became available to actually quantify whether these stories contained an element of truth. Nobody would believe a plane with one wing would fly, but an Israeli pilot landed an F15 in 1983 with a wing missing after the plane was involved in a collision with another aircraft. There is always something new to learn and reality doesn't aways match the theory. As you rightly point out, it is just my considered opinion that this was what prompted the experiment at the time, but 45 years on I suspect all current helicopter pilots are benefiting to some extent from those experiments.

SASless

For those folks that have trouble getting to sleep at night....and as a reminder to most of us the difference between working pilots and Test Pilots....I recommend this Research Paper for some light late evening reading. It was done in 1985.


http://www.ntrs.nasa.gov/archive/nas...1986020337.pdf

The statement that jumped out at me was the comment about Autorotation being an Energy Management Technique.

The aircraft used in this study was a Jet Ranger with a High Energy Blade System....weights in the Spar Cavity at the end of the blades for those of us that have trouble tying our shoes.

GipsyMagpie

So glad I am wasting your time. I love a challenge so time to engage the brain in a quest to supress smart arses like you. I have thought on the subject some more and realised I was wrong but so are you. The pitch up on engine failure in forward flight is not solely due to the retreating blade stalling (Although I suppose at high speed this could also occur). It probably has to do with the following factors:

1. The reduction in rotor thrust on engine failure

2. The relationship between the thrust line and the fuselage aerdynamics such as the amount of tail down force in forward flight

3. Flapback

So:

I think we can all agree that thrust reduces on engine failure.

So in forward flight you need a download on the tailplane to balance out the moments generated. If you change that balance by a loss of thrust (and for hubs with a hinge offset, the hub moment too) you still have the tail download so you pitch up.

Finally there is flapback. This depends on the advance ratio - as you go faster forwards the advance ratio increases (forward speed over rotor speed - giving differential lift between the advancing and retreating blades which gives maximum rate of flap up on the advancing side and vice versa - net effect is flapback). So if rotor speed suddenly slows then advance ratio increases and you get flapback.

There are probably exceptions of course. I believe the aircraft standards specify that there must be no more than a specified maximum change in pitch, roll and yaw. I seem to remember the spec saying a change which assists the pilot reaching optimal autorotative parameters is preferable.

topendtorque

Gypsy, go back to your caravan in Romania, that's frog's manure. I've been silent but I'll come back sometime soon with what I do, it's saved me and others heaps of times.

Gouli, mate, there ain't a plot behind every tree.

cheers tet

SASless

Suck Backs...and Blow Backs in the game of Uckers i fully understand....but most of what is said here might as well be Swahili to me.

DB,

The latest NASA Paper I linked.....says the US Army did not teach the "Check" method.....which I faintly recall being the case.

We sometimes started the Collective Pull with the Nose of the aircraft still a bit above level after the Flare and held that till the Heels of the Skids almost touched then getting the skids level as full touchdown was made using the rest of the Collective Pitch. The Pitch Pull was one steady movement from the first application of Collective till the end of the maneuver.

Hughes500

Sasless

All the 300 have the spoiler, never flown one without, it's bad dough with one on !
Have fun

GipsyMagpie

I rather think you have missed the point. What I have explained is why a helicopter will pitch nose up when the engine fails (all by itself with no help from you) NOT what a pilot should do. What you do is really of interest to me but trust me when I say I have explored and survived every corner of the avoid curve. Recovering rotor speed with lever is critical but there is much more to it. Ever tried from the hover at the top of the avoid curve? Trying to balance the need to maintain rotor speed against the need to gain forward speed in the height available. Marvellous fun. The one from the knee is also eye popping (low speed and low height).

And anyway, so glad your racial prejudice is alive and well.

Tailspin Turtle

I was at Bell at the time. (The paper says OH-58A but I remember it being a Jet Ranger.) The object was to provide increased safety in nap-of-the-earth flight within the low altitude/high speed avoid area. If I remember correctly, it eliminated both avoid areas. One demonstration was rolling the throttle off at flight idle on the ground, lifting off and making a 360-degree pedal turn, and landing back. (There was a light on the cowling to indicate that the throttle had been closed.)

Of course, the rotor would still be turning the next morning...

Lonewolf_50

Uh, at the moment of engine failure, if you aren't already in retreating blade stall it is unlikely that losing an engine will cause it. But that depends. If you are at max conserve airspeed, probably won't hapen. If at max range, maybe. In a twin going at max, I suppose that losing one and trying to fly at the same speed (instead of slowing down to max S.E. air speed as one should) might get one into such a flight regime, since my back of the napkin sketch shows a decrease in Nr which influences AoA which gets you nearer to where the retreating blade might stall in higher speed flight. I will suggest that such combined factors influence why the test pilots lay out the charts to identify why you don't go faster than X in a twin with one engine off line. (HC earlier made a point about the underpowered S-76 and it not so great single engine performance, maybe there you'd be more likely to see it ... )

The rest of your post: I am not sure what flight regime the helicopter is in before engine loss.
Huzzah, we can indeed.
Which model of aircraft are you referring to? Some have horizontal stabs that change their pitch a bit to accomodate the airspeed one is flying. Others do not.

In closing, I'd like maple syrup with that order of flapbacks, sir, two strips of bacon, grits, and a cup of black coffee. Cheers.

SASless

Turtle,

The Photo shows a Jet Ranger and the Report says OH-58A.

Just typical Bell attention to detail!

As I am not one for interpreting Hieroglyphics in the Original Greek....can we trust the findings of the Test Data in light of the slight error we have detected in which aircraft was used?

Why is it Jet Ranger Blades turn....turn....turn...and turn....while you are busting for a Pee and there are people standing around gawking at the pretty helicopter?

How many pair of Army issued half leather flying gloves ever got wrapped around the T/R drive shaft of a 58A?

topendtorque

I will spend a couple of seconds replying before I get out, do a bit as I am fearful of what newbies might read into your deliberations. They should refer to the basics until they become operational where they should then be taught survival in whatever mode they operate in and don't clutter themselves with your, ahhhh, procrastinations.

It was explained to me in the beginning that the helicopter would slowly pitch downward with only the collective bottomed after engine either stops or is rolled off quickly, and it is easily demonstrated. Try it, lock the cyclic and see what happens. What it might or might not do momentarily is of no consequence.

Mate I live in the avoid curve, have done for forty years and I do the avoid curve stuff as a straight line to any height down to fifteen knots in the 47 and 25 knots in the R22, I have survived and had pupils survive sudden stoppage at 60 and 70 feet (one of which in my case a free-wheel failure, the accompanying noise is terrifying) without a scratch in the '47 and regularly do the hover stuff at down to 250 feet in either, I have had heaps of failures and practices at any speed any higher height, never ever have I experienced nose pitch up of its own violation that has been a worry. I did tho, bend the skids of an R22 when it failed at fifty feet and just starting to translate above trees at max gross and had to do a 90degree turn port to get into the only avbl space on a stinking hot day with moisture dripping everywhere. However I found later that machine was rigged wrongly (auto RPM too high) as the beacon went off in my headset, prior to the low RRPM warning horn, so I had unwittingly signed myself to heartache by doing the automatic full down quick time.ROD too high.

If you are an instructor or are influencing anyone with your theories please talk to your counsellor, I do think you need some medication.

I should add that we also practice controls locked or jammed in various scenarios and the resultant swings that one can get by locking the cyclic and playing with throttle, and pedals, should not confuse this discussion.

John Eacott

Do pay attention SASless: 368 posts ago

henry_crun

As a side issue, it does seem that autorotative flight training is limited by descent time. Would it not be beneficial to keep a few small autogyros and use them to gain longer experience of flight with unpowered rotor? I suppose the surviving autogyros are now in museums, but could not some designs be put back into production for training and sport purposes?

Did I just want to break up the discussion with a nice piccie? Er, yes m'lud, guilty as charged.

SASless

Eacott....better start wearing a Hat while outside.....the Sun is working on your bald spot!

Some where back in the few pages of this thread.....I endorsed that notion.


Now that Henry brought it up....I too thought about Auto Gyro's and the fact they are always in autorotation. Plus, they have no Collective.

My first and only crash in a Rotor Winged device was one of them things that was loosely chained to a platform built on the bed of a Pick Up Truck.

We got the Rotors to spinning by Hand.....the Truck Driver took off down the runway and we flew the Bensen Auto Gyro over the platform staying about six inches to a foot off the platform.

Mind you we were like 15 years old or so....and in our course of instruction no one reminded us of the dangers of pulling too hard on the chains by applying aft cyclic and "climbing".

As the Chains were far stouter than the Rotor Blades....at some point two of us learned the hard way about that sad situation when the Rotor Blades went 600 different directions all at once except for the remains of the one blade which purely beat the Hell out the two of us that were flying the machine. Not only did it whip hell out of us....it did it really quickly when the blade made about three rotations down across where we were sat.

I should have learned from that beyond what i did.....never again had anything whatsoever to do with Auto Gyro's....and refused even to do Biennial Flight Reviews for Auto Gyro Pilots as I did not want any mention of an Auto Gyro in my log book when they went out and killed themselves.

My next experience with Rotor Craft was an Air Force H-21 at Langley AFB one Summer while a Civil Air Patrol Cadet. We got a ride in the thing and made it all of about three minutes when it dumped a Jug and made a Forced Landing.

Autorotations have been a part of my flying career from the start it would seem.

I digress but it does make one wonder why auto gyro's (well designed and professionally built) died out.

newfieboy

I have followed this thread and read every post as a 13500hr utility pilot. Be interesting to know just how many posters have had actual engine failures, single or twin. Myself have had three all below 1000ft in single turbines. Dumped the pole on everyone didn't have to think about cyclic inputs. It just happened instinctively to keep nose up and RPM. Most of my time on the end of a 100ft line, if you guys can't decide the right action, too late. Me I have a cunning plan every turn in the curve....tis to stay alive whatever it takes. Worked up to now.

SASless

Just shy of 13,000 hours....one engine failure in a Hughes 500D....landed with no damage to the Helicopter. One in-flight shut down on a single engine on a 212.

One engine failure in the cruise, one engine shot out flying low level with a forced landing due to being too heavy, and one event where one engine had terminal compressor stalls followed seconds later by the other engine doing the same....while dropping a sling load on a mountain top....autorotated down the side of the mountain and regained the use of one engine, in the Chinook.

Only the dual engine problem was a very near thing.....and it was a dilly.

As Newfie says....have a plan in mind if time is short as you do not have time to cook something up sometimes. The Dive off the Mountain had been planned months before in a discussion over several Beers as we flew to that site often....and there was no place to land there. Granted, the discussion was about a single engine failure.....not both at the same time!

newfieboy

Right on SAS, now we getting somewhere....hats/beret off. Lets start another thread tilted Been there, Seen it, Got the tee shirt thread......only can post real life adventures...