Autorotation Question

[Go Smoke]

Hi I'm a fixed wing pilot with a question.

Assuming 2000' QFE what sort of size radial distance does one have, if you have suffered engine/gearbox, whatever, failure and have to autorotate in R44 or similar, to select a landing area?

Assume nil wind too.

Hope that makes sense - I was thinking about single engined operations over large cities.

I'm sure there are many variables and I just wanted a ballpark idea really.

Many thanks for any help.

GS.

[SASless]

By QFE....one assumes you mean AGL? The beauty of the helicopter is the very small size of the area needed to land in...thus from 2000 feet above the ground....that allows a lot of choices.

Cannot help you on glide distance for an R-44.

[Go Smoke]

Hi,

Thanks for the reply.

Yes I meant AGL.

I wasn't specifically interested in R44 it was just the first 'large', singled engined, common helicopter I thought of.

Please bear in mind that I know very little, if anything, about heli's.

Cheers,

GS.

[Grainger]

Depending on weight etc., you'll go down at between 1500 to 1800 fpm in autorotation in an R44.

Airspeed for maximum range auto is 90kts. So from 2000ft agl, you'd have an autorotation range of about 1.5nm in the event of engine failure - enough to give you plenty of choices in most situations.

For single engined ops over built-up areas, the requirement for a heli is to "land safely" in the event of engine failure (as opposed to "land clear") - plus of course you still have to comply with the 1000ft rule [recently changed from 1500ft].

You mentioned gearbox failure too: sadly, that's likely to be rather more terminal - however many engines you have !

[Go Smoke]

Thanks for that info Grainger, much appreciated.

GS

[autosync]

I heard some drunken bar talk somewhere, that the glide distance in an Auto for a 206 is approximately 6:1
I don't know how true or accurate that is.

[Ascend Charlie]

More like 5:1, a little less than 1 mile per thousand feet.

Your area for choosing a spot isn't a circle with you in the centre, either. You have forward speed, and the longest you will go is in the forward direction. Start to turn, and you lose a lot of height. For a 180 turn from 1000 feet (to get into wind maybe, or a better spot) you will land around a quarter mile back from the spot you were over when the engine failed. So, the area is more like if somebody standing behind you shone a torch at your feet - the area spreads out from just behind you.

If you are flying over a built-up city, flit your eyes from one park or golf course to the next. In the CBD, you would be plopping into the street and somebody would be hurt. Watch for the taxi that will run into you as he changes lanes.

This of course opens the old argument of landing on a main road - take the side where the traffic is going the same way as you, or the other way? If the traffic is coming at you, they can at least see you in the last stages of the auto, and have a chance to avoid you. When the traffic is coming from behind, the first time the car sees you (you are over his roof) will be as the stinger comes through the front window.

[delta3]

That looks very optimistic.
I calculate the max to be 11 degrees or 1:5.
The example by Grianger approaches the 13 degrees or 1:4.5 which is more realistic.
You can squeeze some extra fractions of a degree by slowing the MR, pulling collective and going to 90-95 kts in an R44, to get maybe to 10. 5 degrees, but 1:6 = 9.5 degrees looks bar talk to me

Delta3

[The Rotordog]

In general, guys are inclined to hyperbolic exaggeration. Their cars are always the fastest, or get the most gas mileage. Or they caught some huge fish. Or they have the biggest...um, watch. It never ends.

I was once part of a cadre of BO105 pilots. The ships were basically all alike, but one of them had an optimistic airspeed indicator. We'd all flown it, checked the ASI against the GPS and privately knew what was what. But the pilot who was regularly assigned to it swore...swore that it was a good ten knots faster than the rest of the fleet. When asked to explain this seemingly miraculous feat of aerodynamics, the pilot could not even hazard a guess. Laws of physics meant nothing to him. The ship was "his" and therefore just had to be the fastest of the group. I suppose his ego prevented any other reality.

...And so we come to the subject of autorotative gliding distance.

I never really gave it much though, actually. My initial instructor, a grizzled, old Bell 47 pilot simply told me to figure 3:1 and I always have. (I am, you see, the prototypical Harry Reasoneresque pessimist.) But my grizzled old initial instructor did not have access to a ship that cruised at twice it's best-auto speed. Come to think of it, neither did anyone at the time. He did not have the option of 90/90 or some such (90 on the airspeed and 90 on the rpm clock). He did not have the option of pulling the nose up and holding altitude while lazily decelerating to best-auto speed; he was at it all the time!

Out of curiosity, I pulled out two fixed-wing AFM's that I keep by my bedside. Cessna says that their U206G will glide three miles from 2,000 feet (about 9:1). Piper, on the other, more optimistic hand, says that their PA-28-161 will glide four miles from 2,000 feet (wow, 12:1). Maybe a helicopter could do half as well as an airplane. I rather doubt it. I'll stick to my glass-is-half-empty 3:1 and I'll probably never be wrong.

But whether a Jetbox can glide 4:1 or 5:1 is really moot, is it not? Pick a spot somewhere between the pedals and the top of the instrument panel: that's where you're probably going to land.

[ConwayB]

G'day,

Just in case you're interested...

Autoration in a Chinook (which autos like a brick, incidently) is done at 100 KIAS for best range and 70 KIAS for minimum ROD.

From the manual, from 2000' you can expect to travel about 1.4nm at best range and 1.1nm at minimum ROD.

Cheers
CB

[overpitched]

If my calculations are correct (I said IF ok) then an airspeed of 70 kt in nill wind is about 7090 fpm across the ground. Compare that to a ROD of roughly 1700 fpm in auto and you have a glide ratio of 4:1 approx.

[cyclicpushover]

If it's any help, R22 flight manual states maximum glide distance configuration is 75 KIAS, 90% RRPM, glide ratio is about 4:1 or 1 nm per 1500ft.

[delta3]

Best range (no wind)


R22 1:4.2
Chinook 1:4.3
R44 1:4.5


I do not think a 206 beats the R44 (rather equal I think)


Delta3

[MightyGem]

AS 355 is 1:3.28 at high weights.

[Quick Release]

Delta.

ever done a touch down auto in a Chinook? i would love to see that, i just cant seem to imagine it looking poetic, but im guessing it would be a run on with a resonable speed?

Cant say ive flown any thing that can glide as far as the As350 max speed min rpm config, blew me away at the time, thought i was in a glider. :D


(edit for a typo)

[Bertie Thruster]

15 nm from 12000' (Gazelle, NI 1984)

[SASless]

In another life we did touchdowns in the Chinook....with little or no ground roll....but that was after doing 1100-1200 hours in them in one year. Standard procedure called for some ground roll....and lots of brakes!

Rate of descent in a spiraling descent with a steep angle of bank and out of trim provided a sensation of being a set of streamlined car keys....when combined with a real nose low attitude.....more like a low drag anvil.

[Jonp]

What is interesting is the distance, or percieved distance you can travel. I am currently finishing of the final few hours of my PPL(A) and also have about 700hrs PPL(H).

Having done a load of FW PFL's recently, I went back and did some Auto's in my R44, and it takes a bit of getting used to as to how far you need to be looking for that ideal landing site, as I believe FW's glide at about 10:1, as against 4.5:1 - so it does take some adjusting.

I rekon the best thing, is to make sure you are rally current with Auto's for all types you fly. I try to do 4 or 5 with an instructor every couple of months to keep my hand in.

JonP

[Quick Release]

cheers SaS...... :ok: