Question about autorotation for helicopter professionals

[Frederf]

I'm not sure how valid the criticism of the given auto-rotation procedure is simply because "the world doesn't explode if you do it a different way." The procedure is designed to provide the best safety situation in the most marginal conditions. The procedure is taught so dogmatically because it has to be a "do now" action with no time for evaluation.

 

That being said, the question is now "Is the FM correct?" In the real Ka-50 is there a significant difference in how low the RPM gets or how the blades work aerodynamically when the RPM is made to lower to its minimum and what is that minimum (compare: DCS.)

 

Maybe the real Ka-50, no matter how much you do actions during an auto-rotation you cannot get the RPM below 50%. How DCS does it might be perfectly right. A large or total stalled blades region of the disk doesn't mean that they stop turning, just that the drag and rotor-motive effect during auto-rotation is worse. In fact the worse your RPM, the faster you fall, the more air is flowing through the disk; there has to be some minimum RPM.

 

When RPM drops the rotor disk will "cone" effectively decreasing blade AoA as well. It wouldn't surprise me to learn that there is always ability to recover RPM with enough altitude.

 

Also note that a sim doesn't have to model turbulent air flow to model stalling well enough. Even statistically if driven %, driving %, and stall % of disk area were tracked (and I think the DCS FM is a bit more complex than that) it would be enough to handle all auto-rotation regimes.

 

16m/s, 23m/s... very high descent rates. I think proper procedure gives I think 7m/s or so sustained?

[Pirke77]

 

When RPM drops the rotor disk will "cone" effectively decreasing blade AoA as well. It wouldn't surprise me to learn that there is always ability to recover RPM with enough altitude.

 

 

what is minimum RPM when rotor disk ''cone'' will be crashed because rotor blades dont have enough centrifugal force and go up and crash like umbrella? or this will never happen because constructor made helicopter do never lower RPM below this minimum at all attack angles of rotor blades in autorotation? i now that for every helicopter is the different minimum RPM but did any have info and experience with some other helicopter?

and if RPM drop below minimum can we recover RPM to safe range?

in real life i dont have courage and balls to TEST this because i still have gray little thing in my head :)

maybe constructors test this in airflow tunnels but why this information didnt for public??? this information will be BIG thing for pilots.

all this is reasonable for testing ONLY on high altitude minimum 3km because helicopter have time to get or not to get in autorotation in this extreme situations. i think because helicopters fly on low altitude most of their flights, this kind of situation didnt learned and teach to much. because that only safest way to helicopter get in autorotation on this altitude( below 1km) is to drop collective down and keep safest progressive speed and be in constructors limits and all instructors teach new pilots this routine, because this is only reasonable and correct way, because on this altitude helicopter will only like this get and keep RPM in safe range. all other way is forbidden way and because that and older pilots didnt now what will be in this extreme situations and they just say ''NO NO dont do this''.

[Pirke77]

this is some schemes from my school book.

on first pictures is accelerated , decelerated and stabilize running of RPM in vertical autorotation.

on second picture is 3 way of autorotaion (vertikal autorotaion, combinated autorotaion or normal autorotation and plane landing autorotation ) . you see use of kinetic energy only of rotor RPM , then combination of kinetic energy of RPM and kinetic energy of progressive speed then only kinetic energy of progressive speed.

on third pictures is blade angle of attack from min to max collective position and reserve of RPM in this conditions.

Edited August 21, 2010 by Pirke77

[Pirke77]

this is scheme in witch direction will be running of rotor from 0-180 angles of attack if rotor disk when we drop it from some big altitude didnt running at all. this is info from airflow tunnel.

from second picture you see if we in diapason of normal RPM rising or dropping collective isnt important from vertical speed velocity in autorotation (its is exactly same for all angles of blades) .

on third picture is scheme of progressive speed / vertical speed in autorotation .

Edited August 21, 2010 by Pirke77

[Pirke77]

here is restriction of rotor stall in autortotation.

from test:

-speed of planing 152km/h(42m/s)

-RPM 300 r/min

-collective 6 degrees

 

on 6 degrees we have stall rotor so from scheme we must drop speed to 100 or 110 km/h or lower collective to 3-4 degrees.

 

from formula in this i can put in 15 degrees collective on 0km/h or on small speeds with 10 degrees and there i dont have rotor stall.

Edited August 21, 2010 by Pirke77

[Pirke77]

in all this schemes we see if we have collective all way UP we have stall blade ( only at theoretical at 0km/h we dont have stall blade) and we cant control helicopter at all speed diapasons(in theoretical if speed is 0km/h we can control) and RPM go decelerating. decelerating to some limit??? (this limit i dont now)??? this limit is when centrifugal force because lowering RPM is not enough to keep blades in normal position and they go UP like umbrella and reap off rotor. secret magic information :( HOW MANY RPM IS THIS LIMIT IF EXIST ???

 

Did RPM go to some limit of rotor blade crash? or we just drop like brick and have some RPM and we cant recover anything in this point and go to GOD?

 

in DCS BS is all strange from my test or coaxial rotor have Master of ring top secret or some kind of magic :(

 

P.S.

all this i was testing is for single rotor helicopters .

maybe coaxial rotor can do this???

Edited August 21, 2010 by Pirke77

[Pirke77]

from first picture we see that A2 is smaller then A1 (A angle of attack)

so angles of attack of blades of second upper rotor must be bigger then first down rotor(construction solution) .

 

from second pictures in autorotation one rotor must have accelerated running and second rotor decelerate running.

 

maybe because of this moment of 2 rotors we can always have RPM no mater what because one rotor helps other and all again in circles ???

 

this is all my knowledge(its so small) of coaxial rotors so if someone fly coaxial rotor helicopters pls give us some information and explanation how it works in AUTOROTATION .

 

P.S.

in russia some aspect of coaxial rotors is still top secret for public and we only know what they mean we can know...

Edited August 21, 2010 by Pirke77

[Mikoyan89]

P.S.

in russia some aspect of coaxial rotors is still top secret for public and we only know what they mean we can know...

Good old mother russia:D

 

Are those schemes of mi-8 or gazelle, or are they all from a generic student's book?

[Pirke77]

Good old mother russia:D

 

Are those schemes of mi-8 or gazelle, or are they all from a generic student's book?

 

 

from generic russian student's book :)

[Slayer]

I'm not sure about the real Ka-50 but I also think that DCS Blackshark is a bit too forgiving regarding (auto rotation) rotor stall.

 

On MAKS 2009 I found out how quickly a "real" helicopter can get in to a rotor stall.

 

I knew I had to lower the collective and I did, though not completely.

 

Here is a video of the "accident":

(engine cutoff at 08:35)

 

Wow that is hilarious haha I was laughing for 10 minutes. "I'm going to show you something" "See you suck" :lol:

[Frederf]

what is minimum RPM when rotor disk ''cone'' will be crashed because rotor blades dont have enough centrifugal force and go up and crash like umbrella?

 

When I said "cone" I mean maybe 1-10° normal flex, not folded up. Probably Ka-50 rotors are strong enough to not "fold" when plummeting even straight down at 0 RPM. Of course falling straight down at 0 RPM the apparent wind will be nearly AoA 90° which will not be a very efficient AoA to motivate the rotor and RPM recovery would be very slow, none, or even backward.

 

Very low RPM you still have some pitch/bank control, not a lot, but still enough to recover to an attitude that can jump start any small rotor RPM value... if you have enough altitude.

 

The FM has a mimimum RPM during auto rotation so that is your magic figure (+ safety margin) to keep above.

[Pirke77]

in DCS BS i fly with 30% of RPM in autorotation and if i fall below about 20% nose prop up and blades cut of little of peak blades. in this situation if i have collective all way UP rotor stop turning to zero RPM then go backward and forward and then if i put collective all way down rotor progressive accelerated and over speed and all blades because high running acceleration and centrifugal force go away from rotor.

from track you see you can fly with control on 30% RPM all below this is very risky!!!

because i only in this way with high speed about 360km/h i get 30% but when i try to lower speed or go up collective rotor get prop up moment and RPM drop to 20% or less and blades collide ;( little centrifugal force and rotor stall from diagram. to not happen rotor stall i must have little or 0km/h progressive speed but i cant get this speed in this situation :( . for little centrifugal force and blades collide i dont have solution because i cant test it in right parameters :(

if any have solution how to put helicopter from 6km with no turning rotor and smallest possible progressive speed (can in mission editor make this) this will be great test :)

30%.rar

Edited August 22, 2010 by Pirke77

[Pirke77]

autorotation in night situation without any lights in cockpit and landings lights , only position lights.

night.rar

[Vecko]

Still no answer from "higher command"?:)

 

No Pirke, you can start from air with 0 speed but there is no way to set rpm 0 in editor...

[Pirke77]

autorotation in extreme thunderstorm with maximum wind and turbulence velocity.

autotunder.rar

[Pirke77]

If flying were the language of man , autorotation would be its poetry :)

[Yo-Yo]

Before I take a look at the tracks try to explain the real accident with Mi-8. After the helicopter lost rudder control (the linkage was broken or jammed) it was trimmed for the speed about 150 kph. As the trim for hovering is very different, the safe landing became not possible and the commander decided to bail out. They flew to the safe area then bailed out FROM TRIMMED HELICOPTER. After it had run out of fuel the helicopter landed safely and was almost intact. If somebody move collective up before touchdown it would be completely intact. But nobody took care to decrease collective when the fuel went out and engines stopped.

Edited August 23, 2010 by Yo-Yo

[Pirke77]

Before I take a look at the tracks try to explain the real accident with Mi-8. After the helicopter lost rudder control (the linkage was broken or jammed) it was trimmed for the speed about 150 kph. As the trim for hovering is very different, the safe landing became not possible and the commander decided to bail out. They flew to the safe area then bailed out FROM TRIMMED HELICOPTER. After it had run out of fuel the helicopter landed safely and was almost intact. If somebody move collective up before touchdown it would be completely intact. But nobody took care to decrease collective when the fuel went out and engines stopped.

 

good information and thnx for futures help Yo-Yo.

but in serbia from last 20year mi8 pilots dont weary parachutes :( if machine go down we go with machine :) because of that i need all knowledge i can get to safe my little life :)

Edited August 23, 2010 by Pirke77

[Slayer]

I tired Pike77's tracks and it does the same thing on my setup. Very stange indeed. At first I thought it was because of no weapon load and half fuel but it does it too with full fuel and weapons.

[Pirke77]

I tired Pike77's tracks and it does the same thing on my setup. Very stange indeed. At first I thought it was because of no weapon load and half fuel but it does it too with full fuel and weapons.

 

[Sticky]

LOL in MY case the guy on the left is me flying the Ka50, and the guy on the right is me TRYING to fly the Su25T.

[Pirke77]

Before I take a look at the tracks try to explain the real accident with Mi-8. After the helicopter lost rudder control (the linkage was broken or jammed) it was trimmed for the speed about 150 kph. As the trim for hovering is very different, the safe landing became not possible and the commander decided to bail out. They flew to the safe area then bailed out FROM TRIMMED HELICOPTER. After it had run out of fuel the helicopter landed safely and was almost intact. If somebody move collective up before touchdown it would be completely intact. But nobody took care to decrease collective when the fuel went out and engines stopped.

 

 

i do some test of this accident and i have same results :)

good testing :)

mi8 accident test.rar

[SCEADU]

I flew R/c Helicopters for about 5 years. We always said that helos beat the air into submission thats why they fly.

 

 

The neatest thing I have ever seen an R/C heli do was in an exteme manuever the blades cut the carbon fibre tail clean off. The pilot immediately shut the engine down and was able to auto it in without a tail. I would have never believed it if I didn't see it with my own eyes. he was probably 150 feet up when the tail was sheered.

[Callsign.Vega]

While I do not fly a coaxial helicopter, I can shed some light on some of the auto rotation questions. I fly a single main counter-clockwise fully articulated rotor aircraft, the UH-60. I have also flown Bell 206 and OH-58, but those are semi-rigid teetering designs which I will not discuss.

 

In the UH-60, unrecoverable rotor RPM is around ~74%. If the rotor drops below this approximate number, no amount of collective nor cyclic movement will recover the decay. The aircraft will effectively fall out of the sky. Rotor RPM in the UH-60 decays very rapidly as it is a low inertia rotor system. It has very little weight.

 

Does anyone know if the KA-50 is high or low inertia rotor system? What about blade weight numbers?

[Callsign.Vega]

Before I take a look at the tracks try to explain the real accident with Mi-8. After the helicopter lost rudder control (the linkage was broken or jammed) it was trimmed for the speed about 150 kph. As the trim for hovering is very different, the safe landing became not possible and the commander decided to bail out. They flew to the safe area then bailed out FROM TRIMMED HELICOPTER. After it had run out of fuel the helicopter landed safely and was almost intact. If somebody move collective up before touchdown it would be completely intact. But nobody took care to decrease collective when the fuel went out and engines stopped.

 

Could you explain a little more? Did you say a MI-8 flying trimmed at 150 kph, with no pilots on board, ran out of fuel and the helicopter with no pilots landed safely?

 

That doesn't make any sense. :confused:

 

A lot of things happens when the engines quit in a helicopter. It yaws and pitches. A trimmed collective position for straight and level flight would never allow an successful auto-rotative descent. Although, both engines are unlikely to flame-out at the exact same time, allowing one engine operation for descent. Not to mention the MI-8 has a high center of gravity making level touchdowns even more imperative.

 

Most of the earths surface is rough and uneven with many obstacles. It would be extremely hard to do a roll-on landing in a wheeled helicopter in some farm field somewhere at 150 kph successfully with an expert pilot let alone a helicopter with no one at the controls. When you say "almost intact", did you mean the fuselage broke apart? Do you have any pictures by chance?