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autorotation fail since most recent update


skypickle

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Last week I was autorotating like a champ. Putting the Huey down in one piece and even on the runway sometimes. But after the last patch I have noticed something weird. 

I turn down the throttle and lower the collective like I usually do. Then I pitch down and try to keep rotor rpms in the green while keep speed to 80 knots. Except now, once I turn the throttle down, the rotor rpms drop and never come back up. The collective is all the way down and I am pitched 30 to 45 degrees down. 

Then I started wondering, why does the rotor keep spinning in an autorotation anyway if the collective is all the way down. If I want the rotor to spin up as I fall, shouldnt the rotor blades actually need to angle to the ground a bit?

4930K @ 4.5, 32g ram, TitanPascal

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80 knots is probably a bit quick. try 60-70.

Autorotation requires airflow coming up through the rotor disc. The relative airflow at a high rate of descent creates a "driven" region on the blade that can maintain RPM. 

Not sure it's modelled, but pitching forward will temporarily reduce RPM and pitching backwards, "flaring", will increase it.

The Huey has a high inertia rotor system, so that's great if you maintain your RPM, but if you lose RPM early it's harder to get it back.

 

So try think of what is driving the blades as the airflow from below. Keep the aircraft a bit more level. If you aim for 60-70 knots and maintain a steady speed this should take care of itself. Then use collective to maintain Rotor RPM in the green arc.

 

Good luck!

 

i7-9700F, 32Gb RAM, RTX 2080 Super, HP Reverb G2.

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14 hours ago, skypickle said:

Then I started wondering, why does the rotor keep spinning in an autorotation anyway if the collective is all the way down. If I want the rotor to spin up as I fall, shouldnt the rotor blades actually need to angle to the ground a bit?

It would seem so, but no.  

The trick to the rotor maintaining RPM without power - is lowering the pitch angle enough that the total aerodynamic force (light blue vector on the chart) points slightly forward.

The rotor needs to be producing virtually zero lifting forces, because those lifting forces cause the total aerodynamic force vector to move rearward.  "C" is what you want.  The TAF (total aerodynamic force) pointing slightly forward of vertical.  As the diagram indicates, this only occurs on portions of the blade.  The driving region of the rotor maintains rotor RPM during autorotative flight, overcoming the areas that are still a net drag on the rotor speed.  The more you twist the blade, the more you rotate that TAF rearward.  

To ensure this is actually the case should you need it as a pilot, the rotor linkages are adjusted and or checked for correct rigging during maintenance test flights.  Under XYZ conditions, when power is removed and collective is lowered  - the RRPM must maintain within certain limits.

 

Fig6-2.JPG

Fig_2-85.gif


Edited by cw4ogden
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Thank you. I did discover that I wasn’t resetting trim before autorotation. Reset helps.

 

@cw4ogdenthank you for those diagrams. I don’t know if it was intentional but the autotrotative force in region C seems to occur with a more angled blade (more collective). Autorotation requires no collective to minimize drag on the blade.

 

Also shouldn’t lift always be perpendicular to the blade? After all the wing shape is not changing. As the blade is angled back with more collective, the lift force generated by the airflow over the wing is related to the wing. The lifting force relative to the wing should remain constant but relative to the aircraft the vector should point more aft- the drawing shows the lift vector moving forward. Inflow as labeled in the diagram is the sum of airflow due to aircraft motion plus rotor motion. If we hold aircraft motion constant, then increasing collective should angle the lift vector backwards?

4930K @ 4.5, 32g ram, TitanPascal

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5 hours ago, skypickle said:

Also shouldn’t lift always be perpendicular to the blade?

Lift in rotary wing is perpendicular to resultant relative wind.  

If that doesn't answer the other questions that followed let me know.  

 

 "I don’t know if it was intentional but the autotrotative force in region C seems to occur with a more angled blade"

- only speculation, but possibly they are trying to show the twist (angle of incidence) of the blade increases as you move inbound.

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Easy. Do not pitch down to maintain RPM. You pitch down to maintain airspeed. 5 or 10 degrees should be more than enough. You want airflow to go through your rotor system from below, not parallel to it.

Editted to add:

did a test. Intentionaly left some collective up until rotor drooped down to 250 RPM with about 30 degrees nose down attitude. Just by pulling back to about 5 degree nose down recovered some RPM. Dropping collective all the way down recovered RPM quite fast. IMO, nothing changed. 


Edited by admiki
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  • 4 months later...

Hello,

what about Governor, is it necessary to set it to en emergency mode?

 

I am still unsuccessful with the autorotation. Throttle down, collective down, no trim, cyclic back, pedal right, governor emergency, speed about 60 knots but all I can see is falling down without any control.

__________________

Huey in the air, Spitfire in the hangar 🙂

The last version of OpenBeta (all terrains)

MFG Crosswind V2; Thrustmaster HOTAS Warthog; TrackIR 5 (still not in use)

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Here's a track showing how to do it.  To be honest, it took me a few tries becasue I kept losing the main rotor on landing.

As you can see, I didn't switch the governor to Emergency, and it worked nonetheless. TO me, the most diffcult part is the inital dive: if I dive too much, I cannot recover.

Huey_autorot.trk

At any moment in the track, you can hit Escape and use the "Take control" feature.

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Don't accept indie game testing requests from friends in Discord. Ever.

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2 hours ago, jpuk said:

Hello,

what about Governor, is it necessary to set it to en emergency mode?

 

I am still unsuccessful with the autorotation. Throttle down, collective down, no trim, cyclic back, pedal right, governor emergency, speed about 60 knots but all I can see is falling down without any control.

If you can put up a track or record a video we can probably help you out.

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11 hours ago, Flappie said:

Here's a track showing how to do it.  To be honest, it took me a few tries becasue I kept losing the main rotor on landing.

As you can see, I didn't switch the governor to Emergency, and it worked nonetheless. TO me, the most diffcult part is the inital dive: if I dive too much, I cannot recover.

Huey_autorot.trk 113.38 kB · 0 downloads

At any moment in the track, you can hit Escape and use the "Take control" feature.

Thank you very much, it helped me a lot. I used my way but the governor emergency had to be initiated immediately after the throttle and collective down. I also had to be more aggresive with the pedal and the cyclic. Then I was able to descent 2k knots/min and land relatively safely.

__________________

Huey in the air, Spitfire in the hangar 🙂

The last version of OpenBeta (all terrains)

MFG Crosswind V2; Thrustmaster HOTAS Warthog; TrackIR 5 (still not in use)

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19 hours ago, Flappie said:

Good! After a few tries, you'll master it. 👍

Are you able to recover to normal flying when "fuel" autorotation? With "governor" one it is not a problem.

__________________

Huey in the air, Spitfire in the hangar 🙂

The last version of OpenBeta (all terrains)

MFG Crosswind V2; Thrustmaster HOTAS Warthog; TrackIR 5 (still not in use)

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2 hours ago, jpuk said:

Are you able to recover to normal flying when "fuel" autorotation? With "governor" one it is not a problem.

I'm not sure what you mean. I cut the fuel in my track and I was able to land.

Whatever the reason for the engine stop (lack of fuel, engine burnt...), you still can land thanks to autorotation as long as you're flying high enough in order to get some speed from your fall.

Or maybe you mean to cut the fuel, execute an autorotation, then put the fuel back and restart the engine? I've never tested this. 😀


Edited by Flappie

Don't accept indie game testing requests from friends in Discord. Ever.

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1 hour ago, Flappie said:

I'm not sure what you mean. I cut the fuel in my track and I was able to land.

Whatever the reason for the engine stop (lack of fuel, engine burnt...), you still can land thanks to autorotation as long as you're flying high enough in order to get some speed from your fall.

Or maybe you mean to cut the fuel, execute an autorotation, then put the fuel back and restart the engine? I've never tested this. 😀

 

Not really. Not sure how it is in real life, in DCS  I can do vertical, 0-speed auto all the way to the ground. I remember one mission flying up the hill with slingload, 30 knots at about 150-200 ft AGL. Lost TR, pickled the load and did straight down auto.

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I assume both vertical and/or horitzontal speeds help the main rotor to gain RPMs. I remember @molevitch (hey, mate!) taught me I could do autorotation at 0 horizontal speed. It was aboard an Mi-8, but it most probably works the same with the Huey.

After all, the main rotor is like a giant kid's windmill. Blow air to the side of a kid's windmill: it spins. Blow air in front of a kid's windmill, it spins even faster.

Don't accept indie game testing requests from friends in Discord. Ever.

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On 5/23/2022 at 9:15 PM, Flappie said:

I'm not sure what you mean. I cut the fuel in my track and I was able to land.

Whatever the reason for the engine stop (lack of fuel, engine burnt...), you still can land thanks to autorotation as long as you're flying high enough in order to get some speed from your fall.

Or maybe you mean to cut the fuel, execute an autorotation, then put the fuel back and restart the engine? I've never tested this. 😀

 

When I start auto at 3000 ft atg, I can change my mind at eg. 2000, set gov to auto, throttle up and continue flying. With fuel cut I wasn't able to restore the flying. 🙂

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__________________

Huey in the air, Spitfire in the hangar 🙂

The last version of OpenBeta (all terrains)

MFG Crosswind V2; Thrustmaster HOTAS Warthog; TrackIR 5 (still not in use)

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