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Rotor Vibration due to steep dive


Tiramisu

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I have noticed that I get rotor vibrations leading to catastrophic engine failures, when I throttle down the collective too much. The vibrations start to occur within a very short time span and the vibration warnings come too late for me. Probably there is a way to aniticipate vibrations early enough, but I could not find any helpful indicators in the cockpit, yet. Of course I can try to move the collective very carefully, but sometimes I need to make a steep dive, so I need to know exactly where the limits are.

 

Failing rotors have already messed up my first mission in the first Ka-50 campaign many times. This mission is just about following a helo and getting familiarized with the area, but I believe since it takes place in a mountainous area the catastrophic failures happen much earlier than on lower altitudes. Either I make steep risky dives or I loose the other helo out of my sight leading to a poor mission rating. The duration of this mission is very long, so I do not want to fail any more. :cry:

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The vibrations you speak of sound like VRS. Throttling down too quickly with little airspeed can cause the aircraft to get entangled in unstable air induced by it's own rotors, and lead to a loss of lift. There really aren't any indicators to show this. When the helicopter starts to vibrate, it falls on you to know a situation is developing that you need to be aware of. That comes with experience.

 

Best course of action to get out of VRS is to increase collective while going stick and rudder in opposite direction to get lateral movement, or side-slip. You will slip out of it pretty quickly, and if done right when caught soon enough, you lose at most 20 meters of altitude.

 

An excellent video showing and explaining more clearly:

 

As for making steep dives, trust me she can handle it. I've put her into a dive exceeding 380 km/h. Just don't make any sudden stick or rudder movements. If you're going to push the limits, you need to be smooth and steady with the controls; and again that knowledge comes with experience.

 

Not sure what you're doing in the mission, but the mission itself certainly isn't hard. I think all you need to get to the end, is just more seat time to catch the little mistakes that are adding up on you.

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I think you are right! Thx! So I will practice this and do exactly what you wrote. I am a total beginner in flying helos, which is why I was not aware that this terrifying vortex effect can be so dangerous.

 

Not sure what you're doing in the mission, but the mission itself certainly isn't hard.

 

Yeah I need much more practise. The other helo I have to follow sometimes does unpredicted maneuvers and when I overshoot him with too much speed or altitude I loose him very easily. It seems like you have to be close to him during the flight, because using the autopilot to visit all the waypoints does not complete the mission. lol

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The other helo I have to follow sometimes does unpredicted maneuvers and when I overshoot him with too much speed or altitude I loose him very easily.

 

 

You are talking about the "Deplyment" campaign? I've done the first mission last week and the leading helo did crazy maneuvers some times. At the third try I left some more room between him and myself and was successful. Hope that helps a bit.

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You are talking about the "Deplyment" campaign? I've done the first mission last week and the leading helo did crazy maneuvers some times. At the third try I left some more room between him and myself and was successful. Hope that helps a bit.

 

Right, it is the Deployment campaign. I have already tried to keep more distance to that helo, but then this sneaky bastard vanished somewhere behind the hills. :D

Anyway, now I managed to win this scenario following the tips of Baaz, which allowed me to make safer steep dives. So this time I did not reduce my collective too much when flying with low speed, which helped me to avoid rotor vibrations as well.

 

One thing I recently noticed is that the mission description recommends to consult the "altitude-velocity envelope limitations" of the Ka-50. I am not sure if that has also something to do with rotor vibrations, but it would be helpful if I knew where to find such limitation-diagrams. Regarding the limit for avoiding Vortex Ring States I have found a general limit of about 500 feet per minute descent rate (according to

).
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When you dive at a steep angle, floor your collective to flatten the blades so they aren't grabbing air. It will smooth things out and keep you from ripping your blades off or crossing them.

 

 

Yeah, the shaking cockpit is a big sign of VRS. It happens when you drop the helicopter vertically at over 10 meters / second. Your falling into your own downwash, so there's no stable air for the rotors to push on.


Edited by 3WA
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Um but if your in a dive it's not going to be VRS as you literally have very high relative airspeed.

 

Don't the rotors collide if you exceed VNE? Which is very easy to do in a dive. :)

Control is an illusion which usually shatters at the least expected moment.

Gazelle Mini-gun version is endorphins with rotors. See above.

 

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Um but if your in a dive it's not going to be VRS as you literally have very high relative airspeed.

 

Don't the rotors collide if you exceed VNE? Which is very easy to do in a dive. :)

 

Not with collective at minimum. Easily go past 400kmh safely

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Yeah, your rotors aren't pushing any air, so they just spin flatly, safely away from each other. It's pulling out of that high speed dive you have to watch out for. That's when it gets dangerous. SLOWLY level out and SLOWLY start increasing the collective, giving the minimum collective you can. Even flat, your blades seem to act as a giant wing, giving you some lift ( especially at high speed ). So, you don't really have to give it too much collective or too fast.

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Make sure you put your free turbine speed governor to low and collective to zero, do a spiraling dive to slow your descent rate and don't use any rudder at all while doing that it will clash the rotors instantly

Simflyin' since 1985 :smartass:

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You can dive with well over 400km/h, just be gentle and keep the collective FLAT until you have slowed down to way below 300km/h, then gently raise collective and ease off cyclic as you apply more and more collective. IIRC around 450-460 km/h is most I ever could achieve 90° nose down.

 

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