can a helicopter not have a rotor brake? - ED Forums
 


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Old 09-04-2019, 05:50 AM   #1
aledmb
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Default can a helicopter not have a rotor brake?

hey everyone,

i'm asking this because a topic where i was looking for that answer was locked in another fourm.

our huey does not have a rotor brake lever.

does that mean it does not have a rotor brake?

how does this work on that helicopter?

thank in advance!
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Old 09-04-2019, 06:37 AM   #2
ghost84
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Not every helicopter and not every huey has a rotor brake.

According to wikipedia (https://en.wikipedia.org/wiki/Bell_UH-1_Iroquois) the marine corps hueys had a rotor brake for shipboard use to stop the rotor quickly on shutdown.
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Old 09-04-2019, 06:49 AM   #3
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nice!

does that mean that if some heavy wind strikes, the blades could start turning out of control if they are not tied?
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Old 09-04-2019, 07:15 AM   #4
Fri13
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IIRC the rotor brake is used for winds, and heavy winds requires cables anyways. They are not to be used brake rotor rotation as they are ineffective in that, but they do help a little bit in the final free rotations to stop that sooner.
But it is like a wheel brakes on aircraft, but without anti-skid. So you will burn brakes and wear the mast as it is just ineffective. It is faster to slow by increasing blade angle of attack after while the turbine is turned off and when rotor can't anymore generate lift or caught with the wind.

In ships the rotating rotor is a high risk, why you need to get it locked quickly in one position.
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Old 09-04-2019, 07:22 AM   #5
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cool, thank you very much for clearing that up!
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Old 09-04-2019, 05:24 PM   #6
BaD CrC
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@Fri13, stopping the rotor by increasing the collective?? My instructor told me to just never do that ever IRL as you can't tell how slow is slow enough to not produce some lift. But maybe you have a different IRL experience?
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Old 09-05-2019, 03:22 AM   #7
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Quote:
Originally Posted by BaD CrC View Post
@Fri13, stopping the rotor by increasing the collective?? My instructor told me to just never do that ever IRL as you can't tell how slow is slow enough to not produce some lift. But maybe you have a different IRL experience?
Haha, this. Using collective to slow the rotor is strictly forbidden in the B412 I fly.

In fact, it’s exactly the opposite of Fri13s statement - the rotor slows quickly on its own to about 40%, which is our brake limit. At 40% we pop that sucker on and the blades slow down quickly. If the rotor brake is MEL’d, it takes forever to fully stop! The rotor brake is 100% designed for slowing down the rotor on shutdown, we don’t leave it on afterwards to secure the rotor as it puts stress on the hydraulic system that powers the brake. We have tie downs for that.

It also does not wear the mast down, as it is all connected to a disk brake just like in your car. It doesn’t put friction on the mast at all, but rather on the attached disk brake.
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Old 09-05-2019, 11:07 AM   #8
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Oddly enough, I've never seen a helicopter without a rotor brake. Granted, I'm referring to aircraft I've actually worked on, so it's a relatively small subset of helicopters.

Rotor brakes are used, as Sandman1330 mentions, to slow down the rotor during shutdown. Different aircraft have different limitation on when you can start using the rotor brake. On the B412, for example, it's 40% rotor rpm. On the Mi-8, it's 12-20% depending on what it says in the flight manual. Some aircraft also use the rotor brake during start to keep the rotor from spinning during engine start, typically in heavy winds where the blades might flap too much before they build up enough speed. On the Mi-8, you can't start the engine with the rotor brake on, and we use the rotor brake routinely while the aircraft is parked if we don't tie down the blades.

And also as Sandman mentioned, there is no wear on the mast, in all cases I've seen, the rotor brake is always attached to something hanging off the main gearbox. Usually just a disk brake that's geared into the main gearbox, but on the Mi-8 it's a drum brake attached to the tail rotor output shaft.

Oh and you never, ever, increase rotor pitch angle to slow down the rotor blades...ever.
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Old 09-05-2019, 11:16 AM   #9
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Quote:
Originally Posted by BaD CrC View Post
@Fri13, stopping the rotor by increasing the collective?? My instructor told me to just never do that ever IRL as you can't tell how slow is slow enough to not produce some lift. But maybe you have a different IRL experience?
You would be aware of your helicopter weight all the times you know where about is your COG, and knowing your RPM and AoA gives you fairly good idea how much you can adjust.

Idea is not too crank collective up as soon as possible.... But when a situation calls, you can assist the air braking with collective.
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Old 09-05-2019, 11:22 AM   #10
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US chinooks don't have rotor brakes as far as I know. That's what we have always been taught (work on UK chinooks). When I worked overseas they always let the blades spin right down, whilst the UK ones would apply the brake at an acceptable speed (rpm)
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