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!

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.

nice!

does that mean that if some heavy wind strikes, the blades could start turning out of control if they are not tied?

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.

cool, thank you very much for clearing that up!

@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?

@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.

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.

@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.

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)

Why should you not use the collective to slow down the rotor?

The rotor blades are not stable enough to support the weight of the helicopter. If you lift the helicopter at the blade tips, the rotor-blades will bend and then brake. Same will happen if you apply collective and positive pitch at low RPM. :(

When the rotor is spinning at his normal operating speed, the centrifugal force acting outwards prevents the blades from too much bending. Only in combination with the centrifugal force they can support the weight of the helicopter.

You may use collective to slow down the main rotor when you are willing to risk a lot of damage for winning a few seconds. And if you are absolutely sure, the rotor will not produce enough lift to bend the blades ad very low RPM. :doh:

A rotor brake is optional and not standard.

It depends on the type of operation. It's an additional part that needs to be maintained and may cause problems besides the fact it's "unnecessary" weight."

But if you are for example a rescue helicopter and land at tide areas with a lot of things around you do not have under control? You will stop your rotor as fast as possible for safety reasons.

... when a situation calls, you can assist the air braking with collective.

Yes, when ditching. Otherwise you can seriously damage vital parts of the rotorhead.

Do you really do this to stop the rotor in a manned helicopter???

Why should a rotorbrake not be able to stop the rotor effectively? That's only a question of construction. As AlphaOneSix said, the rotorbrake can be so strong that it can hold the Rotor even with one engine running. Example: Lynx, Super Puma.

Fox

Yes, when ditching. Otherwise you can seriously damage vital parts of the rotorhead.

 

Do you really do this to stop the rotor in a manned helicopter???

 

Why should a rotorbrake not be able to stop the rotor effectively? That's only a question of construction. As AlphaOneSix said, the rotorbrake can be so strong that it can hold the Rotor even with one engine running. Example: Lynx, Super Puma.

 

Fox

As mentioned before. There are like always pros and cons,

Holding the Mainrotor during engine running also stops N2 in the hot section of the turbine and burns it away because all the freewheeling parts to separate them in case of an engine failure working only in the opposite direction.

During my active time, I also heard a lot of problems with rotor breaks just one of them is when the break does not release for 100 %. In the Huey, this appears as Rotor will not start turning at 10 or 11 % N1 because of the friction applied by the rotor brake and you have to abandon engine startup and call for a technician.

As mentioned before. There are like always pros and cons,

Holding the Mainrotor during engine running also stops N2 in the hot section of the turbine and burns it away because all the freewheeling parts to separate them in case of an engine failure working only in the opposite direction...

And also again: It is a question of construction. You can hold the rotor of the Super Puma with one engine running for up to 5 Minutes during start up. No problem for the freewheel part. It is made for this. That way you can start the rotor in very high wind conditions.

...

During my active time, I also heard a lot of problems with rotor breaks just one of them is when the break does not release for 100 %. In the Huey, this appears as Rotor will not start turning at 10 or 11 % N1 because of the friction applied by the rotor brake and you have to abandon engine startup and call for a technician.

Different experience here. If the german army or air force had this "lot of problems with rotor brakes" there would have been more information available about that to the aircrews. As with every mechanical part the rotor brake can fail, but that is not a general problem.

Fox

That way you can start the rotor in very high wind conditions.Fox

For me, this is as well a very good reason for a rotor brake. :thumbup:

It would be interesting to see what side effects that have, in concern of coasts, additional weight, and what the limitations to engine power output are besides the 5 minutes.

Engine running I suppose means ground idle and the 5 minutes gives you the time to start up the second engine. Makes perfect sense if the rotor starts turning when bove engines running and the timeframe in which the rotor may produce thrust, while there is no or less controllability, is minimized.

And for sure a rotor brake is much cheaper than a helicopter blown off a ship or an oil rig.

For me, this is as well a very good reason for a rotor brake. :thumbup:

 

It would be interesting to see what side effects that have, in concern of coasts, additional weight, and what the limitations to engine power output are besides the 5 minutes.

Engine running I suppose means ground idle and the 5 minutes gives you the time to start up the second engine. Makes perfect sense if the rotor starts turning when bove engines running and the timeframe in which the rotor may produce thrust, while there is no or less controllability, is minimized.

 

And for sure a rotor brake is much cheaper than a helicopter blown off a ship or an oil rig.

Just above idle. Costs and weight are neglegtible(considering the total price of the aircraft and its weight). You don't start the second engine, while the rotor is still stopped. The brake is released and simultaneously throttle is adjusted so that the rotor spins quickly to nominal rpm.

Then the second engine is started.

Fox

Just above idle. Costs and weight are neglegtible(considering the total price of the aircraft and its weight). You don't start the second engine, while the rotor is still stopped. The brake is released and simultaneously throttle is adjusted so that the rotor spins quickly to nominal rpm.

Then the second engine is started.

 

Fox

Thanks for the explanation. It's very interesting. Under normal circumstances, you don't hear about such needs and procedures.

If you like to show me how it works in RL just send me a message. I will find some time :smilewink:

Do you fly to oil ricks?

During my active time, I also heard a lot of problems with rotor breaks just one of them is when the break does not release for 100 %. In the Huey, this appears as Rotor will not start turning at 10 or 11 % N1 because of the friction applied by the rotor brake and you have to abandon engine startup and call for a technician.

In windy conditions we just used to grab a Huey blade with a tie-down strop and stand out the front holding the blade for as long as it was possible during start - then just let it go and gtfo and it usually spun up pretty quick. :thumbup:

The rotor blades are not stable enough to support the weight of the helicopter. If you lift the helicopter at the blade tips, the rotor-blades will bend and then brake. Same will happen if you apply collective and positive pitch at low RPM. :(

 

When the rotor is spinning at his normal operating speed, the centrifugal force acting outwards prevents the blades from too much bending. Only in combination with the centrifugal force they can support the weight of the helicopter.

What in the...How have I never heard or seen this before?! It makes perfect sense...it ALSO reminds me of why I have always considered Helicopter evil critters!

Thanks for posting this...

Just a story related to that topic

I asked a french army pilot flown the Gazelle and other types about the rotor brake.

He told me. not only the Gazzell, many other french helicopters basically equipped with rotor brakes.

He also told me that they opened the rotor brake usually during the preflight check because it would often be forgotten during startup. And as I stated in an earlier thread, even if the pilot realized this quickly, in many cases this leads to heavy damage on the engine.

Rotor and N2 Turbine stage in the Gazelle are rigged together and when the rotor is blocked N2 refuses to turn as well.

[...]

Rotor and N2 Turbine stage in the Gazelle are rigged together and when the rotor is blocked N2 refuses to turn as well.

That doesn't sound too healty :music_whistling:

Literally every turbine helicopter on the planet operates this way. If the rotor doesn't spin, neither does the N2 turbine in the engine.

(EDIT: Now that I've made such an absolute statement, someone will find a way to prove me wrong)

Literally every turbine helicopter on the planet operates this way. If the rotor doesn't spin, neither does the N2 turbine in the engine.

 

(EDIT: Now that I've made such an absolute statement, someone will find a way to prove me wrong)

The Gazelle's Turbomeca Astazou XIV Turbine doesn't have a power turbine "N2", instead it uses a centrifugal friction clutch that engages at 27,000 - 34,000 RPM (idle=25,500 RPM).

If the mechanical clutch isn't allowed time to engage fully (Engine and Rotor RPM sync), before increasing the Engine/Rotor RPM to Full (43,500 / 378 RPM), the friction clutch will overheat and destroy itself.

I imagine, either the rotor brake or the centrifugal clutch would be destroyed if the rotor brake wasn't released.

It was Frank Robinson from Robinson Helicopters telling us Flight Instructors, that is one of his worst decisions to give Helicopter flight training to his engineers. :doh:

After the training and the knowledge, what etherizing can go wrong or is just a compromise the engineers had more safety concerns and construction of new things getting more complicated. :cry:

While the average helicopter pilot does not think about physics and compromises he just enjoys flying :thumbup::pilotfly: