View Full Version : How does a wheel brake work?
hotzenplotz
10th Nov 2005, 16:18
On a transport helicopter with a three point gear, how does the wheel brake work?
Lynx, Merlin, NH-90, Cougar, S-76, Dauphin etc. any differences?
Do all wheels have a brake, or just the rear wheels?
:confused:
NorthSeaTiger
10th Nov 2005, 16:22
The rear wheels (mains) have a brake unit each, the axel has the actual brake unit physically attatched through which a disc runs which is driven by the wheel, braking is achieved by hydraulic power acting on the brake unit calipers which provide friction against the disc thus giving braking.
hotzenplotz
10th Nov 2005, 16:28
That means that all three wheels can be braked?
What is the "axel"?
Can the front wheel be steered?
Or does it just react to the tail rotor inputs?
Just like a car - the wheel is attached to the brake disc and both rotate on the axle - the caliper is fixed to the undercarriage leg and clamps the disc when you press the brake pedal.
The 3rd wheel, nose on the Merlin and tail on the Sea King, are castoring and allow the differential braking on the main wheels (and or the thrust of the tail rotor) to turn the aircraft.
hotzenplotz
10th Nov 2005, 17:16
Sorry, maybe it's because english is not my natural language, but I just don't get it.
The two main gear wheels can be braked.
What's about the castoring third wheel?
Can it be braked?
And if so, is there a seperation of the brakes?
Maybe it is better to understand when you tell me how the pilot practically brakes.
Farmer 1
10th Nov 2005, 17:25
The nose wheel does not normally have a brake. It acts like the wheels on a shopping trolley - if you push the tail in one direction, the wheel turns in the opposite direction.
Each main wheel has a brake, which is operated by a pedal above the tail rotor pedals. If you push on one brake pedal, the brake on that side operates, but it has no effect on the other brake.
This has the effect of turning the helicopter towards that side, and the nose wheel turns to follow it.
Cyclic Hotline
10th Nov 2005, 18:26
And don't forget your chocks either! :eek:
MightyGem
10th Nov 2005, 21:49
Apart from the British Army's Mk9 Lynx. Its brakes are operated by a
lever on the cyclic
Cyclic Hotline
11th Nov 2005, 03:33
That was a unique Westland concept, found on many of their products!
Westland learned everything they knew about wheels and brakes from Raleigh! Including the brake lever.
cl12pv2s
11th Nov 2005, 07:31
hotzenplotz,
It is just like Farmer1 said. Have a look at a car's disc brake as they are pretty similar. It's just that you have two 'independant systems' in a helicopter
In most aircraft, to apply the brakes you simply push the top of the tailrotor pedals.
This means that you can use the brakes at the same time as applying tailrotor yaw control. The action of doing these at the same time can mean you can almost turn on the spot.
cl12pv2s
Dave Anderson
11th Nov 2005, 14:14
I have a bunch of time in the Mi-8,17,24/25 and they all have the same wheel brake system. The nose wheel is a simple caster like the grocery cart and the main wheels are braked simultaneously using a bicycle type hand brake installed on the front of the cyclic grip.
It is a very simple system. No extra master cyliders for each wheel are needed since there are no brake pedals on the floor for individual wheels. One uses the tail rotor pedals (and tail rotor thrust) to do the steering. Squeeze the handle and she stops. The only really weird thing is that they are actuated using compressed air, much like a truck!
I liked the system. Western OEM's ought to look at this.