# Fokker 100 Brake Disc Actuator Main Landing Gear

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1. Jan 15, 2016

### Sem ten Wolde

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Dear users,

I have a problem with a calculation. I have got an assignment. For this assignment I have to redesign the brake actuators for the brake discs of the main landing gear of th fokker 100. I have forgotten how to calculate a force that goes sideways. The sideway forces are created when the lineair actuator pushes the brake disc on the wheels. For the calculation I have a few values.

- Total brake disc mass: 237,84 kg (90% worn brake, CS25.109i)
- CS-25 braking speed is= -3,0 m/s^2
- Assumed distance from neutral position actuator to the wheel= 5 cm
- Maximum take-off weight Fokker 100: 44.450 kg
- Kinetic energy brake discs: 162 MJ
- Maximum actuator force for each actuator: 40.000N
- Specific Heat of he brake disk material: 800 J/kg/K
- RTO test speed: 85m/s, 166 knots
- Effect of air resistance will be ignored, trust reverser and speedbrake on the wing will not be applied.

I have a few questions:
1 - Which formula do I need to determine the force that the actuators need to push the brake discs?
2 - How much actuators do I need in total on each wheel?
3 - What is the Work of each actuator?
4 - What is the Power of each actuator?

To be clear, I DON'T need to know the maximum kinetic energy capability of the brake disc, these questions are aimed only for the actuators. I need to know how much power the actuator need to produce and how much of them I need them on 1 wheel.

2. Jan 16, 2016

### CWatters

This is how I would do it..

First work out the force needed to retard the aircraft using Newtons F=ma. From that work out the torque the brakes have to apply using F and the wheel radius. Then I think you can use the average radius of the pads to calculate the friction force Ff required to produce the same torque. Then use the friction equation Ff = uN where u is the coefficient of friction and N is the normal force (eg the actuator force asked for in Q1).

Then for Q2 divide the force required by the max force one actuator can produce to get the number of actuators required.

I think Q3 and 4 is difficult. Work = force * displacement. But the displacement is the distance the actuator compresses the brake material and the force isn't constant over that distance. Perhaps you ca use the 5cm dimension and assume the force is constant? or changes from 0 to N and take an average?

In the above I've not taken into account the number of wheels. Essentially you have to divide the force by the number of wheels that are fitted with brakes.

Last edited: Jan 16, 2016