High School

An Embraer ERJ-145 has a mass of 12,007 kg when empty. The three landing gear suspension systems share the load evenly. When loaded with 4,000 kg, the suspension system pictured deflects 0.2 m.

What value of viscous damping in the suspension system would cause the system to be critically damped?

Answer :

The value of viscous damping in the suspension system that would cause the system to be critically damped is approximately 5,600 Ns/m.

The natural frequency of a system can be calculated using the following formula:

ωn = √(k/m)

In this case, each of the three landing gear suspension systems share the load evenly, so the weight supported by one suspension system is:

W = (4000 kg) / 3 = 1333.33 kg

The deflection of the suspension system, δ, is 0.2 m.

The spring constant k of the suspension system can be calculated using Hooke's Law:

k = F/δ

Since the weight is supported evenly by all three suspension systems, the force exerted by one suspension system is:

F = (1333.33 kg) x (9.81 m/s) = 13098.67 N

Therefore, the spring constant is:

k = 13098.67 N / 0.2 m = 65493.35 N/m

The mass of the system is the mass of the loaded plane plus the mass of the suspension system. Since the plane has a mass of 12,007 kg when empty and is loaded with 4000 kg, the total mass is:

m = 12,007 kg + 4000 kg = 16,007 kg

Now we can calculate the natural frequency of the system:

ωn = √(k/m)

= √(65493.35 N/m / 16007 kg)

= 1.064 rad/s

To find the value of viscous damping that would cause the system to be critically damped, we need to use the formula:

c = 2mωn

For critical damping, the damping coefficient must be equal to the critical damping coefficient, which is:

cc = 2√(km)

cc = 2√(k m)

= 2√(65493.35 N/m x 16007 kg)

≈ 5,600 Ns/m

Therefore, the value of viscous damping in the suspension system that would cause the system to be critically damped is approximately 5,600 Ns/m.

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