I have noticed lately when I load a flight the needle in the ciruclar break pressure indicator has been just out of the green section and in the yellow seciton.

 

Any idea why it's doing this?

 

Kind Regards,

 

Dan

When hydraulic pumps are off pressure in the hydraulic system goes to 0, however the brake system is designed to supply some extra brake possibility using an hydraulic accumulator.

this accumulator has a 1000psi of nitrogen precharge and then will be pressurized to 3000psi when pumps are running. What you read in the gauge is the accumulator pressure.

When you turn off the pumps check valves prevent the hyd fluid to go out from the system, using brakes will then remove when braking and releasing fluid and pressure.

So, if you push the pedals with pumps off you can brake but pressure will drop. When pressure reaches the precharge value the brakes will no more work until you apply sys B pressure.

It is useful to know also that if you leave for hours or days the aircraft unpowered, the brake accumulator will release some pressure due to internal leakage in the various valves.

It is useful to know also that if you leave for hours or days the aircraft unpowered, the brake accumulator will release some pressure due to internal leakage in the various valves.

 

And is this simulated by pmdg?

I don't know, probably not as really few users leave the plane for hours unpowered in FSX.

I would have definitely thought PMDG simulated this since it has been around on a few other FS addons for a while.

It is simple to do that, but it is also useless as noone (I hope) will spend hours with the plane parked without hyd pumps.

And the rate of pressure decrease is not standard, it could take days to reach the precharge value. It is also not linear due to friction in the accumulator, temperature change and so on.

It could be nice to know it is working but useless at all as noone will see that.