In relation to rocket launches... explain to me the concept of

[sao123]

and why they throttle down during it...

 

[dkozloski]

As the fuel burns off the mass of the rocket becomes less and less and the rate of accelleration can increase to where the people on board would be subject to blacking out from the G forces.

 

[imported_Tick]

Originally posted by: dkozloski
As the fuel burns off the mass of the rocket becomes less and less and the rate of accelleration can increase to where the people on board would be subject to blacking out from the G forces.

And blacking out is bad.

 

[sao123]

and this would happen in the first 60 seconds of flight?

 

[gamefreakgcb]

According to the guide down at NASA center down in TX, the shuttle burns 12 tons of fuel per secong during phase 1, so if you dont compensate your rate of acceleration to that of the reduction of the mass of the rocket, you would be in trouble. Do not quote me on this as it is 3AM here and I am in no mood of confirming my reply, have fun.

 

[AeroEngy]

Actually Max- Q does not have anything to do with g forces or acceleration. Max-q refers to the point in the flight where there is the highest dynamic pressure. Dynamic pressure being the pressure felt from bringing a moving fluid to rest. Like sticking you hand out of the car window and feeling the air push on you.

q = 1/2* density of air * Velocity^2 (For subsonic)
q = 1/2 * gamma * pressure * Mach^2 (For supersonic)

Sense in a rocket launch the density is decreasing rapidly with altitude and the velocity is rapidly increasing. The plot of Q over time looks kind of like a bell curve. The top point of that plot is the Max-Q point. This point is usually very important because the highest aerodynamic stresses (and Drag) are exerted on the vehicle at this point.

So not only is the shuttle losing mass from fuel burn. After the Max-Q point the drag is decreasing from lower dynamic pressure and less dense and air. This means they have to reduce throttle to keep a more consistent acceleration.

 

[sao123]

Originally posted by: AeroEngy
Actually Max- Q does not have anything to do with g forces or acceleration. Max-q refers to the point in the flight where there is the highest dynamic pressure. Dynamic pressure being the pressure felt from bringing a moving fluid to rest. Like sticking you hand out of the car window and feeling the air push on you.

q = 1/2* density of air * Velocity^2 (For subsonic)
q = 1/2 * gamma * pressure * Mach^2 (For supersonic)

Sense in a rocket launch the density is decreasing rapidly with altitude and the velocity is rapidly increasing. The plot of Q over time looks kind of like a bell curve. The top point of that plot is the Max-Q point. This point is usually very important because the highest aerodynamic stresses (and Drag) are exerted on the vehicle at this point.

So not only is the shuttle losing mass from fuel burn. After the Max-Q point the drag is decreasing from lower dynamic pressure and less dense and air. This means they have to reduce throttle to keep a more consistent acceleration.

Excellent description... thanks