Question

[ccc111]

Hi can any one explain this question.

What happens to the indicated mach number in a long range cruise as weight decreases at the same flight level.

The answer is that it decreases. Its probably really simple . (its saturday and im at work)

Cheers

[Blinkz]

well as weight decreases, so does lift needed, which in turn means that drag reduces and so that the speed for max range (1.32Vmd) decreases also. I think thats right :confused:

[AerocatS2A]

Yeah mach number decreases because the long range cruise speed decreases as weight goes down. So as you're cruising along, you are constantly reducing power and airspeed to follow the long range cruise profile.

[Maude Charlee]

As the weight of the a/c reduces, the natural tendency would be for it to climb if the speed and AoA remain unchanged. In order to remain at the same level during the cruise, speed must be reduced in order to reduce the lift available.

[eckhard]

I think all of the above are correct, but are missing the important point that long range cruise for a particular airframe has just one angle of attack (usually around 3 degrees for a modern jetliner) that gives the best ratio of speed to drag. As the weight reduces, the speed must be reduced to maintain level flight at the same a of a.