Wind effect on Max Range Cruise

[wiseoldowl]

Hello all!

Can anyone tell me what the effect of wind is on MRC?
I've read that when flying into a headwind, the range increases because the best range speed will be a little faster...The only thing I see with a headwind is that the ground speed would be slower, and so the flight would take longer and thus consume more fuel...Or is it a question of Angle of Attack? I must say I'm a bit confused :ugh:

Thanks for your help!

[keith williams]

The headwind will decrease our groundspeed and this will increase our flight time.

But if our airspeed remains unchanged then our fuel flow rate will also remain unchanged.

So for each hour of flight we will burn the same amount of fuel, but we will have flown less distance over the ground.

So headwinds will decrease our max range.

To reduce the amount by which our max range is reduced, we need to reduce the amount of time that we are fighting against the headwind. To do this we must fly a little bit faster.

But if we make the mistake of increasing our airspeed too much then the additional fuel that is required to provide additional thrust equal to the additional drag, will outweigh the benefit of reduced flight time. This will reduce our max range.

So speed for max range in a headwind is slightly higher than it would be in still air.

But the overall effect is still a reduction in max range.

[eckhard]

I agree with Keith.

Similarly, in a tailwind, the max range will be achieved at a speed slightly slower than that for still air. We want to spend a little more time in the beneficial tailwind, so slowing down a bit helps overall.

For a jet, the max range speed is found on the 'drag v speed' graph. A straight line drawn from the origin which just touches the curve will have a minimum angle to the x-axis. The speed corresponding to this tangent (vertically below) will be the speed for max range.

To visualise the effect of wind, move the starting point of this line along the x-axis from the origin. Move it to the right for a headwind and to the left for a tailwind, in each case by the number of knots of headwind or tailwind. This new starting point will then produce a line which makes a tangent to the drag curve at a different speed to that for still air. The tangent will occur at a faster speed for a headwind and at a lower speed for a tailwind.

Much easier to see graphically than trying to explain it!

For a piston powered aircraft, the same can be done on the 'power required v speed' graph.