Which one will have a longer glide distance?

Question

Two aircraft of the same make and size are flying at the same altitude and speed under similar atmospheric conditions. One aircraft is at its all up weight (AUW) while the other one is flying empty. Assuming that they both develop engine failure, which of the two will have a longer glide distance and why?

Answer 1

You assume wrongly Michael C. Asuming zero wind they'll both glide the same distance. When flying the best L/D airspeed the glide ratio is identical regardless of aircraft weight. However best L/D is increasingly proportional to aircraft weight. So the heavier airplane which will glide faster will get there sooner. It's rate of descent will be faster because its going downhill faster, but the glide path will be the same. This is why competition sail planes carry water ballast. It's helpful when lift is strong so they can go fast. But it can be dumped when lift is weak and  a minimum decent rate is needed to stay up or climb.

In a headwind however, the heavier aircraft will glide further as the higher speed means that the headwind will negatively affect the groundspeed for a shorter time period. The reverse is true with a tail wind as the lighter slower decending aircraft can be helped along by the tailwind longer.

Answer 2

The other one

Answer 3

Is the best L/D speed proportional to the aircraft's √[(gross weight)/(max allowable gross weight)]?

Answer 4

An empty aircraft can be half the weight of a full aircraft.

I will assume that the lighter aircraft will be able to glide further and possibly ditch safer than a fully laden aircraft.

the only advantage that a heavier aircraft has is the higher momentum but then a heavier aircraft would have a higher stalling speed as well.

Answer 5

John B when I saw the Q I thought it will take time for someone to get this right. You did a good job explaining. Top marks.

To get to the Q John is spot on. He has to get best answer.