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The Effect of Weight on Descent

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tszchun.anson created the topic: The Effect of Weight on Descent

Hi,

When it comes to a glide, weight is not affecting glide angle and glide path, but the heavier aircraft glides that path faster according to the study guide. I would like to confirm my understanding:

Both heavier and lighter aircraft need to maintain AoA of 4 degrees to maximise the L/D ratio. Also, as long as the weight is higher, lift needs to be higher for the balance. Therefore, IAS (dynamic pressure) needs to be higher for the heavier aircraft to ensure sufficient lift.
That's why the heavier aircraft will have the same glide path but faster (like a escalator going down set to be running at a higher speed),
provided that their L/D ratio is the same.


However, I am confused about why the heavier aircraft can glide further in headwind. I have brainstormed a bit:

assuming both aircrafts have the same L/D ratio of 10:1.
Without wind, both of them can glide 10 units (horizontal distance) per unit of height loss.
With headwind, thinking of moving "air box", I thought that both of them will have steeper glide path and greater glide angle.


I would be thankful if you could help provide me with some insights. Really thanks very much for your support!

Anson
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tszchun.anson replied the topic: The Effect of Weight on Descent

I have done some revision on lift as well. I was reminded that if AoA remains constant, raising airspeed increases the magnitude of total reaction, hence its components, lift and drag, are increased by same proportion (L/D Ratio). Back to the topic of descent, the heavier aircraft glides the path faster (@higher airspeed), supposedly its lift/drag ratio remains unchanged hence there will not be any change in glide distance per altitude loss (or glide angle).

Then I doubt about how headwind plays a role in the descent. I thought it just simply increases the IAS of the aircraft and has the same effect as raising airspeed on L/D ratio (which is no effect).
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bobtait replied the topic: The Effect of Weight on Descent

In no wind, the light aircraft and the heavy aircraft travel down the same path within the 'box of air' that contains them. However, in a headwind, the heavier aircraft travels down that same path more quickly and therefore hits the ground sooner (assuming that they both started at the same time, height and ground position). Therefore the light aircraft spends more time in the air.

Now if you consider the wind to be a 'moving box of air', when the heavy aircraft hit the ground, the light aircraft was still in the 'box of air' and therefore was still traveling downwind. The light aircraft spends more time in the air so the wind has more time to act on it.
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tszchun.anson replied the topic: The Effect of Weight on Descent

Thank you so much! I have got my understanding sorted out.

Merry Christmas!
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