Two identical Cessna 172's at exactly the same altitude both experience engine failures at the same time. The pilots then maintain best glide speed, per the aircraft POH. One of the planes is heavier than the other one, so it (the heavier one) will glide farther. True or False?
A little aviation trivia for ya...
- Thread starter AlexSP
- Start date
EatSleepFly
Well-Known Member
Best glide speed varies by weight, whether the POH lists it or not.
If both aircraft are maintaining best glide according to their respective weights, they should go the same distance, right?
If both aircraft are maintaining best glide according to their respective weights, they should go the same distance, right?
TheShortOne
Well-Known Member
not knowing anything about gliding, but basing this off of my rusty physics I would guess that the heavier one would go farther because it has more momentum (P=mv)
TheShortOne
Well-Known Member
Re: Why
Hey I was right! and if that's true then I would still bet it is cause of the momentum thing
Hey I was right! and if that's true then I would still bet it is cause of the momentum thing
Cherokee_Cruiser
Bronteroc
Simple physics...
the weight will not affect how far it'll glide, though the heavier one will just get there faster than the lighter one.
Next!
the weight will not affect how far it'll glide, though the heavier one will just get there faster than the lighter one.
Next!
BobDDuck
Island Bus Driver
Re: Why
Here's how I see it. The heavier aircraft will accelerate at the same speed as the lighter aircraft. However, because it weighs morethe AOA needed to keep the ideal glide speed will be different (more down pitch I think). Because of the increased downward pitch it will decend faster... but now I am killing my own argument, because if it is decending faster but traveling at the same speed it will go LESS distance then the lighter aircraft, which is not what I said to begin with. So that said, I really don't know, although I still think I have heard my first answer somewhere else before.
Ethan
Here's how I see it. The heavier aircraft will accelerate at the same speed as the lighter aircraft. However, because it weighs morethe AOA needed to keep the ideal glide speed will be different (more down pitch I think). Because of the increased downward pitch it will decend faster... but now I am killing my own argument, because if it is decending faster but traveling at the same speed it will go LESS distance then the lighter aircraft, which is not what I said to begin with. So that said, I really don't know, although I still think I have heard my first answer somewhere else before.
Ethan
EatSleepFly
Well-Known Member
[ QUOTE ]
Simple physics...
the weight will not affect how far it'll glide, though the heavier one will just get there faster than the lighter one.
Next!
[/ QUOTE ]
Really? Prove it.
Best glide is the minimum ratio of rate of sink, to forward speed. Glide ratio doesn't change based on weight. BUT...
A heavier aircraft has a higher wingloading, which means it has a higher rate of sink at the same airspeed as the lighter one. Therefore, best glide for a heavier airplane is higher than that of a lighter one. If each aircraft is flying a best glide speed according to their respective weight, they'll glide the same distance.
This is all in theory. In reality, the difference is negligable- thats why most POH's only have one number for best glide.
Simple physics...
the weight will not affect how far it'll glide, though the heavier one will just get there faster than the lighter one.
Next!
[/ QUOTE ]
Really? Prove it.
Best glide is the minimum ratio of rate of sink, to forward speed. Glide ratio doesn't change based on weight. BUT...
A heavier aircraft has a higher wingloading, which means it has a higher rate of sink at the same airspeed as the lighter one. Therefore, best glide for a heavier airplane is higher than that of a lighter one. If each aircraft is flying a best glide speed according to their respective weight, they'll glide the same distance.
This is all in theory. In reality, the difference is negligable- thats why most POH's only have one number for best glide.
Acadia
Well-Known Member
The heavier aircraft can go further.
The way I understand it is that a published best glide speed (for most GA aircraft) is based on standard conditions at max gross weight. So if a Cessna 172 lists 65 KIAS as best glide that is L/D max at max gross weight. The further you are from max gross weight the further you are from L/D max assuming you are still flying 65KIAS. Unless the heavier aircraft is over weight then it must be closer to max gross weight than the lighter one so its getting the best lift to drag ratio (L/D max) and if all else is equal it can glide further.
That seems to jibe with the more technical description of power off gliding in both "The Illustrated Guide to Aerodynamics" by HC Smith & "Aerodynamics for Naval Aviators", USN.
The way I understand it is that a published best glide speed (for most GA aircraft) is based on standard conditions at max gross weight. So if a Cessna 172 lists 65 KIAS as best glide that is L/D max at max gross weight. The further you are from max gross weight the further you are from L/D max assuming you are still flying 65KIAS. Unless the heavier aircraft is over weight then it must be closer to max gross weight than the lighter one so its getting the best lift to drag ratio (L/D max) and if all else is equal it can glide further.
That seems to jibe with the more technical description of power off gliding in both "The Illustrated Guide to Aerodynamics" by HC Smith & "Aerodynamics for Naval Aviators", USN.