Gliding Distance

Certainly there is some loss of efficiency when gliding at higher weights, as the best glide speed will come with increasing parasitic drag. Is it simply negligible?
 
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OverTQ said:
Certainly there is some loss of efficiency when gliding at higher weights, as the best glide speed will come with increasing parasitic drag. Is it simply negligible?
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Parasitic drag (aka "0 lift drag") is part of the L/D equation, so it's taken into account and is not negligible, e.g. see here.
Bear in mind that when you are gliding downwards, drag actually counters gravity and helps keep you up the air, so it's not all bad.
 
luvflyin said:
c) is the answer...The point is increase airspeed to increase energy so ya got some to deal with things.
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Glad I got it right. But my reasoning had nothing to do with "increasing energy", but with minimizing the time in the headwind.

There's no free lunch, so in a glider it sure seems like any increase in energy has to come from a decrease in altitude, and I still think that's a net negative in general.

But, again, I'm no glider pilot.
 
FastEddieB said:
Glad I got it right. But my reasoning had nothing to do with "increasing energy", but with minimizing the time in the headwind.

There's no free lunch, so in a glider it sure seems like any increase in energy has to come from a decrease in altitude, and I still think that's a net negative in general.

But, again, I'm no glider pilot.
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If you are slower than your max L/D, then increasing your airspeed (hence kinetic energy) will actually reduce your altitude loss (per mile).
This is why I said that question is bogus.
 
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RotorDude said:
If you are slower than your max L/D, then increasing your airspeed (hence kinetic energy) will actually reduce your altitude loss (per mile).
This is why I said that question is bogus.
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Good point.

Had to go back and review the question, and I made an unwarranted assumption - easy to do since the question does not even mention the aircraft's present speed.
 
FastEddieB said:
Glad I got it right. But my reasoning had nothing to do with "increasing energy", but with minimizing the time in the headwind.

There's no free lunch, so in a glider it sure seems like any increase in energy has to come from a decrease in altitude, and I still think that's a net negative in general.

But, again, I'm no glider pilot.
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Thats pretty much it. Doesn't necessarily have to be a loss of altitude, just how fast you're going down in the piece of air you're in. If it's going up pretty fast you can be going down in it, but gaining altitude.
 
luvflyin said:
Thats pretty much it. Doesn't necessarily have to be a loss of altitude, just how fast you're going down in the piece of air you're in. If it's going up pretty fast you can be going down in it, but gaining altitude.
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Which is the whole deal with wave soaring. You're flying forward fast enough not to move over the ground, but airspeed is relatively high, and you're going up like a freight elevator.

Old Sol provides glider pilots (and power pilots who need it and recognize it) with lots of "free lunch".

If you haven't thermaled a power plane, you're missing out. Very little glider time and you'll learn how to feel the "bump" of running into a nice solid updraft, and the automatic reaction to circle in it. Heh.

I've done it in the 182 to hurry up the climb out of a valley. Thump, turn, find the center, move the edge of the circle, try to spot the feature on the surface that's creating the heat source, just for reference, ahh nice, 2000+ fpm up with full power...

2nd floor, housewares, kitchen appliances, going UP! :)

Always fun to see where the beanstalk goes. Ha.

Hang out in a thermal for a minute or two, and bail at your proposed cruising altitude and no need to slog along at low airspeed for miles in the climb. Now you're already at cruise speed or can get there real quick.
 
This supposedly happened at HIO which has one of those foreign airline pilot schools. Out in the practice area instructor asks student where he would land if the engine quit. "I land at airport." Instructor thinks he misunderstood and says it again, what would you do if the engine quit. "I go back to airport and land." Instructor decides to communicate non verbally by pulling the throttle. Student, who had already recognized "the air" on the way out to the practice area glides back to the airport and lands.
 
luvflyin said:
I'm getting it that when weight changes, airspeed must change to maintain the best glide angle available . But I'm having trouble getting my head wrapped around that the glide angle will be shallower and I will travel farther, or the same distance over the ground when I'm heavier. Wouldn't that make the whole Newton and the Apple thing a lie?

I've just started on getting a Glider add on rating. Here's a question on the Pre-solo test I've been given to do.

A sailplane pilot should do which of the following when flying his final approach into a 20 mph headwind and seems to be under shooting.

a) Raise nose to slow just above stall speed and decrease the sink rate.

b) Use spoilers

c). Lower nose to increase penetration

d) Stretch the glide by flying at minimum sink speed

Everything I've read so far tells me that "minimum sink speed" is the same thing as "minimum rate of descent"' so I'm throwing out a) and d) because angle is what I need, not rate. I'm tempted to go with b), but that implies I have some spoiler out and my "use" would be to bring them back in. c) I don't get. Is there some thing called "penetration" that is the answer? All I can see is penetrating something short of the runway.
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luvflyin said:
Ok. I'm at the Gliderport. c) is the answer. The point is increase airspeed to increase energy so ya got some to deal with things. It isn't about trying to "stretch" the the glide by shallowing the glide angle which obviously won't work. It may get you down in ground effect which might get you to the runway. If there are "things" on short final you might have some energy to "jump" them.
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Ok as one of the resident glider nerds, here is the reasoning for answer C.

First the wrong answers.

a) Just above stall speed is even worse than min sink.

b) should be obvious. When low you do not need to increase your sink rate

d )Min sink is good for thermaling, but it had a lower glide ratio than max L/D. You will maximize time in the air, but not distance.

Correct Anser

C is correct because a headwind is reducing your ground speed. since glide ratio is a function of sink rate (time aloft) and ground speed, the optimum speed in sink and/or a headwind will be greater than your best L/D speed (no wind/no sink). As an added bonus you will have some extra energy when encountering the likely wind gradient in this scenario.

For some good L/D explanations this site is very good.

http://avia.tion.ca/documentation/polar/
 
denverpilot said:
Which is the whole deal with wave soaring. You're flying forward fast enough not to move over the ground, but airspeed is relatively high, and you're going up like a freight elevator.

Old Sol provides glider pilots (and power pilots who need it and recognize it) with lots of "free lunch".

If you haven't thermaled a power plane, you're missing out. Very little glider time and you'll learn how to feel the "bump" of running into a nice solid updraft, and the automatic reaction to circle in it. Heh.

I've done it in the 182 to hurry up the climb out of a valley. Thump, turn, find the center, move the edge of the circle, try to spot the feature on the surface that's creating the heat source, just for reference, ahh nice, 2000+ fpm up with full power...

2nd floor, housewares, kitchen appliances, going UP! :)

Always fun to see where the beanstalk goes. Ha.

Hang out in a thermal for a minute or two, and bail at your proposed cruising altitude and no need to slog along at low airspeed for miles in the climb. Now you're already at cruise speed or can get there real quick.
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Actually Wave Soaring Uses the standing lee wave in the lee of the mountain. think of it like the waves in a stream that form past the rock. while there is a lot of wind involved, you climd because the air mass is going up. The neat thing about wave is that the rising air in the wave is pretty much laminar, so it is very smooth (the rotor not so much)

OSTIV_MWP_Wave.jpg


What you describes is akin to dynamic soaring where you can extract energy out of the wind gradient. RC Modelers have gotten to about 400mph using dynamic soaring techniques, but no one has really done this in a manned glider yet.
 
What you describes is akin to dynamic soaring ... no one has really done this in a manned glider yet.[/QUOTE]

See this.
 
Hank S said:
They both . . . float?
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Ah, but what *else* floats on water?

<really enjoying the technical knowledge & debate in this thread but couldn't resist two holy grail references in the same thread.>
 
vontresc said:
Ok as one of the resident glider nerds, here is the reasoning for answer C.

First the wrong answers.

a) Just above stall speed is even worse than min sink.

b) should be obvious. When low you do not need to increase your sink rate

d )Min sink is good for thermaling, but it had a lower glide ratio than max L/D. You will maximize time in the air, but not distance.

Correct Anser

C is correct because a headwind is reducing your ground speed. since glide ratio is a function of sink rate (time aloft) and ground speed, the optimum speed in sink and/or a headwind will be greater than your best L/D speed (no wind/no sink). As an added bonus you will have some extra energy when encountering the likely wind gradient in this scenario.

For some good L/D explanations this site is very good.

http://avia.tion.ca/documentation/polar/
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I am sure you have vastly more experience than me in gliders, but I disagree with C.
The reason is that the question doesn't tell us what speed the glider is at to start with.
So if, for example, it is already at max L/D + 20 kt, it is extremely unlikely that going faster would gain anything, and would very likely only shorten the glide distance. In that case, the correct answer would be "find another landing spot within range and land there." So as I said, that question is bogus and has no correct answer, IMO.
 
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True, best answer would be to not be in that situation in the first place. I guess I should have said "best answer" and also stated that the assumption would be that the glider is at the book landing speed.
 
vontresc said:
True, best answer would be to not be in that situation in the first place. I guess I should have said "best answer" and also stated that the assumption would be that the glider is at the book landing speed.
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"Book landing speed" (in my Schweizer books) is "Max L/D + headwind component", so if we make that assumption, lowering the nose won't help. Many other books (FAA too, IIRC) recommend half the headwind, in which case you might get a tiny bit of help in some cases.
I accept your first "best answer", however. :)
 
Well if you are low and slow in a Schweizer you are pretty much frucked anyway...
 
You should feel right at home in something with the glide ratio of an auto rotating helicopter ;-)

Btw where are you flying?
 
vontresc said:
You should feel right at home in something with the glide ratio of an auto rotating helicopter ;-)

Btw where are you flying?
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You are right about that. :)
In fact, I only recently realized that auto-ing a helicopter is the most fun I have in it, and in a glider you get to do it much longer. :)
Will PM you the rest.
 
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