Any which way the wind blows (physics brainteaser)

ThinAirDesigns

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A couple physics brainteasers have been being tossed around over on the "classic physics" thread. One involves a 'light tight' caboose and the ability/inability to determine direction of travel. Here's a related one that may involve a little specific knowledge related to soaring flight but may be fun for others anyway.

Can a pilot of an uninstrumented and unpowered soaring aircraft make any useful determination regarding which direction the wind is blowing at flight level *without* using clues seen outside the cockpit?

I will define the soaring conditions as thermal rather than wave or ridge lift.

The following information isn't important to the answer, but I will specify it just so everyone can use the same numbers.

A: use 250fpm sink rate for soaring craft
B: use 500fpm for strength of thermals
C: wind is from north to south @ 6mph

Again, not a classic 'solved by the equations' problem. Take it or leave it as you wish.

Fire away.

JB
 
I think this is a brainteaser only for those who know the meaning and understand:
1) soaring (is there a difference between soaring and dynamic soaring?)
2) thermal, wave and ridge lift conditions

For others (like me) its just a couple of strange terms. Because I don't understand I must conclude it cannot be "common knowledge";-)

I've seen this soaring term in the other threads and I've seen the speed record video. I understand it utilizes the speed difference of two airmasses and understand it works, but I can't really work it out in my head precicely how it works. I tried to google the thing quickly, but didn't come up with anything that looked "easy to digest".

So, I would appreciate a link or a short explanation. Otherwise I haven't a clue, but I would definately guess no. (There a slight chance of yes in my mind by feeling the g-forces, but without instruments...)
 
huh34 said:
I think this is a brainteaser only for those who know the meaning and understand:
1) soaring (is there a difference between soaring and dynamic soaring?)
2) thermal, wave and ridge lift conditions

For others (like me) its just a couple of strange terms. Because I don't understand I must conclude it cannot be "common knowledge";-)
Click to expand...

The term "soaring flight" or "soaring aircraft" is rather generic I admit.


From Wikipedia: http://en.wikipedia.org/wiki/Soaring

Soaring is a mode of flight in which height is gained by using air that is moving upwards. It arises in the flight of both aircraft and birds.
Click to expand...

"Dynamic soaring" (the speed record video to which you refer) does not require air that is moving upwards, but rather a rather sharp shear area between to masses moving relative to each other.

"Ridge lift" soaring involves the aircraft 'surfing' the standing wave of air created when wind encounters a ridge.

Rather than go into any more detail with the different terms I will again refer you to wikipedia: http://en.wikipedia.org/wiki/Lift_(soaring)

JB
 
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Are the directional winds buffeting the aircraft constant or variable? If variable, wouldn't that cause you to sway from a center position to either left or right, or forward or backward. The opposite of what you sway towards would be the direction of the outside wind. If the directional winds were constant? It would take a clever person with perhaps some sort of gyroscope
 
Tumbleweed said:
Are the directional winds buffeting the aircraft constant or variable? If variable, wouldn't that cause you to sway from a center position to either left or right, or forward or backward. The opposite of what you sway towards would be the direction of the outside wind. If the directional winds were constant? It would take a clever person with perhaps some sort of gyroscope
Click to expand...

For the purpose of this problem, the directional winds are constant.

JB
 
ThinAirDesigns said:
A couple physics brainteasers have been being tossed around over on the "classic physics" thread. One involves a 'light tight' caboose and the ability/inability to determine direction of travel. Here's a related one that may involve a little specific knowledge related to soaring flight but may be fun for others anyway.

Can a pilot of an uninstrumented and unpowered soaring aircraft make any useful determination regarding which direction the wind is blowing at flight level *without* using clues seen outside the cockpit?

I will define the soaring conditions as thermal rather than wave or ridge lift.

The following information isn't important to the answer, but I will specify it just so everyone can use the same numbers.

A: use 250fpm sink rate for soaring craft
B: use 500fpm for strength of thermals
C: wind is from north to south @ 6mph

Again, not a classic 'solved by the equations' problem. Take it or leave it as you wish.

Fire away.

JB
Click to expand...
If by "Unistrumented" you mean no Vario, altimeter, and airspeed gages, and no peeking at the ground and horizon, I don't think it's possible.
Given 2 of the 3 instruments and a means to maintain wings-level, yes.
 
Okay then you hang one before you take off and mark where the point hits. amd you mark where north is. Then you soar. Since the wind is "pushing" on the aircraft, and you are NOT going straight up or down ( in relation to your starting point) because of that north wind, the plumb bob is no longer going to be on the same point as when you were motionless. Then it's merely a matter of calibration, sun dial style
Think about it: If you hung one in a room and then pushed on that room, the plumb bob sways away from vertical
 
If you are NOT allowed a starting point reference, then it becomes a relativity thingie, where the "set" of conditions on a moving train are seperate - almost - from the "set" of things off of that moving train. I say almost, because the people in the moving train "set" will becpome quite aware of their relative velocity if they hit a brick wall. Much the same since we don't "sense" traveling 8 miles per second in space - until a meteor comes along. Its kind of like two intersecting circle sets. They share something in common yet they don't as well.
 
Tumbleweed said:
Okay then you hang one before you take off and mark where the point hits. amd you mark where north is. Then you soar.
Click to expand...

This fails for all sorts of reasons and I'll pick only one for now:

The spot you marked will only remain under that plumb bob as long as the pitch angle (think nose to tail) remains the same. Once the aircraft leaves the ground, changes in pitch from speed and lift changes will alter the planes orientation relative to vertical ... meaning that the bob can hang in many different spots, even in still air.

An example of this would be: if I'm flying in a straight line in perfectly still air @ 60knots and I mark the plumb bob spot and then I speed up to 70knots, the bob will now hang *forward* of it's previously marked location. This happens simply because to speed up I had to reduce the angle of attack of the wing and I did that by lowering the nose. This alters the aircraft orientation relative to vertical and is reflected in the new bob position.

The position you marked on the ground will reflect all sorts of things unrelated to it's positions in flight including something as simple as how much air is in the aircraft's tire(s).

JB
 
Since the thermals are generated from a fixed position on the ground, they will appear to the pilot that the are moving north( in relation to the air mass ). The pilot has to compensate for this if he/she wants to stay in the thermal

Rehn
(ex hang glider pilot )
ps: the server is veeerrryy slow today....
 
No.

I could give an explanation but the server is so slow that keying it all in would cause the server to crash. ;)
 
rehn said:
Since the thermals are generated from a fixed position on the ground, they will appear to the pilot that the are moving north( in relation to the air mass ).
Click to expand...

Like a balloon, thermals are considered to drift *with* the airmass -- and even without addressing the finer points of that argument, certainly to an aircraft circling in a thermal, the aircraft and the thermal are moving laterally at the same speed.

Why to the pilot (or anyone else for that matter), would they appear to be "moving north (in relation to the air mass)."?

JB
 
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