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-   -   Did the Captain do a "fly by"? (https://www.flyertalk.com/forum/travelbuzz/925225-did-captain-do-fly.html)

Zarf4 Feb 25, 2009 10:08 am


Originally Posted by Djlawman (Post 11319834)
"Wind in their face" is more likely for the purpose of giving additional lift to the wing surfaces than to slow the plane down.

Actually "Wind in their face" to slow down is probably more accurate, but it's in reference to groundspeed, not airspeed. At any indicated airspeed the plane doesn't care if it's a headwind or tailwind, the wings are generating the same lift -- but from the runway's perspective (which hopefully isn't traveling at the same speed at the wind :)) wind in the face (or "low groundspeed") is good.

Bobster Feb 25, 2009 10:46 am

A fly-by is a stunt performed at air shows with no passengers on the plane. The pilot keeps the wheels up, maintains a safe altitude and zooms over the runway at 300 miles per hour or so.

Clearly that did not happen. What happened was a rejected landing.

ktakahashi Feb 25, 2009 11:24 am


Originally Posted by Zarf4 (Post 11319943)
Actually "Wind in their face" to slow down is probably more accurate, but it's in reference to groundspeed, not airspeed.

Planes take off and land facing the wind for lift purposes (enter Mr. Bernoulli and his principle). Although not 100% mathematically correct, the following statements are directionally/conceptually correct.

If Plane A's take off speed is 150 mph, all 3 below scenarios will achieve proper lift to support take off:
- Plane A taking off at 150 mph - wind calm
- Plane A taking off at 125 mph - 25 mph headwind
- Plane A talking off at 175 mph - 25 mph tailwind

If Plane B's landing speed is 150 mph, all 3 below scenarios will achieve proper lift to support landing:
- Plane B landing at 150 mph
- Plane B landing at 125 mph - 25 mph headwind
- Plane B landing at 175 mph - 25 mph tailwind

Of course there are tons of other variables at play here (like altitude, air pressure, weight, etc.) but I think this conveys the right picture. By taking off and landing into the wind, the plane requires less runway in order take off and land.

Zarf4 Feb 25, 2009 12:34 pm


Originally Posted by ktakahashi (Post 11320418)
Planes take off and land facing the wind for lift purposes (enter Mr. Bernoulli and his principle). Although not 100% mathematically correct, the following statement are directionally/conceptually correct.

I agree that t/o & landing into the wind minimizes runway distance but this has NOTHING to do with lift. Lift (and its complementary vector, gravity) by themselves make the plane go up or down, period.

All aircraft have a recommended airspeed for takeoff rotation and landing touchdown. Airspeed and groundspeed are not the same thing. If the recommended takeoff airspeed for your airplane is 100 kts indicated and you have a 50 kt headwind, you only have to accelerate to 50 kts on the ground and you're ready to rotate. This burns a lot less real estate than if you had a 50 kt tailwind and had to accelerate to 150 kts.

Other primary factors of t/o distance are engine performance and density altitude. Landing distances also have runway friction coefficients (wet/dry) to deal with.

Lastly, Bernoulli isn't the only thing that make planes fly, Newton's 3rd is often overlooked -- if the only factor was the vacuum created by the extra distance of the elongated curved top surface of the wing those little balsa gliders we bought as kids with the flat wings should be as aerodynamic as rocks.

ktakahashi Feb 25, 2009 12:47 pm

Zar4, you are indeed correct. My statement should have read:

... Planes take off and land facing the wind in order to optimize lift ...

Bobster Feb 25, 2009 1:08 pm

No. It is done to minimize takeoff and landing ground speeds.

ktakahashi Feb 25, 2009 1:20 pm

Runway length is far more of a limited commodity than speed.

LarryJ Feb 25, 2009 6:19 pm

Who was it who first said that a little information is dangerous? This thread is a perfect example.

The airplane's airspeed for takeoff or landing is the same regardless of which way the wind is blowing. You do not get more lift with a headwind or less with a tailwind. Aircraft performance is related only to airspeed. Groundspeed is irrelevent to how the wings fly. To the wing, the air is always calm. The airmass is the point of reference, not the ground.

If you have a tailwind the ground speed will be higher than airspeed while with a headwind it will be lower. The groundspeed translates directly into runway length required so less runway is required when you have a headwind than when you have a tailwind because of the reduced groundspeed.


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