Would You Feel Any Wind If...

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HerrGruyere

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Hey All,

Wasn't sure of a good thread title. Anyway, my coworkers just proposed a hypothetical situation based on a video they saw today. A man is standing on a runway and a Harrier flies over at a high rate of speed maybe around ten feet above the man's head. The cameraman shakes, but the man remains stationary as if nothing happened.

Would there be any sort of wake or "downburst" from the plane passing overhead? I imagine there might be a small wind behind the plane, kind of like when a large truck passes. However, I don't think you would feel any jet blast nor would there be a wind being blown downward from the lift produced by the wing - mainly because that's a high pressure area and the lift is going upward.

Any thoughts?
 
Depends how low. There is lift and downwash being created. Also thrust from the engine going aft. If it was low enough, say 1 foot above his head the jet exhaust would blow him over.

Not sure why you made it a Harrier. My thought is because of the downward vectored thrust. If so then that wouldn't be a factor at all with a high speed as the vectored thrust is only used at low speed.

Remember, the most wake comes off of planes when they are heavy, dirty and slow. I harrier at high speed is none of that.
 
If a Harrier did a hover pass over someone at ten feet, they would probably be barbecued.
 
If the pass was within ground effect, I would expect a considerable amount of turbulence to be generated.
 
Air doesn't keep moving downward. It only moves down a little bit, then curls around and make a kind of vortex. The actual downward distance isn't that far.

For example, google "airplane flying vortex" and look at images.
 
I don't know about a Harrier, but my kids stood at the end of a relatively short runway when we moved a 747. I asked them later what they thought, and they commented about all the "wind" and about how "cold" it got as we went by.

When we're doing drops with other tankers on active fires, the effects of vortices are very noticeable from the preceding aircraft, as seen by the smoke.
 
Just like when a car goes by the air is disturbed and wind is created. A harrier flying over head is pushing air away from it and a wake trailing behind it. Youtube has a vid of F-16s departing at low altitude in Afghanistan and they are leaving a dust trail behind them. At 10 feet, you're gonna feel something.
 
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I believe that if a Harrier jet unexpectedly passed at high speed ten feet over my head, what I think I would feel is the mess being made in my pants.

-John
 
Actually, now that I think about it, many years ago I was driving up I-15 to Las Vegas on business. I was driving a little 240 Z. This was about three in the morning up in the high desert. I guess I was doing seventy or eighty, I had the road pretty much to myself. This was about 1974 or 5. I was in a long straight stretch past Barstow.

Some clown driving an F-14 or some such thing passed very close above my head at full burner. I'm guessing on that, but there was a lot of fire coming out of his twin exhaust.

I was not expecting it. I felt my car being literally lifted up off the road for a second or two. It was loud and powerful. It made me very wide awake, but I did not lose it in my pants. I was a lot younger at the time, and although I was a T'd off about it, I chalked it off to someone as young as myself having a little fun.

I would guess he was below fifty feet above my car when he passed over me.

So yes, you would most assuredly feel it.

-John
 
Yep, jack Thelander was the lead Aerodynamics engineer for Douglas and one of my instructors. When he taught aerodynamics it was fun with real experiments. The best one was calculating the weight of a plane using a graphing barometer and flying over it. We took the sampling tube size and multiplied it to the area of the wing and multiplied that with the barometric spike that occurred when we flew over it, and what do you know, it came out perfect to the measured weight. His comment was, "This is proof that Bernouli's law is merely an observation of Newtons laws." I thought it was pretty cool. He also had great stories about flying Corsairs off carriers in WWII and taught me how to make every landing every time no matter your approach. He was a great instructor.
 
bflynn said:
Air doesn't keep moving downward. It only moves down a little bit, then curls around and make a kind of vortex. The actual downward distance isn't that far.

For example, google "airplane flying vortex" and look at images.
Click to expand...

It travels down further than you might think.


http://www.skybrary.aero/bookshelf/books/660.pdf
4.jpg

Wake vortices spread laterally away from
the aircraft and descend approximately 500
to 900 feet at distances of up to five miles
behind it. These vortices tend to descend at
approximately 300 to 500 feet per minute
during the first 30 seconds.
 
Read "Stick and Rudder by Wolfgang Langewiesche. It is a very old book but it is still one of the best. Wings create lift by moving air downward.

-Skip
 
I understand the air moving downward to be a result of the lift. The air on top gets displaced up and then snaps back down (from the low pressuer you could call it 'sucked' back down) aft of the wing at a greater velocity resulting in a down wash.
 
Captain said:
I understand the air moving downward to be a result of the lift. The air on top gets displaced up and then snaps back down (from the low pressuer you could call it 'sucked' back down) aft of the wing at a greater velocity resulting in a down wash.
Click to expand...

Opposite, the lift is the equal and opposite reaction, the air being pushed down is the action.
 
Thanks for the responses, everyone. I said Harrier because that was the video in question. It was some goof standing on the runway when a Harrier whizzes by a mere 10 feet over his head at some ridiculously high rate of speed - I'm guessing 350+. The goof just stands there.

Someone mentioned dirty and slow produces the most wake. I forgot to factor that in. Anyway, I think he would feel a little bit, but nothing too serious. Perhaps he would feel more if he hung around and waited for the sinking vortex or didn't have the plane pass directly above him.

Edit: Here's the video in question: http://www.youtube.com/watch?v=Q9BCoV5uYTI
 
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OK, what would happen if you were on a treadmill?
 
Don't forget heavy.

The harrier is clean, fast and light. If the plane is high enough to keep out of the jet blast then little wake would be felt. It would be loud as crap though. Harriers are machines owned by the government designed to turn jet fuel into noise and they are very good at it!
 
HerrGruyere said:
I like things that turn jet fuel into noise..
Click to expand...

Ugg, not me, what a shrieking waste of energy. Have you ever seen the Harrier demo at OSH? Bloody painful that is and far too long hovering there for minutes just doing yaw turns and slight side shift while belching that stench and emitting such a noise that the combination makes me physically ill. :vomit: The Harrier demo should be a dive in with a quick stop and pivot course reversal, reverse back and GTF outta there. That would be quite sufficient to demonstrate the capability that is needed from it, dash in, provide CAS on the spot and get out after strafing the enemy position. Done, no need to hurt people and make small children cry from the painful noise.

The noise I would prefer hearing is a low pass from a B-36 with just the 6 4360s turning:yesnod:
 
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Hahaha I've seen a Harrier demo at Cherry Point. I was moderately entertained, although just hovering there got kind of lame. I recently saw an F-22 demonstration. It was awesome.

I really like high speed passes on full afterburner.
 
Captain said:
Depends how low. There is lift and downwash being created. Also thrust from the engine going aft. If it was low enough, say 1 foot above his head the jet exhaust would blow him over.

Not sure why you made it a Harrier. My thought is because of the downward vectored thrust. If so then that wouldn't be a factor at all with a high speed as the vectored thrust is only used at low speed.

Remember, the most wake comes off of planes when they are heavy, dirty and slow. I harrier at high speed is none of that.
Click to expand...

He made it a harrier because this is an actual video...
 
Not to get nitpicky on terminology, but "rate of speed" refers to acceleration, not velocity. If he's going fast, he's going at a high speed. If he's accelerating quickly, he's going at a high rate of speed.
 
Sac Arrow said:
Not to get nitpicky on terminology, but "rate of speed" refers to acceleration, not velocity. If he's going fast, he's going at a high speed. If he's accelerating quickly, he's going at a high rate of speed.
Click to expand...

Actually if you really want to get nitpicky.... acceleration is rate of change of speed.
 
Not to get nitpicky on terminology, but "rate of speed" refers to acceleration, not velocity. If he's going fast, he's going at a high speed. If he's accelerating quickly, he's going at a high rate of speed.
Click to expand...

"rate of speed" refers to velocity. Acceleration is a change in velocity or direction. Rate of speed could be expressed in meters per second, miles per hour, etc. A high rate of speed, or high speed, doesn't imply acceleration unless a change is taking place.
 
airguy said:
Actually if you really want to get nitpicky.... acceleration is rate of change of speed.
Click to expand...

Stated another way...

DouglasBader said:
"rate of speed" refers to velocity. Acceleration is a change in velocity or direction. Rate of speed could be expressed in meters per second, miles per hour, etc. A high rate of speed, or high speed, doesn't imply acceleration unless a change is taking place.
Click to expand...

I would agree that "speed rate", meaning a rate, speed specifically, would mean velocity in a redundant manner. A couple of my profs always used to beat on students mercilessly for using the term "rate of speed" when discussing velocity.
 
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Today's version of that commercial would be, "Remember when airlines had flight attendants below the age of 50? Remember?" hahaha.
 
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