Wake turbulence - with automobiles

[swj737 0]

Hi All, I searched the forum and no one has asked this (that I could find), but has there been documented incidents involving the wake turbulence of an aircraft taking off and it's effect on automobile traffic on roads/highways near the end of the runway. Case in point, I was recently traveling down I-10 in Phoenix on my way to Sky Harbor when a US Airways 757 passed over the highway just after takeoff (at a right angle), ahead of me about 1/4 to 1/3 of mile (estimate), when I reached the point in the highway the aircraft had crossed over, it felt like I was hit by a very strong gust of wind in the same direction as the departing aircraft. I was traveling south, aircraft west. At the moment of the gust the aircraft was maybe 3/4 of mile (estimate) west of me. Could it have been wake turbulence, or was it just a gust of wind? If it was wake turbulence has an automobile accident ever been attributed to it? It was a strong sideways push and if caused by the aircraft I was glad it wasn't a 747. Just curiousThanksSteve

[John_Cillis 2,406]

I live in Phoenix and drive that stretch of I-10 often. It's so hard to tell this time of year what causes an odd gust of wind. I usually hit several dust devils during a typical half hour commute--and quite often there's no visible signs if I hit one of these when it is over the interstate. Some of them are very strong, and I have to apply a lot of rudder...uhhh...I mean steering wheel to compensate.Still, I know that wake turbulence of even a B200 can upset the Allegro I train in, and I was told wake turbulence of a C-5 could upset a 737-200. I think it plausible that if you were in the right spot at the right time, wake turbulence could hit you. On the other hand, that stretch of I-10 is traveled fairly often so if any wake turbulence does hit the drivers there, they probably wouldn't know it unless they were familiar with the concept.-John

[Roger Mazengarb 0]

G'day Steve,>very strong gust of wind in the same direction as the departing >aircraft.I've always equated "wake turbulence" as a generic name for trailing wing tip votices. These vortices are at right angles to the direction of flight. The fact that you experienced a gust in the direction of flight would tend to make me guess that your gust was unrelated to aircraft.Cheers,Roger

[Guest]

The Mythbusters a few years ago investigated that urban legend and concluded that while a car can get damaged by jetblast (mainly because of the heat which at close range can over time get things to melt) it won't get blown off the road.They placed a fullsize American car directly behind a jetliner at close range and turned the engines to full power.

[Roger Mazengarb 0]

Didn't see Mythbusters but this is no myth. When I was an apprentice we were ground engine running a B707 and a small delivery ute (Japanese NOT American) decided to skirt around the back of the aircraft not realising the power was at take off level. The vehicle was rolled.What most people don't understand is that the modern high bypass engines accellerate a LARGE MASS of air relatively slowly. Apply Newtons 2 & 3 laws and you can see how thrust is generated.Attached is a schematic showing the 30 kt (50 ft/sec) boundary behind a 747 at take-off power. Obviously the closer you go towards the engines the higher the velocity. I have got a better chart showing the actual velocity and temperature verses distance but just can't find it at the moment. cheers,Roger

[Guest jboweruk]

There's been several vids doing the rounds debunking any theory that a car would NOT be affected by jets. One shows an Air France 747 spooling up and people up against a wall behind it watching all getting hurled into the sea by the blast. Another shows a pickup truck being turned over by a 747, and a BBC program 'TOP GEAR' actually ran several cars behind a 747 on thrust, all of which were destroyed not by heat but wind.

[Murmur 3,941]

>They placed a fullsize American car directly behind a jetliner>at close range and turned the engines to full power.So I guess this is special effects?http://www.youtube.com/watch?v=zSxMOzBsOeQ&search=747%20carMarco

[Guest CRJ700FO]

>The Mythbusters a few years ago investigated that urban>legend and concluded that while a car can get damaged by>jetblast (mainly because of the heat which at close range can>over time get things to melt) it won't get blown off the>road.>>They placed a fullsize American car directly behind a jetliner>at close range and turned the engines to full power.no they didn't. their insurance company didn't allow them to use a full size jet liner so they simply placed a hollywood wind machine (a jet engine) in front of a car.anyways, they ended the episode showing how true it was and showed some south american airport where it happened and a car was blown 40 or so feet.besides this is jetblast and not wake turbulence, two different problems.

[John_Cillis 2,406]

The post isn't discussing jetblast, however--it's discussing wake turbulence. Wake turbulence can extend for miles BEHIND (not at a right angle as one post suggests) a heavy jet and can upset aircraft even the size of a 737. The stretch of I-10 mentioned in the opening post is very close to the threshold of the new runway at Sky Harbor. It's possible that the churning air left in the wake of one of these jets could make for odd gusty conditions on the ground. I've never experienced it, but it is possible--and quite a bit different than what Mythbusters was trying to discuss.-John

[KevinAu 441]

>The post isn't discussing jetblast, however--it's discussing>wake turbulence. Wake turbulence can extend for miles BEHIND>(not at a right angle as one post suggests) a heavy jet and>can upset aircraft even the size of a 737. The stretch of>I-10 mentioned in the opening post is very close to the>threshold of the new runway at Sky Harbor. It's possible that>the churning air left in the wake of one of these jets could>make for odd gusty conditions on the ground. I've never>experienced it, but it is possible--and quite a bit different>than what Mythbusters was trying to discuss.>>-JohnThough the area of vortices do trail behind the aircraft, the actual direction of the wind felt when within the vortex *is* perpendicular to the direction of the generating flight. If you felt a strong gust of wind in your car as you drove behind a plane starting its takeoff roll, what you felt is jetblast, the wind generated by the jet engine. Wake turbulence is an entirely different thing which is caused by the movement of the aircraft through the air as its wings create lift. If there is no lift, there is no wake turbulence. In the example cited at the top post, the wake turbulence would not be generated until after the 757 has gathered enough speed on the runway and the wings began developing lift. So the poster would have to have been driving across the runway downfield after the passage of the 757 to feel any wake turbulence. What he felt in his car coming from the 757 was jet blast.

[Roger Mazengarb 0]

G'day John,>, however--it's discussing>wake turbulence. Wake turbulence can extend for miles BEHIND>(not at a right angle as one post suggests) My post mate but you've misunderstood the point I was making. Read it again - slowly :-) I wasn't saying the votex extended at right angles but the gust vector within the vortex is at right angles to the direction of flight. Thus the gust the original poster felt trying to blow him off the road, in the direction of flight, was probably not a result of wake turbulence. To expand on what I was saying, the wingtip vortices form the major component of what is commonly called "wake turbulence". It is of concern at low speed/high angle of attack where it is a maximum and is thus a major problem around airports. The LH wing vortex spins clockwise and the RH wing vortex spins anti-clockwise and stream backwards and drift down slightly off the wingtips. Yes, if there is a crosswind then the vortices will drift with the crosswind BUT the turbulence within the vortex is still essentially at right angle to the direction of flght. Just my thoughts on whether the original poster felt wake turbulence or not.Cheers,Roger

[John_Cillis 2,406]

Sorry Roger--sounds like I misunderstood what you were trying to say. What I am trying to say is I-10 passes at a right angle to the western thresholds of all three runways at Sky Harbor, and fairly close to the south runway threshold. In theory, a car passing the threshold at just the right time could be hit by wake turbulence. The driver isn't going to know what direction the air is spinning and may not even be able to perceive what direction the gust is coming from, but they could be in choppy air. And at the distance the threshold is from I-10, the gust might be perceived as coming from any direction as the churning air interacts with the ground and nearby structures.-John

[John_Cillis 2,406]

Thanks Kevin--please see my reply to Roger. I believe all three runways have jetblast barriers given their proximity to I-10. I driven that stretch with aircraft in position without even a whisper of air. My theory is that a landing aircraft may have caused what he felt. Without restating my reply in great detail, the churning air behind the aircraft may make it quite impossible to really determine what direction the air is swirling. My point is that wake turbulence trails some distance behind an aircraft, and I-10 passes by all three runways on the west. Given the time of year, and that we're averaging about 105 or so, what you end up with is a disturbed mass of air behind a heavy jet that extends some distance. Whether the air is going up or down, right or left, or into a parallel dimension in that mass of air, it's hard for anyone caught in it to know where the hits are coming from.-John

[swj737 0]

Thanks everyone for all the interest and comments! If this will make it any clearer. I was traveling south, and the aircraft was departing to the west from a northern runway and it "felt" like a gust hit the left side of the truck (the gust traveling in the same direction as the departing aircraft), so I do not think it would have been jet blast, as I would have felt that hit the right side of the truck. In relation to the aircraft I was behind and below by about 3/4 mile to a mile when the gust hit. I do not live in the Phoenix area but have visited a few times so many of you posters may be more familiar with the local meteorological conditions/phenomenon, however it was a clear day with temps in the 103-108 range.Steve

[John_Cillis 2,406]

"however it was a clear day with temps in the 103-108 range."Then I suppose it would be hard to pin it on wake turbulence, but still possible. When we're up in that temp range, little dust devils are forming on a fairly regular basis--I usually hit three or four during the trip home from the office, although only once "head on", so to speak. Often times you don't see a thing--you'd suppose you would see a swirling cloud of dust, but that's not always the case.-John