Plane Stopped in Midair

jharper aaatttt cisco dddooottt com wrote:

One thing to add to what the other posters have said...
in a climbing turn a plane can easily appear to be
stationary for a short while. Not sure about the optics
of this but from my office area I can see planes taking
off from San Jose and starting the right turn for the
standard departure course, and this illusion is quite
common. Combine that with a strong headwind and the effect
of the size of the plane, and you could easily believe it
had stopped.

John

yes, but as best as I could tell, the plane wasn't turning. It appeared
to be taking a straight path up, or trying to anyway.

Debbie

jharper aaatttt cisco dddooottt com wrote:

One other thing... it's essentially impossible to
stop a fixed-wing airplane in midair.

yep, that's why I was expected the plane to fall from the sky.

(You can have
zero ground speed due to headwinds, but not zero
airspeed). If you try, the nose drops and it glides
towards the ground. If you try to stop that, it will
eventually perform an aerodynamic stall, which WILL
make the nose drop, but it still won't come to a halt.
About the only way to reach zero airspeed is to
pull the plane into a near-vertical climb. And even
then it reacts by dropping the nose and building
up some speed again (or if you are truly vertical,
it can fall tail-first and then it will at some point
snap into a more normal posture and then start
to fly nose-first again). It's fun to do though, in
the right kind of airplane - a small aerobatic one -
and with enough altitude.

John

if it had been an airshow kind of situation I wouldn't have given it a
thought but this was a commercial jet and it was over a populated area.
No fun...

Debbie

C Kingsbury wrote:

Debbie,

A large transport jet (such as a DC-10 operated by FedEx) can climb, lightly
loaded, at speeds around 150mph. This would be unusual (170-200mph is more
normal) but well short of impossible. It might have been a maintenance
flight, for instance.

Now, with that in mind let's apply a few more factors. First, windspeed.
Let's say the wind is blowing at 40mph. This would not be unusual for the
Northern half of the country this time of year. An airplane flying into that
wind would only need to move at 110mph relative to the ground. Windspeed can
vary strongly from the ground to the first few thousand feet as well, so you
might not have noticed the wondspeed on the ground. Now, you also mentioned
you were in the car going at least 40mph, so relative to you, the plane
would only appear to be moving at 70mph.

Last, you need to do a little trigonometry, I'm afraid. Imagine putting a
ladder up against the side of your house. The ladder goes up ten feet, and
at its base is set back perhaps three or four feet from the house. Now, when
you climb that ladder, you are traveling ten feet, but you only move forward
three or four. A similar thing is going on when you compare your speed in
the car to the plane's speed in the air. So we can reduce the difference to
perhaps 55 or 60mph.

What you perceive as speed is going to be based on changes in angle, in
other words, you expect to see the plane "pulling ahead of you" at a certain
rate. It turns out that the human eye is quite poor at judging small angles.
A speed difference of 60mph at a distance of half a mile is going to produce
very small angular changes, which your eye will not perceive well. So, even
though the plane is moving at sufficient speed to fly quite safely, to your
eye it will appear to be standing still.

I can assure you that even us pilots, who know all these things, still often
see the very same illusion you describe, especially with very large
airplanes. It's simply a combination of factors that produce an overwhelming
optical illusion.

-cwk.

yes, I've imagined the whole trig thing. That's why I was looking at the
buildings and other higher geographic markers to get a fix on how it
appeared to be moving relative to those things. Plus, for a moment I was
stopped and pretty much next to it, although of course I was on the
ground and it was probably a couple of thousand feet up or less. And, if
it makes a difference in possible explanations, the plane was headed
east and I was moving west. I'm 99.999% sure it wasn't moving or was
moving very slowly.

Note, I've driven in this particular area for more than a decade and
I've seen hundreds of planes moving in the sky from many vantage points
under many different weather and cloud conditions. I'm pretty sure of
what I saw. Your explanation makes great sense but I'm still not
convinced that it was an optical illusion. Really hope so though because
it was quite disturbing.

Debbie

Darrell S wrote:

"As I was moving relatively slowly" quoting from your post, it sounds like
you were in your car driving. The APPARENT relative movement of an aircraft
being observed from a moving vehicle changes drastically if either the
aircraft or the car change relative headings. That could make it appear as
if the forward motion of the jet had stopped.
As for then "it continued climbing" is hard to explain. Perhaps you just
thought it had stopped climbing due to the apparent stoppage of any forward
movement.

yes, I was paying particular attention to how high it was, for obvious
reasons. When I fixed on its altitude relative to buildings, power
poles, the freeway, etc., for a few seconds the altitude didn't seem to
be changing. And for a few seconds my car wasn't moving at all and it
didn't seem to be moving either, or if it was it was going slower that
you'd expect a plane in takeoff to be moving. Then suddenly did it start
moving forward and up. It was just like a helicopter, except it wasn't a
helicopter.

Debbie

DM wrote:

snipped

thank you to everyone who replied. I've been considering all the
explanations offered and appreciate the information. I'm pretty close to
accepting the "optical illusion" idea but am not quite there yet. I was
looking hard at that plane because I really didn't want to believe what
I was seeing. If it weren't for the fact that I could read the name of
the carrier on the plane, I'd probably be going for a UFO explanation!

Fly safe everybody.

Debbie

"DM" wrote in message
...
Yesterday I saw a cargo jet (a major air express company) come to what
seemed like a dead stop in midair as it was making its ascent. After
about 20 - 30 seconds of hanging without dropping out of the sky, it
continued climbing and apparently did not crash.

As others have said, it's just an optical illusion, unless the wind picked
up suddenly to bring the aircraft's ground speed to zero (unlikely).

At Raleigh-Durham International, there used to be a road that paralleled one
of the main runways. A couple of times, I just happened to be on that road
at the end where a large commercial jet (B737or similar) was just starting
its takeoff roll. I floored the car and left the jet behind. About the time
I got to the speed of around 70 mph, that jet blew past me about midway down
the runway going so much faster it was hard to believe. It brought home the
fact that those jets are moving very fast when they look like they are going
the slowest.

-Trent
PP-ASEL

"DM" wrote in message
...
thank you to everyone who replied. I've been considering all the
explanations offered and appreciate the information. I'm pretty close to
accepting the "optical illusion" idea but am not quite there yet.

Airliners simply don't stop in midair. You have no choice but to accept the
"optical illusion" idea.

[...]
Fly safe everybody.

We do. Now, since you brought it up, how about you quit panicking every
time you see an airplane go overhead doing something other than what you
think it ought to be doing. We're not the dangerous boogey man that you,
the general public, apparently think we are. Tell your friends.

Thanks.

Pete

DM wrote:


yes, I've imagined the whole trig thing. That's why I was looking at the
buildings and other higher geographic markers to get a fix on how it
appeared to be moving relative to those things. Plus, for a moment I was
stopped and pretty much next to it, although of course I was on the
ground and it was probably a couple of thousand feet up or less. And, if
it makes a difference in possible explanations, the plane was headed
east and I was moving west. I'm 99.999% sure it wasn't moving or was
moving very slowly.

Put me in for $100 on that 99,999-to-1 odds bet! g

Seriously, it sounds like you are trying to understand what you
perceived, and I think the responses here have been right on target.
I'm betting on the laws of physics and hope some explanation here will
lead to an "aha" for you, to understand what caused your perception.
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

"Peter Duniho" wrote in message
...

We do. Now, since you brought it up, how about you quit panicking every
time you see an airplane go overhead doing something other than what you
think it ought to be doing. We're not the dangerous boogey man that you,
the general public, apparently think we are. Tell your friends.


Methinks the man doth protest too much.

-cwk.

DM wrote:

interesting, but no, it wasn't particularly windy on the ground.

I have the winds aloft forecast for yesterday morning. Where was this?

George Patterson
If a man gets into a fight 3,000 miles away from home, he *had* to have
been looking for it.