A newbie doubt, if it's ok...

"Ramapriya" wrote in message
om...

I know cars and trucks tend to skid even at low speeds in sleet and on
ice, with braking often proving ineffectual. This leaves me wondering
why is it that we don't ever hear of aircraft skidding and going
off-track while taxiing or even during takeoff/landing? Is the lack of
such incidents only because of the meticulousness of ice clearance by
airport authorities?

These things do happen, though mostly to small planes and not generally
fatal so they're not big news items.

Why doesn't this happen with airliners? I'll hazard the following guesses:

1. Thrust reversers provide braking power even if the tires have no grip at
all
2. Landings are made in a straight line on a flat runway. It's curves and
hills that cause trouble on icy roads.
3. Weight-to-tire-area ratio: I'm guessing here, but it seems to me that
airliners put a lot of weight on a relatively small amount of tire area
compared to cars. This would improve traction.
4. Operator skill: Trained pilots vs. idiot/unskilled drivers

In my (limited) experience, you're lucky if the runway is cleared of
snow/ice better than the highways, especially during/after a large storm.

-cwk.

"C Kingsbury" wrote

These things do happen, though mostly to small planes and not generally
fatal so they're not big news items.

Why doesn't this happen with airliners? I'll hazard the following guesses:

1. Thrust reversers provide braking power even if the tires have no grip
at
all
2. Landings are made in a straight line on a flat runway. It's curves and
hills that cause trouble on icy roads.
3. Weight-to-tire-area ratio: I'm guessing here, but it seems to me that
airliners put a lot of weight on a relatively small amount of tire area
compared to cars. This would improve traction.
4. Operator skill: Trained pilots vs. idiot/unskilled drivers

In my (limited) experience, you're lucky if the runway is cleared of
snow/ice better than the highways, especially during/after a large storm.

-cwk.

Add more factors.

Airplanes have aerodynamic surfaces that help maintain directional control,
especially at high speeds, where loss of control from lack of traction is
usually a problem for cars.

Airplane wheels are not powered, to make them lose traction during
acceleration. Also, brakes are not used much for stopping small planes on
long runways. If there is slush on a runway, it has the effect of slowing a
small plane, all by itself, with using even less brakes.
--
Jim in NC


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"Ramapriya" wrote in message
om...
Is a non-aviator airing a doubt ok with you folks?

Sure.

I know cars and trucks tend to skid even at low speeds in sleet and on
ice, with braking often proving ineffectual. This leaves me wondering
why is it that we don't ever hear of aircraft skidding and going
off-track while taxiing or even during takeoff/landing?

Perhaps you just aren't receiving your information from sources that would
mention such an event.

Is the lack of
such incidents only because of the meticulousness of ice clearance by
airport authorities?

At some airports, yes. Generally, the more important an airport is to the
national transportation system (and all airports are important at least to
some degree), the better quality of maintenance, including keeping the
pavement clear of snow and ice. Some of the largest airports even have
heated runways, I believe.

Even so, once in a very long while, an airliner does wind up skidding off
the runway or taxiway somewhere. I don't know the exact frequency, but
probably on the order of once a decade or so.

At smaller airports, this happens more frequently, but as with cars, it
rarely involves more than some bent sheet metal. Accidents are likely to be
low speed (almost all taxiing happens at relatively low speeds...5-10mph at
most), and those that happen on landing (i.e. at higher speed) often don't
wind up in the news because they happened at the airport, rather than
somewhere that would make for something that sells ads on the evening news
(like a residential neighborhood).

Another factor is that airplanes have more to control them than just the
tires. In particular, the faster the airplane is going, the more likely the
same surfaces used to control the airplane in the air can also be used to
control the airplane on the ground.

Just as a "for example", I landed at the Reno, NV airport once on a VERY hot
day, while flying a small four-seater single-engine airplane. I landed on
the same runway that the big airliners use, and touched down in the same
spot that they do. Well, it turns out that when they touch down, each one
leaves a little rubber. By the time I'd arrive, there was a WHOLE LOT of
rubber, at a very high temperature. It was as slick as any ice, perhaps
slicker.

I had no braking whatsoever. But I didn't lose control of the airplane,
because I still had plenty of rudder control to keep me going in the right
direction. I simply "flew" the airplane while on the ground, until I got to
the pavement that was clear, made a normal stop and taxied off the runway.

This same effect helps prevent takeoff accidents...long before the airplane
leaves the ground, the tires are no longer required to keep the airplane
aligned with the runway. Rudder control is perfectly sufficient, especially
on a runway that is nice and flat.

Of course, all of the things that "cwk" mentions are relevant too. The
bottom line is that it's not actually true that airplanes don't have trouble
with ice, but it IS true that there are reasons those issues come up less
frequently than they might with automobiles.

Pete

In article , Ramapriya wrote:

Is a non-aviator airing a doubt ok with you folks?

Depends on the doubt. Some "doubt"s sound like trolls.


I know cars and trucks tend to skid even at low speeds in sleet and on
ice, with braking often proving ineffectual. This leaves me wondering
why is it that we don't ever hear of aircraft skidding and going
off-track while taxiing or even during takeoff/landing? Is the lack of
such incidents only because of the meticulousness of ice clearance by
airport authorities?

Good question. In fact it does happen on occasion. Sometimes
airlines run off the end of the runway, the equivalent of a (very
expensive) fender bender, with few injuries.

It doesn't happen often because the main difference between airplanes
maneuvering on the ground and road vehicles is that airplanes are
going much slower, so the brakes remain relatively effective (add
extra distance for the stopping distance). At higher speeds when
taking off and landing, they're getting their drive and control from
aerodynamic forces.

A number of years ago when the world was younger, a buddy who was/is
(lost touch with him) a Greek national, who's mother work(s|ed) for
the airline told a story of sitting in the jump seat of a 747 leaving
NY.

It was the first plane out after a closure (usually, the first airline
out "sweeps" the runway) The copilot, who didn't have any winter
driving experience (not a lot of winter driving conditions in Greece)
turned onto the runway, applying too much power, spun out. No
damage, except to pride.

Normally, when that happens, you go back to the end of the line (there
will be a long line of delayed planes waiting to leave under those
conditions). The pilot of the #2 aircraft "politely" let them try
again anyway (so he got the freshly sweeped runway).


Morris

In article ,
(Ramapriya) wrote:


I know cars and trucks tend to skid even at low speeds in sleet and on
ice, with braking often proving ineffectual. This leaves me wondering
why is it that we don't ever hear of aircraft skidding and going
off-track while taxiing or even during takeoff/landing? Is the lack of
such incidents only because of the meticulousness of ice clearance by
airport authorities?

It happens. I worked Crash/Rescue at a large airport for 20 years and
saw several aircraft that had problems on icy surfaces.

747 was blown off of icy taxiway by high winds, about $22 million to
repair the aircraft, some serious injuries.

747 landing on icy runway had a reverser problem and went off edge of
runway into deep snow.

747 taxiing on icy taxiway missed a turn going off edge.

747 taxiing to gate lost control on icy ramp striking some ground
equipment and another aircraft. The aircraft that was struck was
salvaged due to the damage.

DC-8 landing during snowstorm was unable to stop and nosewheel went just
a few feet of end of runway.

747 landing on icy runway with strong crosswind went off edge of runway
taking out several runway lights.

--
Dale L. Falk

There is nothing - absolutely nothing - half so much worth doing
as simply messing around with airplanes.

http://home.gci.net/~sncdfalk/flying.html

"Ramapriya" wrote in message
om...
Hi there,

Is a non-aviator airing a doubt ok with you folks?

I know cars and trucks tend to skid even at low speeds in sleet and on
ice, with braking often proving ineffectual. This leaves me wondering
why is it that we don't ever hear of aircraft skidding and going
off-track while taxiing or even during takeoff/landing? Is the lack of
such incidents only because of the meticulousness of ice clearance by
airport authorities?

Look forward to a comment on this from you experienced folks

Cheers,

Ramapriya


They WILL skid but don't ordinarily. Many of the older aircraft did very
well without brakes. You taxi slowly and don't generate any centrifugal
force in a turn.

If you take off in a straight line, which aircraft do, 99% of the time there
is no force which can cause the aircraft to skid. You use rudder and
aileron to correct against any force, like the wind or torque of the
propeller, to keep your takeoff under control.

I see skid marks on our runway all the time. Tires skid as soon as they
touch down. It takes them a few feet to spin up. Sometimes a pilot will
get on the brakes a little too heavy and skid, but that's either because
he's had poor training or is about to run out of runway on landing rollout.

The brakes on my old airplane from the forties are very poor and only
effective enough to allow me to turn during taxi by differential braking.
Otherwise I never use them except when landing on a very short field when I
can see the bark on the trees ahead.

1. Ground vehicles rely on their tires for propulsion, which can lead to
loss of control on slick surfaces. Airplanes use propellors or turbines
which push air around for propulsion.

2. Ground vehicles rely solely on their tires for directional control,
which lose traction on slick surfaces. Airplanes can utilize thrust
(including differential thrust) and flight control surfaces (rudder) for
directional control on slick surfaces.

3. Ground vehicles rely solely on brakes and tires for stopping. Many
airplanes have thrust reversers to help them stop. Single engine piston
airplanes have the same problem as ground vehicles when it comes to
stopping.

As you can see, airplanes possess a number of advantages over ground
vehicles for manuevering on slick surfaces. They aren't completely immune
to the problem, but less prone to loss of control.

Dean

"Ramapriya" wrote in message
om...
Hi there,

Is a non-aviator airing a doubt ok with you folks?

I know cars and trucks tend to skid even at low speeds in sleet and on
ice, with braking often proving ineffectual. This leaves me wondering
why is it that we don't ever hear of aircraft skidding and going
off-track while taxiing or even during takeoff/landing? Is the lack of
such incidents only because of the meticulousness of ice clearance by
airport authorities?

Look forward to a comment on this from you experienced folks

Cheers,

Ramapriya

I'd just like to throw in one more factor. Most airports shutdown when the
runways are to bad to be used. Roads on the other hand don't shut down until
a car can get stuck. Thus a car can drive on a sheet of ice and people
thinks it okay because no one told them not to do it. Because of that,
people don't think to use caution
"Ramapriya" wrote in message
om...
Hi there,

Is a non-aviator airing a doubt ok with you folks?

I know cars and trucks tend to skid even at low speeds in sleet and on
ice, with braking often proving ineffectual. This leaves me wondering
why is it that we don't ever hear of aircraft skidding and going
off-track while taxiing or even during takeoff/landing? Is the lack of
such incidents only because of the meticulousness of ice clearance by
airport authorities?

Look forward to a comment on this from you experienced folks

Cheers,

Ramapriya





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(Ramapriya) wrote in news:30a8759c.0411041049.2c558a22
@posting.google.com:

Hi there,

Is a non-aviator airing a doubt ok with you folks?

I know cars and trucks tend to skid even at low speeds in sleet and on
ice, with braking often proving ineffectual. This leaves me wondering
why is it that we don't ever hear of aircraft skidding and going
off-track while taxiing or even during takeoff/landing? Is the lack of
such incidents only because of the meticulousness of ice clearance by
airport authorities?

Look forward to a comment on this from you experienced folks

Cheers,

Ramapriya


You've had a number of good responses having mostly to do with the
mechanics of the airplane, and I think that's important to recognize and
understand. But I think there is more, too...

Most public-use runways in the US are at least 2500' long (that's about 1/2
mile) and even many small airports have runways between 3000' and 6000'
long (6000' is over 1 mile). The runways are generally very straight and
very level.

Even Single Engine piston airplanes can use back elevator and flaps to
increase drag and reduce speed without brakes and without reverse
thrusters. If the runway is long enough, the plane can coast to nearly a
complete stop without ever using the brakes. A car can too, but we're not
trained to coast our cars to a full stop on a highway when a curve is
coming up, or a snow bank steers you toward the guardrail, or the car 2
seconds in front of you starts to slow down. You're rarely 2 seconds away
from the plane in front of you, and when you are, there are usually MANY
more options for getting around safely...

A road that is largely covered in snow, slush, and ice is dangerous to
drivers of both cars and planes. But I think many drivers feel unduly
secure in their cars. As they get some traction going, they start to push
the limits and pick up speed. They want to get the hell off these horrible
roads and get where they're going. Then, all of a sudden, they get a wake
up call when they start to feel a skid. Depending on a combination of luck,
experience, and skill, they either spin out and have an accident, or they
recover, and slow down for a while until they start to feel secure again
and the process starts over.

Most pilots attitude toward taxing is different. Taxiing is only at the
very beginning or end of the trip. They are not trying to get up to the
"speed" limit. They are generally focused on getting to their runway or
parking spot safely, not quickly.

Another factor is that if a driver is on a bad road on his way to work, he
probably has a long trip in these dangerous road conditions, which will
perpetuate the cycle of killer comfort. Pilots, spend most of their travel
time in the air, and only a very small percentage of time on the ground.
The ice, sleet, and snow on the ground have no bearing on the air time.
(Although ice and sleet in the air is a whole other conversation and can be
very dangerous.) Once the clouds move off, and maybe even the sun comes
out, a plane can fly very safely and comfortably in the air, while driving
conditions are still extremely risky.

Another thing relates to the propulsion.
Note that cars have their accelration from the wheels, which
place a very high force on the surface through friction.
Sine plans, the force is applied to air, and exceeding the
coefficient of friciton on the "driving" wheels won't happen
due to driectly driving the wheels.

Turning is still pretty much the same (more or less).
But planes do slide.

Bigger planes have more pressure on the tires per square inch, and therefore
the force to overcome the added friction must be higher, too.