Two conveyor belt scenarios

[[email protected]]

An airplane lands on a conveyor belt that's moving at a constant speed
of Vref

(a) in the direction of the airplane's landing
(b) in the opposite direction of the airplane's landing

What do you suppose will happen? (b) will be rather more dicey than
(a), methinks. Presume a healthy long runway for the moment...

Ramapriya

[Judah]

wrote in news:1159120091.823667.280400
@m7g2000cwm.googlegroups.com:

> An airplane lands on a conveyor belt that's moving at a constant speed
> of Vref
>
> (a) in the direction of the airplane's landing
> (b) in the opposite direction of the airplane's landing
>
> What do you suppose will happen? (b) will be rather more dicey than
> (a), methinks. Presume a healthy long runway for the moment...
>
> Ramapriya

Is this a powered conveyor or a gravity feed conveyor?

Rollers, Mattop, or Belt?

[Peter Duniho]

> wrote in message
ups.com...
> An airplane lands on a conveyor belt that's moving at a constant speed
> of Vref
>
> (a) in the direction of the airplane's landing
> (b) in the opposite direction of the airplane's landing
>
> What do you suppose will happen? (b) will be rather more dicey than
> (a), methinks. Presume a healthy long runway for the moment...

We had this thread already. Looks like r.a.student had it already too. See
Google Groups.

Bottom line: since an airplane doesn't rely on the wheels for propulsion,
conveyor belts have nothing to do with whether an airplane can land or
takeoff, regardless of whether that conveyor belt is moving or not moving,
forward or backward.

During takeoff, there are no real secondary issues. During landing, braking
may be an issue, but at that point the question has nothing to do with
airplanes.

Pete

[Jose[_1_]]

> (a) in the direction of the airplane's landing

The airplane will touch down, and the tires will not spin.

> (b) in the opposite direction of the airplane's landing

The airplane will touch down as before, and the tires will spin twice as
fast as they would have landing on still ground.

Jose
--
"Never trust anything that can think for itself, if you can't see where
it keeps its brain." (chapter 10 of book 3 - Harry Potter).
for Email, make the obvious change in the address.

[Allen[_1_]]

> wrote in message
ups.com...
> An airplane lands on a conveyor belt that's moving at a constant speed
> of Vref
>
> (a) in the direction of the airplane's landing
> (b) in the opposite direction of the airplane's landing
>
> What do you suppose will happen? (b) will be rather more dicey than
> (a), methinks. Presume a healthy long runway for the moment...
>
> Ramapriya


Oh Gawd, not again!

[Grumman-581[_3_]]

"Allen" > wrote in message
...
> Oh Gawd, not again!

Yeah, you would think that the ****in' trolls could at least make the effort
to be a bit more original...

[[email protected]]

Grumman-581 wrote:
> "Allen" > wrote in message
> ...
> > Oh Gawd, not again!
>
> Yeah, you would think that the ****in' trolls could at least make the effort to be a bit more original...


I did read the conveyor belt thread (of Aug 04?) on takeoff, which made
me ask about this landing scenario (don't remember seeing one similar).


And find out what a troll means before using the word, Grumman.

Ramapriya

[[email protected]]

Peter Duniho wrote:
> > wrote in message
> ups.com...
> > An airplane lands on a conveyor belt that's moving at a constant speed
> > of Vref
> >
> > (a) in the direction of the airplane's landing
> > (b) in the opposite direction of the airplane's landing
> >
> > What do you suppose will happen? (b) will be rather more dicey than
> > (a), methinks. Presume a healthy long runway for the moment...
>
> We had this thread already. Looks like r.a.student had it already too. See
> Google Groups.
>
> Bottom line: since an airplane doesn't rely on the wheels for propulsion,
> conveyor belts have nothing to do with whether an airplane can land or
> takeoff, regardless of whether that conveyor belt is moving or not moving,
> forward or backward.


Takeoff is clear, Pete. But I doubt landing would be that cut-and-dry.
Remember I said the conveyor is moving at a *constant* Vref. I'm sure
that'd cause problems once the plane loses aerodynamic braking and has
to rely on ground braking.

Not sure, of course - which is why I asked you guys :)

Ramapriya

[Jose[_1_]]

> I'm sure
> that'd cause problems once the plane loses aerodynamic braking and has
> to rely on ground braking.

You never said what you wanted the plane to do. First, the plane will
alight onto the conveyor belt. The tires will (or will not need to)
spin up.

Now what? That depends on what the pilot does, which depends on what
the pilot wants to accomplish. You didn't state that.

Jose
--
"Never trust anything that can think for itself, if you can't see where
it keeps its brain." (chapter 10 of book 3 - Harry Potter).
for Email, make the obvious change in the address.

[Peter Duniho]

> wrote in message
oups.com...
> Takeoff is clear, Pete. But I doubt landing would be that cut-and-dry.

It is.

> Remember I said the conveyor is moving at a *constant* Vref. I'm sure
> that'd cause problems once the plane loses aerodynamic braking and has
> to rely on ground braking.

You said nothing about braking, nor made any stipulation about braking
performance. If you have further facets to the question you'd like to
explore, feel free to post those. But as the question was stated, my answer
is accurate (as is Jose's).

And for the record, if you're concerned about issues with braking, why
aren't you concerned about issues during takeoff (in which the airplane is
theoretically stopped on the conveyor belt to start with)?

There is nothing aerodynamically interesting about the question. The only
interesting parts happen with respect to the wheel/belt interface, which is
the same whether you are talking about a plane, car, or whatever.

Pete

[Peter Duniho]

> wrote in message
ups.com...
> [...]
> And find out what a troll means before using the word, Grumman.

For the record, while I disagree with his usage of the word in this case, he
has used the word in a perfectly correct way, grammatically speaking.

Not to defend his knee-jerk response, but it might be helpful to know that
the newsgroup has been under siege from another particularly troll-like
individual, putting lots of people on-edge. Grumman is usually already
pretty on-edge as it is, so he didn't have far to go before snapping at you.
:)

[[email protected]]

Peter Duniho wrote:
>
> Not to defend his knee-jerk response, but it might be helpful to know that
> the newsgroup has been under siege from another particularly troll-like
> individual, putting lots of people on-edge. Grumman is usually already
> pretty on-edge as it is, so he didn't have far to go before snapping at you.
> :)


k, sure :)
And just for the record - I *never* troll anyone. Jest often yes, but
troll never :)

Ramapriya

[Gary Drescher]

> wrote in message
ups.com...
> An airplane lands on a conveyor belt that's moving at a constant speed
> of Vref
>
> (a) in the direction of the airplane's landing
> (b) in the opposite direction of the airplane's landing
>
> What do you suppose will happen?

Motion of the ground relative to the air is equivalent to motion of the air
relative to the ground. So:

(a) That's equivalent to landing on stationary ground with the headwind
increased by Vref.
(b) That's equivalent to landing on stationary ground with the headwind
decreased by Vref.

--Gary

[Grumman-581[_3_]]

"Peter Duniho" > wrote in message
...
> Grumman is usually already pretty on-edge as it is, so he didn't
> have far to go before snapping at you.

Yeah, I'm a grumpy old man... If I knew I was going to live this ****in'
long, I would have taken better care of my body when I was growing up...

[Peter Duniho]

"Grumman-581" > wrote in message
...
> Yeah, I'm a grumpy old man... If I knew I was going to live this ****in'
> long, I would have taken better care of my body when I was growing up...

There's a joke in there. You'd probably get it, and even think it's funny I
think, but I suspect everyone else would have apoplectic fits of offense if
I posted it. Oh well...

[Doug[_1_]]

There are three speeds here. Speed relative to the air. Speed relative
to the belt. Speed relative to ground.

And actually, this does have a real world analogy. Taking off in a
seaplane on a river that is moving. Now add in wind blowing upstream or
wind blowing downstream and the takeoff and landing upstream vs
downstream comparison gets quite complicated.

[Bob Noel]

In article >,
"Peter Duniho" > wrote:

> "Grumman-581" > wrote in message
> ...
> > Yeah, I'm a grumpy old man... If I knew I was going to live this ****in'
> > long, I would have taken better care of my body when I was growing up...
>
> There's a joke in there. You'd probably get it, and even think it's funny I
> think, but I suspect everyone else would have apoplectic fits of offense if
> I posted it. Oh well...

go for it.

--
Bob Noel
Looking for a sig the
lawyers will hate

[Gary Drescher]

"Doug" > wrote in message
oups.com...
> There are three speeds here. Speed relative to the air. Speed relative
> to the belt. Speed relative to ground.

The only velocities that matter are that of the plane relative to the air,
and that of the air relative to the landing surface (in this case, the
constant-speed conveyor belt). The landing surface's velocity relative to
the surrounding ground has no physical effect on the landing (except perhaps
with respect to turbulence, but that's not part of the hypothetical
scenario).

> And actually, this does have a real world analogy. Taking off in a
> seaplane on a river that is moving. Now add in wind blowing upstream or
> wind blowing downstream and the takeoff and landing upstream vs
> downstream comparison gets quite complicated.

If the river is arbitrarily long (as we're assuming the conveyor belt to be)
and you don't care where on it you end up, then the landing isn't
complicated at all: you just ignore the land completely, and pay attention
to the wind speed relative to the water. (It helps to have a wind sock
that's riding on the river or on the conveyor belt.)

--Gary

[Doug[_1_]]

Actually, on a moving river, water speed matters and frequently speed
(well, distance really) relative to the ground matters. The ideal setup
is to have a headwind while pointing downstream. That way you have
slowest waterspeed and shortest run. BUT....local obstructions dictate
you concern yourself with distance of run relative to the land....

Like I said, it can get complicated.

Gary Drescher wrote:
> "Doug" > wrote in message
> oups.com...
> > There are three speeds here. Speed relative to the air. Speed relative
> > to the belt. Speed relative to ground.
>
> The only velocities that matter are that of the plane relative to the air,
> and that of the air relative to the landing surface (in this case, the
> constant-speed conveyor belt). The landing surface's velocity relative to
> the surrounding ground has no physical effect on the landing (except perhaps
> with respect to turbulence, but that's not part of the hypothetical
> scenario).
>
> > And actually, this does have a real world analogy. Taking off in a
> > seaplane on a river that is moving. Now add in wind blowing upstream or
> > wind blowing downstream and the takeoff and landing upstream vs
> > downstream comparison gets quite complicated.
>
> If the river is arbitrarily long (as we're assuming the conveyor belt to be)
> and you don't care where on it you end up, then the landing isn't
> complicated at all: you just ignore the land completely, and pay attention
> to the wind speed relative to the water. (It helps to have a wind sock
> that's riding on the river or on the conveyor belt.)
>
> --Gary

[Gary Drescher]

"Doug" > wrote in message
ps.com...
> Actually, on a moving river, water speed matters and frequently speed
> (well, distance really) relative to the ground matters.
> ....local obstructions dictate
> you concern yourself with distance of run relative to the land....

Sure. That's why I said that *if* the river is arbitrarily long, and if you
don't care where you land, *then* you just ignore the land and care only
about the speed of the air relative to the water. (Those stipulations make
the situation analogous to the hypothetical conveyor belt scenario.)

> The ideal setup
> is to have a headwind while pointing downstream. That way you have
> slowest waterspeed and shortest run.

The plane's speed relative to the water (the plane's waterspeed) depends
only on the plane's airspeed and the speed of the air relative to the water.
It doesn't depend in any way on the speed of the water relative to the land;
hence, it doesn't depend on whether you're going upstream or downstream.
Rather, it just depends on whether you're going upwind (relative to the
water) or downwind.

As for making the shortest run (relative to the land), wouldn't you want to
be going upwind (relative to the water) and upstream, rather than upwind and
downstream?

--Gary

[Peter Duniho]

"Bob Noel" > wrote in message
...
> go for it.

Too late. I could have posted the joke, or posted a comment about the joke.
Doing both would be terrible form, and I've already done the latter.

Basically, I'm much better at ruining jokes than telling them. :)

[Doug[_1_]]

I honestly don't know. I know that this is argued in the Seaplane's
pilot association newsletter ad nauseum. One thing to further
complicate things is with a Seaplane, water speed DOES matter. Faster
water speed gets you on the step quicker and that means shorter takeoff
runs. Also, TOO fast a water speed (on landing) can cause a bad
accident (this would be landing upstream with a tailwind). People who
takeoff on fast moving rivers do report shorter runs (relative to the
ground) going upstream. What is debated is whether they are getting
shorter runs relative to the water, than a downstream run with the same
headwind. But like I say, I dunno. The real world scenario is NOT
trivial. My bottom line is I need to have plenty of room to take off,
so I never really pushed the issue. I always wanted 2 or 3 times as
much distance as I needed. If I didn't have it, I found a longer lake
or river. Rivers tend to be plenty long, at least the ones I've dealt
with. My experience with rivers is limited to one or two and they were
fairly easy, plenty long. I always just took off into the wind.

Gary Drescher wrote:
> "Doug" > wrote in message
> ps.com...
> > Actually, on a moving river, water speed matters and frequently speed
> > (well, distance really) relative to the ground matters.
> > ....local obstructions dictate
> > you concern yourself with distance of run relative to the land....
>
> Sure. That's why I said that *if* the river is arbitrarily long, and if you
> don't care where you land, *then* you just ignore the land and care only
> about the speed of the air relative to the water. (Those stipulations make
> the situation analogous to the hypothetical conveyor belt scenario.)
>
> > The ideal setup
> > is to have a headwind while pointing downstream. That way you have
> > slowest waterspeed and shortest run.
>
> The plane's speed relative to the water (the plane's waterspeed) depends
> only on the plane's airspeed and the speed of the air relative to the water.
> It doesn't depend in any way on the speed of the water relative to the land;
> hence, it doesn't depend on whether you're going upstream or downstream.
> Rather, it just depends on whether you're going upwind (relative to the
> water) or downwind.
>
> As for making the shortest run (relative to the land), wouldn't you want to
> be going upwind (relative to the water) and upstream, rather than upwind and
> downstream?
>
> --Gary

[Peter Duniho]

"Gary Drescher" > wrote in message
. ..
> [...]
> As for making the shortest run (relative to the land), wouldn't you want
> to be going upwind (relative to the water) and upstream, rather than
> upwind and downstream?

He didn't say anything about "relative to land". If you want the shortest
run relative to land, the only thing that really matters is the wind
direction and speed. But I think that's not what he was talking about.

Of course, since you're on the water, if you do it this way you ignore some
important factors. In reality, it's all a trade-off. There is no perfect
scenario the way there might be on a paved runway. For one, with the wind
against the water, waves can be an issue. So even though downstream with a
headwind minimizes water speed and maximizes the headwind, it means you're
operating in rougher conditions. A headwind going downstream may be better,
since it still reduces your water speed (helping compensate somewhat for
landing against the current), while not stirring up the water surface so
much.

And, of course, all of that ignores any local features of the landing area.
Terrain, rocks, course of the river, etc. all come into play as well.
There's almost never one absolutely best way to land a seaplane, though
there are usually more bad ways than good ways. :)

Pete

[Grumman-581[_3_]]

"Peter Duniho" > wrote in message
...
> There's a joke in there. You'd probably get it, and even think it's funny
I
> think, but I suspect everyone else would have apoplectic fits of offense
if
> I posted it. Oh well...

Sounds like it might offend some of the political correctness sensibilities
around here... Go for it !!!

[Montblack[_1_]]

("Peter Duniho" wrote)
> Basically, I'm much better at ruining jokes than telling them. :)


A politician, a piece of string, a priest, and a frog all walk into a bar
together:

Bartender says: What is this, some kind of a joke?


Montblack