Go Back   Science Forums Biology Forum Molecular Biology Forum Physics Chemistry Forum > General Science Forums > Physics Forum
Register Search Today's Posts Mark Forums Read

Physics Forum Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.


Effect of spoilers on braking

Effect of spoilers on braking - Physics Forum

Effect of spoilers on braking - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.


Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 11-21-2004, 10:03 PM
Sylvia Else
Guest
 
Posts: n/a
Default Effect of spoilers on braking





Rich Ahrens wrote:




Added alt.sci.physics, sci.misc, aus.science.

Sylvia.

Reply With Quote
  #2  
Old 11-21-2004, 10:18 PM
AbsolutelyCertain
Guest
 
Posts: n/a
Default Effect of spoilers on braking


"Sylvia Else" <[Only registered users see links. ].this.address> wrote in message
news:[Only registered users see links. ].this.address...

Well, I think if you're right, then heavy and complicated landing gear just
became unnecessary. Simply lengthen runways, and put skid plates on the
bottoms of airplanes. With that low coefficient of friction, little damage
will be done, and reverse thrust can do the bulk of the work. After
stopping, just slide some ground-bound wheels under the thing and taxi it
away. Thousands of pounds of weight saved. Didn't I see something like
that on the cover of Popular Science Magazine circa 1953? The
Slide-o-Cruiser?



Reply With Quote
  #3  
Old 11-21-2004, 10:29 PM
Sylvia Else
Guest
 
Posts: n/a
Default Effect of spoilers on braking



AbsolutelyCertain wrote:

You're not meant to run reverse thrust at low IAS. Also there would be
little directional control, runways would cost more, runway occupancy
times would increase, to name but three other objections that come
immediately to mind.

Sylvia.

Reply With Quote
  #4  
Old 11-21-2004, 10:36 PM
AbsolutelyCertain
Guest
 
Posts: n/a
Default Effect of spoilers on braking


"Sylvia Else" <[Only registered users see links. ].this.address> wrote in message
news:[Only registered users see links. ].this.address...
just
damage
it

Yes, yes. So, let me see if I have this right. Two identical and
identically loaded and flown MD-80s land on parallel identical runways which
I presume, a thunderstorm having been in the area, are wet. One airplane
lands wheels up, and other wheels down, and you can prove that the
wheels-down airplane will stop first? Nothing other than braking or
airplane-to-ground friction will provide what you call "stopping power".

Can we see the work on that, please?




Reply With Quote
  #5  
Old 11-21-2004, 11:16 PM
Sylvia Else
Guest
 
Posts: n/a
Default Effect of spoilers on braking



AbsolutelyCertain wrote:

I seem to be a bit short of spare MD-80s right now for doing the
experiments, and the local airline (which initially was quite
interested) demurred when I mentioned the gear up aspect. However, the
underlying principle is quite easy to demonstrate.

Wrap a CD in kitchen foil - it will weigh about 20 grams. Get a rubber
pencil eraser of about the same weight. Place both on a suitable flat
surface, and start tilting the surface. The one that has the lower
frictional force on it will move first.

So which one is it? The metal covered large area CD, or the rubber small
area pencil eraser?

If you think the answer is the small area pencil eraser, then you're in
for a surprise.

Sylvia.

Reply With Quote
  #6  
Old 11-21-2004, 11:41 PM
AbsolutelyCertain
Guest
 
Posts: n/a
Default Effect of spoilers on braking


"Sylvia Else" <[Only registered users see links. ].this.address> wrote in message
news:[Only registered users see links. ].this.address...
is
of
the
like
which
airplane

In other words, you made a guess. You don't know how many square (inches -
cm - feet - meters) of airplane are going to be sliding on the ground. You
therefore don't know what the coefficient of friction is for that
combination of metal and pavement under the hypothetical conditions, because
you don't know the distribution of weight over the area without the area.
You don't know how the sliding and grinding action is going to affect the
area in contact with the ground, and thereby change the coefficient of
friction, and probably the contact area, as the event proceeds. I think it
is also unlikely that the coefficient of friction is going to remain
constant as the airplane slows down. You don't have information necessary to
calculate the stopping distance for this noisy experiment. You just made a
guess. Nothing wrong with that, guessing is fun to do. But you presented
your guess as some sort of authoritative estimate and then mocked people for
challenging your guess even though you had no way to back it up with even
the most rudimentary calculations.

Did I miss anything?


Reply With Quote
  #7  
Old 11-21-2004, 11:58 PM
Sylvia Else
Guest
 
Posts: n/a
Default Effect of spoilers on braking



AbsolutelyCertain wrote:


The basic physics? The coefficient of friction is a dimensionless
constant because the frictional force is not a function of area. So we
don't need to know the area in contact to determine the frictional force.

The result is not a close run thing. I'm not suggesting that the belly
flop landing goes a bit further than the normal full braking action
landing. I'm suggesting that it goes a lot further - the coeffecients of
friction of rubber and metal on a typical runway surface are very different.

Regarding grinding actions, they tend to be self limiting - the grinding
bit gets ground off.

As for mocking people - pots and pans?

Sylvia.


Reply With Quote
  #8  
Old 11-22-2004, 01:02 AM
AbsolutelyCertain
Guest
 
Posts: n/a
Default Effect of spoilers on braking


"Sylvia Else" <[Only registered users see links. ].this.address> wrote in message
news:[Only registered users see links. ].this.address...
(inches -
You
because
area.
the
it
necessary to
made a
presented
for
even
different.

You're guessing.


Reply With Quote
  #9  
Old 11-22-2004, 01:05 AM
AbsolutelyCertain
Guest
 
Posts: n/a
Default Effect of spoilers on braking


"Rich Ahrens" <[Only registered users see links. ]> wrote in message
news:41a13117$0$12467$[Only registered users see links. ]...

Exactly. She made a WAG, and she will never be able to prove that she's
right, IMO. But that won't stop her from resorting to browbeating and
snidery now to cover up for the fact that she really doesn't know how far
that belly-landed airplane would slide.

This is a whole new troll tactic, and I have to admit, it's inventive. But
a troll is still a troll.


Reply With Quote
  #10  
Old 11-22-2004, 01:39 AM
Sylvia Else
Guest
 
Posts: n/a
Default Effect of spoilers on braking



Rich Ahrens wrote:

Yes.

Sylvia.


Reply With Quote
Reply

Tags
braking , effect , spoilers


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
What is Gravity? sdr@sdrodrian.com Physics Forum 1 01-27-2008 02:53 PM
Photoelectric effect is not quantized h_v_ansari@yahoo.com Physics Forum 1 10-26-2006 01:23 PM
Logical justification of the Hall effect h_v_ansari@yahoo.com Physics Forum 1 10-19-2006 07:23 PM
Meissner Effect preclude a "self-created current" ?? Archimedes Plutonium Chemistry Forum 6 10-11-2003 12:14 PM


All times are GMT. The time now is 12:59 PM.


Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Copyright 2005 - 2012 Molecular Station | All Rights Reserved
Page generated in 0.19076 seconds with 16 queries