motorgliders as towplanes

I'd like to turn this around since I'm not a physicist or an engineer.
What force causes a ball to roll down an inclined plane?


At 00:00 18 March 2009, Bob Cook wrote:
At 18:16 17 March 2009, The Real Doctor wrote:

Ian,

YOU did use the term "power" correctly.

What I didn't like about it was that the question I posed referred to
force. (OK, so you gave us some additional information)

I agree that a sailplane, in gliding flight, in still air, has no
"power" at all. (Although, as you said, some wrongly believe that
gliders are "gravity powered")

By some of the responses, I think I am correct in assuming that some
confuse power, energy, and force.

So I again ask, (not to Ian, but to some of the others who answered my
question with "gravity",) how can gravity alone, a force which acts
vertically downward, impart forward motion to a glider or anything for
that matter?


Cookie



I don't. I used "power" because I meant "power"!

Ian

On Mar 17, 5:00*pm, Bob Cook wrote:
At 18:16 17 March 2009, The Real Doctor wrote:

Ian,

YOU did use the term "power" correctly.

What I didn't like about it was that the question I posed referred to
force. *(OK, so you gave us some additional information)

I agree that a sailplane, in gliding flight, in still air, *has no
"power" at all. *(Although, as you said, some wrongly believe that
gliders are "gravity powered")

By some of the responses, I think I am correct in assuming that some
confuse power, energy, and force.

So I again ask, (not to Ian, but to some of the others who answered my
question with "gravity",) how can gravity alone, a force which acts
vertically downward, impart forward motion to a glider or anything for
that matter?

Cookie



I don't. I used "power" because I meant "power"!

Ian



Sigh. No a glider moving through still air even at a constant rate
expends power. A glider has gravitational potential energy, the rate
it converts that potential energy to overcome drag is an expenditure
of power and you can talk about that as horsepower or kW etc. We plot
these things now as polars, just with different display units.

As I explained, Gravity provides the energy but the forward motion
comes from the forward component of the lift vector. The large part of
the lift vector is resisting the pull of gravity and as a side effect
the horizontal part moves the glider forward, and conveniently the
glider needs to move forward to create lift. Lucky thing that.

Analogous to the chicken sliding down a ramp, gravity there also only
acts through the center of mass yet the chicken does not fall
vertically. I think this is obvious to any chicken sliding down a
ramp. You need a chicken and a ramp and do the experiment then ask the
chicken to explain why.

Darryl

Darryl Ramm wrote:
Analogous to the chicken sliding down a ramp, gravity there also only
acts through the center of mass yet the chicken does not fall
vertically. I think this is obvious to any chicken sliding down a
ramp. You need a chicken and a ramp and do the experiment then ask the
chicken to explain why.

That analogy is most fowl.

I felt compelled to google the words chicken and gliders and found this:

http://blog.modernmechanix.com/2006/...n-glider-nose/

That's an excellent analogy.

Mike Schumann

"Nyal Williams" wrote in message
...
I'd like to turn this around since I'm not a physicist or an engineer.
What force causes a ball to roll down an inclined plane?


At 00:00 18 March 2009, Bob Cook wrote:
At 18:16 17 March 2009, The Real Doctor wrote:

Ian,

YOU did use the term "power" correctly.

What I didn't like about it was that the question I posed referred to
force. (OK, so you gave us some additional information)

I agree that a sailplane, in gliding flight, in still air, has no
"power" at all. (Although, as you said, some wrongly believe that
gliders are "gravity powered")

By some of the responses, I think I am correct in assuming that some
confuse power, energy, and force.

So I again ask, (not to Ian, but to some of the others who answered my
question with "gravity",) how can gravity alone, a force which acts
vertically downward, impart forward motion to a glider or anything for
that matter?


Cookie



I don't. I used "power" because I meant "power"!

Ian

It is past mid-night and all this is making me more goofy than usual;
howzabout renaming the thread? (Some of us are certainly tripped up.)

OK, I apologize.


At 03:30 18 March 2009, Mike Schumann wrote:
That's an excellent analogy.

Mike Schumann

"Nyal Williams" wrote in message
...
I'd like to turn this around since I'm not a physicist or an
engineer.
What force causes a ball to roll down an inclined plane?


At 00:00 18 March 2009, Bob Cook wrote:
At 18:16 17 March 2009, The Real Doctor wrote:

Ian,

YOU did use the term "power" correctly.

What I didn't like about it was that the question I posed referred to
force. (OK, so you gave us some additional information)

I agree that a sailplane, in gliding flight, in still air, has no
"power" at all. (Although, as you said, some wrongly believe that
gliders are "gravity powered")

By some of the responses, I think I am correct in assuming that some
confuse power, energy, and force.

So I again ask, (not to Ian, but to some of the others who answered my
question with "gravity",) how can gravity alone, a force which acts
vertically downward, impart forward motion to a glider or anything for
that matter?


Cookie



I don't. I used "power" because I meant "power"!

Ian

The resultant of TWO forces.

The force of gravity downward, plus the force of the ramp pushing upward
and forward, "normal" (at a right angle) to the ramp surface.

This resultant force is parallel to the ramp. When this force is
unbalanced, the ball will begin to roll and pick up speed until drag
becomes equal to that resultant force. Then velocity will remain
constant, and all forces are in balance, and the sum of the forces =
zero.

For glider, substitute lift for the ramp.

Cookie



"Nyal Williams" wrote in message
...
I'd like to turn this around since I'm not a physicist or an
engineer.
What force causes a ball to roll down an inclined plane?

Well, at least I did learn a lot from the previous thread, thanks mostly to
Ian who helped me "tidy up" some of my conceptions.

Yes this is Jr High physics. I think if we took the final exam, Ian would
get an "A", while I would get a "C" and most of the guys would do
worse!


Since everybody liked my "gravity" question so much, here is more from
my pet peeve department.

Q) Two identical gliders on final approach. Glider A has spoilers closed.
Glider B opens spoilers. Glider B will make a steeper approach because
"spoilers reduce lift". True or false? And why.

Q) Two identical gliders on final approach. Glider A has flaps retracted.
Glider B has flaps extended. Glider B will make a steeper approach
because "flaps increase lift". True or false? And why.

Cookie

At 18:22 17 March 2009, Bob Whelan wrote:

Yebbut...imagine a glider magically inserted into earth's atmosphere
after global warming has removed all grabbity. What gets it moving?

It won't move. Why would it?

Jim Beckman

In free unaccelerated flight with no thrust, i.e. no aerotow, winch, or
turbo, a glider IS essentially gravity powered. The resultant force of
gravity plus wing lift, angled very slightly forward, opposes drag. Thus a
glider runs down a very slight slope through the air. The less drag there
is, the flatter the glide angle becomes.

Both airbrakes and large positive flap angles increase the drag, so the
glider has to run down a steeper slope to maintain speed.

Airbrakes both reduce lift, by disrupting the airflow over part of the
wing, and increase drag, so the answer to that question is obvious.

Large amounts of positive flap increases lift, but also increases drag to
a much greater extent.

Derek Copeland


At 12:30 18 March 2009, Bob Cook wrote:
Well, at least I did learn a lot from the previous thread, thanks mostly
to
Ian who helped me "tidy up" some of my conceptions.

Yes this is Jr High physics. I think if we took the final exam, Ian
would
get an "A", while I would get a "C" and most of the guys would do
worse!


Since everybody liked my "gravity" question so much, here is more from
my pet peeve department.

Q) Two identical gliders on final approach. Glider A has spoilers
closed.
Glider B opens spoilers. Glider B will make a steeper approach because
"spoilers reduce lift". True or false? And why.

Q) Two identical gliders on final approach. Glider A has flaps
retracted.
Glider B has flaps extended. Glider B will make a steeper approach
because "flaps increase lift". True or false? And why.

Cookie

"Derek Copeland" wrote in message
...
In free unaccelerated flight with no thrust, i.e. no aerotow, winch, or
turbo, a glider IS essentially gravity powered. The resultant force of
gravity plus wing lift, angled very slightly forward, opposes drag. Thus a
glider runs down a very slight slope through the air. The less drag there
is, the flatter the glide angle becomes.

Both airbrakes and large positive flap angles increase the drag, so the
glider has to run down a steeper slope to maintain speed.

Airbrakes both reduce lift, by disrupting the airflow over part of the
wing, and increase drag, so the answer to that question is obvious.

Large amounts of positive flap increases lift, but also increases drag to
a much greater extent.

Derek Copeland


Just to add a bit to Derek's analysis. I fly a HP-14 which doesn't have
spoilers and totally relies of large span flaps for glide slope control.
The increase in lift is negligible as the flaps are extended beyond 45
degrees to 90 degrees. However, the increase in the drag produced is
massive.

At 50 kts with flaps set at 0 my HP-14 has a glide ratio about 38:1;
however, with the flaps at 90 degrees the glide ratio at 50 kts is some
where between 2:1 to 3:1.

http://www.soaridaho.com/Schreder/St...r_on_Flaps.htm

Wayne
HP-14 "6F"
http://www.soaridaho.com/Schreder


At 12:30 18 March 2009, Bob Cook wrote:
Well, at least I did learn a lot from the previous thread, thanks mostly
to
Ian who helped me "tidy up" some of my conceptions.

Yes this is Jr High physics. I think if we took the final exam, Ian
would
get an "A", while I would get a "C" and most of the guys would do
worse!


Since everybody liked my "gravity" question so much, here is more from
my pet peeve department.

Q) Two identical gliders on final approach. Glider A has spoilers
closed.
Glider B opens spoilers. Glider B will make a steeper approach because
"spoilers reduce lift". True or false? And why.

Q) Two identical gliders on final approach. Glider A has flaps
retracted.
Glider B has flaps extended. Glider B will make a steeper approach
because "flaps increase lift". True or false? And why.

Cookie