motorgliders as towplanes

A glider in steady free flight is always descending through the air in
which it is flying. If you can fly in air that is going up as fast or
faster than the sink rate of the glider, then you can gain potential
height energy. Isn't that what soaring flight is all about?

Derek Copeland
(Qualified gliding instructor with Gold C and 3 Diamonds BTW)

At 22:07 18 March 2009, The Real Doctor wrote:
On 17 Mar, 19:04, Darryl Ramm wrote:

Say what? Gravitational potential energy *increases* not decreases as
the glider climbs.

Sorry, typo.

And that "store" is the transfer mechanism that allows the glider to
glide.

No it's not. The gravity force is necessary, but it's perfectly
possible to soar for extended periods and distances without adding to
or drawing from the potential energy store. It happens any time we fly
level - along a wavebar, running a ridge, following a cloud street.

There is no other mechanism. With no gravity, even with an
atmosphere (which would be difficult to arrange), your glider could
not glide.

You miss, as so many people do, the point. Because the force of
gravity is necessary for a glider to work, people assume that gravity
somehow "powers" the flight. Which it does not.

Guy's this has wandered into junior-high school level physics.

No, it has wandered into junior high school level misconceptions about
physics!

Here's another one for you. Does a glider turn (normally) by (a)
rolling (b) pitching (c) yawing or (d) other?


Ian

Having read all 170 posts in this thread I am still happily ignorant of the
theory of flight!

Jim

On 19 Mar, 07:45, Jim White wrote:
Having read all 170 posts in this thread I am still happily ignorant of the
theory of flight!

Aircraft stay up because they're afraid of the ground.

That said, you might find it interesting to get hold of the TV
programme and video which the Open University made on gliding
mathematics some years ago. The course in question, "MST207 Applied
Mathematics" is defunct, but a fair number of copies of the AV
material lurk around gliding clubs.

Ian

Ok I'll bite.....

Turning flight is accelerated flight, so the forces acting on the glider
are "unbalanced".

Since I am a firm believer that you can't change gravity (although some
of you out there try to in your analysis), gravity remains constant. If
we keep airpseed constant then drag should not change either. So we have
to change lift in order to get acceleration.

So I say we have to change the direction of lift, inward toward the center
of the circle. (centripetal force). This should be accomplished by
rolling.

Since we have added a "Horizontal component of lift", total lift must be
increased. This normally requires additional nose up force on stick or
trim. (angle of attack) You might call this pitch, but I don't think
the actual pitch attitude changes, just the stick forces and angle of
attack.

Yawing can be conidered to be necessary, or at least correction for
adverse yaw.

But to rephrase the question,

Q) What force causes a glider to turn.
A) Lift

Cookie

Here's another one for you. Does a glider turn (normally) by (a)rolling
(b) pitching (c) yawing or (d) other?


Ian

At 12:30 19 March 2009, Bob Cook wrote:

Clearly not a geologist then. I wonder why they do gravity surveys if it
is a constant?

Ok I'll bite.....

Since I am a firm believer that you can't change gravity (although some
of you out there try to in your analysis), gravity remains constant.

Further to earlier post. Gravity is measured in Gals (in honour of
Galileo), 1 Gal = an acceleration of 1 cm/sec2. Average gravity at the
surface is 980.654321 Gals (or so). At the poles it is more at about 983
Gals and on equatorial mountain tops only 977 Gals - a difference of about
0.6%. There are significant local variations. Now if we start to take
height into account...

By the way, what happened to the discussion about slow tows?


At 14:15 19 March 2009, Big Wings wrote:
At 12:30 19 March 2009, Bob Cook wrote:

Clearly not a geologist then. I wonder why they do gravity surveys if
it
is a constant?

Ok I'll bite.....

Since I am a firm believer that you can't change gravity (although
some
of you out there try to in your analysis), gravity remains constant.

On Thu, 19 Mar 2009 17:00:04 +0000, Big Wings wrote:

Further to earlier post. Gravity is measured in Gals (in honour of
Galileo), 1 Gal = an acceleration of 1 cm/sec2. Average gravity at the
surface is 980.654321 Gals (or so). At the poles it is more at about
983 Gals and on equatorial mountain tops only 977 Gals - a difference of
about 0.6%. There are significant local variations. Now if we start to
take height into account...

I notice that's not an SI unit. Is the Gal some sort of engineering or
specialist geological unit? Its a pretty big unit for gravimetry, since
the maximal variation at the earths surface is only 6 Gals.

The SI unit is uM/s^2 (micrometers per sec squared), or 0.1 milliGals,
which looks more in tune with what satellites and aerial surveys are
measuring these days.

By the way, what happened to the discussion about slow tows?

Got too slow and stalled in.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

Dear Big,

You are on to something here. Get one of those geo surveys, and fly your
glider only over areas of higher gravity. This extra gravity will give
your glider extra power, and you will be the best glider pilot!

Cookie

At 14:15 19 March 2009, Big Wings wrote:
At 12:30 19 March 2009, Bob Cook wrote:

Clearly not a geologist then. I wonder why they do gravity surveys if
it
is a constant?

Ok I'll bite.....

Since I am a firm believer that you can't change gravity (although
some
of you out there try to in your analysis), gravity remains constant.

At 00:45 20 March 2009, Bob Cook wrote:

You are on to something here. Get one of those geo surveys, and fly
your
glider only over areas of higher gravity. This extra gravity will give
your glider extra power, and you will be the best glider pilot!

Well, that should work. The important thing is that you have to find and
use thermals only in *low* gravity areas, and then do your inter-thermal
cruising in the *high* gravity areas. Next best thing to dynamic
soaring.

Jim Beckman

Bob Cook wrote:
Since I am a firm believer that you can't change gravity (although
some of you out there try to in your analysis)

They're just using thought experiments:

http://en.wikipedia.org/wiki/Thought_experiment