motorgliders as towplanes

Jim Beckman wrote:
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

Indeed. But I find it easier to magically insert the glider than to
magically turn off gravity. That's why my chicken has a soft landing
place for her eggs.

And being 100% non-facetious in this paragraph, it appears some folks'
misconceptions may have been clarified to various degrees as a result of
this thread...put me in the camp that believes clear thought is a good
thing. Once a person grasps the essential role of gravity in powering
sailplanes, the lifty bits become distinctly easier to grasp, despite
the pesky intrusion of (ahem) plane geometry into resolving resultant
forces.

Regards,
Bob W.

Bob,

If we are gonna play what if.....

What if there was no lift? (like a brick,)

Sure it would move because of gravity, but in what direction? Down! Not
forward!

So tell me again how gravity imparts a forward force to a glider?


Although "no gravity is not possible, "no lift" is easily
demonstrated:

Next time you fly, try this. Push forward on the stick. Keep pushing
until your angle of attack goes to zero (no lift). Tell me which way your
glider flies!

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

Bob Cook wrote:

If we are gonna play what if.....

What if there was no lift? (like a brick,)

Sure it would move because of gravity, but in what direction? Down! Not
forward!

That is correct and demonstrates a useful "thought exercise".


So tell me again how gravity imparts a forward force to a glider?

By itself it cannot. The presence of gravity *and* air are required for
gliding (forward) motion.


Although "no gravity is not possible,

Sure it is. Place your glider in outer space. Likely? No. Possible?
Certainly.


"no lift" is easily demonstrated:

And lift(as we are using the term) without gravity is not possible.

Regards,

-Doug

Doug,

I was about to give you a "gold star" but then found some more
misconceptions.

There is gravity in outer space. Anywhere there is matter, with mass,
there is Gravity. The moon is held in orbit by the earth's gravity.
Earth in solar orbit, etc.

Lift would be possible without gravity, (if it was possible to have no
gravity.) If you placed an airplane in air, but no gravity, and provided
a propelling force (engine), the wing could certainly produce lift without
gravity . Without gravity, lift would be unbalanced, resulting in your
aircraft doing successive loops!

Air (or other "fluid" if we are taking this into outer space), is needed
to provide lift. But the forces involved in gliding flight are still
three.....lift, drag, and gravity.

Although thought provoking exerceses, better to say "what is" than
"what if.".....

Cookie





At 01:39 20 March 2009, Doug Hoffman wrote:
Bob Cook wrote:

If we are gonna play what if.....

What if there was no lift? (like a brick,)

Sure it would move because of gravity, but in what direction? Down!
Not
forward!

That is correct and demonstrates a useful "thought exercise".


So tell me again how gravity imparts a forward force to a glider?

By itself it cannot. The presence of gravity *and* air are required for

gliding (forward) motion.


Although "no gravity is not possible,

Sure it is. Place your glider in outer space. Likely? No. Possible?
Certainly.


"no lift" is easily demonstrated:

And lift(as we are using the term) without gravity is not possible.

Regards,

-Doug

Bob Cook wrote:
Doug,

I was about to give you a "gold star" but then found some more
misconceptions.

There is gravity in outer space. Anywhere there is matter, with mass,
there is Gravity. The moon is held in orbit by the earth's gravity.
Earth in solar orbit, etc.

You are picking knits and missing the overall points. Clearly I meant
place it in space where gravity is negligible.


Lift would be possible without gravity, (if it was possible to have no
gravity.) If you placed an airplane in air, but no gravity, and provided
a propelling force (engine), the wing could certainly produce lift without
gravity . Without gravity, lift would be unbalanced, resulting in your
aircraft doing successive loops!

Another knit. This discussion is about *gliding*.


Air (or other "fluid" if we are taking this into outer space), is needed
to provide lift. But the forces involved in gliding flight are still
three.....lift, drag, and gravity.

Although thought provoking exerceses, better to say "what is" than
"what if.".....

OK Bob. You want to see things just one way and apparently nothing else
anyone says is going to sway you. No problem here. Have fun. I think
I am done with this.

Regards,

-Doug

Doug,

You're the one who took the coversation into aouter space, not me.

Yes, I only look at this one way. In physics, its black or white,there is
pretty much not a lot of "gray area".

But I think you got my point that the question on the Bronze Badge exam is
flawed, and none of the answers are correct.

Cookie



At 04:17 20 March 2009, Doug Hoffman wrote:
Bob Cook wrote:
Doug,

I was about to give you a "gold star" but then found some more
misconceptions.

There is gravity in outer space. Anywhere there is matter, with mass,
there is Gravity. The moon is held in orbit by the earth's gravity.
Earth in solar orbit, etc.

You are picking knits and missing the overall points. Clearly I meant
place it in space where gravity is negligible.


Lift would be possible without gravity, (if it was possible to have no
gravity.) If you placed an airplane in air, but no gravity, and
provided
a propelling force (engine), the wing could certainly produce lift
without
gravity . Without gravity, lift would be unbalanced, resulting in
your
aircraft doing successive loops!

Another knit. This discussion is about *gliding*.


Air (or other "fluid" if we are taking this into outer space), is
needed
to provide lift. But the forces involved in gliding flight are still
three.....lift, drag, and gravity.

Although thought provoking exerceses, better to say "what is" than
"what if.".....

OK Bob. You want to see things just one way and apparently nothing else

anyone says is going to sway you. No problem here. Have fun. I think
I am done with this.

Regards,

-Doug

On 20 Mar, 01:39, Doug Hoffman wrote:
Bob Cook wrote:

Although "no gravity is not possible,

Sure it is. *Place your glider in outer space. *Likely? *No. *Possible?
* Certainly.

Or just fly a vomit-comet style ballistic trajectory.

And lift(as we are using the term) without gravity is not possible.

Aircraft in a 90 degree bank can still produce lift ...

Ian

The Real Doctor wrote:
On 20 Mar, 01:39, Doug Hoffman wrote:

And lift(as we are using the term) without gravity is not possible.

Aircraft in a 90 degree bank can still produce lift ...

Without gravity how will you get the glider into a bank (or even to
move)? Answer = not possible.

Regards,

-Doug

On 20 Mar, 14:38, Doug Hoffman wrote:
The Real Doctor wrote:
On 20 Mar, 01:39, Doug Hoffman wrote:
And lift(as we are using the term) without gravity is not possible.

Aircraft in a 90 degree bank can still produce lift ...

Without gravity how will you get the glider into a bank (or even to
move)? *Answer = not possible.

An engine. You'll notice that I wrote "aircraft" and not "gliders"...

Ian