motorgliders as towplanes

On 19 Mar, 12:15, Bob Cook wrote:

Spoilers redistribute lift, but not reduce lift.

They reduce the lift over part of the wing. Whether the overall lift
increases, decreases or stays the same depends on what the pilot does.

Flaps change the coeffecient of lift, but not lift.

If you keep everything else the same then they do change lift. Every
tried dumping your landing flap just before the flare ...?

Q) *Two gliders, one is 40:1 racer and glider two is 20:1 trainer. Both
weigh 800#

Glider one has twice the lift of glider two. *True or flase and why.

Depends what they are doing.

Ian

OK. badly worded question.

Here I was trying to point out that DRAG is the major difference between a
40:1 glider and a 20: glider. Not lift, not gravity.


Drag determines the direction of flight.

More drag= steeper glide (spoilers, flaps)

Less drag = flatter glide

Cookie



At 18:23 19 March 2009, The Real Doctor wrote:
On 19 Mar, 12:15, Bob Cook wrote:

Spoilers redistribute lift, but not reduce lift.

They reduce the lift over part of the wing. Whether the overall lift
increases, decreases or stays the same depends on what the pilot does.

Flaps change the coeffecient of lift, but not lift.

If you keep everything else the same then they do change lift. Every
tried dumping your landing flap just before the flare ...?

Q) =A0Two gliders, one is 40:1 racer and glider two is 20:1 trainer.
Both
weigh 800#

Glider one has twice the lift of glider two. =A0True or flase and why.

Depends what they are doing.

Ian

Ian,

If we draw vector force diagrams of two identical gliders, one with flaps
extended, and the other with flaps retracted, we can easily see that
"lift" is essentially the same in both cases.

The direction of flight will be steeper with flaps extended, and drag will
be signifigantly greater.

As for spoilers, vector diagrams will also show lift is not reduced
(except for a tiny, tiny amount) but drag is greatly increased and the
fligth path is steepened.

Remember were are talking about stabilized unaccelerated flight here.

Sudden application or retraction of flaps might have MOMENTARY changes in
lift, but not once stabilized unacellerated flight is resumed.

Misconceptions commonly found in publications and professed by many
"experts":

Gravity powers a glider and provides forward motion.
Flaps increase lift
Spoilers reduce lift
Centrifugal force turns a glider
Aircraft climb due to increased lift
Aircraft descend due to reduced lift

Any more?

Cookie



At 01:00 20 March 2009, Bob Cook wrote:
OK. badly worded question.

Here I was trying to point out that DRAG is the major difference between
a
40:1 glider and a 20: glider. Not lift, not gravity.


Drag determines the direction of flight.

More drag= steeper glide (spoilers, flaps)

Less drag = flatter glide

Cookie



At 18:23 19 March 2009, The Real Doctor wrote:
On 19 Mar, 12:15, Bob Cook wrote:

Spoilers redistribute lift, but not reduce lift.

They reduce the lift over part of the wing. Whether the overall lift
increases, decreases or stays the same depends on what the pilot does.

Flaps change the coeffecient of lift, but not lift.

If you keep everything else the same then they do change lift. Every
tried dumping your landing flap just before the flare ...?

Q) =A0Two gliders, one is 40:1 racer and glider two is 20:1 trainer.
Both
weigh 800#

Glider one has twice the lift of glider two. =A0True or flase and
why.

Depends what they are doing.

Ian

On 20 Mar, 01:15, Bob Cook wrote:

If we draw vector force diagrams of two identical gliders, one with flaps
extended, and the other with flaps retracted, we can easily see that
"lift" is essentially the same in both cases.

What happens if you extend the flaps on a glider while keeping
everything else (AoA, airspeed) constant?

Ian

That would not be possible......only "momentary". You can't "keep"
"everything else" constant.

Yes, there would be a "momentary" increase in lift......but......

Glider would experience "acceleration", change in velocity, and or
direction. (Most likely glider would "nose up" (change in direction)
then "slow down" (change in velocity) finally resume steady flight with
greater drag giving steeper glide angle.

Once "stabilized" flight is resumed, vector analysis shows flaps do not
increase lift. Yes, the coefficient of lift has changed but not the
actual lift (other than a really, really tiny reduction due to new flgith
path)

Similar for spoilers

Cookie




At 09:40 20 March 2009, The Real Doctor wrote:
On 20 Mar, 01:15, Bob Cook wrote:

If we draw vector force diagrams of two identical gliders, one with
flaps
extended, and the other with flaps retracted, we can easily see that
"lift" is essentially the same in both cases.

What happens if you extend the flaps on a glider while keeping
everything else (AoA, airspeed) constant?

Ian

You guys have proven 2 fundamental truths.

1) In any engineering discussion. If you don't define terms at the
start, you just chase yourself around in a circle.

2) Pilots don't need to know much about aerodyanmics to fly well.

Oh yeah,

3) Flight instructors explain these things more to make a point than
to be accurate :-)


Todd Smith
3S

On 20 Mar, 13:29, wrote:
You guys have proven 2 fundamental truths.

1) *In any engineering discussion. *If you don't define terms at the
start, you just chase yourself around in a circle.

What, exactly, do you mean by "circle"?

2) *Pilots don't need to know much about aerodyanmics to fly well.

I suspect it only distracts from the task at hand.

3) Flight instructors explain these things more to make a point than
to be accurate :-)

And how. I just wish they'd tell the rest of us what the point is ...

Ian

A physicist acquantance who wrote a book on Newton and aerodynamics said
that the mathematics was taken over from electrical theory because the
equations balanced, but that they don't explain what is cause and what is
effect. That's the feeling I get when you start talking about something
called theta as if it were proof.

Seems to me we have a new theology going here -- something akin to
pre-milleniumism versus post-milleniumism.


At 13:29 20 March 2009, wrote:
You guys have proven 2 fundamental truths.

1) In any engineering discussion. If you don't define terms at the
start, you just chase yourself around in a circle.

2) Pilots don't need to know much about aerodyanmics to fly well.

Oh yeah,

3) Flight instructors explain these things more to make a point than
to be accurate :-)


Todd Smith
3S

"The Real Doctor" wrote in message
...
On 20 Mar, 01:15, Bob Cook wrote:

If we draw vector force diagrams of two identical gliders, one with flaps
extended, and the other with flaps retracted, we can easily see that
"lift" is essentially the same in both cases.

What happens if you extend the flaps on a glider while keeping
everything else (AoA, airspeed) constant?

Ian

I have really been trying to avoid getting involved in this thread. It seem
too much like "I'm smart and you're not". However, I just want to point out
that to maintain the same AoA while lowering the flaps will require the
pilot to lower the nose of the aircraft. This is due to the change to the
wing's effective angle of incidence.

I really question if it is posible to lower to flaps while keeping the AoA
and airspeed constant. I know that maintaining a constant airspeed of 50
kts while lowering the flaps to 90 degrees on my HP-14 results in a 45+
degree nose down attitude. I am positive the wing's AoA changes while doing
so.

Respectfully,

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