Aerodynamics of carrying water

Reynolds number is not an aerodynamic phenomenon. It's a=20
dimensionless
quantity which is useful in characterising certain aerodynamic=3D20
phenomena, principally those which involve a laminar - turbulent=3D20
transition.

Perhaps I should have said "Reynolds number which characterises
certain
aerodynamic phenomena" and it is a fact that the slope of the lift
coefficient increases with increasing Reynolds number.

What do you mean by "slope of the lift coefficient"? With respect to=20
what?

Ian

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~

the standard curve: plot lift coefficient against alpha (angle of
attack), for the same alpha flying at a higher speed increases the
Reynolds number, at this higher speed the slope is increased slightly
over what it was at the lower speed. It's a well known effect.


Rgds,

Derrick Steed

Subject: Aerodynamics of carrying water
Author:
Date/Time: 17:30 16 October 2005
------------------------------------------------------------

l/d max occurs when induced and pressure drag are the same, not at 75%
induced. (interference drag is (per definition) negociated)

When 75% of the drag is induced you`r flying at Vy-min (min sink)

------------------------------------------------------------

I stand corrected. Apologies.

http://www.av8n.com/how/htm/4forces.html#sec-powers

Rory

In article ,
Rory O'Conor wrote:

Subject: Aerodynamics of carrying water
Author:
Date/Time: 17:30 16 October 2005
------------------------------------------------------------

l/d max occurs when induced and pressure drag are the same, not at 75%
induced. (interference drag is (per definition) negociated)

When 75% of the drag is induced you`r flying at Vy-min (min sink)

------------------------------------------------------------

I stand corrected. Apologies.

http://www.av8n.com/how/htm/4forces.html#sec-powers

Both the 50% and 75% numbers are "wrong" in the sense that either one
could be correct for some particular aircraft, but neither is correct
for all aircraft.


The correct statement is that l/d max occurs at the speed at which a
small change of speed (a small increase, say) causes an increase in the
parasitic drag and an exactly equal decrease in the induced drag. In
graphical terms, it is the point where the slope of one curve is the
same as the clope of the other, but one is going up and the other is
going down. And in the Fig 4.15 in in the link above that is pretty
clearly right around 65 knots or so.

And, yes, it appears that that is at the point, for that aircraft, where
about 75% of the drag is induced drag. But you could make some
modification to the aircraft that moved one (or both) of the curves up
or down (if you could do that without changing the shape of the curve)
and the minimum would still be at the same speed, but the proportion of
induced to total drag could be almost anything.

--
Bruce | 41.1670S | \ spoken | -+-
Hoult | 174.8263E | /\ here. | ----------O----------

Bruce Hoult schreef:

In article ,
Rory O'Conor wrote:

Subject: Aerodynamics of carrying water
Author:
Date/Time: 17:30 16 October 2005
------------------------------------------------------------

l/d max occurs when induced and pressure drag are the same, not at 75%
induced. (interference drag is (per definition) negociated)

When 75% of the drag is induced you`r flying at Vy-min (min sink)

------------------------------------------------------------

I stand corrected. Apologies.

http://www.av8n.com/how/htm/4forces.html#sec-powers

Both the 50% and 75% numbers are "wrong" in the sense that either one
could be correct for some particular aircraft, but neither is correct
for all aircraft.


The correct statement is that l/d max occurs at the speed at which a
small change of speed (a small increase, say) causes an increase in the
parasitic drag and an exactly equal decrease in the induced drag. In
graphical terms, it is the point where the slope of one curve is the
same as the clope of the other, but one is going up and the other is
going down. And in the Fig 4.15 in in the link above that is pretty
clearly right around 65 knots or so.

And, yes, it appears that that is at the point, for that aircraft, where
about 75% of the drag is induced drag. But you could make some
modification to the aircraft that moved one (or both) of the curves up
or down (if you could do that without changing the shape of the curve)
and the minimum would still be at the same speed, but the proportion of
induced to total drag could be almost anything.

--
Bruce | 41.1670S | \ spoken | -+-
Hoult | 174.8263E | /\ here. | ----------O----------

Not true.

Drag varies with 1/Cl^2+V^2. converting to V means 1/V^2+V^2. Changing
that to 2/V^2+V^2 means a higher speed at which l/dmax occurs but both
are half. (Just try to plot it...)

Later more..

The beauty of the soapbox derby example--like Nigel's--is that it points out
that the glide slope is the same. With the added weight you have the same
glide slope but a higher speed.
The other way to make the soapbox derby car go faster was to reduce drag....
"Eric Greenwell" wrote in message
...
Nyal Williams wrote:

The best illustration used to be: Remember when you
rode your coaster wagon downhill alone and also with
a buddy in it? It always went faster with two people.

And I suppose it would go faster uphill, with two people pulling it back:
not a very good analogy, I think, since the heavy glider will climb more
slowly. "Going faster" isn't the issue, but instead, why heavy is better
than light. After all, both the heavy and the light glider can fly the
same speeds right up to Vne. It's because the heavy glider can cruise
faster for any given L/D, and (in strong conditions) loses relatively
little in the climb.

The aerodynamic reason it can cruise faster at any given L/D is that the
angle of attack determines the L/D, and the heavy glider needs extra
airspeed to generate the extra lift for that weight.

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA