Aerodynamics of carrying water

Hi Guys.

I think those numbers are very optimistic. I once heard the pilots of the
Boeing 767 that glided to a landing in Canada describe (at an SSA
convention) how they were surprised by how back the glide ratio was with the
engines out. I believe they said that the manuals numbers were actually
calculated with the engines at idle, or at an rpm setting that overcomes the
drag caused by the engines. They are very big drag devices when not
providing thrust.

Good Soaring,

Paul Remde

"Bruce Hoult" wrote in message
...
In article ,
Jack wrote:

Andy wrote:

Did you know a DC-10 has a glide ratio nearly as good (bad) as a 2-33.
They get over 20:1 but it's at over 200kts.

Cite?

Don't know about the DC-10, but the ancient 707 was about 19:1.

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

A valid response of course. I was given this information years ago
when I worked in Douglas flight test. The numbers I was given were more
precise than I quoted but I don't remember exactly what they were.
MD11 and MD10 CFM don't include the data and that is all I have access
to now. Paul may be correct that this is for an engines idle case. I
expect to be spending a lot of time in MD-10 sims in the next few
months. If I remember I'll get a few data points for all engine out
glide.

Andy

Aerodynamics (polars) will show the affect of ballast but the good old
E=MCC explains it.
Bela

Bela wrote:
Aerodynamics (polars) will show the affect of ballast but the good old
E=MCC explains it.
Bela

No, it does not. The performance increase with ballast has very little
to do with the increase in energy due to the added weight. The reason is
purely aerodynamic.

Performance speeds increase by the square root of the weight change
ratio. If a 750 pound glider and pilot gets its best glide ratio of 40:1
at 50kts, adding 400 pounds water changes the weight to 1150, and so the
new best glide speed is sqrt(1150/750) x 50 = 61.9kts. The best glide
ratio of 40:1 stays the same (ignoring the secondary effects of Reynolds
number and coefficient of lift increases).

Tony V

.......(ignoring the secondary effects of Reynolds
number and coefficient of lift increases).

Sigh, that should read "second order effects", of course.

Tony V.

"Bela" wrote in message
ups.com...
Aerodynamics (polars) will show the affect of ballast but the good old
E=MCC explains it.
Bela

Only if the glider is annihilated to form energy (say a collision with
similar antimateria glider)

hannu

"Performance speeds increase by the square root of the weight change
ratio. "

Why do they?

Andy

and there's your answer, the new performance speed V2 at the
new weight W2 and the original coefficient of lift/AOA/glide
ratio is sqrt(W2/W1) times the old performance speed V1 at
the old weight W1.


Thanks, Todd. For those interested in this stuff but who would prefer to
do without calculus, a nice book is "Flight Theory for pilots" by
Charles E Dole, published by Jeppesen Sanderson Training Products, ISBN
0-89100-432-7. The material that Todd mentions is the first part of
chapter 4, "Lift and Stall". Here's one source:
http://www.avmart.com/itemdetail.asp?pid=2253&cat=48 . A small review of
it on my web site at
http://home.comcast.net/~verhulst/GB...rodynamics.htm

Tony V.

On 11 Oct 2005 06:01:11 GMT, 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.

Who knows anything about coaster wagons anymore?

Think of a 400-pound skier.

rj

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