Ground effect effectiveness

I haven't found a decent reference for this -- can anyone help?

Consider a clean low speed airplane -- maybe one of the kit built ones.
Does anyone have some quantitative measure of how much drag is reduced
if the airplane is flown say half or quarter of a wingspan above the
ocean?

Would we be talking about a few percent less drag, or is it a big
number, like 30%? Sea gulls and other long winged birds tend to fly
just above the water, ducks and geese like to reduce drag by flying in
vees, but don't often cruise just above the water.

References would be helpful: I hate having stories I write wrong for
technical reasons.

On 7 Jan 2007 09:11:36 -0800, "Tony" wrote in
.com:

I haven't found a decent reference for this -- can anyone help?

What you seek is probably contained within this great resource:
http://aerodyn.org/summary.html

Tony wrote:
I haven't found a decent reference for this -- can anyone help?

Consider a clean low speed airplane -- maybe one of the kit built ones.
Does anyone have some quantitative measure of how much drag is reduced
if the airplane is flown say half or quarter of a wingspan above the
ocean?

Would we be talking about a few percent less drag, or is it a big
number, like 30%? Sea gulls and other long winged birds tend to fly
just above the water, ducks and geese like to reduce drag by flying in
vees, but don't often cruise just above the water.

References would be helpful: I hate having stories I write wrong for
technical reasons.

There was an article in Soaring magazine years ago about some tests
done at Edwards AFB by USAF test pilot students on ground effects -
using a Blanik and a Grob-103, I think.

That might be available somewhere - there is a Soaring directory
somewhere, try SSA.org.

In gliding, especially with state of the art gliders (L/D in the 40 to
60 range), failure of your landing drag devices (dive brakes, 90 degree
flaps, even tail chutes) can be a real emergency - you can float in
ground effect for miles without slowing down, unable to land! And with
wingspans of 50 to 80+ feet, slipping at ground effect altitude is a
dangerous proposition! In the pattern, I would much rather have my
gear fail to extend than my spoilers fail!

A classic glider landing mishap is watching a pilot in a new-to-him
glider float the whole length of the runway raising and lowering the
gear, until he does a "tree-stop" off the far end - the result of
confusing the manual gear handle for the spoiler handle!

Kirk
Ls6-b "66"

What a reference!

Thanks for a great lead -- it will help me avoid making at least some
stupid mistakes. I'm sure to make some others in the story, but it
won't be the fault of this reference.

I doubt that anyone buy into the idea that the because the airplane was
painted sky blue it would be lighter -- but a long wingspan powered
glider 5 feet above the ocean surface: that would work, so long as it
avoids boat masts.

If you see that in a technothriller next year, you can smile knowing
you played a part.





On Jan 7, 12:27 pm, Larry Dighera wrote:
On 7 Jan 2007 09:11:36 -0800, "Tony" wrote in
.com:

I haven't found a decent reference for this -- can anyone help?What you seek is probably contained within this great resource:http://aerodyn.org/summary.html

Aerodynamics for Naval Aviators, page 380, figure 6.9 is a graph of percent
reduction in induced drag coefficient versus ratio of wing height to wing
span.

Bob Gardner

"Tony" wrote in message
oups.com...
I haven't found a decent reference for this -- can anyone help?

Consider a clean low speed airplane -- maybe one of the kit built ones.
Does anyone have some quantitative measure of how much drag is reduced
if the airplane is flown say half or quarter of a wingspan above the
ocean?

Would we be talking about a few percent less drag, or is it a big
number, like 30%? Sea gulls and other long winged birds tend to fly
just above the water, ducks and geese like to reduce drag by flying in
vees, but don't often cruise just above the water.

References would be helpful: I hate having stories I write wrong for
technical reasons.

another great lead -- thanks.

On Jan 7, 1:31 pm, "Bob Gardner" wrote:
Aerodynamics for Naval Aviators, page 380, figure 6.9 is a graph of percent
reduction in induced drag coefficient versus ratio of wing height to wing
span.

Bob Gardner

"Tony" wrote in ooglegroups.com...



I haven't found a decent reference for this -- can anyone help?

Consider a clean low speed airplane -- maybe one of the kit built ones.
Does anyone have some quantitative measure of how much drag is reduced
if the airplane is flown say half or quarter of a wingspan above the
ocean?

Would we be talking about a few percent less drag, or is it a big
number, like 30%? Sea gulls and other long winged birds tend to fly
just above the water, ducks and geese like to reduce drag by flying in
vees, but don't often cruise just above the water.

References would be helpful: I hate having stories I write wrong for
technical reasons.- Hide quoted text -- Show quoted text -

"Tony" wrote in message
oups.com...
I haven't found a decent reference for this -- can anyone help?

Consider a clean low speed airplane -- maybe one of the kit built ones.
Does anyone have some quantitative measure of how much drag is reduced
if the airplane is flown say half or quarter of a wingspan above the
ocean?


If I recall correctly it is about 20%. It is enough that the Russians built
an seaplane with small wings that cruised in ground effect to reduce drag.
It is not just a couple of percent for sure. Your technothriller will be
valid to assume a substantial reduction in drag by flying in ground effect.

Danny Deger

wrote in message
s.com...

Tony wrote:
I haven't found a decent reference for this -- can anyone help?
...
In gliding, especially with state of the art gliders (L/D in the 40 to
60 range), failure of your landing drag devices (dive brakes, 90 degree
flaps, even tail chutes) can be a real emergency - you can float in
ground effect for miles without slowing down, unable to land! And with
wingspans of 50 to 80+ feet, slipping at ground effect altitude is a
dangerous proposition! In the pattern, I would much rather have my
gear fail to extend than my spoilers fail!


http://www.soaridaho.com/Schreder/St...und_Effect.htm

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

"Tony" wrote:

I haven't found a decent reference for this -- can anyone help?

Here's an online reference, including some graphs:

http://www.se-technology.com/wig/htm...en=aero&code=0

There are also a number of real-life examples where ground effect was
beneficial.

One was the Ekranoplan ground effect vehicles that operated in the
Caspian Sea. You can search for that name or the "Caspian Sea Monster"
to learn more about them.

Fighter pilots during WWII would often take advantage of ground effect to
extend their endurance when returning from sorties.

There was also the story of the MATS C97 (military version of the
Stratocruiser) that had its #1 prop separate from the aircraft, and lost
both port engines just past the point-of-no-return on a flight to Hawaii.
Initial calculations by the flight engineer suggested that they would
have to ditch 30 minutes from their destination. The captain jettisoned
all excess weight, and flew in ground effect for six hours, with full
right trim, and having to stand on the right rudder pedal with both feet
for the duration of the flight. They eventually landed safely after a
missed approach with 30 minutes of fuel remaining.

On Jan 7, 12:27 pm, Larry Dighera wrote:
On 7 Jan 2007 09:11:36 -0800, "Tony" wrote in
.com:

I haven't found a decent reference for this -- can anyone help?

What you seek is probably contained within this great resource:http://aerodyn.org/summary.html

On 7 Jan 2007 10:30:52 -0800, "Tony" wrote in
.com:

What a reference!

Yes. I thought so. That's what makes the Internet so marvelous.

Thanks for a great lead -- it will help me avoid making at least some
stupid mistakes.

You're welcome. We can both thank the thoughtful users who are among
the readership of this newsgroup for making us aware of it.

I'm sure to make some others in the story, but it
won't be the fault of this reference.

I doubt that anyone buy into the idea that the because the airplane was
painted sky blue it would be lighter -- but a long wingspan powered
glider 5 feet above the ocean surface: that would work, so long as it
avoids boat masts.

If you see that in a technothriller next year, you can smile knowing
you played a part.

Best of luck with your literary work.

If you'd like to contribute something to rec.aviation.stories I'd be
happy to accept your submissions.