Low approaches in ground effect

John Sinclair wrote in message ...
Bill,
If memory serves me right the 4360 had 4 rows of 9
cylinders for a total of 36 jugs. The aft rows were
spiraled to allow cooling to the rear rows, but even
so, the fourth row would run hotter. (KC-97F --circa
1952)
What was the configuration of the 7755?

http://www.enginehistory.org/NASM/Ly...%20XR-7755.jpg
-Dan



At 13:48 19 October 2004, Bill
Lycoming engineers were confident that the R-7755 could
be developed to
produce 10,000 HP.

I was flying a Ka 7 in a very strong wind condition. At stall speed up wind
it appeard to have no forward ground speed. At 900ft above ground i started
my circuit and at about 700 ft on downwind i passed the start of the runway
and did a base and finals in a slow turn. At finals i looked down to the
start of the runway at about 45degrees. The wind blow me past the runway
(downwind) aprox 300 meters. I realized that i would not make it back at my
rate of decent and forward motion.Before me was nowhere to land as it was
only threes . I decided to change my alltitude for speed and out of the
headwind and into ground effect. The last few moment was nailbiting as i had
to get over 2 fences and a road but made it. My point: If there is no
headwind it will be better to approach at beast glide angle as ground effect
will be slightly cancelled by profile drag due to higer speed. If you have a
strong head wind it will help to get out of the wind and use ground affect.

Regards

Andre

"CV" wrote in message
...

First a disclaimer: I understand the security issues involved
in the following and would not encourage anyone to try this
at home, but I am interested in the theoretical side of it.

Imagine you get things wrong and are caught out low on final,
still a fair distance out, and it looks marginal whether you
are going to reach the runway or not.

One technique I have sometimes heard described is to dive for
the deck and complete the remaining distance in ground effect.
For the sake of the argument we can assume fairly flat ground,
free of obstacles, though not necessarily landable.

The advantages claimed are usually better glide performance in
ground effect and less headwind and absence of downdrafts close
to the ground.

On the other hand you'll be travelling at higher than optimal
airspeed for most of the distance.

I am wondering how much truth there actually is to this
technique. Would it significantly increase your range and
improve your chances of reaching the field or not ?

Would it perhaps work better against a strong wind gradient
(as I suspect it might), and maybe not help a lot in calm
conditions ?

I'd be interested in any hard data/analysis or otherwise
enlightening comments on this.

Please note though, that I am not talking about high-speed
competition finishes, rounded off with a beatup and a sharp
pullup and all the dangers and other issues involved in that.

Cheers CV

The R-7755 had nine 4-cylinder inline water cooled blocks arranged around a
crankcase with a 4 throw crank. The liquid cooled radial was intended for
the pusher configurations of the B-35 and B-36. Engines intended for these
aircraft had an integral contra-rotating propeller gearbox in the nose case.
This is the configuration of the XR-7755 on display at the Air and Space
Museum.

The HK-1 was a tractor installation but liquid cooling would still have been
useful, particularly at high power settings used for water takeoff. Engines
for the HK-1 were to be single rotation.

These were VERY advanced engines with overhead cams, 4 valves/cyl, variable
valve timing and would eventually have had turbo-compounding.

Only the B-36 went on to production but with the 4360's it was so
underpowered that 4 jet engines were added. Had it used the R7755's no jets
would have been needed. Convair didn't design the B-36 to be underpowered,
they were forced to use the Pratt. Even so, I fondly remember the
earthshaking B-flat drone of a B-36.

The most interesting of these giants was the radar stealthy Northrop B-35
flying wing. This was the propeller version that was succeeded by the jet
B-49. With 40,000 HP, the B-35 would have been the fastest, longest range
prop bomber of all time even considering the turboprop TU95 Bear. It could
have carried more then 50,000 pounds of bombs to Europe and returned to
bases in North America. But, like Convair, Northrop was forced to use the
P&W 4360.

The cover story that the B35/B49 were cancelled because of "directional
instability" that made precision bombing impossible was nonsense. Just how
accurate do you have to be with a nuclear weapon? The real reason was that
the nuclear weapons of the time wouldn't fit in the Northrop's bomb bays.
Canceling the bomber for that reason would have tipped the Soviets to the
size of US weapons. Size and weight of nuclear bombs was top secret since
the first generation of ICBMs were then under development. The Northrop
flying wings were dead stable about all axes.

The history makes you appreciate the guts of the Smithsonian to put the
XR-7755 on display at all.

Bill Daniels

"John Sinclair" wrote in message
...
Bill,
If memory serves me right the 4360 had 4 rows of 9
cylinders for a total of 36 jugs. The aft rows were
spiraled to allow cooling to the rear rows, but even
so, the fourth row would run hotter. (KC-97F --circa
1952)
What was the configuration of the 7755?



At 13:48 19 October 2004, Bill
Lycoming engineers were confident that the R-7755 could
be developed to
produce 10,000 HP.

On Tue, 19 Oct 2004 21:50:52 GMT, "Bill Daniels"
wrote:


The history makes you appreciate the guts of the Smithsonian to put the
XR-7755 on display at all.

After the crow they had to eat on the Wright/Langley affair, I imagine
they had no intention of colluding in any more coverups.

rj

Daniel wrote:
CV, a group of test pilot trainees at Edwards AFB did an exhaustive
test on ground effect versus distance as a project during their
course; it was reported in the Feb 1990 SOARING magazine. IIRC, they
found that one had to fly a very precise profile - 0.95g push followed
by 1.05g pull, to a precise height - to see any measurable effect, and
concluded that it was better for the casual flier to fly best
lift/drag speed instead... I think they used a G103. The notation

I see. So if the results as reported here apply to calm conditions
it would mean the ground-effect technique wins out whenever there
is any significant wind gradient.

Where there is wind there is usually a wind gradient, certainly
in strong winds, meaning the ground-effect technique would normally
win against a headwind.

As I said before I totally agree about the security issues. If
you end up in a position where you need this something is already
badly wrong. And if you have the option it would be better to
pick a field you are certain you can reach rather than rely on
these effects.

CV

CV wrote in message ...

I see. So if the results as reported here apply to calm conditions
it would mean the ground-effect technique wins out whenever there
is any significant wind gradient.

Where there is wind there is usually a wind gradient, certainly
in strong winds, meaning the ground-effect technique would normally
win against a headwind.

As I said before I totally agree about the security issues. If
you end up in a position where you need this something is already
badly wrong. And if you have the option it would be better to
pick a field you are certain you can reach rather than rely on
these effects.

CV

Actually, no. If I remember correctly, the test concluded that in
order to achieve any noticeable benefit from ground effect, the glider
had to be flown extremely precisely at VERY low altitude - only a
couple of feet above the ground. None of this "half a wingspan" - so
unless you are stetching your glide over the Bonneville salt flats,
just keeping out of the usual bushes, fences, stray airport dogs, etc
would eliminate any ground effect benefit.

If the wind gradient is that strong, the turbulence at ground level
would make any precise low flying sporting and inefficient, anyway.

I think pilots confuse the distance a glider will "float in ground
effect" (with the dive brakes closed) with the simple low drag glide
angle as the glider slows down - and if over the runway this may be
helped a little by ground effect, but remember this "float to the end
of the runway" is usually started at a relatively low speed, so the
drag penalty of diving down to a high speed is not felt.

Try a constant altitude decelleration from Vne to Vstall at altitude
some time; it's amazing how long and far you go! (helps when you get
above the MSH...yeah I know you're not supposed to do it!)

Kirk

Kirk Stant wrote:
CV wrote in message ...

I see. So if the results as reported here apply to calm conditions
it would mean the ground-effect technique wins out whenever there
is any significant wind gradient.

Actually, no. If I remember correctly, the test concluded that in
order to achieve any noticeable benefit from ground effect, the glider
had to be flown extremely precisely at VERY low altitude - only a

I should have worded that differently.

What makes the difference there is less headwind close to
the ground. The ground effect would of course not increase
on account of the wind gradient.

couple of feet above the ground. None of this "half a wingspan" - so
unless you are stetching your glide over the Bonneville salt flats,
just keeping out of the usual bushes, fences, stray airport dogs, etc
would eliminate any ground effect benefit.

With bushes and fences it's not on. I was thinking more along the
lines of a big plowed field, perhaps with some ditches crossing
and maybe just a low fence between the field and the runway.

If there is some ground-effect benefit at 2 ft though, it won't
be magically "eliminated" at 2,5 ft. The effect will decrease
gradually with height.

If the wind gradient is that strong, the turbulence at ground level
would make any precise low flying sporting and inefficient, anyway.

It doesn't have to be very turbulent there. We are assuming
flat ground. When the gradient is strong the surface wind is
much weaker than winds aloft. That is the meaning of "gradient".

I think pilots confuse the distance a glider will "float in ground
effect" (with the dive brakes closed) with the simple low drag glide
angle as the glider slows down - and if over the runway this may be
helped a little by ground effect,

The slowing down factor is a valid point. And ground effect may
help a little, or more than a little, if it is true that it can
doube the L/D as someone mentioned.

but remember this "float to the end
of the runway" is usually started at a relatively low speed, so the
drag penalty of diving down to a high speed is not felt.

Try a constant altitude decelleration from Vne to Vstall at altitude
some time; it's amazing how long and far you go! (helps when you get
above the MSH...yeah I know you're not supposed to do it!)

I suspect at altitude I wouldn't be able to appreciate the exact
distance covered and fail to be amazed.

CV

CV wrote in message ...

What makes the difference there is less headwind close to
the ground. The ground effect would of course not increase
on account of the wind gradient.

I would bet that if the wind is stong enough to have a strong
gradient, then there will be enough residual wind (and turbulence)
down low to affect the ability to stay low enough to use ground effect
- ever tried a high speed low pass on a windy day? It can be scary!

With bushes and fences it's not on. I was thinking more along the
lines of a big plowed field, perhaps with some ditches crossing
and maybe just a low fence between the field and the runway.

The obvious way to check this assumption is to test it with two
gliders - start off in formation, co-speed, on final; then one glider
dives into "ground effect" and the other stays at L/D max. Both land
at minimum speed. Repeat a few times, alternating who does what, and
examine the results.

If there is some ground-effect benefit at 2 ft though, it won't
be magically "eliminated" at 2,5 ft. The effect will decrease
gradually with height.

Apparently the drop off isn't gradual, but rapid - so it may be
significant at 2 feet, but insignificant at 5 feet. The Soaring
article gets into this, I think.

It doesn't have to be very turbulent there. We are assuming
flat ground. When the gradient is strong the surface wind is
much weaker than winds aloft. That is the meaning of "gradient".

Again, if the "gradient" is that strong (and we are talking about the
area up to say 200' above the surface, not 1000'), then there is
likely some surface wind also - especially over smooth terrain that
would favor ground effect?

The slowing down factor is a valid point. And ground effect may
help a little, or more than a little, if it is true that it can
doube the L/D as someone mentioned.

Russian work with Wing-In-Ground Effect (WIG) aircraft is fascinating
(also some German work in the area, and Boeing has a concept for a
huge WIG cargo plane, called the Pelican). Size seems to help, and
the ground effect was augmented by directing jet engine exhaust under
the wing. Double the L/D may be true, but likely only when inches
above the runway!

I suspect at altitude I wouldn't be able to appreciate the exact
distance covered and fail to be amazed.

Easy to do - just time how long it takes to slow down, then it is
pretty easy to approximate the distance. Or use a logger trace. I
tried it once in my LS6 at 8600', starting at 140 knots IAS and
slowing to 50 knots, trying to stay at the same altitude the whole
time (top of the start cylinder was 8600' - surprise!) Note that I
did this several miles outside the cylinder, flying towards it. I
know that it took at least 2 minutes to slow down (a very rough
number, since this was a real impromptu test, and 2 minutes was the
important number for me, for obvious reasons). So that is what? 2-3
miles? I'm sure there is a math whiz who can do the aero math to give
us the theoretical distance it should go.

IMHO, this idea (diving into ground effect) is like the idea that wet
pullups go higher - obvious, but incorrect.

Kirk

It strikes me that an additional benefit of this (assuming you
don't hit anything early on) is that at the point
one perhaps inadvertently stalls, one is quite low (2 feet?)

The fatal accidents I've read commonly involve either stalls at
above 2 feet and/or hitting a wing first (not a wings-level touchdown).

In article ,
CV wrote:
Kirk Stant wrote:
CV wrote in message ...

I see. So if the results as reported here apply to calm conditions
it would mean the ground-effect technique wins out whenever there
is any significant wind gradient.

Actually, no. If I remember correctly, the test concluded that in
order to achieve any noticeable benefit from ground effect, the glider
had to be flown extremely precisely at VERY low altitude - only a

I should have worded that differently.

What makes the difference there is less headwind close to
the ground. The ground effect would of course not increase
on account of the wind gradient.

couple of feet above the ground. None of this "half a wingspan" - so
unless you are stetching your glide over the Bonneville salt flats,
just keeping out of the usual bushes, fences, stray airport dogs, etc
would eliminate any ground effect benefit.

With bushes and fences it's not on. I was thinking more along the
lines of a big plowed field, perhaps with some ditches crossing
and maybe just a low fence between the field and the runway.

If there is some ground-effect benefit at 2 ft though, it won't
be magically "eliminated" at 2,5 ft. The effect will decrease
gradually with height.

If the wind gradient is that strong, the turbulence at ground level
would make any precise low flying sporting and inefficient, anyway.

It doesn't have to be very turbulent there. We are assuming
flat ground. When the gradient is strong the surface wind is
much weaker than winds aloft. That is the meaning of "gradient".

I think pilots confuse the distance a glider will "float in ground
effect" (with the dive brakes closed) with the simple low drag glide
angle as the glider slows down - and if over the runway this may be
helped a little by ground effect,

The slowing down factor is a valid point. And ground effect may
help a little, or more than a little, if it is true that it can
doube the L/D as someone mentioned.

but remember this "float to the end
of the runway" is usually started at a relatively low speed, so the
drag penalty of diving down to a high speed is not felt.

Try a constant altitude decelleration from Vne to Vstall at altitude
some time; it's amazing how long and far you go! (helps when you get
above the MSH...yeah I know you're not supposed to do it!)

I suspect at altitude I wouldn't be able to appreciate the exact
distance covered and fail to be amazed.

CV



--

------------+
Mark J. Boyd