F4U inverted gull wings

On Wed, 7 Jul 2004 01:48:52 -0400, (Peter Stickney)
wrote:

(about the one-bladed prop

Efficiency in the sense of power to thrust. You're right - it won't
work so well at higher speeds.

It's a hovering prop--is that the idea?

You see many-bladed props on turbo-prop commuter planes. That's to get
max efficiency out of a very powerful engine (compared to recips).
There are only two things you can do to use up engine power: increase
the length of the prop or increase the number of props. Length is
restricted by practical reasons: you don't want to strike the ground
or cause the landing gear to be extra long; and you don't want the
tips to go supersonic. So that leaves multiple props.

Working backwards, a single prop would use the least possible power.
So the plane could travel very slowly for a very long time?

(Then there's the factor that the plane came out of the Northrop shop,
which sometimes seemed like a Skunk Works mirror image: wild ideas
that didn't quite pan out.)

all the best -- Dan Ford
email: (put Cubdriver in subject line)

The Warbird's Forum www.warbirdforum.com
The Piper Cub Forum www.pipercubforum.com
Viva Bush! weblog www.vivabush.org

In article ,
no useful info wrote:


Considering the few inches of ground clearance any of those props
provided, does anyone have a good idea of how often the propeller was
damaged by (bad) landings?

I would speculate that after the first negative result the props ground
clearance would increase by several inches.
--

In article , hobo
wrote:


I would speculate that after the first negative result the props ground
clearance would increase by several inches.

no doubt, the question is, how frequently did this first negative result
happen.
--

In article ,
(Tracy White) writes:

I'm not sure if it is the answer - but fitting gull wings (whether
inverted or not) means that the wing root joins the fuselage at approx
90 deg - therebye eliminating the need for a large, drag-producing
wing-to-fuselage fillet.

Uhhh no. The fillets were there to DECREASE drag.

That's only true up to a point - A wing/fuselage joint that isn't at
right angles produces quite a bit of Interference Drag, as the
differing airflows try to sort themselves out. Filleting can ease
that transition.

You only need fillets on high or low-winged a/c

Fillets are used to smooth out airflow and thus decrease drag. The air
over a wing is moving at a higher velocity than the air over the
fuselage, and when the streams mix you get turbulence and drag. The
fillets work to counteract this interaction and the drag it causes.

True as far as it goes, but fillets also add wetted area, and increase
Parasite Drag. They're only drag reduction tools when they are
required, and only if used in moderation. It's all a balancing act,
after all - the designer is balancing out the drag increase casued by
the fillet itself, vs. the reduction in interference drag. The
decision made with the Corsair was to reduce the Interference Drag by
acheiving, as much as possible, a wing-fuselage joint perpendicular to
the fuselage, (The inverted gull wing) with a minimum of filleting,
thus reducing Parasite Drag.

--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster

The
decision made with the Corsair was to reduce the Interference Drag by
acheiving, as much as possible, a wing-fuselage joint perpendicular to
the fuselage, (The inverted gull wing) with a minimum of filleting,
thus reducing Parasite Drag.

Actually, the major driver for the inverted gull was finding a way to make
clearance for the HUGE prop so runways and carrier decks didn't get chopped up.
All the drag reduction trades and benefits were a natural fall out of the
design.

Keep in mind, the wings could have been put have been put at the 90 and 270
position and achieved the same benefit. But the prop would have went chop,
chop. Also, the inverted gull was not the best actor in stability and control.
I am not saying that ultimately it was not good, but even then the spins and
the recoveries were an occurence to behold.

"DJFawcett26" wrote in message
...

Actually, the major driver for the inverted gull was finding a way to make
clearance for the HUGE prop so runways and carrier decks didn't get
chopped up.
All the drag reduction trades and benefits were a natural fall out of the
design.

Keep in mind, the wings could have been put have been put at the 90 and
270
position and achieved the same benefit. But the prop would have went
chop,
chop.


The F6F had the same engine and similar propeller but didn't go chop chop
without the inverted gull wing.

In article ,
(DJFawcett26) writes:
The
decision made with the Corsair was to reduce the Interference Drag by
acheiving, as much as possible, a wing-fuselage joint perpendicular to
the fuselage, (The inverted gull wing) with a minimum of filleting,
thus reducing Parasite Drag.

Actually, the major driver for the inverted gull was finding a way to make
clearance for the HUGE prop so runways and carrier decks didn't get chopped up.

Sorry, but the evidence points in the other direction. There was
nothing particularly outstanfing wrt teh Corsair's propeller diamter -
13'1" for the 3-blade prop, and 13'2" for teh 4-blade - the F6F
Hellcat - no inverted gull wing - low mid-wing, in fact, had no
problems operating in the same environment. - in fact, around the
boat, it was a much better airplane than the Corsair.

The Vought TBU Seawolf, intended to be the successor of the TBF/TBM
Torpedo Bomber, had a mid-wing, and a 13'3" diameter prop.
The low-winged Martin AM-1 attack airplane had a 14'8" diameter
propeller.

The mid-wing P-47 had a 13'2" prop. (And in fact, was flown off of,
but not landed on, carriers in the Pacific, during several of teh
Island-hopping invasions.)

The low-wing Hawker Typhoon & Tempest had a 14' diameter propeller.

The fact is, given the expected speed range of the airplanes, and the
propeller RPM (_Not_ Engine RPM - these are geared engines, all with
a of between 1200 - 1500, a 13' propeller diameter gives the best
advance ratio range for efficiency.

As demonstrated by the small selection of examples above, it was
certainly possible to design an airplane to fit the Corsair's
requirements without resorting to in inverted gull wing to make it
work.

All the drag reduction trades and benefits were a natural fall out of the
design.

Keep in mind, the wings could have been put have been put at the 90 and 270
position and achieved the same benefit. But the prop would have went chop,
chop. Also, the inverted gull was not the best actor in stability and control.

And in fact, it was, on larger aircraft (The TBU, which, interestingly
emough, was the Vought project that followed the Corsair), without any
problems. Stbility wasn't a problem for the Corsair - the objective
numbers Cnalpa, Cnbeta - the Stability deriviatices show that it was
in the middle range for contemprary fighters. Teh stall behavior was
worse than that of the Wildcat & Hellcat, but better than the SBD
Dauntless, the Fw 190, or the P-51. Much of the of Corsair's Torque
Roll tencency at low speeds was corrected by a cuff on the leading
edge of the inboard right wing.

I am not saying that ultimately it was not good, but even then the spins and
the recoveries were an occurence to behold.

From contemporary reports, and objectively obtained data by the NACA,
not any more so than otehr WW 2 fighters, and much less than some.
(You do _not_ want to spin a P-51 with a full fuselage tank, for
example, or a Spitfire with the drop tank in place.)

--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster

Sorry, but the evidence points in the other direction.

I understand exactly what you are saying, the evidence is somewhat in support.
But this is not an issue of evidence, it is an issue of knowing several of the
guys that were on the test program. Witnesses are far better than
circumstantial evidence. Also, you have to take into account the geometry of
the aircraft you specify. There is a significant difference in configuration.

Just remember, what appears obvious may not at all be the obvious.

Look at the geometry, that in itself is the telling tale.

In article ,
Peter Stickney wrote:
In article ,
(DJFawcett26) writes:
The
decision made with the Corsair was to reduce the Interference Drag by
acheiving, as much as possible, a wing-fuselage joint perpendicular to
the fuselage, (The inverted gull wing) with a minimum of filleting,
thus reducing Parasite Drag.

Actually, the major driver for the inverted gull was finding a way to make
clearance for the HUGE prop so runways and carrier decks didn't get chopped up.

Sorry, but the evidence points in the other direction. There was
nothing particularly outstanfing wrt teh Corsair's propeller diamter -
13'1" for the 3-blade prop, and 13'2" for teh 4-blade - the F6F
Hellcat - no inverted gull wing - low mid-wing, in fact, had no
problems operating in the same environment. - in fact, around the
boat, it was a much better airplane than the Corsair.

It's a story which has been around a long time, though - pretty much
as long as the Corsair itself. Norman Hanson was given that as the
reason for the "bent-wing" when he visited Voights in 1943 prior
to picking up the RN's first back of Corsair Is*, so someone at the
factory obviously thought that was the reason. It's possible that the
bent wing was needed to get the big prop. /and/ some other bit of
configuration that Voights thought desirable (which Grumman didn't
adopt for the Gannet/Hellcat or Hawker for the Tiffie).

* source is originally direct - Hans was a family friend - but is
included in his (regrettably out of press) book, "Carrier Pilot".

--
Andy Breen ~ Interplanetary Scintillation Research Group
http://users.aber.ac.uk/azb/
"Time has stopped, says the Black Lion clock
and eternity has begun" (Dylan Thomas)