F4U inverted gull wings

In article ,
(B2431) wrote:

Corsair had a 4 bladed prop. A 3 bladed prop may have been big enough to
irritate the Seabees who had no sense of humour when it came to prop blades
chewing up their runways.

The F4U had a three-blade prop from the XF4U-1. The F4U-4 introduced the
four-blade prop on production Corsairs. (The XF4U-3 had a four-blade
prop, but didn't go into production, and the prototypes were returned to
their F4U-1 initial state.)

The F4U had a three-blade prop from the XF4U-1. The F4U-4 introduced the
four-blade prop on production Corsairs. (The XF4U-3 had a four-blade
prop, but didn't go into production, and the prototypes were returned to
their F4U-1 initial state.)

I have a formerly classified file of a Vought tech-reps final tour report from
1943. The guy traveled everywhere in the South West Pacific theater, checking
on the servicability and operational needs of all US units that used Corsairs
at that point in the war. He hit every island that supported Corsair
operations, recording every nit pick and shortage among each unit, at times
under direct enemy attack. Planes crashed in front of him, he occasionally
landed at forward airstrips in the middle of battles and airraids.

The only serial problem that the report contains is a repeated cry for tires -
since the F6F-3, F4U-1, and TBFs all used the same 32x8 tire, they were in
critically short supply. Other problem areas include the cartridge starters
and nagging issues with the voltage regulators. The report has comments about
every aspect of Corsair operations - surprising to me is that nearly every unit
he visited requested a modification for a locked-wing Corsair, with the wing
fold mechanism removed for weight saving and increased roll rate.

As to props - this is old Jack's only comments:


TOUR OF INSPECTION OF THE SOUTH AND CENTRAL PACIFIC AREAS COVERING F4U-1
OPERATIONS, MAINTENANCE, AND SPARES. 30 DEC 1943 LT JOHN J. HOSPERS, USNR

Page 32 Material and Equipment

56. All Squadrons have been informed that the F6F-3 propellor is
interchangeable with the F4U-1 and that this paddle blade design will improve
the performance of the F4U-1.

v/r
Gordon

====(A+C====
USN SAR

Its always better to lose -an- engine, not -the- engine.

On 03 Jul 2004 04:42:25 GMT, nt (Krztalizer) wrote:


56. All Squadrons have been informed that the F6F-3 propellor is
interchangeable with the F4U-1 and that this paddle blade design will improve
the performance of the F4U-1.

Improved by how much I wonder ?


greg

--
Konnt ihr mich horen?
Konnt ihr mich sehen?
Konnt ihr mich fuhlen?
Ich versteh euch nicht

In article ,
Greg Hennessy writes:
On 03 Jul 2004 04:42:25 GMT, nt (Krztalizer) wrote:


56. All Squadrons have been informed that the F6F-3 propellor is
interchangeable with the F4U-1 and that this paddle blade design will improve
the performance of the F4U-1.

Improved by how much I wonder ?

I _thought_ I'd posted to this thread yesterday, with a few fidbits on
propellers, but the record shows that it didn't make it, for some
reason.

Anyway - The amount of power that a propeller can absorb (and turn
into thrust) is goverened more htna anything else by the total blade
area, and its Activity Factor (Essentially its Solidity - the ratio of
the area of the ptopeller blades to the total area of the propeller
disk.) The higher the solidity, the more power you can absorb.

The Efficiency of the propeller, (The amount of Shaft Horsepower that
it turns into Thrust) is driven by the Advance Ratio (A product of the
propeller's rotational speed vs. the airplane's forward speed), and
the blade angle. With a Constant Speed propeller, the blade angle
factor is removed, within the limits of the propeller's pitch stops,
because the propeller governor will always select the most efficient
blade angle to absorb the shaft horsepower. The propeller's pitch
range is such that, for any power level normally encountered in
flight, the propeller blades are not on the stops, and we can safely
ignore it for the purposes of this post, and only consider Advance
Ratio. Efficiency drops off at both low and high Advance Ratios, so
you can't just shoot for the highest one you can reach. (And, in the
WW 2 fighter case, with geared propeller drives, you start to run into
efficiency losses at high speed as the propeller blades start going
transonic. Other airplanes can get the propeller tips transonic at
lower airspeeds. One of the big reasons for a T-6/SNJ's irritating
snarl is that, with its ungeared R1340, the prop tips are transonic.)

Also, there are purely mechanical considerations - the propeller had
to be able to stay together while its working. Propeller blades are
thin, but they aren't light, and the forces both along their length
(ccentrifugal), and across the propeller disk (Thrust) are high. All
the force is concentrated at the blade root at the hub, so not only
are there high forces, but they've got long lever arms to work with.

You can add blade area in 3 ways - you can increase the propeller
diameter, you can increase the area per prop blade, or you can
increase the number of prop blades. There are tradeoffs for all three
options. Increasing the diameter of the propeller works well
aerodynamically at most Advance Ratios, but the tip speeds are high.
since most of the thrust of a propeller is generated at the tips, it
also puts huge loads on the propeller blade & hub. (And it has to fit
on the airplane).
Increasing the blade area of each propeller blade ("Paddle Blades")
will increase the efficiency at low Advance Ratios, giving better
takeoff and climb performance, but at a cost in high Advance Ratio
performance, and with added problems with structural strength.
It also allows the diamter to be more carefully controlled, with some
benefits at high speed.
Increasing the number of propeller blades also allows the diameter to
be controlled, and doesn't requires as much structural strength per
blade as the other two options. It does decrease overall efficiency.
(A good rule of thumb is 2-3% per blade) This is due to interference
effects of a propeller blade tip running into the vortices of the
blade ahead of it.
So, in general, the order of merit of the three options is this:
1) Increase the propeller diameter, if practicable.
2) Increase teh propeller blade area without increasing the diameter
(Paddle blade)
3) Increase the number of propeller blades.

As to the Hellcat propeller being fitted to the Corsair - it was
certainly done - for example, the tests performed by the USN of a
P-51B vs 2 hotted up Corsairs used Hellcat propellers for both
aircraft. (The preort can be found online at:
http://www.geocities.com/slakergmb/id95.htm

As to how much it would affect performance - The Hellcat propeller
would mose likely by about 2% more efficient at the F4U's climb speed,
and about the same efficency at maximum speed. At climb speed, the 2%
greater efficency would give 40 more Thrust Horsepower at Sea Level
(2000 SHP), and about 34 more Thrust HP at high altitudes. (This is
because the Corsair's geared supercharger delivered less Shaft
Horepower at high altitudes, since more power was diverted to the
supercharger). At teh Corsair's best climb speed of 135 Kts at Sea
Level, that's 95# more excess thrust. it doesn't sound like much, but
since it's all excess, it gives about 108 ft/min more climb. At
22,000', the excess thrust would be about 58#, giving a improved rate
of climb of 95 ft/minute. It doesn't seem like much, but it makes a
difference.

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

"hobo" wrote in message
...

The corsair used a 3-blade prop. Why didn't they use a smaller 4-blade
prop if ground clearance was such an issue?


A 3-blade prop was used on the XF4U-1 through F4U-2 and equivalent Corsairs.
A 4-blade prop was used on the XF4U-3 and subsequent Corsairs.

Very interesting! The only part I question is:

"Peter Stickney" wrote...

Increasing the diameter of the propeller works well
aerodynamically at most Advance Ratios, but the tip speeds are high.
since most of the thrust of a propeller is generated at the tips, it
also puts huge loads on the propeller blade & hub.

How can "most of the thrust" be generated at the tips -- given the
combination of shorter chord, lower AOA, and [vortex] airflow around the
tips -- compared with the midspan of the blade?

On Sat, 3 Jul 2004 11:15:02 -0400, (Peter Stickney)
wrote:

[snip excellent detail]

It doesn't seem like much, but it makes a
difference.

ISTR something about a paddle bladed P-38 being ~40 mph faster than the
stock model.

But it wasnt possible to schedule the production changes to implement it.


I suppose the US war dept had more important things to do like waste money
on the Fisher P75.



greg

--
Konnt ihr mich horen?
Konnt ihr mich sehen?
Konnt ihr mich fuhlen?
Ich versteh euch nicht

In article PyBFc.18031$%_6.5403@attbi_s01,
"John R Weiss" writes:
Very interesting! The only part I question is:

"Peter Stickney" wrote...

Increasing the diameter of the propeller works well
aerodynamically at most Advance Ratios, but the tip speeds are high.
since most of the thrust of a propeller is generated at the tips, it
also puts huge loads on the propeller blade & hub.

How can "most of the thrust" be generated at the tips -- given the
combination of shorter chord, lower AOA, and [vortex] airflow around the
tips -- compared with the midspan of the blade?

Ah, you caught me oversimplifying/underexplaining. Thanks.

Because the airspeed of the propeller is much higher at the tips,
most of the thrust produced by the propeller is higher there. A
simple rectangular prop with a constant chord would, all other things
being equal, be developing a tremendouds amount of force at the tips,
and hardly any near the hub. This sets up a severe structural problem
- a simple propeller shape will have a tremendous bending moment both
at the point where the blade joins the hub, and along the length of
the blade. (As an aside, you also don't want the propeller blades to
be too heavy - a WW 2 fighter propeller blade typically weighed about
100#/45 Kilos). Building strong, lightweight blades that could take
these forces and not have, say, problems with resonance, was a
difficult and involved process, fraught with danger - It wasn't
unusual for a disintegrating propeller to destroy the test cells at
Hamilton Standard and Wright Pat, let alone be something that could be
trusted in the air - so propeller shapes, before WW 2, were tweaked to
provide a fairly constant (at some particular design point wrt prop
pitch and airspeed) distribution of forces. This included reducing
the area at the tips (Which also decreased the strucural issues),
changing the propeller pitch across the propeller blade's length, to
keep the lift coefficient the same, and making the shank of the blade
completely round. (For greater strength, and for making the
pitch-change mechanisms easier to design & build.)
using a progressive pitch ditribution (propeller twist) allows for
more thrust at low speeds.

A typical early WW 2 propeller, with a relatvely narrow propeller
blade chord and a fiarly pointed tip produced its maximum thrust in a
region between 80 and 90% or the propeller radius.
(Ref: NACA Report No. 712, "Propeller Analysis From Experimental
Data", Stickles & Crigler, 1940.)
As structural techniqes improved during the war, it became possible to
make wider chord propeller tips, moving the point of maximum thrust
further out along the blade radius. It still doesn't peak at the
tips, though, because of the tip vortices. It's still a serious load
on the propeller shank.
Compare, for example, the early and later CUrtiss Electric propellers
used on P-47s - the early propeller blades are "toothpicks", while the
later "paddle" blades are nearly rectangular, with the same maximum
chord, but held for a much longer section of the blade radius.
Or the propeller of a P-40 or P-51A to that of a P-51B.


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

GREAT POST Sticky! Much better! Keep it up!

Grantland

(Peter Stickney) wrote:

In article ,
Greg Hennessy writes:
On 03 Jul 2004 04:42:25 GMT, nt (Krztalizer) wrote:


56. All Squadrons have been informed that the F6F-3 propellor is
interchangeable with the F4U-1 and that this paddle blade design will improve
the performance of the F4U-1.

Improved by how much I wonder ?

I _thought_ I'd posted to this thread yesterday, with a few fidbits on
propellers, but the record shows that it didn't make it, for some
reason.

Anyway - The amount of power that a propeller can absorb (and turn
into thrust) is goverened more htna anything else by the total blade
area, and its Activity Factor (Essentially its Solidity - the ratio of
the area of the ptopeller blades to the total area of the propeller
disk.) The higher the solidity, the more power you can absorb.

The Efficiency of the propeller, (The amount of Shaft Horsepower that
it turns into Thrust) is driven by the Advance Ratio (A product of the
propeller's rotational speed vs. the airplane's forward speed), and
the blade angle. With a Constant Speed propeller, the blade angle
factor is removed, within the limits of the propeller's pitch stops,
because the propeller governor will always select the most efficient
blade angle to absorb the shaft horsepower. The propeller's pitch
range is such that, for any power level normally encountered in
flight, the propeller blades are not on the stops, and we can safely
ignore it for the purposes of this post, and only consider Advance
Ratio. Efficiency drops off at both low and high Advance Ratios, so
you can't just shoot for the highest one you can reach. (And, in the
WW 2 fighter case, with geared propeller drives, you start to run into
efficiency losses at high speed as the propeller blades start going
transonic. Other airplanes can get the propeller tips transonic at
lower airspeeds. One of the big reasons for a T-6/SNJ's irritating
snarl is that, with its ungeared R1340, the prop tips are transonic.)

Also, there are purely mechanical considerations - the propeller had
to be able to stay together while its working. Propeller blades are
thin, but they aren't light, and the forces both along their length
(ccentrifugal), and across the propeller disk (Thrust) are high. All
the force is concentrated at the blade root at the hub, so not only
are there high forces, but they've got long lever arms to work with.

You can add blade area in 3 ways - you can increase the propeller
diameter, you can increase the area per prop blade, or you can
increase the number of prop blades. There are tradeoffs for all three
options. Increasing the diameter of the propeller works well
aerodynamically at most Advance Ratios, but the tip speeds are high.
since most of the thrust of a propeller is generated at the tips, it
also puts huge loads on the propeller blade & hub. (And it has to fit
on the airplane).
Increasing the blade area of each propeller blade ("Paddle Blades")
will increase the efficiency at low Advance Ratios, giving better
takeoff and climb performance, but at a cost in high Advance Ratio
performance, and with added problems with structural strength.
It also allows the diamter to be more carefully controlled, with some
benefits at high speed.
Increasing the number of propeller blades also allows the diameter to
be controlled, and doesn't requires as much structural strength per
blade as the other two options. It does decrease overall efficiency.
(A good rule of thumb is 2-3% per blade) This is due to interference
effects of a propeller blade tip running into the vortices of the
blade ahead of it.
So, in general, the order of merit of the three options is this:
1) Increase the propeller diameter, if practicable.
2) Increase teh propeller blade area without increasing the diameter
(Paddle blade)
3) Increase the number of propeller blades.

As to the Hellcat propeller being fitted to the Corsair - it was
certainly done - for example, the tests performed by the USN of a
P-51B vs 2 hotted up Corsairs used Hellcat propellers for both
aircraft. (The preort can be found online at:
http://www.geocities.com/slakergmb/id95.htm

As to how much it would affect performance - The Hellcat propeller
would mose likely by about 2% more efficient at the F4U's climb speed,
and about the same efficency at maximum speed. At climb speed, the 2%
greater efficency would give 40 more Thrust Horsepower at Sea Level
(2000 SHP), and about 34 more Thrust HP at high altitudes. (This is
because the Corsair's geared supercharger delivered less Shaft
Horepower at high altitudes, since more power was diverted to the
supercharger). At teh Corsair's best climb speed of 135 Kts at Sea
Level, that's 95# more excess thrust. it doesn't sound like much, but
since it's all excess, it gives about 108 ft/min more climb. At
22,000', the excess thrust would be about 58#, giving a improved rate
of climb of 95 ft/minute. It doesn't seem like much, but it makes a
difference.

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

In article ,
Steve Hix writes:
In article ,
Orval Fairbairn wrote:

They wanted to keep the main landing gear as short as possible, to
simplify structural loads. The Hellcat had a relatively long main gear
leg.

A four-bladed prop for the same power output should be shorter than the
three-bladed equivalent.

But somewhat less efficient. Each blade added to a propeller knocks
the efficiency down. Later model Corsairs with the more powerful
R2800 'C' series engines had a 4 blade prop, but the diameter is
essentially the same - 13 ' 2".

You also have to tune 'J', the Advance Ratio of the propeller (A
product of propeller rotational speed, propeller diameter, and the
forward velocity of the propeller (and the airplane it's attached
to.) in order to get teh best performance. reducing the diameter for
a given horsepower may have beneficial effects at high speed, but
severely affect the propeller's performance below, say, about 350 mph.

It's all a balancing act - but in ggeneral, you're best off going with
the largest diameter propeller with the fewest number of blades that
you can practically manage.

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