Dtango/HT/Pyro

[whgates3]

F4UDOA - you know anything about alternative props on Hogs?
i'm reading 'Hell in the Heveans' by a VMF 222 pilot. in it he says VF17 tried the smaller F6F prop out on an F4U & they got about 10mph top speed boost (i assume from lower drag)

[F4UDOA]

whgates,

Yeah I have read a bunch about that.

In fact they switched the F4U prop to the F6F prop around 1944. The F4U-1D had it.

The F6F started with the 6501A-0 blade design 13'1". The F4U started out with a 13'4" prop. The British found that at high RPM the F4U's prop was reaching high mach numbers and loosing prop efficiency. They found that the A/C was faster at normal power than MIL. Because of this they were ran at full MAP and reduced RPM to lower prop tip speeds.

Soon after that they switched to the same blade design as the F6F and also found a rise in climb as well as speed. This is mentioned specifically in the P-51vrs F4U report, The FW190 vrs F4U/F6F report and in the F4U flight manual where it says to use the 6501A-0 to get better performance.

It is as esoteric as it gets and is rarely mentioned but it had a huge difference from the F4U-1(3blade) through the F4U-4(4 Blade).

BTW. What book are you reading?? That sounds like really good stuff.

[whgates3]

"Hell in the Heavens" by USMC Captain John Foster of VMF 222 - he says it was a ~10' diameter prop, but he seems to be more of a pilot than an engineer...good book, some unexpected insight into the jolly rogers & info of encouters w/ pappy boyington too...

[dtango]

Sorry, I've been busy with real life stuff guys so haven't been lurking the boards lately !

To add to what HT was saying about data points - what procedures were being used for power-on or power-off stalls?  This could skew results.  I think the stall tests that I was performing isn't the same technique for either a power-off or power-on stall test for a/c.  

To add even more I dialoged a while back with Wells regarding flight testing and he provided me this excerpt from a flight testing book that he has demonstrating the difficulty in accurate "data points".  Just posting for flight tests of stall speeds for the 2 a/c in question here (speeds given in knots IAS)

F6f-5
- flown by11 Army, 2 British, 4 Navy, 10 Contractors
Power off, clean:  65-81, 77 average
Power on, clean:  60-79, 69 average
Power off landing configuration:  55-75, 66 average
Power on landing configuration:  60-70, 65 average
Accelerated 3g:  105-150, 121 average
 
F4u-1C,D
- flown by 13 Army, 3 British, 4 Navy, 8 Contractors
Power off, clean:  65-88, 82 average
Power on, clean:  60-83, 76 average
Power off, L/C:  63-90, 74 average
Power on, L/C:  63-84, 70 average
Accelerated 3g:  130-190, 150 average

So why the differences for a/c that were flight tested that were supposed to be in the same configuration?  What is defined as a stall for a particular test flight?  Procedure used for flight testing for stall?  CG variance in changing CLmax?  Condition of the airframe - e.g. immaculate airframe with fairings sealed etc. or ones in service condition? That's just starters.  It could be a whole host of things.  

I'm not sure that we've discovered any real problem with the FM's in question or just one of these many things that can give you different data points.

Hopefully it is more apparent to folks just what an incredibly complex task it is to research and create high fidelity FM's.

Tango, XO
412th FS Braunco Mustangs

[F4UDOA]

Dtango,

I have that book also.

You want to see something funny?

Take a look at 3G stall for the FG-1A(F4U-1A) on page 272. It has the 3G stall at 130knts. Those are identical to the F4U-1C/D.

I believe part of the problem in those results are two things.

1. They are quanitative not qualitative. Note no weights condition listed. It was more of a feeling out proccess for pilots trying other service/vendors A/C. Read the pilots notes for impressions of performance.

2. They frequently switch back and forth from MPH to Knots. Take a look at the F8F-1 3G stall. It is 190+knts. That was probably the best maneuvering A/C of them all.

The F4U had very light controls so if you pull to hard I think you would really "dig in" and stall if you unfamilier with the controls.

Here is the results from a modern evaluation of the 3G stall for the F6F-5, FG-1D, P-51D and P-47D-30 done in 1989 by a group of professional Military Test pilots using modern techniques.

3G stall decaying airspeed
P-51D 8,900lbs
122knts

P-47D 11,535lbs
109knots

F6F-5 10,681lbs
95knots

FG-1D 11,055lbs
98knots

Notice the P-47 and F6F are severely underweight but the P-51D and F4U are well within combat weights. And these test were performed with modern test equipment with modern test pilots.