F4U-1D/F6F-5 fuel consumption and more

[F4UDOA]

Gents,

I have recently ordered many new Pilots operating handbook with full appendices including F4U-1D, F6F-5, F4U-4 and P-51D.

Some interesting things I noticed.

1. In F4U-1's and F4U-1D's/F6F-5's after the summer of 1944 made a change in carb settings allowing the PW-R2800-8/8W/10/10W to use auto lean instead of auto rich in normal and mil power.

This lowers fuel consumption considerably from 290GPH to 230+GPH at all alts.

2. The dive break on the F4U-1 should be usable at all speeds. The 260knots limitation only applies to extending and retracting the break. In later F4U-1 models and forward the break could be used at any speed as well as being extended or retracted up to 380knots.

3. The F4U-1 was appoved for 2800rpm at takeoff with the right prop hub. I have another Vought doc showing this reduces takeoff distance by 4 to 9%.

He are the my scans.

[joeblogs]

My reading of this is that auto-rich and auto-lean are not the discrete settings we usually think about. The mid war estimates of fuel consumption were conservative, especially at the upper end of the power range. An adjustment to the carburetor settings allowed for somewhat leaner fuel mixtures...

Fuel economy chart to follow.

-Blogs

[F4UDOA]

JoeB,

I was hoping you would catch this.

This sheds a whole new light on the R2800 for me. I wondered why the economy of it was so good on the cruise and so bad on the high power settings. This puts it inline with the other modern engines in regard to SFC.

In the low end power consumption the R2800 is actually more efficient than the vaunted Merlin.

[joeblogs]

These charts compare specific fuel consumption (lbs of fuel per horsepower per hour) based on the data contained in the Specific Engine Flight Chart (SEFC) posted in this thread for the -8W model of the double wasp and another SEFC chart often seen in the threads.

The primary difference appears to be the dates of publication, with this new chart ocurring later in time.

The bottom line is that tweaks to carburetor settings seems to have improved fuel economy, especially at higher power settings.  

-blogs

The first chart is in the neutral blower setting (low altitude)



The second chart is at the low blower setting (medium altitude)



The third chart is at the high blower setting (high altitudes)



The final chart shows the simulated endurance of an F4u-1 on internal fuel (237 US gallons). The fact that the red dots generally lie above and to the right of the blue dots tells you the plane with the -8W can operate longer at the same power setting or can operate at higher power for the same length of time as the plane with the -8. The effect is pronounced at high military power settings, offering an extra 10-15 minutes of endurance.




-Blogs

[F4UDOA]

JB,

My guess why your images are not loading is that you are using the wrong coding to frame you URL. The url must be bracketed with [~img] and [~/img] without the tilda signs of course.

The duration of the F4U increases at mil power to almost exactly 1 hour at mil power(at 30min intervals). The other interesting point that is in other text in the manual in greater detail is shown in the chart is that above the main and low blower stages RPM and MAP are reduced to Max continious or "Normal power" which has unlimited duration time.

Also the F4U engine (probably because of RAM effect) in the main blower stage produces 2300HP. 50HP more than the F6F-5 in the same stage.

[joeblogs]

While the Merlin is certainly vaunted, it was not known for fuel economy.

The engines plotted here are the B series Double Wasp. A number of the late war & post war C series had an SFC as low as 0.42. That is as good as the most fuel efficient engines of the time - certain models of P&W's Twin Wasp, certain versions of Allison's V1710, and the miserly Bristol Hercules.

-blogs

Originally posted by F4UDOA
JoeB,

I was hoping you would catch this.

This sheds a whole new light on the R2800 for me. I wondered why the economy of it was so good on the cruise and so bad on the high power settings. This puts it inline with the other modern engines in regard to SFC.

In the low end power consumption the R2800 is actually more efficient than the vaunted Merlin.

[joeblogs]

The following two charts compare the fuel economy of the -8 and a later version of the -8W Double Wasp with the -21 version used in the P47 (with a turbosupercharger)

The first chart compares the -8 with the -21



The second chart compares the -8W with the -21




The discrepancy between the gear driven and exhaust driven supercharged models is really reduced. That suggests changes to carburetor settings after mid-war really helped the Double Wasp.

-Blogs