Warbird Information Exchange

I've come across a very interesting late 1940's Fuel Quantity Indicator, and it vexes me (phrase borrowed from Commodus in Gladiator).
I seek to be unvexed.

Here are the clues:

It has two scales, one each for fuel type AN-F-48 (up to 16,200 lbs) and AN-F-58 (up to 17,800 lbs). Since the indicator is measuring liquid in a fixed volume system, I'm assuming that the differential in weight is due to differential in density. Given the maximum capacity, I'm guessing it was for a large multi-engine aircraft, e.g., Boeing B-50.

It is labeled as being property of AF US ARMY, placing it before Sept 1947 when it became the US Air Force.

I understand that fuel type AN-F-48 (eventually designated MIL-F-5572) was commonly used in piston-engine aircraft during WWII, and that fuel type AN-F-58 (aka JP-3 or MIL-F-5624) was primarily used in turbine engines, and that some aircraft, such as the B-47A (per its flight manual) could use either to power its turbines.

I'm trying to determine the following, and would greatly appreciate any insights from WIXers:
1) Why would an aircraft be designed to use both grades?
2) What aircraft would have used this indicator?

Any de-vexing information would be appreciated!
BTW, the indicator is here:

with more photos here https://aeroantique.com/products/fuel-quantity-indicator-an-f-48-and-58-fuels-us-army-air-force.
Thanks, in advance!

_________________
JT
AeroAntique
"Preserving Warbird History...one artifact at a time"
http://aeroantique.com/
"All right, Striker, you listen, and listen close. Flying a plane is no different from riding a bicycle; it's just a lot harder to put baseball cards in the spokes."

Maybe it was used on aircraft that used both fuels, like the P2V Neptune, or B-36 Peacemaker?

Since it measures lbs, can we assume a jet engine only? Did any of the post-war large recips ever use lbs instead of gallons?

The totals of 16,200lbs - 17,800lbs equals approx. 2500-2700 gallons of fuel. Could that much fuel be carried in a single tank (B-50?) or is this a "totalizer" for what was on the entire aircraft?

When did 400 cycles become the norm in aircraft instruments?

I think this was for either a KB-29 or KB-50 and used to evaluate how much fuel was in the transfer tanks. The bigger question is whether it was on the FE console, in the drogue/boom operator's station, or somewhere else (like the loadmaster or navigator station).

I think that the KB-29 or the KB-50 guesses are heading in the right direction.

Looking at the Fuel Quantity Table in the KB-50 Flight Manual, it lists two values ("Jet Engine Fuel" and "Gasoline") for each of the 7 tanks that comprise the aerial refueling system (2 Pylon tanks, 2 Nacelle Skate tanks, Center Wing tank, Forward bomb bay tank, Aft bomb bay tank) clearly indicating that each tank could hold a different fuel depending upon the aircraft to be refueled on a particular mission.

The manual also states that a fuel totalizer appeared on both the FE and the Refueler's stations, with a selector switch to show the total in either the main fuel system or the refueling system, excluding the fuel in the pylon tanks. So we are getting close, but adding the individual tank capacity numbers exceed the total to support a full 'totalizer' purpose of this indicator, at least for a KB-50, and no individual or combination thereof seem to get close to the limit of this indicator. So I'm now surmising KB-29... now all I need is its flight manual....

Also, the fuel supply indicators on the KB-50 operated on 115v, single-phase, regulated frequency AC system, per the manual, perhaps explaining the 400 cycle label on the indicator. I don't know when that configuration was introduced. I didn't see that in my B-29 manual.

Some further research on the internet is revealing that the KB-29 had bomb bay tanks holding 2300-2500 gallons of fuel, so perhaps that's it?

_________________
JT
AeroAntique
"Preserving Warbird History...one artifact at a time"
http://aeroantique.com/
"All right, Striker, you listen, and listen close. Flying a plane is no different from riding a bicycle; it's just a lot harder to put baseball cards in the spokes."

Early jets used either fuel, avgas and JP-3,4, etc.

We regularly used avgas in our CH-47A with the Lycoming T-55-L-7 and L-7B when we couldn't JP 4. There was no alternate fuel and avgas was the emergency fuel.If I remember right, the engine guys had to do a hot end inspection after 50 hours of avgas use.

The following pages from a KB-29P Flight Manual seem to show a similar, if not the same indicator on the Flight Engineer's In Flight Refueling Panel. Unfortunately, the image isn't quite clear enough to read the scale, but it shows the dual markings. also, the forward bomb bay fuel tank, which was used for in flight refueling has a total volume of 2654 gallons. At 6 pounds per gallon for Avgas, that comes out to 15924 lbs. and for jet fuel at 6.5 to 6.7 lbs. per gallon that would be 17,251-17,782 lbs. That pretty well matches the scales on your indicator. Here are some relevant pages from the manual. the last page here has a warning to be sure to drain and flush the in flight refueling tanks when switching to or from Avgas and jet fuel. I also checked my KB-50 and KC-97L mauals and neither had the dual scale on their fuel indicators.

Larry, I think you nailed it!
Thanks so much for the info. It took a bit of digging, but it looks like you have a solid ID.
I really appreciate the effort and the result!

I owe you a beer or two, or three...

_________________
JT
AeroAntique
"Preserving Warbird History...one artifact at a time"
http://aeroantique.com/
"All right, Striker, you listen, and listen close. Flying a plane is no different from riding a bicycle; it's just a lot harder to put baseball cards in the spokes."