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I've done a handful of short flights and fuel management wasn't really an issue. In the RW, I switch tanks in the Cherokee every 30 minutes... But with the P-40 I've got more tanks to deal with!

So my thoughts are: (from full fuel)

1) Startup, Taxi, Depart, and Cruise on the main fuselage tank.
- My reasoning is that since it's aft, I can burn that fuel first and have less of a risk of stall/spin during high g maneuvers by moving the CG forward as quickly as she burns it off

2) Switch to drop tank

3) Then wing tanks

4) And finally reserves...


I'd love to hear y'alls input on the matter. Should we be flying switching tanks every given amount of time? Or is my reasoning correct? Or should the order in which tanks are burned be changed?

Cheers!

Bud

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Buddy Morgan



i5 2500k - Asus P8P67 Pro - G.Skill Ripjaw 8GB - EVGA GTX 570 Fermi

In real life the drop tanks are designed to be the first you go through so that you can jettison them prior to combat. The FSX skies are generally friendly though so not much of a concern however

Actually, the drop tanks are usually 3rd on the list. Both Allisons and Merlins at high power send a LOT of unused fuel back from the carb. This requires that a return line be installed to accommodate that returning fuel. Just as an example, in the Mustang that vapor return line unless diverted to the fuselage tank in the field runs to the left main. If you take off on any other tank but the left main in a 51 and that left main is full, the return will overflow the tank.

In a combat scenario, you would generally take off on the tank with the return line and climb initially on that tank usually up to your cruising altitude. At reaching cruise upstairs, you would switch to the fuselage tank if installed and if fuel in that tank caused a cg problem when maneuvering such as in the Mustang. After burning off the fuselage tank down to a known minimum for a good balanced cg, THEN you would go to the drop tanks. The "theory" behind this is that of all your fuel on board you can drop the external tanks if you get jumped on the way in to the target area. Fuel gone in the drop tanks and you get rid of them going onto the wing tanks. You burn them in equal time periods if you're smart as that balances out the weight and helps with the roll inertia issue.
Most pilots will on returning home, land on the fullest tank.
Dudley Henriques

According the the WWII Training Manual for the P-40 (written primarily for the later models) :

"The fuselage tank is called the vented tank, which means there is an overflow line between this tank and the carburetor. The fuel line carries excess gas from the carburetor back to the fuselage tank. At high engine rpm, the fuel overflow may run as high as 10 or 15 gallons per hour.

Always use the fuselage tank for takeoff. During takeoff the chance of fuel overflow is especially high, and unless you are using the fuselage tank--the only one built to handle overflow gas--the overflow is lost.

After takeoff, always use at least 15 gallons from the fuselage tank before switching to another fuel tank.

The fuselage tank accumulates possible overflows from the other tanks during flight. Always turn the selector handle to the fuselage tank if it appears you have run out of gas. The fuselage tank probably contains a few gallons of overflow fuel."

The training manual later suggests: "Climb at a speed of 150-160 mph. When you reach 1000 feet, switch from the fuselage tank to the belly tank and fly on the belly tank until it is empty." I believe one of the considerations for doing this is that the belly tank does not have a fuel gage, so it is best to use this fuel first and have a known quantity in the other tanks.

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120th Fighter Wing, Montana Air National Guard

The PDF manual on page 32 says to start on the reserve tank. Is that in error? That is what I have been doing, then switching to the fuselage tank.

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Jim

Here is some more good advice from the WWII training manual:
Arrange the sequence of tank changes so that you always change directly from an empty tank to a full one without passing the selector through another empty tank. When you pass through and empty tank to get to a full one you run the risk of getting a vapor lock.

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120th Fighter Wing, Montana Air National Guard

I'm looking at a reprint of the P-40D/E flight instructions from circa 1943. What's interesting is that in this POI, the startup instructions say to prime and start the engine on the reserve tank and to keep the selector valve on "Res." during preflight check and takeoff. Here is the sequence it gives for the tanks following takeoff:

c. Order of Fuel Tank Use.
Belly tank (if installed).
Fuselage tank.
Main tank.
Reserve tank.

d. Belly Tank.
(1) If the airplane is equipped with a belly tank, the fuel selector valve should be set at "BELLY" as soon at practicable after take-off.
(2) If the belly tank is dropped during flight, a slight heaviness will be observed.

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120th Fighter Wing, Montana Air National Guard

My first post references the fuel system of the later P-40s, and after comparing the diagrams for the P-40D with the P-40N I see there are some significant differences. The most obvious difference is that the seperate tanks referenced in the P-40D as "Reserve" and "Main" seem to have been combined in the later models to either a single "Wing Fuel Tank" or to a "Wing Forward Fuel Tank" and "Wing Aft Fuel Tank" combination. (The Fuselage Tank remains for all models.)

This might simply be a change in nomenclature, or it might reflect significant plumbing changes.

In other words, my first post probably is not very applicable to the P-40B/C models.

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120th Fighter Wing, Montana Air National Guard

You should start the engine, taxi, take-off and land using the reserve tank. This is the tank with the fuel return line from the carburetor. I would burn the fuselage tank fuel first (to improve combat ability if you expect to encounter an enemy) then the drop tank (if any), the wing tank next and finally the reserve tank again.

regards
ROB

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A2A Simulations Inc.

Thanks guys! Very, very helpful!

Cheers!

Bud

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Buddy Morgan



i5 2500k - Asus P8P67 Pro - G.Skill Ripjaw 8GB - EVGA GTX 570 Fermi

The Curtis' P-40 pilot training video that was referenced in Scott's video showing off the plane on jacks instructs to use fuselage tank first for taxiing and takeoff. Then switching over to belly tank as soon as "you have climbed a bit" if available. Doing so maximizes fuel since you never know when you will have to jettison the belly tank if finding yourself in combat so better use it while you can. Burning the fuselage tank was also noted as way of moving the center of gravity to allow for a more stable gun platform. Then switch to rear wing tank and finally to front wing tank. This obviously is for a later model P-40, and as Skycat mentions, obviously quite different than the earlier accusim models. Well anyways, no better way to find out what works best for you and this model than doing it how Curtis' test pilots found out: flying the plane! Sounds like a pretty good way to answer the question, sitting in the beautiful pit for a few hours

It occurred to me after Rob's post that the realities of using drop-tanks in combat might have caused the fuel line vent to be moved to the fuselage tank in mid and late production models. It's one thing to plan a long distance flight where your external tanks are just additional fuel stores to expand your range, and quite another to suddenly drop weight and have an unbalanced center of gravity as you go into combat. Rob's suggestion to burn off the aft tank's weight first is practical and most likely this consideration was implemented into later design revisions.

Was the P-40 originally designed to to have drop tanks? Or was it more like the P-47, which underwent a teething process of field modifications and work-arounds to add releasable tanks after it was first introduced into combat in Europe?

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120th Fighter Wing, Montana Air National Guard

I'm still not 100% on tank issue.. As stated earlier, the later models used the fuselage tank for all taxi/takeoff/landing as it was the vented tank allowing overflow to return to the tank. Although from what I'm gathering the early models B/C used reserve as it was the vented tank. I also believe the reserve tank is the forward wing tank, correct?

Also makes me wonder how you'd know when you were running low on the reserve tank as there's no fuel gauge for the forward wing tank? I see a gauge for fuselage and wing tank (rear) but none for the reserve. Also, lastly, I assume the "Aux" marking on the fuel selector is for the belly tank correct?

Also, off-topic, I see your in Great Falls Skycat! I'm from Helena and currently going to school in Bozeman, small world!

Hi Ty,

Yes, it is a small world. I guess you probably know then about the ferrying operations from Great Falls during the war (hence my avatar of the 7th Ferrying Group's patch) and how military planes were being flown through this area from factories to bases and from bases to depots. Many of the planes headed for Alaska went through Great Falls, most notably several thousand Airacobras, King Cobras and other Lend-Lease planes for the Russians. We also had a B-17 training mission here, which is why the Air Force base was originally built in 1943.

I don't have the P-40 w/AccuSim package and I'm not at all an expert on the P-40 so I don't know how well I can address your specific question.

The vented tank collects unused fuel vapor that would otherwise be lost. If the vented tank is full, the recycled fuel running into it overflows and I think it is released out of the fuselage and into the airstream. Quite simply, the mechanism for salvaging unused fuel fails and the 'recollected' fuel is wasted. It is better to burn off some of that fuel in the vented tank at the beginning of your flight so that you create space for the salvaged fuel to go to throughout the rest of the flight. (On a similar note, I recall that P-47 pilots were supposed to switch back to the vented tank every hour--for ten minutes I think--to maintain that empty space.)

I'll argue that in the late 1930s the Army really didn't anticipate needing a fighter that would fly more than 100 miles to engage in combat--after all, the U.S. was concerned primarily about defending the continent against the incursion of a naval superpower and with defending our Pacific stations and territories. Japan's navy was eyed as our major threat. The Army wanted fighters that could scramble to engage enemy bombers approaching our factories, ports, coastal defenses, etc. I'll assume that this is why the P-40Bs did not have provisions for an auxiliary belly tank (or at least not drop tanks). Although the Army originally anticipated that operational units would only need a limited combat range, I suppose experience proved it was necessary to fly military pursuit aircraft long distances even if only to relocate them to new bases. Hence, plumbing for a belly tank was added with the 'C' model.

Let's assume that in 1941 (pre-war) if a P-40C pilot knew he was going to fly a long distance that would require an auxiliary tank, he'd already have his route planned and he'd know how much fuel he'd need to get there since total weight is a major consideration. I'm thinking that having a belly tank installed wouldn't be the normal configuration for a squadron on alert because the external tank automatically reduces the airplane's top speed of by 10 mph, and probably wreaks havoc on the airplane's flight stability as well. If I am correct, the belly tank was used primarily for ferrying operations and recon patrols, not for the direct interdiction role. Let's also assume the pilot isn't going to drop his tanks on some poor farmer's barn halfway between Base X and Base Y, if you know what I mean.

The pilot starts up and takes off with his Reserve Wing tank and burns approximately 15 gallons to give him space for unused fuel that will be recollected from the carburetor. He then switches to the Belly (Auxiliary) tank since he is carrying that extra fuel for a reason--he knows he needs that gas to get to his destination. He'll want to empty the Belly tank in case he has to make a belly landing; also, since it is not a gaged tank he'd probably want to use up the fuel and then switch to tank that gives him a needle to watch. The Fuselage tank is recommended next, probably because it is a large tank and is located behind the pilot and therefore affects the airplane's center of balance. When the Fuselage tank gets empty, the pilot can switch to the other gaged tank--the Main Wing tank which is located approximately under his seat. Finally, when the fuel in the Main Wing tank is consumed, he switches to the Reserve Wing tank, which is located fore of the Main Wing tank and approximately under his feet. By now the pilot should be very close to his destination and shouldn't be sweating the exact contents of the Reserve Wing tank. If the fuel selector that is illustrated in the vintage P-40D/E manual is the same as it was in the P-40C, the pilot will never have to move the selector position through an empty tank if he uses this sequence.

I'm sorry, what was the question?

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120th Fighter Wing, Montana Air National Guard

Thanks Skycat!

I do know about the aircraft that flew around Montana in before/during the way. My grandfather is from Lewistown and used to sneak up to the base to watch the B-17's take off and land, lucky guy!

Anyway, what you said makes sense, I was under the assumption that unused fuel from the carburetor was vented back to the reserve tank, so your saying it was vented off into the airstream? sorry if I misunderstood you. I manged to locate a P-40 B/C POI Manual which I'm slowly going through, so that should help answer some of my questions.

One thing I'm also curious about, the "B" model was never designed for use of an "AUX" or "Belly tank" which makes me wonder why the "B" model in the A2A bird has "AUX" as an option on the fuel selector, is this an error? I do recall in the A2A manual it mentions some differences between the various models in the package, and different fuel selector gauges is one of those differences. Perhaps Scott or someone from A2A could clarify this? It doesn't make much sense to have "AUX" as an option on the "B" model seeings as it doesn't have the belly tank

Anyway, thanks again for taking the time to respond. Take care.

Ty