Wing drop tanks

[Jacques]

If you were flying the P-51 (military) with full wing tanks, full fuselage tank and two 75 gal. wing-mounted drop tanks, would you burn the drop tanks first to eliminate the drag, or the fuselage tank because of the instablility it can cause when it is contains more than x gallons?

[Lewis - A2A]

Ive read pilot accounts that noted different ways to do this, and it seemed personal preference vs unit orders vs overall procedure, as is normal in WW2. Many pilots I recall mention using the tanks and fuse tank and alternating between then to try to get the fuse down quick whilst also having the range should they have to drop early due to mission circumstance.

[Jacques]

I was thinking along those lones as well: get the fuselage tank down to a manageable level by the point you might need to get rid of the drop tanks. So, yeah, it sort of depends upon where you think you might run into trouble that will determine how you choose which tanks to use, and when.
Thanks Lewis, that is very helpful!

[robert41]

Most I have read says to use the fuse tank first down to 20-25gal. Then use the drop tanks, switching between them every 15min or so. Keeping the weight forward as soon as possible for any maneuvers.

[CodyValkyrie]

Keep in mind by the end of the war, the Germans didn't have a lot of fighters or experienced pilots. The planes didn't always stick to the bombers like glue throughout the whole flight, and often there was a rendezvous. Usually when they neared the targets is when they met the most resistance, so as a pilot you'd likely burn off as much fuel from that aft tank to be combat efficient while knowing full well you could end up in a fight. Once you've decided to engage the enemy, those drop tanks go, regardless of fuel, which could also prematurely end the mission, as you lost all linger time. That being said, fuel is cheap, and I'd imagine they would run with as much fuel as possible for such events.

That's a hell of a lot to think about, but this may dictate why most units ran those aft tanks first. Don't forget, however, that you'll want to run your left wing tank every so often, as the fuel returns to that tank (and if overfilled, will be expelled from the aircraft, equating to lost fuel). Either way, once combat commences, you want that aft tank as empty as possible for combat maneuvering. The alternative is to run the drop tanks dry, but then there's no way for you to dump the fuel from that aft tank, which could be the difference between life or death (hence running it first). At least you can get rid of your drop tanks.

[Jacques]

Thanks Gents, all interesting stuff, and it confirms I'm using fuel the most practical way. Now I just need to get the computer to behave long enough for my flight to last more than a few hours to use those drop tanks!

[Alan_A]

Just to elaborate on Cody's post - Jimmy Doolittle put a relay system in place when he took command of the Eighth Air Force,. Instead of having a fighter escort conduct a whole mission with the bombers - flying slowly and burning lots of fuel - several different escorts would be used to cover different parts of the mission, each one flying straight to a rendezvous point to relieve the previous one. Spitfires would handle the short-range responsibilities (cross-Channel escort), then P-47s would handle the advance and the withdrawal. The P-51s would fly to the most distant rendezvous point to cover the bombing run, then cut loose on the return trip for ground attack. That allowed the P-51s to burn down the fuselage tank to 25 gallons first - which had the advantage of "correcting out" the aft imbalance and making the aircraft safe to maneuver in combat - then they could burn the fuselage tanks some or most of the way down, getting the most out of the drop tank fuel, all before they got to the combat area.

There's a quick gloss about the relay system in this article (search on "relay"). Jay Stout is one of several good longer sources if you want to know more.

[Jacques]

Were the fuel tanks (fixed tanks in the wings and fuselage) baffled to any degree? I would guess not, but thought I might ask anyway. Was the instability caused by a certain fullness of the fuselage tank a result of weight alone? Or was uninhibited "sloshing" of fuel in the fuselage tank when loaded with a certain number of gallons also a factor in instability?

@ Alan...It seems that the release from escort duty at each phase and the approval to hit targets of opportunity on the ground was one of the more crucial decisions made towards ultimately shortening the war in Europe.

[robert41]

The instability was from the shifting of the center of gravity too for back, from the weight of the fuel. It is very well modeled on the A2A P51. Take her up with a full aft tank and no drop tanks.

The order to release from close escort came out in Jan 1944 I believe. "To destroy the Luftwaffe in the air, on the ground and in the factories". Was part of the build up for D-Day. The bomber crews did not like it. But I think it did help to shorten the war.

[Alan_A]

@robert41 - January 7, 1944 to be exact. Sorry, but after posting I had no choice but to pull Stout's book off the shelf and refresh my memory a bit. The full story is that there was a series of decisions. The first one, in January, was to implement phased escort - something that had been discussed before Doolittle took over for Eaker (Stout describes this as an example of Doolittle's command style, relying on his staff for advice). Very shortly after that, Doolittle put through the order to replace close escort with aggressive fighter sweeps and combat at much greater distance from the bombers. This was a doctrinal shift - the fighters' main mission became destroying German fighters, rather than protecting the bombers. Releasing the fighters to ground attack came still later - a sort of natural evolution, since the "liberated" escort fighters had started following the Luftwaffe fighters down to the deck, chasing them home to their airfields, then attacking the airfields. It was a predictable next step to let them attack other targets on the ground while they were in the neighborhood. This wasn't strictly tied to the invasion - these attacks were happening deep inside Germany - but the fighters were also being used for ground attack in France during the invasion run-up, so it wasn't a big leap to extend the idea to the escort fighters, too.

@robert and Jacques - The fighter attacks are in fact widely credited with shortening the war by increasing the "combat zone" and grinding down what was left of the Luftwaffe.

And yes, the bomber crews hated the idea. In practice, some fighters were held back to fly close escort while the rest swept on ahead. The close escorts were there to comfort the bomber crews, but also had work to do when the Luftwaffe slipped past the wider-ranging fighters.

When phased escort started, the long-range work was mostly handled by P-38s. The Mustangs took it over (and flew farther) as they came into service.

All of which is stuff to think about during the time it takes to burn through that fuselage tank...