WWII Warbirds and Tip-Tanks?

[John Howling Mouse]

Why didn't more WWII piston-engined fighters utilize wingtip tanks?  I always thought that would free up more pylons on the wings for ordnance and/or more fuel.  Was it a power to weight ratio limitation back then or would tip tanks simply not be dependable to jettison once ready to engage the enemy in ACM?  Or were the wings simply not strong enough to handle the fuel's weight on the wingtips?

[elmayerle]

I suspect part of it was that the wings weren't designed for it, either structurally or aerodynamically; especially since that much mass that far out would inhibit your roll rate 'til you could burn the fuel off (operational fix, burn the tip tanks first).  I'm not certain how much extra complication jettisoning tip tanks would introduce, but there'd undoubtedly be some.  I rather suspect tip tanks became more suitable in the jet age when armament was concentrated in the aircraft's nose, leaving wings free for fuel and simplifying the fuel system; as I remember, few piston-engined fighters had fuel in the wings as that's where the armament, cannon or machine gun, went.  Drop tanks have the advantage of being inboard of a lot of that and easier to plumb while tip tanks would have to run the fuel lines past and around the gun and ammo bays in the wings.

[Jeffry Fontaine]

I would also add that most fighter aircraft were designed for short range and air interception close to their own bases.  So the need for drop tanks on the wings or wing tips was simply not considered. 

As far as the structural issues, that may well have been a limitation but I do remember seeing a couple of P-51/F-51 Mustangs sporting wing tip mounted fuel tanks, a pair of ram-jet engines, and a pair of 106mm recoilless rifles at one time or another so the Mustang at least had a wing that could take the load and stress. 

I read somewhere as well that the wing tanks also improved the performance of the aircraft by reducing drag or somesuch thing.  I will leave that to Evan to elaborate on as I have nothing to support that at the moment.

[Ed S]

I suspect that jettisoning tip tanks was a major concern.  When I flew the T-33, we were cautioned about jettisoning the tiptanks.  If one tank hung up and one jettisoned, then you were suddenly trying to recover from an unusual attitude.  The immediate unbalance in weight and yaw could cause loss of control.  Whereas tanks on inboard stations didn't have the moment arm of something way out on the wingtips and didn't subject the a/c to as much yaw and roll.

And, the a/c designers in the 30's and early 40's weren't designing wings for this much weight on the tips.  It wasn't until into the war that fighters started using external tanks.  And even then, they were mostly used for long range escort missions.  The much greater need for fuel in the early jets was the other factor that contributed to increased use of external tanks and the incorporation of tip tanks as part of the design.

Ed

[pyro-manic]

As far as the structural issues, that may well have been a limitation but I do remember seeing a couple of P-51/F-51 Mustangs sporting wing tip mounted fuel tanks, a pair of ram-jet engines, and a pair of 106mm recoilless rifles at one time or another so the Mustang at least had a wing that could take the load and stress.

True, but I wonder what sort of limitations were placed on manoeuvres while these were fitted?

[elmayerle]

I would also add that most fighter aircraft were designed for short range and air interception close to their own bases.  So the need for drop tanks on the wings or wing tips was simply not considered. 

As far as the structural issues, that may well have been a limitation but I do remember seeing a couple of P-51/F-51 Mustangs sporting wing tip mounted fuel tanks, a pair of ram-jet engines, and a pair of 106mm recoilless rifles at one time or another so the Mustang at least had a wing that could take the load and stress. 

I read somewhere as well that the wing tanks also improved the performance of the aircraft by reducing drag or somesuch thing.  I will leave that to Evan to elaborate on as I have nothing to support that at the moment.

Ah, but recoilless rifles don't need anywhere near the extra kit that tip tanks do.  As for wingtip ramjets, they, again, don't need the same total kit that tip tanks do, just fuel lines feeding them as well as suitable attachign structure.  In both cases, I suspect there were localized mods that'd need to be picked up operationally for these wingtip-mounted devices to be used operationally.

Yes, tiptanks can create some favorable interactions with wingtip vortices, much as other tip approaches do, but that's something that needs designing in from the outset to do it right.

As an example of what can go wrong with tiptanks, there was that P-51 based air racer that had the radiators in modified tiptanks and there was an interference with the ailerons that led to the aircraft crashing.

[PR19_Kit]

As an example of what can go wrong with tiptanks, there was that P-51 based air racer that had the radiators in modified tiptanks and there was an interference with the ailerons that led to the aircraft crashing.

That was 'Beguine', one of the best looking Mustang racers ever to my mind, see the whole convoluted history here :- http://www.air-racing-history.com/aircraft/Beguine.htm

Not only did the radiator pods interfere with the aileron airflow, but they also cut the ailerons down in span to fit the pods! Dicing with death there.....