P-51 fuselage fuel tank (5 Viewers)

[ThomasP]

Does anyone know what form of construction was used for the 85 USgal fuel tank - ie aluminum tank with SS outer shell, or maybe total non-metal except for fittings, etc?

 

[MiTasol]

Hi,

I feel that the handling described in the Eglin test report 4-43-23-1 is much more complicated than the illustrations and text in Horkey's information that you posted.

Eng

Language is always changing/evolving so there is also the possibility that terminology/definitions have changed over the years as the phenomena became better understood. Add to that even things that an individual fully understands and writes about in what they consider obvious language does not mean that another person will comprehend, let alone fully understand, what the that person has written - especially some 80 years later. Add to that prior to ww2 and television what a word or phrase meant is New York was often different in LA, let alone London or Sydney because of linguistic isolation.

 

[MiTasol]

Does anyone know what form of construction was used for the 85 USgal fuel tank - ie aluminum tank with SS outer shell, or maybe total non-metal except for fittings, etc?

All the WW2 metal tanks I have seen are either alloy frame with mild steel casing riveted and then soldered to become leak proof (Ki-43) or 100% what appears to be auto body steel with the steel "frame" spot welded to the top half shell then the bottom half shell seam spot welded to the upper shell.

I know some P-39 tanks and the A6M tanks were 100% alloy except for the attachment hardware.

USAAF TO 01-3-46 identifies the steel as Terneplate which is not a material I had ever heard of. The dictionary description is terneplate, steel sheet with a coating of terne metal, an alloy of lead and tin applied by dipping the steel in molten metal. The alloy has a dull appearance resulting from the high lead content. The composition of terne metal ranges from 50–50 mixtures of lead and tin to as low as 12 percent tin and 88 percent lead. The tin serves to wet the steel, making possible the union of lead and iron, which would otherwise not alloy. Terneplate is made by a process similar to galvanizing or tinplating—i.e., by dipping the sheets into a series of heated baths, the first of a zinc chloride flux, followed by the molten terne metal, and finally one of palm oil. Terneplate has the strength and formability of steel and the noncorrosive surface and solderability of terne metal. While it is still used for roofing, gutters and downspouts, and casket linings and in the manufacture of gasoline tanks for automobiles, oil cans, and containers for paints, solvents, resins, and so on, it has largely been replaced by other, more durable steel products that are easier to manufacture.

Remember the prime requirement once the USAAF decided that drops were needed was the use of non critical materials and this was a common material of the day.

 

[MiTasol]

I should have added that other tanks are listed in TO 01-3-46 as terneplate low carbon steel, fibre, low carbon steel sheet, "plywood or aluminum".

There have been mentions in older documents of paper tanks which I think probably means paper reinforced bakelite - the same stuff the Spitfire instrument panel is made from.

Fibre probably means fibre reinforced bakelite.

Both are better known as versions of Micarta.

 

[Engineman]

Does anyone know what form of construction was used for the 85 USgal fuel tank - ie aluminum tank with SS outer shell, or maybe total non-metal except for fittings, etc?

In Bill's great book, P-51B MUSTANG, he writes that the prototype 85gal internal fuselage tank was metal. The production tanks are described as self-sealing Firestone constructed tanks.
Generally, self-sealing fuel tanks have a layer of soft rubber covering that swells and helps stop leaks from a bullet size hole. A better description of the specific "Firestone" construction
might be available somewhere?

Eng

 

[drgondog]

IIRC - the Firestone (and Goodyear) self sealing tanks are flexible - had to be to install as kits per FSB-73-90. The production tanks were laminated for strength. That said I do not recall whether the baffle was of the same material as the tank itself.

The prototype was welded steel, non-sealing, with very similar outside dimensions, but 90gal capacity..

 

[drgondog]

Well, I think Bill is commenting on changes that added weight that moved the C of G rearwards and compromised handling, which then caused the extra modification of the controls, which made the control forces heavier, which makes the general handling characteristics less pleasing.

Eng

On these examples, no to CG effect, Yes to 'compromised handling'. The modifications restricted the ease of roll and rudder authority. They were driven by challenges experienced due to yaw issues encountered (i.e. throttle changes, high speed rudder input during sideslip or terminal dive trying to reduce drift/Hunt to right with left rudder input) which occasionally led to failure of horizontal or vertical stabilizer and subsequent empennage attach failures.

The DF improved vortex flows over the empennage, which increased differential loads (vertical and side) over the empennage. The reverse rudder boost lessened rudder input from pilot at higher speeds, lessening the compound effect of vortex with rudder control surface input.

 

[MIflyer]

The addition of the weight is likely to have increased the stick loads to pull positive G, enough to prevent stick force reversal with a full rear fuselage tank on these aircraft.

Yes, that is what experienced pilots have said. If you want to outturn an F4U, get rid of that bob weight.

 

[Zipper730]

The base line here is that for stability and normal handling in upright normal flight, the horizontal tail produces a downforce to balance the aircraft weight and the wing lift, the lift being behind the C of G weight and the tail pushing down a bit to balance. A simple stable aircraft has a generous amount of stability if the horizontal tail has plenty of effect available compared to the Lift/Weight couple. Now, high performance aircraft generally reduce the margins of control to minimise structural weight and drag, but must still handle well. However, if you take any normal aircraft and put more weight towards the tail, it becomes less stable because the horizontal tail has to generate smaller control forces to balance the aircraft.

Yeah, that's why I would have just thought a pitch-up would result.

If I'm grasping this right, it almost seems that the instability is exacerbated by the amount of stick-force, so the more you pull back, the worst it gets or something. That said, I could be wrong.

 

[Engineman]

Yeah, that's why I would have just thought a pitch-up would result.

If I'm grasping this right, it almost seems that the instability is exacerbated by the amount of stick-force, so the more you pull back, the worst it gets or something. That said, I could be wrong.

Hi,
What we have to realise is, that there are several factors at play here. A conventional stable aircraft can be safely flown and can have manual aerodynamic controls if the control forces
are in the normal relationship, ie, pulling harder generates more positive G. This is usually achieved and limits of C of G are defined by calculation and testing to ensure the aircraft responds normally. However, both the stability of the aircraft (aerodynamic and C of G related) and the control forces (loads and sense of response) can be out of harmony even to the extent that the aircraft is uncontrollable and the design and limitations have to ensure that the aircraft is not uncontrollable. Many modern aircraft are actually unstable, but they fly normally because the computer control systems present the pilot with normal handling laws to his control stick and the controls are fully powered, but the aircraft still has limitations of C of G etc. The "Bob weight" mentioned here is a simple method of replacing an inadequate control force (very low or reversed control force due to exceeding the original design C of G limit over a certain positive G threshold)) with a related extra stick load from the G-influenced Bob weight. The extra load from the Bob weight under G gives extra control loads that make the handling remain conventional to the pilot. This modification still relies on the physical ability of the tailplane/elevator and aerodynamics to perform satisfactorily and the overall effect is to change the control response to allow an acceptable rearward extension of the C of G limit, albeit with some less desirable effects on the stick forces even when the C of G was not so far aft and didn't need the extra Bob weight.

Eng

 

[Zipper730]

This will sound very dumb, but a bobweight is a type of counter-weight right?

 

[Engineman]

This will sound very dumb, but a bobweight is a type of counter-weight right?

See my attachment on post #215

Eng

 

[Reluctant Poster]

Well that is interesting. According to a USMC pilot who flew F4F's from Guadalcanal the tanks they used were made of a "Bean pod" material (presumably nonmetallic) and required the pilot to manually pump the fuel out of the tank.

I find that very hard to believe. If you've ever used a hand pump to transfer fuel out of a 55 gallon drum you'll know it takes time and effort

View: https://www.youtube.com/watch?v=XmzYEioLyU0
A gallon of fuel for every 10 turns of the crank. 550 turns. . Imagine how awkward this would be to do in the cockpit of a F4U. Where would you even fit such a pump in the cramped cockpit of an F4U. A lever style might be a better fit but the effort is greater.

View: https://www.youtube.com/watch?v=LWJHTULL9ko

 

[MiTasol]

Hand fuel pumps were called wobble pumps and were very common on aircraft of the period. All early DC-3/C-47, early AT-6, early P-40, and many others. Many civil DC-3/C-47 aircraft in the 70s still used the wobble pumps.

P-40 installation below

AT-6/Harvard below

C-47

 

[Reluctant Poster]

Hand fuel pumps were called wobble pumps and were very common on aircraft of the period. All early DC-3/C-47, early AT-6, early P-40, and many others. Many civil DC-3/C-47 aircraft in the 70s still used the wobble pumps.

P-40 installation below
View attachment 790302

AT-6/Harvard below
View attachment 790303

C-47
View attachment 790305

Isn't the P-40 installation for priming the engine driven pump for start? It isn't piped for fuel transfer.

 

[MIflyer]

Hand fuel pumps were called wobble pumps

Yep, and in fact I think that Aircraft Spruce still sells a combined wobble pump and fuel valve.

Imagine how awkward this would be to do in the cockpit of a F4U

I said F4F not F4U. A different airplane. And the F4F already had a hand cranked MLG, operated by bicycle chains. See attached.

 

[Zipper730]

See my attachment on post #215

Eng

I'm not on all 8 cylinders today, but If I read this right: This seems like some kind of counterweight that's placed in front of the position of the 85 gallon tank, and when pulling back on the stick, the weight shifts forward to manage the C/G?

 

[MiTasol]

This is one of the several different sized standard USAAF wobble pumps. Some, like the D-3 used on the AT-6, had built in fuel filters and some had a linkage that was connected to a remote pump handle. It is likely that the F4F installation mentioned by MIflyer used a remote pump with only the handle itself in the cockpit - just like the P-40.

 

[MiTasol]

Reluctant Poster asked Isn't the P-40 installation for priming the engine driven pump for start? It isn't piped for fuel transfer.

If you follow the diagram the fuel goes from the tanks to the fuel selector valve (PG-3) to the strainer to the D-11 hand pump to the engine pump and then the carb. On aircraft with a single drop tank the PG-3 selector was replaced by a PG-4 fuel valve and the fourth inlet is plumbed to the drop tank.

Later again the wobble pump and fuel vapor eliminator were replaced by an electric boost pump and slightly different plumbing.

Later again the selector was changed to permit the use of wing drop tanks as well.