Fuel Fraction & Range of WWII Aircraft

[Zipper730]

Who proposed an escort and when?

From what I remember the USAAC had looked into the idea at several different periods: First, they started with a single-engined design (with a rear gunner); then they went to a modified variant of the Martin B-10 in 1935; then they went to the YFM-1

 

[DarrenW]

I didn't know the F6F-3 and F6F-5 were almost the same in weight

It depends on the level of maturity of the F6F-3. There was an gradual increase over time of about 200 lbs as slight changes were made to the air-frame and engine, with the addition of a water injection system being the primarily culprit. Introduced in May 1944, the F6F-5 just incorporated all the piece-meal changes made to -3 variant up to that point. There's very little physical difference between the last -3s and first -5s. Easiest way to tell if it's a -5 variant is by the overall Gloss Dark Sea Blue paint scheme and the modified windscreen (which mimicked the -3N). F6F-5s had strengthened tails and slightly more armor plating which increased weight accordingly, but still not by any appreciable amount (about 60 lbs). A further increase was experienced by cannon armed versions which weighed approximately 280 lbs more than those with standard machine guns but those were in the minority.

 

[Shortround6]

Plus, a lot of proponents of long-range fighters had some bizarre ideas of what they wanted in an escort.

1. Multi-crew
   • At least two, which included a gunner: The idea was a gunship that could rove over the bomber formation and add to the defensive firepower

If you are referring to the Bf 110 this idea is incorrect. The Bf 110 carried the same radio as the He 111 bomber (and some other German bombers). The radios used by single seat fighters in the late 30s and into the beginning of WW II were rather short ranged. On the Bf 110 the rear seater was also part of the loading mechanism for the 20mm cannon. This was also part of the duties of the 2nd crewman on the Beaufighter (and that 2 seater didn't get a gun for the 2nd crew member until late it's career).
Since the Bf 110 needed a 2nd crewman for several functions anyway, why not give him a gun a 1/2 dozen magazines of ammo?

Don't judge prewar or very early war designs by late war capabilities.

Bolton Paul Defiant.

Please note the antenna mount near the firewall and the 2nd mount a few feet forward of the tail wheel, this mount (or both?) had to be retracted for landing, ground handling and take-off. The Defiant used a different radio than the Hurricane and Spitfire and could not talk to them.

Building long range fighters than cannot talk to (or morse code key) their bases or bomber formations in order to set up a rendezvous puts some severe limitations on their usefulness.

Full fraction is an interesting number from a design point of view but only if you are comparing aircraft of similar timing (year/s of design) and requirements.

For somethings it is near worthless. A P-47D-25 could have 305 gallons on fuel on board for a fuel fraction of 13%, filling the internal tanks to 370 gallons gives a fuel fraction of 15.4% and adding a pair of 150 gallon drop tanks gives a fuel fraction of 25.6% but what does that tell you?

 

[drgondog]

That's interesting, I thought the P-51D was cleaner.
the 110 and 165's were how they were able to escort the B-29?

The P-51B and D have essentially the same Parasite drag except the wing racks on the D are cleaner. That said, at Cruise where Induced drag as the same as Parasite drag, the P-51B has lower Gross weight ---> lower Induced drag and optimal cruise speed is slightly higher with same cruise setting for same RPM/MP and fuel consumption. Over 700 miles it will net to 25+ miles of combat radius.

The P-51Ds in Pacific used the 165s

 

[Zipper730]

On the Bf 110 the rear seater was also part of the loading mechanism for the 20mm cannon.

And I guess this was because a really long belt of ammo would jam too easily?

Building long range fighters than cannot talk to (or morse code key) their bases or bomber formations in order to set up a rendezvous puts some severe limitations on their usefulness.

I guess later on with the P-38J, P-51, and P-47N's that this had been worked out with technological changes?

Full fraction is an interesting number from a design point of view but only if you are comparing aircraft of similar timing (year/s of design) and requirements.

Seems like a valid point.

For somethings it is near worthless. A P-47D-25 could have 305 gallons on fuel on board for a fuel fraction of 13%, filling the internal tanks to 370 gallons gives a fuel fraction of 15.4% and adding a pair of 150 gallon drop tanks gives a fuel fraction of 25.6% but what does that tell you?

It can fly further with 2 x 150 gallon tanks

at Cruise where Induced drag as the same as Parasite drag

That's how cruise speed is determined on aircraft? Regardless, the P-51 typically, on long-ranged missions, flew around 300 mph. Probably above the optimum cruise speed.

The P-51Ds in Pacific used the 165s

I remember being told that the B-29's cruised at around 310-320 mph, and the P-51's cruised around 300-305 mph. My guess was part of the range increase was that the P-51's didn't have to S-weave. I figured either the bombers flew slower, or they somehow increased range.

 

[pbehn]

If we rid these specifications from things, it would have been way easier to achieve. The point, was simply a fighter that could do all the stuff a fighter could, and fly very far, and that probably would require two engines if we didn't want to go the way of the A6M.

This post seems to want to get a P-51B/C or D into service earlier. Most planes are designed around an engine and then they go into an airforce structure. When the P-51 was designed the Merlin two stage engine didnt exist and neither did the fuel it used, neither did the bomber force, or the concrete airfields or indeed the few thousand extra pilots needed to take part in a bomber offensive from Europe.

 

[Zipper730]

This post seems to want to get a P-51B/C or D into service earlier. Most planes are designed around an engine and then they go into an airforce structure. When the P-51 was designed the Merlin two stage engine didn't exist and neither did the fuel it used

That's all entirely correct. That said, a twin-engined aircraft with turbochargers could potentially muster adequate range. The Beaufighter could do around 1750 miles, correct?

 

[Shortround6]

And I guess this was because a really long belt of ammo would jam too easily?

It is because, when the design work started on many of these airplanes the 20mm guns didn't have belt feeds. They were drum feed guns and the drums were simply large magazines.
Many of the 20mm guns could trace their parentage back to the Becker gun

Becker is the one on the left. The mechanism is basically a scaled up automatic pistol.
Let's remember that the Browning .50 cal had some real problems in 1939-41 with feeding it's belt. There are several types of jam and some of the most basic are not belt twists but simply having enough power in the mechanism to move the belt or lift the weight of the belt the desired distance against gravity (this is on the ground, not in a hard turning airplane which just makes things worse. The .50 was modified to more than double the belt pull which solved a number of it's problems (but not all).

Somehow you have to translate the power of the burning powder into a ratcheting mechanism that will pull the belt into the gun (usually done by a cam track on the feed and a stud on the bolt ) And then you have to get the ammo out of the belt. This gets a bit tricky as most smaller machine guns in this period pulled the cartridge backwards out of the belt and then shoved it forward into the breech, this required a longer receiver and bolt travel than a magazine fed gun which only needed to get the bolt to travel to behind the magazine (length of the cartridge) and not the amount needed to get the cartridge out of the bolt. A few guns did use push through belts.
The Hispano was in the same difficulty and resorted to a belt feed device on the outside of the gun that pulled the ammo from the belt, discarded the links and presented the ammo to the original drum magazine feed way. It was powered by a spring that was continual rewound by the action of a stud on a recoiling (reciprocating) part.

Adding a belt could be and was done but usually needed a redesigned receiver or some sort of Rube Goldberg contraption on the outside of the gun,

 

[pbehn]

That's all entirely correct. That said, a twin-engined aircraft with turbochargers could potentially muster adequate range. The Beaufighter could do around 1750 miles, correct?

I think, for a twin engine design with turbos, a single seat twin boom design would be best, something like the P-38 for example.

 

[Zipper730]

It is because, when the design work started on many of these airplanes the 20mm guns didn't have belt feeds.

When did they start featuring them?

Let's remember that the Browning .50 cal had some real problems in 1939-41 with feeding it's belt.

I did not know that...

I think, for a twin engine design with turbos, a single seat twin boom design would be best, something like the P-38 for example.

That's to make it easy to mount the turbo and everything?

 

[pbehn]

That's to make it easy to mount the turbo and everything?

In part but you need the minimum frontal and surface area, you could advocate for a whirlwind type configuration with the turbos and landing gear in the nacelles. What you cant do is advocate a sort of Beaufighter as a long range escort, it is just a plane that would be shot down from UK to Berlin. When in a close escort role the Bf 110 was easier to shoot down than a bomber. As I said in a previous post a long range fighter has to be competitive with the opposition where it can reach, simply covering the miles was not enough.

 

[Zipper730]

What speed do you think a design like this could do?

2 x V-1710, 1-2 crew.

Also, what would you think of a design that had a redesigned tail, a contra-propeller, and engines mounted in the mid-fuselage, with a ventral fin to keep the prop from hitting the ground?

 

[pbehn]

What speed do you think a design like this could do?

View attachment 570822

2 x V-1710, 1-2 crew.

Also, what would you think of a design that had a redesigned tail, a contra-propeller, and engines mounted in the mid-fuselage, with a ventral fin to keep the prop from hitting the ground?

Less than a P-38 but better dive performance.

 

[XBe02Drvr]

Less than a P-38 but better dive performance.

Still wouldn't turn and burn with an ME or FW, and if built in USA wouldn't have the climb performance to get on top for a vertical fight, at least not with the engines available.

 

[Zipper730]

Less than a P-38 but better dive performance.

So with the tractor arrangement (as drawn), you'd probably guess somewhere from 330 to 350 mph? As for dive performance, would that be in terms of acceleration rate in the dive or actual mach limit as well?

Still wouldn't turn and burn with an ME or FW, and if built in USA wouldn't have the climb performance to get on top for a vertical fight, at least not with the engines available.

Makes sense, even if its stall speed was lower, it'd have more control forces to make them happen?

 

[pbehn]

So with the tractor arrangement (as drawn), you'd probably guess somewhere from 330 to 350 mph? As for dive performance, would that be in terms of acceleration rate in the dive or actual mach limit as well?

?

It is a drawing!

 

[Zipper730]

It is a drawing!

Generally a shape would give some insight

 

[pbehn]

Generally a shape would give some insight

Compare to a Mosquito or Hornet.

 

[Zipper730]

Compare to a Mosquito or Hornet.

The mosquito and Hornet are less plump, so...

 

[pbehn]

The mosquito and Hornet are less plump, so...

They aren't, you need to find someone with experience of compressibility and plastic flow on sketches.