British escort fighter--what might it have been like?

[don4331]

I'm still going to champion the Whirlwind:
630 mile range on 134 gallon fuel for Whirlwind Mk. I, but that that's really ferry range (max at lean cruise - 210mph). Most realistic is 375 miles at 300 mph (rich cruise).

Whirlwind Mk. I was cleared for 500lb bombs, that would allow 65 gallon wing tanks (reduced slightly from just weight of bomb to allow for tank weight/piping. That basically matches internal fuel, which makes Whirlwind a 350 mile escort fighter by just adding drop tanks. As we add plumbing for the drop tanks, we fix the inability to cross feed.

But, we want Petter's Whirlwind Mk. II where he adds 27 gallon forward/35 gallon aft fuselage tanks, total 196 gallons = 525 miles rich cruise range. As the leading edge slats were wired shut in the Mk. I, there is option for leading edge tanks in the outer wings. Then we need either an additional 65 gallon fuselage tank or single 200 gallon torpedo tank under fuselage. This should equal the Spitfire option.

de Havilland corrects the propeller blade root issue for Whirlwind - there is future for the airplane so worth making changes (same modification they did to Spitfire blades with same problem)

We might need to change to 2 - 20mm/ 3 or 4 0.303 nose - I don't know when belt feed for 20mm becomes available and 60 round drums don't hold much. Belt fed 0.303 is short term solution to that issue (400+ round magazine/gun)

Peregrine I was cleared for 100 octane, but higher boost is really only available at low altitude - we really need RR to step up the supercharger* (not sure if higher gear ratio is possible - historic 9.5:1 increase is getting pretty significant and I don't know how close to limit the impeller is operating. Merlin I supercharger was designed for ~25% more air flow which is close to what the Peregrine 'III' needs).

Lastly, we need fix for throttles - replace the hydraulics with more conventional cables. Training to regularly cycle throttle is short term solution...

*From what I've read - Cdn gov't turned down manufacturing Merlin believing it was too small for any extended production run. Instead wanting Sabre which they believed had more future - but Sabre still had too many issues licensed product. My alt-history - move the Peregrine to Canada when RR 1st wanted to cancel it - with the carrot, Peregrine has lot in common with Vulture. If production of Peregrine is success, Vulture production would be licensed (long term option).

All the above get British escort fighter with ~400 mile range without impacting Merlin/Spitfire. They could start coming on line in mid-41. (Whirlwind being operational end-'40)

 

[nuuumannn]

Didn't Griffon Spitfires get stronger longerons?

Maybe made of steel instead of aluminium?

They did compared to previous Spitfire models as strengthened longerons were an addition to the 60-Series Merlin-engined Spitfires that were converted from earlier fuselages. They weren't steel, which would have induced dissimilar metal corrosion with the surrounding ali frames. Also, you certainly don't need to waste time redesigning the structure to increase the strength of the longerons. They were fitted with a doubler insert that fit within the U shape of the longeron. Bear in mind that the first batch of Mk.XIIs were ordered as 500 Mk.Vcs in August 1941 and underwent conversion on the production line between November 1942 and August 1943, the first XIVs were originally ordered as Mk.VIIIs, 700 of them in July 1942. They underwent conversion on the production line between December 1943 and October 1944 and so on...

The Spit Mk.VIII was the basis for the modifications that went into subsequent Griffon-engined Spitfires as examples were trialled with Griffons after these were fitted to the Mk.IV prototypes. The Mk.VIII had the modified fuselage of the Mk.VII, which was essentially similar in structural detail to the Mk.V, but for the strengthened longerons, (slightly wider and cross-member strengthening to cater to the Griffon when those were fitted), but the number of frames and structural details were exactly the same Frames 5 through 19 making up the fuselage. The Mk.VII fuselage also had a ballast mounting in the rear fuselage, that was carried through into the Mk.VIII and Griffon-engined Spitfires.

 

[drgondog]

They did compared to previous Spitfire models as strengthened longerons were an addition to the 60-Series Merlin-engined Spitfires that were converted from earlier fuselages. They weren't steel, which would have induced dissimilar metal corrosion with the surrounding ali frames. Also, you certainly don't need to waste time redesigning the structure to increase the strength of the longerons. They were fitted with a doubler insert that fit within the U shape of the longeron. Bear in mind that the first batch of Mk.XIIs were ordered as 500 Mk.Vcs in August 1941 and underwent conversion on the production line between November 1942 and August 1943, the first XIVs were originally ordered as Mk.VIIIs, 700 of them in July 1942. They underwent conversion on the production line between December 1943 and October 1944 and so on...

The Spit Mk.VIII was the basis for the modifications that went into subsequent Griffon-engined Spitfires as examples were trialled with Griffons after these were fitted to the Mk.IV prototypes. The Mk.VIII had the modified fuselage of the Mk.VII, which was essentially similar in structural detail to the Mk.V, but for the strengthened longerons, (slightly wider and cross-member strengthening to cater to the Griffon when those were fitted), but the number of frames and structural details were exactly the same Frames 5 through 19 making up the fuselage. The Mk.VII fuselage also had a ballast mounting in the rear fuselage, that was carried through into the Mk.VIII and Griffon-engined Spitfires.

Interesting with one question: Empennage sizing/strengthening. The Attach joint, load path to H.Stab and V.Stab spars have to be carefully scrutinized for not only AoA increases due to increased gross weight, but also asymmetric load increases - I would think.

 

[nuuumannn]

Interesting with one question: Empennage sizing/strengthening. The Attach joint, load path to H.Stab and V.Stab spars have to be carefully scrutinized for not only AoA increases due to increased gross weight, but also asymmetric load increases - I would think.

The empennage was attached to the rear fuselage section that housed among other things the tail wheel, which butted up against Frame 19 on the fuselage. The tailplane spar, to which the hori stab and tail wheel mounts attached ran vertically through the tail section, was Frame 20 and bore the bulk of the loads in the tail section. It was the keel post for the fin and tapered down, from a front view, to swell into an oval cross-section to conform with the fuselage taper. Obviously, this was, like the wings, modified to enable the different configurations. In the photo, Frame 20 can be seen as the doubled frame extending into the vertical diagonal line running up the fin.

Tail section

 

[wuzak]

Hawker Tornado, compared to the Defiant it had almost 3 ft more wingspan. about 33 sq ft more wing (13%) but the fuselage was about 2 1/2 ft shorter.
Accounts differ but it never hit 400mph and either had a Vulture II with 1710hp at 15,000ft when it hit 398mph or it had a Vulture V with ???? power.

The only number I have at hand for the Vulture V is the take-off rating - 1955hp @ 3,200rpm, +9psi boost.

The take-off rating for the Vulture II was 1,800hp @ 3,200rpm, +6psi boost.

The Vulture V was using 100 octane fuel, Vulture II may have been using 87.

 

[PAT303]

Even the much-vaunted Lancaster topped out at 21,400ft which still is nowhere close to the operating altitudes of B-17s or B-24s and is still right in the sweet spot for Flak 88s. Maybe...just maybe....the RAF leadership were smarter than some give them credit?

How good was FLAK directors and control in 1940-42?, it's okay for the FLAK to be able to reach the bombers but mechanical fuses were not accurate at any range and height, so inaccurate in fact it directly lead to the development of the VT fuse. Bomber Command switched to nights because of losses, at least during the day if they had escort Spitfires they had a chance of seeing their intended target, the early years of BC night bombing they were lucky to get bombs within tens of kilometers of them.

 

[PAT303]

From my perspective, the first approach would have been wing re-design (internally) to see if 50+ gal in each wing could be accomodated but still retain 4x20mm or even 4x50 cal with same airfoil section.

Their is more than enough room for 30G per side by extending the tank inboard from rib 7 to rib 1, PR Spitfire's used this arrangment. Once the upper rear aux 42G is burnt off change to the 90G dropper which gets you searching for trouble over the Ruhr, with it dropped you still have 96G left in the main, 60G in the leading edges and 33G in the lower rear tank, more than enough fuel to do the job. In 1940-41 both the .50 BMG and 20mm Hispano are rubbish, stick with the .303's loaded with AP, De Wilde and tracer harmonised to converge within a 1m square at 250 meters.

 

[Shortround6]

How good was FLAK directors and control in 1940-42?, it's okay for the FLAK to be able to reach the bombers but mechanical fuses were not accurate at any range and height, so inaccurate in fact it directly lead to the development of the VT fuse. Bomber Command switched to nights because of losses, at least during the day if they had escort Spitfires they had a chance of seeing their intended target, the early years of BC night bombing they were lucky to get bombs within tens of kilometers of them.

With fused AA fire the errors are exponential.

The shells will fall into circle in the sky 33% bigger diameter at 20,000ft than they will at 15,000.
Which means the shells will be going into an area about 77% bigger.
Minor differences are changes due to wind, and changes in the velocity of individual shells affecting time of flight from ground to altitude.

This is just the variations the shell flight, then we get to the fuses. The clockwork fuses were actually pretty good, at least compared to powder train fuses.
However their accuracy was usually stated in percentage vs time of flight. same time of flight error in shell traveling for 15 seconds is a smaller error than the same shell traveling for 20 seconds. If the fuse has an error of 0.01% of the time of flight? However the shell is traveling a lot slower from 15,000ft to 20,000ft than in the first 5,000ft of travel so the errors are much larger the higher you try to shoot.

This assumes you have good data to begin with and if what you have is optical equipment that also has errors expressed as a percentage of the range. Same percentage of range error at 15,000 and at 20,000ft give different actual height errors.

Put all this stuff together and the errors at 20,000ft are much much greater at 20,000ft than they are at 15,000ft.

British used powder train fuses at the beginning of the war and the Germans used clockwork fuses in much larger numbers.

 

[drgondog]

Their is more than enough room for 30G per side by extending the tank inboard from rib 7 to rib 1, PR Spitfire's used this arrangment. Once the upper rear aux 42G is burnt off change to the 90G dropper which gets you searching for trouble over the Ruhr, with it dropped you still have 96G left in the main, 60G in the leading edges and 33G in the lower rear tank, more than enough fuel to do the job. In 1940-41 both the .50 BMG and 20mm Hispano are rubbish, stick with the .303's loaded with AP, De Wilde and tracer harmonised to converge within a 1m square at 250 meters.
View attachment 742965

For escort, SOP would cause use of 90gal droptank first. At moment of enemy engagement, no pilot wants 90 gal unsealed 'napalm to still be attached and unused;

 

[yulzari]

It occurs to me that the Spitfire's 4x.303 add little to the effective firepower of an escort fighter attacking incoming fighters so perhaps leave in the 2x20mm cannon and have the extra space left for fuel?

 

[PAT303]

For escort, SOP would cause use of 90gal droptank first. At moment of enemy engagement, no pilot wants 90 gal unsealed 'napalm to still be attached and unused;

No it isn't, the Spitfire was only cleared for combat with 33G the P51 35G in the rear tanks.

 

[PAT303]

It occurs to me that the Spitfire's 4x.303 add little to the effective firepower of an escort fighter attacking incoming fighters so perhaps leave in the 2x20mm cannon and have the extra space left for fuel?

Neither the 1940-41 era .50BMG or 20mm Hispano worked as designed, eight .303's loaded with appropriate ammunition did.

 

[Shortround6]

There are a lot problems with a 1940-41 escort Spitfire.
Not insoluble but not quite as quick as easy as it seems.
The 1940-41 Spits had 3 different engines with rather different take-off power.
Also rather different power at fighting altitudes.
Now perhaps we can solve some the power problem in 1941 by jamming Merlin XX engines into the escorts instead of Merlin 45s?
At least makes getting off the ground a bit easier.

In post #627 a fuel load of 321 Imp gallons is proposed or at least given as a max possible. Subject to decrease on the early planes?
Problem #1, without counting the weights of actual fuel tanks and piping and counting the fuel at 7.2lbs per gallon this increases the gross weight of a Spitfire II to more than allowable gross weight of a Spitfire IX operating from a smooth paved runway.

Problem #2, The engine/propellers in the MK I, MK II, MK V are at least 300lbs lighter than the engine/prop in the MK IX making the aft balance problem somewhat worse. The extra weight of the radiator/intercooler may not make up for all of it.

Problem #3, Back to taking off.
Just some figures from a P-40N

Clean....................................8400lbs...........1100ft ground run
75 US drop tank..............8900lbs............1600ft ground run
170 US Ferry tank...........9500lbs............2500ft ground run

Problem #4. mentioned several times in the early part of the thread.

There are performance figures for this MK II in "the Spitfire Story" by Alfred Price (page 137 in my copy). I am perfectly willing to concede that 30mph speed difference at 20,000 between this configuration and a standard MK II would pretty much disappear with internal fuel storage what would not disappear would be the difference in climb. Which at 20,000ft was 2,175fpm for the standard plane and 1,420fpm for the loaded one. At 25,000ft the difference was 1,600fpm to 1,050fpm.
This was for 40(?) IMP gal. With internal tank/s the difference would be a bit closer but if you want another 40imp gal inside??????

It is not enough to show up, escort fighters actually have to fight, at least moderately well.

In 1942-43 you get a lot more powerful engines for not a lot of extra weight, You also get better/bigger airfields.

 

[PAT303]

Now perhaps we can solve some the power problem in 1941 by jamming Merlin XX engines into the escorts instead of Merlin 45s?

The escort Spitfire would be the MkIII with two speed Merlin XX's.

 

[PAT303]

There are performance figures for this MK II in "the Spitfire Story" by Alfred Price (page 137 in my copy). I am perfectly willing to concede that 30mph speed difference at 20,000 between this configuration and a standard MK II would pretty much disappear with internal fuel storage what would not disappear would be the difference in climb. Which at 20,000ft was 2,175fpm for the standard plane and 1,420fpm for the loaded one. At 25,000ft the difference was 1,600fpm to 1,050fpm.
This was for 40(?) IMP gal. With internal tank/s the difference would be a bit closer but if you want another 40imp gal inside??????

P51's, P38's P47's couldn't climb either at the start of their flight out, no fighter that had the fuel load to fight 400 miles out could except the P47, it couldn't climb empty and they were used as escorts. None of the arguments against the Spitfire stack up because the issue's were still their in 1943-44 when escorting bombers hit full swing.

 

[drgondog]

No it isn't, the Spitfire was only cleared for combat with 33G the P51 35G in the rear tanks.

Not sure what your point was here. 'Burn 25-40gal in fuse tank was 'recommended', not a condition for 'combat clearance'. The mission dictated the actual process. Additionally, the stricture was for the extremely low stick force in accelerated turn with aft cg. The bob weight mitigated that issue - but the solution was to avoid turning fight.

SOP for 8th and 9th was to fill to either 65 or 85gal, burn some in climb out to altitude, switch to externals on cruise in. Switch to internal and drop tanks to engage in a fight.

 

[Shortround6]

P51's, P38's P47's couldn't climb either at the start of their flight out, no fighter that had the fuel load to fight 400 miles out could except the P47, it couldn't climb empty and they were used as escorts. None of the arguments against the Spitfire stack up because the issue's were still their in 1943-44 when escorting bombers hit full swing.

Kind of misses the point.

The low Climb figures are for the Spit II with 124 imp gal of fuel onboard. Which is about what you need to do 15-20 minutes of combat after you drop whatever external fuel tank/s you have and you have burned up most of whatever rear fuel tank you have installed and get home.

The P-47D with crap propeller and without water injection could climb at 1900fpm at 20,000ft with whatever fuel it had after taking off and starting the climb test out of 300 gallons.
Spit Vs climbed better.

it also misses the point about the airfields.
The airfields of 1943-44 were NOT the airfields of 1940-41. Many or most of the existing RAF fighter fields were enlarged and had obstructions (building and trees) cleared away. New airfields were built larger to begin with. P-51s had it easy, they were going into fields that been built (or modified) to suit P-47s Which had field requirements almost that of a medium bomber.

A Spitfire long range escort in 1943-44 may very well be doable. In 1940 not a chance. In 1941 maybe, at distances into Holland or France.

 

[drgondog]

P51's, P38's P47's couldn't climb either at the start of their flight out, no fighter that had the fuel load to fight 400 miles out could except the P47, it couldn't climb empty and they were used as escorts. None of the arguments against the Spitfire stack up because the issue's were still their in 1943-44 when escorting bombers hit full swing.

???? Did you miss the memo that P-38s and P-51s were fighting 600mi out when P-47s were turning back for home at 400mi out?

I don't understand your point about climb with a full load of fuel. ALL were piggish in climb to altitude.

Internal fuel remaining at the point of attack was the determinant for Combat Radius. For a Spit to have the same combat radius as any model P-51, it had to have the same internal fuel capacity. Period. Arguing external tankage is only a distraction and more interesting discussing Ferry range - or relatively non-lethal high altitude Recon missions, untethered by escort duties.

 

[PAT303]

I don't understand your point about climb with a full load of fuel. ALL were piggish in climb to altitude.

It was in regards to SR reply in regards to handling and climb when loaded with fuel. You also have to take into account the time frame, the Luftwaffe had a very strong presence on the channel coast in 1941-42, you wouldn't want to be caught by an FW190 with full rear tanks, the full drop tank could at least be dropped as a last resort.

 

[PAT303]

Internal fuel remaining at the point of attack was the determinant for Combat Radius. For a Spit to have the same combat radius as any model P-51

We aren't trying to get the Spit to match the Mustang, we are just trying to get worthwhile range out of it, that's why we are focused on the Ruhr valley from 1941.