Long range, high speed Spitfire fighter: the best approach?

[tomo pauk]

Chin radiators were probably marginally less efficient that the Spitfire's existing radiator set up. Cooling drag is slightly higher overall, and then you have the issues of increased frontal area and, crucially for the Spitfire, nose heaviness.

Not even the greatest Spitfire fans would say that plane's radiators were that good. As for cooling drag being slightly higher overall (for frontal/beard raditor) - why would that be the case; ditto for frontal area? The oil tank would need to be removed, probably under pilot, so that should balance things somewhat.

The clipped wings on the Spitfires actually increased drag at high altitudes, due to much more turbulent wing vorticies and induced drag.

Plus, they have less than desirable effects on climb rate, turn and handling above 20,000 ft.

Guess you're right about it.

LE radiators were slightly more efficient than either the chin or embeded wing radiators in terms of drag, but only marginally so. Napier put them somewhere between 4.5 and 6.5% better in terms of overall drag.

Okay - we could see some 5% increase in speed then - a 20 mph plus?

Where did PR Spits keep all their fuel?

IIRC they had full width leading edge tanks. Is there some what to use them and add 2 cannon, and 2 0.50s or another 2 20mms?

Use the PR wings as the base, while making room for the gun barrels? So instead of 2 x 66 IG, we have maybe 2 x 45-50 IG?
Were the PR wing fuel tanks protected/self-sealing?

 

[Jabberwocky]

Not even the greatest Spitfire fans would say that plane's radiators were that good. As for cooling drag being slightly higher overall (for frontal/beard raditor) - why would that be the case; ditto for frontal area? The oil tank would need to be removed, probably under pilot, so that should balance things somewhat.

I agree that the Spitfire's radiators weren't that good, but the RAE reported that the Mk Vb's powerplant drag was 18.2% of the airframe's total drag, while the Hawker Typhoon's powerplant drag was 27.1% and the Tempest's powerplant drag was 24.2% of total.

To me, that suggests either one of two things: the Spitfire's radiator set up was more efficient than on the Hawker aircraft, OR, that the drag on the Hawker aircrafts' airframe drag was much lower. Given that a Mk XII with 1820 hp (Griffon IV at sea-level) was 3-4mph faster than a Hawker Typhoon with a 2020 hp (Sabre II at sea level), I'd plumb for the first case rather than the latter.

Okay - we could see some 5% increase in speed then - a 20 mph plus?

Not really. As engine/cooling drag is only about 10-25% of total airframe drag. Rolls-Royce estimated that if the Mk IX's radiators were completely reworked and operating at a theoretical minimal drag (which, in reality, was impossible to obtain), then the speed of the aircraft would be improved by 13 mph, which is about 3.2%.

If you want to know what a basic clean up of an airframe, then this Typhoon IB Performance Data makes fascinating reading.

Basic Typhoon IA achieved 405 mph in late 1941 tests. Tests of Gloster production aircraft in May/June 1942 showed top speeds had dropped to 380-385 mph due to addition of the four cannon, the external rudder mass balances and various other protrouberances.

A quick clean up of production aircraft in July 1942, and top speeds were back up to about 392-398 mph. Further clean ups over the rest of the year and production aircraft were back at about 402-405 mph. A few more detail improvements in 1943 and production aircraft were hitting 413-417 mph by the end of the year, which was faster than the Browning armed prototype.

Detail improvements to the airframe meant that the aircraft gained about 35 mph with no increase in horsepower. Makes the effort of completely reworking the cooling system seem maybe a little much.

 

[wuzak]

Basic Typhoon IA achieved 405 mph in late 1941 tests. Tests of Gloster production aircraft in May/June 1942 showed top speeds had dropped to 380-385 mph due to addition of the four cannon, the external rudder mass balances and various other protrouberances.

A quick clean up of production aircraft in July 1942, and top speeds were back up to about 392-398 mph. Further clean ups over the rest of the year and production aircraft were back at about 402-405 mph. A few more detail improvements in 1943 and production aircraft were hitting 413-417 mph by the end of the year, which was faster than the Browning armed prototype.

Detail improvements to the airframe meant that the aircraft gained about 35 mph with no increase in horsepower. Makes the effort of completely reworking the cooling system seem maybe a little much.

There would have been some power improvement in that period. Possibly 10-20% improvement.

 

[Jabberwocky]

There would have been some power improvement in that period. Possibly 10-20% improvement.

Sabre II wasn't re-rated for +9lbs until after July 1943.

The flight trials show only a minimal improvement in top speed (+2 mph), although below critical altitude there was up to 15 mph benefit.

Most of the gains from cleaning up were made before the engine was cleared for higher boost. The May 1943 tests show 410-414 mph top speed, the August 1943 tests show 417 mph, on a repaired aircraft, so its debatable whether its Sabre would have been re-rated or not.

 

[tomo pauk]

I agree that the Spitfire's radiators weren't that good, but the RAE reported that the Mk Vb's powerplant drag was 18.2% of the airframe's total drag, while the Hawker Typhoon's powerplant drag was 27.1% and the Tempest's powerplant drag was 24.2% of total.

Got me puzzled a little bit here - the Spitfire IX three radiators' system was 'accused' to require 400 HP to overcome it's own drag, per 'Aeroplane' article posted on this forum (I cannot post the lik on this instant), vs. P-51 system that required 50 HP to do the same. Guess we could use a thread dedicated to clarify the powerplant/cooling drag for ww2 airplanes.
The Hawker's duo was using an almost under-slung radiator system, unlike the more 'embedded' one we can find at Miles M20, or P-40F.

To me, that suggests either one of two things: the Spitfire's radiator set up was more efficient than on the Hawker aircraft, OR, that the drag on the Hawker aircrafts' airframe drag was much lower. Given that a Mk XII with 1820 hp (Griffon IV at sea-level) was 3-4mph faster than a Hawker Typhoon with a 2020 hp (Sabre II at sea level), I'd plumb for the first case rather than the latter.

Do you compare high speeds at sea level, or at 2nd gear FTH?
The Typhoon have had the greater Cd0 (0.0238 ) and wetted area (12.5% +), vs. Spit Vc (Cd0=0.0218; the Mk.XII was in the ballpark), so it's total drag (as a force) was almost 15% greater.

Not really. As engine/cooling drag is only about 10-25% of total airframe drag. Rolls-Royce estimated that if the Mk IX's radiators were completely reworked and operating at a theoretical minimal drag (which, in reality, was impossible to obtain), then the speed of the aircraft would be improved by 13 mph, which is about 3.2%.

Acknowledged - more material for the new thread

If you want to know what a basic clean up of an airframe, then this Typhoon IB Performance Data makes fascinating reading.
Basic Typhoon IA achieved 405 mph in late 1941 tests. Tests of Gloster production aircraft in May/June 1942 showed top speeds had dropped to 380-385 mph due to addition of the four cannon, the external rudder mass balances and various other protrouberances.

A quick clean up of production aircraft in July 1942, and top speeds were back up to about 392-398 mph. Further clean ups over the rest of the year and production aircraft were back at about 402-405 mph. A few more detail improvements in 1943 and production aircraft were hitting 413-417 mph by the end of the year, which was faster than the Browning armed prototype.

Thanks, I've read the most of the stuff there, but it won't hurt to read it again.

Detail improvements to the airframe meant that the aircraft gained about 35 mph with no increase in horsepower. Makes the effort of completely reworking the cooling system seem maybe a little much.

There was no such thing (35mph improvement) for Spitfires, eg. different 'series' of the Mk.IX on same engine and it's power setting.

 

[nincomp]

That's right. best, absolute best you could achieve would be about 2/3rds of the P-51. Still very useful in '43.

Interesting. Was this due to some characteristic of the fuselage, or would it have taken too much time and effort to do a complete "clean-up?" Other issues?

On the other hand, did I completely miss the point because you are talking about range instead of speed?

edited to add: Rats, I am a moron. I got confused and thought that the quoted comment was about speed.
I hate it when I do that.

 

[OldSkeptic]

Interesting. Was this due to some characteristic of the fuselage, or would it have taken too much time and effort to do a complete "clean-up?" Other issues?

On the other hand, did I completely miss the point because you are talking about range instead of speed?

edited to add: Rats, I am a moron. I got confused and thought that the quoted comment was about speed.
I hate it when I do that.

Not enough room in the wings for tanks basically. The Mustang had 150 (imperial) gallons with a 71 gallon rear tank giving a total of 221 gallons.
The Spit VIII had 96 in the front tanks and 26 in the leading edge tanks, giving a total of 122. With a rear 66 gallon tank that makes 188 gallons in total.

There was no room in the wings for extra tanks with guns basically.

You might have been able to put in another 26 gallons in the outer leading edge if you deleted the 0.303 guns. Bringing the total to 214. But that is a maybe.

Taking the proven numbers the Spit VIII has 85% of the internal tankage.
But The mustang has a higher most economical speed 253mph vs 220mph and it used a little less fuel per hour (around 4%-5%, depending on model and assumptions) .
Still a little bit better even with the 2x62.5 gal drop tanks vs the single 90 gal Spit drop tank, though the gap closed (maybe 2% to 3% better).

Adjusting for all that you get the LR Spit range being around 68% to 70% of the Mustang, depending on plane models (P-51C or D, Spit HF VIII or LF VIII, a few assumptions, etc).

So internal fuel capacity and parasitic drag basically.

 

[wuzak]

Not enough room in the wings for tanks basically. The Mustang had 150 (imperial) gallons with a 71 gallon rear tank giving a total of 221 gallons.
The Spit VIII had 96 in the front tanks and 26 in the leading edge tanks, giving a total of 122. With a rear 66 gallon tank that makes 188 gallons in total.

There was no room in the wings for extra tanks with guns basically.

You might have been able to put in another 26 gallons in the outer leading edge if you deleted the 0.303 guns. Bringing the total to 214. But that is a maybe.

The Spitfire PR.XIX had (from memory) 266 UKG. That was with full length leading edge tanks, but no guns. Would it be possible to put access tubes through this L/E tank to enable 2 x 20mm + 2 x 0.50" or 4 x 20mm? How much capacity would that lose?

Alos, when talking about US and British aircraft it would probably be best to specify which gallon is being used - the UKG is about 20% larger than the USG. Or better yet, talk litres.

 

[OldSkeptic]

The Spitfire PR.XIX had (from memory) 266 UKG. That was with full length leading edge tanks, but no guns. Would it be possible to put access tubes through this L/E tank to enable 2 x 20mm + 2 x 0.50" or 4 x 20mm? How much capacity would that lose?

Alos, when talking about US and British aircraft it would probably be best to specify which gallon is being used - the UKG is about 20% larger than the USG. Or better yet, talk litres.

I did, just used the term 'imperial' gallons.
The PR Spits had 66 gallons in each wing on th leading edge. Some later models had additional 20 gals in each wing (such as the XiX). Bit of course no weapons.

But I might be a little conservative here, just using the inboard 13 gallon leading edge tanks of the Mk VII and Mk VII.
Looking at the 66 gallon design, of you removed the 4-.303s then another 13 gallons in each wing seems possible
Plus reading all the things they tried for the early PR spits, there is repeated mention of 20 or even 30 gallon tanks being placed under the pilot's seat.

If you add those in you get (all gallons are UK ones):
Fronts tanks: 96 gallons
Wing tanks inner: 13 gallons each (26 in total).
Wing tanks outer: 13 gallons each (26 in total).
Under seat tank: 20 galls
Rear tank: 66 gals.


Total: 234 gallons

Now you would assume than and under the seat tank would not affect CoG much, so you don't have to run it down at first and can retain it for the return flight.
And that you can live with the poorer roll caused by the outer leading edge tanks being full (PR pilots did after all), so you can again retain them full for returning.

All that pushes your maximum combat escort radius to 700 miles, using the same assumptions I used before, not that far off a Mustang (about 85% actually).

 

[tomo pauk]

The Spitfire PR.XIX had (from memory) 266 UKG. That was with full length leading edge tanks, but no guns. Would it be possible to put access tubes through this L/E tank to enable 2 x 20mm + 2 x 0.50" or 4 x 20mm? How much capacity would that lose?
...

I've posted this some time ago. The red 'ovals' and trapeze point to the possible places for fuel tanks. The '?' marked place - anybody knows what was there, was it possible to use it as a place for the fuel tank? Were the LE fuel tanks in the PR spitfires protected/self-sealing?

 

[OldSkeptic]

Even in the PR Spits with an extra 20 gal tank in the wing had them more inboard than that (basically where the cannons are).

Remember that far out the Spit's wing is getting very, very thin, especially behind the leading edge, so there is not much room anyway.
Debatable whether or not there is more room than in the leading edge if you dump the 0.303s. Andd at least you know there will be no structural issues using the edge.

Look at my calcs, if you can manage an extra 13 (UK) gals in the leading edges giving 4 x 13 =52 gals.
That plus the front tanks (VIII size) of 96 gals, plus a rear 66 gal then you have 214 gals.

That's not a bad start, if you can also squeeze in another 20 gals under the pilots seat that's 234, which is more than the P-51.

26 wings, plus 96 front, plus 66 rear, gives 500 miles combat radius.
52 wings, plus 96 front, plus 66 rear, gives 600 miles combat radius.
Add another 20 gals then you get 700 mile combat radius.

Remember at cruise you are getting over 6.5 air miles per gallon (the exact amount depending on whether the drop tank is on or not).

 

[Shortround6]

Tomo, look at this drawing.

http://public.sn2.livefilestore.com...Mw4ndMlX6GCY/spitfire_side.jpg?rdrts=42904509


ANd if you want the tanks to be protected you have to subtract the thickness of the protection form the thickness of the wing. Thickness of the protection is constant. Weight per sq. ft. of protection is constant. Thin tanks well out in the wing can weigh a lot more per gallon held than tanks well inboard in the wing.

 

[wuzak]

http://spitfiresite.com/2010/04/concise-guide-to-spitfire-wing-types.html/2

That's 66 UKG per wing.

Subtract some for the Hispano/Browning 0.50" gun bays, and you would probably still be looking at 50 UKG each wing.

So, 100 gals in the wing
+ 96 gals in the front tanks
+ 66 gals in the rear tank

=262 gals.

Add the 20 gals under the seat, and you have 282 gals.

Spitfire Mk XIV Testing

That gives the XIV 85 gallons in the fuselage tanks plus 27 gallons in the wing tanks.

Range was 500 miles, so radius about 200?

 

[OldSkeptic]

http://spitfiresite.com/2010/04/concise-guide-to-spitfire-wing-types.html/2

That's 66 UKG per wing.

Subtract some for the Hispano/Browning 0.50" gun bays, and you would probably still be looking at 50 UKG each wing.

So, 100 gals in the wing
+ 96 gals in the front tanks
+ 66 gals in the rear tank

=262 gals.

Add the 20 gals under the seat, and you have 282 gals.

Spitfire Mk XIV Testing

That gives the XIV 85 gallons in the fuselage tanks plus 27 gallons in the wing tanks.

Range was 500 miles, so radius about 200?

That's pushing it a bit, remember the Spit's wing gets thinner and thinner as it goes out. It was the thinnest wing around, even by today's standards.

50 gals a wing with a 20mm and a 0.5" is probably a bit too far. And it will hit roll rates badly.
26 gals (2 x 13) a wing with just a 20mm seems quite feasible, though it will affect roll rates, but not nearly so much.

Look at my calcs, that still gives a 600 miles combat range. Well beyond Berlin from SE England bases.

 

[wuzak]

That's pushing it a bit, remember the Spit's wing gets thinner and thinner as it goes out. It was the thinnest wing around, even by today's standards.

66 gallons is what they put into that tank according to that website.

50 gals a wing with a 20mm and a 0.5" is probably a bit too far. And it will hit roll rates badly.
26 gals (2 x 13) a wing with just a 20mm seems quite feasible, though it will affect roll rates, but not nearly so much.

I suppose if you can't use that fuel before combat it would. But then again, if you did, roll rates won't lose out by much.

Look at my calcs, that still gives a 600 miles combat range. Well beyond Berlin from SE England bases.

Your calcs are based on the VIII.

I aim to get a XIV over Berlin, or beyond.

While the VIII would be good, and more than competitive over Germany, I think the XIV would dominate.

 

[tomo pauk]

The Mk.VIII has a crucial advantage - it was there a full year before the XIV. With Merlin 70 it was already 25 mph faster at 25000 ft than LW opposition in 1943 (416 mph vs. 391 mph of Fw-190A-5). Conduct some streamlining and another ~10 mph should be there.

Even in the PR Spits with an extra 20 gal tank in the wing had them more inboard than that (basically where the cannons are).

Remember that far out the Spit's wing is getting very, very thin, especially behind the leading edge, so there is not much room anyway.
Debatable whether or not there is more room than in the leading edge if you dump the 0.303s. Andd at least you know there will be no structural issues using the edge.

...

Wuzak covered this - the PR Spits were flying with 2 x 66 of fuel in laeding edge tanks, plus whatever there was in fuselage. With volume allocated for gun barrels, the fuel should be around 2 x 55 IG, in unprotected tanks. The self-sealing would 'steal' some volume.

Tomo, look at this drawing.

http://public.sn2.livefilestore.com...Mw4ndMlX6GCY/spitfire_side.jpg?rdrts=42904509


ANd if you want the tanks to be protected you have to subtract the thickness of the protection form the thickness of the wing. Thickness of the protection is constant. Weight per sq. ft. of protection is constant. Thin tanks well out in the wing can weigh a lot more per gallon held than tanks well inboard in the wing.

Thanks for the link, I just love schematics.
As yo can see, my proposal does not use the outer quarter of the LE volume, so the weight penalty per gallon carried should be reasonable. Using the historic LE tank used in Mk.VIII as a rough rule of thumb, we could expect maybe 2 x 40 IG of fuel there, in self-sealing tanks.

 

[tomo pauk]

duplicate - please delete

 

[wuzak]

The Mk.VIII has a crucial advantage - it was there a full year before the XIV. With Merlin 70 it was already 25 mph faster at 25000 ft than LW opposition in 1943 (416 mph vs. 391 mph of Fw-190A-5). Conduct some streamlining and another ~10 mph should be there.

Yes, and the XIV starts rolling off the production line not much later than the P-51B starts arriving in England.

But not in large numbers.

I wonder what the hold up is?

I suspect it is a combination of factors. 1) The IX has precedence over the VIII in production, 2) Griffons weren't being built in big enough numbers.

The XIV is basically a Griffon powered VIII. The IX wasn't suiable as a base for the XIV. So if factories were spitting out VIIIs in 1942/43 they would have been easier to turn to XIV production than IXs.

 

[OldSkeptic]

Trouble Wuzac that then becomes a 'what-if' alternative history.

I used the Mk VIII for calculations, but if they had really gone for large scale production of a LR Spit in 43 they would have more than likely retro-fitted existing IXs with VIII leading edge tanks (and the larger front tank plus the rear tank) and of course added them to new ones coming off the production line.

So you would have seen a hybrid IX with VIII tanks, at least until VIII production ramped up.

And those wing tanks count, even with just the standard 26 gal ones. Without them you your max combat range is 400miles.

As for the XIV, they did trial 75 gals tanks but when they actually fitted rear tanks they used 66 gals.
But, push comes to shove and with the greater weight and length of the Griffon helping the CoG issue you could theoretically get:
Front: 96 gals
Rear: 75 gals
Wing: 52 gals
Drop tank: 90 gals
Gives 233 gals in total internal (313 with drop tank).

That will get a get a XIV to Berlin and back, though a bit tight.
But if you can be a little less conservative and leave some fuel (say 20 gals) in the rear tank for combat and the return trip, actually even 10 gals would do it comfortably (niot recommended for the IX/VIII but you might get away with it on a XIV perhaps with a whopping big bob weight on the elevator control).

On rough calculations, 10 gals left in the rear tank would mean a reserve for the XIV of 28 gals on a 500 mile combat mission.

Note that I have always allowed an absolute min of 15 gals (more is needed for a XIV) as a reserve for all the calculations shown previously, got to allow a fair amount for winds, weather, enemy action, etc.

 

[Shortround6]

Thanks for the link, I just love schematics.
As yo can see, my proposal does not use the outer quarter of the LE volume, so the weight penalty per gallon carried should be reasonable. Using the historic LE tank used in Mk.VIII as a rough rule of thumb, we could expect maybe 2 x 40 IG of fuel there, in self-sealing tanks.

Look again and look at the rib sections in the lower right hand corner. By the time you get to the 4th gun the wing is about 1/2 the thickness it is at the beginning of the wheel well and start of the "normal" leading edge tank.
Even rib 14 (just inboard of the of the 2nd gun) shows a sizable reduction cross section of the leading edge compared to Rib 5.

And here is a link to a photo of the inside of the leading edge.

http://www.vintagewings.ca/Portals/0/Vintage_Stories/News Stories E/Just Wingin' It/Wings10.jpg

Trying to fit large tanks in the leading edge WITH protection is going to be a nightmare.