At least someone understands the argument, MkV's used slippers over France that didn't increase their range but instead the extra fuel allowed for a higher cruising speed so it made them harder to bounce, another advantage of extra fuel.
P-51 fuselage fuel tank
- Thread starter Barrett
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Plenty of space between rib 5 and 1 to double the capacity without any additional modifications, your argument about chaffing and costly mods is null and void because the tank was already designed. Actually the only change was moving the gun camera, no biggy.
But is there space that could be sealed?
Aft of the spar in the area of ribs 1-5 were the mounting points for the undercarriage. Those mounts were bolted through the spar into the area you want to use for fuel. Diagrams here.
Spitfire MK.VB Undercarriage measurements
Hello, I am currently assisting in the build of a replica Mk.5B and in order for the aircraft to be moved around from location to location, the wings are to be created in two halves, so that the wheels will be attached to the fuselage. Not ideal, but the easiest way for transportation.
There must have been very good reasons for the designers NOT using that space for fuel. What else is in there? Everyone just assumes it was empty space.
I was specifically discussing the BoB because that is what you said it was needed for.
Geoffrey Sinclair
Staff Sergeant
- 926
- Sep 30, 2021
I think you don't seem to understand what you are saying, given tactical advantage is defined as higher altitude at intercept. A full 29 gallon tank will add around 3.5% to the Spitfire I take off weight. The Spitfires are going to take off at the historical times, then climb harder thanks to the extra weight carried and extra altitude gained, because apparently Spitfire climb rates during the Battle of Britain were limited due to the fuel carried. Please provide the examples of Spitfires deliberately climbing slower as a fuel economy measure, lay out the mission profile historical versus 29 gallons more on board, with the same sortie length. Also consider the engine maintenance requirements when engines are pushed harder.
The Spitfire needed more fuel once it switched to offensive operations, the increase in engine weight from mark I to IX made it easier to fit a fuel tank aft of the cockpit.
Shortround6
Major General
There are tests of Spitfires with early extra fuel tank/s. Like the single tank under the left wing of some MK IIs.
Granted it was 40imp gallons and not 29 and yes, it did cause drag, but climb was close to 170mph IAS?
Basically the full tank cut the climb speed from 2925fpm to 2240fpm under 10,000ft or a bit above and increase the time to 20,000ft from 7 min 0 sec to 9 min 48 sec.
More importantly it changed the climb rate from 1600fpm at 25,000ft to 1050fpm.
At 30,000ft it changed the time to altitude from 13m 42s to 20m 18sec and cut the climb rate from 995fpm to 545fpm.
Now maybe the 29 gal tank behind the seat only cuts the change in climb rate in 1/2 (72.5% of the weight increase and no external drag?) but did FC want to increase the time to 20-30,000 by several minutes and did FC want to reduce the climb of MK II with Merlin XII engine to the performance of a Spit I with Merlin III?
For the sake of argument I will accept the internal tank causes no change in speed.
There are performance figures for later marks with either 30 gallon or 45 gallon slipper tanks and again, look at the difference in climb performance.
Granted it was 40imp gallons and not 29 and yes, it did cause drag, but climb was close to 170mph IAS?
Basically the full tank cut the climb speed from 2925fpm to 2240fpm under 10,000ft or a bit above and increase the time to 20,000ft from 7 min 0 sec to 9 min 48 sec.
More importantly it changed the climb rate from 1600fpm at 25,000ft to 1050fpm.
At 30,000ft it changed the time to altitude from 13m 42s to 20m 18sec and cut the climb rate from 995fpm to 545fpm.
Now maybe the 29 gal tank behind the seat only cuts the change in climb rate in 1/2 (72.5% of the weight increase and no external drag?) but did FC want to increase the time to 20-30,000 by several minutes and did FC want to reduce the climb of MK II with Merlin XII engine to the performance of a Spit I with Merlin III?
For the sake of argument I will accept the internal tank causes no change in speed.
There are performance figures for later marks with either 30 gallon or 45 gallon slipper tanks and again, look at the difference in climb performance.
Reluctant Poster
Tech Sergeant
- 1,641
- Dec 6, 2006
There was a firewall between the pilot and the tanks in front of him. Sitting on a unprotected tank would not be popular
Thank you, I stand corrected.
MiTasol
1st Lieutenant
I will try and keep this very very simple so that you can understand.
The 29 gallon tank and the 170 gallon FERRY tank for the mark V were for FERRY operations only. Darwin Spits carried the 30 and 90 gallon OVERLOAD tanks on take off and ejected them before combat.
You need to read and comprehend things like the pilot notes to see what the limitations are.
NOTE (a) - that the aircraft is restricted to "straight flying" until the 90 gallon tank is jettisoned. Because that restriction remains when the tank is empty this means this is an aerodynamic restriction, not a structural restriction.
NOTE (c) - that is because if jettisoned during a manouvre is may hang up or or may hit the tail.
NOTE that para (IX)(b) above says you are wrong about the 29 gal tank feeding the 170 gal drop tank.
NOTE also that para (IX)(b) also requires the pilot to fly 10mph faster than normal when the tank contains fuel as otherwise the aircraft will have not enough elevator control to prevent an aft CofG stall.
The 170 gallon tank required removal of all armament and ammunition, with only gentle turns allowed because otherwise the aircraft was way over its structural limitations and could disassemble itself in flight when you turned too hard.
There are two reasons for removing all the guns and ammo
- The wing is only capable of lifting X pounds/kg of weight before you reach one of two stages
- structural failure, or
- the wing cannot provide enough lift for the aircraft to leave the ground
- the wing attach fittings are designed for the wing lift load to be distributed across the whole span of the aircraft.
- removing the load from inside the wing and replacing it with a load under the fuselage massively increases the structural loads on the wing attachments to the point that hard turns will result in structural failure.
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MiTasol
1st Lieutenant
You keep saying there was no need to redesign anything to fit leading edge fuel tanks.
Let us compare the standard Spitfire wing with the Seafire wing in your post.
First the standard wing. Note the locations of all the ribs and compare them with your Seafire wing. Note also the large diameter pipe that carried hot air to heat the guns. Moving that requires both redesign and modification. (yes I know yours is a right wing and mine is a left but they are mirror image in almost every primary structural detail).
Now the Seafire wing. Note that the fuel tank is immediately inboard of the wing fold so access to fit this tank is probably through the new Rib 8A that does not exist on the standard aircraft. Installing the wing fold and installing rib 8A both require redesign and then modifications. Also note the fuel filler that requires a roughly 3in diameter hole in the top skin - more redesign and modification. Note that Rib 6 is totally missing - yep that is another redesign and modification. I do not have the blueprints for any Seafire wings but I would not be surprised if the leading edge skin was thicker than the normal Spitfire skin (0,128 in) to compensate for all the loss of rigidity that removing Rib 6 and making a new Rib 7 that allows the fitment of the LE tank. Then look at the Seafire Rib 5 which has a solid web and compare it with the standard rib 5 with diagonal bracing. Yep - more redesign and modification.
Fitting leading edge tanks to a non folding wing will be a whole different exercise and involve lot of different design work and modifications.
MiTasol
1st Lieutenant
And again you get it backwards. Again I will keep it very very simple to show where you are wrong.
The slipper tanks did not ALLOW a higher cruise speed. The slipper tanks REQUIRED a higher cruising speed for two reasons.
- Firstly the aircraft is significantly heavier with overload tanks fitted (90 Imp Gal fuel weighs 670lb and the tank itself is not light) the only way to get the extra lift required to carry that extra weight is to fly faster, and
- Secondly the slipper tanks are aerofoil shaped and as such MAY create a small amount of negative lift. The problem is that lift is downwards so a percentage of the additional speed MAY be required to offset the negative lift that the slipper tank may cause.
It was used for fuel in the PR Spitfires,
But it was okay for P51 pilots to have 85G of fuel in the same spot, or Me109 and P47 Thunderbolts that had the pilots seat bolted to the fuel tank?. The rear fuel will be burnt off before engaging in combat, you know that.
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I will try and keep this simple so you can understand, the 29G ferry tank was only used for ferry operations but the MkIX which used the same fuselage was fitted with a 33G permanent tank in the same position, this is my argument, why fit a 29G ferry tank that doesn't create drag only to remove it and fit a 30G slipper tank that does?.
One of the reasons Spitfires got shot up was because they had to fly slow to conserve fuel and yes the slipper tank added drag but an internal tank doesn't.
"Reduce the revs and boost the boost, you'll have enough petrol to get home to roost."
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So simply increasing the original MkVIII/Seafire MkIII tank by 9 Gallons is out of the question yet they were able to design it to take not only four Hispano's but another complete cooling system for all the two stage Merlins?.
drgondog
Major
The field mod to P47 in SWP to add 40gal aft of seat (where 100gal aux tank was placed) created severe aft cg issues and soon discarded.
SOP was always to retain at least 20gal for both P-51 and P-47 auxiliary tanks as reserve. That said it was reasonably safe to retain 50-60gal in 85gal fuse tank for normal maneuverability.
Peter Gunn
Master Sergeant
Bill,
I know you've posted something like this before but blame closed head injuries and alcohol.
For a typical long range penetration with P-51 using say two 75gal drop tanks, what's the order of tanks that you'd use from start up to mission end? I seem to recall you start with the left wing tank or am I mistaken?
Blame my obsession with minutia for this.
Thanks
MIflyer
1st Lieutenant
According to"Combat Profile Mustang" by Roger A. Freeman. which has by far the best detailed description of a Mustang mission in the ETO that I have ever seen:
1. Startup: Fuel Selector to left Main Tank. This allows the fuel return from the carb, which can be as much as 10 gal/hr, to go into a fuel tank rather than be vented overboard.
2. After takeoff, typically at an altitude of about 1500 ft AGL, switch selector to 85 gal fuselage tank.
3. About the time the supercharger switches to High, the pilot looks back over his Left shoulder at the fuselage tank fuel gauge and confirms it is down to a safe level, which typically would be about 25 gal.
4. Pilot switches fuel selector to Right Combat Drop Tank. After about 10 min he switches to the Left Combat Drop Tank and switches back and forth about every 10 min. He can expect the drop tanks to provide about 2 hours of fuel.
I read that a P-51 pilot flying his first combat mission, out of Italy, was No.4 in a flight of three other experienced pilots. It was standard procedure over Yugoslavia to make steep turns every few minutes to prevent getting into a flak trap. As the drop tanks depleted it got to the point that during those sudden turns the tanks would unport and the engine would stutter for a split second. He did not like that so he switched to the main tanks and punched off the drop tanks, while the other three kept their drop tanks. The result was he barely made it home.
The type of drop tanks used was based on the mission needs. The units detailed to cover the withdrawal of bombers usually did not carry the larger paper tanks.
1. Startup: Fuel Selector to left Main Tank. This allows the fuel return from the carb, which can be as much as 10 gal/hr, to go into a fuel tank rather than be vented overboard.
2. After takeoff, typically at an altitude of about 1500 ft AGL, switch selector to 85 gal fuselage tank.
3. About the time the supercharger switches to High, the pilot looks back over his Left shoulder at the fuselage tank fuel gauge and confirms it is down to a safe level, which typically would be about 25 gal.
4. Pilot switches fuel selector to Right Combat Drop Tank. After about 10 min he switches to the Left Combat Drop Tank and switches back and forth about every 10 min. He can expect the drop tanks to provide about 2 hours of fuel.
I read that a P-51 pilot flying his first combat mission, out of Italy, was No.4 in a flight of three other experienced pilots. It was standard procedure over Yugoslavia to make steep turns every few minutes to prevent getting into a flak trap. As the drop tanks depleted it got to the point that during those sudden turns the tanks would unport and the engine would stutter for a split second. He did not like that so he switched to the main tanks and punched off the drop tanks, while the other three kept their drop tanks. The result was he barely made it home.
The type of drop tanks used was based on the mission needs. The units detailed to cover the withdrawal of bombers usually did not carry the larger paper tanks.
