Vol 2 All the Spitfire questions here

[Johnson]

Hi Dennis,

 

6 hours ago, Corsairfoxfouruncle said:

This profile is from the New Tamiya kit

 

The colour scheme page from the Tamiya instructions you posted shows the Spitfire with IFF aerial wires going from the tailplanes to the fuselage. This is incorrrect for FZ-L in mid-1939.  IFF wasn't fitted until Sept/Oct 1940; http://spitfiresite.com/2010/04/spitfire-masts-and-aerials.html/2

 

Cheers,

[Ray_W]

6 hours ago, Corsairfoxfouruncle said:

This profile is from the New Tamiya kit, its where my decals come from. 

 

Just think of the different colours and schemes that K9906 saw during its life. From http://www.airhistory.org.uk/spitfire/p001.html

 

FF 21-3-39 65S 'FZ-L later 'YT-T' 24-3-39 64S 17-4-40 FA 23-5-40 7OTU 11-10-40 ASTH 18-10-41 Cv PRIII Type C 1PRU Benson 26-2-42 FACE 18-3-42 8OTU 17-6-42 Scottish Aviation 29-11-42 RNDA 22-5-43 759S Yeovilton 7-43 to 9-43 u/c collapsed landing Cat Y 16-8-43 (S/L PD Gardner)

 

A good subject to do in all its guises.

 

1 hour ago, Work In Progress said:

By "summer 1939" the order for Night and White undersides

 

My vote for an early 1939 summer version. White rear fuselage as well.  Have fun studying pictures for the demarcation line on the actual aircraft. You decide whether the aircraft was left with factory finish aluminium painted aileron underside so as to not upset the balance.

 

I would not go with the Aluminium painted rear fuselage, more appropriate for a factory job post February 1940 (if we still believe Goulding's Ducimus title). Then an Aluminium painted rear fuselage and black and white wings would be appropriate. 

 

If you're choosing an earlier serial number for 1938 then aluminium painted undersides is appropriate.

 

Ray

[alt-92]

4 hours ago, Ray_W said:

My vote for an early 1939 summer version. White rear fuselage as well.  Have fun studying pictures for the demarcation line on the actual aircraft. You decide whether the aircraft was left with factory finish aluminium painted aileron underside so as to not upset the balance.

 

I would not go with the Aluminium painted rear fuselage, more appropriate for a factory job post February 1940 (if we still believe Goulding's Ducimus title). Then an Aluminium painted rear fuselage and black and white wings would be appropriate. 

Curious.. why the white rear fuselage for that intermediate period between late 1938/early 1939 and the factory job after that?

[72modeler]

@Corsairfoxfouruncle is correct. Those could be the blisters to cover the Coffman starter, but am wondering why there are two of them on the sprue. Might also be the landing gear pintle blister fairings seen on early Spitfire  Mk I-II upper wings. See the attached photo of one of my favorite Mk IIa's, P7665 from No. 65 Squadron, that has a good view of the starter fairing, which was only on the RH side of the cowling.

Mike

 

https://www.armedconflicts.com/Supermarine-Spitfire-Mk-IIA-t46081

 

This just in! Found this very interesting account of the loss of YT-L while being flown by F/O Hill. Has photos I have never seen before as well as the history of the pilot, who survived the war. Definitely going to be a tribute modeling project now!

Mike

 

65 Squadron Spitfire II P7665 YT-L P/O. Hill (aircrewremembered.com)

Edited January 6, 2021 by 72modeler
added text, added link

[Ray_W]

8 minutes ago, alt-92 said:

Curious.. why the white rear fuselage for that intermediate period between late 1938/early 1939 and the factory job after that?

 

Page 9 of the original Ducimus publication devotes the whole page to underside variations.  It introduces the early 1940 factory standard, but also all the application variations and interpretations of the night/white rules prior to February 1940. So you could have an aircraft supplied all factory painted aluminium underside then night/white painted locally as interpreted with fuselage painted or left unpainted. Also black/white ailerons on opposite coloured wings or painted aluminium. A lot of variation going on and really needing detailed study of the particular airframe and date portrayed for 100% accuracy. @Troy Smith usually chimes in with a link to this publication.   

 

Ray

[alt-92]

I have seen the reference to AMO A.154/39 (april 1939) but that is rather unambiguous in stating "the lower surface of the starboard plane and half the underside of the fuselage is to be painted white. The corresponding port side is to be painted black."

Presumably there would have been a previous, more vague order that left room for interpretations?

[Troy Smith]

2 minutes ago, Ray_W said:

with a link to this publication.   

 

it's back up

https://boxartden.com/reference/gallery/index.php/Camouflage-Markings/Supermarine-Spitfire

 

the underside variations are better shown in the Hurricane monograph, see page 15

https://boxartden.com/reference/gallery/index.php/Camouflage-Markings/Hawker-Hurricane

 

many variations,  if no specfic photo, you need to examine other planes in the squadron at the time, after that, it's an educated guess. 

[HOUSTON]

  amazing information  

thank you.

[Corsairfoxfouruncle]

Ok well I did a little digging and found this Photo. 
 

https://www.asisbiz.com/il2/Spitfire/RAF-65Sqn-YT/pages/Spitfire-MkIa-RAF-65Sqn-FZR-line-up-RAF-Hornchurch-summer-1939-web-01.html

 

The photo is in my timeframe and looks like the fuselage is split down the centerline Black to port White to Starboard. 

[Johnson]

There's a little bent pipe that sticks down in front of the radiator in a Mk.1 Spitfire (maybe later marks as well, but this is a Mk.1).

 

Can anyone tell me what it's purpose was?

 

 

Sorry, not terribly clear.

 

Thanks,

[72modeler]

If that's a photo of a restored Mk 1, it could be a spray bar- many restored inline-engined aircraft have had them fitted. They spray water into the radiator face to prevent overheating, usually while on the ground, but many aircraft used for racing had them to prevent overheating while running at full throttle and high manifold pressure. These are most often seen on restored P-39's and P-63's, as they got very little airflow to the radiators until airborne. In the Pacific they were often towed to the starting point, because if they were taxied for any distance, they would be boiling over. I don't think it's a vent for overflow from the coolant system, but one of our Spitfire savants will know. Bet our dear departed Edgar Brooks knew!

Mike

[Johnson]

Hi Mike,

Thanks - I'll bet Edgar would have known!

It's a 1940 photo, I got it from the IWM's 'Daily Inspection of a  Spitfire' film. It's also present on the Mk.1 at Cosford which is pretty original.

I guess it could still be a spray bar to cool the rad, it must do something!

Cheers,

[Work In Progress]

3 minutes ago, Johnson said:

I guess it could still be a spray bar to cool the rad

A very reasonable deduction, but no. No sort of spray arrangement on production Spitfires, though I know someone added that kind of arrangement to the Hurricane at Chino a few years ago rather than doing the decent thing aod putting in a proper modern radiator core.

[Ray_W]

Hi Charlie,

 

My understanding is that it is a vent for air used to pressure the self-sealing tanks . If the tanks were holed the pressure air was vented as pressurised tanks would work against the self sealing tanks. Now I just have to find where I got this from. 

 

EDIT: Found it here http://mail.hyperscale.com/2017/reviews/kits/eduard70122reviewmd_1.htm

 

Ray

Edited February 2, 2021 by Ray_W
Updated information

[Johnson]

 

8 minutes ago, Ray_W said:

Found it here http://mail.hyperscale.com/2017/reviews/kits/eduard70122reviewmd_1.htm

 

And a much better photo, thanks Ray.

[Ray_W]

I did a little hunting to see if I could find primary source support for the comments in Hyperscale. I could not find the radiator GA  (yet) showing the vent, but I did find the GA for the fuel tank with reference to the fuel tank vent being 38" from the aircraft centre line starboard side only, which I think you will find is the centre line of the radiator. 

 

 

 

 

 

Ray

[Ray_W]

Thinking about this further, I would challenge that it was there only with the advent of the self-sealing tanks as early Mk I's also show the Fuel Tank Pressurising Cock Control as can be seen here:

 

 

So I think the pipe at the front of the radiator is probably more accurately described as just the fuel tank vent or fuel tank pressure dump pipe.

 

EDIT: I have since found a drawing of the early fuel tank assembly drawing. It still has the vent line, has no cockpit control as shown above, but still calls for vent 38" from fuselage centre starboard only.

 

Ray

Edited February 2, 2021 by Ray_W
Updated information

[Johnson]

39 minutes ago, Ray_W said:

Thinking about this further, I would challenge that it was there only with the advent of the self-sealing tanks as early Mk I's also show the Fuel Tank Pressurising Cock

 

Which raises the question (in my mind at least) when were self-sealing fuel tanks installed in Spitfires?

 

Also, if they weren't self-sealing in early Mk.1s, why the control cock? Presumably for more than just the reason given on the Hyperscale explanation for the pipe;

 

* In service the Spitfire’s fuel tanks were pressurised with regulated vacuum pump exhaust air to prevent the fuel in the tanks from boiling and vaporising at high altitudes. If the fuselage fuel tanks got punctured continued pressurisation was not recommended as this would work against the self sealing compound trying to seal the leaks; so the pilot would change from pressure venting to normal venting by switching a cock in the cockpit, which then redirected the vacuum exhaust air vent to the atmosphere. The outlet for this redirected vacuum exhaust air is that little vent pipe at the front of the starboard radiator. Most restored Spitfires have the pressure venting cock locked in the "normal venting" position as pressurising of the fuel tanks is not necessary.

 

My underlining.

[malpaso]

A.P.1565E, vol.I, Sect.8 para 15 states “[one vent] pipe extends...downwards to a Venturi at the front of the radiator fairing.”

This is from the Mk.V manual which shows the vent in the various fuel schematics.

[Work In Progress]

19 minutes ago, Johnson said:

Also, if they weren't self-sealing in early Mk.1s, why the control cock?

It doesn;t matter whether the tanks are self-sealing or not.

Pressurising the fuel tanks of an aircraft intended to fly at up to 36,000 feet is very likely to be necessary especially on something which is not high-winged, with wing tanks providing a positive head of fuel pressure. 

The Spitfire fuselage fuel tank is at much the same level as the engine so needs fuel to be pumped to it. Without some pressure in the fuel tank it is extremely likely that vapour locking would occur at the low ambient pressure (about 0.23 bar) associeted with operating at its service ceiling.

 

Obviously if you get a small leak you need to release the pressurisation, otherwise all the fuel will blow out very quickly, and descend quickly to a level where you can get some fuel pressure back in the system.

 

Self-sealing helps against this, but if you don't have it, you need the ability to depressurise the fuel stystem even more, not less.

 

We don't need to pressurize the tanks on Spitfires today as no-one flies them above 10,000 feet anyway. 

 

This overall vapour problem is one of the most important reasons why AVGAS is differently formulated from automotive petrol, and that even on aircraft & engine combos approved for car petrol why we don't use it for flying at high altitudes, generally not over 5,000 feet. And mostly they are high-wing types, so that the fuel system has gravity helping rather than hindering.

Edited February 2, 2021 by Work In Progress

[malpaso]

Reading the manual the fuel tank is not pressurised (on most Mk.Vs anyway).  Up to 25,000ft the Merlin’s fuel pump draws fuel from the tanks , hence why a vent is needed otherwise a vacuum would build up in the tank and starve the pump.  Above 25,000 the pilot had to switch on a second pump inside the lower tank, this pump pushed the fuel through to the engine pump, again a sealed tank would starve the engine.

Tropical fuel system differed in not having the second pump and above 25,000ft the tank was pressured by “air from the exhaust side of the vacuum pump”.   But this air pressure had to be released to atmosphere via a cock if you were in trouble above 25,000 as the lower tank “self-sealing is not effective under pressure “!!!

[Magpie22]

A bit more on pressurised fuel tanks on MK.VC. The RAAF had this installation fitted to their aircraft as they spent a lot of their time well above 25,000 ft.

The sections below are the relevant parts from AP 1565E, Pilot's Notes Spitfire VA, VB, VC and Seafire I and II, with ammendments into 1943.

Note that the diagram for the 'tropical' system shows that the immersed pump was removed from the lower tank. The vent pipe remained.

The bottom two photos show the vent pipe fitted to a Westland built A/C on the left and a CB built aircraft on the right. Bothe were fitted with pressurised fuel systems.

Peter M

 

 

 

 

     

 

    

[Ray_W]

Seems clear. Remaining question I have is that with all the possible locations for the vent, why into the radiator? Was this to take advantage of a velocity drop into the radiator leading to a pressure increase maintaining a positive pressure in the tank?

 

Ray

[Magpie22]

I think you are pretty much correct there, Ray.

 

You would want replacement air to be drawn from a source well above ambient static pressure.  The highest positive pressure you can normally get on an aircraft is 'half rho vee squared', (I can't write the symbols here). In a duct with some blockage, this would present as an even higher static pressure. Note that the vent is facing aft so that it effectively drawing air from a plenum with a static pressure above the ambient static pressure.

 

@Graham Boak can probably explain it better than I can.

 

Cheers,

Peter

 

[Graham Boak]

Gee thanks Peter.  I think I may know just enough to be uncertain about things.  However, in my language a vent is for letting air out, not in.  Therefore an aft-facing hole is relying upon the air passing at some speed to reduce the static pressure and allow the air to vent from the tank. Now as to blockage increasing static pressure, it will do this because the air slows down whilst passing through the blockage.  This is fine if the blockage fills the duct, as on a simple installation. 

 

However the Spitfire radiator installation isn't so simple.  It relies on something called the Meredith effect, after its inventor/discoverer at the Royal Aircraft Establishment.  The duct between the face of the inlet and the radiator face increases in area, because the radiator is set inside the wing.  Because the flow then slows down and reduces in pressure, the temperature drops.  This improves the cooling effect of the air.  On leaving the rear of the radiator the duct reduces in area giving a small jet effect, controlled by the rear flap.  Overall the drag of the installation is reduced and the cooling improved.  This is the same effect as seen, to somewhat better effect because of the increased length of duct, on the P-51, and provides much of the benefit of the superior performance of that airframe.  (Not the over-publicised so-called laminar flow wing section.)  It was also used on the Bf.109, both this and P-51 benefitting from the diversion of the boundary layer before the radiator - although this was removed from later Bf.109s to simplify production without apparently significant effect on the aircraft's performance.  It was also seen on the Ring Cooler on the Fw.190D and Ta.152, with similar installations on other late-war types.

 

So the forward face of the radiator does not see a higher static pressure because of blockage, but a lower one because of expansion through the duct.  Now the question is, given this, how is the tank pressurised in the first place?  Given that the tank would otherwise have a lower pressure as the fuel level falls (theoretically a vacuum) then pretty well any inlet will do as the air will be drawn in, but it will need to come from a source at a higher static pressure than the radiator inlet.  The standard pitot static system might do but preferably not, or a duct from the engine exhausts as used on Russian fighters for fire suppression. The right hand diagram above shows the pump controlling this.