PR Spitfire wingtip vents

[Peter Roberts]

The Spitfire PR IV was equipped with what I believe was called the 'D' Type wing, which had a leading edge fuel tank. I believe this tank was prone to splitting during development, due to changes in pressure, so a small tube vent was installed to prevent this.

These tube vents can be seen just inboard of each wingtip, exiting the wing upper surface foward of the wing spar, and pointing to the rear along the wing upper surface.

Having recently examined photos of Sptfire PR XIX's I notice that this vent now exits from behind the wing spar, and points forward.

Can someone help with two questions please?

1. Why the change?

2. What was the set up on the PR XI? (I presume the same as the PR IV, as I understand it had the same wing, but I dont like to presume )

TIA

PR

[Edgar]

As you can see, on the XIX, it doesn't point forward, but back, and disappears through the wing, emerging underneath.

And this is underneath (not much to see.)

I don't have anything on the wings of the IV or the XI, but it's possible that the former was slightly cobbled together, while the latter (and the XIX) had a better arrangement.

Edgar

Edited November 1, 2013 by Edgar

[Test Graham]

What a horrible thing to stick on a wing uppersurface. Is that really the production fit and not some modern fudge?

That buckled panel with a forward-facing gap would be sent back for retrimming too!

[Col.]

Thank you for posting that photo Edgar. There's so much interesting detail in that small section alone. The vent of course but also that the wing walkway line sits ahead of the panel line, that the rivets deform the skin slightly, the use of lockwire on that cap.

May I ask a secondary question? You mentioned the vent emerged below the wing - is this a visable feature?

[Edgar]

What a horrible thing to stick on a wing uppersurface. Is that really the production fit and not some modern fudge?

As far as I know the BBMF don't use the wing tanks any more, so presumably have no need for something cosmetic. Also, when Peter Cooke photographed Benson's XIX gate guardian, around 35 years ago, it sported an identical fitting.

Edgar

[Test Graham]

It would be interesting to know the reasoning behind it, but if it isn't in any of the paperwork you've found over the years, the logic may have died with the designers. Normally you would expect to vent to a low pressure area, and so the uppersurface is a better place than the undersurface. It's odd that one pipe goes into the wing, but two come out. This might imply that there was an undersurface vent on the earlier examples that show a simpler aft-facing uppersurface vent.

[Edgar]

I'm no aircraft engineer, so am rather blind on this one, but, as it was told to me, the major problems occurred while the aircraft were on the ground, in the full glare of the tropical sun. Maybe they only wanted the airflow to do the job, not low pressure; it's worth remembering that the early vents, to draw the heat through the wing, then exhaust it, were also underneath.

Edgar

[gingerbob]

Here are the best I could do for a PR.XI - both crops from images found online, so you may have to save and enlarge.

The second image is the starboard wing, outboard being to the left. Note the fuel cap.

It is possible that the vent tube is a smaller diameter, or maybe Edgar's excellent close-up just makes the one on the XIX look bigger! It is hard to see on most photos of the airplane, but if you squint sometimes you can make out the 'line of the line' running fore/aft.

EDIT: There are a couple of better shots in Ventura's (No.11) "Merlin PR Spitfires in detail", p.55 The caption says, "Experience with PR.IVs in the Middle East showed that after a long period sitting in the sun they could burst their wing tanks. This led to introduction of air expulsion valves [really vents?]..."

(There's also a shot on p.4 of BP888, a PR.IV, showing something similar (too small to make out))

bob

Edited November 2, 2013 by gingerbob

[MilneBay]

I'm no aircraft engineer, so am rather blind on this one, but, as it was told to me, the major problems occurred while the aircraft were on the ground, in the full glare of the tropical sun. Maybe they only wanted the airflow to do the job, not low pressure; it's worth remembering that the early vents, to draw the heat through the wing, then exhaust it, were also underneath.

Edgar

Like Edgar I'm no aircraft engineer but the same thought occurred to me. If the fuel needed venting because of expansion then the simple use of gravity would be fine. Equally if the need occurred while airborne then it would suffice as well.

[Peter Roberts]

Edgar, thank you so mauch for posting those photos! I was misslead by the shape at each end of the tube - it lloked like it ended forward of the wing spar - it didn't occur to me that the vent vented through the lower surface! That is brilliant info, and photos I was unable to source on the net which explain so much. Great details.

Ginger Bob, also a BIG thank you for the photo work there. It looks like the XI has the same set up as the XIX. But, I'm going out on a limb here and going to suggest this may have changed sometime during the build of the XIs if your photos are of WW2 a/c. I did find one picture of a PR XI on the net that shows staining on the upper wing surface that appears to come from a vent. But you first photo seems to match the set up of the XIX that Edgar posted (?), so perhaps a change?

Thank you so much gentlemen, appreciate your help!

PR

(self confessed Spitfire enthusiast! And still earning heaps!)

[gingerbob]

Yes, it is claimed to be an addition. And yet, a fuzzy photo of one of the first two "Type D" seems to show what might be the same sort of thing. I did also spot it on other PR.IVs, but it also doesn't appear to be there on other PR.IVs and XIs. I also saw a shot, maybe the same one, with a big "trail" on the starboard wingtip.

If it was added as a mod, I'd expect Edgar would be able to present us with a mod number and some sort of date?

bob

p.s. The search was worthwhile- in the process I found some great photos of Danish XIs and IXs!

[Edgar]

I've never found a modification, just the drawing (below.)

Note the number, which, as it begins 365--, indicates that it originated with the XI, giving the impression that it was only added to any IVs built after the XI production started (were there any?)

Note, too, that the underside pipes would not have been visible, being covered by a fairing, which was, itself, covered by a fabric patch, presumably painted blue, and just leaving two small holes to see.

Add in a second (blue?) fabric patch, over the point at which the pipe disappears through the wing, and it's not surprising that the pipe appears to have been the wrong way round.

And, no, I have no idea where the second pipe came from.

Edgar

Edited November 3, 2013 by Edgar

[gingerbob]

There was a bit of overlap- Supermarine claimed the first PR.XI delivered in Nov '42, and the last PR.IV first week of Feb.

bob

[Fernando]

Hi, all,

On pg.25 of the Ventura book (it's n° 11), there is a picture showing the tip of the right wing in a PR.IV (it is the picture showing BR416 in its Royal Blue finish), showing something similar to the drawing.

Geez, you never end finding things in these pictures...

Fernando

[Peter Roberts]

Edgar, many thanks again for going to the trouble of posting that plan.

Some more good points - the fairing on the lower wing is missing in the photo, but the attachment holes are there (for screws I guess). It's good to know what you are looking for.

Interesting points about the fabric patches too. The holes shouldn't be obvious therefore on a model.

I'm away from home at the moment but will see if I can check on build dates. Good info about the XI.

Does the drawing have a date by chance? I can't make out details (in the side notes) from the enlargement I generate of this drawing.

Thanks again, great info!

PR

Edited November 5, 2013 by Peter Roberts

[Peter Roberts]

Thanks Fernando. My understanding was that the vents on the early PR versions simply vented over the upper wing surface, which I have to admit, surprised me a bit. I recall fitters saying how they used fuel to strip the paint off aircraft, and my simple brain thought this would have the same effect (?).

I'm inspired to look back over my references now, but these vents don't always feature well in photos, being more visible on the upper surface. Most of the photos I have seen don't show this well. That fairing on the lower wing shown in Edgar's post above will be a bit of a give away now.

PR

[gingerbob]

If I read that drawing right, the 'fairing' around the tube-ends is open at the front, which would provide a mild pressurization. There's a note pointing up to the 'other one' which I can't make out. I'm guessing it is for another tank?

bob

[Peter Roberts]

Ginger Bob - sorry, didn't read your post well re production dates.

Would be interesting to know if the XI had this vent (passing through the wing) from the start of production, or if it was introduced during production, unless I have misinterpreted the set up on the IV and it was there from the start (?).

PR

[Test Graham]

Fuel will stain an aircraft's paint, and weaken it, but you'd add some elbow grease if you wanted to remove it properly.

Possibly the "mild pressurisation" could be to prevent any syphoning effect of the airflow rushing part the pipes?

[gingerbob]

Well, I just remembered that I have a PR Spit manual (on disc). No XIX, unfortunately. According to this manual, there is a float valve on both PR.IV and XI "to prevent fuel spillage during acrobatics". But that wouldn't help with wing tanks baking in the Mediterranean sun- perhaps that's where the "air expulsion valves" come in? It didn't say anything that I noticed about the routing of the vent.

One point that I hadn't thought about was that when the Merlin 70 was fitted, so were immersed fuel pumps in the leading edge tanks. I don't know that this would make a difference to our vent, but it does reinforce the idea that a bit of pressure from that fairing would (on the earlier types without the immersed pump) help the fuel feed from the tanks- they certainly wouldn't want an aft-facing pipe-end in the slipstream (as Graham suggests).

bob

Edited November 3, 2013 by gingerbob

[Fernando]

Hi, Peter,

Interestingly, the instructions in the Airwaves set for the PR.IV shows a circular panel to be scribed on the upper starboard wing to represent a "vent" or "valve", but no "pipe". That's the way I use to finish my conversions. Usually they are pretty accurate, though things move on.

Fernando

[Peter Roberts]

Hi Fernando

My understanding with this is that was the way the wing was first made. I think it was access to a valve float mechanism (?). But I stand to be corrected on that, possibly.

PR

Edited November 5, 2013 by Peter Roberts

[Edgar]

The filler point/cap, for each wing tank, is out near the wingtip, and normally covered by a circular plate, which "on the P.R.U.'D' only" was locked, with locking wire, from November 1941. From the photo, it looks as if that went on, to the XIX, as well, so was very likely to also have been on the XI, I'd say.

Edgar

[Peter Roberts]

I agree with you Edgar, the filler cap location seems to have been fairly standard for all versions.

I'm afraid I wasn't too clear in my previous post, apologies there. Some diagrams I have seen, which appear to have been for the early wings, show two circular panels on the upper surface near the wingtip. The one in board for the filler cap, the one outboard for a float. These diagrams make no reference to a vent, so I am presuming (hmm, dangerous, I know) that this is the original version of the 'D' wing, before the installation of the vent. Perhaps this (the vent) replaced the float mechanism?

PR

[greatgonzo]

Hello!

Anybody copied the pictures presented here by Edgar? I didn't do it before and, sadly, I can't just mail him and ask for help, as I used to not so long ago.