Blenheim intakes aftermarket + extra still required for tropical

[Graham Boak]

Two things came together today. Firstly Quickboost have produced two sets of Blenheim intakes, one temperate and one tropical, which look nice enough in the photos. Open ends, and the tropical filtered one looks more convincing than the Airfix.

Secondly, I've spotted that tropicalized Mk.IV Blenheims have an additional intake on top of the nacelle amongst the gills, standing proud to get clean air above them. At about 11 o'clock viewed from the front. Pardon me if everyone knew this already, but Quickboost and I didn't, and I don't know of any kit that has included it. It doesn't seem to be visible on Mk.Is.

EDIT: Barracuda also have a set, which looks as though it is better value. It may be possible to use the temperate intake from this set as the additional tropical one, but I notice that there is also an outlet at about 1 o'clock that stands proud of the gills when closed - presumably the exhaust from the oil cooler. This seems to be on all Mk.IVs - and Mk.Is?

Edited February 6, 2015 by Graham Boak

[mhaselden]

Graham,

To ensure I'm understanding your post correctly, does the pic below show the additional intakes?

IIRC this was an airframe-specific installation (ie not on every airframe operating in theatre) to overcome condensation locks (but working from memory here).

Cheers,
Mark

[Nick Millman]

Some discussion about this from post # 358, page 18 (!) onwards ..

http://www.britmodeller.com/forums/index.php?/topic/62197-27-sqn-blenheims-at-singapore-in-colour/page-18

[mhaselden]

Thanks Nick...I knew it was in that thread somewhere but even Google failed to track it down for me.

[Graham Boak]

Mark: Could this simply be an engine change, taking one off a Mk.IV or from replacement stock? The upper intake looks to be identical to the production modification, too much so to be a coincidence. Alternatively, it could be that a batch of modification kits had arrived but not all operational aircraft had been so equipped.

Another alternative could be that the local mod had been adopted by Bristol, unchanged, but this would rather imply enough time for all the Far East fleet to have undergone such a mod locally, which doesn't seem to be the case. Perhaps it was, which means it should be on Scarf's aircraft too?

Edited February 9, 2015 by Graham Boak

[Graham Boak]

Update: Theo Boiten's book Bristol Blenheim include a different photo, of L8364 which crashed at Sembawang 25th January 1941. Sadly the date is probably wrong, or the unit. As 84 Sq took Mk.IVs out to Singapore in January 1942, the photo is possibly of 34 Sq. The date suggests an early introduction, but other photos of Mk.Is in the Far East don't show this. Odd. Perhaps more do but no-ones looked for it?

Also: Brian Cull's Blenheims Over Greece and Crete has a photo of 211 Sq's Mk.I L1434 at Paramythia, April 1941. Other Mk.Is in Greece didn't have it, but the Mk.IVs did.

Edited February 11, 2015 by Graham Boak

[mhaselden]

None of the pics showing 27 Sqn Blenheims show the additional intake, and those pics were taken in Apr 41. As noted, I believe this mod was only applied to aircraft that needed it. Certainly, a perusal of Warner's tome on the Blenheim as well as available pics in Bloody Shambles and elsewhere show relatively few Far East Blenheims with this mod, other than the one included previously in this thread.

[Dave Swindell]

Perhaps it was, which means it should be on Scarf's aircraft too?

Blenheim Warpaint P7 has a photo of 62 sqn Blenheims L1107/FX-L and ?/FX-U supposedly just before the Japanese invasion. The extra "11 O'clock" intake is clearly visible on both aircraft, together with tropical filters and 2 x light series bomb carriers under the aft fuselage, so I'd say based on this it's likely that Scarf's Blenheim was similarly equipped.

Regarding the "1 O'clock" outlet, a quick flick through shows some Mk1's with the outlet, and some MkIV's without. P11 shows 8 Sqn L6653/HV-Y in Aden with tropical intake and both 11 O'clock intake and 1 O'clock outlet.

[Graham Boak]

I think the outlet is present on all aircraft, not just the tropicalized ones, and presumably feeds from the oil cooler. It is very difficult to distinguish when the gills are open. I'm not sure, but suspect from some views that the one on the Mk.IV may be longer.

We seem to be building up a small store of Mk.Is with this intake, but by no means all. It may be that fitting was progressive, and photos from Malaya showing aircraft without this were all taken before the (presumed) mod programme had worked its way through the fleet. I still feel that the intention would be to have this on all tropicalized aircraft, but perhaps the more troubled ones would be the first to get attention?

[Dave Swindell]

I think the outlet is present on all aircraft, not just the tropicalized ones, and presumably feeds from the oil cooler. It is very difficult to distinguish when the gills are open. I'm not sure, but suspect from some views that the one on the Mk.IV may be longer.

If we're right in assuming this is the outlet from the oil cooler, and it's poition would suggest this is correct, then yes, the outlet will be present on all aircraft.

However, on some photo's especially with the gills closed, the outlet is not visible, and there is no cutaway in the gills at this position. The outlet must be shorter and end inside the nacelle with the air exiting with the engine cooling air through the gap at the aft end of the gills.

This was obviously not giving enough cooling in certain situations, and the first stage in improving this was to extend the outlet beyond the edge of the gills and to cut the rear edge of the gills away to clear the outlet when closed.

As you say, there could be different lengths for this extended outlet, but I'd have to check more closely to say one way or the other.

A rough and ready observation so far is the photo's without the gill cutaway/outlet extension (MkI & MkIV) appear to be 1940 or earlier, those with appear to be 1940 or later.

[mhaselden]

Which gets me back to the question of whether it was a fleet-wide fit or only applied to specific airframes as needed? If our cut-off for seeing the extended intake is 1940, one would expect it would have percolated to the furthest reaches of the Empire (eg Singapore) by April of the the following year. However, that's clearly not the case as evidenced by the 27 Sqn machines. I've seen a pic of Blenheim L4827 'MU-X' of 60 Sqn also lacking the extended intake. There's also a photo on p.561 of Warner's book showing an Indian AF Blenheim dated from 1942 which clearly lacks the extended intake. I have a hard time believing it was universal when there are pics showing airframes without it even late in the type's operational life, particularly if the mod meant the difference between an engine functioning correctly and it failing.

I accept I could be entirely wrong and, to be honest, it doesn't really matter. Either it was a standard installation but there were exceptions where individual airframes didn't get the mod, or it was only applied to specific airframes which needed it. Those of us who want to build an accurate model will strive to find a pic of the original and modify to meet that reference material. Those who are less interested in accuracy won't care. If you don't have an image of the original airframe, as in Scarf's case, then it's open to conjecture. Graham's observation about FX-N and FX-L has merit but, equally, it could just be coincidence that 2 airframes with extended intakes happened to be flying in formation on that day. We just don't know so arguing about it is pretty futile.

As I looked around for examples, I did note that Bisleys seem to lack the extended intake. I fully realize in saying this that I'm merely inviting someone to prove me wrong...

[Graham Boak]

Not me, I saw the photo but missed the relevance! Dave's 1940 cut-off is referring to the outlet not the intake. It is still only an assumption that the intake is linked to the examples of fuel vapourisation, though a fairly safe one I feel. If so, it will have been noted in 1940, and the solution appeared in Mk.IV tropicalisation early in 1941. Unless someone can find a photo of a tropicalized Mk.IV without this? Conversion of Mk.Is could well have been on an as-and-when basis, the obvious time being at a major overhaul. It clearly wasn't regularly available in the Middle East in April. It does make me cast doubt on the January 1941 date for L8364, which was indeed 34 Sq - but nothing more is known to the Air Britain serials book.

I still find it difficult to understand why such a problem would be limited to a few aircraft, and a response tailored that way on one Mark but not on the other. However, the Mk.IV could have been expected to required more cooling because of the more powerful engines and so have priority on supply of the parts.

The Mk.V or Bisley has a redesigned system, so possibly these large inlets were only seem as a temporary measure. It has inlets in each wing outboard of the engines, and the two long inlet pipes have been replaced. There is a small inlet at 12 o'clock.

[Walter Lindekens]

Graham & all,

Allow me to post a link to a thread on Hyperscale on the subject of Blenheim in- and outlets and which should answer some of your questions :

http://www.network54.com/Forum/149674/thread/1406750054/1/Addendum+to+My+Airfix+Blenheim+Review+-+Things+I+Missed%21

Just hope pasting the link works!

[Graham Boak]

Thank you Walter, that does make the matter of the oil cooler exit clearer.

[Dave Swindell]

You just bet me to it Walter! That thread is most useful, but it doesn't pick up on Graham's point that started the thread, and raises another point that's been niggling me this afternoon whilst scanning through Blenheim photo's - namely the two oil cooler intake tubes on the starboard side of the nacelle increased in length and gained bell mouths when the oil cooler outlet ducting was added.

To sum up the intake/ outlet for the oil cooler

1

Blenheim I, and IV manufactured/in service before approx early 1940 had:-

Short cylindrical intake tubes flush with the front edge of the exhaust collector ring (or slightly recessed behind it)

Internal Nacelle outlet duct covered by full length cooling gills

2

Blenheim IV manufactured after approx early 1940, and earlier Blenheim IV's, and I's still in service could have been modified to:-

Longer bell mouthed intake tubes protruding in front of the exhaust collector ring

Extended external outlet duct and cut back cooling gills to clear same when closed

3

Blenheim V (Bisley) did not have either of above, as the oil cooler was relocated to the wing L/E as per the Beaufighter

4

Blenheim I's and IV's destined for North Africa/Middle East/Far East were modified to take a Vokes dust filter on the carburettor inlet

5

Some Blenheim I's and IV's in the North Africa/Middle East/Far East were modifiedwith the addition of an extra inlet to the oil cooler at approx 11 O'clock on the nacelle.

This appears to have been common enough for machines to have been modified in the same or very similar manner in all 3 theatres

All photo's I've so far seen with these intakes show (where visible) vokes filters fitted, ie I've yet to see the extra intake in combination with a standard carb intake

There's plenty of photo's of Blenheims with Vokes filters definitely without the extra intake

Re Mark's comment about Scarf's Blenheim I fully concur. I was merely pointing out that there was photographic proof that 2 of the squadrons machines had been so modified prior to his VC, therefore it is possible or even likely that his machine was also modified. If all the photo's showed them without the mod as per the 27 sqn photo's, then it would seem unlikely that his machine was modified. We're unlikely to ever know for certain, but my model, when the round tuit's arrive, will now have Graham's 11 O'clock intakes.

[Graham Boak]

I can recommend Barracuda Studio's resin set. With both tropical and temperate intakes, you even have spares that you can put in that top position. The base may need a little extending, I haven't tried it yet. I'm reserving judgement on Scarf's machine.

One thing isn't quite clear: have you found any photos of trop. Mk.IVs without the top intake?

Thanks for pointing out the shorter cooler intakes on the Mk.I, without the bell mouths.

What this is making clear is that no-one has looked that closely at Blenheim development below the Mark level. (OK, no-one in the modelling or publishing worlds.) Only a small handful of types have received the close scrutiny of the Spitfire/109/Mustang kind. It helps to confirm that all aeroplanes are complex beasts, especially over long production runs.

Edited February 12, 2015 by Graham Boak

[Walter Lindekens]

Dave, re your post 15, I concur with all your points except No 2 where you limit the oil cooler inlet and outlet extensions to the Mk IV. Whereas I have only studied the Mk IV modification leaflets, I have found that several of the Mk IV mods have also been applied to the Mk I, the oil cooler inlet (bell or trumpet mouths as I call them) and outlet (duct necessitating cut-away cooling gill) extensions amongst others.

I recently bumped into this great pic of a Mk IF on the internet and which clearly illustrates my point:

Ok, this photo only shows the trumpet ends but I'm pretty sure the outlet duct is there too, just like on this Mk I night fighter:

Other Mk IV mods also shown on the Mk IF photo are the anti-icing shroud on top of the aerial mast and the re-positioned forward light series bomb carrier.

I fully agree with Graham that only very few people (can't say no-one!) have looked closely at the finer details of Blenheim development so I thought I'd share the index of the Mk IV modification leaflets held at the RAFM with you, if only to whet your appetites :

Of special interest to Graham should be Log Book No 42, Mod No 703, Tropical oil cooling system - Inlet and outlet pipes - introduction!

And sorry but, no, I haven't made a copy of that leaflet ... Pretty sure this covers the 11 o'clock inlet though so where is the matching outlet?

[Graham Boak]

Indeed. Also Logbook 20, Mod 675 Oil cooler: extensions to inlet and outlet ducts.

Re Dave's point 2, I suspect Mk.Is are covered by his "still in service" comment.

[Kari Lumppio]

Hi!

Brilliant stuff Walker! Thank you very much for the Blenheim modification list.

Log book No. 6, "Painted strip on tailplane and fin - Introduction". Would lvoe to see the Leaflet No. A.1.
I think these strips were mentioned in the endless thread of 27 sqn Blenheims.

Another goodie is the Log Book No. 43/ Mod. No. 786, Leaflet J.9. "Rear fuselage - Draught screen for cabin - Introduction".
I wonder if this is similar to the one on the Finnish Blenheim sarja V and VI, where there was buttoned heavy curtain behind the pillot and observer. Also the the sarja I Blenheims (from year 1937) apparently had such curtain. At least BL-117 repair report from Winter War mentions repaired zipper for one.

Cheers,
Kari

[Walter Lindekens]

Always happy to share Blenheim stuff Kari! I checked the leaflets I have but the one covering the rear fuselage draught screen isn't among them. Mind you, the RAFM's collection of mod leaflets does not appear to be complete. Not how the log book nos jump from 43 to 107.

I think that the draught screen being referred to is the one clearly visible in these two photos of what I think was an experimental wireless installation:

Sorry to Graham for diverting from the original intakes question.

Cheers,

Walter

[Graham Boak]

I'm happy. The specific questions have been answered, and the more that other aspects are enlarged upon, the better.

[Dave Swindell]

Hi Graham & Walter

Sorry for the delay in replying, been away for a few days.

One thing isn't quite clear: have you found any photos of trop. Mk.IVs without the top intake?

Er, no, hadn't twigged that. On looking again all the photo's of Blenheims that I can find with Vokes filters and definitely without the 11 o'clock intake are either MkI or MkV

Dave, re your post 15, I concur with all your points except No 2 where you limit the oil cooler inlet and outlet extensions to the Mk IV.

Sorry Walter, my poor explanation. As Graham points out below, MkI's were supposed to be covered by the "still in Service" comment. So some MkI's were modified after manufacture, but none had the mod on the production line as production had ceased by the time the mod was introduced. Some MkIV's on the other hand were produced with the mod, and some modified at a later date. Original post edited to reflect this.

Re Dave's point 2, I suspect Mk.Is are covered by his "still in service" comment.