Bristol Blenheim Mk V

[Admiral Puff]

I'm looking at converting an Airfix Blenheim IV into a V, but am at a standstill for want of decent information. My references are somewhat limited, being not much more than William Green's old Famous Bombers of the Second World War, Volume 2 and the Aviation News drawings. The latter show the aircraft as having the outer wing panels swept forward to give a virtually straight leading edge, but the couple of pictures in the Green book suggest that this was not so; indeed, the text says that the Blenheim V was basically a Blenheim IV with a revised forward fuselage  and a two-gun Bristol B.X turret. Wikipedia says that "... production aircraft were renamed Blenheim Mk V and featured a strengthened structure, pilot armour, interchangeable nose gun pack or bomb-aimer position and another Mercury variant with 950 hp (710 kW). The Mk V was ordered for conventional bombing operations, with the removal of armour and most of the glazed nose section" , which backs up what Green had to say. I am more than reluctant to put much reliance on the Aviation News drawings, as in the past I have had frequent instances of distortion because of the number of times the drawings have been copied or otherwise reproduced. 

 

Can anyone confirm the situation, please? I'd be very pleased if the Green book is right, and what the drawings show is simply distortion (my copy shows much evidence of that!), thus saving me the pain of having to faff around altering the wings, but I'd like to be certain before moving on.

[Ed Russell]

The Maintrack conversion instruction sheet has a straight leading edge but it is not mentioned in the instructions. I would not put much reliance on the drawings but I have sent you them anyway! In six pages about Mk. V development in the Graham Warner tome, no wing changes are mentioned, apart from relocating the pitot, so I think you can assume it did not happen.

Edit

The oil coolers were moved from the engines to the outer parts of the wing consoles, in the leading edge of which, next to the engine nacelles, air intakes were made.

Edit

In these picture, the wing looks like a Blenheim

https://www.worldwarphotos.info/gallery/uk/raf/blenheim/bristol-bisley-i-ad657/

https://www.haf.gr/en/history/historical-aircraft/bristol-blenheim-mk-v-bisley/

[dad's lad]

I have the MPM kit in my stash and from what I recall, the Mk.V/Bisley also has revised undercarriage in the form of full doors rather than the semi-retracted earlier models of Blenheim. 

 

This may help: https://www.scalemates.com/products/img/1/8/9/112189-78-instructions.pdf

 

Clive

[JWM]

Making more straight wings means moving forward point where resulting aerodynamic lift force is acting. Center of gravity is a bit forward to it, the shorter is the distance between them the less stable is airplane. So what could be a rationale behind it in case of Blenheim?

Contrarily, wings of many airplanes (just to recall Ilyushin Il2 and  Il  4 or Martin 139) with its development got a bit swept outside parts of wing to improve the stability. The only example of going more straight, which I can recall now,  is Me 410 - but it was done together with much bigger engines, so also the CoG has changed its position...

 

6 hours ago, dad's lad said:

also has revised undercarriage in the form of full doors rather than the semi-retracted earlier models of Blenheim

Sure, there is a difference

https://www.ww2wrecks.com/wp-content/uploads/2021/11/27436973.jpg

Regards

J-W

 

[Walter Lindekens]

In essence, the Blenheim Mk I, IV and V share the same basic airframe aft of fuselage former 0.25, which is the one where the nose section attaches to.   So the wing planform is identical between the three marks.

 

As for the Mk V (Bristol Type 160), apart from the completely re-designed nose and a dorsal turret change from Bristol BI Mk IV to Bristol BX (the latter requiring a larger cut-out in the top fuselage as it was of larger diameter) other visible changes were:

 

- Oil coolers repositioned in the wing leading edge (Beaufort and Beaufighter style)

- Pitot tube repositioned from under the nose to under the port wing

- "Apron" style single undercarriage door replaced by "clamshell" type doors fully enclosing the main wheels

- Tail wheel replaced by a type which had a "knuckle" oleo strut

- A much larger rudder trim tab, extending beyond the rudder trailing edge.

 

Admiral, if you PM me your e-mail address I'll be happy to send you some more detailed Mk V info.

 

Cheers,

 

Walter

[Admiral Puff]

Thanks all.

 

@dad's lad- I'd forgotten about that MPM kit! I may have to track one down. No point in labouring over a conversion if the work's already been done ...

 

@Walter Lindekens- PM inbound.

[TISO]

Another shot of wheel bay doors. Is that a small fillet on the wing fuselage joint?

Blenheim Mk V of No.114 Squadron:

 

 

[Ed Russell]

Anti wing root stall device, also on Blenheim IV

See p171 of the Blenheim IV Profile for a good picture.

[Graham Boak]

A bit unusual, such things are more commonly seen further outboard to prevent wing drop on landing.  I wonder if it is linked to prop rotation and just what is on the starboard wing root?

 

@JWM the reduced sweep outboard was part of the general Me210 fixes, to increase the distance between wing and tailplane.  The Me410 just carried it over.  It was also seen on the competitor Arado240.  Not sure about the other struggler with stability in this period, the Hs129.  I suspect dodgy advice from some external authority.  Later German twins had straight leading edges, eg He219 and Ta154.

[leyreynolds]

For the "100 Years of Failure" comp'?

[Work In Progress]

38 minutes ago, Graham Boak said:

A bit unusual, such things are more commonly seen further outboard to prevent wing drop on landing. 

Different purposes, I think, fromthe sort of local stall-inducing strip which ensures lots of user-friendly buffeting, a la Chipmunk and many other types, and makes the inboard wing go before the outer wing goes. In contrast this looks to me to be more of a vortex generator intended to energise the airflow at high AoA and roll it up into a tubular vortex which will then attach to the upper wing fillet, keeping the airflow orderly down the fuselage towards the tail surfaces. Mini version of the classic tubular vortex which flows  off a modern LERX. 

 

[Graham Boak]

Modern use yes  but a simple stall strip seems more appropriate for the period and size.  Perhaps preventing nose pitch at or near the stall.  On both sides then this would seem an explanation.

[Work In Progress]

If it were a simple stall strip, it would be a simple stall strip. I think you're under-estimating Leslie Frise. However, for modelling purposes it doesn't make any difference, so long as we reproduce it.

Edited October 31, 2024 by Work In Progress

[Graham Boak]

I have no doubt that he was a far superior aerodynamicist than I ever was.  But having effort put into increasing lift inboard would result in an increase of the likelihood of the tip stalling first.  Not recommended.  The large vortex seen on the F-18 comes from work done, over here for Concorde, into controlling to increase the lift over the upper wing as a whole.  This idea (or at least its application) was new in to 60s and had it been considered as early as the Blenheim, there would have been a great many different wings seen on early jet fighters.  Here it is only a little wedge, it isn't shaped or sized to create any sizable vortex.  A small one at best.  I'd still like to know if there was a similar one on the other side.  It could be acting as a diverter to prevent propwash killing all lift inboard on one side.

[Ed Russell]

4 hours ago, Graham Boak said:

if there was a similar one on the other side.

Yes - the Aircraft Profile referenced above has multiple pictures of Mk.IV Blenheims with these little triangles. it does not seem to be on the Mk.I but there are not as many pictures.

[Admiral Puff]

I recall reading somewhere (don't ask me where, it was a long time ago) that those little wedges were intended to deal with changes to airflow that were induced by the longer, different shaped nose on the later Blenheims.

 

@leyreynolds- How did you guess?

[gingerbob]

Good view of the "wedge" here:

http://adf-serials.com.au/CMS/index.php/raaf2/blenheim

 

and this photo shows it on starboard side, too:

https://www.destinationsjourney.com/wp-content/uploads/2021/12/841101_274321459383987_1395104089_o.jpg

[leyreynolds]

454/456/459 (RAAF) Sqns - I hadn't realised we were so unlucky!

 

DC- my IV is on the bench after the Defiant.

[Walter Lindekens]

Frankly, I have my doubts about that "wedge" being an anti wing root stall device...  I mean, if it were an important modification to improve the aircraft's flying characteristics then it's use would have been much more wide spread.  And there are a great many photo's of Mk IV's out there without the wedges.

 

I have yet to find documentary proof but I'm pretty sure that the wedge is in fact a cable deflector and mounted on Blenheim IV and V aircraft that are fitted with balloon cable cutters.   On these aircraft there is one cutter near the fuselage and one near the engine nacelle on the inner wing section, and some more on the outer wing.     Any ballon cable brushing against the side of the nose would become lodged in the corner where fuselage and wing meet.   A triangular wedge would neatly lead that cable into the cutter.

 

Many, if not all, photos of Mk IV's and V's that show the wedge also show these aircraft to be fitted with cable cutters.    These cutters are installed in "containers" that are mounted into the wing leading edge.   When installed the cutters protrude beyond the leading edge, obviously, but when the cutters are not fitted the containers are closed with a blanking plate.    I think such a blanking plate is shown in the photo in @TISO yesterday's post. 

 

The photo in the Profile on the Mk IV, on page 171 that @Ed Russell refers to clearly shows the cable cutter fixed next to the wedge.     And the web is full of photo's of 13 OTU's FV-B, serial V6083 which clearly shows balloon cable cutters in conjunction with the wedges.    Here's a link to one of the many:   https://www.worldwarphotos.info/gallery/uk/raf/blenheim/blenheim-iv-v6083-13-otu/ .

 

Early MK V's would appear to have the cable cutter set up as a standard fit, as AP1530C Vol I, the air publication covering the Mk V in detail, actually states:

 

Quote

Early aircraft have barrage cable protection plates fitted to the leading edge of the main plane except in way of the oil cooler air intakes, the wing gun door and the landing lamps.   Thirteen containers are welded to the protection plates to take the cable cutter units, eight to port and five to starboard.  Three of the cable cutter units are double headed, one being fitted on each side of the fuselage, and one nearly midway between the starboard nacelle and the wing tip, the remaining ten are single headed.   Leading edge cable cutters are described in AP2051 A Vol I.

Unquote

 

The wedge, sadly is note mentioned in that para, nor anywhere else in AP1530C, some illustrations show it and some don't.

 

As for the Mk IV,  earliest mention of balloon cable cutters I've come accross so far is in an account of the 16.07.1941 raid on Rotterdam.

 

I'll be happy to be proven wrong but "Smudge" Smith, president of the Bristol Blenheim Society shares my opinion and he knows a fair bit about the Blenheim :). 

 

Cheers,

Walter

 

PS Nearly forgot to mention that these wedges cannot be a permanent fixture, like riveted in place.   The leading edges of the wing centre section (the bit between fuselage and nacelle) actually come off completely to enable servicing of the engine and aileron control runs that are mounted on the forward face of the front spar. 

[Tail-Dragon]

Stall strips are usually near the wing root, the idea being that they "encourage" the flow break down and buffeting to start earlier at the root, while leaving the ailerons effective.  Still used today on some light aircraft and STOL kits, however, they are usually wedge shaped strips that run along the leading edge for 12" -18".

Those triangular leading edge extensions are something else.

Edited November 1, 2024 by Tail-Dragon

[Graham Boak]

Stall strips are not always near the root, despite the good reason given, for example the Corsair.  Of course here the roots are full of other kit.

 

I do like the suggestion that these wedges are to divert balloon cables into the cutters, though I do wonder how the cable gets past the prop.  I was tending to the belief that they were flow straighteners because of some peculiarity with the extended fuselage, although I couldn't see what would cause this.  These things can be subtle.  However if Mk.IVs were flying around without them then this seems unlikely, unless of course this is a feature of early examples.  If not, perhaps they were only fitted to a subset of aircraft intended for night operations, where balloon barrages could be considered more of a threat?

[Kari Lumppio]

Hi!

 

Stalling tests on a Blenheim A.R.C Technical Report R. & M. No 1966 (December 1939)
https://reports.aerade.cranfield.ac.uk/bitstream/handle/1826.2/1443/arc-rm-1966.pdf?sequence=1&isAllowed=y

 

The above may be interesting reading about Blenheim stalling characteristics. It says: "The favourable effect of opening the engine gills is due to their increasing the root turbulence." The wedge would give the same effect with less drag?

 

Cheers,

Kari

Edited November 2, 2024 by Kari Lumppio

[Walter Lindekens]

On 02/11/2024 at 09:29, Graham Boak said:

Stall strips are not always near the root, despite the good reason given, for example the Corsair.  Of course here the roots are full of other kit.

 

I do like the suggestion that these wedges are to divert balloon cables into the cutters, though I do wonder how the cable gets past the prop.  I was tending to the belief that they were flow straighteners because of some peculiarity with the extended fuselage, although I couldn't see what would cause this.  These things can be subtle.  However if Mk.IVs were flying around without them then this seems unlikely, unless of course this is a feature of early examples.  If not, perhaps they were only fitted to a subset of aircraft intended for night operations, where balloon barrages could be considered more of a threat?

I've been wondering about balloon cables and props too, Graham.  But seeing that all aircraft equipped with these cutters had a number of them in the part of the leading edge that is covered by the propeller arc(s) one would assume some cables could get past the prop in some cases.   NA file AIR 14/1489 "Balloon Cable Cutters" has lots of interesting documents on the subject though not related to any specific aircraft type.   The oldest document in the file, titled Martin Cartridge Fired Cable Cutters for Aircraft Protection and which covers instructions for fitting and handling the device is actually dated 03 June 1940 so they were available fairly early in the war.

 

As for night ops,  the Blenheim Mk IV Rotterdam raid I mentioned in my earlier post was a daytime raid.   I suppose that if crews had to attack a target defended by a balloon barrage, negotiating the cables would be equally hazardous by day as by night. 

 

Cheers,

Walter

[Graham Boak]

Sliding along the side of the fuselage after hitting the nose?  Probably thin enough to pass, taking off the venturis on the way.