Super Blenheim fighter

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Admiral Beez

Major
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Oct 21, 2019
Toronto, Canada
Before the Beaufighter and Brigand, there was the Bristol Blenheim Mk IF, armed with 4 × 0.303 in machine guns mounted in a ventral gun pack beneath the fuselage (shown below), plus another in the in dorsal turret.



With a maximum speed of around 266 mph at 11,800 ft, and powered by two 860 hp Bristol Mercury radial engines, the Blenheim fighter is not going to win any races. The primary IJAF bomber over Malaya, the Mitsubishi Ki-21-IIb "Sally" was at least 30 mph faster.

Let's have Bristol set a 300 mph target for their fighter Blenheim, to be in service by (EDIT) mid-1938. How do we get there? Streamlining, with turret delete? Engine swap for liquid cooled Merlins? RAF specs could be calling for a twin engined fighter based on immediately available airframes that could be used for nightfighting, coastal command and bomber interception. Could we keep the internal bomb bay and doors? My hope is to have several squadrons available for overseas service at Ceylon, Burma, Malaya, etc.
 
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Admiral Beez said:
Let's have Bristol set a 300 mph target for their fighter Blenheim, to be in service by mid-1940.
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Errr...Bristol Beaufighter is basically what you are competing against as it had a max speed of just over 300mph and actually entered operational service 27 July 1940. I think you will need to set the target entry date a bit earlier to make any difference.
 
GTX said:
Errr...Bristol Beaufighter is basically what you are competing against
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Good point. Let's change up the entry date of our Blenheim fighter to 1938, so we don't conflict with the Beaufighter. I want to get the most out of the Blenheim airframe before the introduction of the Hercules.
 
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Supposedly No. 600 Squadron (Auxiliary Air Force) based at Hendon, was the first squadron to take delivery of the Mk IF in September 1938. By 1939, at least seven squadrons were operating them as fighters. Perhaps have something done earlier - say an in-service date parallel to the Bomber variant in March 1937? It's going to be challenging though given how fast things were developing. Another option might be to give it a pair of 20mm cannon to give it something more than the 4 MGs.

In reality, the Mk IF proved to be slower and less manoeuvrable than expected so it is going to be a challenge to do something, again given how fast things were developing back then. I like the idea, I am just struggling with anything that makes practical sense.
 
GTX said:
I like the idea, I am just struggling with anything that makes practical sense.
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Merlins. It's our only hope. Interestingly, outside of prototypes and testbeds, the Merlin was rare in twin engined applications before the Mosquito. There's the Armstrong Whitworth Whitley Mk IV of 1939, but nothing beforehand. Maybe the Merlin-powered Blenheim fighter can get operational beforehand.
 
Diverting Merlin's away from Hurricanes and Spitfires in 1938 seems a folly, especially into an airframe that will never be able to match its dedicated twin engine fighter counterparts, like the Bf 110. Maybe more productive to focus on the Whirlwind as the cannon armed fighter twin, and let the Beaufighter program progress as necessary?
 
I wouldn't go for a Merlin since that means having to introduce radiators etc. Maybe the Bristol Taurus - giving something somewhat similar to the Gloster F.9/37:



Especially if one goes for the same armament of:
  • Four 0.303 in (7.7 mm) Browning machine guns
  • Two 20 mm Hispano cannon
 
There is a point being missed here.

The Blenheim If fighter was produced by conversion of Blenheim I bombers (which had entered squadron service in March 1937) as the latter became surplus to requirements. From early 1939 Blenheim IV bombers began to enter service freeing up Mk.I airframes for conversion to fighters or transfer overseas to re-equip squadrons in the Middle & Far East. As Mk.IV later became surplus to requirements they too were converted to IVf fighters and used by a number of CC squadrons, pending production of enough Beaufighters.

According to the information I have, 600 squadron did not convert from the Hawker Demon to the Blenheim If until Jan 1939.
 
Clayton Magnet said:
Diverting Merlin's away from Hurricanes and Spitfires in 1938 seems a folly,
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Much of this forum is most of us telling most of the rest of us why some idea would not, should not or could not have happened. But let's chuck our contrarian tendencies into the bin for a moment. It's early 1938, the Air Ministry sees the new Blenheim and the gun pack concept, and asks, what can you do to make it faster? We know why it won't be done, but how can we do it with the engines and tech of the day?
 
Admiral Beez said:
Let's have Bristol set a 300 mph target for their fighter Blenheim, to be in service by (EDIT) mid-1938. How do we get there?
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Throw it out and start over?
Basically if you want a 300mph Blenheim at 15,000ft you need engines that will give you 1200hp each at 14-15,000ft. That assumes no change in drag. In 1938 the British do not have a 1200hp engine in service. They have engines planned (hoped for) that will give 1200hp in few years.

Now we get the complaint that some of us are being contrarians but it is not a question of won't do it, it is a question of can't do it.........................unless you repeal the laws of Physics.
The Gloster twin shown used a smaller wing (82%) used a smaller fuselage, It uses smaller diameter engines, It may have used thinner wing sections. Yes it went much faster.

Fastest Blenheim known was good for about 290mph, but it was a Photo recon plane

from an earlier thread.

Sydney Cotton and crew took a Blenheim MK I and modified it considerably for photo recon use. I am going y memory so bear with me.
Mods included clipping the wings, removing the turret and plating over the hole. Adding metal fairings to the nose (shape not described), They fitted the engines with constant speed propellers instead of the two pitch props and ran it on 100 octane (this was in 1940), they also painted and sanded the airframe with about 20 coats of paint. There may have been other modifications, can't remember if they tried spinners on the prop hubs. They got it over 290mph using 9lbs of boost?

Note there was no gun tray. Cotton used lower drag but you can only go so far doing that.

Service aircraft are never going to get 20 coats of paint sanded between coats.
AND by the way, the particular Taurus engines used in the Glostor twin were only flown in one aircraft and after a crash, they were never seen again. No later Taurus made that much power at that altitude.
 
There is a simple way to estimate needed power. Take the cube root of the existing power, multiply it by the percentage of increase you are looking for, and then cube the result to get the estimated power.
Please note that this does not work well in the mid to high 300mph range as the drag co-efficient change. It also assumes no change in drag (fitting larger engine causes more drag, changing the cooling system changes things).

The estimate will always be lower than what was actually needed.

The Blenheim, while streamlined for 1935-37 was sort of a brick by 1940-41. The thick wing (good for STOL) the draggy landing gear, the draggy cowling and more and more,
 
The Beaufighter was essentially a Beaufort with a new fuselage and 40% more horsepower so to make a Blenfighter you would need to follow a similar process.

The Mercury VIII in the Blenheim 1 was 825hp so as mentioned earlier you are looking at a new fuselage and a 1200hp class engine and they did not exist other than the Merlin in potential.

I go with Clayton Magnet - fix the Whirlwind instead. We now know that the main problems with that were the propellers and the designer. The first was an easy fix if they had paid attention to the vastly superior performance of the one and only Whirlwind fitted with Rotol props.

The later, given Petter's later history with the Folland Gnat, would have required someone in the government or Air Ministry to do like Beaverbrook did to Lord Nuffield at the CBAF, snatch control of the project and give it to someone who was not so self important.
 
MiTasol said:
The first was an easy fix if they had paid attention to the vastly superior performance of the one and only Whirlwind fitted with Rotol props.
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What performance advantage was held by the Rotol prop outfitted Whirlwind vs. the 'normal' Whirlwinds?
 
Thank you for the feedback.
Seems like there is no definite 'Rotol-outfitted example was faster by so-and-so' answer. Further, seems like that RR was of opinion that ram air intake was badly designed on the Whirlwind - from the same web page:

A recent exchange of letters published in "Aeroplane" magazine also referred to a whirlwind that was returned to Rolls Royce in an attempt to improve the power of the peregrine engines. Rolls Royce found that the air intakes to the engines were too small and followed a convoluted path , they modified the aircraft sent to them and gained a considerable increase in power. Apparently the modifications were dismissed by Westland because Rolls Royce were just car engine people and knew nothing about aeroplane construction. I think that it's great that you are building a Whirlwind and look forward to seeing it at Hawkinge.

Also, I don't know why the author resorts to the too many 'coulds', 'mights' and 'mays' - not a good thing in an article trying to prove a point 80 years after the fact.
 
Well do you have a flyable Westland Whirlwind to go prove his research for certain one way or another
 
I am just an old firefighter but with water putting kinks and turns in hoses/pipes can lead to a lot of pressure/flow losses.
I imagine that air is the same. The Allison P-40 and P-51s had a really nice intake, Long and smooth with one roughly 90 degree turn into the carb.
109 used one 90 degree bend, Early Spitfire used one 90 degree bend

Some of the "using an intake in the leading edge of the wing" may look nice but how many twists and turns does it make getting to the carb?
How many 90 degree bends in the Whirlwind intake? at least two? maybe more but shallower bends?
The supercharger multiplies the inlet pressure so just a small drop is a significant change near or above critical altitude.

Whirlwind exhaust was pretty terrible also from a thrust stand point. Might have been good for flame suppression?
 
An improved Whirlwind, and Spitfire Mk. III's. Now THERE is a What If scenario for 1940!

Slapping some Merlin I's with big chin radiators on a Blenheim will make it go a little faster, but it is still dragging a bomber fuselage and wings through the air. It would still struggle to intercept the German Schnellbombers, or Ki-27 and G3M's in the far east. A lot of effort to bring a 15000 lb airplane into firing range, eventually, with just 4x .303 machine guns.
Maybe the bomb aimers position could be faired off, and replaced with a battery of Hispano's?
 
MiTasol said:
I go with Clayton Magnet - fix the Whirlwind instead.
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Leave the Whirlwind as is beyond increasing the ammunition capacity. Outside of the aircraft design itself, address the deficiencies in the powerplant and cannons. Then send them all to Malaya. I wonder what the Blenheim would do with a pair of Peregrines or early Merlins, both with chin rads.
 
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