Bristol's twin-engined planes?

tomo pauk · May 16, 2012

We have a plane that grows from 12500 to 26000 lbs, in two steps; Blenheim V is no stepping stone for Beaufort/Beaufighter. I do not buy that it took simple changes, like cutting the front fuselage, or installing the new engines: if that was the case, a Blenheim suddendly grown to Beaufighter would've disintegrated in mid air because the structural limits would've been to great to bear.
Seem to me that Beaufort was the step where the most of the redesign took place?

After reading the second part of the your post, going with a design tailored for Hercules/Merlin (instead of Taurus), for 1940, seem like a missed opportunity. My idea about Pegasus-powered version of the plane does not seem like a bright one.

Shortround6 · May 16, 2012

The Beaufort was a redesign, It used light alloy in places where the Blenheim had used steel, Structural weight of the Beaufort was actually less than the Blenheim. But it kept much of the original Blenheim design, much like the LA-7 kept much of the LA-5 and Lagg-3 or the various Yaks kept much of the design even though wing spars changed from wood to metal and so on. Or like the P-51H kept much of the design of the P-51D even though there are few interchangeable pieces.
The British had a major problem with engines in 1938-41, they had no easy way to upgrade from their 800-900hp class engines unless the plane was rather big. The Wellington was big enough to go from an 1100 pound engine to 1600-1800lb engines (Hercules or Merlin with radiator). The British had no 1200-1450 pound engines like the P&W R-1830 or the Wright R-1820 or the ones they had were low powered (Tiger/Dagger) or unreliable (Taurus).

For a somewhat comparable aircraft see the Martin Maryland and Baltimore.

If the British had had a 1000-1200hp engine of 1200-1400lbs perhaps a better Blenheim or Beaufort could have been built. The Sleeve valve problems mean even a Hercules powered plane started in 1937-8 won't show up in more than handfuls until late 1940, much like the original Beaufigter. And for a twin to be any good with Merlins it needs the MK X. The 880hp take-off rating of the MK III without 100 octane fuel doesn't bear thinking about in a 16,000-20,000lb plane.

Tankworks · May 16, 2012

i think, like the Martin and A-20, the Bristol designs were too small to allow much development without designing a completely new aircraft. The B-25 would be an example of an aircraft large enough to allow all sorts of tweeking.

Shortround6 · May 17, 2012

Tankworks said:
i think, like the Martin and A-20, the Bristol designs were too small to allow much development without designing a completely new aircraft. The B-25 would be an example of an aircraft large enough to allow all sorts of tweeking.

While the B-25 does allow for quite a bit of tweaking it is also too large to fill at least one of the roles Tomo wants to fill, that of night fighter. To be even a moderately successful night fighter a plane has to have enough of a performance advantage over it's contemporary bombers (using same class/power engines?) that it is usually too small to be a first class bomber (Mosquito excepted, with reservations).

Juha · May 17, 2012

Shortround6 said:
...And the idea that ANY bomber, no matter how well it might roll or turn or loop for a bomber, had the ability to bring a single fixed .303 gun to bear on an enemy fighter simply boggles the mind...

I agree but still had to add that some Finnish Blenheim pilots claimed that a light short-nose Blenheim Mk I could out turn the standard 1937-40 FiAF fighter Fokker D. XXI, now tests seems to contradict this. And for all pilots Beamont, incarnation of company loyality, told a story how he had a hard turning combat in France in May 40 with an aggressive Do 17Z pilot, who had initiated the combat by attacking Beamont who was flying Hurricane.

Juha

tomo pauk · May 17, 2012

Shortround6 said:
The Beaufort was a redesign, It used light alloy in places where the Blenheim had used steel, Structural weight of the Beaufort was actually less than the Blenheim. But it kept much of the original Blenheim design, much like the LA-7 kept much of the LA-5 and Lagg-3 or the various Yaks kept much of the design even though wing spars changed from wood to metal and so on. Or like the P-51H kept much of the design of the P-51D even though there are few interchangeable pieces.

Thanks for the details about the changes Blen - Bfort. Unfortunately, the empty weight grew for an 1/3rd (circa 3500 lbs), the heavier engines being main culprit (2 x 350 lbs, dry).

The British had a major problem with engines in 1938-41, they had no easy way to upgrade from their 800-900hp class engines unless the plane was rather big. The Wellington was big enough to go from an 1100 pound engine to 1600-1800lb engines (Hercules or Merlin with radiator). The British had no 1200-1450 pound engines like the P&W R-1830 or the Wright R-1820 or the ones they had were low powered (Tiger/Dagger) or unreliable (Taurus).

Well, I'm surely not proposing a 'Welington a-la Bristol' here A Bf-110-sized plane, powered by Hercules or Merlin and here we go.

For a somewhat comparable aircraft see the Martin Maryland and Baltimore.

As above - Bf-110 sized, or akin to A-20.

If the British had had a 1000-1200hp engine of 1200-1400lbs perhaps a better Blenheim or Beaufort could have been built. The Sleeve valve problems mean even a Hercules powered plane started in 1937-8 won't show up in more than handfuls until late 1940, much like the original Beaufigter. And for a twin to be any good with Merlins it needs the MK X. The 880hp take-off rating of the MK III without 100 octane fuel doesn't bear thinking about in a 16,000-20,000lb plane.

Yep, the Hercules seem like logical 1st call.

Shortround6 · May 17, 2012

tomo pauk said:
Well, I'm surely not proposing a 'Welington a-la Bristol' here A Bf-110-sized plane, powered by Hercules or Merlin and here we go.

As above - Bf-110 sized, or akin to A-20.

Well, the Bf-110 and A-20s had smaller wings but the Bf-110s smaller fuselage makes for a poor bomber. Hanging the bombs outside means more drag than the enclosed bomb bay. The multi role is going away and being replaced by a fighter and bomber wannabe.

The Beaufort could carry a 2000lb SAP inside (or partially inside) and carry 2000lb a longer distance than the A-20 could. Since you can't have everything, even with 1700hp engines, what attributes do you want to down play in order to get the performance you want? Also please remember that a Beaufighter was carrying almost 500lbs worth of 20mm guns and over 700lbs of 20mm ammo + 130lbs worth of .303 guns and over 360lbs of .303 ammo for about 1800lbs worth of guns and ammo, not counting mounts, heaters, ammo boxes, chutes, etc, which can run 20-40% more in weight. Carrying heavy gun armament + bombs and going fast and far isn't going to happen. Pick 2 or even 3, ALL 4 is out.

I will try to post picture of a Blenheim IVF fighter later. The machine gun pod was about as crude as you could get. The Blenheim could have been 15-20mph faster without too much trouble even with the same engines.

fastmongrel · May 18, 2012

Shortround6 said:
The machine gun pod was about as crude as you could get. The Blenheim could have been 15-20mph faster without too much trouble even with the same engines.

I think just hanging the guns underneath with no cover would have been more aerodynamic than the pod they used. If they had given a first week apprentice 2 hours, some plywood, fabric and dope he could have done a better job.

Juha · May 18, 2012

Shortround6 said:
...I will try to post picture of a Blenheim IVF fighter later. The machine gun pod was about as crude as you could get. The Blenheim could have been 15-20mph faster without too much trouble even with the same engines.

IIRC the mg pod was made by a firm whose usual production was connected with railroads/rolling stock.

Juha

Shortround6 · May 18, 2012

Here are a couple of pictures.

http://plawner.org/plane1/compressed/bristol Blenheim Mk IVF_2.jpg

and

http://www.grahamtall.co.uk/wgs1955...etters/Coe Gordon/Coe-Bristol-Blenheim-IV.jpg

Sorry, I am getting invalid URL when I try to attach them.

The First really shows how "dirty" a Blenheim could be. External bomb racks under the rear fuselage, The Fuel jettison pipes, the large gaps around the main wheels. The large "box" holding the under belly guns.
For a night fighter version a decent aerodynamic clean up could have done wonders. Loose the turret and replace with small observation dome/bubble, clam shell landing gear doors instead of the apron style to close up a lot of the gaps and fair the wheels a bit better. Smaller or different fuel pipes. Get rid of the bomb racks for interceptor duty.
You might be able to pick up a quick 10-15mph without too much trouble even with the same power plants. Getting some constant speed propellers instead of the controllable pitch ( a way of saying two-pitch without sounding bad?) may help performance.
If Bristol had manged to fit the Mercury engine with a two speed supercharger drive from the Pegasus it would not have done much for altitude performance but it might have increased take-off and low level power by about 13%, 820hp instead of 725hp. That is with 87 octane fuel.

tomo pauk · May 18, 2012

Shortround6 said:
Well, the Bf-110 and A-20s had smaller wings but the Bf-110s smaller fuselage makes for a poor bomber. Hanging the bombs outside means more drag than the enclosed bomb bay. The multi role is going away and being replaced by a fighter and bomber wannabe.

The Beaufort could carry a 2000lb SAP inside (or partially inside) and carry 2000lb a longer distance than the A-20 could. Since you can't have everything, even with 1700hp engines, what attributes do you want to down play in order to get the performance you want? Also please remember that a Beaufighter was carrying almost 500lbs worth of 20mm guns and over 700lbs of 20mm ammo + 130lbs worth of .303 guns and over 360lbs of .303 ammo for about 1800lbs worth of guns and ammo, not counting mounts, heaters, ammo boxes, chutes, etc, which can run 20-40% more in weight. Carrying heavy gun armament + bombs and going fast and far isn't going to happen. Pick 2 or even 3, ALL 4 is out.

I will try to post picture of a Blenheim IVF fighter later. The machine gun pod was about as crude as you could get. The Blenheim could have been 15-20mph faster without too much trouble even with the same engines.

Doh

'Sized' needs to be read here as 'about same length, wing span area'. I've twice stated that my idea is to have a mid- or high wing plane, not too thick a wing, only 4 LMGs being a 'permanent' gun armament (replaced by 2 belt fed Hispanos as they become available). The LMG/cannon ammo is in the space above fuselage. The bomb bay does not need to be too wide (accomodating a torpedo or two decent bombs (2 x 1000 lbs?) in tandem, or one big bomb(2000 lbs)), so two fuel tanks can be located aside the bomb bay. 4-6 LMGs in the nose, the night fighters can use the bomb bay to bulk out their gun armament, so the night fighter can have either 8-10 LMGs, or 4-5 cannons, when available.
So a 'Hercules Bristol' for 1940-42 can carry, say, 4 wing-root LMGs (or 2 cannons), plus 4-6 nose LMGs AND a torpedo, while being fast with decently long legs (it has far less drag, since it has a thinner wing, and the torp is in the bomb bay). Or, with some good Merlins, really fast long legged, we avoid the drag increased consumption of extra 2 x 1000 cubic inches of powerplant (like the A-20 had to).
Hmm, that being said, an A-20 with inlines really sound tempting, starting with single stage Allison F series, via V-1650-1, up to 2-stage Allison. Faster than Zero Oscar at any/most of the altitudes, much better range than A-20?

For the general layout, my Bristol would looked like the A-20 as tail dragger, or like Ta-154 tail dragger.

wuzak · May 19, 2012

tomo pauk said:
Hmm, that being said, an A-20 with inlines really sound tempting, starting with single stage Allison F series, via V-1650-1, up to 2-stage Allison. Faster than Zero Oscar at any/most of the altitudes, much better range than A-20?

If you can keep the nacelle small enough to take advantage of the in-lines. If you start with the A-20 you'd probably want to keep the nacelle and firewall as is to minimise changes for production. That means that some of the aerodynamic benefits of using an in-line will be lost. Still, that should be plenty of space for a radiator, oil cooler and intercooler (I stll don't know why Vega put th eradiators in the leading edges of the XB-38 - surely having it all in the nacelle would have allowed for easy conversion?).

The R-2600 is a fairly wide engine. You know what in-line is aout the same width? Yep, the V-3420.

Push the V-3420 development harder and you may get some production by 1943. Then they become available for the B-29/B-39 program. Again, mount every thing in the nacelle so the conversion is basically a bolt on proposition.

Maybe then Martin will build the proposed V-3420 powered B-26!

tomo pauk · May 20, 2012

If you can keep the nacelle small enough to take advantage of the in-lines. If you start with the A-20 you'd probably want to keep the nacelle and firewall as is to minimise changes for production. That means that some of the aerodynamic benefits of using an in-line will be lost.

Agree with that. An A-20 with in-lines should harvest on the increased aerodynamic efficiency (even if the engine installation is less than perfect), along with having the engine with substantially less swept volume. Weighting against that is the decreased take off power (2 x 1600 HP vs. 2 x 1150 up to 2 x 1350 HP for single stage engines (unless overboosted/WER in service, for take off?); more power with two stage engines). So both in-line radial 'versions' of the A-20 being produced?
The A-20 using at 1600 HP, WER, of the two stage V-1710 would've been quite a performer from early 1944.

Still, that should be plenty of space for a radiator, oil cooler and intercooler (I stll don't know why Vega put th eradiators in the leading edges of the XB-38 - surely having it all in the nacelle would have allowed for easy conversion?).

Agree again.
The installation from the P-40 seem like natural choice for A-20 (of course, no intercooler here, unless we go with two-stage Merlin, or the turbo V-1710).

The R-2600 is a fairly wide engine. You know what in-line is aout the same width? Yep, the V-3420.

Push the V-3420 development harder and you may get some production by 1943. Then they become available for the B-29/B-39 program. Again, mount every thing in the nacelle so the conversion is basically a bolt on proposition.

Maybe then Martin will build the proposed V-3420 powered B-26!

Yep, I've seen the artist's impression in the 'Vee's for victory'. Quite a sleek bird. The V-3420 for the A-26, too?

stug3 · Jan 1, 2013

German transport column on the Agheila-Agedabia road, south of Benghazi, under cannon attack from Bristol Blenheim of No. 113 Squadron RAF. The first two lorries are running off the road.

Aozora · Jan 1, 2013

Just for interest, here is Bristol's proposed design for a single-seat, twin engine day/night fighter, the Type 153...resembles something else...guesses? (From Buttler, British Secret Projects, Fighters and Bombers 1935-1950)

Aozora · Jan 1, 2013

Shortround6 said:
The Beaufort was a redesign, It used light alloy in places where the Blenheim had used steel, Structural weight of the Beaufort was actually less than the Blenheim. But it kept much of the original Blenheim design, much like the LA-7 kept much of the LA-5 and Lagg-3 or the various Yaks kept much of the design even though wing spars changed from wood to metal and so on.

Beaufort construction v Blenheim

The modular construction was one reason why the Australians selected the Beaufort over the Blenheim, plus the torpedo and better overall performance, made even better by replacing the bugged Taurus with the R-1820s.

Re the A-20 with V-1710s and A-26 with V-3420s; changing from radials to inlines would make both more vulnerable, for not enough gain (if any) in overall performance. As it was the R-2600s of the A-20 put out more power than most V-1710s, without having the added weight and complication of a liquid cooling system.
The engine cowlings and nacelles of the A-26 were very carefully designed to provide minimum drag and maximum cooling for the R-2800s; simply bolting V-3420s to the firewall would have been a waste of time because such an installation would have created aerodynamic problems which would have nixed any possible performance advantages. The same thing happened with the B-29 when one of them was redesigned for the V-3420; there wasn't enough of a gain in performance to warrant the change.

And, after all that, they would both have been far more vulnerable to flak.

tomo pauk · Jan 1, 2013

The main reason the Aussies choosing anything over Blenheim being the planes obsolescence?
The B-29 trial installation of the V-3420 was too late to matter, since the R-3350 was finally gotten to work okay. The Flak was of no concern for B-29 duties historically, either when flown during daylight or night.

wuzak · Jan 1, 2013

Aozora said:
Re the A-20 with V-1710s and A-26 with V-3420s; changing from radials to inlines would make both more vulnerable, for not enough gain (if any) in overall performance. As it was the R-2600s of the A-20 put out more power than most V-1710s, without having the added weight and complication of a liquid cooling system.
The engine cowlings and nacelles of the A-26 were very carefully designed to provide minimum drag and maximum cooling for the R-2800s; simply bolting V-3420s to the firewall would have been a waste of time because such an installation would have created aerodynamic problems which would have nixed any possible performance advantages. The same thing happened with the B-29 when one of them was redesigned for the V-3420; there wasn't enough of a gain in performance to warrant the change.

An A-26 with V-3420s would have 300-400hp more per engine, but potentially 400hp more on top of that (ie 3000hp per engine). Longer term the V-3420s would have been capable of pumping out 4000hp.

A V-1710 with all cooling systems should be comfortably lighter than an R-2600, though it will have less power early in the war.

The XB-39 was 50mph faster than the B-29A.... The XB-39 program was delayed because of the sudden urgent need to develop a long range fighter - the XP-75 - which took engineering resources away from the program.

Aozora · Jan 1, 2013

wuzak said:
An A-26 with V-3420s would have 300-400hp more per engine, but potentially 400hp more on top of that (ie 3000hp per engine). Longer term the V-3420s would have been capable of pumping out 4000hp.

A V-1710 with all cooling systems should be comfortably lighter than an R-2600, though it will have less power early in the war.

The XB-39 was 50mph faster than the B-29A.... The XB-39 program was delayed because of the sudden urgent need to develop a long range fighter - the XP-75 - which took engineering resources away from the program.

V-1710 with cooling systems would have been about on a par with the R-2600, but simply bolting it to the front of an engine nacelle designed for a radial would have created too much drag without a redesign to take advantage of the V-1750's smaller frontal area.

The V-4320 was heavier than the R-2800 and still needed the cooling systems on top of that. At the very least a redesign of the A-26s engine nacelles would have been needed and, again, for the A-26's role as a medium bomber and for ground strafing the V-3420s would have been far more vulnerable to flak, without extra armouring. It would have been much easier adapting the design to a 'C' series R-2800, which was reliably giving 2,400 hp and was much easier to maintain. The B-29 (B-39) with Allisons did perform better than the B-29 but, then again, the R-3350 didn't become fully reliable until the late/post war period.

Anyway, back to the Bristol designs...

tomo pauk said:
The main reason the Aussies choosing anything over Blenheim being the planes obsolescence?

No, the Blenheim was not considered obsolescent at the time the Beaufort contract was signed - the Beaufort was chosen partly because the Aussies wanted a flexible, multi role aircraft which could carry a torpedo, and partly because the Beaufort would be easier to build in dispersed locations.

wuzak · Jan 1, 2013

Aozora said:
V-1710 with cooling systems would have been about on a par with the R-2600, but simply bolting it to the front of an engine nacelle designed for a radial would have created too much drag without a redesign to take advantage of the V-1750's smaller frontal area.

Surely not 700lbs worth of cooling system? Sounds a bit far fetched to me.

It depends on the size of the nacelle at the firewall (where the R-2600 is taken off and the V-1710 put in its place) as to whether much could be done about drag reduction.

Aozora said:
The V-4320 was heavier than the R-2800 and still needed the cooling systems on top of that. At the very least a redesign of the A-26s engine nacelles would have been needed and, again, for the A-26's role as a medium bomber and for ground strafing the V-3420s would have been far more vulnerable to flak, without extra armouring. It would have been much easier adapting the design to a 'C' series R-2800, which was reliably giving 2,400 hp and was much easier to maintain.

More vulnerable to flak....we've had this discussion before.

I thought the A-26 did use C-series R-2800s.

A QEC engine module could have been designed to bolt up the R-3420 in place of the R-2800. As was done for the XB-39, and in many cases in Germany.

Annular radiators could have been used too.

http://www.warbirdsresourcegroup.org/BARC/images/tempest-4.jpg
http://farm6.staticflickr.com/5070/5674825997_6c4f6de516_z.jpg

The Germans liked their annular radiators
http://www.nationalmuseum.af.mil/shared/media/photodb/photos/071017-F-1234S-015.jpg

Annular radiators would also be easier to armour.

Aozora said:
The B-29 (B-39) with Allisons did perform better than the B-29 but, then again, the R-3350 didn't become fully reliable until the late/post war period.

The problem with the XB-39 program was that it was delayed, as mentioned before, so could not be evaluated early enough to put it into production. There was also the matter of interrupting production to make the change, though the V-3420 installation was designed as a QEC which would have been basically a bolt up job.

Bristol's twin-engined planes?

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