Bloch MB-157

Apteryx

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Hello all...


I am wondering if there are any sources of information on the French Bloch MB-157 fighter--the successor to the ill-starred MB-152. The best source I have is the ancient entry in Wm. Green's War Planes of the Second World War, Vol. 1, which is over fifty years old. Green claims superlative performance for this plane, of which only one prototype was built.


--Ian
 
Sorry....I've nothing more
Bye
 

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something more.........
 

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Aviafrance http://www.aviafrance.com/bloch-mb-157-aviation-france-293.htm
 
My understanding is that the prototype had no armour or weapons which might explain its outstanding performance. It seems probable that with armour and weapons added it wouldn't have been quite so outstanding. It would still have been a good fighter, but maybe not a miraculously good one.
 
Apteryx said:
Hello all...


I am wondering if there are any sources of information on the French Bloch MB-157 fighter--the successor to the ill-starred MB-152. The best source I have is the ancient entry in Wm. Green's War Planes of the Second World War, Vol. 1, which is over fifty years old. Green claims superlative performance for this plane, of which only one prototype was built.


--Ian
Because it were captured by Germany during the battle of France !
 
From
-"Le Bloch MB.152" by Serge Joanne
Lela press 2003
 

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From
-Les Ailes de Gloire nº3 by Patrick Marchand and Junko Takamori
Indochina 2000
 

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From
War Planes of the Second W.W. Vol. one
by William Green
Macdonald 1963
 

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Thanks, everyone.


I'm willing to believe that the MB-157 was a "mature" design with good performance. The stated top speed of 710 km/h, however, seems not credible when you look at comparable designs. Nick Sumner speculates that it might have slowed down had its military equipment been installed, but weight seems to be a minor factor in top speed of high-performance airplanes compared to surface area, aerodynamic efficiency and power.


--Ian
 
Apteryx said:
I'm willing to believe that the MB-157 was a "mature" design with good performance.

I'm still skeptical that an aircraft whose engine thrust line is angled (to counteract unexpected torque troubles) can be viewed as a "mature" design.
 
The Gnome Rhone 14 R engine was allways a technical nightmare for the french engineers, even after the war. It was foreseen for a lot of planes, but a great part of them flew finally with other engine(s). Maybe the Bloch MB 157 could have been a good fighter, but not with this engine...
 
Stargazer2006 said:
I'm still skeptical that an aircraft whose engine thrust line is angled (to counteract unexpected torque troubles) can be viewed as a "mature" design.

AFAIK all versions of the Bloch MB.15x series had the engines angled to counteract torque. Other designers used different
solutions, but not necessarily with better effect, e.g. the Messerschmitt Bf 109 had a fin with an asymmetrical profile, but
was notorious for difficult handling during take-off, although exagerated in this case by the narrow tracked landing gear.
 
I don't see how an aircraft with braced tail, powered by a radial engine, could do 441mph with just 1600hp.

It just does not make sense to be faster than P51D on less power with a far more drag. There was not even good exhaust design to boost speed as in FW190. I mean Griffon powered Spitfire XIV did 446 mph, come on.

441mph was either attained in a dive or this was an error carried over from Greem/Swanborough books over the years which other books used as resource.

It probably did mid to high 300s at best
 
Apart from the braced tailplane the MB157 looks like a reasonably clean design. As for a 1600hp radial engined aircraft being less likely to attain 441mph, bear in mind the German Fw190A, Russian La-7 had radial engines too, of similar power output. The La-7 attained 430mph on 1700hp.
 
La7 was smaller in size with ejector exhausts. Wings were 90cm shorter. No cannons in the wings nor tilted cowling. Not to mention having a very smooth cowling and oil cooler under belly. MB157 had no advanced aerodynamic features, other than overall cleanup. And I would not underestimate the drag of tail braces at high speeds.

May be MB157 did a flight with tailwind much like Sqn Ldr. Gillian who did over 400mph in an early Hurricane!

I still think it was an printing or recording error though.
 
MB157: normal loaded weight 3230kg, span 10.68m, length 9,70m, wing area 19.40m2
La-7: loaded weight 1904 3380 kg, span 9.80m, length 8.50m, wing area 17.51m2

All data from William Green. I'd say they're comparable in size, the MB157 is somewhat lighter.
<edit> fixed weight conversion :-[ </edit>
 
Gents, I guess the trick is in the engine's power. Document pasted by Justo M. says max power 1580 cv (hp) is attained at 5,000m. This is ‘au banc’ (on the stand) so one may expect in the real aircraft max power at some 5,500-6,000m, because of air compression in the carburetor duct inlet. And this attitude should roughly correspond with the altitude of maximum aircraft's speed. But the same doc says MB157 reaches Vmax at 7,850m, so clearly too high.
Scan 1 by toura says GR14R delivers 1700hp at 8,000m, a really remarkable power, if true. R2800-18 from F4U-4 delivers some 1800hp at 7,000m, so more or less the same. Then it's clear that MB157 could reach the same speeds as F4U-4, being probably less advanced in terms of aerodynamics, but much lighter.
Have no clue which power of GR14R is real. Maybe there was a ‘boosted’ version, or some limits were released for short time of MB157 tests?
 
I'd agree with Arjen that the 42L BMW 801 or 41 L ASh-82 might make a better comparisons than a 46 L R-2800. All BMW 801s (except the 'R) had single-stage superchargers but performances are not too different from the 2-stage GR 14R-4 of the MB-157.

From what little I can gather, the key differences between Gnome & Rhône's 14N and 14R series were number of crank main bearings and supercharger stages. The MB-157's 14R-4 had a 2-stage supercharger but was also intended to run on higher octane fuel.

The earlier Gnome-Rhône 14N-25 produced 1080 hp on 87 octane fuel. The 14N-49 put out 1100 hp on 87 octane, 1300 hp on 100 octane. That's quite a jump. The real question for the 14N-49 or 14R-4 is whether 100+ octane fuel would have actually been available to the Armée de l'Air.
 
Hi! Another MB.157 three side view drawing.
Indeed, the propeller's thrust line is tilted against the longitudinal axis of the aircraft.

https://arnor022.deviantart.com/art/Detail-Bloch-MB-157-570190059
https://www.the-blueprints.com/blueprints/ww2planes/various/82253/view/bloch_mb-157/
Gnome-Rhône 14R engine.
https://en.wikipedia.org/wiki/SNECMA_14R
 

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Found these informations in the book « le BLOCH MB-152 «
Sorry in French only
 

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MB157: normal loaded weight 3230kg, span 10.68m, length 9,70m, wing area 19.40m2
La-7: loaded weight 1904 3380 kg, span 9.80m, length 8.50m, wing area 17.51m2

All data from William Green. I'd say they're comparable in size, the MB157 is somewhat lighter.
<edit> fixed weight conversion :-[ </edit>

I have said numerous time already but La-7 had a 16% thick airfoil. It accounts for a lot of the drag comparatively on this airframe. This is an inheritance from the earlier La-5. In fact, only the La-9 got a significantly redesigned wing section.

Bloch designers were well aware of airfoil sections impact on speed. As early of late 1930s, they choose a 14.5% airfoil section (slightly lower than concurrent designs that were generally 15% for a 5 digit NACA profile) for their MB-152.
Notice that there are multiple factors at play here. A thinner wing profile doesn't make it all.
 
Found these informations in the book « le BLOCH MB-152 «
Sorry in French only
The book was published in 2003, LELA Presse.
Quite a bit more recent than William Green's 1960 book. Hopefully, not simply parrotting of the earlier work. Serge Joanne provides some performance numbers not mentioned by Green.
 
The following might be of interest.

Faced with the task of sprucing up the Bloch MB 155 with the new, powerful and unproven Gnome et Rhône 14R engine, a young engineer by the name of Lucien Servanty (1909-75), future chief designer of the SNCASO SO.9000 Trident and SO.9050 Trident II / Trident III rocket-powered interceptors (8 or so aircraft built) and major player in the design of Concorde, quickly realised that a simple adaptation using the same airframe, a version known as the MB 156, would not take advantage of the potential of the new engine.

Servanty thus undertook a thorough redesign of the airframe, with an larger wing and various improvements. The prototype of the MB 157, incomplete in June 1940, was seized by the Germans as it was being evacuated to the southern part of France. Oddly enough, the German authorities eventually allowed development to continue, under their control, in Bordeaux.

Completed in early 1942, that prototype flew around March or April. Its pilot may well have been Bloch test pilot Zacharie Heu (1890-1953).

The aircraft was later moved to Orly, near Paris, where it was (partly?) disassembled and stored. It was eventually destroyed during an Allied bombing raid, in 1943 or 1944 I cannot say.

The very high speed of the aircraft might have been mentioned for the first time in a publication in an April 1954 issue of the bimonthly Aviation Magazine (https://gallica.bnf.fr/ark:/12148/bpt6k5322336j --- p. 15, col. 3).

According to http://sam40.fr/les-derniers-chasseurs-bloch-157-100-1011-1040-entre-mythe-et-realite/, that speed seemingly made its appearance no later than 1943, in a company brochure, as a predicted or expected speed (441 mph at 25,750 ft), under some sort of wartime emergency power condition - and not as an actual speed achieved during testing.

It is worth noting that the aircraft was then referred to as the SO 157. Marcel Bloch, who was Jewish, was no longer an acceptable chief designer. Indeed, he had been interned / arrested by the Vichy government in October 1940.
 
Last edited:
I agree. I have got an original copy of this SO 157 notice. I can confirm that these performances are calculated.
Unfortunately, I never found flight reports about this plane.
 

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