Bloch 151 altitude of top speed

[greybeard]

I couldn't find at what altitude Bloch 151 reached its maximum speed of 460 km/h.

Thanks for any help,
GB

 

[waroff]

For the MB 151 Gnome Rhone 14N35, GR prop variable pitch, MB 152 GR14N/25 Chauviere variable pitch; the flying manual(1939) gave
375 kmh IAS (around 458kmh TAS) at 4000m, 820mm Hg and 2400rpm
151 vs 152
engine : GR 14 N35 / GR 14 N25 or 49
propeller : GR 3.05m dia / Chauviere 371 3.05m dia
power at sea level : 815cv / 870cv
max power Take Off : 895 / 1100
power at altitude full pressure :920 / 1000
altitude full pressure : 3000 / 3600m
nominal admission pressure : 820 / 800mm Hg
nominal rpm : 2360 / 2250 rpm
ratio gear box: 2/3 / 2/3
exhaust : GAL / GAL

 

[greybeard]

Thanks for detailed answer.

Please, could you explain what does GAL mean?

 

[waroff]

GAL was the name of manufacturer. The GAL exhaust for MB 151/152, Br 691, 693,
was a ring collector and flame damping exhausts. They (five on MB) was a multi slot outlet. the flames were blown by the relative wind.
These exhaust were around the cowling

 

[greybeard]

Thanks for your answer.

So, if I understood correctly, it doesn't matter of the H75-type jet exhaust, giving some increase in thrust, and so in speed, seemingly in use on late MB 152. May I ask what improvement in speed should give it?

 

[Bretoal2]

Thanks for your answer.

So, if I understood correctly, it doesn't matter of the H75-type jet exhaust, giving some increase in thrust, and so in speed, seemingly in use on late MB 152. May I ask what improvement in speed should give it?

I never heard Curtiss H-75 exhaust ring collector was a jet type !

In France, jet exhausts for radial engines were individual, develloped from Mercier (LeO 451) patents. They could not fit single engined airplanes owing to exhaust leakage in cockpit. Late Bloch 152 had ring collector with lower outlets.

Individual jet exhausts were fitted on LeO 451, Amiot 351, Bloch 174 and late Breguet 693.

Early Breguet 693 with GAL flame dampers had a 475 km/h top speed. Late models reached 495 km/h, i.e. + 20 km/h.

 

[greybeard]

I never heard Curtiss H-75 exhaust ring collector was a jet type !

My guess was due to what already mentioned HERE.

Thanks for your kind reply,
GB

 

[Bretoal2]

OK.

Drix seems to have made a mistake, he wrote "pipeS". He obviously believed that the latest versions of the Bloch 152, without GAL flame dampers, had received individual jet pipes, but, as said above, this is impossible in a single-engined airplane because exhaust gases would enter the cockpit.

Also, I do not think the ring collector of this late version was copied to the H-75. More complex models, fitting 14 cylinders two-rows radials (while the H-75's Wright was only 9 cylinders, single-row), were drawn long before the Curtiss fighter arrived in France. You see them on many older French airplanes (such as MB 210 bomber). And the large outlet could not give any jet thrust !

 

[greybeard]

Thanks for your competent comment.

So, now, the question arises: why they changed it? And, above all, was speed increase between early and late model of MB 152 due only to diameter reduction of engine cowling air intake?

 

[Bretoal2]

The 14 N 49 engine (mounted on late MB 152) is significantly more powerful than the 14N 25 .

Rated power : 1,000 hp / 1,070 hp
Rated altitude : 3,600 m / 3,700 m

Normal power at 0 m : 870 hp / 920 hp
Max. takeoff power: 1,120 hp / 1,180 hp

Maximum War Emergency power : 1,220 hp / 1,300 hp
At : 2,250 m / 2,250 m

Power at 4,000 m: 950 hp / 1.020 hp
Power at 6,000 m: 720 hp / 750 hp
Power at 8,000 m: 520 hp / 560 hp

Obviously it deserved a better exhaust system - and a better induction ducting able to boost ram effect.

Regards
Alain

 

[greybeard]

Allow me to disagree. 80 hp on about 1000 are a mere 8%. Given that power required increases with the cube of speed, this brings to a 2% more velocity, that's to say less than 10 km/h.