Bristol's 1-row radials: realistic limits of power?

[tomo pauk]

... on the tech and fuel as available between 1935-45.

Main 3 engine types that I'm interested: Perseus (sleeve-valve type) and Mercury and of 24.9L, Pegasus of 28.7L, later two with poppet valves. For comparison, Wright managed to push the 29.9L R-1820 to 1300-1350 HP without water injection by 1944, on 2800 rpm and 46.5 in Hg (a bit above +8 psi) for the 1300 HP -56 version. You can 'kill' Aquila and Taurus to balance the need for more development of the listed engines in second half of 1930s.
Improvement of supercharging, at least as what Bristol can do, is also needed.
Finally, once the engines are there, where to install them?

Bore and stroke remain as-is.

 

[tomo pauk]

State of supercharging.
At altitude of 14000 ft, the max boost was for the FS Mercury was +5 psi, while the Pegasus in FS gear was good for +5.5 psi at 15500 ft. Perseus FS version - +3psi at 15500 ft. Seems decent, until we look at impeller's diameter. Mercury - 10.75in, Pegasus 11.25 in for the FS versions, or, in other words, the respective impellers were huge. Perseus - 9.25 in. All this is for
The 9.5in impeller on the V-1710-39 was managing ~39 in Hg, or +4.4 psi at 15000 ft, the same impeller on -81 and the like gave +6.7psi there. Nobody was heaping praise on the supercharger of the V-1710 engines (with good reason), but Britstol's superchargers seem to be really bad.
Problems, at least when accompanying Calum's book with stuff found here, looks to me as coming from few important details. Like forcing the incoming air to fight it's way before finally entering the impeller, and lack of the curved vanes preceding the straight vanes. (see here for how the curved vanes might look)
So the order of the day should be clearing the air passage right before the impeller, and designing the separate curved vanes that can be attached to the impeller front. Hopefully we'd get same result as the later R-1820s or mid-war Sakaes and Zuiseis - 42-43 in Hg at 18000 ft, or +6 to +6.5psi. Or, perhaps 950-1000 HP at 18000 ft.
A better and more efficient supercharger together with better fuel available to the British should make useful power at lower altitudes, too.

 

[Shortround6]

Problems are strength and cooling.

as mentioned many times the 1300-1350hp (and beyond) R-1820s shared very little except the bore and stroke of the 1200hp R-1820 (which didn't share very much with 1100hp R-1820).
The H series R-1820 went to 20 hold down bolts per cylinder instead of the 16 per cylinder used on the mid/late 30s engines.
The H series also used a whole new cooling fin system to dissipate the heat.

I am not saying it can't be done but it is going to require large amounts of change in most parts of the engine (including crankshafts and crankcases)
BTW the Aquila was already dead by 1937-38, they built something like 7 engines total.

and what have you got when you are done?

If you make the HP per cu in (liter) as the 1350hp R-1820 you have an 1127hp engine for either the Mercury or Perseus (adjust a bit as needed).
In 1943 I don't know what you would use such engines in aside from powered Hamilcar gliders?

Don't forget that part of the Cyclones "high" power came from using a low supercharger gear to get that takeoff rating. the take off power was only good to around 2000 or so???
correction welcome. AHT says the R-1820 in the FM-2 was good for 1000hp at 17,000ft. A Mercury or Perseus would be good for about 830hp at the same altitude if developed to the same level? or good for another 3,000ft over what the Mercury could do on 87 octane?

 

[tomo pauk]

Problems are strength and cooling.
as mentioned many times the 1300-1350hp (and beyond) R-1820s shared very little except the bore and stroke of the 1200hp R-1820 (which didn't share very much with 1100hp R-1820).
The H series R-1820 went to 20 hold down bolts per cylinder instead of the 16 per cylinder used on the mid/late 30s engines.
The H series also used a whole new cooling fin system to dissipate the heat.
I am not saying it can't be done but it is going to require large amounts of change in most parts of the engine (including crankshafts and crankcases)
BTW the Aquila was already dead by 1937-38, they built something like 7 engines total.
and what have you got when you are done?
If you make the HP per cu in (liter) as the 1350hp R-1820 you have an 1127hp engine for either the Mercury or Perseus (adjust a bit as needed).
Don't forget that part of the Cyclones "high" power came from using a low supercharger gear to get that takeoff rating. the take off power was only good to around 2000 or so???

Mercury's cooling & strength seem to work to up to 1000 BHP, with supercharger consuming more power than needed? Not having to deal with other two engines (Taurus mostly), a combination of better S/C and stronger interals might net us ~1100 HP Mercury/Perseus if also the MS (low) drive is used, and/or ~1200 HP Pegasus.

In 1943 I don't know what you would use such engines in aside from powered Hamilcar gliders?

Yes, in order for the improved 9 cylinders to be useful, the work on substantial improvement of S/C need to be started a few years before ww2. Likely users will still be the historical users of Bristol's 9 cyl engines, plus Beaufort and Albacore.

correction welcome. AHT says the R-1820 in the FM-2 was good for 1000hp at 17,000ft. A Mercury or Perseus would be good for about 830hp at the same altitude if developed to the same level? or good for another 3,000ft over what the Mercury could do on 87 octane?

Seems like that 1000 HP for the engine on FM-2 was at around 17700-17800 ft, not at 18000 ft I've posted before:

If our new brave Mercury uses +6 psi at ~17500 ft, this puts it perhaps at 850-900 HP there (it was turning extra 150 rpm vs. R-1820 and have had a 4 valve head); at +9 psi (let's not yet assume that over-boosting is to be beyond historical values, this is 950-1000 HP at 13500-14000 ft; perhaps 50 HP more for Pegasus, and another 100 HP at low altitude?