Best British poppet valve radial?

[Admiral Beez]

Bristol's best poppet valve radial seems to be the sub 1000 hp Pegasus. The Armstrong Siddeley Tiger was about as powerful but needed better bearings. Anything else in the poppet valve radials? Was the smaller Mercury a better engine for its size?

Could these British engines be upsized to 2,000 hp if given money and time.

 

[yulzari]

The Italians tried to make a twin row version of their Pegasus and simplified the valve gear by reverting to a two valve head but ran into vibration problems IIRC. However, if a two row Pegasus were made and worked then it could have been a 2,000bhp engine early in the war. Not a small 'if' if one is to reach the four valves on each head including those not on the row with the driving gear. Possibly why the Italians went back to the two valve?

 

[b0ned0me]

Bristol's best poppet valve radial seems to be the sub 1000 hp Pegasus. The Armstrong Siddeley Tiger was about as powerful but needed better bearings. Anything else in the poppet valve radials? Was the smaller Mercury a better engine for its size?

Could these British engines be upsized to 2,000 hp if given money and time.

For the Tiger, wasn't it more that it needed more bearings rather than better bearings? As far as I know it just had no center bearing, just like the GR-14K and many other early two-row engines that started disintegrating when asked for more than 1000hp.
So more bulk to fit the extra bearing, longer crankcase, longer crankshaft, more weight because of all that, rework all the vibration analysis and then hope it gains enough power to offset the added weight. Pegasus / Mercury are inherently simpler because only one row of cylinders but that also limits the power a lot.

With enough time and money any of these could be upsized but they are all old technology so to come up with something that gives 2000hp at a competitive size and weight you need to not just scale them up but adopt new heads, valve gear, induction, materials, manufacturing techniques - by the time you have finished it's a brand new engine 'inspired by'. Which is what the Aquila/Perseus/Taurus/Hercules/Centaurus should have provided but - unexpected gremlins in the sleeve area.

 

[Shortround6]

Could these British engines be upsized to 2,000 hp if given money and time.

That is what a lot of people thought about other 9 cylinder single row radials.

Given enough time and money it could be done.
It also took years in actual practice.

 

[don4331]

For the Tiger, wasn't it more that it needed more bearings rather than better bearings? As far as I know it just had no center bearing, just like the GR-14K and many other early two-row engines that started disintegrating when asked for more than 1000hp.
So more bulk to fit the extra bearing, longer crankcase, longer crankshaft, more weight because of all that, rework all the vibration analysis and then hope it gains enough power to offset the added weight. Pegasus / Mercury are inherently simpler because only one row of cylinders but that also limits the power a lot.

With enough time and money any of these could be upsized but they are all old technology so to come up with something that gives 2000hp at a competitive size and weight you need to not just scale them up but adopt new heads, valve gear, induction, materials, manufacturing techniques - by the time you have finished it's a brand new engine 'inspired by'. Which is what the Aquila/Perseus/Taurus/Hercules/Centaurus should have provided but - unexpected gremlins in the sleeve area.

I agree 100% on the lack of center bearing limited power, but adding one seems to me to be more bearing (better bearings wouldn't have hurt in addition). And time is more the enemy - gov'ts are throwing cubic £/₣/₤/$/¥ at the issue.

If you are keeping stroke length "reasonable"/crankcase diameter as compact as possible, by the time you get to 7 or 9 cylinders per row, the 2nd row is offset enough that crankcase/crankshaft length to fit a center bearing really isn't an issue. However you are changing the crankcase dramatically - for 99% of engines built, you are adding a center section to the crankcase = more weight. Then you need to do something to fit the crankshaft throws through the center section (without resorting to a bearing of 10" or more. Additional piece(s) to split the center case to accommodate: top center, bottom center + a handful of fasteners = more weight (P&W R-2800). Or you split the crankshaft, and you assemble the 2 pieces through the center section meaning the center bearing must be larger = more weight (BMW 801).

Aside: It's little wonder with all the area to be sealed, that radials leak...

Then you can have the disappointment that the new engine with center bearing is making less power. First, you need to figure out what the issue is: the new engine seems to be retaining oil. Then develop a solution: some strategically placed cutouts in center section allowed P&W to pull several gallons of oil which was being whipped like toffee off the crank and gain 100hp back.

Finally, you need to order the new press/dies, the machine tools, assembly jigs and redo the line to build your modified core section. All of which takes time - which you don't necessarily have when the enemy is dropping bombs on you.

Just when you get it all working, some joker comes along and says, btw; you that engine you are set up to build using 80 octane, well we have access to 87 octane and engine needs to be strengthened to sustain >25% additional power. And you no sooner complete redoing the line and the same joker now says, let's build it for 100 octane with similar increase. And the Perseus goes from 580hp to 800hp to 1,200hp. And the joker is talking 115 octane + water injection.

Someplace in there, you either need to improve the supercharger efficiency from mid 30% when engines are 1st being run, to mid 60%s by time you are implementing the 100 octane engine - without Stanley Hooker on your team. (And when you fix the supercharger, your going to have to redo the tooling and assembly, yet again).