Author Topic: A Canadian Raven in Spain  (Read 1208 times)

Offline jcf

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Re: A Canadian Raven in Spain
« Reply #25 on: August 01, 2021, 02:33:47 AM »
The exhaust and intake valves are in the heads, not the cylinder barrels.
Fedden's practice, and thus Bristol's, was steel cylinders with separate
aluminum heads, which he had used beginning with his work during WWI.

Bristol heads were of two types: poultice heads with vertically set valves
and always cast; pentheads with the valves angled out from the center
to accommodate the pentroof combustion chamber, these could be cast
or forged.

I've been futzing with quickie thumbnail scribbles of a possible two valve
head design retaining the Fedden-esque pushrod and rocker arrangement
to continue the Bristol look as much as possible. It'll be a hemispherical
chamber design with angled valves.
“Conspiracy theory’s got to be simple.
Sense doesn’t come into it. People are
more scared of how complicated shit
actually is than they ever are about
whatever’s supposed to be behind the
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Offline apophenia

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Re: A Canadian Raven in Spain
« Reply #26 on: August 01, 2021, 04:36:58 AM »
Good stuff Jon  :smiley:

I realized that the valves were in the heads. My thought was: retaining the same cylinder barrels are an economy but Fedden's approach seemed to be causing him grief in developing a twin-row radial (or was it that he had just become obsessed with Ricardo's sleeve valve concept?).

On sleeve valves, my understanding is that most (if not all) of Bristol's needed tooling was sourced from the US. Not as much fun as a whif ... but maybe just jumping straight into Hercules production in Canada makes more sense?

Moving US-made/sourced tooling to Central Canada would be a lot simpler - and no risk of its transport being torpedoed halfway across the North Atlantic!
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Offline jcf

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Re: A Canadian Raven in Spain
« Reply #27 on: August 01, 2021, 09:28:11 AM »
The cylinder barrels are simply that, and being completely separate from the heads they have no impact
on valve gear positioning.

The piece of US sourced production machinery was specialized grinders rather than tooling.

Here's a Pegasus recovered from the water, the heads have corroded away and you can see the
lack of a relationship between the cylinders and the valve gear.



Here's a disassembled Jupiter cylinder and head.
« Last Edit: August 02, 2021, 03:34:39 AM by jcf »
“Conspiracy theory’s got to be simple.
Sense doesn’t come into it. People are
more scared of how complicated shit
actually is than they ever are about
whatever’s supposed to be behind the
conspiracy.”
-The Peripheral, William Gibson 2014

Offline apophenia

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Re: A Canadian Raven in Spain
« Reply #28 on: August 02, 2021, 07:15:40 AM »
Okay, so basically Fedden could have positioned his push rods anywhere he'd wanted to ... if he'd been really serious about a two-row radial design with poppet valves. None of that would have any effect on the cylinder barrels  :smiley:

... Here's a Pegasus recovered from the water, the heads have corroded away ...

That is a very cool image  :D
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Offline jcf

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Re: A Canadian Raven in Spain
« Reply #29 on: August 03, 2021, 08:08:44 AM »
I think one of Fedden’s concerns was probably with how crowded it would be under
the cowling leading to problems with proper airflow for cooling. The Alfa Romeo 135,
basically a twin-row Mercury, was plagued with overheating problems.

The intake air feed to the front row also looks problematic, and the close proximity
between the exhaust ports of the rear row and the intake ports of the fwd. row are
probably something that didn’t help with performance. The aft exhaust piping would
be heating the fwd. air intake trunks, internal combustion engines perform best with
cool intake air, and as the 135 didn’t have an intercooler the intake air would already
be carrying the heat added by supercharger and would be heating up even more as
it passed through the heat zone of the exhausts, not a good combo for performance.
The close cowling and poor airflow would also be increasing the temperature of the
intake trunks.

The 135 was in development from 1934 until 1945 without becoming a production
engine, which suggests to me that Fedden’s doubts were valid.



“Conspiracy theory’s got to be simple.
Sense doesn’t come into it. People are
more scared of how complicated shit
actually is than they ever are about
whatever’s supposed to be behind the
conspiracy.”
-The Peripheral, William Gibson 2014

Offline apophenia

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Re: A Canadian Raven in Spain
« Reply #30 on: August 04, 2021, 04:39:43 AM »
Yes, a decade's development and no production is pretty damning. The overheating of the Alfa Romeo 135 has me wondering more generally about other twin-row radials. The G-R 14K/14N series had a reputation for running hot (as did the 14M Mars. Overheating was even worse for the BMW 801s.

But then there's the R-1830. Other than the XF4F-2 with a spinner, [1] I don't recall reading about any overheating problems for Pratts in conventional cowlings. But, weirdly, the CAC Cicada single-row derivative seems to suffer from overheating before being derated.
-- http://www.enginehistory.org/Piston/CAC/cac.shtml

This is drifting well off topic but I'm also puzzled but comparative overheating of single-row radials. The single-row Wright R-1820 had a worse reputation for overheating than the twin-row Pratt (supposedly, one of the reasons why the Finns re-engined some of their Wright-engined Hawks). And, weirdly, the CAC Cicada single-row R-1830 derivative seems to have suffered from overheating before being derated.

-- http://www.enginehistory.org/Piston/CAC/cac.shtml

Did Twin Wasps tend to be provided with extra-generous cowlings? Did Pratt have some other trick that somehow didn't get passed on to the Cicada?

_________________________________

[1] Like much in life, this too befuddles me. Why did having a spinner overheat the R-1830 when the roughly equivalent Sakae seemed to suffer no ill effects from having a spinner fitted?

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