Engine technology free-for-all

[J.A.W.]

.......As BMW found & Bristol belatedly confirmed, radial engines - with their inherently problematic mixture distribution, did gain significant benefit from direct injection.
& Bristol had found that sleeve-valve merits included ( as Ricardo predicted) certain flow dynamics,
which enabled aspects of improved port injection performance, too..

charge distribution problems can be worse with DI or PI than with carburation or similar at the throttle body
(for the best current appreciation of the practicalities the appropriate forums can be googled)

DI helps in low boost engines by enabling the raising of CR .....
it loses in high boost engines the large saving in supercharger work etc of fuel-evaporation cooling

The complex/chaotic area of practicable flow dynamics - does tend to cruel those simple assumptions T-C,
case in point, a flow choke/stall of a fuel-air column can cause problematic 'back-firing' - & it can't, with DI..

[J.A.W.]

This interesting review includes discussion of direct injection merits & limitations of poppet valves..

http://www.flightglobal.com/pdfarchive/ ... 00669.html

(& what is amazing, is its 75 years old - Nazi-science tech published in wartime - disseminated by 'Flight'!)

[J.A.W.]

Another period gem from 'Flight' with a dissertation on air-cooled aero-engine tech from a Bristol boffin..
& including data presenting sleeve valve merits - such as volumetric efficiency - naturally..

http://www.flightglobal.com/pdfarchive/ ... 02008.html

[J.A.W.]

More on the big Bristols (inc' 3,500hr TBO reference)..

https://www.newcomen.com/wp-content/upl ... assell.pdf

& a Kevin Cameron article giving reasons why H-D has had to go with liquid cooling on big twin poppet-valve heads..

https://www.cycleworld.com/writing-abou ... y-davidson

[Tommy Cookers]

your 3500 hr TBO only means that 1 civil operator (were they civil ?) was worried about engine availability and .....
threw resources into a unusually lavish ground operation (and imo eased the air operation)
TBO is not universal - it's operator and operation-specific
in similar circumstances the Wrights in Mars fire bombers got a similarly mega-TBO

is there general evidence that sleeves were better than poppets in real world life ?
a poppet valve or ring job in a duff radial cylinder takes half a day
an acquaintance in his B-25 bug sprayer when Redex caused EV sticking on the ground unstuck the EVs at inspection time .....
without opening the cowlings, using of a broom handle and a hammer up the stacks
a sleeve valve job probably means a replacement engine

your source says the Centaurus 173 of 2740 hp went into Sea Furies - this I doubt
the high power Hercules destroyed the Hermes due to lack of spares and service from Bristol (and lack of 115/145)

the Wrights on the B-29 had the worst mixture distribution ever (driving them to DI)
lean cruising overheats valves if/when it slows combustion

the Wright 3350 always was a 115/145 engine
Pratt & Whitney never went beyond 108/135 (in reality 115/145 with less TEL)
did any Bristol ever establish service beyond 100/130 ?
the Centaurus had an impressive lack of 'real' customers
Canadair made the Britannia design into Argus patrol aircraft by losing the Proteus engines and fitting Wright TC 3350s
and the Shackleton patrol aircraft had Griffons

[J.A.W.]

T-C, in NZ the Bristol Hercules engines were very well regarded, being in civil use with the Freighter, Solent & Argosy,
plus with the RNZAF powering the Freighter, & Hastings. They were well maintained, but paid their way with durability.

TBO periods were established by examination of wear on a stripped engine, if no deterioration was evident in
regular operation, then the TBO could safely be extended.


AFAIR, the Hermes was doomed by typical BOAC buggerising about,
& the usual British 'wait for the proper job' - which never seem to arrive..

Far more parts chattering about, with joints to leak oil, in a pushrod radial cylinder, of course too..

Here's a period British piston-engine data table which includes some power/consumption figures:

https://www.flightglobal.com/pdfarchive ... 01491.html

As for the Sea Fury, this ad from 'Flight' in 1951 states max hp rating is a couple of hundred less, but since
these aircraft were in service through the 1960's perhaps a later, more powerful Centaurus was duly fitted?

https://www.flightglobal.com/pdfarchive ... 00783.html

[johnny comelately]

T-C, a couple of quick correction points..

About F1 4-stroke bore/stroke ratios being unsuitable for effective 2-stroke power outputs..
..of course, a fundamental issue being that the naturally aspirated 4T is inherently handicapped..
..& must find a method to compensate ( maximising rpm, an expensive battle) for its lazy torque production..
..a 2T makes power on every down stroke..& thus.. its cylinder architecture is predicated accordingly..

If you read Fedden's reasoning for sleeve valves, you will see that port/time/area & swirl/combustion/ign'
advantages accrue from not having incandescent poppets crammed into the combustion space.
(& not having the valve gear mechanicals above the piston was important for aero-mill frontal area.)

Hitting the nail on the head there

[Tommy Cookers]

the wrong-side-of-history nail ?

or the never-let-the-facts-get-in-the-way-of-a-good-story nail ?

[johnny comelately]

the wrong-side-of-history nail ?

or the never-let-the-facts-get-in-the-way-of-a-good-story nail ?

When you are chasing fuelling to the lean side (not lean of peak) poppet exhaust valves can be a source of pre-ignition and unreliability.
VE or ME is increased.
I know there are downsides, but I was nailing the upsides.

[Tommy Cookers]

I suggest the sleeve valvers weren't ever run particularly lean by aviation standards
eg Lancaster IIs were disliked for their inferior endurance
eg the fuel cost of eg 1000 hrs use is far greater than the engine (2 stroke, SV or whatever) cost new or overhauled
remember Avro /Bennett chose the Merlin postwar for this

Britain forced the world into 100/130
if it had stuck at what became called 80/87 the SV might have had a temporary advantage in radials
till the PVs came out with equally high-swirl ports as NACA showed
the best-ever SI British bsfc was that quoted for the compounded (by auxiliary prop) Merlin
in efficiency terms (normalised re altitude and fuel heat/lb) equal to the Nomad and the Wright TC

there's many older posts with useful references and links

the irony is that HMG didn't choose to favour RR
Napier was their choice (to 'emulate' the Curtiss V12 and so dominate instead of RR) but Napier refused the job
then chosen, RR was forced to make as the standard a (rather small) V12
Bristol and Napier then had 100000 chances to prove that the SV was better
btw postwar RR accidentally made by improvisation the rather good turboprop Clyde - and then refused an HMG order for 50
btw the Deltic 3 crankshaft cleverness was an HM Admiralty draughtsman's idea not Napier's

[J.A.W.]

Beaufighter, Halifax & Lancaster went to war with alternative 'power-egg' fits from Bristol & R-R.

A major part of the Merlin Lanc's advantage was due to its serendipitous underwing location,
which allowed a markedly improved aero-airframe performance, the other two went better on Bristols..

Compare Hercules & Merlin running data - as presented in this 'Flight' table..

http://www.flightglobal.com/pdfarchive/ ... 01491.html

The Merlin is running harder ( check that boost level) to match the Bristol, not so good for TBO,
(& the Merlin was noted for marked cam-follower wear, even in N/A duty - as a Meteor tank mill)..

[Tommy Cookers]

the serendipitous engine location was therafter reproducible by any designer using Merlins (or Griffons)
but unavailable to those using big radials
the air passing over the top of the wing should be sacred
and the sleeve valve saves no frontal area wrt the usual (ie hemi) poppet radial

my point was the perceived greater chance of the Merlin having enough fuel for a safe return
lots of pilots dropped half their bombs in the sea outbound to improve prospects overall
apparently all the bombers were by rule cruised quite slow to save engine life - despite increased exposure to hostilities

Griffons were used hard on the Shackleton till 1991 at c.2500 hp t/o
Centaurus use ended in 1966

[J.A.W.]

T-C, bolt an OHC poppet valve head on a Napier Sabre block & the frontal area will jump - markedly!

Bristol radials were long-stroke, which together with the substantial finning air-cooled heads required,
reduced the ability to keep diameter/frontal area down, however the regular shaped cylinders,
& lack of protuberances (as needed by OHV - to accommodate the chattering gubbins) allowed really
effective cowl-ducting, ensuring even the humble Freighter - featured a spinner/cowl that was
more air-flow efficient - than the radial powered US fighters of a just few years earlier..

Commercial Merlins fitted to DC-4's had to occupy the same nacelle as fat radials, albeit with room to spare..

& 1966 was when R-R finally subsumed Bristol, & thus gained monopoly status as THE Brit aero-engine maker,
so its no surprise how quickly they canned the Centaurus..

The Shackleton would've likely been better served by the Centaurus*, but R-R got the gig as a contra-deal,
since Bristol had ousted the Griffon from the Sea Fury, even though the Griffon was 'dedicated' as
as the 'Naval' engine for the FAA, & was already aboard ship in Seafires & Fireflies..

* & the Napier Nomad, too.

[J.A.W.]

Does any member here - happen to know what became of this curious Aussie-built engine?

If it met its bold claim of a - "BTE @ 37%", it surely ought to have been - a goer, or has it been 'suppressed'?

https://web.archive.org/web/20130816170 ... /home.html

[gruntguru]

Fascinating. On the one hand you have four well-credentialed guys and (apparently) a glowing report from Prof Harry Watson. On the other hand you have a claimed BTE of 37% and 100 hp/litre from a small side-valve engine at 6,000 rpm!! There is no radical technology in there except pneumatic valve springs. Doesn't add up.