SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
That's a pretty cool airplane.
Engine choices for P-51 mustang ?
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wuzak
Captain
The R-2800 didn't have roller main bearings or big end bearings.
I think it is a bit of a stretch to say they were developed for the Wyvern. The Wyvern was seen as one potential use for them but its Spec was originally written around a piston engine.
The initial Spec N.11/44 dated Jan 1945 for the Wyvern specified the use of the Rolls Royce 24 cylinder Eagle engine (the 1944 Eagle with H cylinder layout, not the WW1 engine of the same name). The design was to be such that the wings and if possible the tailplane, fin and rudder could be fitted to a different fuselage to take a turboprop.
The prototype Wyvern TF.1 flew in Dec 1946 with the Eagle engine followed by 5 other prototypes and an order in June 1946 for 20 pre-production aircraft of which 7 were completed. The last of the latter, VR137 which never flew, is now preserved at the Fleet Air Arm Museum at Yeovilton as the sole remaining Wyvern.
When Rolls Royce decided not to continue developing the Eagle the Spec was rewritten as N.12/45 issued to Westland in Jan 1946 to be powered by a Rolls Royce Clyde turboprop. The first Clyde powered prototype Wyvern TF.2 flew in Jan 1949 and was followed by 2 more powered by the Armstrong Siddeley Python turboprop. It was the latter engine that powered the remaining Wyverns after RR decided to concentrate on developing the Avon jet engine and dropped the Clyde (although it formed the starting point for the later Dart).
As originally specified the role envisaged in both N.11/44 and N.12/45 was as a gun armed aircraft for air combat with a secondary land and sea attack function. It took so long to develop that it finally entered front line service in the strike role in Feb 1953.
swampyankee
Chief Master Sergeant
- 4,022
- Jun 25, 2013
You mean the Gloster Trent-Meteor? Gloster Trent-Meteor - experimental aircraft
Part of the start up procedure of the R2800 is to turn the engine over to drain the oil from the bottom cylinders and pre oil the main bearings so they aren't scuffed.
FLYBOYJ
"THE GREAT GAZOO"
IIRC the sparkplugs are removed from the bottom cylinders and then the prop is pulled through by hand several revolutions, especially if the aircraft was sitting for awhile.
Is this true of all radials?.
FLYBOYJ
"THE GREAT GAZOO"
All? IDK, Most? I would say yes...
wuzak
Captain
Also, meant to mention that the Daimler Benz inverted V-12s had roller big end bearings (mains too?) for a while.
Mike Williams
Senior Airman
- 572
- Oct 19, 2006
I was reminded of this topic when reading about Evan Mackie from when he served with 243 Squadron in North Africa.
"At about this time (mid April 1943) Mackie managed to wangle for himself a set of 12 special stub exhausts for his Spitfire VC, of the type then fitted only to Mark IXs."
"They gave the aircraft a few more miles per hour..."
"Mackie was known to be very proud of his special exhausts" p.77
"I was firing and I was well within range and I was really scoring hits - and the next thing another Spitfire from above came down and knocked my propeller blades forward.'
"I had just enough power to carry out a wheels up landing in, would you believe, a field of wheat in Tunisia."
"The next morning I borrowed a spanner and took off my special little stub exhausts, which at the time were just coming into use. I got the first set and nobody else had them. So I took them off, put them in a sack and arrived home by army truck the next day." p.80
"Mackie was given a new Spitfire VC on his return and the machine was fitted with the stub exhausts". p.81
Spitfire Leader, The Story of Wing Cdr Evan "Rosie" Mackie, Avery & Shores, Grub Street, London 1999
MiTasol
1st Lieutenant
Get real
What you are saying is that the Mustang should have been designed around an engine that was totally unreliable when the Mustang was designed meaning it would not have entered service in numbers until far later in the war. The Mustang was in service long before the Sabre gained any sort of reliability.
By saying the Allison was the worst engine you prove your total lack of knowledge. It was far more reliable than the Merlin at all stages of the war, it required less maintenance and was far easier to maintain. The only reason it had crap high altitude performance was that the USAAF refused to allow Allison to produce a two speed supercharger version or to fit an integral two stage supercharger and insisted that adding a turbocharger was the answer to everything. Eventually they accepted the external second stage which made the engine far longer than it should have been.
Allison was so crap that Rolls Royce fixed its Merlin/Griffin bearing issues by making Allison bearings under licence.
One of the reasons for the low reliability of the Merlins in Spitfires/Hurricanes etc was that the carb intake was on the bottom of the engine so that it sucked in all the dirt and shit thrown up by the propellor while all the large American engines of the time had the intake at the top of the engine where they got clean air. North American at least had the sense from day 1 of its Merlin design to move the intake as far forward as possible to massively reduce that problem.
And where did the Sabre have its carb intake - on the bottom of course.
MiTasol
1st Lieutenant
Yep - just as long as you add a heavier and longer fuselage to support the engine weight and an bigger wing to support the fuselage and engine weight and then more wing to support the heavier guns and bombs and by then you have so much drag that the performance is no better than you started with and the manoeuvrability has gone.
Please give yourself a cranial-rectomy
I always thought the reason for the P-51 intake was that a Spit or Hurricane style intake would disturb the airflow going into the radiator, but this sounds like another nice feature of it.
IIRC when Typhoons started operating from France they had to pronto design a new counterflow carb intake to reduce the amount of dust, as the dust on the airstrips around Normandy was apparently of some particularly abrasive variety.
Shortround6
Major General
It is a bit more complicated than that.
Somebody once said that with a two stage supercharger the 2nd stage multiplies all the mistakes made in the 1st stage (or something close).
US superchargers were not as good as some other countries and not as bad as others. Next to nobody was building superchargers for use in aircraft in the 1920s so most of the work was done in under ten years. Some were faster than others.
In the US GE, maker of the Turbo, was the sole supplier of aircraft superchargers or at least supercharger designs in the early/mid 30s. Wright and P&W were buying superchargers and supercharger parts from GE for their radial engines. Allison was actually acting as a subcontractor for GE and making parts (like impellers) to GE designs/specifications. This was OK when everybody was using 80 octane or even 87octane fuel and not using much boost. A 600hp P&W R-1340 engine used about 3lbs of boost for take-off while using 91 octane fuel.
GE was NOT using crankshaft power to drive the turbo chargers, They were using the exhaust turbines and the exhaust turbines could supply more than enough power to drive the compressor/s so GE was not real interested in designing more efficient compressors, they were working on keeping the turbine from disintegrating
Both Wright and P&W became unhappy with the GE designed superchargers they were bolting on the backs of their engines and started their own supercharger design departments.
A more efficient compressor takes less power to drive (more for the propeller) and heats the incoming air less, which makes more power (denser air) and lowers the temperature of the engine. If supercharger A gives the same boost as supercharger B but supplies the air at 225 degrees instead of 250 degrees, peak temperature in the cylinder will be 25 degrees cooler and the exhaust gases will be 25 degrees cooler.
Allison, being a very small company until 1940, didn't have very many men assigned to supercharger design/development regardless of what the USAAF wanted or didn't want.
Allison actually did pretty good designing the supercharger for the C series engine (long nose) and was not that far behind the Merlin III, problems came in 1940 when Hooker changed the supercharger on the Merlin III and gained several thousand ft of altitude. In supercharger terms this is described as the pressure ratio. How many times can you compress the air over the inlet pressure and still be operating about 70 % efficiency. Things get bad really quickly much below 70% .
Allison was also busy with other things, like not only figuring out how to make more than 2-3 engines a month but make all the different kinds the USAAC wanted. Like the P-39 engines, and the P-38 engines, and the P-40 engines and the V-3420 engines. BTW the Army wanted Allison to develop fuel injection at one point, like Allison wasn't busy enough already.
Allison had already lost 900,000 dollars working on the Allison engine buy early 1939, This is for work the Army ordered but had not paid for at that time. Allison had to "forgive" the Army's dept in order to get permission to export the engine to France and Britain.
The attraction for the Army turbo scheme was that the engine was supposed to think it was at sea level. Air intake pressure would be suppled by the turbo up to the max rated height of the turbo like 25,000ft while the intake temperature would be held to sea level (or 30-40 degrees hotter) by the intercoolers and the exhaust system would only see a slight increase in back pressure, and to put the cherry on the top, the engine supercharger could use a very small gear ratio since it only had to compress the air at sea level to the desired pressure and not try to compress the air at 10,000ft.
Unfortunately things didn't workout quite as planned. Once they wanted more pressure temperatures rose quickly, Turbo controllers were badly designed (and were USAAC supplied, not GE or engine company ) and so on.
And designing two stage superchargers was not as easy at it seemed. Or even two speed.
MiTasol
1st Lieutenant
Agreed. I was trying to keep it simple enough that the OP might understand and considered I was probably being optimistic.
Maybe a better choice would have been... a two stage Allison V-1710.
In the book "V-1710 and V-3420 Designs and Concepts" by Dan Whitney and John Leonard, pages 124 thru 127 show installation of the Allison V-1710-45 (F7) two stage engine in the NA X-73 (Mustang I prototype). The drawing notes that the firewall and instrument panel would have needed to move back 2 inches (or the engine forward 2" and the engine oil tank relocated behind the pilot to maintain balance). Moving the firewall 2" does not seem to me to be an overwhelming issue.
Now, in interest of full disclosure, the aux. stage supercharger used by the F7 version was externally smaller than the aux stage unit used in the P-63, XP-40Q, and the XP-51J. The later aux. stage unit (in the P-63, etc.) with its 12-3/16" diameter impeller was better than the earlier F7 aux. stage, but... with 80 years of hindsight this may have been a case where better was the enemy of good.
Second, as I recall Allison did not get production of two stage engines going until late in 1943 (for the P-63), so delivery of fly-able aircraft at a time to influence the war in Europe likely would have been an issue.
MiTasol
1st Lieutenant
The P-51 intake was as far forward and as high above the ground as possible because the designers thought right from day one of the Merlin conversion - how do we have a single unit that works in all operational environments without any drag penalties. Having it as high and far forward as possible kept out the debris thrown up by the prop and allowed the installation of an effective air intake filter system which further protected the engine from FOD. This design also included carb heat and alternate (emergency) air provisions for the unlikely event that something actually was ingested and blocked the intake duct, The Spitfire never had this latter feature which meant that if something blocked the filter or a filter collapsed the engine died through air starvation
I have no doubt you are correct about the Spitfire type intake creating a disturbed airflow is another factor.
Worse still the Spitfire equivalent was the big ugly Vokes filter arrangement that created drag and still took the air from too far back and too close to the ground - and had a significant drag and performance penalty.
wuzak
Captain
The V-1710's air intake was above the nose as it had a downdraft carburettor.
The Merlin versions needed an intake below the nose because the Merlin had an updraft carburettor.
Doesn't sound like "the designers thought right from day one of the Merlin conversion".
And if Rolls-Royce hadn't come up with the 2 stage engine, the P-51 may never have been converted.
wuzak
Captain
Rolls-Royce were making Allison type bearings under licence years before the Griffon (why do people persist spelling it Griffin, like a a character from a cartoon?), possibly from around the time of the PV12's initial development in the early 1930s.
Deleted member 68059
Staff Sergeant
- 1,058
- Dec 28, 2015
Because the 37 litre V12 engine which actually flew in WW2 was derived from a much earlier design of the same bore and stroke which lay dormant at RR dating from just after the Schneider Trophy days, which WAS called "Griffin"
The two names were often mixed up ever-after.
