Hawker Typhoon and Tempest with RR Griffon
- Thread starter BarnOwlLover
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Shortround6
Major General
That is what they did, it just took a while or the British wanted to get operational experience before taking the next step.
The air cooling and sleeve valves were certainly problems.
However the Vulture was fresh in their minds and it was in house. They had to de-rate the service engines while they sorted out the problem/s.
Granted on the Vulture they raised the boost and dropped the RPM.
The Thing is that unless the two stage Griffon is running at 18lbs of boost it is not making the power of the Sabre at 9-11lbs and at less than Military rating (like 30 minute rating instead of 5 minutes) the Griffon is hundreds of HP low.
Sabre will not be doing +11 psi unless two things are there: reinforced propeller shaft, and 150 grade fuel.
The +9psi was also not always there, it was approved in July(?) of 1943; max boost was +7psi before that. That is some 200 HP less in 1st gear vs. +9 psi, or 150 HP less in 2nd gear.
Griffon with 2-stage SC was doing +18 psi by September of 1943.
SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
Love the smile on his face.
Shortround6
Major General
I like the tie.
For much of its life, the Sabre was a very unreliable engine and often gave nothing like the expected performance even at full power.
This was belatedly traced to ground crews not understanding its complex but very advanced mechanical governor, (a sort for of mechanical 'FADEC' if you will), and tweaking the throttle stop to set the engines tick over speed rather than adjusting the complex cams and gears by the book.
This could result in the situation after multiple 'tweaks' were the governor got so far out of synch, the pilot could be flying along at max power, a weak mixture, but the prop still in fine pitch and the engine literally thrashing itself to death and seizing . Many Typhoons and Tempests were lost to mechanical failure until that penny dropped.
The Sabre was with hindsight a terrible engine, excessively complex and fragile, it's what happens when a designer gets a bee in his bonnet - sleeve valves - and pushes that design solution in the face of reality.
This was belatedly traced to ground crews not understanding its complex but very advanced mechanical governor, (a sort for of mechanical 'FADEC' if you will), and tweaking the throttle stop to set the engines tick over speed rather than adjusting the complex cams and gears by the book.
This could result in the situation after multiple 'tweaks' were the governor got so far out of synch, the pilot could be flying along at max power, a weak mixture, but the prop still in fine pitch and the engine literally thrashing itself to death and seizing . Many Typhoons and Tempests were lost to mechanical failure until that penny dropped.
The Sabre was with hindsight a terrible engine, excessively complex and fragile, it's what happens when a designer gets a bee in his bonnet - sleeve valves - and pushes that design solution in the face of reality.
- Thread starter
- #28
BarnOwlLover
Staff Sergeant
The theory behind sleeve valves was a solution to raising RPMs in engines to make power. The worry was that OHV pushrod engines couldn't keep up with the increase in RPMs. How inline engines coped with this was going to OHC valve trains. For radials, you can't really go OHC, so in came the sleeve valves. Even then, though, in reality, that was a solution looking for a problem. Radials (and even to a degree inline engines) got bigger in capacity to make more power, and also turned to supercharging to make more power as well. Also, sleeve valves do have problems with sealing that can cause oil consumption problems.
There's reasons why also in the performance car world why many high performance engines are OHC, and sleeve valves are dead in that realm (and actually that started to happen for race car engines and such before it happened with aero engines).
Also interesting to point out that the Rolls-Royce Griffon and the Napier Sabre are both approx. 37 liters. The Sabre got a lot of its power from high RPMs (3500-4000 rpm vs the 2700-3000 of other engines) and oversquare cylinder dimensions (most other engines were undersquare). But even there I don't know what advantage that sleeve valves in reality would've gotten the Sabre over a SOHC or even a DOHC valve train.
There's reasons why also in the performance car world why many high performance engines are OHC, and sleeve valves are dead in that realm (and actually that started to happen for race car engines and such before it happened with aero engines).
Also interesting to point out that the Rolls-Royce Griffon and the Napier Sabre are both approx. 37 liters. The Sabre got a lot of its power from high RPMs (3500-4000 rpm vs the 2700-3000 of other engines) and oversquare cylinder dimensions (most other engines were undersquare). But even there I don't know what advantage that sleeve valves in reality would've gotten the Sabre over a SOHC or even a DOHC valve train.
wuzak
Captain
The theory behind the sleeve valve was that they could run higher compression ratios without detonation.
This theory gained a lot of support in the 1920s, when fuel was not so good.
One of the problems that poppet valve engines had was the hot exhaust valve causing the detonation. The sleeve valve eliminated that problem. But the sodium cooled exhaust valve had been invented by the end of the decade, and by the time of WW2 a lot of engines sued them.
The Armstrong-Siddeley Deerhound was an air-cooled radial with OHC. As was the Jumo 222.
