BrendAn Posted July 20 Share Posted July 20 That is a lot of timing gears. 1 1 Link to comment Share on other sites More sharing options...
onetrack Posted July 20 Share Posted July 20 A friend is a former Bristol radial mechanic, he was in the RAN, and the RAN still ran Bristol Pegasus powered Sea Furies up until 1963. Despite their complexity, the Bristols were exceptionally quiet, and the Japs called the Bristol Hercules-powered Beaufighters, the Whispering Death, because the Australian Beaufighter pilots could sneak up on them at low level. 3 Link to comment Share on other sites More sharing options...
Ian Posted July 21 Share Posted July 21 (edited) The gears are for supporting the sleave valve engine design rather than the current poppet valve. https://en.wikipedia.org/wiki/Bristol_Hercules https://en.wikipedia.org/wiki/Sleeve_valve They have better volumetic efficiency and because you can have better combustion area design and no hot valve you can run them at higher compression rations on the same octane rating. The main drawbacks were the complex drive mechanisms, cooling the junk head and the tolerances required between the sleve and cylinder block. Modern machining techniques solved the latter and I've always thought that modern electronics and active cooling could solve the former points pretty simply. Does anyone a few million to waste on developing a new IC engine? They're quiet because the valves motion is radial not slamming shut and opening like poppets. Edited July 21 by Ian 1 2 Link to comment Share on other sites More sharing options...
facthunter Posted July 21 Share Posted July 21 They are a double sleeve valve arrangement and also twin row of cylinders A small link rod moves each sleeve in an elliptical motion. In cold conditions there's a lot of oil drag when starting, which can break the link rods. Bristol freighters had them too. . Exhaust noise is dependent on valve timing to a great extent and POWER output. Pressure when the port opens. . Two strokes unmuffled are VERY noisy and they have no poppet valves in most cases. Clunking noises when starting some radials are from the dynamic balance weights on the crankshafts at slow RPMS. Nev 2 Link to comment Share on other sites More sharing options...
Ian Posted July 21 Share Posted July 21 I think that the Bristol and all of there aircraft engines were a single sleeve arrangement. From the wikipedia article https://en.wikipedia.org/wiki/Bristol_Hercules#Design_and_development "The rationale behind the single sleeve valve design was two-fold" Some earlier British cars used a dual sleeve arrangement and there was a patent fight at some point from memory. The lower noise might relate more to the rate of the valve opening as it would be sinusoidal openings to a cross section rather than rapid release of a poppet. I'm not sure if I've even seen one in practice. The oil drag at low temperatures is an interesting point. I wonder whether modern oil chemistry solved this to any extent. Another engine design that is mind boggling is the Deltic which was derived from the aircraft engine the Junkers Jumo 204 which even today remains more efficient than even modern Lycoming diesels. The deltic was both light and powerful. https://en.wikipedia.org/wiki/Napier_Deltic https://en.wikipedia.org/wiki/Junkers_Jumo_204 https://en.wikipedia.org/wiki/Brake-specific_fuel_consumption 1 1 Link to comment Share on other sites More sharing options...
facthunter Posted July 21 Share Posted July 21 I think the double sleeve is a later development. It's far harder to do and IS more efficient. Quicker port opening. Very high exhaust port temps are common on early sleeve valve cars causing distortion. of the Blocks. . . I use Wiki a lot but sometimes it's annotated as requiring more confirmation.. Sleeve valves won't be making a comeback. Think of the load the pistons put on the cylinders when the conrods are at an angle. Those little link rods have to handle that. Nev 1 1 Link to comment Share on other sites More sharing options...
Ian Posted July 21 Share Posted July 21 The double sleeve was actually an earlier development and used on some European cars. If you look closely you can examine the pictures of the cutaways on the wiki page and see that it's a single sleeve. The design of the dual sleeve was very different at a fundamental level so I'm not sure how you'd go from one to the other. It doesn't really make sense to change the design from a single to a dual sleve especially given the fact the single sleeve was a later development. Not sure about the failure rates, however they were a complex engines compared to poppet valve. 1 1 Link to comment Share on other sites More sharing options...
Red Posted July 21 Share Posted July 21 (edited) 5 hours ago, Ian said: I think that the Bristol and all of there aircraft engines were a single sleeve arrangement. From the wikipedia article https://en.wikipedia.org/wiki/Bristol_Hercules#Design_and_development "The rationale behind the single sleeve valve design was two-fold" Some earlier British cars used a dual sleeve arrangement and there was a patent fight at some point from memory. The lower noise might relate more to the rate of the valve opening as it would be sinusoidal openings to a cross section rather than rapid release of a poppet. I'm not sure if I've even seen one in practice. The oil drag at low temperatures is an interesting point. I wonder whether modern oil chemistry solved this to any extent. Another engine design that is mind boggling is the Deltic which was derived from the aircraft engine the Junkers Jumo 204 which even today remains more efficient than even modern Lycoming diesels. The deltic was both light and powerful. https://en.wikipedia.org/wiki/Napier_Deltic https://en.wikipedia.org/wiki/Junkers_Jumo_204 https://en.wikipedia.org/wiki/Brake-specific_fuel_consumption Deltic was a work of art, but as far as aero engines are concerned wasnt the Napier Sabre the pinnacle of Reciprocating engine developement? P.S. leaving aside the turbine compound wrights in B29s etc Edited July 21 by Red 2 Link to comment Share on other sites More sharing options...
facthunter Posted July 21 Share Posted July 21 The turbo compound Wrights had the best specific fuel consumption of the time. . Nev 1 1 Link to comment Share on other sites More sharing options...
Red Posted July 21 Share Posted July 21 Indeed which is why I mentioned them, but going back to Pure piston Aero engines as discussed were there any that beat the Napier sabre in SFC? Link to comment Share on other sites More sharing options...
Ian Posted July 21 Share Posted July 21 Possibly the Klöckner-Humboldt-Deutz DZ 710 In wikipedia it has a claimed SFC of 201 g/kWh https://en.wikipedia.org/wiki/Brake-specific_fuel_consumption However another source puts it as equivalent to the Napier. https://oldmachinepress.com/2013/08/17/klockner-humboldt-deutz-khd-dz-700-dz-710-and-dz-720/ It's taken a long time for turbine engines to approach the efficiency of diesel engines, if the commercial aircraft industry is forced to pay to capture it's CO2 emissions higher efficiency engines might find a niche. However "adding lightness" was always the hardest design step. 1 Link to comment Share on other sites More sharing options...
facthunter Posted July 21 Share Posted July 21 One of the biggest advantages of Turbofan is long-life and reliability as well as Power to mass ratio.. There's also no reduction gears. Nev 1 1 Link to comment Share on other sites More sharing options...
Ian Posted July 22 Share Posted July 22 Yes however as costs change sometimes business models do as well. Fuel is between 22-35% of an airlines operating costs. It's not a small part of their costs, if there was a requirement to be carbon neutral it would make this an even larger factor. https://gprivate.com/6ccs0 1 Link to comment Share on other sites More sharing options...
facthunter Posted July 22 Share Posted July 22 I don't think the System would accommodate the unreliability, Noise, the slow speed and vibration. and reduction in anti icing capability. and worse turbulence in lower levels. It won't happen. We've been there done that and best left in the annals of history. Nev 1 Link to comment Share on other sites More sharing options...
Ian Posted July 22 Share Posted July 22 Certainly I wouldn't invest in it. But from an economic perspective the stars align more now than 40 years ago. If zero emissions are mandated aviation costs will increase and different design compromises will be required. 1 Link to comment Share on other sites More sharing options...
facthunter Posted July 23 Share Posted July 23 (edited) The Past is rarely the future... The reliability of a turbofan engine is at least 20X that of pistons . and they are much more easy to manage and suit high altitude flying and facilitate de icing with bleed air. The speed Jets cruise at warms the Aircraft about 30 degrees C. Nev Edited July 23 by facthunter more content. 1 Link to comment Share on other sites More sharing options...
Ian Posted July 23 Share Posted July 23 But change is inevitable. Climate change and zero emissions will place significant pressure on the industry. Hydrogen fuelled turbines are even less likely, there's a reason why Elon Musk uses methane in his rockets. Link to comment Share on other sites More sharing options...
danny_galaga Posted July 24 Share Posted July 24 This forum needs a 😲 smiley 1 Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now