Question on Sebra and sth others

Discussion in 'Engines' started by rousseau, Dec 14, 2010.

  1. rousseau

    rousseau Member

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    The Sabre which was fitted in Hawker Typhoon was the most numbered cylinders piston engine I have known. This cause some question:
    1) Are there any piston engine contains more cylinders?

    2) The more output power each cylinder provides, the better engine it is, but precondition here is the capability of each cylinder is not enlarged.
    So the Sabre works with 24 cylinders! Supposedly, they are quite small cylinders compare to other cotemporaneous comparably engine, am I right?

    3) The more cylinders the more power the engine gives, it's true but you can not pile up cylinders like wheat because it will bring too many heat to burn the engine up, so the main problem for engine at that period was cooling.
    I felt the more cylinders the engine contains, the more the engine's cylinder arranged with star shape, never beyond 12 cylinders aligned V shape, because the air flow will bring the hot air from frontial cylinder to rear cylinder, thus leading to the rear cylinder too hot to cooling down, Whereas, star engine with cylinder surround the axie, so there is only three rows even 18 cylinders has to be fitted.
    Now we move to the Sabre, 24 cylinders with not star aligned. How it resolve the cooling problem? And how the cylinder aligned with? Search by google, I found a couples of photos to show what this engine look like, but if without cutaway, I hard to understand its structure.

    4) As we're aware of a piston engine if not star shaped, then its cooling mainly rely on liquid. however, the liquid is also need to cooling down so there is inlet we usually see underside of V engine aircraft's wing or fuselage.
    But the inlet under the Typhoon is beneath the engine, not the oil cooler's inlet under P-51 is mounted rear of cockpit. This makes me ask if refrigerating oil is not transferred to far away from engine, then so much heat centralized around the engine, how it be cooling down?

    By the way, I saw two inlet on P-51B/C version, on is smaller just behind the propeller under the nose, the other is much larger under cockpit, but with same engine, the P-39 merely has one inlet not so big behind canopy. Why?
     
  2. Shortround6

    Shortround6 Well-Known Member

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    The air inlet behind the canopy on the P-39 is the engine air (carburetor) inlet. The P-39 has 3 other inlets in the leading edge of the wing roots for the oil cooler and radiator. The P-51B/C used the nose inlet for the engine air (carburetor) and the under fuselage inlet/duct is for the radiator and oil cooler. The P-51B/C used a two stage Merlin and not an Allison like the P-39 and also needed space and air for an intercooler for the supercharger set up. Higher flying also means a larger volume of air is needed (less dense air) for the same cooling 'power'.

    Even if the radiators and oil coolers are mounted under the engine they are mounted in ducts with a sheet metal wall to control the airflow between the radiators/coolers and the engine.

    http://www.p40warhawk.com/Models/Reviews/Models/Scratchbuilders/P-40B-C/P-40coolers.jpg
     
  3. WJPearce

    WJPearce Active Member

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    1) Yes, the P&W R-4360 had 28 cylinders, other odd balls like the Wright Tornado had 42 cylinders, Lycoming XR-7755 had 36. There are more but you get the idea.

    2) Yes, the Sabre with it's 24 cylinders displaced 2240 cubic inches. Compare that to same displacement of the RR Griffon with 12 cylinders. Each Sabre cylinder displaced half of each Griffon cylinder.

    3) The Sabre was liquid cooled so it did not have the cooling issues like a long air cooled engine does. Imagine it's arrangement as that of two horizontal engines stacked on top of each other. It had two crankshafts, one for the top 2 banks of horizontal cylinders and one for the bottom two banks. These cut-aways should help: http://www.khulsey.com/masters/makoto_ouchi_napier_sabre.jpeg and http://www.italiansportsbikeclub.com/uploads/24/Napier_Sabre.jpg

    4) The giant and distinctive chin radiator used on the Typhoon and Sabre Tempest house the radiator for the coolant and also the oil cooler. It has rather large inlet and outlet so a lot of cooling air passed through. http://www.fiddlersgreen.net/aircraft/Hawker-Typhoon/IMAGES/Hawker-Typhoon-Cutaway.jpg

    Cheers,

    WJP
     
  4. rousseau

    rousseau Member

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    Many thanks for your reply.

    As rewards, your comments reminds me of Diamlar-Benz BD606 that He-177 used to drive propeller, which aussi is twist with two engine basically. This associated to cooling problem too, we are well known the cooling problem made alot of trouble to the BD606, the main reason or say the only source of this trouble was twisted two engine into one nacelle. Why the Sabre didn't get such burden?

    Otherwise, the coolant was moved far away from nacelle will be good for cooling effect, if my brain does not be broken. Certainly, a long distance between coolant and engine maybe needs some pipers to transfer the cooling liquid, but the effect for cooling down will be better. This is why the design of Mustang is better than Typhoon according to my judgment. What do you think?

    Here is grateful to you ShortRound

    Your respond give me another question. Does that canopy raised influenced carburetor air-intake or say go against the carburetor gets sufficient air flow, if you see what I mean...:p

    Rare piston aircraft mounted both of coolant, radiator and carburetor's inlet all under nacelle. This is not an appropriate way to exert the engine power. Only two aeroplane has their big jaw, one the Typhoon, the other is Curtiss Tomahawk. Although there may be others to make Tomahawk unappreciated, but the engine system designed like that would be the majority I wonder.
     
  5. WJPearce

    WJPearce Active Member

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    From the start the Sabre was designed as a complete 24 cylinder engine while the DB606 was two DB601s coupled together. Many times when you take an existing component and modify it far beyond what it is designed for you will run into problems.

    Issues with the DB606 seem to be more from the common exhaust manifold for the inner banks, leaking fuel and oil lines, oil circulation problems, combined with a tight installation which made proper service difficult. All of this lead to something flammable coming into contact with something very hot and starting a fire. I don't think is was just the engine overheating due to ineffective engine cooling.

    But the Sabre had more then its share of difficulties too.

    I agree. I think moving the radiator to the belly like the Mustang results in lower drag. But you do have the penalty of added complexity for the coolant pipes, pumps, etc. Added to that is the vulnerability issue. The Typhoon can take a bad hit right behind the wings and the engine will not have any issues because everything associated with it is in the front. However a Mustang taking the same hit will destroy the radiator and a few moments later the engine will fail. You basically have two very vulnerable areas; the engine and the radiator.

    But everything above is just my opinion and thoughts.

    WJP
     
  6. rousseau

    rousseau Member

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    You've taught me lot, appreciate very much
     
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