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From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Comparative analysis of piston and ring details and a discussion on engine ring flutter speeds.

Identifier  ExFiles\Box 132\4\  scan0106
Date  19th October 1937
  
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flutter at 2780 r.p.m., so that under dive bombing conditions at 2830 r.p.m. oil consumption can be expected to be excessive. For Merlin we should suggest that the radial depth of ring be increased .232, which should give a flutter speed of approx. 3300 r.p.m.

The 'KXL' engine ring so we find should flutter at approx. 3600 r.p.m., so that in this case the ring has not sufficient radial depth to control oil at 4000 r.p.m. The ring we suggest for this engine is one with a radial depth of .1825 with a corresponding flutter speed of 4250 r.p.m., this should be the absolute minimum radial depth for this engine and limit of manufacture of the ring should positive so that no ring is produced under this dimension.

Fig.XII shows a comparison of various piston and ring arrangements, it is interesting in that it shows that 4 1/4 litre Bentley flutter speed is much lower than corresponding American practice. Another interesting feature is that it shows

FIG. XII
PISTON & RING DETAILS

TABLE PART 1:
Headers: TYPE OF CAR | TYPE OF PISTON SKIRT | MATERIAL OF PISTON | WEIGHT OF COMPLETE PISTON(LB) | No. OF COMPRESSION RINGS | No OF SCRAPER RINGS | WALL PRESSURE COMPRESSION RINGS (LB/SQ") 1ST, 2ND, 3RD | WALL PRESSURE SCRAPER RINGS(LB/SQ") 1ST, 2ND | DIAMETRAL LOAD COMPRESSION RINGS(LB) 1ST, 2ND, 3RD | DIAMETRAL LOAD SCRAPER RINGS(LB) 1ST, 2ND | WIDTH OF RING. COMPRESSION RINGS 1ST, 2ND, 3RD | WIDTH OF RING. SCRAPER RINGS 1ST, 2ND
3 1/2 BENT (R.R.PISTONS) | SPLIT | ALUM | 1.417 | 3 | 1 | 9.2 | 9.2 | 9.2 | 9.8 | - | 3.36 | 3.36 | 3.36 | 4.12 | - | .0855 | .0855 | .0855 | .148 | -
3 1/2 BENT (AEROLITE) | SOLID | " | 1.437 | 2 | 1 | 11.6 | 11.6 | - | 20.5 | - | 4.6 | 4.6 | - | 7.77 | - | .098 | .098 | - | .177 | -
ORIGINAL 4 1/4 BENTLEY | SOLID | " | 1.562 | 2 | 1 | 11.35 | 11.35 | - | 18.7 | - | 4.8 | 4.8 | - | 7.56 | - | .0937 | .0937 | - | .177 | -
PROPOSED 4 1/4 & WRAITH | " | " | - | 2 | 1 | 18.0 | 18.0 | - | 32.0 | - | 7.76 | 7.76 | - | 13.0 | - | .0937 | .0937 | - | .177 | -
CHEVROLET | SOLID | C.IRON | 2.25 | 2 | 1 | 28.8 | 43.8 | - | 47.5 | - | 15.5 | 13.8 | - | 10.9 | - | .125 | .123 | - | .186 | -
OLDSMOBILE | T SLOT | ALUM | 1.58 | 2 | 2 | 25.2 | 25.2 | - | 38.7 | 38.7 | 13.5 | 13.5 | - | 10.85 | 10.85 | .125 | .125 | - | .186 | .186

TABLE PART 2:
Headers: WIDTH OF BEARING SURFACE OF RINGS COMPRESSION RINGS 1ST, 2ND, 3RD | WIDTH OF BEARING SURFACE OF RINGS SCRAPER RINGS 1ST, 2ND | RADIAL DEPTH COMPRESSION RINGS | RADIAL DEPTH SCRAPER RINGS | RATIO D/T COMPRESSION RINGS | RATIO D/T SCRAPER RINGS | En VALUE COMPRESSION RINGS | En VALUE SCRAPER RINGS | ESTIMATED ENGINE R.P.M AT WHICH RINGS FLUTTER COMPRESSION RINGS 1ST, 2ND, 3RD | ESTIMATED ENGINE R.P.M AT WHICH RINGS FLUTTER SCRAPER RINGS 1ST, 2ND | CYLINDER DIA. | GUDGEON PIN DIA.
3 1/2 BENT (R.R.PISTONS) | .0855 | .0855 | .0855 | .098 | - | .113 | .113 | 28.75 | 28.75 | 15x10^6 | 15x10^6 | 4380 | 4380 | 4380 | 4190 | - | 3.250 | .750
3 1/2 BENT (AEROLITE) | .098 | .098 | - | .0885 | - | .112 | .127 | 29.0 | 26.65 | 15x10^6 | 15x10^6 | 4350 | 4350 | - | 4480 | - | 3.250 | .750
ORIGINAL 4 1/4 BENTLEY | .0937 | .0937 | - | .0885 | - | .120 | .130 | 29.2 | 26.9 | 15x10^6 | 15x10^6 | 3920 | 3920 | - | 4120 | - | 3.500 | .750
PROPOSED 4 1/4 & WRAITH | .0937 | .0937 | - | .0885 | - | .134 | .130 | 26.1 | 26.9 | 15x10^6 | 23x10^6 | 4600 | 4600 | - | 4650 | - | 3.500 | .750
CHEVROLET | .123 | .073 | - | .052 | - | .133 | .142 | 24.9 | 23.3 | 16x10^6 | 16x10^6 | 5000 | 5000 | - | 4790 | - | 3.312 | .987
OLDSMOBILE | .093 | .093 | - | .062 | .062 | .150 | .145 | 22.3 | 23.7 | 13.1x10^6 | 13.1x10^6 | 4760 | 4760 | - | 4280 | 4280 | 3.437 | .856
  
  


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