exhaust valves arepartially filled in thestems with metallic sodium.
of pilots, nothing but advantage can result from the use ot the power lever control.
Rocker gtar is very similar in design to that of the Further to ensure the most advantageous and sale operation of the engine, a boost regulator unit is fitted the purpose of which is to restrict boost pressure below Merlin, the central camshaft operating valves through cantilever rocker arms. selves are of reasonably quick-lift profile the two rows of The cams them- and are designed full-throttle height realised, although a safe maximum. As may be to the to give harmonic negative acceleration. valve are employed, of opposite helix and differing periodicity, the latter being an anti-surge measure. Two springs per maximum boost of the pressure 65 is nominally 21 in., the blower is of delivering nearly Griffon lb. /sq. capable ROLLS-ROYCE GRIFFON (CONT INUED) (65) twice this pressure at low tudes, and in order that alti- the The ignition system of the Griffon is well worthy of much as a p i l o t c a n s l a m f o r w a r d t h e p e attention, not so lever to obtain worry about the safe maximum boost limit, system, for the plugs and screening harness are standard, but in view of theunusual timing arrangement and very effi- cient magneto. This is a B.T.H. duplex type which runs "at half engine speed, being driven through bevel gears from an inclined shaft taken from the base of theport bank camshaft drive. Thetiming arrangement is " built-in " tothe inclined shaft arid comprises a hydraulic ram, at the base of the shaft, subject under control to engine oil pressure which is used to alter, as required, thelinear position of the inclined without having to power and to save the possibility of the engine tion with expensive noises, a regulator which limits the delivery below throttle from disintegra- unit is installed height for what- ever boost is being used in the appropriate regulator comprises ananeroid-controlled relay The linked gear. piston the throttle butterflies by differential gearing shut to to a off the degree of piston is subject throttle opening as to the differentials The relav intake and necessary. of blower shaft. At the top end, the shaft is helically splined to motion of the shaft delivery that if, for example, combat climb pressures, so the mag.-driving bevel so that linear is required from the ground up, aneroid capsule tasting the boost to admit the pressure difference as eJtitude is gained will move a piston valve across the blower tothe will, via positions the of helical splines, cause the cam and rocker a change in pad in the the relative magneto to achieve the desired timing—i.e., the camis caused strike to relay tain piston boost open the throttle progressively to full-throttle height. and main- to up the pad tionally, at an earlier or later as the power input point of crank to change the angle. timing Addi- is pro-
Powers and Future Use
extremely operate a
light; in smal! pilot
fact the valve to
only load is that needed to regulate oil flow to the ram.
Mention of pilot's controls leads one naturally tocon- sideration of what, in the writer's opinion, is most aptly
called the 'power lever control" this means is that, instead of the ment comprising separate throttle
system. Briefly, what normal cockpit arrange-
r.p.m. controls a single governs the boost, r.p.m
" p o w e r " lever is fitted which andignition. Maximum perform-
ance (that is, max.r.p.m. and max. boost) full forward movement of the single power intermediate positions of the lever suitable
is obtained at lever, and at combinations
of boost and conditions.
Whilst on the question of powers it is noteworthy that the continuous cruising powers of the Griffon 65 are well over i.ooo h.p. from sea level up to over 30,000ft. Com- pare this with the original Merlin at the outbreak of war which had a maximum S.L. power of 880 h.p. (at 6Jlb. boost) rising to 990 at 12,250ft., the maximum rated height.
Although the Merlin is ^uch a magnificent engine—the outstanding engine of all time—as an alternative for future air liners, it would surely be sensible to instal a derated Griffon to give similar performance more economically and,
at the same velopment.
time, gain all the benefits It is not without significance
of advanced de- that the Griffon
one of thevery, very few engines ever to have succeeded general service without experiencing modifications neces-
There is little doubt that this scheme is a most useful one in that it relieves the pilot from responsibility in ensuring that the engine is always operating \mder the best conditions.. However, it is rather essential that an override control be fitted to allow normal separate settings of boost and r.p.m. when required—for example, when landing or in combat. The Griffon is provided with an over- ride lever for these particular functions, and there is every reason to suppose that, despite the innate conservatism
There is, too, a good
tage the Griffon has over the Merlin servicing and maintenance.
of advan- subject of
We have mentioned that the maximum boost of the Griffon 65 is 21 lb./sq. in., but there are other models in existence which have been passed for 25 lb./sq. in. maxi- mum boost (with 100/1,50'grade fuel) and the maximum powers in the respective moderate and full supercharge gears have thus been stepped up t o : MS, 2,375 b.h.p. at 1,250ft., and FS, 2,140 b.h.p. at 15,500ft.
HIGH PRESSURE OIL FROM ENGINE DRIVEN PUMP
COMPRESSED AIR FROM AUTOMATIC ANEROID GOVERNOR
Diagrammatic illustration of supercharger change-speed unit showing (left) MS gear engaged ; (centre) changing from MS to FS gear ; and (right) FS gear engaged.