Originally Posted by
Chris Scott
Yes. Sadly, the days of rushing out into the garden in reaction to the first, distant rumblings of an approaching pair of Gipsy Queens (or, for that matter, Twin Wasps) seem to be over...
Did Silphenuz replace the Stellite listed in Janes, or are they one and the same? (I hasten to admit knowing nothing about valve-stem coatings, except that they are relevant to the lead content of fuel.)
No. Stellite is a austenitic steel which is particularly effective in applications involving high mechanical loadings and elevated thermal conditions. It is a favoured material in the manufacture of exhaust valves and seats which are subjected to both these demanding conditions.
"Silphenuz" was applied by De Havilland to the exhaust valve guides/stems of some models of their aero engines but why they did this, I do not know. Evidently, this material was something like an early Teflon and suffered many of the problems which caused Du Pont to try to deny sales of their product to third parties - a court ruling barred them from restricting sales in this way. A fundamental concern with Teflon was that unless the application processes were ideal, there could be problems with adhesion of the product to the parent material and I suspect this is what happened in my case, with the stuff becoming detached, being forced into a solid mass and resultant jamming of the reciprocal parts. Fortunately, the DH104 was pretty good on one engine. I suspect that the Silphenuz was intended to provide an interface of friction resistance but from this one might suppose that there had been a history of inadequate lubrication in this area but such is not characteristic of inverted engines in general and I'm not aware of any issues in this regard specific to DH engines. In any event, one has to question the wisdom of employing this type of synthetic compound at the point of highest operating temperature of an air-cooled unit.
Because of their superior mechanical balance (120 deg crankthrows), in-line sixes naturally sound good. It could also be that any lack of engine/prop sync seems to be amplified in these engines. I wrote a post a few years ago about the soporific drone of approaching engines in the balm of a summer's evening, but in this case I was aroused from my doze by the wonderful, lumpy and unmistakable sound of a pair of ROUND ENGINES. These were attached to a Beech 18; a nice aircraft to fly and a very pretty example of the pre-War American style of twin taiidragger. However, with its wide track and short wheelbase, it could be a swine on the deck - "Ground loops, anyone?"
De Havilland could be a bit cavalier with their engine appellations. DH needed a 200hp engine so the remarkably clever Major Halford simply grafted a couple of pots onto the front of a Gipsy Major. Thus was born the Gipsy "Six" which went through much development and several production series as a naturally aspirated power plant. In 1944, The first Queen to be so styled was a RAF version of a "Six", series II and the.last of the N/A Queen series developed 250hp. In 1944, a single-stage blower was fitted to become the GQ50 at 295hp with subsequent supercharged models rising to the 380hp of the Queen 70/3 which was fitted to "my" Dove-8.
Since the "Six" and "Queen" were derived from the "Major", would it not seem reasonable to extend the CAA's waffle to the six-cylinder variants too?