Methuselah said:
Great to have a knowledgeable critique here, thank you. I have to go mostly by what people write down, which is not always accurate.
Fair enough I can see that the carbs were not turned sideways. But their intake ducts were - see attached images. Also, the flame trap arrangement for the warm air inlet was rather different.
A contemporary account I came across did report that DH found the ram effect to be noticeable. I seem to recall something like 5 mph on the top speed.
The Ratier adapter was developed on-the-spot at DH by their UK representative M. Dreptin. One development crank shaft had been cut down to test the Ratier design, but by the time of the prop change all the engines had been built and certified, and there was not time to strip, modify and rebuild them all, and re-certify them, hence the adapter as a last-minute fix. Shuttleworth's Six R has one fitted; the prop only looks forward-positioned because the adapter pushes it forward. More images attached.
But I should like to know more about the SBAC spline. The Hamilton-Standard props were developed for the big American radials and the SBAC spline would not have been their standard fitting (which had a central oilway and was presumably the US spline). DH designed the R crankshaft to take those props specifically; there is no evidence of any adapters for them. Are you implying that Hamilton's must have designed specials to order, or that DH would have decided to fit spline adapters after all, or what? And was the DH SBAC adapter available in 1935 anyway, when Fontes bought her engine and the Six II was not yet available? Indeed, when was the SBAC No.1 spline defined, and why? So I am not yet clear that such an adapter would have been either available or appropriate for the engine when Fontes bought it.
Accuracy is an issue. For example - even some contemporary sources have errors, as do even some of the autobiographies of people involved at the time, so on occasions, some extra digging-around is required. Official manuals and documents are the most reliable sources if relevant and available.
The inlet extension-duct was just that - it allowed the air at the front of the nosebowl to be split and some channelled-back for induction and the parasitic drag of the side intake to be eliminated. (See first photo below.).This relates to the speed-gain too, as drag increases exponentially with speed, and so losing the drag from the side intake was well worthwhile. EWP experimented with taking the intake-duct right up behind the airscrew, but I don't think they were able to measure any advantage.
The alteration to the intake manifold (See second photo below.) is the deletion of the side intake (Facing you in the upper, original config'.) and the provision of a front opening into which intake air from the nosebowl can be directed by a fabricated duct. Note the warm-air flame-trap arrangement is basically
unchanged.
The different position of the centre of mass of the Ratier
is significant - given the moment arm from the CofG. The DH 1000-Series spider (See third photo.) positions the airscrew disc about halfway along the splines, quite close to the front of the engine (See fourth photo.), so the difference (Perhaps 6"+ ..?) is enough, given the mass of the airscrew(s) - metal VP airscrews are heavy assemblies. The PD30/211/1 assembly weighs 70.1 Lbs - the standard spinner weighs another 7.6 Lbs - so 77.7 Lbs total. Remember you have to double the weight as there are two airscrew assemblies - so 155.4 Lbs - all well forward of the CofG. OW, Derby or KF might supply you with the W&B for the Comet so you can work out the effect on the CofG of moving that lot 6". Look again at your photo of the Ratier on the R at OW - it is a significant difference at that weight and moment arm. Did DH act on this issue...? I have no idea.
I would also point out that the 3/4 view sketch clearly shows the adapter made to fit the Ratier and the sectional sketch of the Ratier shows that there is no space for the shaft to intrude inside it. Thus - just possibly, if the CofG issue reared it's head, they may have wanted to reduce the extension and thus need to cut down the crankshaft end. Do I think on the balance (No pun intended...!) of probability that they cut the cranks down...? No.
The issue of the whys & wherefores of Jack Cross's alterations to Alex's R is quite another matter and I'll avoid further muddying the waters here.
Splines etc;- DeHavs Licensed the Hamilton design for firstly the Bracket Type airscrews, then later the Hydromatic. DH's didn't design the R's crank
for these airscrews - it was effectively already the SII crankshaft. The SBAC Splines were agreed SBAC standards across the UK aviation manufacturers. Having already introduced the Gipsy Six, DH's set-out to produce an uprated version to utilise a VP airscrew which eventually became the Gipsy Six Series II - a surprisingly different engine to the SI - despite appearances. (Again - I'll avoid further muddying the waters here.). The SII was
already in development when the 1934 race cropped-up. They had finished development of neither the engines, airscrews nor spinners however. The R was therefore, cobbled together from an - at that time - unfinished project. The potential for problems was compounded by uprating the new engine, then using an undeveloped and untested airscrew (It took DH's another two years to sort the SII & PD30.) - all on a new type of machine. There is an old maxim in aviation - 'Don't use a new engine type on a new type of machine'.......
All these hydraulically-operated airscrews were fed by modulated pressurised oil via the crankshaft - and the DH versions all followed the US design in that respect. The detail inside DH's spider was to the UK SBAC spline-form to suit UK engines. Forget what the Americans used, it's irrelevant - DH's never used the US splines on the Bracket Type airscrews. There was no such animal as a UK-US adapter. We are talking about a) What was made to allow the Ratiers to be retrofitted to the No.1 splines, and b) The standard DH adapter that allowed a FP airscrew to be fitted onto an SBAC splined crank end intended for a VP engine, such as a SII or QII. I've got one somewhere but I can't put my hand on it just now - anyway, it was a DH listed assembly. I think there is an illustration in the SII & QII handbooks. It's worth noting that, as this adapter slipped-over the splines, it kept the mass at the same station.
I'm not sure what year the SBAC standard for splines came into effect, but since it wouldn't have been necessary before VP airscrews arrived, I'd say early 1930's - but it's a detail anyway.
I know little about the Mmmmiles a/c and the Fontes. Pretty much all the images that I have ever seen of Speed Sixes have had FP airscrews fitted - usually FR. I have a wooden DH FP airscrew that came from Croydon and was reputed to have come from a Speed Six, but I doubt this claim, as the pitch looks too coarse. Still - it's a nice dust trap.
G-ORDY's post from 21/03/21 - and other images on the web, seems to show machines fitted with FR FP airscrews - including G-ADOD. If so - Ruth's R would have been fitted with the standard DH adapter to enable fitment of the FR airscrew - as long as the crankshaft hadn't been tampered with. Do you have any other images of Ruths machine as raced with the R fitted....?
Hope that clears things up.