Monthly Archives: February 2017

Draft plans


It might not look much, but a lot of thought and calculations have gone into producing this drawing. Bob has been hard at work putting the base dimensions together, working out the minimum rod length we can get away with to make a compact engine.

The rod length is critical as too short will have it colliding with the sleeve, but too long sees an unnecessarily tall engine. The clearance between the sleeve and flywheels is also critical, as I wanted to avoid having to chamfer them. For balance we now know that the maximum rod deflection happens 74 degrees either side of TDC.

A slight surprise to me is the overall height of the engine. Ok, so a 2.75 litre single is never going to be small, but the complete motor is looking like 30″ top to bottom. (or 75cm if you prefer). On the Dnepr outfit that puts the head level with the top of the tank!

But it’s still doable. In fact I like the fact it will look imposing, neat and different. All I need to do now is locate someĀ parts!

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Clear Props!


Part of the upcoming Centenary celebrations for the RAF sees the most interesting exhibits being dug out and cleaned up for display. One of each type of Ejector set, one of each type of prop etc.. The spares were hanging on a scaffold pole and made quite a nice photo. What a shame that there isn’t the limitless space required to display it all for the public!

Then again, it would take a few weeks just to look around! I’m still smiling after my visit. šŸ™‚

The RAF Museum Reserve Collection.


What an amazing place the RAF museum reserve collection is! It’s a real Aladdin’s cave for any aircraft or aero engine enthusiast. I was lucky enough to be allowed a visit in my quest for information on the Bristol Hercules engine and surviving examples. The collection is basically stuff that would normally be on display at various museums, but isn’t at the moment. Down to a lack of display space and the need to keep things interesting by varying the exhibits, they store a lot of stuff out of the way in the reserve collection. It’s not open to the public except by invitation.

I’d been in contact with the museum to see if I could source some drawings, or take direct measurements from a sleeve drive crank if they had one. They put me in touch with Ian Alder, manager of the collection. You couldn’t find a more helpful person! Ian invited me down and took time out of his day to show me all around. He seemed genuinely interested in my project and was able to put his hands on a crank for me to measure. Unfortunately there wasn’t an easy datum to measure from, so while I have an approximate value I’m still chasing a drawing. Ian was also able to help there with some contacts at Rolls-Royce Heritage, who may have some original drawings.

The collection is a mind blowing array of interesting and well preserved articles, particularly engines! How about a NEW Bristol Hercules in a crate, as delivered but never fitted? Or one removed from an aircraft still in the nacelle? Sitting right next to…. a Centaurus in nacelle as remove from another aircraft! How about a motorised cut-away Hercules then? It’s all there! I saw Gnome engines in crates, Rolls-Royce Eagle engines in housings – part of a replica Vickers vimy (the whole thing), a couple of Merlins (or Griffons maybe?), Pratt and Witneys…. The list goes on. Then there are lots of aircraft (complete but disassembled), ejector seats, lifeboats – you name it.

Very interesting indeed! The collection is well cataloged with exhibits all photo tagged and computer logged, so I don’t fancy my chances of getting any bits. But that’s not what it’s about. I was looking for information and fresh leads, and Ian was kind enough to provide them. Thanks very much!

More light reading….


I returned to the section on balance in Mr Irving’s book to re-read the calculations. I will need to run them for my engine to help decide on the balance factors. At the moment I know the bore and stroke, but without a Piston I can’t weigh the reciprocating mass.

Unlike a conventional (poppet valved) engine, I also need to consider the weight of the sleeve. This is moving at half engine speed and through less distance. Around one third of the distance the Piston travels. However, the weight of the sleeve is significant compared to the piston, which at times will be moving with – or against it. Interesting engine to balance!

Rpm is definitely a factor, with imbalance forces rising in proportion to the square of the rpm. I know that the max rpm of the Hercules was 2880, and I considered that 3500 to 4000 would be my peak rpm. I guess the calculations will tell me once I know all the masses!