I've built one, 20 odd years ago now. I don't remember any issues with the drawings but I do tend to make things to fit rather than make a collection of parts and then assemble them all. The problem I had was with the bronze inserts for the valve seats. There is so little meat on them after drilling all the holes that I couldn't get them to stay put in the cylinder head. I ended up making a solid bronze head that is kept in place by the remains of the aluminium head with the middle cut out. I also forgot to make the front housing threads left hand which meant that I had to peg it to stop it unscrewing.

It ran very well with a cast iron piston ring in the mild steel cylinder and I must have run it for some tens of hours all together with no obvous signs of wear. It is enormously satisfying when one fires it up and it runs for the first time. Incidently, I could feel very little compression on mine when turned over by hand but once an electric starter got it going it sings along very nicely. I worked out some hp figures based on the prop and rpm. If I can find them I'll let you know.

have fun

Rod

Mike,

I made the crankshaft from a large HT bolt. The crankpin hole was drilled using my Arrand milling spindle on the cross slide with the crankshaft held in the 3 jaw chuck. I then pressed in a piece of silver steel with a shoulder turned on it for the crankpin

I've (amazingly) found my power curve. I used the prop factor equations from Martin Simons "Model Aircraft Aerodynamics". Maximum power was 0.44 HP at 8000 rpm with a 12×6 prop. Maximum rpm was just over 9000 with a 10X6. I thought that was pretty impressive for a home built. This was using the carb as described and (probably) 5% nitro.

cheers

Rod

I built the Matador when it was first published, and had no particular problems with dimensions. The valve pockets were tricky in bronze but I managed them ok. I mounted the Merco type copy carb on a downdraught intake to lower it to approximate tank level for aircraft. It only needs about three turns of the prop with the finger choking it and it is away every time. The robust cam gear augers for a long life. I do not know from where I sourced the particular piece of C.I. I made the ring from, but when I split the ring it seemed very springy so I did not heat treat it and the compression has remained very good, after a good many runs. I bought the gears from SH. Muffets – very good if a bit pricey.

I remember I machined the cylinder with an HSS parting tool without bother 'til I had to face the lower face of the last fin, when the flex of the tool work hardened the face and took the edge right off. I then resorted to a TC tool to finish it OK.

All in all, a good design, resulting in a pleasant, powerful engine.

Tom.

Mike, very nice indeed – much prettier than mine. I posted a video of my Wyvern by putting it on Youtube and then posting the link using the Youtube button in the reply box.

As to Neil's point, if anybody would care to give some figures for the maximum speed with prop diameter and pitch for their Lynx then I can calculate the HP, at least to the same accuracy as my Matador.

Cheers,

Rod

25 odd years ago I constructed some graphs of BHP versus rpm for various prop diameters and pitches. I'm not quite sure now where I got the calculation from since it is not spelt out (as I thought), in Simons' book. However, I've found a formula on the net which seems to pretty much agree with my figures:

BHP = 7.105*10^-18*D^4*P*rpm^3 where D is prop diameter and P is the prop pitch (both in inches) and rpm is revolutions per minute (that's 10 raised to the power of -18, D raised to the 4th power and rpm cubed)

This gives 0.81HP for the Lynx on a 14×7 at 7500

and

0.45HP for my Matador at 8000 on 12×6

This figures are pretty approximate since they make some assumptions – principally air density. The proper way to measure the power of an engine is to measure the torque. When I was fiddling around with these engines all that time ago I made a simple dynamometer to measure the torque reaction. The problem was damping the vibration, which is inherent in these single cylinder engines. Perhaps I'll look out the bits.

Jason, you have pm.

HTH

Rod

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Edited By Roderick Jenkins on 15/04/2014 13:03:36

Mike Your engine looks very good and it sure is a thrill when they fire up for the first time. In the 1970s the German firm of Graupner produced a set of props for measuring the power of model aero engines. They were mounted in a special case and had power graphs for each prop – I think they were quite expensive! I would have loved to have had a set but cost prevented purchase.

George.

Kevan,

For my single Matador I bought my 45 degree helical gears from HPCgears.com. What gears does the twin Matador call for?

HTH,

Rod

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Well, you did ask

Needs a bit (!) of refurbishment. It used to run very nicely…

Rod

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