Model Engine Gallery Page 8

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Here we have Malcolm Beak's ETW Kiwi, with a difference. It's been converted to compression ignition, with some rather surprising results. I'll let Malcolm explain:

For some years now, I've had a set of castings for Westbury's Kiwi. More recently I came across an article in the ME for 15 Dec 1965 about a Channel Islands Special built as a CI engine by a Mr C E Starnes. So I have attempted to use a similar approach for the Kiwi. Basically, the spark plug is replaced with a 3/8" diameter contra piston in a solid cast iron head. The head and cylinder holding bolts are increased from 4ba to 2ba, and the con rod has been beefed up. And obviously the combustion chamber has been reduced in size. The 1/8" gap between the piston and head is now about 50 thou.

At the moment it only has a small commercial carb fitted, but this should soon change - I'm thinking of making one of Gerry Howel's two jet throttles. The main thing is it started without too much trouble (I should have made the pulley a larger diameter - there's lots of compression on a 15cc single). Based on Mr Starnes experience, I'm using 5% ether and 95% paraffin. The main problem is with pre-ignition, but at least it keeps running. When it's hot it will even start and run on 100% paraffin.

Love your web site,

Yes, that's right, 100% kerosene. The Kiwi has a separate oil delivery system, so there's no need for any oil in the mix at all. How about a little header tank for starting, with a fuel cock that switches over to the pure kero tank after it warms up? Ok, maybe we've not eliminated the ether altogether, but we've sure reduced it. Well done, Malcolm. Incidentally, plans for a 3.8cc CI 4-stroke overhead-valve by Australian model engineer, Rex Swensen, appeared in the ME, number 3722 of February, 1982.

This small, compression-ignition V-twin is the work of Norman Fallows. Thanks go to Ken Croft and Norman for providing the pictures and the following words of explanation:

In the last couple of years Norman, an ex Rolls Royce engineer, has moved on to IC engines, and so far has built two "New Atom Minors" [because he thought he lost the first one], a Majesco 4.4, and AHC diesel, and a Pepperell. The Atom Minors and the Majesco were machined from barstock.

Norman is now flying his latest little gem, a 1cc offset Vee Twin (see the pictures). It started easily and turned its very large 9x4 at around 5500 to 6000rpm at a guess. It did sound a bit laboured but that was due to the over-large prop. I have attached Norman's sectioned drawing of the engine so you can see inside. Norman's RR heritage is clear to see in the details. Most builders would prevent the comp screws running back by just bunging a spring underneath the tommy bar. Not good enough for a Rolls Royce engineer as you will see. Norman's work really is exquisite, particularly bearing in mind that the sand blasted case is once again machined from the solid. I like the use of the screwed-in carb to locate the centre crankshaft bearing bobbin.

For those interested, the motor is in a 49" span free flight "Challenger" which was previously powered by the Peperrell, and before that by the AHC diesel.

While the Figtree Pocket Twin from the Motor Boys Model Engine Plan Book was designed by the late Russell Watson-Will as an air-cooled engine, Malcolm Beak (UK) saw possibilities for it as a marine power-plant. These shots show his progress as of late February, 2006. In addition to the very neat, O-ring sealed water jackets, Malcolm has re-oriented the exhaust to the rear (or perhaps that should be the front as the drive will face aft). This makes sense for a marine installation as directing the exhaust at the floor is neither a good idea, nor does it lead to easy installation of the exhaust manifold.

Malcolm has also been indirectly responsible for the plan update download that now appears on the Motor Boys Book page. He could not see a way in which the big-end straps could be assembled as drawn. He also noticed a missing dimension—and quite an important one—on the crankcase drawing. In both of these assessments, he was quite correct. So after emailing him corrected plan pages, the idea of making an update available to the rest of the world dawned (better late than never).

Another change is the use of separate mounting plates that attach with the front and back-plate screws. This does significantly simplify the machining of these components, and greatly reduce the swarf in the bucket afterwards.

As designed by Russ, the conrod big ends where like those in the Westbury Ladybird: U-shaped straps machined to wrap around the upper rod section. ETW permanently secured these with rivets. Russ used long, countersunk head screws that threaded into one face of the U. Obviously, there will not be a lot of thread engagement, but this was necessary as the only access to then is through the open hole where the reed valve mounts. The Ladybird, having a split case, allowed the shaft assembly to be easily inserted after permanently peening over the rivets.

Malcolm duplicated this design detail, assembled the engine and started it up. Joy! It runs! Agony! It's stopped—suddenly! The screws had worked out with the obvious result. Luckily, Malcolm had two reed valve holes (don't ask) so new rods were made with four screws entering from both sides. Another start! Another sudden stop! More strong words! Where others may have given up, Malcolm redesigned again, using lock nuts this time and was rewarded by success.

To the best of my knowledge, Malcolm's engine is the first to be completed from our book plans. It's a magnificent effort that he can be justly proud of.

These photographs were taken by Ken Croft at Old Warden in 2004. They show the D.A.P. Fairy Queen, an historic model build by DA Pavely (hence "D.A.P."), a UK pioneer in the development of compressed air power. This is his actual model and engine built in 1920, not a reproduction. The model was preserved in the collection of the late Alwyn Greenhalgh and was there for static display only.

This very nicely made Gotham Hobby Deezil was made by Aaron Novak. It's Aaron's first effort, and the first time he's run a compression ignition engine (he has the sore fingers to prove it). Here's what Aaron says about the experience:

I want to thank you, the rest of the "Motor Boys", and everyone else for helping me find this hobby of model engine building. Since I found a hand built ignition engine in my great grandfather's machinist tool chest (including 2 spare case castings and the wooden pattern), I have wanted to build my own engine. With the help of Roger Schroeder's Deezil castings and plans, I was able to do this. The first test run was on my 25th birthday. The engine is true to the plans save for the cooling fins and mounting lugs. I knew the offset mounting lugs would bother me and looked too fragile to actually fly, so I welded extra material on to Rogers beautiful castings. The engine taught me much, and I'm already looking for a second project. Thank you!

These pictures were sent in by Ralph Barnette, of Coldwater Mississippi, USA []. They show his scratch-built Ford Tri-motor, powered by three scratch-built, cox-based, two-stroke, five-cylinder radials.

Ralph says that they turn an APC 10x3 GFN prop at 9,400 RPM, and will spin a 7x4 at an ear-splitting 14,000 rpm. They weight in at 300 gm each—that's about 10-1/2 oz—but he feels they could be made lighter. The fuel used is 20% oil with 15% nitro. The carb fitted is a standard Enya 09 job. The diameter to the plug tips is 4" and it uses a four vane blower. The pistons are connected in the standard master/slave rod configuration.

Ralph has committed a lot of R&D effort to perfecting his 2-stroke radial design. The bottom photos show his larger size engines: a five cylinder, 2 cuin radial and a three cylinder 0.84 cuin version. He reports they now run fine, and can be hand started by port-priming the upper cylinders. The development path required to reach this state was not straightforward and Ralph has a box full of broken parts to prove it!

For a discussion of the challenges faced by the builders of such engines, see the Two-stroke Radial page.