Boll-Aero .49 Glow Engine

[KEITH BEAUMONTParticipant @keithbeaumont45476]

These are photos of my latest engine builld,They are another of Chris Bolls bar stock designs, this time with rear disc induction and single ball race to crankshaft. All kept simple in order to encourage modellers with minimum equipment,to make it. It was originally featured in ME in 2016, Nos 4549, 4551, 4553. Chris thought they made a p[oor job of it at the time, with small drawings and several incorrect dimentions. I have worked from full size A3 drawings obtained direct from Chris. Chris is happy for makers to modify things as they wish and I have changed the outside profile to soften it, somewhat. Internally I have changed the combustion chamber to a hemisphere,in place of the angular shape,as drawn. Also,I have used oiled Nylon for the disc valve,in place of the aluminium one specified. I had realised that,by changing the cumbustion chamber to a hemi,that I had decreased the area and might have some backfire problems. I therefore made two spacers,0.030" and 0..020" to lift the head if required. I did get backfire, so fitted the 0.030"spacer and it started smoothly first flick. So far it has had 30 minutes of run time, mostly about 3 minutes a time,on a rich setting, hence the smoke. allowing cool down between each run.All with 5% fuel and an11"x4" APC Nylon prop. Revs have continued to increase with each run from 6500 RPM to 8800 RPM latest. It is still a bit stiff so I am expecting to get to 10,000 RPM before I put it on the shelf. Starting is always first flick,so Chris has designed a docile ,if noisy engine (I love the noise) and I recomend it as an interesting project.

Edited By KEITH BEAUMONT on 01/07/2022 11:08:55

[KEITH BEAUMONTParticipant @keithbeaumont45476]

[JasonBModerator @jasonb]

That's turned out very nicely.

[HopperParticipant @hopper]

Superb bit of work indeed. Did you do the anodising yourself?

[KEITH BEAUMONTParticipant @keithbeaumont45476]

Thanks Jason. Was the Pun intended?

Hopper, I have a friendly ,local firm that do the anodising.

[JasonBModerator @jasonb]

Hadn't noticed the pun

If anyone is tempted to have a go there was a thread at the time that covers some of the drawing issues

[KEITH BEAUMONTParticipant @keithbeaumont45476]

That was interesting reading that thread ,Jason . I had not seen it before. I thought the fixing of the fins was going to be a problem ,so used two 10BA csk screws to hold the cylinder in place.then everything is held down by the 4 long screws.

Keith

[chris boll 1Participant @chrisboll1]

As always, Keith's workmanship and finish is far superior to my efforts, it gives me great pleasure to see what others make of my designs.

It proves that the engine is a good runner when made to the correct drawings, I much prefer working of a big sheet than thumbnail drawings scattered about.

[chris boll 1Participant @chrisboll1]

As always, Keith's workmanship and finish is far superior to my efforts, it gives me great pleasure to see what others make of my designs.

It proves that the engine is a good runner when made to the correct drawings, I much prefer working of a big sheet than thumbnail drawings scattered about.

[Steve WithnellParticipant @stevewithnell34426]

That's delightful! What a lovely job.

[Ramon WilsonParticipant @ramonwilson3]

Wow Keith, that's come out well

Really looks the part. I can well imagine the noise – takes me back to when we flew with 35's on open exhaust all the time.

Lovely result indeed.

Hope you are well

Tug

PS as an aside I used oil filled nylon for my first rotor in the Racer only to find out it can distort under rotational/centrifugal loads! Made all others following from Tufnol which is a much better material for a rotor but the nylon one remains and still works

[KEITH BEAUMONTParticipant @keithbeaumont45476]

Thanks, Steve and Tug for your kind words.

Tug, I took the back of after 30 minutes of run time, to check if the disc was showing any sighn of wear/distortion and was pleased to see that it was still as it was originally . This is the first rear disc induction engine I have made, so was not quite sure of using Nylon. It was convenient as I had a sample piece, but I did order a piece of Tufnol later ,just in case I had to re- make it

Keith.

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