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Paw twin

Old 10-11-2015, 12:18 AM
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Default Paw twin

Here's the new PAW .38 twin, one of only 15. Nicely made, and a very smooth runner. Quite an achievement by the blokes at PAW.
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Old 10-11-2015, 12:40 AM
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Ahh, we need a video with that...

Is it a limited run only or a new product from PAW?
Old 10-11-2015, 01:03 AM
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Limited run, 15 only.
Old 10-12-2015, 01:45 AM
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Very nice Steve, is it Daves?

Thanks.
Old 10-12-2015, 02:24 AM
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Hi Chris, it was sent to Dave by Tony Eifflaender to have a look at and do a bit of running. It'll then go to Maris for testing (which will presumably appear in Aeromodeller in due course), after which Dave will sell it on.

Steve
Old 10-12-2015, 05:42 AM
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So, Both cylinders fire at the same time? If they alternate that thing would shake like a paint mixer. Looks like it would be better as an inline twin.

Max
Old 10-12-2015, 01:20 PM
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Yes, they fire simultaneously, so it feels much like a normal big diesel to flick over, and sounds much like one. Very much smoother, though. Not really sure why it'd be better as an inline twin.
Old 10-12-2015, 05:00 PM
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Originally Posted by steve111
Not really sure why it'd be better as an inline twin.
If the firing order was 0/180 degrees then an inline twin would shake less but since its an opposed twin then the current firing order of 0/0 makes sense.

The only drawback may be the large offset between piston centres introducing a rocking couple but hey, who cares?

Highly desirable engine.
Old 10-12-2015, 09:22 PM
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Originally Posted by Chris W

The only drawback may be the large offset between piston centres introducing a rocking couple but hey, who cares?
I wondered about that too, but there was nothing of the sort evident when running on the bench
Old 10-12-2015, 11:04 PM
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Never noticed too much of the 'rocking couple' on my BMW boxer. It is there but is not anything to complain about.
Old 10-13-2015, 03:14 PM
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BMW boxer is a four stroke and they fire at the same time and they are smooth just like the VW engines. Without getting into too much , this is much easier with a four stroke as they use valves instead of crank compression to feed the cylinders. Why better inline? A lot more compact and easier to mount. Also, alternate firing twins just sound SO much better .

Max
Old 10-13-2015, 03:51 PM
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"... alternate firing twins just sound SO much better. "

No disputing that!

I suspect cost of production / design issues with an inline are greater. After the drama I and others have had with the CS .30 twin, I can see that producing an inline twin for the general consumer market is not an undertaking to be approached lightly.

Last edited by fiery; 10-15-2015 at 07:42 PM.
Old 10-13-2015, 10:05 PM
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Originally Posted by maxtenet
BMW boxer is a four stroke and they fire at the same time.......

Max
I am fairly certain that the 180 degree parallel twin or 'Boxer' engine as used by BMW actually does not fire both cylinders at the same time.
They alternate left on combustion accompanied by the right on exhaust and then 360 degrees later the reverse happens.

The same firing timing is used in their normal 360 degree parallel twins - hence the reason they sound quite similar.
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Last edited by Chris W; 10-13-2015 at 10:09 PM.
Old 10-15-2015, 07:45 PM
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Steve,

What was the prop size on the twin? Any (indicative) RPM figures?

I know Maris will publish his prop data using APC's in due course; however some figures on a 'user friendly' prop would be useful.

Last edited by fiery; 10-15-2015 at 07:47 PM.
Old 10-16-2015, 01:27 PM
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Hi Derek, that was a 12x6. RPM was in the 8000-9000 range, although I didn't get a really decent reading. Sorry I can't be more definitive, but it gives you an idea, anyway.
Old 10-16-2015, 06:39 PM
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That is fine performance. Thanks Steve.
Old 10-20-2015, 04:51 PM
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Originally Posted by Chris W
I am fairly certain that the 180 degree parallel twin or 'Boxer' engine as used by BMW actually does not fire both cylinders at the same time.
They alternate left on combustion accompanied by the right on exhaust and then 360 degrees later the reverse happens.

The same firing timing is used in their normal 360 degree parallel twins - hence the reason they sound quite similar.

I stand corrected!
Max
Old 10-28-2015, 11:02 PM
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Just wondering what the crankshaft counter weight situation might be here since with an opposed twin that fires simultaneously it needs to counter nothing!

Perhaps just enough for flywheel effect?
Old 12-29-2015, 09:16 PM
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Default PAW.38 twin cylinder

PAW.38 twin cylinder quad ball race diesel on the stand.

Easy to hand start. Once I worked out a procedure I was rewarded with a couple of 'first flick' starts. Powerful and very smooth running. Finesse coupled with patience is required to set compression and mixture for optimal safe running. As such, it is not for beginners. For the experienced it is rewarding to operate if approached with respect. Once settings are found it is no more difficult to manage than any other 'performance' sport diesel.

Throttling with the supplied 'varijet' carburettor is very good. It was however missing a tensioner spring to hold the barrel against the cam. A rummage through my carb spares box soon located a spare (O.S.) spring which I put to use.

This engine oozes class. A superb model engineering achievement. 'Well done' to Tony Eifflaender and the lads at PAW Macclesfield. Notwithstanding its complexity, as one would expect of a PAW it makes the grade as a practical power-plant. It is not destined to become an earthbound display bauble, even though it would look great in a glass cabinet. I'll make it earn its keep. I want to see how durable it is in field use. I have the plan and build notes for Arthur Fox's "Ladybird 2X". At 84" span, it is a 200% KeilKraft Ladybird. While not true vintage, it looks to be ideal as a suitable 'Old Timer' type aircraft for the PAW .38.

Video of engine running:

https://www.youtube.com/watch?v=7uf0...ature=youtu.be
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Last edited by fiery; 02-06-2016 at 04:48 AM.

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