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Author Topic: Davies CO2 Cox conversions  (Read 805 times)
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tonsberg
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« on: September 10, 2014, 03:34:05 PM »

Hello Folks ,
I am a bit out of my league here! I have the opportunity to buy several Cox 0.02 and 0.049 Davies CO2 conversions. These are reputed to be very powerful CO2 units. I am used to scaling down OT designs for CO2. With the Cox units maybe closer to 1:1?
Seriously what would make good models for these two types of power units? Has anyone any experience of flying them, any tips or black marks? I understand that they are getting to be collectors items with a corresponding price tag! Anyone know what they fetch these days? These conversions have never been used (Like I suspect the majority of them!). Any information would be welcome.

Andrew.
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faif2d
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« Reply #1 on: September 10, 2014, 03:40:52 PM »

I once held a .049 version and I think it pulled like a .15 glow.  It was VERY impressive.
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danmellor
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« Reply #2 on: September 10, 2014, 04:18:04 PM »

I have a couple of the .049 conversions. They will happily swing a 10"-12" prop! I'm planning on using one in a "Little Juan" autogyro when I get round to it.

Cheers,

Dan.
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ffkiwi
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« Reply #3 on: September 10, 2014, 04:46:27 PM »

Andrew-they never seemed to make much headway in the market when they were in production. There must be a reason why, as I have no doubt they were quality items-all Davis stuff is. A few issues you might want to consider:

(1) spare parts....CO2 motors need regular maintenance just like any other form of power system. I don't know what sealing technology was used in the Davis ones-but spare seals would be desirable
(2) tanks...the 049 is significantly bigger than any other CO2 engine on the market (the 020 is comparable to the Modela and G-Mot GM300 in size)-what is the appropriate size for a decent run (would you want to fly R/C for example). Is there a negative scale up effect with tank icing/cooling when you have a larger CO2 motor with a big tank? [I suspect there might be]
(3) how does the Cox metallurgy cope with the continued cooling while running-the opposite of what it was designed for? [what does that do to fits/friction etc-bearing in mind most CO2 motors have plastic pistons, not steel ones...]
(4) CO2 props tend to be impressive in diameter-and high pitch. You might end up having to apply rubber trimming techniques rather than typical IC setups, depending on the model type [which might not be amenable, for example to large thrustline offsets....]

 My 10c worth...!

 ChrisM
 'ffkiwi'

PS If you do go down this path, Hobby Club stocks a range of CO2 tanks which might be useful for longer running times if required. I have no idea what the neck thread is however, so some kind of adapter might be required if you went down this route...
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tonsberg
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« Reply #4 on: September 11, 2014, 04:51:52 PM »

Hi Chris,
Interesting observatons. As far as I am aware most of the Cox stuff is retained with a spike welded or brazed onto the top of the cylinder. I am not sure about the heads, but it isn't going to be a big deal to replicate them. Half a day on the Myford should produce several. The cranks and cases are readily available for the 0.049, plus the P/Ls and will be likely to be so for a good many years, although I have enough 0.049 spares to last me out of the rest of my modelling career.
The 0.02 stuff is getting scarce, but I have lots of the hard to get cases and P/Ls, to keep my Pee Wee fleet in running order.
  I have stocked up on some of the larger tanks from Hobby Club, because I have several Gasparin Anzani motors which I think are 160 cu mm per pot and they are not too easy to swop tanks about between models!
  I believe that there are no seals on the pistons, I think they are just as Leroy made them! But I could well be wrong there. Still making up pistons with o ring grooves is not a big job, but with the huge Cox exhaust ports I don't think o rings will survive long!
  The two points you make about icing and the use of big props does bother me. The icing could be a fun experiment, but I don't fancy trying Wakefield type trimming, I am too old to get into that. Otherwise some fairly large R/C designs with quiet motor would be great for the village playing field and the grandchildren!
  I don't want to pay collectors prices for something that doesn't work too well. But I suppose I can always sell them on for collectors money if they don't work out. Thought it worth asking before making a decision.

Thanks,

Andrew.
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