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Author Topic: Correct glow plug for COX head adapter  (Read 1126 times)

Offline Mike Griffin

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Correct glow plug for COX head adapter
« on: February 22, 2022, 05:11:12 PM »
What plug do I need to use for a COX .049 head adapter.  I have quite a few Thunderbolt RC long plugs but do not know if they will fit or are to hot for the engine. 

Thank you
Mike

Offline Dave Hull

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Re: Correct glow plug for COX head adapter
« Reply #1 on: February 22, 2022, 10:41:14 PM »
There must have been a dozen different makes of Cox .049 glowhead adapters. Unless we know which one you've got, we can't really say.

Doug Galbraith made one for years to support the FF community. These fit a Nelson plug. Either the Regular or the Heavy Duty plug worked well. (As I recall, Henry stopped making one or the other a few years back--everyone wanted the one type, so little demand for the other.) Anyway, the Nelson setup is a performance improvement over the stock Cox head.

The Kamtechnik source makes a head that is compatible with the turbo-style plug, as made popular in R/C cars. These, like the Nelson setup, seal at the nose of the plug and do not degrade performance.

A myriad of heads were made with 1/4-32 threads to fit a traditional glow plug. MECOA sells both a long and a short plug aftermarket head. These do diminish the peak performance but may be fine for sport models of moderate size.

The "standard thread" head I tried (brand unknown) needed the short plug. Others may be different, so you need to look. The tip of the plug should be flush inside the head, and not sticking in. The opposite is just as true. Getting one to run well with a short plug in a "long plug head" is likely a fool's errand....

I don't think there's a plug made that is "too hot" for a Cox. Unless you are trying to run really high nitro? What you need to do is add/remove head shims until you get rid of the crackle if you run it hard. The sure sign you have too little head clearance is when you quickly blow plugs. If you are not competing for huge dollar prizes, it makes sense to set up with plenty of head gaskets and maybe (if you have the choice) a "less than hyper-hot" plug. If you are satisfied with the performance, then it will likely last a long, long time. If you need more, start reducing shims. There are actually shims of varying thickness out there. Be sure of what you have, or approach it fat and then start pulling them out.

For a lot of sport flying (such as FF) the planes do not need every bit of oomph from a Cox .049. A lot of the 1960s planes were still using other brands, and as far as I could see, they didn't have the performance of the Cox, unless maybe we are talking about Holland Hornets? As an example, a hot Cox reedy is not needed on a Wagner Dakota, but the weight of an .049 instead of an .020 helps a lot with the balance.

Hope this helps a little, and isn't simply old news...

Dave

Offline BillP

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Re: Correct glow plug for COX head adapter
« Reply #2 on: February 25, 2022, 10:58:15 AM »
I bought the conversion head for a Cox 049 from MECOA back in the early 1990s. If memory is right I used a Fox standard long. It did ok on 10% nitro and better on 25%.  Flew it on an ACE Wizzard
Bill P.


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