Can a COX TD O51 run on standard fuel?

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Can a COX TD O51 run on standard fuel?

Postby SCROWOASH » Wed Nov 19, 2014 1:50 am

Hi Everyone,
I live in an area (Zambia) where nitromethane does not exist and there are no hobby shops. Fuel would only be available by mail, but I think it will be disallowed due to its hazardous nature. I can get methanol and castor no problem.
Can a TD 051 run on straight castor/methanol mix? If so, what modifications are needed to accomplish this? I want to fly this in a 1/2 A scale plane designed for this engine. Engine is hardly used, but run in.
Is there a throttle available for this engine?

Thank you all and thank you for this great forum.

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Re: Can a COX TD O51 run on standard fuel?

Postby ron bennett » Thu Nov 20, 2014 10:46 am

These COX engines were designed to run on 30% Nitro but they will run on less to no Nitro. BUT, they are a real pain to get started on low or no Nitro fuels. To get it to start and run on no Nitro, you should raise the compression.
Ron Bennett
ron bennett
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Re: Can a COX TD O51 run on standard fuel?

Postby ffkiwi » Thu Nov 20, 2014 12:56 pm

I agree with Ron-they're designed for nitro fuels and tend to be less than happy on straight fuel-you can often hear the revs drop when you disconnect the glowplug leads when running on straight fuel. As well as higher compression, a hotter plug is desirable-which poses a bit of a problem since Cox heads only come in one heat range! You can increase the compression by reducing the number of head gaskets (but with a minimum of one, obviously!)-TD's usually came with up to 3 gaskets fitted, ex-factory (the instructions made specific mention of this)
As far as a hotter plug is concerned-the only option is to use an aftermarket head adaptor-which come in a variety of styles from those taking a standard 1/4-32 plug, to drop in inserts, to Nelson plugs. Obviously this entails the additional expense of purchasing the adaptor head, and sourcing the appropriate plugs. Merlin glowplugs ( offer a range that will dazzle you for choices-including std hot plugs ( for 'small engine') , Nelson plugs, Globee types, and their own aftermarket Cox drop in inserts with a clamp ring. Mecoa sell std 1/4-32 adaptors for Cox 049s as well-and even offer them in a choice of long or short reach plug options. The catch will using an adaptor with a standard 1/4-32 glowplug is that it invariably results in a performance loss compared with a Cox glowhead-due to a combination of poorer head shape, and the dead volume around the glowplug element-exactly what you don't want in your specific situation.
Doug Galbreath is the man behind the Nelson plug adaptor head for 049/051s-a google search on 'Doug Galbreath' will pull up his contact details and website listing. That head adaptor is generally considered the best, for performance and can add at least 1000rpm over a standard Cox head under normal conditions-but you need also to consider the availability of the plugs [if you're not familiar with Nelson plugs, they are larger in the body than a standard glowplug-they use a 11/32-32 thread, and have a truncated cone base-which is where they seal in the head-they do not use a copper washer gasket like a normal 1/4-32 plug. In this respect they are like the 'turbo' plugs the R/C car people use (though the Nelson plug has been around a lot longer than the turbo plugs)-but the turbo plug has an 8mm metric thread, so they are not interchangeable. Just as with the turbo plugs, there are a lot of variants-standard Nelson plugs come in cool standard and hot grades, and there are globee style flat coil inserts in the range as well-giving about 6 alternatives in total.

From where you are in Zambia, you need to decide what option you want to pursue-regardless, you will need to assure yourself of a supply of heads or plugs from overseas-and that may determine what route you choose to go down. If you have access to a lathe it is possible to machine (with a lot of care-and the use of a custom made collet to hold the head!) a Cox head on the seating face and increase compression by doing so-I'm talking about taking 3-5 thousanths off the face-not great chunks of material! And even then you need a supply of gaskets to fiddle the clearances and deck height to a point where starting and running is consistent-but it can be done, with skill and attention to detail.

As a complete alternative-can you get hold of diethyl ether and kerosene in Zambia? [I imagine kerosene will be no problem, given its wide use for cooking, heating and lighting]-if yes then you can convert your TD 051 to diesel operation-by buying a head from Mecoa-look in the accessories menu on this website-the 049/051 heads are $24.99. It's a simple screw in replacement for the Cox head-and you can then forget your nitro issues.

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