50 weight cadtor

Yabby,

Your numbers are spot-on for old Cox engines. I could quote anecdotal evidence from the fliers that doctor theirs with a bit of synthetic and find no negative effects. I want to say I've seen where the castor content must be there, but nothing saying just how low the castor content may be before realizing net loss effects.

To that end, I buy high nitro/low oil fuels and use Andy Batts' two fuel mixture spreadsheet to ensure I have roughly 20% oil. Sometimes the castor content has been as low as 5% total, with the remaining %15 being synthetic (1 part castor to 3 parts synthetic). I did find the plane had less thick exhaust goo and was easier to clean up. I also noted the higher synthetic content fuel seemed to flow easier in colder weather.

Note I don't fly very often, but in spurts (quite a bit per outing). Nor do I measure and check for wear either.

I'd recommend trying a quart (or liter) set up for 50 methanol, 30 nitro and 20 oil (50/50 castor/synthetic and see how your engine runs. Of course, if you want to go higher nitro, I'd suggest trimming out the methanol vs oil. I won't blend less than 15-18% oil regardless of how much (or how little) castor is in the fuel.

Hi Yabby, I don't know if you're familiar with these OEM Cox fuel formulas.. but I'm attaching photos for you to refer to; just in case you haven't seen them.







What's happening.. that's causing you to investigate your current fuel-blend?

thanks @gkamysz , @944_Jim , and @roddie for your feedback. All valuable. I am going to try 20% oil at 50 castor and 50 syn and i will buy syn made for glow modelling, 20 nitro and 60 methanol.

It is also possible I have changed the way and time for which I run in new engines. I used to run in with many short hot cold cycles slowly building up time and revs. Of late I have run in with only several cycles and longer ones before flying a motor at peak revs.

It has been a bit frustrating as I used to get really good peak life out of my engines. they still run for ages just under peak. but I like flying them when the TD makes that milling crackling scream like its going to explode. you can fly long lines, great tension, easy start. they are aewsome. I think I need to go back to building them, preparing them, and running them in the way I used to. I will do that first and see how it goes. Then I will look at the oil mix. one thing at a time so as that I know whats affecting what.
my last 3 trips to the field have been no-fly trips as my engines wouldnt run properly - not enough revs. its been very disheartning as I have never had this trouble before. the engines were the one thing I really could do well. I did also try someone elses fuel that ran their motors great and same result on mine, so that sort of eliminated bad fuel. maybe my engine discipline has dropped as ive concerntrated more on trying new flying manauvers. back to controlled basics with a couple of new engines I think will resolve things.

The infamous engine testor Peter Chinn recommended no more than 25% Castor in then all Castor fuels, (found on Sceptre Flight Engine Tests archives), because of Cox's small fuel metering passages.

Gary,

PM your email address so I can send you the two fuel blend calculator. I usually buy truggie or helicopter fuel with 30% nitro (or higher) with mostly (if not all) synthetic oil at low oil values (I seem to remember my last had only 9% synthetic oil). Then I use the two fuel blender to mix in methanol and castor. The second fuel is initially represented as 80% methanol and 20% castor to start playing with numbers. The spreadsheet takes some playing with to determine final mixes.

While the spreadsheet is built in USA volumes, just substitute the numbers as your favorite unit of measure and make smaller batches...after all, the ratios stay the same if using ounces, cc's, liters or whatever unit (is "beers" an acceptable quantity?).

i'd like 2 beers worth of premixed, ready to fly please?

Charles,
You gotta keep the ratios simple.
50 beer bottles of methanol, 30 beer bottles of nitro, 10 beer bottles of synthetic oil, and 10 beer bottles of castor oil. The trouble will be keeping up with the count as you empty the bottles of beer!

Yabby if you have a smaller prop I would try that on the more worn engines like > 4.5 X 4 < > https://coxengines.ca/propellers/cox--049--051-propeller-grey-4-5-x-4-3.html They scream !

hey thanks Eric good idea  I hadnt considered that.