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Author Topic: Doctoring Fuel blends  (Read 1656 times)

Offline Dennis Toth

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Doctoring Fuel blends
« on: January 09, 2014, 12:29:14 PM »
Guys,
I asked about this in a prior thread but it got lost and I thought a separate post might be a better approach. The local hobby shop carries Byron fuels at a reasonable price and I would like to support him. I have seen posts in the past that spoke very highly of the Byron fuels. The fuel I am looking at is 5% nitro, 20% oil blend (I think 50/50). Since I am running a iron/steel engine I would normally use around 28% oil. This means adding about 11.5 oz of oil. I know this will drop the nitro level but at 5% its more or less just and ignitor so if it drops to 4.5% ish should not be a big deal.

Originally I had been using 95% castor and 5% Klotz the idea being to remove heat with the high castor and have the Klotz keep the engine clean. That didn't work to well. The question is to avoid a repeat of the varnish issue but still remove heat, I am going to the 50/50 oil Byron's but want to increase the oil to say 27% what oil should be added - Klotz (50/50) or straight synthetic or castor?

Best,       DennisT
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Offline Jim Thomerson

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Re: Doctoring Fuel blends
« Reply #1 on: January 09, 2014, 12:58:25 PM »
For some years I have been flying all my engines on Sig Champion 10% nitro, 20% oil half and half.  Iron and steel engines include TD 09, McCoy 19 and Fox stunt 35.  I got results to suit me without adding castor.

I have, a couple of times, run engines on someone's fuel said to be the same as my Sig Champion.  I had to change the needle quite a bit and was not impressed with how the engine ran.  So I hesitate to tell you that 20% oil, half and half, is all you need.
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Offline Jim Kraft

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Re: Doctoring Fuel blends
« Reply #2 on: January 09, 2014, 04:59:27 PM »
You might want to check which Byron fuel your hobby shop is carrying as most of their syn. castor blend has only 20% castor to 80% syn. That is their most common aircraft fuel and if that is the case I would use castor to bring up the percentage you need as that will bring it closer to a 50-50 blend.
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Offline Andrew Tinsley

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Re: Doctoring Fuel blends
« Reply #3 on: January 10, 2014, 03:21:50 AM »
I have on occasion doctored fuel in the way you suggest. It worked well. You need a goodly amount of synthetic to stop varnishing. 50% seems to work well, I have not experimented to see what is the minimum amount of synthetic you need to stop varnishing.
I usually mix my own fuels and would just warn that normally modellers quote by volume and manufacturers by weight. If you are going to check with the manufacturer then ask that question. I know the SG of castor but not synthetics. Just be careful you have what you think you have in terms of percentages, weight or volume!
I even use half and half castor to synthetic on my diesels, so far it has worked well. It seems to take some of the crackle out of the running sound. Folk law has it that the crackle is due to carbon particles on the piston. So it could be that carbon fouling is reduced by using synthetic with castor. This is speculative, because I don't really know what causes the crackle!

Regards,

Andrew.
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Offline Tim Wescott

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Re: Doctoring Fuel blends
« Reply #4 on: January 10, 2014, 09:03:43 AM »
At the moment I'm running Wildcat fuel plus castor.  The Wildcat is their synthetic/castor mix; it's something like 14% synthetic and 4% castor.  Then I add eight ounces of castor, which brings it up to 14% synthetic and 7 or 8% castor (I can't remember the numbers exactly -- you're welcome to check my math).

It's working great for me in an LA-46 and an LA-40.  If I were running iron/steel engines I might bump the castor up until I had 25% total oil.
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Offline Phil Krankowski

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Re: Doctoring Fuel blends
« Reply #5 on: January 10, 2014, 04:44:19 PM »
Write a simple spreadsheet.  Let these funny things called "computers" do the heavy lifting for you.  

This is written for "Omega" 15% (Morgan fuel) but can be edited as you see fit.

The added oil happened to fit in the head space of the bottle so I did not need to remove fuel from the bottle.  There should be about 8 ounces of head space in most gallon bottles.  If you remove fuel the starting quantity is reduced.

Phil
« Last Edit: January 10, 2014, 05:33:57 PM by Phil Krankowski »
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Offline Steve Helmick

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Re: Doctoring Fuel blends
« Reply #6 on: January 10, 2014, 07:40:46 PM »
There usta be a program to plug your fuel and desired fuel into, I think on the Tulsa Glue Dobbers website.
 http://www.tulsacl.com/index.html  Even if it's not there now, there is plenty of other good info and articles saved there.

I found a couple of them I'd saved to my confuser, too. I'm not sure if the spreadsheet will work or not, but maybe, just maybe...  H^^ Steve
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Offline Phil Krankowski

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Re: Doctoring Fuel blends
« Reply #7 on: January 10, 2014, 08:46:02 PM »
That is a whole lot nicer and more polished than my spreadsheet.  Thanks Steve.

Phil
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Offline MikeMorgan

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Re: Doctoring Fuel blends
« Reply #8 on: January 11, 2014, 06:13:05 AM »
here is a link to the formula calculator  to change nitro/oil content from any percentage to another.

i use it to up nitro content all the time. you put in what you have in percentages of nitro and oil, and amount, then put in what you want to end up with and it tells you what to add.

http://www.nitrorc.com/fuelws/allmix.asp

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Offline Dennis Toth

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Re: Doctoring Fuel blends
« Reply #9 on: January 11, 2014, 10:31:10 AM »
Guys,
Attached is the spreadsheet I use to get a starting point on oil/nitro % (it also does venturi calcs), it was developed by Rollin Kesler. It  works very nice. Since it is all % you need to determine if your are dealing with weight or volume based fuel. For me I just do weight and once I get a % that works I just use. Today I flew the El D with the devarnished Fox 35 on Byron 10%N/18%oil that had 12 oz of castor added came our about 27% total oil, worked fine.

Best,         Dennis
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