Retuning when changing fuels???  
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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> RC Fuels >> Retuning when changing fuels???
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Retuning when changing fuels??? - 4/25/2004 12:51:39 PM   
Capt Jim


 

Posts: 1116
Joined: 4/14/2002
From: Boca Raton, FL, USA
Status: offline 		Re-tuning the needles when changing brands/formulation of fuels is something I have heard time and time again, but can anyone tell us exactly what is happening, because of specific differences in fuel composition, to require the retuning. My example is...all my motors run perfectly and happily and reliably on Omega (Morgan Fuels) 10 or 15%, which is a castor based fuel. However, I get tired of removing motors from the airframe and "cooking" then in a crock pot of anti freeze to clean off the crud. In an attempt to eliminate the brown baked on castor crud I purchased a brand new jug of Wildcat 15% 2 & 4 stroke fuel, (a popular fuel locally), which is supposed to be a more synthetic oil based fuel. The low needle was left unchanged since it appeared to be only slightly off the original numbers, but idling acceptably. The high needle was retuned approprietly. The transition seemed fine on the ground. I have experienced a flame-out, (dead-stick) on each and every flight on my Saito 150 using this new fuel. For what its worth, I have an on-board glow, simply for starting convenience, she idles well even without the glow system turned on. The flame out usually occurs at about 5 minutes into a flight...quite unpredictable and sometimes sooner. The last one cost me a very nice DP Ultimate. Losing a $400 plane is bad, but losing it one week before the IMAC event makes it more dramatic. I'm out of the competition now. I also noticed that the Wildcat fuel seemed to be quite foamy when defueling...something the Omega never ever did...in the very same instalation. Is Wildcat known to be more prone to foaming than Morgan fuels? This performance, and the loss of my plane has made me decide to simply not use Wildcat fuels anymore, and I am back to using Omega, but still unhappy with the castor crud. Would I have been better advised to go with Morgans "Cool Power"? So...to the point. What specifically is going on with the needles in conjunction with the use of a different fuel? This forum is such a magnificent resource for us, giving us access to the fuel manufacturers and blenders...I Thank you all very very much for shedding light on this mystifying subject.
Happy Landings.

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Captain Jim
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RE: Retuning when changing fuels??? - 4/25/2004 2:15:30 PM   
Hobbsy



Posts: 10876
Joined: 12/2/2001
From: Colonial Beach, VA, USA
Status: offline 		That is most interesting, I use WildCat fuels exclusively in my fourstrokes and have never had a problem. I use WildCat Premium Extra 10% nitro in my Saito 150 and high compression .80 and Premium 15% nitro in the rest except I use WildCat ProMix 20% in my YSs. I use the ProMix because it has a little castor in it. I have never used the 2/4 fuel and never would. Experience has taught me that not much in this life that is multi purpose, serves any purpose well.

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RE: Retuning when changing fuels??? - 4/25/2004 3:25:25 PM   
bentgear


 

Posts: 2752
Joined: 3/25/2002
From: Brandon, MS, USA
Status: offline 		Capt Jim, general rule, if you go to a higher nitro content, same fuel brand/type you will have to richen up the needles a small amount. Just the opposite when you go to a lower nitro (same brand/type). With small changes, 5% or less, you may not see a need to change the needles.

When switching brands there is no general rule for needle settings. With different fuel blenders using different oils, the fuel viscosity changes from brand to brand. The correct setting with a lower viscosity fuel would require the needles to be less turns out as the fuel moves thru the needle easier.

It sounds like you may be going lean in the air.

Ed M.

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RE: Retuning when changing fuels??? - 4/25/2004 10:31:30 PM   
Capt Jim


 

Posts: 1116
Joined: 4/14/2002
From: Boca Raton, FL, USA
Status: offline 		Hey guys, thanks for the comments. I agree...multipurpose usually entails serious compromises...i am reminded of the old Kirby vacuum cleaners...they were sold as the do it all household tool. Well let me tell you, it was a great vacum cleaner, a lousy drill/buffer, and an absolutely rediculous paint sprayer. Many local flyers have enjoyed the same good results from using other Wildcat fuels as you have, and some have had good results with the 2cy/4cy stuff, but typically in 2 cycle motors. The 4 strokes just seem to dislike it for some reason, and I would like to know what that reason really is. You mention the possibility of varying viscosities accounting for the need to retune, and that does sound like a reasonable thought. As for the nitro level, and the need to retune, especially for the higher concentrations of nitro,...we are aware of that, and the nitro level is the same in both fuels tested. As for going lean,... the same tuning procedures are employed with each fuel, and the Omega, (castor) does just fine, while the multipurpose Wildcat (synthetic) does not. The simple fix is to go back to Omega, which I have done, but I hope to be able to learn something from all of this...after all, the loss of a plane should carry some educational benefit...shouldn't it? heh heh...lets hope so. I went back to Omega today on a piped OS46FX and picked up a couple hundred RPM over the Wildcat 2c/4c, and noticed much less oily, goopy, residue on the plane after the flight. Thats a good thing.
Thank you everyone for the words of wisdom.

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RE: Retuning when changing fuels??? - 10/26/2005 1:29:57 AM   
vlizard


 

Posts: 100
Joined: 9/8/2005
From: westland, MI, USA
Status: offline 		It isn't a viscosity change that causes a need to retune the engine. Nitro does not require air to combust, at least not as much as the methenol in glow fuel. It carries it own oxygen so to speak. When you switch to a higher nitro content it is like leaning the engine out do to the fact that with the added nitro that more of your fuel is bringing its own oxygen into the mix. This is the same a leaning the engine out with the needle, although chemically. As a result if you don't richen the needle you may have a to lean situation, complete with the overheating and all that goes with it, like quitting all of the sudden. I explained this to my kids this way. Think of nitro as air in the fuel. If you run the higher nitro richen your needel to compensate. You should be fine.

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RE: Retuning when changing fuels??? - 10/26/2005 3:36:59 AM   
downunder



Posts: 3279
Joined: 10/10/2002
From: Adelaide, AUSTRALIA
Status: offline 		Viscosity would have a small affect especially when changing between an all synthetic and an all castor fuel but the main culprit is nitro. Nitro is a fuel (which means it combines with oxygen) but in fact is a very poor fuel. The only reason it gives more power is because you have to burn a huge amount more for the same amount of oxygen. For the same volume of air (oxygen) you need to pump in at least 2.5 times as much nitro as you would with just methanol. But nitro is peculiar in that it's not at all critical for needing the right fuel/air ratio. You can pump in 10 or more times as much nitro as you could with methanol and it'll still work just fine. That gives some idea of how much more open the needle needs to be with nitro (depending on the blend). And why the needle seems less sensitive too.


(in reply to vlizard)
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RE: Retuning when changing fuels??? - 10/27/2005 3:30:10 PM   
speedster 1919



Posts: 1476
Joined: 12/17/2004
From: Martinsville, IN, USA
Status: offline 		First of all wildcat is good fuel. But there are 2 main blends in each type of fuel. One is total synthetic which some of oil is burned and adds to combustion. The second is the 20/80 castor and syn oil blend. Closer to omega 30/70 castor/syn blend. On the blend the castor part doesn't really burn so their is less syn to burn in combustion. It is said for every %1 oil you can take out of fuel is worth 2 1/2 % nitro increase. Nitro produces more heat in engine. So by switching fuels you have to retune because of oil % and types, amount of nitro, viscocity of oil in fuel product.

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RE: Retuning when changing fuels??? - 10/27/2005 3:52:52 PM   
Jim Thomerson



Posts: 2858
Joined: 10/9/2002
From: Austin, TX, USA
Status: offline 		I ordinarily fly Sig Champion 10% nitro, 20% oil, 50:50 synthetic:castor. I have tried the same fuel from Powermaster and Riche's Brew. Both required major readjustment of the needle. So I am sticking with Sig fuel. Not saying the other fuels are better or worse, just different when I expected them to be the same.

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RE: Retuning when changing fuels??? - 10/31/2005 6:02:14 AM   
Fuelman


 

Posts: 1070
Joined: 12/31/2001
From: Jordan, NY, USA
Status: offline 		Any fuel changes from brand X 15% fuel to a brand Y 15% fuel will normaly require a needle valve change in both the high speed needle and sometimes the low speed needle.
Why?, there are several factors that contribute, which has the most influance, I don't know. The oil viscosity has a part to play as well as the quantity of oil, diferent oils have different flash points which have some influence on how the combustion takes place with flame speed. Some companies have a lot of additives which have differing effects on the combustion process. Defoamers, rust inhibitors, fragrances, friction modifiers, etc... all have an impact on the way an engine tunes. Needle settings are generally affected, . The safe bet is to richen the needle a bit if staying within the same nitro percentage and then lean into the correct settings. Make your inital settings at about a half tank of fuel. It may take a couple tanks to sneak up on the optimum needle settings for brand Y vs. brand X.


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Cooper Fuels LLC

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