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Engine basics => Engine set up tips => Topic started by: frank mccune on August 18, 2015, 09:03:55 AM
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Hi All"
Is there anybody using or has used FAI fuel or fuel with no nitro? If so, what are your opinions of it for stunt/sport flying?
Tia,
Frank McCune
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I use it almost exclusively for stunt competitions. Of course, I'm flying with Stalker engine power, which for me, run best in almost all conditions. on FAI fuel. They, like most eastern block engines have the high compression needed to use fuel with no nitro. most of the engines in use today have reduced compression.
Cheers, John
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Most use nitro, even if it is a small amount, most all engine will run and needle better, even high compression ones, there are not many stunt engines made that are higher compression that Aero Tigers, PAs and others. best deal is to try what you have. Many people using DR engines are using a small amount of nitro in their fuel.
Randy
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Hi Frank,
Well, not exactly "FAI-fuel" as I use a mix of castor/synthetic as oil, instead of full castor.
Powerwise no problem, it's just a question of certain parameters to compensate the lack of nitro. Mainly compression ratio, I mean.
Some say that needle setting is easier with nitro but I can't comment on that. I have no issues with that. Because of smaller consumption, you must be more carefull when measuring the correct amount of fuel in tank.
So you need slightly higher compression ratio (I use 10:1) and more efficient combustion chamber geometry for same stability.
And as you can't vary nitro % to compensate variations in atmospheric conditions, you must be ready to make changes in head and venturi size.
Also, not all synthetic oils can handle the required higher CR, in that full castor is better.
Lauri
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In the last 55 years I've never used nitro. The engines I've used for stunt began with a Merco 35 then Enya 45 (6001), ST G51, Stalker 61RE, VF 40/45, Irvine 40RLS and Enya 61CXLRS. All were box stock standard with one exception. One flick starts were the norm so nitro can't improve on that :).
The one exception was with the Enya 61 because I knew that engines with zero nitro fuel can handle much higher compression and that makes them more efficient which translates to more power. Its standard compression is ~8.8:1 so I made a new head button which gave 12.4:1 using a smaller combustion chamber volume but also decreased squish clearance from .026" to .006". On the test stand this showed an increase in HP (at peak revs) of 26% but of course peak revs are never used in flight so its main effect was to extend the 4 stroking revs.
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Many times, 2-cycle stunt engines respond best to a combination where it burns a LOT of fuel, especially where you are flying in competition and need to control run-time very carefully. The more fuel loaded, the less precise the measurement needs to be. Plus, the engines often are just happier getting more fuel and more oil through them. I'd expect every engine would be different in its needs.
If I lived where I couldn't get nitro, I'd expect to run a bigger venturi and more oil (especially more castor) in the fuel. I think Brian Hampton wrote about having a terrible result with the G.51 until he changed to 25% castor??? That would increase the fuel burned for a given flight time. When I flew CL Speed, I mixed my own fuel, and discovered that 65% nitro ran the same rpm, whether it was 15%, 20% or 25% oil (synthetic). I thought less oil should run faster, but it didn't. I didn't think about run time, but should have found that 25% ran shorter, and 15% ran longer.
For sport flying, I'd suggest trying zero nitro and see what happens and how you like it. D>K Steve
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I think Brian Hampton wrote about having a terrible result with the G.51 until he changed to 25% castor???
Yep, and it took some time for me to figure out it was because it was so amazingly economical there just wasn't enough oil flow to keep it from overheating. It only needed a 60cc (~3 ounce) tank for 6 minutes of engine run time. With 20% oil that meant the tank contained 12cc of oil and 48cc of methanol (the actual fuel). Raising oil to 25% meant there was now 15cc of oil and 45cc of methanol which would have reduced the run time by ~22 seconds so I had to add slightly more fuel/oil mix to the tank to regain the 6 minutes plus of course slightly open the needle valve to keep the correct flow rate of methanol into the engine.
If you're wondering about the 6 minute engine run, that's because I fly to FAI rules where the time limit is 7 minutes from signalling ready to start the engine until a full stop on landing.