Hey Gang

I have decided to instead of just talking about gasolines, to run some tests. I will need your input on exactly what I will need to do it. It will be a few weeks before I can run the tests. I have a newRCGF 26 that Bowman rings are on the way for. (Voided warranty). What I want to do is try these gasolines, pump, 100LL Av gas and 110 racing fuel. I was going to try Coleman gas but I read on the BPRCGF26 site that to use it, you need octane booster. I need these questions answered as this is my first rc airplane gasoline engine to fly.

What size prop should I use to put enough load on the engine to adequatly test the torque or RPMs?

Any suggestions on a thermometer to properly test the running temp would be helpful.

Any suggestions on any other type of test that should be done for performance would be helpful.

I will also make comments on the ease ofstart up during these tests

The reason I am doing this is there are some rc pilots who do need optimum performance from thier planes and, it just sounds like fun. As I said it willbe a few weeks before Ican do it. I am still waiting on parts for my plane and I need to breakin the engine for equal performance on each gasoline.

Bassard</p>

The 26cc RCGF and RCG engines work good with a 18x8 propeller. Using a smaller prop puts the engine at risk of exceeding its maximum RPMs rating. Using regular pump gasoline with some ethanol in it and that odorous butane like stuff in it too, I got these numbers.
I was running a RCG 26cc gas engine that is shown in a thread over in the Engine tachometer readings category.
I nevewr tried running naptha based fuel (ColemanCampFuel), so I don't know if you need octane booster or not. I do know others have used the fuel in othergas engines before without mentioning usingoctane booster.
I have used a infrared digital thermometer I got fromHarbor Freight Tools OK on many engines.

Propeller RPM numbers so far gathered:
Master Airscrew 16x8 composite prop 8,480
Xoar 17x8 wood prop 7,780
Master Airscrew 18x6 Classic composite prop 8,130

I did some further tests and got these results using some 18x8 props
Master Airscrew Classic 18x8 prop 7,095
APC 18x8 prop 7,095 (WARNING dangerousto do as the prop hub is weakened by the drilling for the prop screws).
Vess 18x8 Sport prop 7,225
Xoar 18x8 prop 7,180

RPM figures are nice but for me is really a small part of how I want my engine to perform. I would suggest the you run your tests without any adjustments to the engine other then mixture. stick with the same prop throughout. Log information such as ease of starting, transition, temps, vibration and of course top end RPM. Give hard figures such as temps after landing and RPM. Transition and vibration will obviously be more subjective. Once that is done do the same tests but try advancing the timing a tad with the higher octane fuels. if you really want to fiddle you could try some thinner base gaskets to bump up the compression with the high octane fuels.

Now for the disclaimer, for this to really mean anything IMO it has to all be done with the engine in the airplane and airplane in the air. Make the change, fly the engine for a gallon worth of fuel taking notes on handling charicteristics then at the end of the gallon record RPM figures. It will be a lot of work but at the end it will be good useful information. One thing I did notice of interest. Today when I picked up some Sthil HP ultra oil I read in the directions their recommendations to use only 89 octane. I wonder what they know that I don't
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What that guy knows...is 89 octane is high enough for low compression engines.

Be sure to include pump 87,89 and 91 in your tests!

Put more flights on the VV 20 today.Love that little engine.Going to put a 16x8 on it and let it scream,see if I can hurt the rod or crank.I have a bunch of DLEs and have never had a crank or rod problem. The only problem it is hard to get enough time on them to even tell how they will do in the long hall.Doub't if any of them are even broken in.I am going to fly the snot out of the VV 20 to see how it will do with some time on it.Going to fly tomorrow.
Bill C, BCCHI

I have been running gasses on 87 octane as per DA for over 15 years without issue. My question is what is there about the oil that works better with 89 octane. Remember that Sthil packages the oil and states two things of interest. The first is that it is recommend for all air cooled engines and to use 89 octane. Dosent that make you curious?

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There's some good advice here already.

Like has been said already

Run all your fuels with the same prop - measure your max rpms, and take your temperature at the same place under the same conditions with each fuel test.

Buy all means run the Coleman fuel right along with your other tests. You will find that it runs well. You also have the temperature gun to spot any over heating right away.

Readjust the needle valves as necessary for each fuel type.

Then you may try taking advantage of the higher octane ratings, first by timing change and then maybe by increasing the compression.

You will soon find out that the engine will for a second or two run at a faster rpm and then drop by 100 or 200 rpm and then stay steady. Take notes of these drops.

Find the hottest place on the cylinder and take all your measurements at this hottest position.

Been there, done that. Ran reg gas, av gas, coleman fuel. Engine 3.2 Sachs
What I found, coolest reg gas. Coleman and av gas ran hotter +50 deg. Power was reg gas, coleman -50 rpm, avgas -75 rpm

Sounds about right.

This is what you could simply predict by composition of the fuels.