Wanting to get more power from my saito .56 four stroke, I decided to try some 30% heli fuel (saito says this is fine). I definitely got a performance boost. I don't know by how many RPM's, as my tach is broke, but I could tell the difference. This is my question:
Will this cause the engine to consume fuel more rapidly? I seemed to have ran out of fuel a little sooner than normal, which caused me to make a dead stick landing. I thought the engine had just died, since I should have had maybe 4-5 minutes left. I Sucked the fuel out of the tank, but there was very little left, making me think the engine sucked air and died. Does this indeed affect fuel economy? It reasons that it would since there are more RPM's and all. Just wondering...
thanks

Yep more power means more fuel but one other benefit of the 30% is you do not need as much throttle to do the same things

Saitos and especially YS engines love the 30% nitro

It would seem to me... and I will stand corrected... That...

The Nitro is helping to increase the Air which is in the cylinder each time the engine fires... By Nature of what Nitro is...

With more Air in the cylinder you can burn more fuel... and so while power goes up, so does fuel consumption...

Someone else will explain better... I am too used to fuel injection these days... But normally a power increase requires a fuel increase... or a major increase in the efficiency of the engine.

There fore, when you Turbo an engine, adding Nitro kind of has the same effect, you don’t make the engine more efficient at burning fuel, you burn more fuel and thus have more power per stroke…

I think…

Matt

A couple of basic things you should alos understand are that...

Fuel... Has a potential chemical energy, a normal Piston engine will turn about 12% of that potential energy into power to drive a car etc... The rest is wasted in heat, sound, and other types of energy...

I am not sure what the percentage for a glow engine would be, but it is porbably much worse than 12%

So when an engine becomes more powerful it is either...

1. Burning fuel more efficiently, and so extracting more than 12% of the potentil energy in the fuel...

or

2. Burning more fuel, and thus producing more power, in a single stroke.

That's a very basic look at the physics behind buring fuel for energy but it should give you a good idea of why you are now using more fuel...

Also a Chev engine probably only extracts about 3% of the potential energy in the fuel it burns... Sorry could not resist...

Matt

One last comment...

Basically the other interesting fact my comments lead to is...

Each time you pay for a Gallon of gas, at best only 20% of the actual potential energy in that gas is used... the rest is wasted...

So if you pay $2/Gallon... You could almost say you are getting 40c of gas energy and burning $1.60 for nothing...

Such is the Internal Combustion engine... (A glow engine is a bit different obviously...)

Phew...

Matt

Yeah your fuel consumtion will increase, a trade-off for more power. Some things to consider with nitromethane: it does not require as much oxygen as gasoline to combust, so it is in effect, a richer mixture, it burns hotter than gasoline, so its caloric release is greater, it burns faster than gasoline, and it has a lower flash point than gasoline, so it will ignite at a lower temperature. All these reasons are why drag racers love it. The down sides are that it is hideously expensive when compared to gasoline, and has a propensity to blow engines up when too high a percentage is used in a high compression engine. It also, by virtue of some of the characteristics above, has the effect of advancing ignition timing in the engine, which is also responsible for increasing power, and causing detonation. Of course, drag racers use (best I can recall) about 75% nitro, so they're really pushing the envelope. I made the above comparisons to gasoline, but pretty much the same holds true for methanol.

Thanks guys. As I said earlier, I've noticed a good increase in power. I did finally get my tach working, and was able to get a direct comparison today. Using the 15 % byrons fuel, I was turning somewhere around 10500 with a 12 x 5 mas prop. In comparison, I was getting over 11500 with the 30%. Not much increase, but 11500 is pushing the mechanical limits of this engine. I may notice an even larger margin of difference when I go to a higher pitch prop. I'm thinking maybe a 12 x7 or something like that. I have some 12 x 8, but I still think they are too much. I will, however, try them again using the 30%. Another thing I noticed today. The other day when I first used the 30% I had to richen it up quite a bit. I attributed it to the cold weather. However, today when I went back to the 15% (for comparison purposes), I had to lean it up quite a bit (after having already flown on 30% with no problems at all). So, running more nitro does require me to open the carb up quite a bit. Almost a 1/2 turn! I'm attributing that to more power, more RPM's, more need for fuel!
So, there is the verdict. A 100+ RPM difference between 15% and 30% on the Saito .56. I shall try the same experiment with my Saito 100 someday and report on those differences as well!

would using 30% also mean that you can expect a shorter life from your engine?

Well, I sure hope not. Saito actually recommends 30% for performance. It's in the manual. Besides, this powermaster fuel actually has more oil than the 15% that I was using, so it should be lubing better than it was before!

It’s inevitable that the engine will not last as long using 30%...

This has nothing to do with the 30% fuel… It is the fact the components are moving faster and so wearing faster…

More power = more wear…

But that does not necessarily mean the engine will fall apart over night…

Might only last 4 years instead of 5… Depends on the engine…

Matt

But, it would also stand to reason that more lube (20% as opposed to 18%) would equal less wear. Who knows. I'm sure your right. I would certainly hope that a 250 dollar four stroke engine would last more than 4 or 5 years. Maybe not. I will keep you all informed as to the outcomes of these experiments. Thanks for all of the input!

More Nitro = Richer mixture

Less Nitro = Leaner Mixture


I dont really see a need to be using that much nitro, unless your doing some seriously off the wall stuff, or pylon racing.

More nitro and more rpm also means more heat. That's usually not a problem, but if you're running a cowled engine that is not well cooled to begin with, more nitro can make things worse. Obviously not a problem with the orgional poster's setup though.

The extra RPM means more strokes per unit of time, which means faster piston/liner wear, but it also means more heat in the conrod, bearings, etc. So you get more wear in those areas. The extra (and IMHO, better) oil in the PM fuel over the Byrons will help, but it's anyones guess as to weither it will help more than the increased heat and RPM will hurt.

If it was me, I'd do what you are thinking of doing, going to a bigger prop to move more air with that extra RPM. If you like your level flight speed now, consider going up an inch in diameter rather than in pitch.

Well, thanks montague (and others). that's why i'm trying all of this. I feel as though the contender, while weighing only 6 pounds, is underpowered with this engine. It is, however, at the bottom of the recommended list by the manufacturer. With the short stubby wings of the contender, a lot of air must pass under them to keep the ship afloat. I feel as though if I could turn more prop at slightly higher RPM's, then I could pull the plane with a little more authority. I want to keep this engine on this plane, but I feel as though I need to do something. one thing I've figured out is to land it faster. I think that may be a characteristic of the plane anyway.

I tend to disagree with the use more fuel theory. I don't think that higher Nitro necessarily means use more fuel. What it does mean is that you use more nitro and more nitro = more power. What uses more fuel is the fact that you are increasing the RPM for each throttle setting by using the same prop. Because fuel draw is more correlated with RPM than with the fuel itself.

In other words, if you could prop it up so that you are getting the same max rpm as you were getting with 15%, you would be getting around the same fuel consumption. Not only that, as Montague mentioned, you would also be getting better wear characteristics.

Also... pulling with authority DOESN'T mean you should up the pitch... it means you should go down on pitch. Lets take 3D planes for example, they are the planes that need to the most pulling "authority" and they use the least pitch. Pitch is like your gears in the car (you drive a stick you'd know better). Higher pitch is higher gear like 5 or 6 on a manual. Lower pitch is like 1 or L. You see, for pulling authority, you use lower pitch but for faster flight you use higher pitch. Then, once you know what you want, you choose the prop diameter to ensure you are in the powerband of the engine.

The contender doesn't look to be a fast airplane and with a thick airfoil like that, it won't need to be going too quick to create good amount of lift. I would recommend you stick with the recommended prop sizes and go UP at diameter and DOWN a pitch if you want more engine authority.

More Nitro = More Power but what about the different kinds of oil in your fuel. Some fuel contains 50% natural castor oil and 50% synthetic while others contain 80% synthetic and 20% castor.

I know in high performance cars they run on straight synthetic oil but is it the same for model airplane engines.

Forestroke,
I was flying a MAS 12 x 5 and getting 1150 RPM out of it. Are you saying to maybe go to a 13 X 4 or something? Is that too much prop? Maybe just go to a 12 X 5 APC or something like that? What about a three blade prop? I think the scale look would be nice.

2 slow, i certainly hope you are missing a zero in that rpm figure :-) Is that RPM reading for 15% or 30% nitro?

From the hip, I would say that that isn't enough prop for the engine. I would say you should run a 12 x 6 APC on 15% nitro. And 12 x 7 on 30% nitro. For a three blade prop, you can go one lower in pitch or diameter. In my experience APC props are much more efficient than MAS but don't look near scale.

Try the APC 12 x 6 first and the 12 x 7 second. You should still be able to get 10~11k on the tach. Remember, 11k on the tach would certainly go to 12k unloaded in the air... that is pretty much the limit (as per manufacturer's specifications).

Forgot to mention that should be around sea level at a nice flying temperature!

Thanks, forestroke. Yes, all of those numbers are X 10. I will pick up a 12 x 6 this week and give that a try (apc, of course). Thanks again...

You might as well try the 13x4 and 13x5 while you are at it. Trying props is the way to go, since engines are non-linear, and more diameter means more pulling power. Heck, I wouldn't rull out a 13x6, but I kinda doubt it will run well with that one.

For example, my OS .61FS (15+yr old engine), which is probibly about the same power as your .56 (if I'm lucky, on a good day), turns a 12x6 and a 13x6 at almost the exact same RPM on the ground. Needless to say, much more pull with the 13x6 in the air. I even tried a 14x6, and I have a 14x4 around here I'm going to try next (doesn't fit the !#@$ spinner, which is why I haven't tried it yet).

On my Waco with an OS .32F two-stroke, I just finished prop experiments, I tried a 10x5, 10x4, 10.5x4.5 and finally settled on an 11x4APC. (I used a 10x5 on that engine in the past, in a different, cleaner and faster airplane, but it was just wrong for the Waco).

Honestly, I'm not sure about more nitro meaning more fuel consumption at the same RPM. But I do think the fuel consumption will go up a little. The reason (I think) is as stated above, more nitro means you need less air for a proper fuel mixture. Since our engines are often limited more by air intake than anything, needing less air means you can get more fuel in the engine for the same amount of air, and that means more fuel per stroke of the engine. So, at the same RPM, you get a higher fuel useage. It's probibly a very small amount though, much smaller than RPM effects, or just playing with the throttle. I suspect you'd only be able to measure the difference (for a small nitro change) on a test stand, in the air, I don't think it would matter.

Wes, Yes, different oil packages and % will change the power output of fuel, sometimes by quite a bit. I've seen 500rpm difference between two brands of fuel with the same nitro%. (and I think they even both had 18% oil, just differnet oil packages. change the oil %, and the RPM changes even more. Btw, oil is one of those "just right" things. Not enough oil, and you have too much internal friction, and RPM goes down. Too much oil, and you loose "burnables", and raise compression and engine temp, and RPM goes down. It should come as no surprise that for every last RPM, you need to play with your fuel to find out what oil works best in any particular engine, there's no "X% is best" rule). But for most guys sport flying, most fuels are pretty much going to be interchangeable. And yes, there is 100% synthetic oil airplane fuel. A lot of guys run it. Personally, I like a dab of caster, about 3-5%. YMMV.