CLBetten

My Feedback: (16)

My local hobby shop has fuel that has all the same specs except the nitro content for the same price. So 5, 10, 15, and 20% cost the same. I've always ran 10 or 15% and been perfectly happy. Is there any point in getting the 20 or is my temptation to do so likely sparked by being programmed to expect the higher nitro to cost more?

1QwkSport2.5r

Most sport engines destined for the US are set up to handle up to and around 15%. Some take 20% fine, others not. 20% will burn faster than 10-15% will; but it will make a little more power. For some reason guys in the US like to burn a lot of nitro. I've not noted real huge gains (200-300rpm gain for every 5% nitro I added) of power so I keep the nitro at 5-10% for general running. 5-20% all being the same price? Interesting to know this. The shop must get a volume discount or something, or they truly are greedy.... Because straight nitro is around $50/gal. 20% should cost a lot more than 5% by all rights.

mattnew

My Feedback: (2)

What are you trying to do?

... For sport flying, sunday flying and just in general enjoying the hobby I'd say to stick with 5-10% nitro and be happy with it. Engines run well in that range and you aren't pushing them to their limits so they in general will last longer. As you increase nitro you will get some gains in output, but you'll also be putting more stress on the engine and likely shortening the times between either rebuild or replacement.

...If you are using the engines in competition, then it might be different and you might be more concerned about that last few hundred rpm. It didn't sound like from your original post that that was the case...


disclaimer: there are some engines that manufacturers suggest higher nitro content... for these they may not run well on 5-10%. In general though most engines do seem to run well in the 5-10% range.

SrTelemaster150

200-300 More RPM can be significant.

My high compression FA180 engine W/CDI will make 400 RPM more on 30% nitro than on 15%. 8850 RPM W/an 18 X 8 prop compared to 8450 W/the same prop on 15%. That's a difference of 3.44 HP for the 15% & 3.95 HP for the 30%. That's a 15% increases in HP.

If you are flying something that you want vertical performance from, that can make a big difference. If all you want is flat level scale-like performance from your 1/4 scale J-3 Cub, run straight methanol W/O any nitro if the engine will burn it. (CDI doesn't require any nitro)

Nitro reqires a much lower A/F ratio (less air/more fuel) so it does burn up faster than low nitro content fuels. A CDI converted Saito FA180 could get close to gasoline cost of usage @ the same power output W/straight methanol & 10% lube content fuel if a person lived where bulk methanol was available to mix their own...

CLBetten

My Feedback: (16)

Thanks guys. I'll stick to the 10 or 15 percent. None of my planes are short on power. It stands to reason that there is a higher energy value in a less nitro, greater methanol mix since the nitro is basically an oxidizer not a fuel.

SrTelemaster150

What? There is definately more "energy" value in nitro @ the proper A/F ratios, & 27% more enrgy value in metahnol compared to gasoline.. Top fuel dragsters run 90% nitro, 10% metahnol.

As far as volumetric energy value, gas has more than methanol & methaol has more than nitro, but that's only a very small part of the picture.

If your engine produces ample power on 15% then by all means use it.

CLBetten

My Feedback: (16)

I stand corrected. I didn't realize the BTU per gallon of nitro was nearly the same as methanol.

SrTelemaster150

BTU per gallon is only part of the equasion. Methanol has less BTUs per gallon than gasoline yet there ia 27% more potential HP in methanol.

That's why I use methanol based glow fuels W/my CDI (spark ignition) Saitos. CDI/15% Cool Power usually produces about 22% more HP than a similar "gas" engine. When compression ratios that are higher than what is practical W/gas are emplyed that difference is over 40%.

Sport_Pilot

I have mentioned this also. A 300 RPM increase does not seem like much but usually it also takes more torque to get that RPM, sometimes a lot. Thus you will notice a signifcant power increase because HP is torque time RPM. Also a 300 RPM increase in the ground will spin up to a lot more in the air.

Sport_Pilot

They used to run 100% but stopped because engines were exploding. I believe they stopped when a low flying airplane got hit or almost got hit, not sure which, by a few pieces of shrapnel at Pamona. The dragstrip is right in the approach of a small airport.

If the fuel was just and oxidizer the dragsters would just sit there.

jester_s1

It's not a simple equation of more nitro = more power. Extra nitro also advances the ignition, which then requires you to run richer to dial it back to where it needs to be. Compression and glow plug heat also affect ignition timing, so there's a point with any given setup where the gains that nitro give you balance out against the losses that running rich cost you. That point is around 15% nitro for most sport engines running the medium hot plugs like the OS #8. Some of the real gearheads will reduce compression and run colder plugs to compensate and get more power, but at some point simply moving up to the next size bigger engine starts to make a lot of sense.

SrTelemaster150

Nitro requires a much richer A/F ratio whether you run glow ignition or CDI.

The richer needle settings required have little to do W/ignition timing. Nitro makes more power because you can burn more of it. It requires far less air to achieve the proper A/F ratio. The same can be said for mathanol compared to gasoline. Gasoline has more BTUs per gallon, but you burn more methanol per cu ft of air & there is about 27% more HP potential for methanol.

Granted, W/glow ignition A/F ratio, compression ratio, glow plug heat range, ambient temperature, relative humidity, density altitude, oil content, moon phase, etc, will affect ignition timing. That is not the primary reason for the richer needle setting when nitro % is increased.

Unstable ignition timing is one of the primary reasons GI engines require so much more oil than those W/CDI whether the spark ignition engine is using gasoline or methanol based fuel.

The real "gearheads" ditch GI & run CDI firing off methanol/nitro AKA glow fuel.

BTW: Contrary to some opinions, more nitro will also make significantly more HP W/CDI too.

jester_s1

I imagine you are right, srtelemaster150. With the ability to time the ignition independently, one can get the power benefits without having to compromise anything.

I have done a little bit of experimenting with nitro myself. In my TT .46 Pro, I found that going from 10% to 20% got me about 200 rpm more top end power using a 10x6 prop. Lowest possible idle speed was the same, and transitions were roughly the same. My needle setting to get peak RPM was 5-6 clicks richer with the 20% fuel, so the fuel use was significantly higher. That's all with an OS #8 glow plug. So on the ground I went from 14400 to 14600 for a horsepower gain of about 1.5%. I know the fuel should give me more gain than that, but without getting into changing compression or going to colder plugs (or maybe switching to CDI ignition) I can't realize the benefit due to the ignition timing issue. I went back to using 10% nitro since the performance improvement was so small.

Sport_Pilot

Nitro retards the ignition, however it burns slow so you need the ignition advanced more than it retards the ignition. Full or near full nitro racers have the ignition advanced 60 degress BTDC and even then the fuel is still burning when it leaves the zoomies, thus the flames from the exhaust of nitro dragsters and funny cars. If you are using a mix of nitro and methanol then you are compromizing the compression ratio and timing somewhere between the ideal for nitro and methanol. Thus the issues of detonation and cold plugs.

Sport_Pilot

You had an RPM increase of 1.4%. To get the higher RPM the engine had to produce more torque, Since the torque to spin the propeller increases exponentially the torque increased much more than the RPM so your HP increase was probably much higher maybe over 5% or more.

You were also using the same plug. If you had used a colder plug the incrase should have been more like 400 to 600 RPM with a much higher HP increase.

SrTelemaster150

A 10 X 6 @ 14400 RPM produces about 1.22HP. @ 14600 RPM that increases to 1.27HP. That's a 4% increase in HP.

Here is a STATIC THRUST CALCULATOR that is a useful tool for comparing power gains.

jester_s1

I stand corrected. Still not enough of an increase to justify the cost of the extra nitro fuel IMO, but definitely more than I was thinking.

SrTelemaster150

As Sport_Pilot pointed out, further tuning would most likely result in more of a performance boost.

It all depends on what you want. To someone that needs that last little bit of power it might be worth it.

I run 15% Cool Power in my high compression CDI FA180 & it makes 3.4HP. Upping the % to 30% boosts HP to 3.9. Just for occasional kicks, I like to have unlimited vertical availible. In most airframes the 15% will do that but in my 16#+ PT-19 that might be marginal.

Due to the increased effeciency of CDI compared to GI, I can make that 3.9HP while burning slightly less fuel than a stock FA150 on GI.

Propworn

My Feedback: (3)

(The following is the third in a series of articles exploring all facets of model engine fuel. The writer is Don Nix, founder and former owner of POWERMASTER FUEL.

Nitromethane…..everybody knows it’s there, but few, it seems, really know much about it. Although most seem to know - at least vaguely - that’s its primary purpose is to add power, we still get an occasional call or letter asking, "Why do you use it in model fuel?" At best, there is much misinformation regarding this somewhat exotic ingredient. Let’s see what we can do to clear some of it up.
Nitromethane is just one of a family of chemicals called "nitroparaffins." Others are nitroethane and 1-nitropropane and 2-nitropropane. Nitroethane can be used successfully in small quantities. (Top fuel drag racers, which generally run on straight nitromethane, sometimes add a little in hot, humid weather to prevent detonation.) At one time, nitroethane was only about half as expensive as nitromethane, but its cost now is so nearly the same, using it to lower cost is hardly worth the trouble. Neither of the nitropropanes will work in model engine fuel. Incidentally, nitromethane is made of propane, in case you didn’t know (and I’ll bet you didn’t).
Yes, NITRO = POWER! But….there are conditions and contingencies. First of all, it doesn’t add power because it’s such a "hot" chemical. Not at all. This may come as a surprise to most readers, but the methanol (methyl alcohol) in the fuel is by far the most flammable ingredient….nearly twice as flammable as nitromethane. As a matter of fact, if nitro were only 4 degrees less flammable, it wouldn’t even have to carry the red diamond "flammable" label!
In actuality, nitromethane must be heated to 96 degrees F. before it will begin to emit enough vapors that they can be ignited by some sort of spark or flame! (I demonstrated this not long ago to a friend by repeatedly putting a flaming match out in a cap full of nitro. I might add that he insisted on standing about 20 feet away during the demonstration.)
So….how does it add power? We all know (I think) that although we think of the liquid part substance we put in fuel tanks (in our automobiles or model airplanes) as the fuel, in truth, there is another "fuel," without which the liquid part would be useless. Remember what it is? Right….just plain old air (in reality, the oxygen in the air).
Every internal combustion engine mixes air and another fuel of some sort….in our case, a liquid…glow fuel. The purpose of the carburetor is to meter those two ingredients in just the right proportions, and every individual engine has a requirement for a specific proportion of liquid fuel and air. Try to push in too much liquid without enough air, and the engine won’t run at all. That’s the purpose of the turbocharger on full-size engines….to cram in a lot more air than a simple carburetor or fuel injection system can handle.
Now…..suppose we were to find a way to run more liquid through our model engines without increasing the air supply? That would add power, wouldn’t it? Well, guess what….we can! An internal combustion engine can burn more than 2 ½ times as much nitromethane to a given volume of air than it can methanol. Voila! More Power! That’s how it works, and it ain’t all that complicated. Nor do we have to spend a lot of time thinking about it in the course of a normal day’s sport flying.
However, there are some factors we do need to consider. As a practical matter, virtually all our everyday sport flying can be done on model fuel containing from 5% to 15% nitromethane. If you’re flying something like a trainer or a Cub or similar model, there’s probably no reason why 5% won’t work perfectly well. Need a little more power? Move up to 10% or 15%. In most of our sport engines today, I really wouldn’t recommend going any higher than that. It probably won’t hurt anything, but it won’t do you much good, either.
We sell more 15% fuel than any other single blend, and for good reason. Most of the popular engines on the market today are built to run on something very near that blend. Typically, European engines will successfully run on lower nitro blends, because they are built to do so. Why? In Europe, nitro can cost between $150 to $200 a gallon! Reason enough?
Nitro does more than just add power. It also helps achieve a lower, more reliable idle. One good rule of thumb for checking to see if a particular engine needs a higher nitro blend is to start the engine, let it warm up for a few seconds, set throttle to full idle and remove the glow driver. If it drops rpm, move up to a 5% higher nitro blend. If there is no discernible drop, you should be fine right where you are.
One of the most popular misconceptions is that by adding substantial nitro, the user will immediately achieve a huge power jump. Just ain’t so. Most will be surprised to learn that in the 5% - 25% nitro range, you will probably only see an rpm increase of about 100 rpm static (sitting on the ground or on a test stand) for each 5% nitro increase. In the air, it will unload and achieve a greater increase, and it will probably idle better, too.
My pet rule is this: If you have a model that’s doing well, but just isn’t quite "there" powerwise, go up 5% in nitro. If that doesn’t do it, you need a bigger engine, not more nitro!
Most of our popular sport engines in use today aren’t set up to run on much more than 15% or 20% nitro. Increasing the nitro has the effect of increasing the compression ratio, and each specific engine has an optimum compression level. Exceed it and performance will probably suffer, not gain, and the engine will become much less "user friendly."
High performance racing engines, for example, are tuned entirely differently….compression ratio, intake and exhaust timing etc….and are usually intended to run on much higher nitro blends. One exception, of course, are racing engines used in certain international and world competition (FAI). By the rules, these engines are not allowed to use any nitro at all, and they go just as fast as those that run on 60 or 65%! The first question that comes to mind, then, is, "Why aren’t all engines designed to run on no nitro, so we can all save a lot of money?" Ask any of the world-class competitors. Those engines are a serious ***** to tune and run, and are definitely not user-friendly! In fact, they are well beyond the skill levels of most average flyers. There’s a price to everything.
Another statement we read or hear frequently is that nitromethane is acidic and causes corrosion in engines. It isn’t acidic, and the manufacturers say it doesn’t happen…..can’t happen. However, at least one noted engine expert and magazine writer insists that it does. Flip a coin. (I once asked Dave Shadel, 3-time World Pylon Champion, and a fellow who works on more high performance engines than anyone I know, how frequently he encounters rust in engines that have been using high nitro blends. His answer? "Never.")
Why does nitro cost so much? While I have no clue as to the cost of manufacturing, other than it takes a multi-million dollar investment in a large refinery to produce it, there is one pretty good reason: There is only one manufacturer of nitromethane in the Western Hemisphere. Figure it out for yourself.
Also (and this will come as a big surprise), our hobby industry only consumes about 5% of all the nitromethane produced; and full-size auto racing about another 5% or so. This means we have no "clout" whatever, and simply must pay the asking price. Where does the rest of it go? Industry. It’s used for a variety of things - a solvent for certain plastics, insecticides, explosives (yes, it was an ingredient in the Oklahoma City bombing) and I’m told it’s an ingredient in Tagamet, a well-known prescription ulcer medication (no wonderthat stuff is so expensive!). Please note that while nitromethane is aningredient in making some explosives, under normal use, it in itself, is not exploseve. (Remember….the guy used fertilizer, too.)
Hardly a month passes that someone doesn’t call to ask, "I hear more nitro will make my engine run cooler. Is that true?" Nope. The higher the nitro content, the higher the operating temperature. Fortunately, in most of our sport engines, the difference in operating temps between 5% and 10% is negligible, and there are lot of other factors (proper lubrication, etc.), that are much more important.
Finally, remember in the beginning of this, we said that nitro adds power because we can burn more of it than we can methanol, for a given volume of air? This also means that the higher the nitro content of the fuel, the less "mileage" (or flying time) we will get. In a typical .40 size engine using 15% nitro, we can usually get a minute to a minute and a half flying time for every ounce of fuel. The Formula 1 guys are lucky to get 2 minutes out of an 8 oz. tank!
What’s the practical side of this? If you go to a higher nitro blend, be sure to open your needle valve a few clicks and reset before you go flying. Otherwise, you’ll be too lean, and could hurt your engine. Conversely, if you drop to a lower nitro blend, you’ll have to crank ‘er in a little.

Firepower R/C

My Feedback: (10)

Great explanation propworm. I learned a lot! Thank you for taking the time to write this.

Propworn

My Feedback: (3)

I cannot take credit for this I made sure to credit the person who wrote it at the beginning of the post Don Nix

SrTelemaster150

Great explanation but for one thing. The dropping a match into a FULL cup of nitro doesn't really prove it is less volitile than gasoline as the same can be done W/gasoline in a well ventilated area under the right conditions. Gasoline itself will not burn unless it is mixed W/air (vaporized) & then the proper raito of air & gasoline is present. That's why an engine can "flood". It doesn't necessarily mean that there is a flood of liquid, but there is too much gasoline & not enough air present.

Now, if you drop the match into a partially filled container that will contain the vapors, then gasoline will ignite @ a much lower temperature than nitro.

Propworn

My Feedback: (3)

I think Mr. Nix as the founder and former owner of a well known fuel company has a better grasp on the subject than everyone here. My opinion is his explanation is more than adequate. You’re entitled to your opinion of course free world and all. What does it mater about dropping a match in gas or nitro it has nothing to do with how it performs in our engines which after all seems to be the crux of the discussion eh!!!!

Dennis

SrTelemaster150

Not disagreeing with his explanation at all, just the fact that a full cup was just not the best example.

2walla

My Feedback: (10)

I suspect most fuel manufacturers lie on the nitro content. I used to run 10% red max and gave a gallon to a friend that was out of 15% of his major name brand fuel. His motor picked up 700 rpm with the lesser nitro fuel. If you short the oil, people will notice, short the nitro, how would the average user know? The two most expensive things on glow fuel are oil and nitro pick something to short to increase profit...