Why Design an Engine to Use Nitro If It Is Not Necessary?
 

I understand that many 2 cycle model aircraft engines are designed to run without nitro and indeed run very well using no nitro fuel to wit Moki engines, for instance. That being the case, what is the reason that other manufacturers design engines that require nitro, which of course significantly drives up the cost of the fuel, in order for their engines to operate at their best? :eek:

RE: Why Design an Engine to Use Nitro If It Is Not Necessary?
 

More power. Nitro can be converted into gas without using the air that the methanol uses and thus more power per stroke, trouble is nitro will detonate if the compression is to high.

RE: Why Design an Engine to Use Nitro If It Is Not Necessary?
 

No manufacturer designs their engines specifically to use nitro. In fact, in many places, nitro is illegal. R/Cers in those areas use the same engines as we do and run no nitro. This is called FAI fuel. Due to the characteristics of nitro, most engines will run better and develop more power with a little nitro. Try some FAI fuel one day. Your engine may not develop as much power, and will probably have to be retuned, but it will run just fine.

Dr.1

RE: Why Design an Engine to Use Nitro If It Is Not Necessary?
 

this engine is designed to use nitro, it is a lower compression moki. http://www.davepatrickmodels.com/frame.htm

RE: Why Design an Engine to Use Nitro If It Is Not Necessary?
 

Some nitro in the mix will give you less sensitve needle settings and better starting in cold weather.... you will use more fuel and have shorter run times though.

Ernie

RE: Why Design an Engine to Use Nitro If It Is Not Necessary?
 

All engines will run quite happily with zero nitro but adding nitro to the fuel gives a little more power, can make the idle lower and makes tuning easier because the engine can handle a much wider air/fuel ratio. The only real reasons engines are made with a low enough compression to handle nitro is because the American market is huge and nitro happens to be very cheap there. The Moki mentioned before was only made because of a special request to suit the American market where the average modeller thinks nitro is a necessity.

Just to clear something up though, a fuel with zero nitro isn't necessarily an FAI fuel. FAI fuel is 20% pure castor and methanol and is only specified for a few FAI competitions. A fuel with zero nitro and 18% oil is not FAI fuel. Neither is any fuel with synthetics.

RE: Why Design an Engine to Use Nitro If It Is Not Necessary?
 

try a irvine engine (at least the REAL irvine engines...) they usually run max of 10% nitro, happiest at 5%, and ran great on fai fuel.

RE: Why Design an Engine to Use Nitro If It Is Not Necessary?
 

Nitro is not necessary and most engines are initially designed to run on a methano/Castor oil mix.

The Top-Fuel drag racing heritage in the USA and the relatively low cost of nitromethane make 15% nitro fuels the most popular.


Engines made in Europe (especially the east), where nitro and gold are just about liquid and solid states of the same stuff (at least from a cost perspective...), are designed to run on methanol, with a very high compression ratio.

They will not behave on 15% nitro and will perform less than perfectly, if the head is shimmed up.

Some engines (MVVS) are now designed, so performance will not to be significantly compromised by shimming the head.

Most Japanese engines (and their clones), as well as Webras destined to the USA, have larger combustion chambers than their European siblings, just so they could run on 15% nitro.
These engine will not have very good power, or reliability, on less than 5% nitro.

RE: Why Design an Engine to Use Nitro If It Is Not Necessary?
 

I run all my engines, 46 and smaller, on 25% nitro for the reliability, idle and cold weather performance. Worth the cost. By the way, havn't replaced a brg. yet, especially on the FPs.:D

RE: Why Design an Engine to Use Nitro If It Is Not Necessary?
 

I have run all my two stroke engines on Fox 5% nitro fuel with 20% 50/50 lube for about 10 years now, it doesn't matter if it's Fox, MDS, OPS, SuperTigre, Irvine or OS LA .46 and .65, they idle just as well. Anyway, it's more fun to just use a bigger engine if more grunt is required.

RE: Why Design an Engine to Use Nitro If It Is Not Necessary?
 

I run ONLY 0% nitro in my Moki 1.80 and Moki 2.10. They run awesome on the stuff, more power than with higher nitro since the engines are designed to run on 0% nitro. I have an Irvine 53 but never tried 0% nitro in it. One of these days I will.

RE: Why Design an Engine to Use Nitro If It Is Not Necessary?
 

Correct me if I am wrong, and I am sure you will;), but I believe nitro methane is just a cooling agent. This cooling property allows you to run a leaner mixture, thereby gaining more RPMs and power. The downside is higher exhaust pollutants, more noise and reduced engine life. For some people, the power gains are irresistible, while others just want to fly and have fun. Kind of like buying a YS over a comparable displacement OS or Saito.

RE: Why Design an Engine to Use Nitro If It Is Not Necessary?
 

Nitro is a power enhancer as it increases the amount of oxygen available in the fuel for combustion. The down side is that it generates more heat (often needs a lower combustion ratio) and CAN contribute to rusting of the engine internals (caused by the acidic by-products of the combustion).

The use of small amounts of nitro will help most engine run smoother, especially at idle.

Nitro methane will not increase rpm, but as it’s combustion produces more energy, the engine will develop more torque, allowing the use of bigger propellers, or better operation under high loads.

A classic example of this is R/C aerobatics where adding nitro to the fuel will give a big performance increase in vertical climbs.

Dar Zeelon is correct in his pointing out that in Europe, Nitro and Gold are of comparible price. So European manufactureres make their engines to run on very low or no nitro content fuels.

However, in the USA, where Nitro is relatively cheap, it is a common addative and in large % quantities. Most engine manufactureres making engines destined for the North American market (which is the largest in the world) realise this and therefore make engines destined for that market, compatible with high nitro content fuels. The same engine sold elsewere in the world, may have different compression ratio specifications to its North American market counterpart.

RE: Why Design an Engine to Use Nitro If It Is Not Necessary?
 

Most of what you've said is right -- but if you stop and think about it -- this bit is clearly wrong.

If you're producing more torque and aren't changing the load on the engine (propellor) then you *will* get more revs.

Indeed, because the effect of nitromethane is to slightly advance the ignition timnig of the engine, they tend to benefit from reving higher when run on increasingly higher percentages of nitro. In fact, the limiting factor that determines just how much nitro any given engine will handle is the point at which the ignition becomes so far advanced that detonation occurs. This is why engines designed for high nitro fuels have a lower compression ratio than those designed for straight or low nitro fuels. Reducing the compression ratio effectively retards the ignition, thus reducing the tendency to detonate.

RE: Why Design an Engine to Use Nitro If It Is Not Necessary?
 

I have heard this story before, I think they are refering to the maximum rpm the engine is capable of, will not increase. Obviously if the engine produces more power with the same size prop it will have to be spinning faster.

RE: Why Design an Engine to Use Nitro If It Is Not Necessary?
 

FP's are a bushed engine.[:-]

RE: Why Design an Engine to Use Nitro If It Is Not Necessary?
 

Nitromethane

Nitromethane is a chemical compound with chemical formula CH3NO2.

Applications

Nitromethane is a fuel that is used in racing, particularly in drag racing, to provide more power. When you hear the term "nitro-burning funny car" or "top-fuel dragster", that means that the engine burns nitromethane. Model aircraft fuel contains about 10% nitromethane.

Nitromethane's chemical formula is CH3NO2. For comparison, gasoline is typically C8H18. The oxygen in nitromethane's molecular structure means that nitromethane does not need as much atmospheric oxygen to burn -- part of the oxygen needed to burn nitromethane is carried in the fuel itself.

You need 14.6 kilograms of air to burn a kilogram of gasoline, and only 1.7 kilograms of air for the same amount of nitromethane to burn. A cylinder can only hold so much air on each stoke, and with that amount of air you can burn 8.7 times more nitromethane than gasoline. By pumping in 8.7 times as much nitromethane per stroke, you get about 2.4 times more power per stroke. Gasoline provides 18,000 BTU/pound (42 MJ/kg). Nitromethane provides 5,000 BTU/pound (12 MJ/kg). The amount of nitromethane also provides some cooling, making the charge a bit denser and increasing power.

The flamefront does not move as quickly in nitromethane as it does in gasoline, meaning that there is not enough time to burn all the nitromethane in the cylinder when the engine is running at high RPM. When the exhaust valve opens, burning nitromethane flows out through the exhaust pipe. That is why Funny Cars and dragsters "spit fire" from their exhaust pipes.

RE: Why Design an Engine to Use Nitro If It Is Not Necessary?
 

Mostly 4 stroke engines and small size engines need nitro to keep running. Some time we need nitro to improve idling in small engines. Sometime we need more nitro to keep the engine running in winter who some engines are using less nitro in summer.

Jens Eirik

RE: Why Design an Engine to Use Nitro If It Is Not Necessary?
 

I'm with you, Hobbsy.

I'd rather pay for a more powerful engine, than blow the money out the exhaust port, never to be seen again.

Nitro is for newbies. <G>

Ed Cregger

RE: Why Design an Engine to Use Nitro If It Is Not Necessary?
 

All the smaller engines I know of will not run happily on 0% nitromethane fuel at all [yeah yeah except diesels:)]. A Cox .010 for example runs like crap below about 25%. Most .049's require about 15% to run smoothly, and run better on 25-30%. Increasing compression ratio won't help much - small engines suffer from excessive heat loss relative to their displacement, and run much more happily with a dose of nitromethane. Fuel economy is also much less of a concern in the smaller displacements so nobody complains too much. I doubt that any level of compression ratio increase will make the little guys behave well, but if it can well then live and learn.

Nitromethane noticably improves idle and throttle response and the effect is most noticable as the displacement gets smaller. I wouldn't run a .15 for example on less than 15% out of personal preference. I run my "North American" spec .40's on 15%, .61's on 10%, 1.20's on 5%. Never bothered with less. Nearly every review I have read on a large displacement engine designed for 0% nitro indicates that the motor was happy on 5% and the throttle response and idle were improved. It also broadens workable needle settings somewhat as well, though in small doses as in normal sport fuels you won't see that too much. You will in high doses such as for racing applications.

It is no surprise to me that as displacement increases, the "need" for nitromethane in order to realize the handling benefits diminishes to the point where in the larger engines they are happy with none. But as mentioned elsewhere, to run "nicely" on low or nitro the compression ratio needs to be increased in comparison. It is also quite true that the larger engines, if set up in terms of compression ratio and cooling area to use nitromethane, can of course generate more horsepower than on no nitro fuel. But at considerable operating cost. And since they generally are not set up to run on appreciable amounts of nitromethane, they will get very cranky when you feed them some, overheating and detonating and what else. Hence descriptions of large engines running better and making more power on zero nitro fuel are accurate, in that they are set up for them.

Now if you want some fun, run tetranitromethane:D... apart from the high cost and it's nasty properties, the term "detonation" [preignition] when applied to engines will take on its more literal meaning.[X(]

So only newbies run nitromethane eh? I guess only newbies run small engines! ;)

RE: Why Design an Engine to Use Nitro If It Is Not Necessary?
 

Using nitromethane in model fuel makes carburetor adjustments less critical. This makes engine handling easier and setup simpler for those unaccustomed to running glow engines.

Finer threads on needle valves are necessary when running low or no nitro fuel. Hence, the recent trend toward coarser threads on such devices.

Part of nitro's popularity is simply because of its powerful sounding name. Notice the shift away from using the term glow engines, to that of nitro engines. It is a marketing ploy that appeals to the younger folks.

I am all in favor of using 5% or less total nitromethane in model fuel. It makes the engines much easier to start, handle and adjust for sport flying. More than that is not necessary.

No, I don't think nitro is evil. <G>

RE: Why Design an Engine to Use Nitro If It Is Not Necessary?
 

I'm with you Ed on the "nitro" marketing thing! Man, I was almost ill when the term "nitro" started to creep into model aviation from the car scene. Not the term "nitro" as a short form for nitromethane when discussing fuels, that's fine as it saves wear and tear on the oil' vocal cords. But as a term meaning "glow engine powered" - I absolutely hate that, makes it all seem cheap. What about "meth power" - at least it's more accurate.. though the connotations may be less than desirable to the lawyers.

Terms like "nitro plane" are for Neanderthals!

Mike D.

RE: Why Design an Engine to Use Nitro If It Is Not Necessary?
 

Well, I have to give you this one. You are right.

The thing is, I don't mess with tiny engines any longer - unless they are Diesel, so I tend to forget about them in these discussions. Thanks for the reminder.

Ed Cregger

RE: Why Design an Engine to Use Nitro If It Is Not Necessary?
 

For the most part I agree with you on the 1/2A size engines. However the 1/2A Texaco fliers commonly use 10% or even 15% in their .049s to gain longer engine runs on a limited amount of fuel (admittedly these engines are, at least for me a bit finicky as to needle settings.) These little engines use much lower compression than their high-reving cousins. Note: the greater fuel economy/leaner setting possible with low/no nitro is diametriacally opposed to some theories posed in this thread, #12, for example. Bear in mind, the methanol is the "fuer". Oil, nitro, etc are "additives".

As for "newbies" running small engines-nonsense, the small ones require far more expertise.

I will go on to say that, beyond a bit to reduce needle sensitivity, the benefits of "High Nitro" are over stated, and "Nitro Engine" is a misnomer. "Glow engine" is more correct. ("Meth Power" would not be, as ignition engines are often run on methanol, not to mention the drug conotations;)).

jess

RE: Why Design an Engine to Use Nitro If It Is Not Necessary?
 

Texaco is a specialized application. Power requirements are low, fuel economy and engine run duration are paramount. Nitromethane reduces fuel economy due to the progressively increasing stoichiometric ratio of fuel to air as the nitromethane content increases. Nitromethane is still a fuel by definition, as it has a negative oxygen balance. However it is considered an additive in glow engine fuel simply because the primary fuel is methanol.

The Texaco engines run extra cooling fins and lower compression to cope with the stresses and operating temperatures resulting from what is essentially gross overpropping, which 2 strokes hate as a rule, and yup are very fiddly on the needle valve as one would expect. The ill handling of engines set up this way is the price paid for optimizing fuel economy and run time. Not a nice way to treat a poor llittle .049!

So in terms of general use the comments about progressively higher nitromethane percentages for small engines are still quite true. They run better and are happier than larger displacement engines to run the higher percentages. Specialized applications are just that.

And the next time an ill-informed hobby store salesperson sells a buddy 5% or 10% fuel for their .049, or all-synthetic oil fuel, I'm going to... well.. do something! Happened more than once.

Oh yeah, I agree 100% - it takes a lot more skill to get those wee engines to behave. I have 7 .010's, I love 'em! Wish they were $5.99 too... [:o]

As to higher nitro, fine. But the right amount is certainly right, and the handling benefits of "some" are well known. The right amount varies a lot with displacement, and varies depending on engine design/setup within that parameter. Lots of nitomethane is good for specialized applications requiring maximum power - when you cannot use "cubes" for more horsepower due to displacement limits, then you need other help - either forced induction or different fuel. And more rpm of course :D.

And lower amounts to the limit of good handling are certainly sensible for most applications, for economy, longetivity, whatever else. With the big engines that is zero to 5% typically.