Why use nitro?

[Dallas Healey]

Until recently I just always used nitro in my stunt fuel because it seemed to be the thing to do. Then I started stuggling to try and get decent stunt runs out of two new ST51s and eventually resorted to 0% nitro fuel. I am now completely lost as to why I bothered using nitro in the first place. I now get a much nicer 4-2-4 break on my two LA46 & two ST51 models. The difference in run time is also amazing. On one model I was only getting a 5 1/2 minute engine run with 10% nitro. The next flight I used the 0% nitro fuel, found I had to lean the needle off about 1/4 turn, got a much nicer run and an extra 2 1/2 minutes from the same amount of fuel. I found no difficulty in starting the motors with no nitro either. Am I missing something here? Why do stunt flyers use nitro at all? Is it only useful where the power of the engine is marginal for the size/weight of the model? Should it only be considered when battling strong winds in competition? Can anybody out there actually explain the function of nitro methane in the fuel mix? Considering most stunt motors actually have an additional head shim, smaller venturi and often even a slight raising of the exhaust port to tame the power delivery, why do so many flyers use nitro in the fuel?

[Paul Smith]

I tried to run zero-nitro fuel in engines when I briefly dabbled in F2a.  I didn't like it.

Despite the high price of nitro in Europe, they still use 10% of it in F2d, basically 'cause getting a decent run without it is no fun. 
Can you live without, sure.  Fun? No.

Glowplug engines do not have all the spark adjustments of an ignition engine.  Therefore, jockeying the nitro is a good way to adjust timing.

[Circlejerk]

Given the average age of this group, chest pain comes to mind!

[Bradley Walker]

You don't need nitro.

The Retro/Shark just won the Nats and got second in the Team trials, and it runs on 0% nitro.

I saw the Yatsenko brothers fly all week in the WC's in 2004.  They never changed props, fuel, or even touched the needle that I remember.  I personally saw them go from 2 MPH winds to 25 MPH winds and NEVER changed one single element of their system (and put in some kick butt patterns at slow speeds too).

It does not surprise me that the ST 51 performs better on 0% nitro.  It is over compressed for nitro fuel in my opinion.  The first thing I would do if I had one would be to decompress the head to get a deeper 4-2 Break.

[Randy Powell]

Brad,

I think you just proved Ty's point. Some engines are designed to use nitro. Some aren't. Best to match the fuel to the engine design and conditions. Were I running a Retro, I'd use fuel with no nitro because that's what's it's designed for. I would also note that the Shark/Retro combination, while obviously a very good setup, didn't win anything. Orestes Hernandez did. A minor quibble.

[Bradley Walker]

I would also note that the Shark/Retro combination, while obviously a very good setup, didn't win anything. Orestes Hernandez did. A minor quibble.

How about this.

Orestes just won the Nats flying a 0% nitro setup.

Better?

[Ron King]

why do so many flyers use nitro in the fuel?

Ty gave you the layman's chemical view - basically nitro promotes ignition and provides a TON of power when it ignites. I generally check with the local airport and get a Density Altitude reading before I decide what fuel to run. This is the actual air density the engine sucks in when it's running. If the DA is up there, I need a little more nitro.

The reason I use a little nitro in my fuel is it also broadens your needle valve range. When I was racing and we were using 0 percent nitro (FAI fuel), the needle valve was very sensitive and would go from too rich to too lean too fast.    We found that a little nitro (about 3 percent) gave us a much better needle response and saved a lot of engines. So we only used the FAI fuel when required by rule.

My .02,

Ron

[Brian Hampton]

My first post in this forum and on a subject I got slammed for maybe a year or so ago elsewhere . I'm from Australia where we're quite used to using little if any nitro and it's something I've never used so I can't say what real difference, if any, it makes. However I've never had any problem getting any engine (RC or CL) to run perfectly. Now I know that "perfect" can mean different things to different people but to me that means instant starts every time, consistent settings flight to flight and all the power the model requires with the type of run I like which happens to be a continuous 4 stroke. This is what my G51 does better than any other engine I've ever had, including my Stalker 61, and in a model that could hardly be considered to be small although reasonably light at 58 ounces. My only other "modern" stunt engines are the VF40 and Irvine 40RLS (if you think the VF is good you should try the Irvine...wow!) and both are faultless on zero nitro.

There's one thing to consider though when using zero nitro and that's to make sure there's enough oil in the mix. Because of the lower fuel consumption this means a proportionately lower flow of oil through the engine. My G51 only uses 60cc (about 3.5 ounces) of fuel for <6 minutes FAI flight and needs around 25% oil to avoid overheating.

[Bradley Walker]

Hi Brian,

Very interesting.  I would really like to know what propeller you are using.

Nothing you said in your post really surprises me BTW.

[Bill Little]

HI Brad,

Since most of the World uses "no nitro" FAI fuel, we know that it can and does work.  And we know that at the Worlds Stunt is relieved of the "no nitro" rule.

But, as we also know, us Americans like to play with engines when it comes to CLPA.  So much so that some even ruin them, or NEVER get them to run right! 

The key, to me, is to use a proven set up, and gain the experience that makes it work.  Sometimes it takes years of running stunt engines to eeven know what a pilot likes in his engine runs.  As has been said many, many times, a whole lot of pilots have never experienced a real stunt run.  It was an eye opening experience when I did, and have experienced what an engine run can do for your flying.

[Brian Hampton]

Hi Brad
I use a stock standard 12x5 Zinger wood which happened to suit the engine/model/my preferred way of flying so well I've never even bothered experimenting with anything else. I mentioned the model wasn't exactly small and at 830 sq inches I guess it isn't but the ST dragged it around like there was nothing there. The only complaint I have with the ST is that the in-flight revs bear no relationship to on-ground settings so some trial and error flights were needed to crack the tune. The Stalker OTOH, what you set on the ground is precisely what you get in flight.

If I can go on a bit more about zero nitro, compression has no affect on ease of starting. During my initial "trying to figure out the run-away problem" I tried many different compressions all the way down to 6:1 (not with the original cylinder head of course) and even then it'd start first flick as usual. I still had the run-away but power in both 4 and 2 stroking was way down.