Like most Americans, my exposure to running engines without nitromethane is limited...tho I have done it. Letsee...ST G.15, Taipan 2.5 rear exhaust, Cox Conquest, and Rossi 2.5's. F1C was the game. I noticed that head shimming was much more critical, too big a venturi was very touchy on the NV, etc. Pre-Ignition can be a problem...glowplug choice will be more critical. Starting should be better. When I flew A, B, C and B proto speed, I found that the engine would love more compression with more nitro, limited mostly be the strength of the piston crown! I got the ST G.21 .29rv pretty well figured out...cut the squishband and gasket seat .040", bolt it on, dump in 75% nitro/20% UCON oil and 5% Propylene Oxide, and you'd get a nice power boost, if the P&L fit well. That much nitro without the PO would be very difficult start.

So, I'm wondering how some typical stunt engines might run on zero nitro fuels. I'm thinking that the Magnum XLS .36 might be real good, maybe even stock. And the .40LA-S might be better on zero nitro than on the 10% pop that we typically feed them. Something like the PA's and .40/.46VF's might just like it fine?

What I'm hoping for, is that somebody might have some experience to share (or time to experiment) with zero nitro fuel for stunt, in mainstream engines, just in case we're forced to burn 80/20 corn squeezin's and soybean oil....  LL~Steve

Alan,

Just pour it in anyplace---the result will be the same!!

Cheers,
Jim

I guess I can answer that about "mainstream" engines because I've never used nitro in the last 50 years...well, once in a K&B .15 but that was for a rat race competition.

Early days for stunt was with a Merco 35 then an Enya 45 model 6001 at 25% all castor. For later engines I've used zero nitro with a 40VF, Irvine 40RLS, ST G51 and Stalker 61. All except the ST used 20% castor, the ST uses 25% castor because it's extremely economical and needs the extra oil for enough oil flow. All engines are stock standard other than a CF Bolly Supermuffler on the ST and a normal venturi on the Irvine instead of the supplied Irvine venturi. Just for interest's sake, my Irvine is the one used in a report by Derek Pickard in the June '96 issue of Aeromodeller magazine.

All of them start with one flick (the VF though only once it's been warmed up) and none of them show any lack of power. The G51 in fact has far too much power if it broke into a full 2 stroke as it did in the beginning. That was with a model weighing 59 ounces and 830 sq inch of wing so it wasn't exactly small. Tamed into a continuous 4 stroke (by adding the extra oil) it hauled it around effortlessly. I've never found any difficulty in setting the needle valve but of course any possible sensitivity is quite normal to me.

I think it's a issue of compression. I ran a Stalker 61RE for a couple of years. the thing was finicky as heck on 10% nitro. I lowered the compression in steps using head gaskets until it settled down. Later, I went to some FAI fuel. This particular mix was 18% all synthetic with methanol and a bit of propylene oxide. Put it back into stock configuration (read, took at the 4 or 5 head gaskets that I had stuck in the thing) and it ran just fine again. Pretty high compression compared to what I was used to, but the engine ran really well. I couldn't tell much difference in power between the two setups.

Orestes Hernandez uses no-nitro fuel. 

"Since stock FP.40s are famous for running away on standard stunt fuel, and decompressing is one solution, I wonder if running one stock on no nitro would cure that tendency without the need for engine mods.  Has anyone tried that experiment already?"

Not a bad idea at all. I don't have any FP .40's, but have a bagfull of Tower .40's. I guess that'd work. Hmmmm.
Don't everybody try it!  Steve

 One thing good to know, if you raise the compression in order to compensate lack of nitro, is that differend oils behave in differend manner in high temperature and pressure. Some synthetics do not work well as they start burning at lower temperatures. That can  cause detonation. Also, engines (like Retro Discovery) that are designed to be operated with FAI fuel usually have a very tight piston fitting in tdc. Many synthetics fail in the high surface pressure.
 If you do experiments with such, it's recommended to start with castor oil only and then test with synthetics to learn the possible difference.
 Because of carbon buildup I fly with 15%/5% castor/synthetic mix when I practise and when there is no risk of speeding up but prefer all-castor in contests. Many people use Retro's with more synthetic, at least Micro Motul and Carbulin brand synthetics seem to work ok.
 Just a few thoughts.. LM

Steve,
In this business, sometimes a little actual experimentation can be worth more than a lot of theorizing.  Last time I saw Eliott Scott start the Rustler-Merco .61 on FAI fuel, it didn't strike me as having an especially noticeable pinch, and engine runs don't get much nicer than that one on a muffler.   

Since you have the Tower .40s on hand, why not give it a try with one of them, and see what happens?  Nothing to lose.  If it doesn't like a vegetarian diet, toss it some meat!!   

Kim

 Steve,

 The Micro Motul is manufactured in France, propably Carbulin too. Carbulin is a very old oil and I think that the only good thing about it is that it's burning properties are similar to Castor's. I don't think it's a very good lubricant if you compare it to modern oils like Klotz, Aerosave or Motul. Try www.motul.com
 You don't necessarily need to hear the "Sqeek" in tdc. In my best Retro's I can hear it when there is Synthetic oil in the mix. With all-castor it feels more normal.