OS 4 stroke 20% nitro.

[Mike Watters]

Quick question for the engine experts. 

Would running OS 4 strokes on 20% nitro be too much for these engines and lead to failure / damage. 

The instructions say up to 5-15% nitro.

The reason why I ask is, I fly with the YS 4 strokes also, which I run on 20/20 fuel. 

If possible I didn't want to keep lumping two fuel bottles to the field with varying nitro content, if one fuel would run all my engines, that would make things easier. 

The OS 4 strokes I'm running are 26, 40 & 70 engines. 

Thanks 

 

[Paul De Tourtoulon]

I run all my four strokes on 10% nitro but I don't have any YS engines, won't it run on 10% that would be cheaper,,,

[Jon H]

YS are a special case and are designed for high nitro. Your OS engines are not and you may run into trouble. 

 

For normal flying of normal engines just use 5% nitro with 15% synthetic oil. I use this mix on my OS, Saito and Enya 4 strokes and they all perform perfectly. 

[john stones 1 - Moderator]

I ran mine on Coolpower 30% ? Never broke one and they got flown a lot, wouldn't trouble me personally.

[Mike Watters]

Paul, no 15 - 30% nitro for the YS 4 strokes.

 

Jon, thanks I'll go with your recommendation and stick with taking two fuels to the field. 

 

Cheers. 

[Mike Watters]

1 minute ago, john stones 1 - Moderator said:

I ran mine on Coolpower 30% ? Never broke one and they got flown a lot, wouldn't trouble me personally.

Interesting John. I read somewhere running motors on higher nitro in hot weather made them run cooler. I can't remember if this was for 2 or 4 strokes. That's what got me thinking about using higher nitro. 

[john stones 1 - Moderator]

Can only speak from my own experience Mike, mine ran well and never broke, all O.S n Y.S.

[Mike Watters]

OK, thanks John. 

[Jon H]

The addition of high nitro into an engine that is not tuned to take advantage of it will not offer many advantages. Even in engines that can take advantage of it and provide more power there are substantial disadvantages to consider like significantly increased fuel consumption, increased fuel cost, and increased chance of corrosion in the engine. Some engines may also knock and Enya supply head shims with their engines to cover this. 

 

The cooling advantage of high nitro is not really a factor in most fixed wing engines. Model cars, helicopters and (in the old days) ducted fan engines have very limited access to cooling air and so the high nitro fuel is a cooling advantage here. The only reason high nitro fuel runs cooler is because you run a richer mix with higher nitro and the methanol in the fuel is used a coolant (spill some on your hand and you will see why) in the engine to keep the temperature down. The snag is you do not burn all of the methanol and so things tend to go rusty. Also in a 4 stroke the cooling effect is only felt on the combustion chamber and not the whole engine as in a 2 stroke used in helis/cars/DF models

 

In the case of fixed wing with better cooling lower engine temperature can be a disadvantage as you need heat in the glow plug to keep the engine running reliably. The oils in the fuel also operate better at higher temperatures and the engine too is designed to operate at a given temperature (90-120'c ish) so running it cold will not do it any good. 

 

I am yet to find any performance related justification for using more than 5% nitro in standard fixed wing engines. That isnt to say 10 or 20% will do the engine any specific harm, its just that you are unlikely to see any meaningful advantage either while bearing an increased running cost. 

[Don Fry]

Jon, query.

Paragraph 2, last sentence, justification please.

[Mike Watters]

Very interesting Jon. Thanks for explaining the high nitro therory. 

[Jon H]

errr, you mean the bit about the combustion chamber? Pretty simple really as 2 strokes have fuel all over the place but 4 strokes do not so the cooling advantage is much lower. 4 strokes also have a cool down between ignition strokes but 2s do not. Overheated 2 strokes in the applications i mentioned tend to blow holes in their pistons as there is always a heat concentration right under the plug. Cooling the bottom of the piston crown with the crankcase fuel charge is a good way to prevent this. 

 

Again though, its most apparent in things like helicopters as the cooling is poor. You wont be doing any harm in a acrowot. 

 

[Andy Stephenson]

I recently completely stripped and serviced my YS63FS and I found after having run it on 30% Nitro (when it was legal) and also I should add let it stand since it last ran a few years ago, there was absolutely no sign of rust at all. In fact the parts looked new. This leads me to believe that the materials used must be some kind of stainless steel that resists nitro and methanol remnants. I guess it's not worth the extra cost to the manufacturer of using stainless materials on their engines if they are not expecting them to be run on such hot fuels.

[Jason Channing]

I use 20% nitro in my OS four strokes with no issues what so ever , very noticeable increase in power over the 5% and I've also used the 30% that is used in my YS  as well when I've forgotten the other fuel container and the difference is even better , the difference between 5 and 20 is the ability for the old Quaker Flash to climb out vertically ?

[Engine Doctor]

YS engines are built specifically for use with high nitro fuel. Unlike normal fourstrokes a YS takes a charge of fuel air mixture into the crankcase and that is then pushed into the cylinder on the intake stroke like a supercharger. So internals are continually washed with fresh fuel that clears away any burnt blow-by residue and acids from combustion that may find its way past the piston. Any residual fuel left in the case is sealed from atmosphere far better than any two stroke or ordinary four-stroke ( no c/case breather for atmosphere to get in) so water absorption and resulting rust is unlikely and relatively rare. I still run them dry when hot to clear any fuel residue.

I've only had to rebuild one YS 140 bought cheaply on ebay due to rusty bearings and obviously Ben left full of old fuel. Fortunately it was salvagable. Bearings tend to wear out after many hours of use rather than rust like normal aspirated fourstrokes and two strokes.

I use the same fuel in most of my engines but, always a but, as John says Enyas don't like it and can and often do throw a prop unless the head is shimmed to reduce compression  so keep some lower nitro fuel for those. Also many Enya 4c engines especially the older models don't have a lock nut to lock the prop on in case of pre ignition. Only benefits is not having to carry two types of fuel . Ive noticed no meaningful power gain from using high nitro in other fourstrokes as John says  just higher fuel consumption and cost.  

Edited December 12, 2021 by Engine Doctor

[Gary Manuel]

I had a model with a Saito 82 fitted and it used to run beautifully on Bekra 10. My local model shop is not brilliant at keeping stock of fuel and on one occasion I had to settle for Bekra 5. The model overheated and the engine cut every time I tried flying it. Switched back to a 10% fuel and the engine started behaving again.

This has nothing to do with 20% fuel, but does prove (to me at least) that higher nitro fuel can lead to cooler running.

[Jon H]

I was going to mention the YS's sealed crankcases but you beat me to it ED! 

 

One thing is for sure, with all you blokes using such high nitro fuel i can see why there are so many tears before bedtime regarding the running costs vs petrol. It must cost you all a fortune!

 

A chap at my club asked me to test fly his saito 150 powered P47. He had a 16oz tank and 16% nitro fuel. I knew it would chew through the fuel quite fast, but i was not prepared for it to demolish all 16oz in 3 minutes. 3 minutes! This left me with a dead stick while on a low fast pass the wrong way down the runway. Gear up in the field was the only option available and damage was light. In any case, no amount of extra power is worth that sort of fuel consumption and to be honest, the power wasnt even there. 16x8 apc @ around 8600rpm which was barely above the 8400 i used to get on my saito 150 when i used 5% SMC fuel. You would get the same 8600rpm performance from an OS or Laser 155 on 5% nitro and with 16oz of fuel aboard both would fly at least 10 minutes and i suspect the laser would run for near 20 if i was nice to it.

 

This conversation actually reminds me of one being had years ago on another forum regarding the saito 450r3. I had one and was getting more or less the same revs on 5% nitro as the american guys were on 20+ and running permanent glow to keep the thing alive. The 450r3 was a thirsty beast even on 5% but these chaps were chewing up almost a litre of fuel in about 5 minutes on 20%. It was mad! 

 

 

[Martin McIntosh]

I have a couple of OS 26`s which I needed to turn larger props so added a head shim to each and ran them on YS mix. The result is that they will now turn a 12x5 at respectable revs and a 4oz tank is still adequate.

[Jason Channing]

I can get my engines to run past 50 minutes if i dont use the throttle and use idle. ?

 

[Jason Channing]

Everyone to their own, me personally I would never touch ML70 through any of my engines and I stick to Optifuel and the fact remains, that in practical flying the difference is quite noticeable when  changing over to higher nitro , the flight time may go down a small bit but nothing noticeable to me as I have a timer set to 7 minutes ,one or two clicks on the needle between summer and winter and reliability is set other than changing the glow plug once the idles starts to hunt.

[Jon H]

Nowt wrong with ML70. Gets a bit gloopy when cold but other than that there is no issue with its performance. 

 

As for the facts, they do not support your statement on power output increasing with nitro. Not all engines will perform better and if they do, the increase is often not worth the cost. 

 

As for glow plugs, if you used less nitro they would last longer. Some of mine are nearly a decade old and still working fine. 

[Scott Edwards 2]

46 minutes ago, Jon - Laser Engines said:

As for glow plugs, if you used less nitro they would last longer. Some of mine are nearly a decade old and still working fine. 

 

A decade ! Streuth. Round here we class that as nearly new. I've had the same Super Tigre Orange plug in a Laser 70 since 1995, it's been thrashed to blazes in about 10 hack models since then. I dread to think how many hours it's got on it ?

[Martin McIntosh]

YS recommend a new plug every 20 tanks. At today`s prices, ouch. Thankfully that is not the case.

[john stones 1 - Moderator]

I've had same wife since 1975, glo plugs, childs play. ?

[Jesus Cardin]

I ruined my vintage OS 40FS using by error a 16% Modeltechnics fuel, so I personally do not recommend going over 10% on OS Engines.......