fs 70 on 30%

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fs 70 on 30% - 9/7/2006 1:25:21 PM

captainpitts-RCU

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From: fairmont, WV, USA
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I have an os 70 surpass and I was wondering will it handle 30 heli fuel o.k.? I have ran it in saitos and y.s. engines but am curious about o.s. I have a couple of gallons sitting around and would like to use them.

thanks

Post #: 1

RE: fs 70 on 30% - 9/7/2006 1:41:56 PM

DarZeelon

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From: Rosh-Ha'Ayin, ISRAEL
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Steve,

According to the Tower web page for this engine, the maximum allowable nitro percentage is 20%.

Unless you can shim up the head, stay with that percentage. You will only see about 100-200 RPM boost, if you do shim up the head and run 30%, so it is not worth the trouble (or the much greater cost of the fuel and more of it).

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Post #: 2

RE: fs 70 on 30% - 9/7/2006 1:47:39 PM

captainpitts-RCU

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From: fairmont, WV, USA
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thanks just had a couple of gallons sitting there and thought about using it but I'll stick with the 15%

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Post #: 3

RE: fs 70 on 30% - 9/7/2006 10:44:00 PM

alan0899

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From: Cundletown, NSW, AUSTRALIA
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G'day Mate,
Just add some methanol & some oil, & bring the mix down to 20%. you should be able to work out how much you will need to add.

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Post #: 4

RE: fs 70 on 30% - 9/12/2006 4:30:07 AM

John Patterson

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From: , TX, USA
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I am just getting back into flying now that my son is attending college out of state. Most of the guys I fly with are using a 30% nitro/24% syn oil fuel for their four strokes, both OS and Saito, all .90 or bigger. Suprises me that they can get away with that much nitro on stock engines without adding any shims. We are at 700' elevation if that makes much difference.

I have two OS 4 strokes I flew with back 20 years ago, an FS.61 and an FS.90. Looks like the 61 is fine, just pulled backplate off to check bearing and its still clean so I plan to start running it again soon. My .90 has about 500 hours on it and I would have to de-carbon the head every 100 hours or so to prevent it from pre-detonating and throwing the prop off. Back when I flew these engines we used a 10 or 15% nitro with castor oil which probably contributed to the carbon build-up. According to the guys using the 30% nitro/syn oil, they don't have any problems with carbon buildup.

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Post #: 5

RE: fs 70 on 30% - 9/12/2006 5:52:17 AM

DarZeelon

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quote:

ORIGINAL: John Patterson

...Most of the guys I fly with are using a 30%
...According to the guys using the 30% nitro/syn oil, they don't have any problems with carbon buildup.

John,

The reason those guys have no carbon build-up problems has nothing to do with the 30% nitro.
Your engine neither needs it, nor is it optimized to run on it.

You would not believe how much richer your engine must be run with 30% nitro, compared with 15%, just to prevent detonation.
OS tells you to use up to 15%, because it cannot be optimized to run at an ideal mixture setting; not because it cannot possibly run at all on 30%.

The guys at your club are doing a foolish thing by using only 30% and actually doubling their fuel bill, with no benefits whatsoever. Using 15% all synthetic will keep their engines just as clean and since 30% must be run very rich; 15% run much leaner (earlier ignition) will give about as much power too.

The only engines that actually benefit (power-wise) from 30% nitro, are the YS four-strokes.
Saitos more or less peak at 20%.

I do recommend some castor oil for added protection, but if you are careful, all except the ABN OS.70FL, can safely use fuel with all synthetic lubricant.

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Post #: 6

RE: fs 70 on 30% - 9/12/2006 6:39:40 AM

Rcpilot

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From: Arvada, CO, USA
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quote:

ORIGINAL: captainpitts-RCU

I have an os 70 surpass and I was wondering will it handle 30 heli fuel o.k.? I have ran it in saitos and y.s. engines but am curious about o.s. I have a couple of gallons sitting around and would like to use them.

thanks

Split it 50/50 with some 5% or 10% fuel.

Dump half of it into a half jug of 5% or 10%. Dump half the 5% or 10% back into the heli fuel jug. Now ya got 2 gallons of something else. Don't ask me to do the math for ya. I'll run out of fingers before I figure it out.

But, it will be better on your motor.

Or do like alan0899 said and dilute it with more methanol and oil. Turn it into 1.5 gallons of fuel at 15% or something like that. I can't find methanol around here.

Or, buy some FAI 0% fuel and dilute it with that.

Good luck.

< Message edited by Rcpilet -- 9/12/2006 6:42:13 AM >

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Post #: 7

RE: fs 70 on 30% - 9/12/2006 12:40:34 PM

Harry Lagman

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Captain, just try the 30% and report back your findings.

The subject of nitro percentage brings up all sorts of myths about which engines will benefit from nitro and which engines don't.

I've tried OS four-strokes out on higher nitro and they respond just like any other modern four-stroke. My OS .91 S2 loves running on 20/20. I have tried it on 30% nitro. It has never, ever detonated or thrown a prop and it happily yields about 100 more rpm (approximately 3% more power) per 5% nitro used.

If you get 2-300 more rpm out of your FS .70, that could equate to approximately 5-10% more power. If that's important to you , you'll likely continue to use that level of nitro.

In any case, just try it. You'll be amazed at the myths you can bust when you try stuff.

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Post #: 8

RE: fs 70 on 30% - 9/12/2006 1:20:31 PM

DarZeelon

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quote:

ORIGINAL: Harry Lagman

In any case, just try it. You'll be amazed at the myths you can bust when you try stuff.

Grant,

Those who regard uncomfortable facts as myths are the same drag-racing people, who blow their engines up, trying to run more and more nitromethane mono-propellant, from a hydraulic lock...

With fuel recommendations, there is always a good reason for the manufacturer to make them and also for the users to follow them.

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Post #: 9

RE: fs 70 on 30% - 9/12/2006 1:29:35 PM

Hobbsy

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Dar, has seen me write this before, you'd be amazed at how smoothly a Saito runs on 5% nitro, there is no such thing as a Saito (needing) 20% or 30% to run correctly.

< Message edited by Hobbsy -- 9/12/2006 1:30:40 PM >

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Post #: 10

RE: fs 70 on 30% - 9/12/2006 1:43:23 PM

DarZeelon

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Dave,

I know it does and never wrote it needed 20%, or 30%.

I just wrote that it can be adjusted to run ~optimized, unlike the OS that must be set overly rich, to prevent detonation.

Saito has reduced compression, so as not to re-encounter the case of those (past thankfully) detonating, prop throwing .82s, but not to the point of transforming their engines into 'nitro hogs'.

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Post #: 11

RE: fs 70 on 30% - 9/12/2006 5:06:31 PM

loughbd

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From: Bremerton, WA, USA
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I will never understand why half the world thinks you need 30% nitro in ANY sport engine. After 30 years of running four cycle engines I'm convinced that any more than 10 to 15% is a waste of money. The ONLY engine that I have run that seems to like even 20% is my YS120NC and even it will run resonably well on 10%. NONE of manufacturers recommend anywhere near 30% in their instructions. Most recommend 10 to 15% with at least 18% oil.

The only time I ever used more than 20% nitromethane was when I was racing boats and and control line speed. I used as much as 60% then but in boats found out that you could make up any speed loss from using lower nitro by improving your driving skill. In control line speed idling was was not a factor. The engine ran full blast for about two minutes. Went through a plug a flight and the engines didn't last very long. Broken rods and cranks were a way of life. Did that foolishness for about 6 years. You ought to hear a McCoy 60 turning 22,000 rpm touch the ground and loose both prop blades. It sounds like this, RRRRRRRRPPPPP! I bet they turn 40 grand before they let go. Nothing you can do until the plane which was going 170mph finally coasts to a stop. By then you need a new engine.

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Post #: 12

RE: fs 70 on 30% - 9/12/2006 5:14:00 PM

Hobbsy

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From: Colonial Beach, VA, USA
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I was agreeing 100% with you Dar, I just ran my Saito 1.00 on 5% Fox fuel with 20% castor.

Saito 1.00
Prop==Graupner 14x7
RPM==9.300 give or take a few, picture no good.
Plug==Fox Miracle
Idle== awesome at 1,825, rock steady.
Amazingly, no smoke at full song.

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Post #: 13

RE: fs 70 on 30% - 9/12/2006 5:43:14 PM

Sport_Pilot

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From: Acworth, GA, USA
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Actually since he lives in mountanious West Virginia, 30 percent nitro is probably a good idea. The thin air will prevent detonation and because of that he will see more gain than just 200 RPM. The engine may run smoother and cooler as well. Just use a colder plug, such as a K&B 4S plug.

They use 30% nitro with good effect on the OS .91 FS with good effect, this without the thinner air at altitude. I suspect it is hard to get good nitro overseas. Maybe the bulk of it is replaced with nitropropane and nitrobenzene?

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Post #: 14

RE: fs 70 on 30% - 9/12/2006 5:46:28 PM

Sport_Pilot

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quote:

Those who regard uncomfortable facts as myths are the same drag-racing people, who blow their engines up, trying to run more and more nitromethane mono-propellant, from a hydraulic lock...

Maybe, but it like, is Cowabunga fun!

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