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OS SF 61 + pipe

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Old 09-05-2016, 04:35 AM
  #1
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Default OS SF 61 + pipe

I bought this 80s pattern motor from a popular auction site in very clean, used condition. It's an old engine but nice. This is the regular (non-pumped) "ABC" version.

APC 12x10, 5% nitro, Enya #3, Novarossi 50400 pipe at about 18" plug to baffle (header is 6").

10,300

Any shorter on the pipe and she wasn't having it, so that RPM was it. I've seen a couple hundred more RPM quoted when a bit more nitro is used. Super easy to handle when the carb was set up - prime, plug on, couple of flicks and go. And great throttle response.

Note Novarossi pipe is very similar to Hatori 700.

Correction: header is 6 3/4"

Last edited by SuperNash; 09-06-2016 at 01:48 PM.
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Old 09-11-2016, 11:45 PM
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Did a couple of baseline runs on the standard silencer

APC 12x6, 11400
APC 13x6, 10500

Consistently about 500rpm short of where this motor should be.

I checked my RF 61 and that was also a few hundred RPM down. Fuel is the only common factor there, so I'm going to replace my (very old) fuel and retry.
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Old 09-12-2016, 06:39 AM
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Don't forget that if it seems like the pipe is too short on the ground, that it will unload a lot in the air, and likely be on the pipe. This will be even more pronounced with the high 10" pitch prop. It will need to be more rich than you may think too, as it comes on the pipe. This is just general practice, YRMV
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Old 09-12-2016, 08:31 AM
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FWIW, Dub Jett has said in regard to his engines that they need to be launched very rich on the ground because once unloaded and really on the pipe, they really need the extra fuel. So rich in fact that you may think the plane won't even fly. This is of course in regard to the LX piped sport engines and up to the race engines too.

For piped engines, one must regard the head clearance and glow plugs too. Read the plug after a good run. If you pop plugs often, the fuel mixture is probably too lean. The base of the plug should be clean to brown and element still shiny when the engine is on the pipe.

Also FWIW, if the pipe is too short on the ground, it will be way too short in the air I believe. As I understand it, you don't want the engine on the pipe on the ground.
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Old 09-12-2016, 09:51 AM
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That is accurate, except for being too short on the ground. It will catch up when unloaded. On the FAI speed planes, we had to whip them up to speed to get them to unload enough to be on the (short) pipe in the air. I has to do with the wavelength of sound/rpm which are the same ideally. If you blow plugs it could very likely be too lean, but a piped motor needs less compression than an unpiped one. normally. Interesting enough the wavelength can be halved or doubled to make the motor happy. It will like to be resonating at, say, 15,000 rpm, 7,500 rpm, or 30,000 rpm. Listen to an F2A speed plane from a Youtube video start on the ground and it will be about half the rpm of the air rpm after it is up to speed. Most likely it will be 20,000 on the ground and 40,000 in the air. One octave higher. Maybe a musical "E". https://www.youtube.com/watch?v=4vAw1CC4A3g

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Old 09-12-2016, 10:49 AM
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I read from a former F3B guy mention awhile back that a pipe that's too short on the ground is too short in the air with the reason being it will be staged or even on the pipe at launch and be over staged (not sure what the proper term would be here..) in the air.
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Old 09-12-2016, 04:22 PM
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If it is on the pipe on the ground, then the pipe will hold it back in the air, not letting it rev much higher than what the pipe is set at. If the pipe is way too short, then it may never get on the pipe even in the air though. A smaller prop is sometimes used to get the air rpm matched on the ground and then the larger flying prop put on to fly. A higher pitch prop can unload 3,000 rpm in the air . .which would make the pipe want to be shorter than if it was peaked on the ground..If the pipe is shorter yet, then a dive would bring it on to the pipe, maybe getting much over the 3,000 rpm. Of course if throttled down, it would have to start over. Experimenting is a good thing, and the only way.Trimming prop tips etc. Isn't F3B winch gliders?

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Old 09-12-2016, 07:34 PM
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I don't know what F3B is, but the guy I knows his stuff - he flies in IMAC contests I think. I'd have to double check that he said it - it might have been on RCG where I'd seen it mentioned recently.

FWIW to the OP, I ran an old used FP .60 with a 60c carb and Jett tuned muffler on a 12x6 APC and got 12,600 peak on 10% nitro 20% castor fuel. I'd be curious to see what an SF would do with a Jett muffler. If I can fab up an adapter, I'll tach my .60FSR on the Jett muffler and 7B carb. I ixnayed the pump and Perry carb.
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Old 09-12-2016, 10:27 PM
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F3B is a glider class - do you mean F3A? That's the pattern aeros.

Quote:
F2A speed plane
Those things are on another planet

Quote:
a pipe that's too short on the ground is too short in the air with the reason being it will be staged or even on the pipe at launch and be over staged (not sure what the proper term would be here..) in the air.
For this kind of motor that sounds good. It's got to be able to come on pipe at any time when the throttle is opened - you can't rely on unloading. In the contest aero classes, you're looking for engine braking on downlines; it's a "constant speed" flight. Diving to get on the pipe would hold no value, it's got to be on the pipe when pulling vertical - slow speed, maximum load.

Quote:
old used FP .60 with a 60c carb and Jett tuned muffler on a 12x6 APC and got 12,600 peak on 10% nitro 20% castor fuel
That sounds like a good result from an FP. How much does the Jett add?

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Old 09-13-2016, 03:21 AM
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Quote:
Originally Posted by SuperNash View Post
F3B is a glider class - do you mean F3A? That's the pattern aeros.



Those things are on another planet



For this kind of motor that sounds good. It's got to be able to come on pipe at any time when the throttle is opened - you can't rely on unloading. In the contest aero classes, you're looking for engine braking on downlines; it's a "constant speed" flight. Diving to get on the pipe would hold no value, it's got to be on the pipe when pulling vertical - slow speed, maximum load.



That sounds like a good result from an FP. How much does the Jett add?
I never ran the FP on the stock muffler, so I don't know. It seems as though the FP .60s I've seen run on YouTube and tached were getting around 11,000 on a 12x6 give or take a little. The Jett muffler is supposed to be good for 500-1,500rpm depending on the engine's timing and such, but I think part of the power boost came from he 60C carb (from a 61fx I think). The engine came to me without a carb. The engine was barely on the pipe - the tuned range is 12,000-15,000rpm. My ST S90 turns a 12x6 at 14k on 5% fuel on the same muffler. The red (12k-15k) Jett mufflers are the lowest in the tuned range rpm, then gold (15-18k) , then black (20k+) for the Q40 type stuff.

I traded the FP .60 for a ST X60 pattern engine with a fellow modeler here on RCU.
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Old 09-13-2016, 07:11 AM
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60C is a 9.5mm venturi, no? I don't know how big the FP's normal carb is, 8mm or 8.5mm I'd guess. Worth a bit, certainly.

The Jett exhausts look good.
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Old 09-13-2016, 07:43 AM
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Sounds like a good trade you got there. Does the Jett muffler give 500 to 1,500 rpm from the other mufflers, or open exhaust? I usually get my rpms on an open exhaust because it is apples to apples comps. I have a rear exh .61 Rossi to try hopefully this year time permitting. Don't have to many big props to experiment with.
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Old 09-13-2016, 08:31 AM
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Quote:
Originally Posted by aspeed View Post
Sounds like a good trade you got there. Does the Jett muffler give 500 to 1,500 rpm from the other mufflers, or open exhaust? I usually get my rpms on an open exhaust because it is apples to apples comps. I have a rear exh .61 Rossi to try hopefully this year time permitting. Don't have to many big props to experiment with.
The 500-1500rpm gain is over the stock muffler I believe.

I don't habitually run engines without mufflers larger than .40/.46.. I have run a few 10cc engines sans muffler. On the engines I've put oversize mufflers onto I have run open exhaust to compare how much power the stock muffler eats and how much power the bigger muffler works. I did this test on an Enya SS30BB. Open exhaust, stock muffler, and a .46 sport muffler as well as a .46 size Jett muffler (red). The .46 mufflers gained a bit over open exhaust on some props and broke even on others. Overall I gained roughly a 1000rpm average using the .46 mufflers over the stocker. The larger .46 mufflers had an average gain of 200-300rpm over the open exhaust with the .46 Jett muffler edging the TT .46 muffler out by 100rpm or so.

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Old 09-13-2016, 08:32 AM
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Quote:
Originally Posted by SuperNash View Post
60C is a 9.5mm venturi, no? I don't know how big the FP's normal carb is, 8mm or 8.5mm I'd guess. Worth a bit, certainly.

The Jett exhausts look good.
I don't know off hand what it is. I'd have to measure the other 60C I have. My 60FP didn't come with a carburetor, so I don't know what the stock carb choke is.
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Old 09-16-2016, 09:33 AM
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Fresh fuel. No real difference.

Maxflash 6 plug (warm). 5% nitro. Std silencer.

Apc 12x6 11400
Graupner gray 12x6 11700

Which was a surprise. I always thought the apc were easier to turn than the Graupners. The pe reivers spreadsheet lists a higher prop const for graupner.

Back on pipe the 12x10 read the same, 10300. The odd flicker to 10400. Closely followed by the insulation blowing out of the plug core. Yup, too lean. Ho hum.
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Old 05-02-2017, 08:27 AM
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Put this one back on the bench for a couple more runs .

Os 8h carb (heli version of the 86 pumper carb)
Pump to match
macs 1260 old style pipe
header cut to approx 5.5"
enya #3
5% / 18% synthetic
apc 12x8
11k2 steady

pipe length was optimal.

might try another run with a couple of different plugs at some stage but I don't imagine there is many more rpm to find

The standard sf engine seems much happier on this prop vs the 12x10

excellent throttling as always from the pump carbs

very sensitive low speed needle, very reluctant to start to begin with until that was dialed in about half right, but instant starts every time after settings were established.

Last edited by SuperNash; 05-02-2017 at 08:35 AM.
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