Engine basics > Four strokes only

OS FS 26 Surpass - Fuel Tank Setup

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Colin McRae:

--- Quote from: Dennis Toth on March 28, 2024, 03:13:20 PM ---Colin,
I agree about the short clunk tube. Sullivan had a very thin wall silicon tubing just for clunk lines I looked on Brodak's site and don't see it. You might be able to use a heavier clunk, maybe Jim Lee and help on this (Lee's Machine Shop in vendor section). The second choice is surgical tubing, this will work but needs to be change twice a year as it gets soft and may leak but in a plastic tank it is not a problem.

Last option is to use a conventionally vented 2 ish oz tank. Again, make sure the vents are in the free air stream.

Best,    DennisT

--- End quote ---

Thanks Dennis

I'm still going to initially try a Brodak 2 oz wide wedge uniflow tank w/ muffler (restrictor) pressure on my Brodak Shark 402. I actually did get in a couple of flights with this arrangement and the setup seemed to run well. But I still need to home in on the best prop, needle setting, throttle opening position, ground rpm, tank height, and line length to use. A bit of trial and error. I'll also eventually try different tank setups for comparison.

Colin McRae:
Was able to get in a few more flights on my Brodak Shark 402 (profile model) with OS 26 FS Surpass this morning. Overall, a good experience. I was using 10% nitro, 20% oil (32% castor, 68% syn). 60' - 65# test Spectra lines. Also ran a 2 oz metal wide wedge uniflow tank on muffler (restrictor) pressure.

I first tried a 9.5-6 MAS prop. It was cut down from a MAS 10-6 so a pretty wide prop. I was having trouble setting the needle. My impression was that the wide cut-down prop put too much load on the engine.

I then tried a BY&O 9-6 wood prop. I was able to get a good needle setting at 10,000 rpm on the ground. Model flew fine with engine running pretty much constant rpm no matter what stunt I was doing.

The tank center was in line with the engine intake header. I was getting equal lap times inverted. So, tank height seemed OK.

One thing that was interesting. My lap time with the BY&O wood 9-6 (@10,000 ground rpm) was a little over 5 sec. Same approx lap time on the Shark with a stock OS 25 LA. But since the FS engine is much less noisy, it seemed that the model was flying slower with the FS, but it was not. Really strange feeling. But part of the FS learning process, I guess.

Another observation. Some have said that four-stokes, in general, vibrate a lot. Not the case in my limited experience. I can say I did not notice any undue model vibration, even compared to the OS 25LA which I have run on this same Shark model.

One other note. The 26FS seemed to like the carb throttle around 90% open vs wide open. No power loss as far as I could tell, but nice smooth CL operation.

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