Engine basics > Four strokes only

OS FS 26 Surpass - Fuel Tank Setup

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Colin McRae:
I recently acquired a new OS 26 Surpass 4-stroke engine. My plan is to use it on a profile CL model in the future, maybe a warbird flown for sport and stunt.

My question relates to fuel tank type and related setup for this engine on a profile model.

1. What tank design is considered optimum for a CL application. Uniflow wide wedge tank? Clunk tank? Other?

2. Tank height location in relation to the engine on a profile setup?

Also, will the 26s pull say a typical 40" wing profile model? I believe it is less powerful than an OS 25LA. Any model suggestions would be appreciated.

Thanks in advance.

Dennis Toth:
Colin,
The OS 26 with pull ships like a strong FOX 35, 45 - 48" span, 40 oz ish weight. I had mine in a TF Tutor (original version) and ran 10 x6 prop, 10% nitro, 22% total oil (mostly synthetic). From my notes you want a wide blade prop (like an RSM or BBYO) around 9900 rpm. I needed 2 3/4oz of fuel for the PA pattern. Use a tank tall and skinny clunk works with the fuel pickup tube being 5/32" OD and drill out the cluck to 5/32" (this gives better fuel draw), use large fuel line and wire onto fuel nipple. Set the centerline of the tank inline with the center of the carb/venturi to start and adjust up/down to get equal lap times. Set up vent for standard vents (not uniflow) and muffler pressure.

Best,   DennisT

Colin McRae:
Thx Dennis. 4-stokes are new to me so I have much to learn.

Can you please help me understand why your recommendation for a 'tall and skinny' type tank. And standard vent vs a uniflow design. Also, I have been reading up a bit and some mention to use a clunk tank, but don't explain why.

A guy I know has this particular tank (see attachment) on a profile model w/ a Magnum 30 four stoke. It is a standard vent design (not a clunk design) and seems to work fine in the air.

If a clunk tank is the way to go, I looked at Sullivan and Dubro and don't see a 'tall & skinny' design per se.

Thx again for your help.

Dennis Toth:
Colin,
The tall tank is just the regular cluck tank stood on its side. This minimizes change in fuel head being about 1 1/4” vs. 2 1/4” if set on its bottom. 4strokes don’t have as much pumping fuel draw as higher rpm 2 strokes that’s why they usually run better on conventional venting. One tip is to use 5/32” fuel pickup tube (drill out the cluck too) and larger fuel tube .

Best,  DennisT

Colin McRae:
Thx much
Dubro makes a 2oz rectangular tank that I can try.

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