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Author Topic: OS FS 26 Surpass - Fuel Tank Setup  (Read 652 times)

Offline Colin McRae

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OS FS 26 Surpass - Fuel Tank Setup
« on: December 19, 2022, 04:43:26 PM »
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.

Online Dennis Toth

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Re: OS FS 26 Surpass - Fuel Tank Setup
« Reply #1 on: December 20, 2022, 07:13:51 AM »
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
« Last Edit: May 01, 2023, 02:52:07 PM by Dennis Toth »

Offline Colin McRae

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Re: OS FS 26 Surpass - Fuel Tank Setup
« Reply #2 on: December 21, 2022, 08:26:53 AM »
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.


Online Dennis Toth

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Re: OS FS 26 Surpass - Fuel Tank Setup
« Reply #3 on: December 21, 2022, 09:06:52 AM »
Colin,
The tall tank is just the regular cluck tank stood on its side. This minimizes change in fuel head being about 1 1/4Ē vs. 2 1/4Ē if set on its bottom. 4strokes donít have as much pumping fuel draw as higher rpm 2 strokes thatís why they usually run better on conventional venting. One tip is to use 5/32Ē fuel pickup tube (drill out the cluck too) and larger fuel tube .

Best,  DennisT

Offline Colin McRae

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Re: OS FS 26 Surpass - Fuel Tank Setup
« Reply #4 on: December 21, 2022, 02:36:19 PM »
Thx much
Dubro makes a 2oz rectangular tank that I can try.

Online Dennis Toth

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Re: OS FS 26 Surpass - Fuel Tank Setup
« Reply #5 on: December 23, 2022, 08:59:11 AM »
Colin,
Change out the fuel pickup line to 5/32" (copper is best for nitro) and drill the cluck tip to same.

Best,    DennisT
« Last Edit: May 01, 2023, 02:54:35 PM by Dennis Toth »

Offline Robert Zambelli

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Re: OS FS 26 Surpass - Fuel Tank Setup
« Reply #6 on: December 23, 2022, 02:26:51 PM »
I have a number of planes flying with the Surpass 26, hundreds of flights.
One plane flys with THREE of them.
Iíve had very good results with a plain VECO two-ounce metal tank, non-uniflow, over/under venting, no muffler pressure. The engines are profile mounted.
Up to now, Iíve been using Brodak 10/23, 50-50 castor/synthetic but I plan to mix up some 20/20, 18/2 synthetic/castor to try out.
The Surpass 26 is a very good four cycle engine, requiring minimal fussing and maintenance.
The OS four cycle plug works perfectly.
Best of luck!!
Bob Z.

Offline Colin McRae

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Re: OS FS 26 Surpass - Fuel Tank Setup
« Reply #7 on: December 23, 2022, 06:19:48 PM »
Colin,
Due change out the fuel pickup line to 5/32" (copper is best for nitro) and drill the cluck tip to same.

Best,    DennisT

Thx Dennis, will do!

Offline Colin McRae

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Re: OS FS 26 Surpass - Fuel Tank Setup
« Reply #8 on: December 23, 2022, 06:38:48 PM »
I have a number of planes flying with the Surpass 26, hundreds of flights.
One plane flys with THREE of them.
Iíve had very good results with a plain VECO two-ounce metal tank, non-uniflow, over/under venting, no muffler pressure. The engines are profile mounted.
Up to now, Iíve been using Brodak 10/23, 50-50 castor/synthetic but I plan to mix up some 20/20, 18/2 synthetic/castor to try out.
The Surpass 26 is a very good four cycle engine, requiring minimal fussing and maintenance.
The OS four cycle plug works perfectly.
Best of luck!!
Bob Z.

Thx for the info Bob, much appreciated.

4-stokes are new to me so I have lots to learn. I just like the sound and plan to use the 26s on a future warbird model. Maybe a Brodak Yak 9. Might even set it up for 3-line w/ throttle control.

I normally use Brodak 5 & 10/23 fuel. So, I will already have a bunch of the correct fuel for the 26s.

A friend of mine has a Magnum 30 four-stroke on a Wildcat warbird model and uses a metal profile standard vent tank. Not sure if he uses muffler pressure. In any event his model runs great. I will play around w/ the various options to see what works best.

A few experienced members recommend a clunk tank for a 4-stroke, but don't really explain why. My guess is that they fly the pattern and want the clunk design for that purpose. But if one flies sport (and a few basic stunts), not sure it makes any real difference. Others have said a metal non-clunk works fine. I have both and will experiment for best operation.

And I do have the OS F glow plug.

I am excited to get my feet wet w/ a 4-stroke on a CL model!!

Offline Robert Zambelli

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Re: OS FS 26 Surpass - Fuel Tank Setup
« Reply #9 on: December 23, 2022, 07:28:27 PM »
I used one of mine in a Sterling Mustang.
Flew great, took home many trophies in OTS and classic stunt.
I once beat a Super Tiger 60 powered Cardinal with the Mustang.

Bob Z.

Offline Colin McRae

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Re: OS FS 26 Surpass - Fuel Tank Setup
« Reply #10 on: December 23, 2022, 08:23:19 PM »
The Brodak Yak 9 (40" wing) is about the same size as the Sterling Mustang, so should work well for the 26s.

I recently retired and have picked up the CL hobby again after some 50+ years. (built and flew 1/2a's as a kid in Hawaii)

Not sure any competition is in my future, but I am working on practicing the pattern. So far, my squares are not very 'square', and my overhead 8's look more like 7's. But I am working on it.

Fun stuff for sure!!

Offline Robert Zambelli

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Re: OS FS 26 Surpass - Fuel Tank Setup
« Reply #11 on: December 24, 2022, 07:16:14 AM »
Colin:
Donít worry about competition - just go out and get as much enjoyment out of the sport as you can.
If you do decide to compete, you can take advantage of one of the four skill classes.
The important thing is to have fun!

And, keep us posted on your progress with the 4-stroke engines.
Keep in mind that the Sterling Mustang and Yak 9 are very close in performance.
Build them light and if you want, make the flaps non-moveable. Iíve done them both ways and couldnít tell the difference.
Bob Z.

Offline Colin McRae

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Re: OS FS 26 Surpass - Fuel Tank Setup
« Reply #12 on: December 24, 2022, 11:30:29 AM »
Colin,
Due change out the fuel pickup line to 5/32" (copper is best for nitro) and drill the cluck tip to same.

Best,    DennisT

Dennis, I was putting together the small Dubro 2 oz rectangular clunk tank and noticed an issue. Since the tank overall length is so short, the short piece of flex fuel tubing inside the tank between the stopper and clunk is too stiff (being so short) where the clunk does not drop to the bottom (or top) of the tank.

Is there a 'trick' for these small clunk tanks?  (Some type of tubing that is more flexible than the normal silicon fuel tubing we get from SIG or Brodak? Surgical tubing maybe, but can surgical tubing be used with glow fuel?)

I guess I could use a larger clunk tank and just not fill it full for the OS 26s, but don't really want to.

Or just use a 2 oz standard vent metal tank (no clunk).

Thoughts welcome.
Thanks

 

Online Dennis Toth

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Re: OS FS 26 Surpass - Fuel Tank Setup
« Reply #13 on: December 24, 2022, 12:11:26 PM »
Colin.
For the short tanks the Sulllvan tubing is very thin walled and flexible but surgical tubing will be more flexible for the 2oz tank. Other option could be a round tank with a fixed copper tube and conventional vent pointed to the inside of the circle side of the tank, just make sure you mount the air side of the vent about the tank and on the inboard side of the fuse (this gives clean airflow to the vent).

Best,    DennisT

Offline Colin McRae

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Re: OS FS 26 Surpass - Fuel Tank Setup
« Reply #14 on: December 24, 2022, 03:42:44 PM »
Colin.
For the short tanks the Sulllvan tubing is very thin walled and flexible but surgical tubing will be more flexible for the 2oz tank. Other option could be a round tank with a fixed copper tube and conventional vent pointed to the inside of the circle side of the tank, just make sure you mount the air side of the vent about the tank and on the inboard side of the fuse (this gives clean airflow to the vent).

Best,    DennisT

Dennis, do you know if the Sullivan silicon tubing is more flexible than the Dubro provided tube that came w/ the tank? I have some Brodak pink tube, but it is just as stiff as the Dubro product.

And I know surgical tubing was used years ago for glow fuels, but now pretty much replaced w/ silicon. The surgical tubing does not have to be hot-fuel proof in this case, but how does it hold up (chemically) to typical nitro glow fuels. 


Online Dennis Toth

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Re: OS FS 26 Surpass - Fuel Tank Setup
« Reply #15 on: December 25, 2022, 09:08:22 AM »
Colin,
Yes the Sullivan tubing is thinner walled and more flexible than the Dubro. Again use the 5/32" copper tube and drill out the cluck.

Best,   DennisT

Offline Colin McRae

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Re: OS FS 26 Surpass - Fuel Tank Setup
« Reply #16 on: December 25, 2022, 09:36:57 AM »
Colin,
Yes the Sullivan tubing is thinner walled and more flexible than the Dubro. Again use the 5/32" copper tube and drill out the cluck.

Best,   DennisT

Thx Dennis
Merry Christmas !!

Offline Colin McRae

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Re: OS FS 26 Surpass - Fuel Tank Setup
« Reply #17 on: May 01, 2023, 01:50:11 PM »
I have a number of planes flying with the Surpass 26, hundreds of flights.
One plane flys with THREE of them.
Iíve had very good results with a plain VECO two-ounce metal tank, non-uniflow, over/under venting, no muffler pressure. The engines are profile mounted.
Up to now, Iíve been using Brodak 10/23, 50-50 castor/synthetic but I plan to mix up some 20/20, 18/2 synthetic/castor to try out.
The Surpass 26 is a very good four cycle engine, requiring minimal fussing and maintenance.
The OS four cycle plug works perfectly.
Best of luck!!
Bob Z.

I still have a question in the OS 26FS relating to fuel pressure (muffler pressure) versus standard over/under venting for a full speed CL application. A few have said they use no muffler pressure. However, the FS26 owner's manual shows the recommended fuel system set up and shows muffler pressure applied to the fuel tank. It seems muffler pressure just enhances fuel draw.

I plan to set up the carb to be about 1/3 open to start and allow for some brief warm up. Then ground adjust to desired full speed before takeoff.

The 26FS is basically designed as an R/C engine. Maybe fuel pressure not needed for a fixed speed CL application?

Online Dennis Toth

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Re: OS FS 26 Surpass - Fuel Tank Setup
« Reply #18 on: May 01, 2023, 03:06:02 PM »
Colin,
You can try it both ways but for the no pressure option you need to get the vent line in the free air stream above the fuse sides either off the back engine bolt or through the fuse and up about 3/16" above the fuse side profile. I used the pressure and was very satisfied with the run. Attached is a photo of the vent I use on a 2 stroke powered Ringmaster. You can see it is off the back bolt, just a small piece of copper or brass tube.

As for the 1/3 carb to warm up that is not necessary. These 4 Strokes warmup quick, most people wire the carb fully open and adjust the engine to a solid lean run. Adjust lap time speed with pitch, the 10x6 is a good match on 10 - 15%N fuel.

Best,   DennisT

Offline Colin McRae

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Re: OS FS 26 Surpass - Fuel Tank Setup
« Reply #19 on: May 02, 2023, 11:43:44 AM »
Thanks Dennis.

Concerning the speed adjustment, I got this idea from a flying buddy who has a few CL 4-stroke models. I installed a simple aluminum gear (a part from a hobby shop intended for an RC car) on the carb. The gear teeth are in contact w/ the choke rod and keep the carb where you set it. So I can set the carb partially open to start. Then rotate gear to full open before takeoff. My opinion only, and maybe not necessary as you say, but it is not a bad idea to start at a lower speed and allow for some brief warmup. With all the FS moving parts (compared to 2-stroke) a brief low speed warmup can't hurt.

Offline Robert Zambelli

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Re: OS FS 26 Surpass - Fuel Tank Setup
« Reply #20 on: May 02, 2023, 03:52:27 PM »
Very good idea!!!   y1  y1  y1
But, here's something I've found with some of the Surpass engines.
The clearance between the moving throttle drum (valve) and the bore can vary quite a bit.
If this clearance gets too large, you will get some erratic runs due to air leakage.
What I do is remove the throttle arm and install a washer that is coated with RTV.
Tightening the screw will seal any leak and hold the throttle drum in place - wide open.
Note that I've owned around twenty OS 20 and 26 four cycle engines and although rare, this situation does occasionally occur.
I've not seen it in the larger engines.
I've NEVER witnessed it in a SAITO.

Bob Z.

Offline Dan McEntee

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Re: OS FS 26 Surpass - Fuel Tank Setup
« Reply #21 on: May 02, 2023, 10:31:38 PM »
  To add to what Bob is saying, an R/C carb that is wide open is way bigger than what a restrictor venturi with a spray bar through it would be and add to that all the clearance around the throttle barrel passing air. Closing down the throttle decreases the opening and adds some choke to help with fuel draw, and 4 strokes are all about fuel draw. I would test it at about 1/3 closed, and run muffler pressure. In my limited experience with both OS and Saito four strokes, this has always worked the best for me. It's more or less the "Bob Reeves" philosophy or running a 4 stroke engine and has worked pretty well for me. I applied what I learned running and flying my Saito .56 to an OS.70 and it responded the same as the Saito did. I had to use the carb closed off, as no one made any bolt on venturi for C'L stunt for it. Flying four strokes has been fun and is a viable power plant, and I hope to get my Top Flite Score recovered soon and get back to it, and maybe a couple of other models in the future, but I haven't sold off any of my 2 stroke engines just yet!
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Offline Colin McRae

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Re: OS FS 26 Surpass - Fuel Tank Setup
« Reply #22 on: May 03, 2023, 09:30:37 AM »
Dan, not sure I fully understand. Are you saying you have had good luck with 4-strokes (on a CL application) with the throttle maybe 66% open (to simulate a venturi restriction), then adjust the needle for desired full speed?

Or if the engine is not running well at full throttle (due to air leakage), test and start to close the throttle to see if the engine performance improves?

Thanks in a advance.

Offline Dan McEntee

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Re: OS FS 26 Surpass - Fuel Tank Setup
« Reply #23 on: May 03, 2023, 03:19:35 PM »
Dan, not sure I fully understand. Are you saying you have had good luck with 4-strokes (on a CL application) with the throttle maybe 66% open (to simulate a venturi restriction), then adjust the needle for desired full speed?

Or if the engine is not running well at full throttle (due to air leakage), test and start to close the throttle to see if the engine performance improves?

Thanks in a advance.

   That is exactly correct. Search out threads on here by Bob Reeves. He and some others did a lot of research and experiments into this. You could also go to the Tulsa Gluedobbers web site and a lot of it is posted there. Bob has since passed away but he left a lot of information behind. Bob advocated for the low RPM/high pitch prop method of running 4 strokes. If you happen to have a C/L venturi on an engine, he came up with the idea t add a screw to the throat of the venturi that goes in on one side only, and by running the screw in and out, you effectively change the venturi choke area. Running it in makes it smaller and draws more fuel, out makes it bigger and draws more air. Not really a new idea, the speed limit combat guys have been doing the same thing for a long time to get their engines to run a constant speed.. As you turn the screw in, you turn the needle in next to get a max RPM setting just above 8000 RPM. That is what he said to do for a Saito 56/62. props are in the 6 and 7 inch pitch range. If the weather gets warmer, you can screw the blocking screw out just a bit to let more air in and reset the needle. When it gets cold out,  you do the opposite, screw in in to let in less air and reset the needle. It will kind of go against everything you already know about engines and props for 2 strokes, but it works. With an R/C carb, the barrel takes the place of the screw. Just play with it and get familiar with it. For a 4 stroke that small, i don't know if you need a new RPM range or not, but just experiment, go by lap times and line tension. before you try any maneuvers. The engine might not sound like it will pull your hat off your head, but just ignore that and go by lap time and feel. This set up with muffler pressure will make the engine run very consistently where ever it is flying. You will have to get used to that and if you have been flying 2 strokes for any length of time it will sound foreign to you.   The 4 stroke is a different animal, and resist all temptation to run it like a two stroke. This low RPM set up lets the engine get plenty of fuel, and thus it runs cooler. I have run several gallons of fuel through my Score and Saito .56 and all of the chrome is still shiny. I ran all of this by Gilbert Berringer from France. He is one of the top stunt pilots in Europe and helped bring the 4 stroke engine along. He has a large manufacturing company that makes aircraft wheels and brake systems, and comes to Oshkosh every year, along with Sun and Fun in Florida during the winter. He flew my Score several times and was impressed by it. He sets his engines up with a very small venturi to start with, no bigger that 6mm, he told me, and when you put a spray bar through that, the choke area is pretty small. I run Powermaster YS-20/20 for the most part, and it's getting pricey now, but i only use about 3.5 ounces per flight, so it lasts a while. Try some of the Powermaster synthetic blends in the 15% range. It would not hurt to add some extra synthetic oil to get the total oil content up closer to 20% like the YS blend. I have been trying not to add any castor, as there are a LOT more and smaller moving parts in these engines, and even smaller yet for your .26. If it sets up and runs the lower ROM ok, it might not be necessary. It will take a lot of attention on your part as you go through the motions. Everything from starting them to picking props and setting the needle will be different and again, the big thing is DO NOT run it like a two stroke!! The closest thing I have to your engine is a Saito Black Knight .30 but I have yet to pick a model for it.
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Offline Colin McRae

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Re: OS FS 26 Surpass - Fuel Tank Setup
« Reply #24 on: May 03, 2023, 05:29:56 PM »
Thx Dan. I have a lot to learn about 4-strokes and this is very helpful.

I decided to pick up the OS 26 FS since I got it at a very good price. It is for a future model. I am thinking about a profile Yak 9 warbird.

Online Dennis Toth

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Re: OS FS 26 Surpass - Fuel Tank Setup
« Reply #25 on: May 04, 2023, 03:40:07 PM »
Colin,
Dan gave some very good information. Here is an engine review of the OS 26FS Surpass (http://sceptreflight.com/Model%20Engine%20Tests/OS%20FS-26%20Surpass.html). I like to run mine in the 9500rpm range and use a higher pitch (like 7") with a wide blade, diameter around 10". The point Dan made about the sound is important. With the muffler it is like flying electric, but the note is a little flat compared to 2 stroke (think Harley vs, Yamaha). You will notice that you may be flying faster lap times with the 4 stroke and but it will seem like it is slower because of the sound.

The Yak is a very good ship for this size engine.

Best,    DennisT


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