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Old Aug 27, 2014, 06:23 AM
Capt. Kelso
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United States, FL, Yulee
Joined Dec 2011
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OS 40 FS Broken Air Bleeder Screw

I was breaking in a new OS 40 FS with the help of another club member. Long story short, the air bleeder screw broke during one of the adjustments (fully screwed in). After normal tuning adjustments, the engine seems to run OK and idles fine. However, the top RPM I get is around 9,000. In the air it seems OK. But, it really seems sluggish on takeoffs .

Its a SIG Four Star 40 and I have been running a 11x6 prop. I've flown it a number of times but wonder if I need to replace the Bleeder valve to improve performance?

Thanks
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Old Aug 27, 2014, 10:13 PM
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I think an 11X6 is a lot of load on that engine. You might want to back it down a little, maybe try an 11X5? or a 10X7? Depending on your airframe or flying requirements. I am running an OS40Surpass and it wasn't happy under too much load.
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Old Aug 27, 2014, 11:30 PM
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Israel, Ramat HaSharon
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Kelso,


The normal starting position for adjustment of the carburettor's air-bleed screw is half-way across the hole. Your setting (i.e. fully closed) should make the engine run too rich at idle, but with nitro in the mix it might still work...

To regain idle mixture adjustability, you should get the broken screw out and replace it.
I don't think there's an 'easy-out' that small, but if you slot its end with a small Dremel disk, you might get a small screwdriver to fit...

I agree with Jeff that an 11x6 prop is too heavy... And it is just managing a very mediocre .34-.37 HP (supposing it is a black MA - a bit more if it's an APC).

The old OS SF is rather weak among four-strokes.
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Old Aug 27, 2014, 11:34 PM
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Quote:
Originally Posted by Capt. Kelso View Post
I was breaking in a new OS 40 FS with the help of another club member. Long story short, the air bleeder screw broke during one of the adjustments (fully screwed in). After normal tuning adjustments, the engine seems to run OK and idles fine. However, the top RPM I get is around 9,000. In the air it seems OK. But, it really seems sluggish on takeoffs .

Its a SIG Four Star 40 and I have been running a 11x6 prop. I've flown it a number of times but wonder if I need to replace the Bleeder valve to improve performance?

Thanks
The purpose of the bleeder screw is to adjust the low speed mixture. I will NOT affect the high speed. .I agree with Jeffie. Your prop is too much for an FS40. An 11X5 is more appropriate for that plane and engine. Should turn 10500 - 10000 on the ground. A sliperier plane might like a 10X6.
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Old Aug 28, 2014, 12:17 AM
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Keep in mind also that not all props are created equal, a Master Airscrew Scimitar is not like a K series. K series props move a lot more air with their wide blades and work great on 4 strokes but if you are already overloaded switching to a Scimitar of the same size can lower the load on the engine and get you where you want to be. Just as an example.
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Old Aug 30, 2014, 12:42 AM
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Hi Captain,
Yeah like the others say the air bleed won't affect your high end at all, but you'll be wanting to adjust it for a good idle and transition. I hope you can get the broken bit out OK, and replace the screw.

Are we talking Surpass or non Surpass engines here ? (Surpass has two bumps on the rocker cover). My Surpass .40 turns an APC 11X6 at around 9500 static on zero nitro fuel. It flies a 6 1/4 lb 69" Bücker Bestmann (German between the wars low wing trainer) in a very scale like manner. It's certainly not over powered but it has a reasonable turn of speed, loops from a slight dive, and takeoff and climb is fine. I do notice slightly more power as the rpm comes up once I get to cruise speed though. A 12X5 Graupner works fine too, with better acceleration and climb, and slightly reduced speed.

A Four Star 40 normally flies with a .40 two stroke as a minimum so a .40 four stroke is never going to give stunning performance in that airframe, but that's fine. I quite enjoy flying a model like that, if you conserve energy and momentum and become comfortable flying at low speeds you can make it look like you have way more power than you actually do.

Dave H
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Old Aug 30, 2014, 02:16 AM
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I fly a 40Surpass in my 4.5 lb Dazzler with a 10X8 Scimitar and its a good match. My particular Surpass isn't happy loaded down below 10,000 much, it gets very sensitive to needle settings and erratic at idle. It all depends on the application.
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Old Aug 31, 2014, 12:22 PM
Capt. Kelso
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United States, FL, Yulee
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It is a Surpass. I knew the .40 FS might be a little underpowered but for my skill level I was OK with that. Based on others feedback I changed the prop from 11x6 to a 10x7 and RPM's increased from to 10,000. It flew fine, slow and steady. Still has enough zip to do basic maneuvers. Next I will change the fuel from Omega 15% to 10%. The manual notes to use between 5-10%, practical RPM 2,500 - 10,000. So, I guess I'm on target.
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Old Sep 01, 2014, 04:55 AM
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Sounds like it.

Did you get the air bleed sorted?

10,000 rpm static is not a bad place to be. It's well worth the small cost of trying a few different sizes and brands of prop to see which works best on a given model. The difference is even more noticeable when you don't have much power to play with.

I found that my engine improved quite a bit after an hour or two running so you may have more to come yet.

Dave H
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Old Sep 01, 2014, 01:44 PM
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Good you got a Surpass, I run mine on 15% all the time with no problems. My plane is about 4.5 lbs dry and it pulls it around great. Here it is on youtube, please excuse the sideways video I have no idea why it came out that way it doesn't play that way on my computer and I don't know how to fix it except to delete it and start over and it wasn't even windy so I don't know why the audio is so breezy.
Great Planes Dazzler with an OS40Surpass (4 min 52 sec)
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Old Sep 01, 2014, 03:03 PM
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United States, AZ, Golden Valley
Joined Sep 2011
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Just an f.y.i. the intake and two needle carbs off the os fs 52 thru 56 or whatever size they're up to now bolt right on these smaller engines if you just make a small adapter (I made mine out of a small piece of ply) to bolt onto the back of the engine that you then screw the carb down to. I couldn't get my 40 to idle reliably with the engine installed inverted so I swapped the carb out from a wore out 52 and now I can trust it on a long glide.
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Old Sep 01, 2014, 08:26 PM
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Cool can you post a photo. The carb body for the 40 is out of stock.
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Old Sep 02, 2014, 03:59 PM
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United States, AZ, Golden Valley
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yeah I'll try to get one put up after work.
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