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Engine basics => Engine set up tips => Topic started by: Bootlegger on February 27, 2020, 01:00:12 PM
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What is the venturi size in the O S 30 Stunt, this engine is single by pass, also it has one of Randy Smith's 40 size needle assy's, and what other venturi will fit this engine? Thanks...
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Gil,
I have a 6.5mm (.257") diameter venturi in one of my OS .30S engines and it runs really well, in a 4-2 mode pulling a pretty light combat streak. This is a nylon venturi, so it is aftermarket, not stock. The needle is OS--I would have guessed .135" diameter, but without taking it out it looks fatter than that. If it is .135, that equates to a passage area of about 0.0172 in^2. I don't know what the PA needle valve diameter is to calculate the equivalent.
Dave
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Thanks Dave,now the questions, where did you get the venturi, and what other engine does it fit, (O S 20-25) or any other, and again thanks a lot, what fuel do you run in your O S 30 ???One more what prop did you beak it in with ? Thanks
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Legs in Boots,
Them's a lot of questions....so lemme try.
I bought the engines used (ie. broken in too much) back when I had a couple crashes in a row and thought I needed to stock up on expendable motors. I got two. Both came with the venturi. One had a pretty tired P/L fit, so I found myself only using one engine. Since then I found a replacement (NIP) P/L set, so I'll probably keep flying lighter planes with it since it runs really sweet.
One of the engines came with an R/C carb. The bore in the case is .359" ID with a depth (actually, carb length) of .352".
I've heard that the venturi for a 35S also fits, but I don't know what bore they have or if you need something a bit smaller. The 35S that I have is not stock, and has an ST needle valve so checking it does us no good. I don't know if any other stock venturis will fit. That's a good question for Air Ministry, who seems to have one of everything, and keeps track of crazy engine part swaps....
I found the OS .30S will pull a wood 9x5 Zinger (or 9x6?) pretty well. I run 10/25 or 10/28 all castor fuel with no issues. Twenty-five percent castor should be plenty, but I keep the 28 around for Foxes, and run whut I brung.
Jim Lee probably has or can make these. If you can't find what you need already out there, let me know. I temporarily have the ability to make these.
If you are breaking one in, then use a bit less pitch than your flight prop, and be sure the prop is balanced. No muffler. The OS instruction sheet says 30% castor for break-in and 25% after that. Lot's of short runs to heat cycle the engine parts, say 2 minutes each. If the fits are tight you may initially find that the engine quits if you pull the glowclip off. Keep going. Short peaking after a few runs. I would start flying it if it will hold a peak setting for a couple of minutes on the stand without overheating.
The Divot
"Leaving holes in the ground wherever airplanes are flown"
OS Break-in Instructions
Every OS engine is tested before shipment however additional running is necessary for long life and highest performance. Break-in your engine the following way.
1) Run your engine for a total of 20 to 30 minutes, with 9x5 or 10x4 propeller and a mild fuel. Let the engine run with a rich needle valve setting (4-cycle) at this stage, so as to avoid overheating. Running time is best accumulated by running the engine for periods of about 2 minutes with a short cooling-off period between each run.
2) Then, with the same propeller and fuel, run the engine with a 2-cycle setting, for a further 20 to 30 minutes. If the engine stops or the revolutions fall off at the maximum R.P.M. setting, your break-in is not complete. In this case repeat above procedure.
[Note that these are the R/C instructions, which is all I have.]
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Jim Lee does a little button set up , plugs in the crank pin . stops the rod walking back and going C L A N G when it SNAPS .
If yr getting a Venturie from him , grab a $ 2 con rod button too .
(https://apis.mail.yahoo.com/ws/v3/mailboxes/@.id==VjN-DtEvyYWWRAPjKLM02sJ3GEAztr4fdmEgbrScfxXACvAaMYtD_4NrdXySrbAQKr5eQJ6K568PQGf9C0THqe7uUA/messages/@.id==AIZC4e0aGZI7XiNGmAJtGJFsQIY/content/parts/@.id==4/thumbnail?appId=YMailNorrinLaunch)
Photos of Max 35s by ' Big Art ' kindly sent by starlit . you can see the TALL intake , Id thing vastly superior o the factory short one ,
of which ive many . ( But in Aus . )
The Big Art set up ' X ' 's the front face of the rod , for lube flow . Picture in recent FP 40 thread of detail . If youve a small half round file .
Old Top flite 10 x 6 , a 9 x 6 , and Try a 11 x 4 too , if you have one . The 35s are pretty good on em , for a ' walking pace ' flight . But
it keeps it moveing .
you know you wanna run 20 % + Castor . NOT synthetic, Huh .
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IIRC the PA and ST are the same size -- .156 (5/32) or .157 (4mm). Compare against a 5/32" drill bit, or measure with calipers, if you have a pair.
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The stock venturi is right at .300 , a 255 will be TOO small, and if you are going to run a OS 703 muffler you will need from a 285 to a 305 venturi, with open tube or tongue you would want a 265 venturi in it, The PA Needle is the same as the older OS ones at .157 diameter
If you have the steel spacer behind the drive washer, then you do not need any buttons in the crank pin
Sounds like some one put an OS 25 venturi in you engine if it is .255
They will pull and use
10 x 6
10x 5
9.5 x 5.5
9,5 x 6
9 x 6
props
they run great nice 4 2 and more power than a fox or Red head
Randy
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Thanks for the info, Randy.
On my .30S, I have a tongue muffler with 10 3/32" diameter holes. It knocks the noise down a bit which is nice.
I also found a .280" diameter nylon venturi in one of the boxes. Not sure I've tried that one before.
Dave