stunthanger.com
Engine basics => Engine set up tips => Topic started by: Vince Mankowski on September 25, 2007, 05:20:02 PM
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Building a twin engine model (56") and have the four-stroke bug just 'cause I like the sound. It just seems appropriate.
Problem is..... I'm not 4-stroke aware.
I have recently been looking at OS 30 & OS 40 engines. But none of advertising gives a hint about propellor size.
Eleven inches of propellor, shallow pitch, at 10K would move the required air. Bigger diameters would be more "scale-ish."
Anyone know what these Surpass 30's & 40's will turn, prop-wise?
Vince
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Building a twin engine model (56") and have the four-stroke bug just 'cause I like the sound. It just seems appropriate.
Problem is..... I'm not 4-stroke aware.
I have recently been looking at OS 30 & OS 40 engines. But none of advertising gives a hint about propellor size.
Eleven inches of propellor, shallow pitch, at 10K would move the required air. Bigger diameters would be more "scale-ish."
Anyone know what these Surpass 30's & 40's will turn, prop-wise?
Vince
Hi Vince
You maybe want to choose the OS 40 over the 30 , If the plane will take the weight of the engines.It will turn a much larger prop. You can use a 12 to 12 1/2 x 5 ..or whatever pitch works best for that particlular plane prop, you maybe could use as high as a 13 inch if it was a prop that was very easy to turn
The 40 weighs 12.5 ounces the 30 only weighs 10 ounces, How much do you think the plane will weigh finished?
What type of plane is it and how are you going to use it? If it isn't that large of a wing you maybe better off with the lighter 30s and may not need to use larger diameter props.
You maybe able to use 11 x 5 props on the 30 and they might work well on the plane. also.
Regards
Randy
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Vince -
Two .30s should be more than adequate for a 56 inch stunter. y1
If you have not yet made a purchase, I would strongly recommend the SAITO .30 over the Surpass.
We have run them both extensively and most people were disappointed in the OS. :'( :'(
This seems a bit strange because virtually every other engine in the Surpass line exceeded my expectations.
Two Surpass .40s will just be too much power - from the testing I've done, they can comfortably replace a Super Tigre .46. Right now, I have a Surpass .49 on a 55 inch, 59 ounce stunt plane and it goes like a bullet.
Regarding props, the absolute best I've found for the SAITO .30 is the APC 9 1/2-6 - seems perfect in just about every application.
The Surpass .40 has worked the best with a Master Airscrew 11-7 plastic and an AHC 11 1/2-6 1/2 wood.
I would not go below 6 pitch on any 4S engine.
If you want to join a fine 4-stroke information exchange, e-mail me at <rzambelli@moog.com>. We have over 100 4S enthusiasts who are more than willing to share ideas and information on these wonderful powerplants.
Bob Z.
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Hi Bob
Vince didn't say this was a "stuntship". Only hinted that he wanted to run larger props, and said they would be more scale looking...
That is why I asked him what type of plane this will be.
I would really like to know that before recomending engines. It maybe that he doesn't want to run 9 inch props
Vince tell us what type of plane this will be <=
Regards
Randy
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Hi Vince,
I'll have to agree with Bob on prop and engine choices, NEVER use anything below a 6 pitch on a four stroke. If you go the Saito web site and look at prop recommendations you won't see anything below a 6 pitch.
http://saito-engines.info/prop_sizes.html
I haven't ran my 30 since I discovered what I believe is the holly grail to making Saito 4 strokes run but when I do I am going to start with a 9-7 and maybe end up with 9 1/2 or 10-7. Would believe the 30 would pull an 11-6 but I have had such excellent results with 7 pitch props I would stay with them.
The Saito prop recommendations are obviously for RC and I have found at least on the 40a and 56 we can run a little larger diameter than the Saito site shows.. For example I run an 11-7 on my 40a and a 13-7.5 on my 56 but picking a prop is only the start. Wide open my 40a will turn an 11-7 at 10 grand, of course I wouldn't want to be on the handle.
Hopfully if you go with Saito 30's you will be able to run the RC carbs without inconsistent air leak issues. Try it and if it doesn't work out we can talk about venturies. You will need some way to adjust the throttle (intake area), don't just wire it wide open. Use a clunk tank, the Hays 3 ounce tanks would be perfect, PowerMaster YS 20-20 fuel on muffler pressure. With a 7 pitch prop.. set your ground rpm with the throttle at about 8200, adjust the needle so it's just on the rich side of peak RPM.. You may have to play with the throttle and needle to find the ultimate combination of lap times and needle settings but once you have found it you can pretty much forget about it.
Sadly the Saito 30 is no longer being imported but can still be had from Kaz in Japan. If you can't find them in the US contact... Kaz Minato email... bluemax.minato@nifty.ne.jp I ordered a 40a and received it in 4 days, He said it depends on if he has stock or not.
My 4 strokes run so well and are so consistant I have all but given up on 2 strokes. Two weeks ago went from Tulsa to a contest in Memphis and didn't have to touch the needles on either the 40 or the 56, while watching other advanced and expert flyers diddle with run time issues and needle settings on two strokes, I just fueled and flew.
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So far....More information then I hoped. These boards are getting to be a great resource. Thanks everyone!
Have you ever wondered why the "best" stuff (Like the Saito 30) is always made of "un-obtainium?"
More on my model. I started with 56" span, but I am really leaning toward going to a 68 inch span for a variety of reasons (AutoCAD is a wonderful thing).
'Building a twin engine stand off scale model..... Well, I WILL be building it after I sort out a few more details...700 sq in .... Weight to be (hopefully) under 100 oz. Four stroke(s), retracts, electronic controls and a few dis n' dats.
Why? I have had this in project mind since the early 1950's. I am not gonna compete with it.... it’s just something I wanna do. My Pop picked up a DFC, the Air Medal and a couple of Purple Hearts drivin one of these...(Europe, Pacific & Korea) My son picked up a national championship a few years ago with Pop's last A-26 as a plastic model.
Normally I would run twin 29-40's in something like this and would probably end up with the 40-size because basically I "trust in thrust" and can prop it for the tasks at hand.
Soooo.... I am after that tick-over idle....the sound .... smooth transition to good thrust & not necessarily having to cruise around at max rpm, but having it available.
Years ago I built one of those Sterling PT 17 kits.... all 65 1/2 inches of both wings. (this is my "big model" experience)I flew it with a Fox 59 that had the prop diameter just peeking over the dummy engine /fuse. Essentially it looked stupid, but it flew very well. I was a dB shattering mismatch to any "scale sound" and at rest, the prop always looked like someone clipped in half. I ended up with more weight in the nose then any of my other models weighted! Arse-ee guys get to balance by shoving around recievers, batteries and all kinds of stuff. The Stearman ended up with lead in the nose (a lot of lead).
I fiddled with a two chamber diverter, which could be plumbed to exhaust stacks on each side of a fuselage. Why? "Cause the exhaust "puffed" here & there at the 6 stacks and it did emit a staccato engine noise. Even though it looked cool & sounded cool running, there was no place to put it in the PT 17 it was too heavy to fly around with on anything else. I can't imagine making two of them for the A-26! 'Course weight-wise, something like this is usually plum full of recievers, batteries and stuff..... But I think I'll stick to 4-strokes & make life simpler.
I'd appreciate your thoughts,
Vince