RE: New SV Gassers
 

Assuming that yours is off the same amount as mine was, here's a pic to show the position, but I would make a degree wheel and make sure your at 30 degree's BTDC.

RE: New SV Gassers
 

I don't feel so bad now about not technically breaking in my engine now, I justb found this bit of info on the net.
Running in a gas motor is not like running in a glow motor.
Due to the difference in design and running requirements, a gas motor should be broken-in, in the air.

In most cases, you should do your running range checks, motor off, motor on, and insure the needle settings are close enough to fly, erring on the rich side, then fly the plane in a gentle fashion for several flights.
Gentle being no extended full throttle usage, no gyroscopic's and no snaps.
After three flights of at least 10 minutes, you are free to fly as you please but remember, the nicer you are to the motor when it's new, the better it will run in the long run.

The fuel you use can be the same as the fuel you plan to fly with, there is no need to use a different oil or a different ratio.

If you must break it in on the ground, you should use a propeller several sizes too small, i.e., if your motor normally turns a 26-10, use a 22-10 on the ground and make sure not to exceed red line by going to full throttle. This will keep the load low and the internal temps down.

RE: New SV Gassers
 

Alcohol lacks lubricity, while gasoline does have some lubricating qualities, which makes a considerable difference during those first few engine runs.


Ed Cregger

RE: New SV Gassers
 

Hi Ed, and thanks for that. I have a question for ya, since im new to gas here. I read where these engine should be static at 6500 to 7500, is that right ? Boy, im turning 8200 ! I do need more prop. If thats true, I think I want to be around 7200 ? Sound right ? I have an 18x8, but I havn't officially tried it yet. It was out of balance when I did. Would that be too much prop for it ? I have access to a 16x10 also, and an 18x6, I just have to drive for those though. I perfer an 18 inch prop on this plane for the appearance. The biplane weighs about 15 lbs

RE: New SV Gassers
 

It really depends upon how the engine is tuned/ported as to which prop will present the most effective load for the engine. Then you have to factor in the type of model, its weight, drag and the performance desired.

A 16x8 to a 17x6 are the traditional sizes used on many 26cc engines. This is not to say that all 26cc engines should be limited to these prop sizes. I am far from expert in this matter. I look to folks such as Dick Hanson, Ralph Cunningham and Bob Postorello for my information in gas engines. There are others on RCU that are just as expert, but their names elude me at the moment.


Ed Cregger

RE: New SV Gassers
 

But what about the rpm range that I want to be in at full throttle, restrained ? Do you agree with the 6500 to 7500 for the most torque from your experience. As I said, im at 8200 right now. What have you read on the 26's about that ? Im afraid that im reving it higher than necessary, and missing out on some power because of it.

RE: New SV Gassers
 

From what I have found, as a rule of thumb.
Take any engines manufacters rpm range, ( SV 26cc range is 1400 - 9000 rpm ).
80% of the max rpm would be about the best tourqe of the motor.
If you can get it proped in that 80% range, it is a good starting point and you can experiment and tune from there.
So, the SV 26cc, I would say, should be proped at around 7200 rpm.

On the other hand:
With 2-strokes, and propellors, you basically want to turn the prop as fast as you can without ripping it ( tips going super sonic ), because when it rips it loses efficiency. Most props gain 10% or so in RPM over ground RPM numbers when they unload.
But that all depends on what you want to do ,3D, pattern, speed, etc.

We all know that you can turn a 15 X 4 at 9500 rpm but a 18 X 6 at 7200rpm gives you much more power.

I do it the first way listed and it has never let me down.

RE: New SV Gassers
 

Basically, I just fly slow most of the time. I like the scale look and sound up there, but with the 16x8, my engine is winding it's guts out. I'll give the 18x8 another try today. Thanks !

RE: New SV Gassers
 

I'm running a CRRC Pro GF26I with a Xoar 18 X 6 @ 7650 rpm with a idle of 1850-1900rpm.

RE: New SV Gassers
 

I'm running a CRRC Pro GF26I with a Xoar 18 X 6 @ 7650 rpm with a idle of 1850-1900rpm.

That sounds alot better than the 8200 rpm mine is turning, thats for sure ! We'll see what the 18x8 does today. Maybe i'll get lucky, and get close to the 7200 im looking for without vibration. The 16 inch prop looks too short for this plane anyway. The 18x8 looks alot more scale.

RE: New SV Gassers
 

Here's todays results... Holy Mackrel Andy ! I removed the 16x8, and put the 18x8 on in it's place. Started it up and it took maybe a minute for it to transition good, and static full rpm was 7100 without touching the needles at all, so we decided to just go for it. I wanted to video it, so I handed Greg the TX and went hunting for the camera. I didn't see the take off, but he said that it jumped into the air and loved the new prop. I cut this video short because another one of our friends was practicing his hovering about 20 feet away, yikes ! Anyway, you can still hear the SV26 enough to get the idea of how it sounds now. Now it sounds like a real plane up there ! Oh, and now it won't shut off by the trim anymore, it would rather idle at 930 rpm until you get tired of waiting for it to die and shut it off. I love that ! After Greg flew it around for a while, he handed me the TX, and I flew it for maybe 10 minutes then landed, but someone stole my tailwheel and 1/2 the wire it was on ! lol My first donut !
Im installing one of those leaf spring tailwheel assemblies on er tonight, so tomorrow is gunna be awesome. I think you'll agree that the new lower rpm sounds alot better, and the pull we gained is amazing.
http://www.youtube.com/watch?v=b1FbGg2c58w

RE: New SV Gassers
 

That's pretty close to what I was saying the SV should be proped at.
Your @7100 rpm and my 80% of the 9000 rpm is 7200.

My CRRC Pro GF26I rpm range is 2000-9500.
So 80% of 9500 is 7600rpm, and with my Xoar 18 X 6, I am @ 7650.
On a digital scale I have 14.4 lbs of pull at wide open with it hooked to the tail wheel of my plane.
My plane is @ 11 lbs. 2 oz.

RE: New SV Gassers
 

I guess it's time to find a fish scale.

RE: New SV Gassers
 

Hell, just order 3 SV26's, and if your lucky like us, someone will forget their reading glasses that day and give ya 2 SV 26's and a 50 by accident. It happened to us, but were not didn't complain about them messing up our order.

RE: New SV Gassers
 

Well, Greg came over and we played like we were A&P techs again, cut a chunk of the rear out and epoxied in some hardwood, and installed the new leafspring tailwheel assembly. The tire is a bit soft, and looks like it's a little low on pressure, but thats ok for now. We also put the landing gear cover on under neath, so aside from the cowl, the plane is done. Any one know of a better muffler, I really don't want to cut my cowl up.

RE: New SV Gassers
 

These numbers are with the CRRC Pro pitss muffler and only 3/4 of a gallon of fuel run through the motor @ 40:1.
The stock muffler may produce more rpm's, since most pitts mufflers are more restrictive.
The CRRC motor is replacing my OS 1.60FX which was getting 7250 rpm with Bisson pitts, and a junky Master Airscrew wooden 18 X 6.
I am gaining 400 - 450 rpm with a much, much better prop and it weighted 2 oz less then the 1.60FX.
And this is from an engine that is suppose to be equal to a 1.20
Please, some of you guys with the SV 26 post some numbers with a Xoar 18 X 6.
I would like to see how they compare.
I got my CRRC @ the door for $195.00
http://bigbikeriders.com/photopost/d...er_200_004.jpg
http://bigbikeriders.com/photopost/d...9pg0111_lg.jpg

RE: New SV Gassers
 

------------


I'm an old schooler that doesn't believe in choking down two-stroke engines - gas or glow. Let'em rev. However, today we must be noise conscious, especially with gas two-strokes, so experimentation is definitely a good idea. If you can pull more prop at a lower rpm, your sound numbers should drop considerably. In the video, yours sounds great to a two-stroke model flyer, but it was awfully loud and would get you in trouble at some of the flying fields around here.

The fastest, high revving gas two-strokes utilize rotary valves. The SV engines are equipped with reed valves. These are usually used for a strong midrange or bottom end torque. There is no absolute correlation between intake types, however.

Your SV-26 sounds really great in your Super Stearman 1.20. Experimentation is great, but I'd say that you were probably very close to optimum power as it is. But if you can find a satisfactory compromise in a larger prop that lowers volume, it will have to be a good move.


Ed Cregger

RE: New SV Gassers
 

2robinhood,

I am using a APC 16x8 & 18x6w on my SV-26 and I am getting 8100RPM with the 16x8 and 7300RPM with the 18x6w. I Don't have a Xoar 18x6 prop but I would love to try one ont this engine to compare numbers. My plane is a Goldberg Stiinson and with the APC 18x6w I only have about 1/2" ground clearance. So it looks like I will be using the APC 16x8. My plan weigh's 12lbs and wiith the 16x8 it is getting real close to 12lbs on thrust using a digital fisj scale so I know it will fly OK for my type ot flying.:D

I would love to try another carb on this engine so I would have a choke, but the new walbro WT-644 I got would not pull feul once the engine started. With the choke closed it pulled in the fuel, but once the engine started and you opened the choke the carb stopped pulling fuel. I am thinking about trying a WT-433 carb and give it none more short. I want a choke because my engine is inside a cowl and it is very hrad to get started when it is cold out.

RE: New SV Gassers
 

Im not choking my engine down, im just keeping it in the power band by limiting the rpm with pitch. My engine was doin 8200 with the 16x8, but it didn't have any grunt. Keep in mind, my Stearman weighs 15 lbs, so I needed to grab alot of air to get it moving. Before, I would slam the throttle, the engine would instantly go to 8200, but the plane would just slowly accellerate, and after about 50 to 75 feet, liftoff. Once it got going, it would get with the program, but it just didn't seem right to me. Now, with the 18x8, I slam the throttle, and the plane instantly pulls away hard and fast, and leaps into the air within maybe 20 feet.
It still flys as fast, it just gets there alot quicker, and with alot less rpm. It sounds more like a real plane now too. Also, before, Greg couldn't get a knife edge out of it, but now it does it effortlessy. The fact is, more rpm is not always better. I lost 1100 rpm static, but gained a ton of thrust, power, accelleration. Top speed is about the same, but now it gets there pronto.

RE: New SV Gassers
 

And that is why I say that you must experiment with props (as you and many others know) to find the right combination for the engine, airframe and your expectations. Were you flying a giant Dirty Birdy or Chaos with that engine, chances are the 16x8 or 16x10 would be the best choice.

You would really cringe if you saw/heard my Zenoah G23 running. I prop it for 10k rpm on pattern type models. It likes it up there and it howls, much to the surprise of the scale types that love to lug their engines down. The Zenoah G23 thrives up around 10k rpm. No shortened life and lots of other problems disappear too. I don't give a hoot about scale-like anything, especially sound. Why? Because it can't be done with a small model engine no matter how many cylinders, how many strokes nor whichever rpm one is running. It is a lost cause. Quiet is another matter entirely, though.


Ed Cregger

RE: New SV Gassers
 

Good to see ya all headen the right way:D,,,18x8 ,,7200rpm ,,,10lb under for 3D;)

RE: New SV Gassers
 

Some engines develope their power at 12000 and some at 2000 to 2500 like a deisel truck.
The SV's power band is supposedly 6500 to 7500, and if thats true, you don't want to exceed that rpm, or your just wasting gas and missing out on power. The same goes with any engine.
At 7100 static, that supposedly put me at maybe 7600 unloaded in the air, and thats 100rpm too much, but close enough for me. I think we need to get the fish scale out and compare numbers between props. I guarantee that with an 18x8, my SV 26 will pull lots harder than it will with the 16x6. Im guessing by a couple of pounds at least, judging by the way my 15 lb Stearman jumps into the air now. It actually startled Greg. I wasn't watching as I was looking for the camera, but I heard him hit the throttle, and I heard him say "Wow ! it really likes that prop !" Greg didn't think that the 26 would pull the 18x8. Surprize ! It does it quite well. Bottom line: I don't care what an engine is bolted to, once ya go outside the power band, your losing horsepower, and the excessive rpm uses more fuel as well. Wait till ya see my next video, you won't believe the difference !

RE: New SV Gassers
 

Rember ,,your not at WOT for very long times at all ,,unless your raceing,,and the bigger the prop ,,,the longer spool up time,,,So there is combo's for different type's of flying

RE: New SV Gassers
 

It grabs its R's just as fast, just less of em, but now it takes off like a rocket compared to the 16x8 turning 8200. Top speed is probably the same, but it gets there a hell of a lot faster now. Just a few seconds actually now, when before it took the plane maybe 20 seconds to get to top speed. More like about 10 seconds now from a dead stop. Suttle rpm changes yes, for different types of flying, I agree, but to over rev or lug any engine is a waste, and also hard on the engine. In my opinion, a 16x8 prop is not suitable for the SV26 on any plane. Not with the stock carb anyway. Just my opinion which I have developed in the last couple of days from my own experience.

RE: New SV Gassers
 

Im amazed you reckon no differance in spool up time ,,,I realy noticed the diff between even the 17x8 to the 18x8 on mine made a diffrance,,a lot more low end torq but a lot longer to spool up,,,when i was useing a chep prop there wasent much diff but the blades were flating out,,but with a no flex blade i found a big diff,,just my 2 cents worth from useing this motor for 2 months now