SpinnerRow

I have a brand new ST G-90 that I plan to put a pipe on. It is a Macs Muffled Tuned Pipe for a 10cc engine (yea a bit small for this motor) and I'm going to use a Macs 2900 header (for a G-60 and G-75 - yea a bit small here as well). The header and pipe aren't ideal for this motor but I'm not looking for every ounce of power as it will be going in a small plane (New Ultra Stick 40). I've started a thread on the plane in the ARF section if you are interested in following this insanity.

Breaking this motor in on a Zinger Pro 13x6 and it seems pretty freaking strong on the stock muffler. I'm looking for a touch of speed and good vertical (no 3D stuff) out of this plane and don't want to lean to far in either direction and would like to keep the pitch above 6" for decent speed. The size of the plane limits me to no more than a 13" prop I would think and would like to run a 12" for clearance. What would you guys recommend prop-wise for this motor on a 10cc pipe? I'm trying to avoid buying all kinds of props to test with. Right now I have a Zinger Pro 12x8, 13x6, 13x8 and a 13x7 Evolution ($1.99 hard to pass up). I'd like to stay with wood if I can to keep the weight down up front but am willing to run whatever prop that works well. The Master Airscrew 3 blade 12x8 has come to mind but I don't know if that would be too much or not. Maybe a MAS Scimitar 12x8 wood. From what I have read about this motor, it looks like I need to keep the RPMs in the 11,000 range.

TFF

The first thing to do is pick one of your props, I used a 13-7 Zinger on a 90 pattern plane, muffler baffle removed, and test back to back with your tuned set up and the stock set up. The tuned one might hurt because it is too small. I like wood props and almost only run them, but an APC 12-8,9 would probably be the screamer.

SpinnerRow

How do you remove the baffle on a Super Tigre muffler. The thing looks pressed together.

I was going to run all of the above mentioned props with the stock muffler setup first to get a base line. I can't imagine the non-optimal sized pipe would hurt it. The inside diameter of the header pipe is larger than the stock muffler setup and the pipe exit is larger than the muffler exit. I think it will be fine. I probably won't cut that much off the header though before it hits the sweet spot.

daveopam

My Feedback: (9)

The baffle removal is easy. Stick a screw driver in the end and drive it forward. Then roll it up with a pair of needle nose through the header opening, and pull it out.

13x7 or 13x8 would be my choice of props.

David

spaceworm

ry this link for Billington's review and results: F:\COMO\SuperTigre G90 Product Review.mht

I have the S90 and love it. Good luck

SpinnerRow

Do you have a URL? That file looks to be on your hard drive.

spaceworm

Sorry 'bout that, picked wrong file: Here is the URL: http://www.supertigre.com/engines/supg0235-man.html

SpinnerRow

Thanks, I've read that before. Good info for anyone wanting to play with the G-90.

Thanks!

SpinnerRow

OK, got some prop numbers.

Ritch's Brew 5% Nitro, 11/11 castor/syn blend oil
Temps were about 50 degrees.

Motor had about 36 ounces of fuel through it when the tests were run.

Stock muffler and stock Super Tigre plug:

Zinger Pro 13x6 - 11,500
Zinger Pro 12x8 - 11,100
Zinger Pro 13x8 - 10,400
APC 12x10 - 10,400

Uncut Macs 2900 header and 10cc (for a .60-.75 motor) muffled tune pipe with stock Super Tigre plug:

Zinger Pro 13x8 - 11,500
APC 12x10 - 11,500

I didn't test the other props as they weren't going to be enough prop I thought. I'm not sure if cutting the header will give me any gains since this is a rather short pipe for a .90 size motor but next time I'm going to cut a half inch off and see what that gets me. But an 1100RPM increase by just bolting the header and pipe is about what I expected. The 12x10 at 12,000rpm gives about 12lbs of thrust which should be just right for my 6lb model! I think the APC 12x10 is going to be the prop I run but I'm going to buy a wood MAS Scimitar 13x8 and try that one next. I was surprised how well the G-90 pulled the 12x10. I'll post more numbers as I get them.

How do these numbers compare?

sarpet

webra .90P5 with webra pipe and no nitro apc 12x12 11500rpm

SpinnerRow

I guess I have some pipe tuning to do!

Kweasel

My Feedback: (29)

I think you can get best overall performance with 12" props with 8-10" pitch spinning at least 12000 rpm. It wont take long to find the best prop/pipe combo. Just get the pipe surge at 80% throttle on the ground. If you damage APCs too easily then try a plastic MA scimitar, they perform about the same, handle prop strikes better, and are half the price.

brjensen71

My Feedback: (1)

With a few modifications I was able to get 13500 from my ST90 with a 11 x 12 APC prop

http://www.rcuniverse.com/forum/m_8086613/tm.htm

SpinnerRow

Good information! Thanks for posting.

Are there currently any OS carburetors that will fit an ST G-90? I seem to be able to tune the transitions better on an OS carb while running a pipe.

SpinnerRow

Tuned the header length a bit today. The sweet spot seemed to occur after cutting about 1.5" off the header. 3/4" first, 1/2" the second time and the 1/4" the last cut. It only got maybe 100rpm the last cut if that. Left it alone right there

Ritch's brew 5% 11/11 castor/synthetic. Motor has about 48 ounces through it so I still got a ways to go on breaking it in.

APC 12x10 > 11,900 with a pinch into 12,100 or so
Zinger Pro 13x8 > 11,900

I'm going to run the 12x10 as I need the ground clearance. This engine idles happily at 2400RPM and can even go down to 2200 but not as reliably. Near instant throttle response. Transition after letting it sit on half throttle for 15-20 seconds is a little sloppy as all of my Super Tigres on a pipe seem to be. Tuning the low end until it does a lean bog on a throttle blip and then richen it up a bit.

All in all a nice engine for about $120 after Tower's discounts.

NM2K

My Feedback: (14)

The instructions say that you can run a prop as small as an 11x8 without encountering a problem with this engine. I was thinking that one of the old long stroke pattern props would probably be the best for lots of speed with a tuned pipe. If you had a 15cc sized tuned pipe, I would go with a 12x7 or 8. However, since you are going to run a 10cc sized pipe, I would drop down to an 11x11 or 12 sized prop. Don't forget to install a head shim or extra head gasket in order to reduce the compression. If you don't, you'll go through glow plugs like someone goes through popcorn at a movie theater. Good luck and come back to this thread with the results/findings of your experiment.


Ed Cregger

SpinnerRow

Speed is going to be enough with the 12x10, an 11x12 would be nuts. This is going on on Ultra Stick .40 sized plane. I think I need to stick with the 12" or 13" prop. I'd probably rather run the 13x8 but I don't think ground clearance will let me.

Where can one procure head shims for this G-90? I usually run 15% nitro fuels and I thought about running a head shim on this engine to allow me to run the higher nitro fuel. I really don't want to carry two fuels to the field.

NM2K

My Feedback: (14)

Back in the old days, I'd pick up the phone and call World Engines, but you knew that too. Today, I'd give Tony Stillman of Radio South a call. If he has a spare moment, he could probably point you in the right direction. He may even have them in stock himself. Anyone else?


Ed Cregger

SpinnerRow

Tried a wood Master AirScrew Scimitar 13x8 and that is my favorite prop on this engine so far. Throttle response is insane and the engine would spin that prop 11,700-11,800.

SpinnerRow

Here is a video for you guys. At about 54 seconds in, I let it sit at part throttle for a bit and then nail it WOT. There is a slight hesitation there for a couple of seconds with smoke pouring out the back. This is the rich transition that I seem to experience with all of my Supertigre engines. Not sure how to tune that out. My OS engines don't have this problem. When I put the tach up, i richened it up a few hundred RPM as it was sagging when I would do a quick pinch of the line. The throttle response with this MAS 13x8 is real nice. The heavier APC 12x10 doesn't have this kind of snap to it. I like this prop enough that I made a set of landing gear for my Ultra Stick last night that is 1.5" taller than stock so that I can run this prop. The Zinger Pro 13x8 gives me close to 12,000RPM but I think I'm going to stick with the Scimitar and maybe put 1/4" or so back into the pipe length. The engine seemed smoother with the extra length.

Opinions?

Flyer95

My Feedback: (1)

Nice results! A slightly longer pipeheader is always a good idea. I have had better succes with OS-F plugs on my 90 or larger twostrokes. It can clean up the midrange slightly and give more explosive throttle response too. 22% oil is actually too much as 15-18% is more than enough. Too much oil in the fuel gives more adjusting problems, rich midranges and more risk for deadsticks.

SpinnerRow

Could I just order a gasket set from Tower and put an extra head gasket in it? The price is right at $1.49 !

Flyer95

My Feedback: (1)

Yes, if the engine does not responds so well to adjusting the main needle, or sounds rough on wot, then the compression probably is too high and would be better with an extra head shim.

SpinnerRow

After the engine was mounted up on plane, I found the high speed needle valve was just about worthless. I had a 13x8 Master Airscrew Scimitar on it and it was turning 11,500 or so and struggle to get that. It was running lean and no amount of high speed needle adjustment would fix it. So I decided to try a Zinger Pro 13x6 and it responded with 12,600 coming up on the pipe and running super rich. The needle valve was useful again. I had to turn it in almost two turns to get it to lean out but it was no longer running lean. Motor was running strong with good throttle response. Is the pipe too short for the 13x8? Any of you pipe gurus care to explain why this is happening?

Cyberwolf

My Feedback: (4)

I have follwed this thread from the start but I didn't make any comments on it untill now, Your probley not going to like what I have to say, but here goes. At one time I to tried to use a 60-75 pipe on a ST K-90 I ordered the wrong one by mistake. I had two of the same planes both using the St-90 engines one was the K and one the S series The S series I had the correct size pipe on and it ran like gangbusters, I didn't have any lag or run up problems using a 13x8 MA prop, now the other pipe set up was nothing but trouble I couldn't get the turns out of it, it would get hot if I tried. I know it was the pipe doing it cause I changed setups and got within 100 RPM's of the other engine and things worked out good. So I bit the bullet and bought the correct set up and solved all of my running issues.
I know the G-90 is more of a torquer than either the S or the K series engine are and your not going to see the RPM's I did when using that size of prop, but I still think the wrong pipe may be adding to some if not all of your problems.
Normally when the HSN won't adjust it not getting enough tank pressure, but why it would change with a smaller prop is strange, maybe the extra RPM's is supplying just enough to operate that prop????