Got this engine for a trainer for my dad. Didn't want the engine to be to much so i settled with the ST 40. I was sceptical but am very surprised. Break-in went smoothly. Idle was rock solid and transition was great. Leaned her out to just under peak and i was shocked [X(] at the rpms reading. 13,500 turning a 10-6 prop. Is that to much, should i move up to a 11-6. Was expecting like 12,000 but 13,500.
Thanks
Cameron

The 10-6 will be fine

I do not know the wt or wingspan of the trainer but I would try the 11x6 you will get plenty of thrust at a lower rpm you do not need
13K on a trainer I have a couple of VMAR apache lls that are HEAVY and the irvine 40 diesels in them turn a max of 10000 and
they do fine they are swinginq 12x6 props the ST40 is a fine long lasting engine a great value, think the tower price $50 and ringed
martin

13,500 on a 10x6 is excellent! My OS LA 46 only does 12,000 on an apc 10x6. Just for kicks I would throw on an 11x5 and see what you get. If it's above 12,000rpm, then I would use it.

Hi!
In a high winged trainer a 10x6 isn't the best prop size . Try a 11x5 or 11x6 APC instead

Thats what i was thinking, don't need screaming rpms. I am going to try a 11-6 when i am confident the engine is broken in. The trainer will be the tower .40 trainer
As you can see, don't want to spend to much on this plane, hard to say how long it will last with my dad on the sticks

Don't waste your money on 11x6 . Thats alittle too much for ST40 . Just stay with the proven 10x6 and use the throttle. 13,000 Rpm is the sweet spot on that motor.

I agree with speedster. My ST's like to turn more RPM's than others like my TT46 Pro. The TT seems to be very happy turning a little less RPM's with a little larger prop like an 11x7. I usually run a 10x6 on my ST40 as it seems to stay more consistant on the mixture setting throughout a fuel run. If I run more prop on it the mixture tends to lean out at the end of a run.

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The one way to seriously limit a two-stroke's useful lifetime is run it excessively hot. The way to do that is to load it down with too much prop. Super Tigres were designed to rev up to "normal" rpm. This normal rpm is higher than what many of today's younger 3D flyers are used to, but they are valid just the same. The problem is that the ignition timing is partially controlled by the high speed needle. If set rich enough, all is well. If not, excess heat is generated. Heat reduces the engine's useful lifespan. One way to reduce heat is to reduce the load placed upon the engine. Finding that perfect compromise between lower temperatures and what is needed to fly the model properly/satisfactorily is the goal.

I'm not saying that you can't run an 11x6 on a .40, but the operator will have to be careful that they do not get off too lean. The same is true with all props, but a 10x6 or 11x5 is less prone to build up as much heat.

Ed Cregger

Hi!
Being an instructor R/C pilot for 30 years I have noticed that 11x5 or 11x6 APC props work best on newbies .40 high winged trainers (at sea level, at +15-+30 degrees centigrade using 0-15% nitro and 15-20% oil). Much better in fact than the more common 10x6 prop.
I agree that it's vital that the engine isn't set too lean and don't load the engine too much. Still ..a big 11x5 or 6" prop provides more uniform pull than a small 10x6 " prop which makes learning much easier for the student.

Regards!
Jan K

I think Ed hit the nail on the head. Some 40 size engines are ported in such a way that an 11x6 will work OK. It has been my experience (which spans almost 40 yrs) that SuperTigres run better turning more RPM's. Others may have different results but I have 3 ST40's one ST45 and one ST51. I also have an extensive collection of other egines including an old OS40 FSR, a Tower 46 ABC, an RJL 60, and various Saito four strokes. One thing I would like to make a point of is that no two brands have the same running characteristics. As with most threads you can get as many opinions as you like and these are mine. I am always amazed at how many experts there are giving their two cents and those opinions vary widely most of the time. I know there are lots of different ways to get the same job done. Good luck.[8D]

Around here we like to use apc 12.25-3.75 or 12-4 on 46-52 engines in trainers to ensure good climbout without too much speed for the new pilots.We have only a short grass strip and 40 engines with 10-6 props is quite a challenge to get up in the air safely.

I think we have overlooked the fact that we are talking about a SuperTigre 40 in specific. Most modern 40's will pull more prop but due to certain configurations used in the ST 40, it is happier turning a bit more rpm's. To get it to turn a little higher one must use a slightly smaller prop. That prop on any other engine will not pull as well and the larger prop on a ST 40 most generally does not pull as well as the 10x6. Again, as with most things in life every brand of prop will behave differently on different engines.

My nephew has an Avistar trainer with an ST40 on it. With a 10x6 MA Scimitar it will get off the ground in 20 ft or less on pavement and climb just shy of vertical. When he first got the plane he was running an APC 11x6 as recommended by the other modlers at his local field. When I got involved with teaching him how to fly, I suggested we try different props to see which worked the best. We bought quite a selection and he tried each. He was most satisfied with the MA scimitar 10x6 for all around performance. That is just but one case as I have favored SuperTigre's for the better part of 20 years.

Most of the manufacturers have backed off a little on port timing in order to increase torque on the lower rpm's and a side benefit is the engines idle just a tick better and slower. I won't invade the discussion again but as I said earlier there are a lot of opinions to be had, mine is just one.

Happy flying!!!!!

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I don't want anyone to think that I was saying not to use props larger than 10x6. I was saying to be careful with the mixture setting.

Personally, I would run-in the ST GS40 with a 10x5 or 6 for a half gallon of fuel or so. This pretty much guarantees that this engine will have enough margin for cooling during break-in. Too much heat can remove the piston ring tension and lead to lower than normal compression. Yes, you might get away with running a 12x8 initially and not suffer this problem, but why take a chance?

The old Super Tigre designs are designed for "old school" flying, which means really revving up to operate in their power band. While you can run them in an over propped condition once broken-in with a rich enough mixture, why? They run best (including midrange throttling) when a lot of air is moving through the carburetor. Over loading the engine and running too much nitro is what causes the bulk of midrange problems that I see folks squawking about with the ST engines.

If you really must use larger diameter/higher load props, buy something like a recently made OS or SK engine. They are tuned to handle it.

The reason that the ST engines are so cheaply priced is because no one has been paid to update their porting/timing. Not because of inferior material.

Yes, larger diameter, lower pitched props get you off the ground faster. No, the lower high speed capability is not of any consequence. That is what the throttle stick is for.


Ed Cregger

We routinely run a 10 x 6 or 11 x 5 APC prop on the SuperTigre GS-40 engines. They should turn in the high 12's. 13K is a good RPM level, and won't hurt the engine one bit. If you're using it to power a trainer, don't worry about the power level. If the 40-size airplane seems overpowered to you, just pull the throttle stick back a bit.

The GS-40 is quite durable, and is very versitile. Bax covered pretty much the gist of it.

For example, some pilots choose the GS-40 for Q-500 sport racing. The engine enjoys the APC 9x6 up front, and turns somewhere just under 16,000 rpm (in stock configuration, stock muffler). Very reliable power.

So do not worry about high rpm - be more concerned about allowing the engine to turn up a bit, and not over-loading it.

The 10x6 is an ideal prop for that trainer application. An 11x4 or 11x5 is a good alternate as others have noted.

Bob