60L on Sundowner 50
 

Bob,
Your post on the 60lx installation in the 50 Sundowner thread was great, and we now have a pretty good idea of what to expect for speed. Dubb estimates that an SJ50 with the lx muffler will only be about 5mph slower, around 125. Both these use the high RPM / smallest prop disc theory, to achieve maximum speed. The SD 50 weighs 5 3/4 to 6 pounds with the fixed gear and intended as a fast sport plane, which is how I would want to fly it, and would be willing to give up a little speed for more torque in the turns.

Someone reported that his 60L set up on a pipe would turn a 10x8 @ 16k. Can you give an educated guess how the 60L with the LX muffler would perform regarding rpm and speed. At what rpm would the low rpm engine timing try to govern itself when asked to turn up? What would be the target rpm using the 10x8 prop? Also, at what rpms would it start staging on this muffler?

Thanks, Joe

RE: Sundowner 50 options
 

Hi Joe,

Thanks for writing......

Adding the LX muffler to the 60L is sorta a waste. The timings do not match up all that well. You will have to match rpm to the muffler, and the LX muffler is tuned for best boost 17.5K and higher, and you want a minimum ground peak rpm around 17,000 so you back it down around 16,300-16,500 for flight The 60L really is not intended to support the higher rpm range. Yes, it will run great, but you are back to a 9x8 prop to get there.

The SJ-50 runs better with the LX muffler than a 60L would.

Do not be concerned too much about the small props. And do not get hung up on the high pitch for speed stuff. The plane performs great. A few too many 3D guys out there have convinced the world that all planes need giant props to pull well in turns. The sundowner with the 9x7 flys as well as it does with the 10x6 in all aspects of flight. The bigger prop only helps it slow down a bit for landing.

A standard Jett-stream (red) muffler fits the Sundowner installation just as well.

Since you are looking for good performance and a better sport balance on the plane......
A regular SJ-50 is probably your best bet. This is just a very simple engine to operate. Adding the LX muffler boost rpm a bunch by trading torque - dropping the prop size a bit... no change in reliability and remains very user friendly

I would suggest either the following setups

1) A standard SJ-50 engine - standard Jett-stream muffler. A standard 10x6 prop is fine, and you can also go with 9x7 or 9x8 if desired. The engien also runs well on a 10x7 on quicker airframes once you have time on the engine. 15,500 to 17,500 rpm range. (I recommend this setup)


2) A standard SJ-60L engine - standard Jett-stream muffler. A 10x6, 10x7 or 11x5 prop. A 10x8 is possible with some time on the engine. Has just a bit more torque than the SJ-50 for the bigger props. Figure on 15,000-16,500 rpm range.

3) A SJ-50 engine with the LX muffler. As dub noted, just short a few MPH on speed from the 60LX, with better reliability. Stick with the 9x7 or 9x8 props. No lack of performance. Looking for 17,000 rpm and higher. Installation will be identical to that shown on the photo pages.

4) OS55AX with jett-stream muffler. Go with a 10x7, 10x8 or 11x6 prop target peak ground rpm 14,500-15,000. Has proven to be a very impressive combination if maximum speed is not your primary concern.


As for the SJ-60L turning the 10x8 at 16K rpm .... on a full size pipe, yeah that is possible. But that is the luxury of a full size pipe - lots of boost, and you can tune it specifically to the prop load. A jett muffler gets about 85% of the power boost possible from a full pipe, but gives you a broader tuning range.

I hope this is helpful

RE: Sundowner 50 options
 

Bob

Excellent answers as always. So what would you estimate the top speeds would be for :

- The SJ-50 with the red jetstream muffler?

- The 60L with the red jetstream muffler ?

Thanks, Joe

RE: Sundowner 50 options
 

Figure the 110-120 range most probably.....

and who knows..... it might surprise you :)