Hey Guys,

I am finishing up a Mystic 90 w/YS 61R with Hatori 650 pipe; want to run a 12x10 or so prop.

Using Cool Power 20/20 Pro Pattern/APC 12x10 with open exhaust, RPM was 10,500.

Any clue as to what overall length of exhaust system should be for best results?

Thanks,

The best RPM range for this engine is 10,500 on the ground. YS made this engine to go against the Hanno special. This engine has loads of low end power. I can not remember what the over all length of the pipe is.....but tune it for this RPM. Give a 12/12 a try too.

Dont think I said so in the first post, but the initial run was exactly 10,500 with the APC 12x10, open exhaust and with pipe/header--could probably shoprten the pipe a little for that prop.

May try the 12x12 just to see what it will do with the pipe at this length.

Thanks,

The Jett Engines website has an excellent step-by-step primer on tuned-pipe tuning especially with respect to propeller size......Mark

hey pattern student,do u have pics of that plane?

No pix right now--may be able to get some in a few days. Will post if I can.

It really looks small for the YS 61R--a good 46-50 2C or YS 63 looks about right--the 61R should be fun!

17.5"-18.5" from the glow plug to the high point on the hatori 650 pipe. If it goes a little lean on the tops of verticals then lengthen the pipe 1/4" and try it again. This is the best way to tune the setup.

Another note is the nitro content could go up. I ran about 25% in mine years ago. I would try the 30% Heli fuels that are around now. The heli motors love them and so do the YS 4 strokes and my OS 140 RX likes it too. I found RPM to be about the 10,500 for best performance.

These are long stroke motors they are basically setup timing wise to a certain RPM. Going with a lower loaded prop is not going to really increase RPM too much. But overloading it will definately drop the RPMs. The 12-11 and 12-12 was a good choice for me. Also the 13-10 was excellent. OS #8 plugs is also a key. This was on 7.5-8lb models. If it got windy or the model was heavy 8+lbs then the 13-10 was a pig.

You ran it open exhaust with only the header this is a really misleading set of numbers

#1 it was not a tuned setup, and #2 the back pressure was not right. Chances are any setting you make are now going to be really lean. I found the motor went rich when the exhaust coupler would burn through or come off. So beware of this. I would open the high speed needle a least before running it on the pipe. I bet you will really have to richen the low end a bunch. I lost a pipe one time and the motor went so rich that it just snuffed out I bet it was like a full turn on the needle to get it to run properly without the pipe.

I found some notes from "Back in the day" on when I ran the YS 61. On a 12x12 I had the set up 16 inches from the glow plug to the first baffle on the pipe. This sounds right.... I remember it being a L-o-n-g set up..... but I would still shoot for the mentioned RPM range as above with what ever the pipe length you use is. It may differ for you since I was in MN at the time and you are in AL.

is the YS61R a 2 stroke engine?

Correct--two stroke, rear exhaust timed for large props (large for a 61 two stroke).

Such engines were used for pattern flying during the "transition period" when fliers were trying to get 61 two strokes to produce the same performance a 120 four strokes.

They were/are still great engines for smaller pattern planes--if you like two strokes.

AAM,

The open exhaust run was only to get some baseline data--I understand that needle settings are very differeent for the pipe.
Not sure I can use the pipe at the longer length because of pipe tunnel on this plane. I intend to run some different props today to find something that will work for this sorta small plane.

Thanks for taking the time to pass along the info.

Sorry for the disturbance, here is a photo of the original Mystic This was powered by a Hanno special.

By the way, I have the YS-61 aswell I have not operated the engine since 1997. I was using as far as I remember an APC 13x9 with a Bolly Carbon/Kevlar pipe. I'll try to find my setting and I'll post as soon as I can.

Here is the photo of my Robbe Saphir I powered by the YS-61 and Bolly pipe.

Made a couple of pix today--will post soon. Cowl left off for test flights this afternoon.

After two flights, we still have an airplane--in one piece!

It goes where its pointed--can't ask for much more. The APC 12x10 at 10500 is plenty fast with LOTS of vertical.

WUSSIE(kidding) Give the 12x12 a try at that RPM. This engine is a work horse.

Only had APC 12x10 & 12x10W--had a Grauphner 12x11 but didn't like the rpm numbers--seemed to bog the engine a little.

Us older guys need to keep things sorta slow and smooth, anyway.

That is why we have a throttle lever and Expo....(LOL)

Impactiq,

I found the left stick!! and the Expo screen--12x12 APC on order!

SWEET!!!!! Don't you feel a little younger now? (LOL)