stek79

Hello guys,
these days I'm trying to setup my engine with the aim to get a more linear response to the throttle stick.

What I observed is the following. From the full throttle position, if I reach the idle on click at time, the engine slowly decreases RPM in a nice linear way (I've previously setup a throttle curve for that).

Despite that good behaviour, if I do the opposite the response is non-linear in the first half stick. I mean, if from idle I advance throttle one click at time, for the first half part of travel, the engine does not increase RPM in a linear way, but very slowly. As soon as I reach half throttle, suddenly RPM increase to a stable level, and from that position to full throttle the response is ok.

Consider the following facts.

1) Hatori header and pipe
2) Pipe quite long, distance from header and pipe is about 2 cm
3) 15% nitro
4) Top end tuned with a RPM meter (some clicks open from the top RPM position)
5) Bottom end is correct according to the 30 seconds the WOT test - good response

Any suggestion is really appreciated!

Thanks

f3a05

When you say linear,do you mean linear as in numbers on the rev counter(for example, half stick gives revs halfway between idle and full)?
If so, as with most piped two-strokes(pattern ones anyway) this will not feel linear when flying.
In my experience, half stick needs to be set about 1000--1500 rpm above the mid-point between idle and full, to give a linearfeel when throttling up in flight.
For example, my OS 160s are set at 1700--1800 idle, they peak on the ground at 8300---8400(so midway is 5100 or so)
And mid-stick gives around 6200---6400.

(Unfortunately,this is an area where the YS160 is superior---you have to be more precise with the throttle stick on a 2-stroke, and there is more margin for error with the YS)

stek79

Thanks for the input, f3a05.

Actually, the aim is to get a linear feel in flight, I've noticed that in the low part of the stick travel there is an on-off behaviour, instead of a proportional power...

I understand that area is the advantage of an YS, but I imagine that the OS can be tuned better in this regard...

You gave me a thing to think, next time I'll measure my mid throttle RPM, perhaps I'm too low.

cchariandy

This is very difficult to define. It depends on the prop, pipe length, needle setting, idle setting, throttle expo, and the fuse volume. You have experiment will all of them until you get the responce you like. You can however eliminate a couple variables like prop and pipe length. Many are using large props to load the OS like 18-10 and 15.75-10 (3Blade). The idle mixture needs to be quite lean (like 1:00 position) to avoid the sharp transition. Those who use the Hatori pipe can give details on lenght. Then you need to add expo to the throttle until it "feels" the way you want it. If the airplane has a large volume it should be a bit easier due to the added drag.

Hope this helps.

stek79

Thanks cchariandy!

Interesting point about lean bottom end. I've actually a much more rich setting, my position is more open than the factory setting - about 10 o'clock.

I'll check that!

rodney tanner

stek79
The final setting will end up around the 12 to 1 o'clock position. Another way to go is to use the 3M 140 twin plug head, with OS#9 plugs.
I have been using that set up with an ES pipe and the transition is perfect. (APC 17x12, 17x13 or 15x13 3Bld).
Keep at it, the 140RX is a great pattern engine.

Super D

Myself and several others run Macs or Mueller header, with an aeroslave or ES comp. pipe.

The typical length is 28+inches from head to end cone. If your shorter you'll get more peak power but less linear feel. Also nearly everyone close to me runs an APC18.1x10 or maybe a 17x12 if its windy.

Maybe someone will post the typical length from head to the first baffle, that may help you on your Hatori rig.

Great engine I have 3.