ASP 180 Four Stroke

I have a ASP 180 4str, swinging a 17x8 prop, installed in my Super Chipmunk. It runs happily and has quite a few flights BUT! it arrives at max RPM (8300) at half throttle which is rather annoying because after half stick there no nothing. The throttle barrel moves fully from idle to fully open so it is not that.

I had a quick discussion up the field with a few members on this issue I would like to resolve. After checking throttle movement it was suggested changing fuel from 5% Nitro 4stroke mix which includes some castor to Content 10 (10% nitro) I have got Optifuel 12% nitro/synthetic oil which is near enough. Albeit, power is not the problem, it pulls like an ox but the throttle.

Any ideas Guys?

Sounds like the carb fitted is just not giving a linear response, I wouldn't think there is much you can do to change that.

If it were me I would just set up a throttle curve to produce a linear response. In your case the curve would be very shallow for the first 3/4 of stick movement from idle and up, then the last 1/4 stick movement to full power would be steep. This would produce movement of the barrell from idle to half open over the first 3/4 ish of the stick movement. As long as you end up with a linear response, it really doesn't matter where the barrell is at each stick position.

Hope that makes sense.

Thanks Jon, I will set it up as per your suggestion so it feels linear on the stick.

Hi Phil, Sound like you are reaching max revs and you cant scale the amount of air that you can get through a set size hole in a given time, need to increase load then larger throttle opening will work, increase the nitro will increase the oxygen content of the induced mixture, as air only as 14% oxygen anything that increases that will help, but I would put on a coarser prop and give it a try you can then throttle down for the same speed ,regards Frank

FrankRobinson wrote: air only as 14% oxygen

Just in case any of our junior members are reading this...air only has 21% oxygen. Make sure you remember this for both your English exam as well as science.

9 out of 10 again

FrankRobinson wrote: 9 out of 10 again

Near enough Frank! :lol:

I have set up a throttle curve anyway for a more linear feel. I'll try the largest prop I have which is carbon 18x8 (Biela) wide blade. That should load it! I will go back to using my Optifuel 12% nitro too.

Hi Phil, Will be interested in the result, Mike was quite right about the oxygen content it is 23% if we want to be right with the facts. The problem with engines is that Oxy is a bit heavy and a slow mover so does tend to get left behind plus the fact that you dont get a complete burn so we always used to work on 14 / 17% when setting up the amount of fuel to use. I can see that general facts are going to be jumped on so will have to whatch my P and Qs Regards Frank

Don't worry Frank it's not personal, there's always someone ready to jump on the smallest error on this forum (quite often it's me )

JonTappin wrote: Don't worry Frank it's not personal, there's always someone ready to jump on the smallest error on this forum (quite often it's me )

Where as in real life it's me! Trouble in reality is there isn't always time to stop and 'reread' what you're about to say!