SonexBuilders.net

Hello Everyone,

Have flown my new to me Sonex/Aerovee a few hours now and love it! I am, however, experiencing a throttle cable issue I would like to ask about.

When the throttle is full open, as during climb out, there is enough back pressure on the throttle cable that the throttle will close to as little as 2000 rpm. This will occur unless I make the throttle lock very tight. Is this normal? Do I need a new cable? Does the AeroCarb need adjusting? Other?

On certified aircraft I have flown, the throttle pretty much stays where you put it. The lock is there as a safety back-up, but the throttle position usually stays stable whether the lock is used or not.

Aldo
Sonex #947

Aldo,
A lot of the cub family has a throttle that creeps down, from my experence. I can't say what is normal for a sonex though!

I believe this is normal. The engine is like a vacuum cleaner trying to suck in air wherever it can find it and in the process sucks the throttle plate inwards at full throttle. As far as I can tell the only significant source of friction is the throttle lock. You probably don't want to add any friction anywhere else either or it could make reducing power difficult. The couple times I've noticed the throttle reduce on me I've given the lock an extra little turn. I never loosen the knob to make throttle adjustments.

I hadn't played with it to discover that it closes to 2000 rpm. That's interesting.

I have the older aerocarb with a Cessna style push pull throttle as opposed to the pull open lever type. If I don't lock the throttle with the friction lock on full power operation the throttle will return to idle setting. I am used to turning the friction lock from driving Luscombes and Cessnas so it's muscle memory, but I have reached over to adjust mixture and the lock wasn't tight enough and the throttle has dropped to idle or slightly above. Things got interesting when that happened but it was obvious what was going on so easy correction. Remember the Aerocarb and aeroinjector are completely different animals than most of us are used to in the certified fleet. With the above to cited planes I would get creep on the throttle if not locked. The Aerocarb is quite a bit more abrupt in it's response to my negligence of locking the throttle before removing my hand from the control to do other things.

Thanks Chris, Bill and Bryan! It sounds like what is going on is very normal. I have the push/pull style as well - so even more likely there is no problem. If you don't mind another simple question:

Is it also common for the mixture cable to result in no noticible leaning until it is pulled out a significant distance? Without measuring, I would estimate I pull it out about half way before noticible leaning starts.

http://www.amazon.com/gp/aw/d/B005LRS4Q ... ot_redir=1

Aldo, here is a link to what I use. It makes setting the friction much easier.

Ken W
Sonex 959
Aerovee 282 hrs

Aldo wrote:Is it also common for the mixture cable to result in no noticible leaning until it is pulled out a significant distance? Without measuring, I would estimate I pull it out about half way before noticible leaning starts.

At WOT I think there is a small band of half an inch near full rich where I don't notice leaning. If I pulled mine out half way at WOT, I'd probably be running rough. At idle, I can pull the mixture out quite far before noticing much affect.

Is your mixture arm at a 45 degree angle when full rich (like shown in the aeroinjector instructions)? I think if you go beyond 45 degrees there can be a region where the mixture control doesn't do anything, but I think you'd have to be way past 45 degrees to matter (even 10 degrees off only corresponds to a small distance on the mixture knob).

I remember you previously discussed tuning your Aeroinjector. How did that go?

Has anyone considered putting a spring on the carb that pulls the throttle open? I know there have been a few instances of the linkage cable breaking at the throttle lever. It would seem to make sense to put in a spring that helps with not only the creep issue but also as a safety in case the cable breaks.

Keith
#554

I found a PTO throttle that I'm going with. It's locking vernier and is heavy duty, no way the cable will break that I can see after pulling it apart. Plus cost was low... http://www.amazon.com/Buyers-Products-VCGTX06-Locking-Adjustable/dp/B00CMTYGZM Now looking for a sister in blue for the mixture.

If you use that throttle with an aeroinjector, won't you need a way to reverse the action so pushing forward still opens the throttle? I'd be concerned about introducing another two possible failure points into the system. Not knowing any details about previous cable breaks, it's hard for me picture how the quadrant and cable I got from Sonex within the last year would fail (that wouldn't also affect this or other throttles). Hearing about cable breaks has caused me to inspect the connection at the throttle quadrant more than I probably would have.