SonexBuilders.net

I bought a Onex in September. I have flown it 27 hours and decided to change the oil, adjust the valves, and put in new spark plugs. I also learned that it was running rich after reading the aeroinjector manual. The engine ran smoothly and there didn't seem to be any problem except the EGT temp differential. At cruise power, the EGT differential was 160 degrees. The manual says if it is more than 100 it is too rich. So today I adjusted the mixture about 1/8 a turn. I started it, let it warm up, and it seems to be running rough. When I did a mag check at 1500, when I turn the primary off the rpm drops 70 rpm. When I turn the secondary off it drops 120 rpm. I know some people have said pilots turn off the secondary while taxing because of the power it uses. I have not been doing that. My aeroinjector has the 3.0 needle in it. My questions are (1) does the rpm drop seem high when I turn the secondary off, and (2) is it normal to be using th 3.0 needle in the AeroVee?

Thanks in advance for your help.

Hi:

IMHO and experience the 50 rpm drop is just a rough guideline. It's going to vary depending on time of year, temperature, mixture position in the cockpit, etc. 70 rpm is more than fine and not cause to change anything that is working. If the engine was running smoothly, then I'd stick with it and look for other signs of richness: black exhaust, black spark plugs (have you had a reason to look at them yet?), excessive fuel burn. I average about 4.5 gph with my AeroVee and AeroInjector in my Sonex. EGTs are notorious for not being accurate. Just a 1/8" difference in where they are located in the exhaust stream will give different results. They are best for noting trends and not for being absolute. Mine happen to run around 1250 deg on average. Using EGTs for tuning never worked for me. Other engines will be different.

The needle size varies between each engine. It's not a high precision piece of hardware. I started with a #2 and it ran too lean no matter what I did. I switched to a 2.5 and got it dialed in pretty quickly. Some people run a #3 and get it dialed in for them. I haven't touched mine in 5 years.

I did extensive testing of the needles, making seven my self, and ended up using #7 which is a virtual copy of #3. Because it allowed the wot mixture setting to be the same as the idle setting. My rpm drops with ignition testing are a little lower than yours but I test at 2000 instead of 1500. I used 1500 on the Cessna mags but the Aerovee system doesn't put out until a higher rpm and I want full voltage when I test. EGT's vary at cruise rpm (2950) about 150 from the hottest to the coldest. I set the mixture a little rich at takeoff wot and lean it out at cruise to get the EGT's in the 12 to 1300 range which gives me a fuel burn of about 4 gal/hr. Plugs are clean and after landing with a hot engine it idles at 900 - 1000 without a mixture change. It's been this way for five years. 325 hrs. and flying. The lower number needles required a major mixture change (leaner) at idle to keep it running. I preheat 24/7 in the winter. My engine thinks it's in Florida. Oil temp always in the 70 - 80's. I figure that way it never goes through the dewpoint temp. where condensation occurs. Does anyone have a comment on that approach? Its just a little box heater next to the nose wheel and a insulated cover over the cowl.

No 3 needle
Mag test at 1800
Mixture - I've just "riched" it up for the winter when the DA is typically minus 2,000ft at Sea Level
Drop is 50 ish. Once really warmed up - a reliable 50
Idles at 900 rpm.
I CAN get it to idle at 750 but after a long descent where the oil gets cooler - it can stop on final or roll out when you throttle right back - so I keep it at 900.

YMMV

I worked on my engine some more today. I also read some more of the manual about timing. As I understand it, the primary ignition is set at 28 degrees btdc and cannot be adjusted. The secondary can be adjusted. When I turn off the primary ignition, and the engine is running on the secondary, the rpm drops 70 rpm. When I turn off the secondary ignition, and the engine is running on the primary, the rpm drops 120. So when the engine is running on the secondary the rpm drop is acceptable. When it is running on the primary, the rpm drop is excessive. But I am supposed to adjust the secondary to get a more uniform rpm drop. What am I missing here?

Just to be clear here. My understanding of the Aerovee is that the "primary ignition" is the magnetrons on the flywheel and the secondary is the 12 volt coils. Is that what you are reporting? I get a larger drop, at 2000 rpm, on the coils.

My experience is that the "mag rpm drop test", when done on the ground, gives me an OK starting point. However, the real test is done during the flight. I might see a 90, maybe 100 rpm drop on the ground but it is right at 50 when done in cruise.

Yes, when I was speaking of the primary I was talking of the Magnetron and the secondary is the 12 volt coils.

I know there are many of you in this forum who are experts on the AeroVee engine. I am trying to learn the fine points and get mine running as well as possible. I am looking for one of you experts who would be willing to talk to me on the telephone about this engine. My number is 205 531 9959. Or you can PM me with your number and I will call you. Thanks in advance.

John

Thanks for all the reply's. A couple of guys did call me and I think them also. I adjuster the mixture 1/8 of a turn and then went and flew it. It flew fine, and when I turned off the primary ignition, so that it was running on the secondary as mentioned in the manual, the CHT's did not change. The rpm drop when the engine was fully warmed at 1800 was about 50 a side. I did two flights and the engine performed well.

The next day I went to fly again and the engine would not start. I realized that I had left the fuel shutoff valve on. When I tried to start it the was a pool of fuel on the ground and it was flooded. So I put it back in the hangar, put the battery charger on it, and went home. Yesterday, two days later, I went to fly again. Again it would not start. The engine turns fine but when I got out there was a pool of fuel on the ground again. I did not have time to troubleshoot it yesterday so I just put the battery charger back on it and left. I will go back tomorrow or Saturday to work on it.

My question is does anyone have any idea why it will not start? It ran fine on Saturday, and Sunday afternoon it would not start. I figured it flooded because I left the fuel valve on, but yesterday when I attempted to start the engine it had been setting for 48 hours with the fuel valve closed. I would have thought that any flooding would have cleared itself in 48 hours. The only adjustment I made was 1/8 a turn on the mixture. I would appreciate any ideas before I go to the hangar to troubleshoot.