The big AeroCarb/AeroInjector thread

[Onex107]

Mike, I have been there with my AeroInjector also. I notice in your testing you don't consider air intake. I found my problem for not having full power at WOT to be restricted air, not fuel flow, due to an air filter I consider too small for that volume of air, especially if it has a little oil on it. Try it with the filter removed. Adjusting the needle won't change that. Also, the play in the needle holder was nearly 1/2 turn. The needle is free to move until you tighten that ball joint by bending or shims.

[SonexN76ET]

142YX,

It looks like you have had to deal with a number of the same issues that I did on my first couple of flights. For many of these same issues I decided to go with the Rotec TBI Mk II also.

I enjoyed watching your first flight video. In the video two things struck me as possible issues that could have compounded your AirInjector tuning difficulties:

1. The AeroInjector will not work properly with pressurized or ram air. As air pressure builds up the AeroInjector leans out erratically. Is the intake on the bottom of your cowling pressurizing the air to the AeroInjector?

2. Sonex states you MUST have your wheel pants and gear leg fairings on when you are breaking in your engine. On the small Sonex airframe the un faired wheels and gear legs dramatically increase drag and thus cause high engine temperatures and reduced air speeds and reduced engine RPM. John Monnett made a big deal over this at the Builder's workshop I attended.

I look forward to hearing about your next series of flights with the Rotec.

Jake

[142YX]

Mike, I have been there with my AeroInjector also. I notice in your testing you don't consider air intake. I found my problem for not having full power at WOT to be restricted air, not fuel flow, due to an air filter I consider too small for that volume of air, especially if it has a little oil on it. Try it with the filter removed. Adjusting the needle won't change that. Also, the play in the needle holder was nearly 1/2 turn. The needle is free to move until you tighten that ball joint by bending or shims.

I hear you on the air intake.. the flights were done with the filter on but all of my ground adjustments were done with the filter off. I am using the same K&N filter that many people report good success with.

I don't think i quite had 1/2 turn worth of slop on mine.. but definitely agree that the slop-to-sensitivity ratio is a little higher than what i would like.

1. The AeroInjector will not work properly with pressurized or ram air. As air pressure builds up the AeroInjector leans out erratically. Is the intake on the bottom of your cowling pressurizing the air to the AeroInjector?

Good eye.. I am running a custom cowl right now, but that scoop in the front is just an oil cooler and not a ram air intake. Air is fed to the AeroInjector the same way it would be with the stock cowl currently. The cowl i am running right now has a lot of areas where it can improved upon and I intend on developing a new cowl a bit later with what i learn from flying this one.

I am going to eventually try to feed the Rotec with a ram air intake in the cowl i am developing.. but i don't want to bring this thread too far off-topic. I will say this though, and it was the only point on which I found myself at odds with the good folks at Rotec when I talked with them at Oshkosh this year. They insisted that ram air not be done with the TBI. It is my opinion that it should be fine if done correctly - but the air needs to be properly recovered and/or straightened as it is fed into the inlet. I can see how air being directed into (instead of being sucked in), at some angle other than a perfectly parallel to the throttle body could do unpredictable things to the AeroInjector, and especially the Rotec with it's integral static port right at the inlet. That could screw with the fuel supply pretty bad. But if the ram air intake feeds a plenum where the ram pressure is recovered and the throttle body is just sipping from that pressure tank, it should theoretically be no different than just operating at a lower altitude. I get why Rotec would be defensive about this however, it is probably very easy to not do correctly and they are at risk of people badmouthing their TBI because it "doesn't work right", which would not be good for business.

2. Sonex states you MUST have your wheel pants and gear leg fairings on when you are breaking in your engine. On the small Sonex airframe the un faired wheels and gear legs dramatically increase drag and thus cause high engine temperatures and reduced air speeds and reduced engine RPM. John Monnett made a big deal over this at the Builder's workshop I attended.

Interesting, thanks very much for this feedback. I had really wanted to get the wheel & leg fairings done before first flight, but i got pretty impatient towards the end of the build. I have some friends who told me the same thing - that i would probably get better RPM once the drag was cleaned up, but I don't remember hearing Sonex's stance on the issue. I totally agree that getting those fairings on there will help with some of the problems i was having. I am still confused, however, as to why my RPM was lower in the air straight and level than i got on the ground statically. I was blaming that on the AeroInjector's sensitivity to the ambient conditions of the day, but there may be more too it than that. Right now i have the wheel pants cut & trimmed and almost ready to be installed, but the parts that give the most bang for their buck, the gear leg fairings, are the two last parts of the airplane i still have to fabricate!

[gammaxy]

Shown here is the leaning out experiment that I performed on flight #2. As the data shows, EGT's increase by approximately 200F, go over limits, without much gain in RPM (only about ~75). The large RPM drop is what I attribute to roughness, well before the engine developed full power.

I find it interesting that EGTs on 5 & 6 respond to leaning very similarly to your other 4 cylinders. If they were significantly leaner than the rest, I expect they might have started to go lean of peak and reached a plateau or decreased in temperature while the others were still rising. Any chance those two probes somehow read a little differently than the rest? I found a procedure from MGL to check EGT calibration using a candle:

With the EGT still connected to your instrument, hold the tip of the probe in the hottest part of a paraffin-based household candle. You should get a reading of 930 deg F (500 deg C) on your instrument. If you do, your sender is good!

As long as the CHTs are fine and the engine is running well, I would consider using smooth running of the engine as the baseline for my EGT limits for now.

On my Aerovee Sonex, the leg fairings make ~8mph difference in cruise and the wheel pants make ~2mph (rough numbers according to memory).

[142YX]

With the EGT still connected to your instrument, hold the tip of the probe in the hottest part of a paraffin-based household candle. You should get a reading of 930 deg F (500 deg C) on your instrument. If you do, your sender is good!

Good call on the calibration - I have used tons of thermocouples in my day and never ran across one that wasn't reading properly but who knows. Certainly good for a sanity check.

If they were significantly leaner than the rest, I expect they might have started to go lean of peak and reached a plateau or decreased in temperature while the others were still rising.

Yea, from the looks of the temps upstream of the leaning i would certainly agree - looks like #s 5 and 6 are leaner. Maybe the better atomization of the Rotec will help a little bit with the distribution?

[SonexN76ET]

142YX,

I have just spent the last couple of months working on a RAM air system for my Rotec TBI MkII. Now I see your comment that Rotec is now advising against ram air. Well, this is why I dislike the Rotec technical support. The Rotec website still shows that RAM air is OK to use. There is much conflicting information on the Rotec web site and conflicting information from Rotec's technical support on various issues. The Sonex technical support is far superior. I have been considering going back to the AeroInjector as a result.

Thanks,

Jake

[gammaxy]

Yea, from the looks of the temps upstream of the leaning i would certainly agree - looks like #s 5 and 6 are leaner. Maybe the better atomization of the Rotec will help a little bit with the distribution?

Actually, I was trying to suggest that despite what it might look like maybe 5 and 6 are not actually leaner than the others. I was basing this on the observation that they follow the same basic curve as the other 4. If they really are a lot leaner, I would expect them to follow a different curve or peak out sooner than the others. A lot of variables could cause those two EGT's to read artificially high--are they positioned at the same location on the exhaust pipe, are the wires identical to the other 4 (adding copper extensions to EGT leads will cause errors)?

If the cylinders actually are leaner, perhaps it is due to an intake leak?

I'm not actually familiar with the Jabiru 3300, but I would think if your 5 and 6 are actually lean that others with a similar configuration would report the same.

In any case, you do seem pretty rich overall. With my Aerovee, I can pull my mixture out 3/4" or so in a climb for maximum power (extra 50rpm or so). When I level out at WOT and the rpm increases by 200-300 rpm it seems to go a little lean and I find myself pushing the mixture in (richer) a bit (maybe 1/4" out or so).

In my experience, too rich has been better than too lean, because at least you can adjust it out with the mixture knob, so I would make any adjustments towards lean gradually, making sure you have sufficient margin at all power settings. For some reason mine seems to go a little too lean around 1400 rpm easily which is a power setting you like to have on approach and taxiing around. This sets the practical limit of how lean I am willing to adjust my aeroinjector. I bet my EGT change at WOT is a bit more than the specified 90-100 F, but probably fairly close.

[fjdoug]

Has anybody tried to use a lubricant on the slider inside the AeroCarb to help prevent sticking? Thanks

i use LPS#2, and give it a good squirt every ten hours or so through the hole that you access the needle.
as part of my preflight i check the throttle operation before start.

my throttle did jam however only when the engine was not running.
it seems in my case,that the vibrations with the engine running free up any sticking.

[LarryEWaiex121]

I fall in the category of loving my Aero-Injector. I appreciate the simplicity of design and lack of moving parts.
In helping others not having the same success I discovered a common thread. Not having ever used the Aero-Injector, they departed from the plans and implemented some "improvements" before ever attempting to operate the engine/Aero-Injector as Sonex spelled out. So much for simple. Integrating more un-knowns before developing a solid understanding of how to set it per the plans.
I can not imagine a simpler carburetor system to install and maintain than the Aero-Injector if the install is followed to the letter without mods of unknown value.
No doubt there are lots of happy Rotec, and other manufacturers of injector systems that have very good success.
I guess my point would be that its difficult for me to see greater success with more components and avenues of departure from the desired outcome than a system with few moving parts, yet, gives incredible adjustability when installed per spec.
Once the range of mixture is established to allow a riching or cooling of 100 degrees from peak, the world is yours. And the instructions tell you precisely where to begin your journey. That's again assuming you have not installed uncalled for gizmos

[rizzz]

If you have a look at my opening post in this thread you'll notice that I'v been a little weary about the AeroInjector, even though I bought one and want to give it a try.
You can't beat the simplicity of the installation, that was pretty much my only reason for choosing the AeroInjector.

I have not yet voted as I don't have enough experience yet, however, now that I've got the engine running, so far things have been running good!
I have a 2.4L VW engine and a 32mm AeroInjector.

The only change I did to it was change the needle to a 2.5.
I installed the 2.5 needle as per the plans and have not touched it since.

I cannot fully test things yet as I'm having issues getting my MGL E1 to give me a proper RPM reading so it's hard to say if things are tuned ok or not, I need to resolve the RPM issue first, but so far so good.
I'm getting good response throughout the power range although I'm probably a little rich near idle, but from what I can see almost perfect near WOT.