AeroInjector Needles (was Guarded Switches)

[builderflyer]

Art,

I wish it was as simple as selecting a needle # and adjustment position from a table, but it's not. The good news is that with a bit of trial and experimentation, and a few tuning sessions, each builder will find what works for their particular need.

Jeff

Exactly. But, as you suggest, with a little extra patience they'll end up with a very well working carburetor. No need to spend any more money than what these inexpensive devices cost.

Art,,,,,,,,,,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,,,,,,,Jabiru 3300 #261

[Panther16]

I have Sonex s/n 1009 which I completed sep 2010 with a areovee. Converted to a second gen Hyd lifter jab 3300 in spring of 2012. I used the aeroinjector, followed the manual set up using the nr 2 needle. The operation of the areoinjector has been excellent. I do use the mixture knob but is second nature. Aggressively lean on the grd at idle, full rich for T/O and then lean as I climb. Once a cruise alt is reached, lean for the egt,s I like to see(mid to hi 1300,s)and once set does not need any adjustment unless changing throttle or altitude until landing. It gives good economy and ease of operation. I have not adjusted the needle pos in 5 years. Use to adjust between winter and summer as I live in Minnesota but no longer feel the need to do that.
Keith Rhode S/N 1009 410 hrs.

[Onex107]

Hey guys, you have figured it out. The "thickness" for a good wot and a good idle don't change, they just get closer together with increasing angle. But, I want to add another important part. Check the amount of linear movement in the ball socket joint of the needle holder. Mine was nearly equal to a half of a turn ( .020 ) of the adjustment screw. A half turn is .030. If the needle can move this far on it's own you will never be happy with any adjustment. Check it out.
This can be eliminated by bending/shimming, what ever it takes to tighten it up. In my case we made a new needle holder using a disk rather than a ball and eliminated the clearance.

[Rynoth]

I swapped from my 2.5 needle to my 3.0 needle today. I haven't ran the engine yet for tuning (still in the middle of my condition inspection) but thought I'd share the method I used and findings.

First I advanced my throttle to WOT (I actually shimmed my throttle a bit shy of WOT since I don't actually use WOT in the Aerovee Turbo) and marked the existing 2.5 needle with a sharpie. The "red" sharpie mark is nearest the idle (allen screw) side of the needle. The green mark is at the fuel outlet. This picture is looking up into the throttle body with the air filter removed:



I then used calipers to my WOT (green) mark on the 2.5 needle and slid the 3.0 needle in to the same thickness:



Then I marked the 3.0 needle so I could insert it back into the Aeroinjector at roughly the same WOT setting that the 2.5 needle was at:



Notice in the pictures how the "idle" position is closer to the full-thickness end of the needle, which should mean less fuel flow at low/idle power settings (and possibly less fiddling with the mixture.)

[sonex1374]

Ryan,

Excellent set of pictures to illustrate the relationship of the #2.5 and #3 needles. I think this will help explain the logic for others that are still determining the correct needle to use for their carb.

One thing that typically works out well in our favor is that starting with a lower-numbered needle should result in a conservative mixture setting across the entire throttle range, assuming that the carb is well tuned at WOT. In fact, even when the low-throttle mixture is overly-rich we can still make due because the engine typically doesn't mind running rich, and we can manually lean with the cockpit mixture knob to help compensate. The real danger comes when a user does not have WOT tuned rich enough in an attempt to get the low or mid throttle positions to run well, and that causes excessive temps, stress on the engine, and such. I think it's best to start with a #2 (AeroVee) or #2.5 (Jabiru/Turbo), try that out for a while, and then determine if a larger needle is desirable based on how much you need to tinker with the mixture knob at lower throttle settings. So long as you always tune for WOT, it will work out fine.

Jeff

[Rynoth]

My initial impression is the #3 needle might be too steep for the turbo. I haven't flown it yet, but after setting up my WOT alignment mark to match the 2.5 needle, I ended up having to enrich the needle position by a full turn just to get it to idle. Until I do some more tuning tests/fly it I won't know just how much more rich this has made WOT. I'm still going to experiment with the 3.0, but I was happy with the 2.5 even with the leaning on the ground and if the 3.0 gives me too much trouble I'll likely go back.

The impression I'm getting is the ground-leaning of the 2.5 needle SEEMS like a large mixture adjustment, but the way the mixture adjustment works on an Aeroinjector is just like slowly closing a ball valve. Since the main restriction is at the needle, the ball valve isn't doing much at idle until it's nearly at full shutoff at such a low fuel flow, hence the large change at the mixture knob. I.e. at low power settings the mixture may be rich but not THAT rich, despite the fact that the mixture knob has to be moved a pretty fair distance.

[Rynoth]

I performed my first flight test today after switching from the 2.5 needle to the 3.0 needle in the Aerovee Turbo. The one other change I made was swapping out the stock paper air filter to the K&N E-3120 filter (fits in the Aeroconversions air filter assembly with slightly longer bolts.) The difference was remarkable.

I saw an across-the-board reduction in CHT of ~30 degrees. This was the first flight I've done in my plane that I never saw 400 CHT, and this was an 80 degree day. Since I changed the needle and air filter together before flying again I can't say for sure how much each contributed, but I'm VERY happy with the result.

EGT were also down by a fair margin. It gives me the feeling that my 2.5 needle setup may have in fact been tuned too lean at high power setting, despite the fact that it was VERY rich at idle (requiring the mixture to be nearly pulled to full shutoff for best idle.)

Previous to the injector needle change, my variance in mixture knob adjustments would range from 7/8 rich (full power) to 1/8 rich (idle on the ground). Today the range was closer to 6/8 rich to 3/8 rich. The "sweet spot" at various power settings was much closer together. I performed in-flight checks at near stall speed at idle and had no issues with the engine when leaned for cruise, when full rich, and didn't have to pull the mixture past 3/8 rich to get it to sputter. At high power settings, when running on the primary ignition-only with the 2.5 needle previously I'd get some stuttering that I feared may be detonation (usually solved by enrichening mixture.) I could not replicate this with the 3.0 needle, the engine ran smoother and cooler than any experience I had before.

I'll be monitoring fuel consumption, in my 30 minute hard-run flight my fuel consumption was ~3.0 gal, which is consistant with the ~5.5-6.0 GPH that I was consuming previously. Need more testing (I don't have a fuel flow meter.)

My idle RPM also increased, from ~950 with a hot engine to about 1200. I can only imagine that the new air filter is the reason since I didn't change the idle set screw on the throttle.

Suffice it to say I'm very excited about my change to the 3.0 needle and the air filter upgrade may be having a large impact as well.