AeroInjector Needles (was Guarded Switches)
Posted: Fri Apr 24, 2020 9:00 am
by sonex1374
[New topic split from previous thread - viewtopic.php?f=28&t=5501&start=20#p42001]
Ryan,
when switching to a different needle, you’ll still tune the engine to the same fuel flow at WOT as the previous needle. In fact, I recommend that before you remove the old needle you reach up thru the carb throat (at full throttle position) and mark a sharpie line on the this-side of the needle where it enters the fuel orifice. Then, when you remove the needle you’ll have a very accurate point on the old needle where you can measure the thickness of the needle to determine the “flow area” that your engine requires at WOT. Prior to installing the new needle you locate the point of the previously measure thickness and mark a reference line. This ensures when you install the new needle and adjust its position via the carrier that the same flow area is present (saves lot’s of tuning steps, assuming the old needle was in fact well tuned at WOT).
The difference in needle taper comes into play at throttle settings lower than WOT (which after all, you set to exactly the same flow area, even if that thickness was physically in a different spot of the needle). In the case of a #3 needle compared to a #2.5, when both needles are installed with identical flow areas, the #3 has a steeper taper, so the needle thickness at low throttle is thicker and results in less fuel flowing at that low throttle setting.
This is complicated to visualize, and I spend an hour during the Firewall Forward Seminar talking about the AeroInjector and how/why it works and illustrating it with graphics. Once you get it though, it all makes sense.
I hope this helps.
Jeff
Re: AeroInjector Needles (was Guarded Switches)
Posted: Fri Apr 24, 2020 9:06 am
by Rynoth
Actually that made total sense, thanks Jeff.
One additional element to this equation for the Turbo in particular is I never operate at WOT as this would cause overboost. I suppose I could additionally mark my throttle position at “max” power before moving on to marking the needle.
Re: AeroInjector Needles (was Guarded Switches)
Posted: Fri Apr 24, 2020 11:19 am
by Onex107
Rynoth wrote:
jerryhain wrote:I’m installing the turbo now and going to change my needle from a 2.5 to 3.0 because from idle to full throttle I’ve always had to enrich the mixture to keep it from dying.
Getting a bit off topic at this point, but when it comes to the 2.5 to 3.0 needle, does it actually change the “curve” of fuel mixture, or just provide more fuel at all power settings? I’m very familiar at this point with needing to lean the mixture at low settings and enrichen at high settings using a 2.5 needle in the turbo, I’m just wondering if the 3.0 needle actually addresses that issue.
When I was setting up my AeroInjector I had the same problem you do. I started measuring the needles and calculating the angle of taper. The angle changes in minutes of angle from the #2 to #3. I determined the sweet spot for wot was where the needle miked about .o80 - .085 thick ( at the entrance to the orifice ) and the difference between the needles was the location/distance of this thickness from the beginning of the taper. The sweet spot for idle is near or at the beginning of the taper and these two sweet spots get closer together as the angle increases. If these two spots are too far apart you have to manage one or the other with the mixture. If you calculate the increasing area of the slide opening from Idle to wot it is pretty linear and the needle taper is flat and linear. I made seven needles with varying/increasing angles and ended up matching the #3. I’ve been running it for 200 hours and do not touch my mixture from one flight to the next except to make a small richer adjustment to cool #1 EGT on takeoff and back leaner on cruise. It’s pretty simple really. The two sweet spots have to match the distance the slide travels from idle to wot.
Re: AeroInjector Needles (was Guarded Switches)
Posted: Fri Apr 24, 2020 12:52 pm
by jerryhain
Sorry about getting off topic here. in describing this I’m using 100% as cut off and 0% for full rich. At idle I’m at about 90%, and as I move the throttle forward when I get to 1800 rpm I need 75% or it dies. At 2400 RPM I move the mixture to 45 to 50% and then full throttle 3000 RPM and above I have to go to about 25%. The mixture changes aren’t just to make it run better it’s to keep it running at all.
I’ve done multiple restarts in the air. This was all done normally aspirated so I might wait to change the needle until I finish the turbo install and start testing again. I’ve started from scratch and used the factory install method twice with the same results.
I believe this means I need a steeper ramp on the needle to even out the mixture setting.
Re: AeroInjector Needles (was Guarded Switches)
Posted: Fri Apr 24, 2020 1:42 pm
by Rynoth
jerryhain wrote:Sorry about getting off topic here. in describing this I’m using 100% as cut off and 0% for full rich. At idle I’m at about 90%, and as I move the throttle forward when I get to 1800 rpm I need 75% or it dies. At 2400 RPM I move the mixture to 45 to 50% and then full throttle 3000 RPM and above I have to go to about 25%. The mixture changes aren’t just to make it run better it’s to keep it running at all.
This is almost identical to what I do with the mixture using 2.5 needle and the Turbo. It’s become second nature to me and the engine is quick to remind me when I add power if I haven’t already moved the mixture richer. I think I’m going to try out the 3.0 needle using Jeff’s install method. Since I don’t use the full length of travel of the throttle (I don’t/can’t ever go WOT w/out exceeding max MAP) it certainly makes sense to have a steeper taper to find the “sweet spot.”
Re: AeroInjector Needles (was Guarded Switches)
Posted: Sat Apr 25, 2020 10:13 am
by builderflyer
sonex1374 wrote:[New topic split from previous thread - viewtopic.php?f=28&t=5501&start=20#p42001]
Ryan,
In the case of a #3 needle compared to a #2.5, when both needles are installed with identical flow areas, the #3 has a steeper taper, so the needle thickness at low throttle is thicker and results in less fuel flowing at that low throttle setting.
f
Hi Jeff,
Take another look at what you said in the above paragraph…“the #3 has a steeper taper”…which is correct but some may be confused by what followed in that it applies to the #2.5 needle, not the #3 needle as it might appear. So for clarification, what it could say is “the #2.5 needle thickness at low throttle is thicker and results in less fuel flowing at that low throttle setting”.
I hope I haven’t confused this any more,
Art,Sonex taildragger #95,Jabiru 3300 #261
Re: AeroInjector Needles (was Guarded Switches)
Posted: Sat Apr 25, 2020 12:45 pm
by Rynoth
builderflyer wrote:
sonex1374 wrote:[New topic split from previous thread - http://www.sonexbuilders.net/viewtopic. … =20#p42001]
Ryan,
In the case of a #3 needle compared to a #2.5, when both needles are installed with identical flow areas, the #3 has a steeper taper, so the needle thickness at low throttle is thicker and results in less fuel flowing at that low throttle setting.
f
Hi Jeff,
Take another look at what you said in the above paragraph…“the #3 has a steeper taper”…which is correct but some may be confused by what followed in that it applies to the #2.5 needle, not the #3 needle as it might appear. So for clarification, what it could say is “the #2.5 needle thickness at low throttle is thicker and results in less fuel flowing at that low throttle setting”.
I hope I haven’t confused this any more,
Art,Sonex taildragger #95,Jabiru 3300 #261
Hmm, I have to disagree, I think what Jeff said and meant were correct. He was suggesting that if either needle is set to the same thickness at WOT, then the throttle is pulled back to idle, the #3 needle would have a leaner(thicker needle) mixture with less fuel flow. In other words, steeper taper means a larger variance in thickness/fuel flow as the throttle is moved. So if they are equal at one end (WOT), the #3 needle will have a larger variance at the other end (less fuel at idle.)
Re: AeroInjector Needles (was Guarded Switches)
Posted: Sat Apr 25, 2020 12:57 pm
by sonex1374
Art,
I understand what you’re saying, and this is confusing stuff. I’m including a picture from the FWF Seminar that I use to explain needle selection and adjustment. This picture is somewhat out of context and is missing most of the information that helps explain it, but it illustrates the central concept. The red lines are the area required (eg thickness of the needle) to flow enough fuel for that throttle position.
Jeff
Re: AeroInjector Needles (was Guarded Switches)
Posted: Sat Apr 25, 2020 4:07 pm
by builderflyer
Jeff, Ryan,
Of course, you fellows are correct. If I’d only gone back to my notes where I had measured the thickness of each needle at each station I’d have noticed my error in thinking. What sent me down the wrong path is that from an operational point of view it appears to me that when I’ve set a #2.5 needle where it wants to be at WOT, it runs quite a bit leaner at idle vs where the #3 needle would be at idle. This is backwards from the way it outta be based on needle thickness at idle. In any event, my 3300 has always preferred the #2.5 needle over the #3 needle, unlike the experience of many others.
Sorry to add to the confusion,
Art,Sonex taildragger #95,Jabiru 3300 #261 (Aeroinjector/#2.5 needle)
Re: AeroInjector Needles (was Guarded Switches)
Posted: Sat Apr 25, 2020 7:35 pm
by sonex1374
Art,
I recently measure my supply of various needles (old brass and new stainless) and reviewed the results. As I’ve mentioned before, the brass needles were generally smaller in diameter by 0.02 mm, and varied in diameter by as much as 0.05mm. By contrast, the stainless needles were generally very consistent in diameter (measuring all identically with my particular calipers and imperfect technique). The one notable exception to this was my #4 needle (I only had this one to try), which was slightly smaller than the others. This particular needle was ordered 3 years after the others, and could have simply been machined from slightly different round stock. In any case, the smaller diameter stock will flow more fuel at idle even when adjusted to the same needle thickness. Again, individual needles can have differences, and individual carb fuel orifices can as well. This explains why each engine seems to prefer something slightly different than the next engine.
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
Re: AeroInjector Needles (was Guarded Switches)
Posted: Sat Apr 25, 2020 10:10 pm
by builderflyer
sonex1374 wrote: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
Re: AeroInjector Needles (was Guarded Switches)
Posted: Sun Apr 26, 2020 2:34 pm
by 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.
Re: AeroInjector Needles (was Guarded Switches)
Posted: Mon Apr 27, 2020 10:56 am
by 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.
Re: AeroInjector Needles (was Guarded Switches)
Posted: Wed Apr 29, 2020 4:16 pm
by 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.)
Re: AeroInjector Needles (was Guarded Switches)
Posted: Wed Apr 29, 2020 6:21 pm
by 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
Re: AeroInjector Needles (was Guarded Switches)
Posted: Tue May 05, 2020 3:56 pm
by 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.
Re: AeroInjector Needles (was Guarded Switches)
Posted: Sat May 30, 2020 2:40 pm
by 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.