The big AeroCarb/AeroInjector thread

[lutorm]

Kerry talked about the tuning process on Episode 7 of SonexFlight, so that might be worth reviewing again for those just joining the conversation.

Interesting: I just listened to that episode and Kerry says (at 32min in):

Once you're at WOT and the EGTs have stabilized ... slowly pull the mixture control back and listen for your RPM to increase and you watch your EGTs and you are looking for an increase in RPM coupled with an increase in about 75-100 degrees. That tells you you're a bit on the rich side for WOT and that's what you want to be.

(my emphasis) He says nothing about the EGTs peaking or the engine starting to run rough. I interpret that statement as meaning you want the full rich EGTs to be 75-100 degrees lower than what they are at peak RPM ie. best power mixture, not 75-100 lower than peak EGT. This actually agrees pretty well with my impression, because peak power EGT is something like 125-150 ROP and full rich then becomes 200-250 ROP. See the plot below, for example.

But that description doesn't sound at all like what I read in the AeroCarb manual, which clearly says to lean until the engine begins running rough.

As for experimental vs not, the Aerovee is an air-cooled, four-stroke, two-valved, fixed-time spark-ignition engine running 100LL. It's similar to a Lycoming or Continental in every fundamental detail. A Rotax has some significant differences, ie liquid cooled heads, but operates on the same physical principles. A two-stroke, or diesel, rotary, or Atkinson cycle engines for that matter, are fundamentally different in their operation and I wouldn't apply any of the ideas here to those. But to say that an Aerovee is different in some way from a certified aircraft engine just isn't true.

[sonex1374]

I interpret that statement as meaning you want the full rich EGTs to be 75-100 degrees lower than what they are at peak RPM ie. best power mixture, not lower than peak EGT. ...[snip] ... But that description doesn't sound at all like what I read in the AeroCarb manual, which clearly says to lean until the engine begins running rough.

One of the main reasons for having Kerry go over the tuning instructions was to add better clarity and understanding to the process. I'm glad his explanations in the podcast helped clear things up.

Jeff

[lutorm]

I interpret that statement as meaning you want the full rich EGTs to be 75-100 degrees lower than what they are at peak RPM ie. best power mixture, not lower than peak EGT. ...[snip] ... But that description doesn't sound at all like what I read in the AeroCarb manual, which clearly says to lean until the engine begins running rough.

One of the main reasons for having Kerry go over the tuning instructions was to add better clarity and understanding to the process. I'm glad his explanations in the podcast helped clear things up.

Jeff

I don't know if it cleared things up, since we now have Sonex saying two almost opposite things... Kerry's explanation makes sense to me (and is largely what I did) so I'll follow that rather than the manual, but I think they need to rewrite the instructions in the manual to be consistent with that procedure, too. Maybe I'll email him and see what he says.

[Bryan Cotton]

So far I'm pretty happy with mine. I've only adjusted the idle stop.

[BRS]

I'm just getting used to the AeroInjector having removed the RevFlow from my Revmaster R2300. Tuning is going well but I struggled with removing and installing the needle stop screw as it kept falling off the allan wrench. So I finally started putting a blob of 'fuel-lube' on the wrench to stick the screw. Another (better?) solution would be to use a steel other than stainless screw so that a magnet could be used on the wrench.

How do you manage the set screw from dropping off the wrench?

aeroInjector stop nut.jpg (69.88 KiB) Viewed 5097 times

[Bryan Cotton]

Because of my nifty throttle reversing mechanism, I have to pull off the carb to adjust. But I also found a normal T handle allen wrench without the ball end works fine. I think the set screw stays on the normal allen wrench pretty good.

[BRS]

In my never ending effort to complicate simple matters, I drew this representation of needles to try to better understand the relationship of idle mixture vs WOT mixture with various needles. Nothing is to scale as can be seen where idle on needle 3 is way before the beginning of the taper. This exageration is actually helpful in visualizing what happens. Three random, but equal thickness, points drawn for each of WOT and idle.

Click to see entire image.

[Bryan Cotton]

Very cool graphic and analysis.

I would assume you would need to to to the #3 needle if you were not getting enough juice at WOT - so you would not set WOT at the same cross-section as on a thicker needle.

Also, the actual attainable travel is a function of the carrier and its position in the throttle plate, so physically I'm not sure you could get the case depicted for the #3 needle.

The bottom two needles are labeled 2, I assume the very bottom is actually a #3.

[BRS]

I might take some actual measurements and draw this to scale so that the case with #3 would not look so absurd. BTW -that is a "3" but for some reason the image got distorted as well as some text missing.

The take-away (for me) is the clear representation of what to do when your idle/midrange is rich after getting WOT dialed in. I always scratched my head that Sonex calls #3 richer and #1 leaner since their instructions are to first tune at WOT then consider changing the needle for other items. Since (it seems) that WOT can be tuned on any needle, the terms richer-needle / leaner-needle does not apply to WOT but to the rest of the range. So if my idle/mid-range is too rich I need a 'leaner' needle. From my pic you can see that would be a higher number (which sonex calls richer?!).

[Bryan Cotton]

From my pic you can see that would be a higher number (which sonex calls richer?!).

Yes, I can see.

I left the #2 needle in, have made two adjustments, and I'm happy with the operation of my Aerocarb.