David and Ralph,
Here's another few data points on STD vs Ext range on the Ballenger:
I started using the AFR400V1 when it was the only choice. I found that when leaning on X-Cs, I could lean past where the AFR held at 16.0. I conducted a lot of tests to balance my injectors, for which the STD is fine...peak is in that 14.7-15.0 range, and I was fine tuning the injectors with EGT and FF, not with AFR. But these tests were a pretty solid validation that the AFR works well...peak was very close to book stoichiometric values. I also tested well into the LOP range, to see when speed fell off, and when the cylinders began to run a bit rough. Again, the primary references were EGT and FF, and with the AFR400V1, the readout was a solid 16.0 for several turns of the mixture, so it was no longer providing any additional test detail or data.
When the V2 came out, I bought it, and moved the V1 to a racing Glasair, replacing a failed system in that plane (different mfgr). Noting that the V2 does have lower sensitivity in Ext mode, I wondered if the reading would jump around more in that mode. After many tests...its hard to say...maybe a bit. But I am now able to read AFRs above 16.0 as I lean, and with balanced injectors, have leaned into the 17s and 18s before rough running occurs. Speed does drop off significantly there too.
I typically run in the high 15s (15.5 to touching 16 occasionally), which is usually a bit less than 50 LOP. Good power and speed, cool CHTs, lower FF than ROP, for sure. After all this testing, given where I run, the STD mode would likely be sufficient. However, if you want to explore the fringes of LOP and see where AFR is, the EXT mode is pretty effective.
Ralph, have you noted more jumping in the numbers in EXT mode?
David, good luck with your closed loop mixture controller. It will be interesting to see the results. Will it use AFR to set the mixture? If so, you may need to dampen the slightly fluctuating readouts. As for Takeoff AFRs, during Reno Racing, Andy (SDS user and our current Sport champ) and I discussed takeoff AFR. I had my AFR 400 V1 on a TIO-580 with 2 mags, standard FI and mixture control, and an automatic waste gate. We both used an AFR of about 10 to provide plenty of cooling. Neither of us was running anything close to full throttle on takeoff or climb, to keep temps low till we were in the chute and racing. In my RV (IO-540, standard FI, 1 mag, 1 EI), full rich sea level takeoffs are in the 10s, and up in Reno, I'll lean to high 9s low 10s. I've seen 8s if I had the mixture in too far, and then corrected. Ran fine, but its not a very efficient place to run.
Hope those numbers give you some data to work with. With that closed loop system, are you trying to replicate the magic that Ross has in his SDS? I'm sure you've thought of this, but be careful how lean you allow the linear actuator to pull the mixture at high power.
Cool project tho.
Someday Ralph and Bill are gonna make me a Ross SDS guy too...just a few projects in the mill ahead of that!
Cheers,
Bob
Ralph - I'm not quite understanding the reason for the Extreme range vs. the Standard range. Is the Extreme range needed because you expect to operate outside the 9 to 16 AFR range provided by the Standard setting? My understanding is that 9 is way too rich. With 16 AFR being around 50F LoP, I could understand possibly wanting more range on the lean end.
Extreme gives you a 14-point AFR range vs. 7 points for Standard, but at the cost of sensitivity. A 1.0v change in the A/D output from the Ballenger is 1.4 AFR in Standard or 2.8 AFR in Extreme.
I'm building an Arduino-based closed-loop mixture controller using the Ballenger box & a linear servo to push-pull the mixture knob. I'm trying to decide how many presets I need, two or three. RoP, LoP, and maybe Takeoff. Thus my question about AFR values during takeoff. It sounds like a small detail, but the answer changes the switchology required, and thus my panel layout.
Thanks!
David
Good luck with your Adrino system, sounds interesting, sounds like a lot of work!
The reason for me using the extreme scale was to adapt the Ballenger output to read on my SDS panel control head. It also came in handy during testing & setup as I did explore leaning values higher than those I decided to be safe and workable for me.
In my case, displaying the AFR is 'displaying the result' of the SDS EI/EFI tuning. It is not used as a controlling factor in the running of the engine as in 'closed loop' systems. The SDS (Aviation) system use OAT/TPS/RPM/MAP/CHT data to run the engine.
Ross has a chart on his website that shows general AFR ratios to power output that might help you, but AFR is only part of the operating story.