REFLECTOR: Balanced Injectors

[Scott Derrick]

Chuck,

Great story and kudo's for Airflow. I was planning on doing the GAMI 
thing on my TSIO520 once its flying. I thought GAMI was the only game in 
town.

I will give serious consideration to Airflow...

thanks again,

Scott

Chuck Jensen wrote:

> A few weeks ago, I posted a request for a recommendation on getting 
> injectors in an IO-540 balanced. I related that I had done the GAMI 
> routine, but after a year, the lowest spread achieved was 1.5 gph. One 
> of the best, if still not great, settings after multiple GAMI 
> injectors change outs was to run #3 and #6 LOP and the other four ROP. 
> Not ideal but it kind of worked. When pressed about why the tuned 
> injectors weren't tuned after innumerable lean test runs and injector 
> change outs, GAMI said "huh, that's odd" but never solved the problem.
>
> Following the suggestion of Ronnie and a couple others, I contacted 
> Air Flow Performance in Spartanburg, SC. After a couple missed 
> appointments due to schedule and weather, we hooked up on Saturday 
> (yes, they volunteered to come in on Saturday to accommodate my 
> schedule). From the baseline flight of 1.5 gph spread, the next set of 
> restrictors dropped it to 1.2, then 0.8, then less than 0.4--done!
>
> In 4-5 hours, I'd resolved the issue that I'd been piddling with for 
> over a year. Now, in all fairness to GAMI, they were very patient and 
> persistent. Over the year, they sent a LOT of injectors. Of course, 
> each required cowl removal, injector change out, then a new set of 
> lean tests, just to find out they really didn't change anything.
>
> After the second flight at Airflow, a 5 minute explanation finally 
> made sense of why the GAMI injector change outs never changed 
> anything. It turns out the Flow Divider opening pressure is around 1.5 
> PSI. Since our test points were around 12 GPH that resulted in a 
> nozzle back pressure of around 1.7 PSI. What was happening was that 
> even though a larger nozzle was being installed in cylinder #6 the 
> Flow Divider was influencing the division of flow to the nozzles. The 
> solution was counter intuitive, but eminently sensible when 
> understood. To make #6 rich, the other cylinders were 'cinched down' 
> with smaller restrictors, which caused the nozzle back pressure to 
> increase driving the Flow Divider more open so that it would not 
> influence the division of flow to the nozzles. With more fuel being 
> pushed to #6 and they dialed right in.
>
> Now, I assume GAMI is probably that smart also, but the advantages of 
> hands-on problem analysis and immediate retesting are inestimable, 
> something that GAMI, due to geography couldn't do.
>
> More important than the 0.5-0.8 gph fuel savings was the smoothness 
> factor. The canard, which is an excellent tell-tale for vibration, was 
> dead calm throughout the ROP area and displayed only a small vibration 
> when I went into the LOP region. That small vibration vibration is 
> still less than anything I’d achieved with the GAMI injectors in 
> either ROP/LOP operations.
>
> Finally, I note there is a difference between GAMI and Airflow for 
> making injector adjustments. GAMI changes out the whole injector 
> whereas Airflow uses an injector body, then they just swaps out the 
> restrictor inserts, which only requires removal of the fuel line nut, 
> relatively easy to do even when we have to work around/through the 
> Velo plenum. With the GAMIs, I was never enthused about screwing 
> multiple injectors into the cylinders. The odds of cross-threading and 
> screwing up the injector or cylinder is low, but still there.
>
> Whether you bring the plane to Spartanburg (SPA) or do it remotely, 
> I’m guessing you’ll come away smarter and with as good or better 
> results than from some of their competitors. The office walls are 
> plastered with all the show pilots they tune, including Patti 
> Wagstaff, Tucker, et al.
>
> And the best part; the total cost for the Airflow injector balancing, 
> including new injectors, was about ½ the cost of the GAMIs...and I 
> didn’t have to do all the work.
>
> So, as you might guess, I’m sold. Without reservation on cost, service 
> or results, Airflow gets my vote.
>
> Chuck
>
> Disclosure: I don’t own or have an interest in Airflow…but I wish I did.
>
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