Vertical induction FI extender to match cowl

jdeas · #1 11-08-2010, 05:38 PM

I am building a Vertical induction FI. After finding out the height difference between the Carb that the cowling was designed for, the difference to the Bendix FI and the problems with the filter box cracking I hogged out a little adapter.

I hope this will line up the intake to the cowl and prevent the cracks

Lars · #2 11-08-2010, 10:24 PM

Nice looking part!

There must be a lot of variation between engines and cowls, because I found with mine that no spacer was needed. I have a Superior vertical induction parallel valve IO-360. The fuel servo is bolted to the bottom of the pan with only the thin (1/4"?) phenolic block and the cable bracket to stand it off. My FAB still required a little bit of upslope to get things to line up.

jdeas · #3 11-09-2010, 09:39 AM

There are variations. My understanding is that the Bendix is 15/16th's shorter than the carburetor used in the initial design. I was also told that other fuel servos varied in size so one size does not fit all.

Thanks for the info. I am going to test the fit next week. Who knows, I may have to shorten this up.

Lars · #4 11-09-2010, 06:07 PM

I fully expected to make a spacer for mine. I was surprised and pleased to discover that it wasn't necessary. One less thing to hassle with.

I did have to re-make the top plate for the FAB (the oval plate that bolts to the bottom of the fuel servo). Due to the inlet on the bottom of the oil pan being shifted to the pilot's side, it needed to be offset to keep the airbox from hitting the bottom cowl.

Since I was re-making it anyway, I made it from 1/16" 4130 chrome-moly steel instead. The real culprit that leads to top plates failing is most likely the intake pulses, rather than being slammed at startup and/or shutdown. The broken examples I've seen look like diaphragm failures. Consider that at 2500 rpm (semi-arbitrary but easy math) there are 5000 pulses (cycles) per minute, that means 30 million cycles per 100 hours of flight time. That's well into the zone of fatigue life for aluminum, at least potentially. Whereas hitting the side of the cowl happens maybe a few hundred times in the same period, and would result in something looking like a bending failure.

Interestingly I messed up the tennis-racket-shaped aluminum flange on the FAB. When I ordered a replacement from Van's, the guy that took my order questioned whether I got the part number correct. I told him I did, to which he replied that they didn't sell many of those, but they sold lots of the top plate. Obviously a common issue.