Air box installation

kthom_441 · #1 09-15-2019, 07:00 PM

I'm looking at the Filtered Air Box instructions and coming up with more questions than answers. Can some with more experience help me out? I am building an RV-9A with an O-320 and fixed pitch prop.

The Air Box instructions on page 2 talk about a "Carb Heat control". But there is no apparent connection to any heated source of air. The first page states that this is a VFR only air box. There is also the Vertical Air Induction kit with the filter bypass door. This is a one time pull of the control with a "remove the cowl and manually reset it" system.

So my questions:
1. Are both of these controls/flaps necessary?
2. Has anyone added a heat source to the carb heat inlet?
3. Where does everyone place these 2 controls on their panel? I'm used to the Carb Heat next to the Throttle (think Cessna), but with heat.
4. How do you label these cables?
5. Any other thoughts or insights?

Thanks to the brain trust,
Ken

N941WR · #2 09-15-2019, 07:14 PM

They are two different things.

The carb heat gets its warm air from a heat muff you need to purchase that goes on the crossover exhaust, in front of the sump. SCAT tube is used to connect the heat muff to the carb heat flapper valve

I started with Van's carb heat muff and didn't like it. Hardly noticed ant RPM drop. I replaced it with a real muff from Wag Aero and it works great! Unfortunately, the vendor no longer makes the muff I have.

The alternate air is a valve that goes on the bottom of the FAB. The idea is that if you sucked in a mythical plastic grocery bag on takeoff, you pull the cable and it opens the FAB and allows you to keep flying.

The alternate air valve is controversial as a number of them have failed, allowing the engine to suck up some parts, damaging engines. (Spoke with a friend last week who realized his valve failed and he is missing some parts and he is starting to use oil. He won't know if they are related until he pulls a cylinder.

I didn't install it but others won't fly without it. 900 hours in all kinds of weather and conditions and have never wished I had it.