Air Induction Injection Filter

Tom Lempicke submitted this tip about the GlaStar’s air induction filter for a fuel-injected engine.

GlaStar air induction filterOne of the things we are up against in putting a fuel injected engine in our GlaStar is fabrication of an induction system. Early on we looked at the SHAI system and realized that a lot of the cost of it was carburetor heat plumbing, which we did not need.

One thing we did have to provide was a system of alternate air. Should the filter get plugged by ice crystals or volcanic dust some means must be provided to get air to the engine. (If you are flying in ice or volcanic dust you really have more problems than this will solve – just go along for the sake of argument – O.K.?)


Our local AutoZone let us rummage through all 200 or so air filters that they had on hand. After measuring most of them we came up with Purolator A30057. It fits the SHAI intake plenum to a tee.

GlaStar air induction filter


The filter is a stand-alone unit within the plenum. In other words, the top plate and bottom plate are held to it with 3-1/2 inch long screws and it will be an air filtration system for the engine whether it is mounted in the plenum or not.

lempicke_airinduction5The flanges for the filter and the fuel servo came from Aircraft Spruce and were about $3.50 each. The .063 aluminum was a piece that we had left over from instrument panel fabrication. You will notice the interesting shape of the bottom piece; this is because that is all the stock we had left.

lempicke_airinduction2The alternate air door will be held closed by a spring. At the time the pictures were taken we did not have the spring installed so use your imagination. About a 1 inch long spring should do the job and we intend to place it experimentally. We expect to have positive pressure inside of the plenum while in flight, so the strength of the spring will not be a big factor here. On the ground, however, we do not want the door opening too early and letting dirty air bypass the filter. In order to make sure that the door does its job we plan to test the system on the ground by covering the NACA opening while running the engine.


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