THATCHER CX4 CONSTRUCTION LOG

The following is the construction log for the engine of my scratch-built Thatcher CX4 experimental airplane.

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The CX4 will have a completely non-standard engine system. I will be using fuel injection and electric spark all controlled by a custom Engine Control Unit (ECU). The ECU will be my own design and construction, as well as the firmware to control it.

2017

The fuel pump is a unit from a Harley motorcycle. The first step is to remove the quick disconnect fuel connection and replace it with an AN fitting. Here is the pump with the fittings removed:

I purchased a spare fitting so I could cut it apart to see what's inside. The section that is currently cut in half will be cut off just past the o-ring sections and then threaded with a NPT tap.

The fuel tank will have a sump added. This is an insurance policy against the pump drawing in air during low fuel and/or maneuvers. It took a couple of tries to get all of the odd curves and holes to line up.

Inside the sump an thick piece of aluminum plate is used as a threaded backer. This allows something for the gaskets to crush up against.

At this point the fuel level sender was changed from an arm style sender to a linear style sender.

The Harley throttle body has a "push-on" fuel fitting. Russell Performance has an adapter, but I opted to modify the throttle body to terminate with an AN fitting.

The throttle "rail" was removed...

...and the fitting was removed from the rail (which is connected by a push-on fitting). The bracket is brazed on...

...so the assembly was heated to remove the bracket (I need the bracket, not the fitting)...

...the fitting will be replaced with a different adapter: Russell Performance 640930 (not brazed on, it will clamp in place)...

...but the Harley push-on fitting is non-standard and shorter, so the Russell adapter was ground down to fit.

2021

The throttle cable arm needs to be completely different. The plan is to replace this mess with just an arm controlled by a push-pull aircraft cable.

For reference, this is the typical Harley injector:

Intake runners were welded up mounting the throttle body on top of the engine. This will likely require a bubble or scoop on top of the cowling.

RPM and crankshaft location information is managed by a hall effect sensor...

...and an 8-1 (eight minus one) trigger wheel is used.

Wiring started! Primary electrical fuse and solenoids:

With battery power I can light up my panel!