Flight Testing

I spent the whole day yesterday helping my buddy Greg get ready for his first flight in his RV-8.  He had his airworthiness exam in the morning, then I gave the plane one last thorough inspection before everything was buttoned up for the first flight.  Since the flight went great and there were no squawks to fix, we decided to meet up for lunch in Watsonville with some other friends and then go do some loose formation work.  Greg got several very nice pictures of my plane in flight.

 

 

 

We traded places and I flew formation next to him for awhile.  I’m new to formation flight, and it’s definitely hard work flying in tight with another plane.  I was constantly adjusting the controls and varying the engine power.

After 15 minutes or so, we broke formation and I headed out to the central valley and climbed to 10,000 ft for some higher altitude tests.  On one of my earlier flights, I had a brief episode where the fuel flow indication briefly dropped to zero.  The fuel flow itself didn’t drop since the engine was continuing to make power and my airspeed didn’t vary.  I had just run a tank dry for the fuel calibration, so I chalked it up to some air bubbles in the fuel line interfering with the turbine in the fuel flow sensor.  Today however, I started getting some fuel flow indication fluctuations in the climb to 10,000 ft, and the flow indication stayed very irregular while I was up there.  When I came back down to 6,000 ft, the fuel flow indications were rock solid.

I’m starting to think the problem might be heating of the fuel flow sensor.  The sensor is after the fuel servo, and below the engine where it is exposed to the heated air that just flowed past the cylinders as well as radiant heat from the exhaust pipes.  The only way the sensor is cooled is by the fuel flowing through it.  Since there is less fuel flowing through at higher altitudes, it can pick up more ambient heat from its environment which can lead to bubbles in the sensor.  I’ve ordered some extra thick fire sleeve from McMaster Carr, and I’ll use that to wrap the sensor and adjacent fittings.  I may also wrap it in some reflective foil wrap to reflect radiant heat from the exhaust pipes.

I landed back at South County with 9.9 hours on the hobbs, so I decided to take the plane down for an oil change and thorough inspection.  While waiting for the oil to drain, I pulled out the interior.

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