Page 26 - Volumer 13 Number 7

is 1,000 pounds so I started heading for Oakland. Periodically I would turn off the autopilot and see how much aileron trim I needed to handle the heavier left wing. Surprisingly, little trim was required. As I slowed for landing, I cranked in more trim as needed but even with the 1,000-pound difference and at 100 knots, I never needed more than half of the available trim. What did catch me by surprise – and I have mentioned this in my book – was how much the airplane wanted to turn left when taxiing. The extra weight on the left main tires surely wanted to pull the plane to the heavier side!
In a week or so the tanks were installed, the vent line was fitted from the tanks through the belly skin, the electric boost pump – on a wooden board fastened to the left seat tracks in front of the spar – was plumbed with the proper fuel lines and wired with power ... we were ready for a test flight. Thirty-five gallons had been added to each of the three, interconnected tanks and the mains had again been filled. The filler cap on each of the ferry tanks would be left off until we got to altitude, allowing cabin air to freely flow in and out of the tanks. We would be operating normally, consuming fuel from the main tanks, until we were in cruise and ready to test.
This time we went up to 17,500 feet – on a clear day, flying VFR – and were fully pressurized to 6.0 psid.
Before opening the manually operated valve to permit the ferry fuel to reach the T-fitting, one of the two “tank guys” in back started installing the tank caps. These were the metal, screw-on type. I heard a “clank” and some metal-moving-on-metal sounds as the first cap was screwed tight. Soon the second cap made the same sounds that I could hear. Remember, since the three tanks were interconnected, cabin air was still inside and outside all of the tanks.
Finally, I heard the last “clank.” However, this time it was immediately followed by a loud string of expletives and a yell of “Take it off! Take it off!” coming from the other installer in back. As soon as the inside of the tanks was no longer subjected to cabin air but started to decrease toward the ambient air at 17,500 feet to which they were vented, the three big box-shaped tanks collapsed as if they were made of tissue paper! On the way back to Oakland I had to bite my tongue to keep the “I told you so!” from leaking out. Six pounds pushing on one side more than the other against every square inch of aluminum adds up to a lot of destructive force.
A meeting was held back in the tanking company’s office to discuss the failure. I proposed the following solution: Retain the existing design but with one small addition: a one-half psi relief valve between the tanks and the cabin. This one-way valve would allow cabin air to flow into the ferry tanks and then go overboard through the belly vent line. No kerosene fumes would ever reach the cabin. The differential pressure between the inside and outside of the tanks would never exceed one-half psid. Also – and this would have to be proven on a further test flight – I was quite certain that the 5.5 psi difference between the ferry fuel and the wing fuel would be sufficient to feed fuel from the cabin tanks into the crossfeed line without needing to run the ferry system’s boost pump.
A week or two later we were advised that they were ready for a second test flight. This time we not only filled the mains but also put 25 gallons in each aux tank, as well as the 35 gallons in each ferry tank. Back in 1978 I had not yet learned the important “trick” of burning a couple of hundred pounds out of the mains before transferring to the aux tanks. So, we took off and climbed to altitude burning main tank fuel that was being replenished from the aux tanks. Once this was confirmed to be normal, we then pulled the left and right aux transfer circuit breakers to shut down the normal transfer. Next the three caps were screwed onto the tanks and, as expected, nothing bad happened. We now opened the valve to allow ferry fuel to feed into the crossfeed line.
How did we know if it was working? Was the right engine actually burning the ferry fuel or was it still using fuel from the right main? The only way to tell was to let enough time pass to see if the right main quantity was or wasn’t decreasing. In about 30 minutes we all agreed
24 • KING AIR MAGAZINE
JULY 2019