N11XD Forth Flight report

The intent of this flight was to expand the flight envelope a bit from the previous flights where the aircraft was flown in the center of its envelope. This was also supposed to be the first flight to retract the landing gear after having repaired the up-lock release cable.

It was a somewhat warmer day (mid 50’s F) than the past few flights. By the time I finished the run-up and was ready for takeoff the coolant temp was up to 110C but the oil temp was still only 80C. Luckily I was told to position and hold on runway 2 which allowed the coolant to cool to 100C before I was given takeoff clearance. There was a 90 degree left cross wind at about 10 knots which, as soon as I broke ground caused the aircraft to weather vane to the left. It took lots of right rudder to straighten it out.

It was also very bumpy close to the ground.

Climb out was 120 MPH at first and then increased to 130MPH to try to improve cooling.

After leveling off at 2000 feet I headed east to the practice area. The coolant temp eventually came back down to 90C once in level cruise and the power was reduced.

Once in the practice area I climbed to 3000 feet where the air smoothed out a bit and did a few clearing turns. There were a few other aircraft in the area but they were in transit away from the practice area. Power was reduced to begin some slow flight maneuvers. Once the speed came down to about 90MPH the aircraft began to rock a bit and the controls became a bit "softer". The aircraft also began to descend slowly.

This is all normal for a Delta.

It was when I throttled back up that things began to be "not" normal.

At full throttle the engine was only making about 50% power.

Here we were, at 2800 feet and 110MPH, and slowly descending.

I went into engineering mode trying to diagnose the problem.

I switched from one fuel pump to the other and the power was further reduced so I went back to the first fuel pump selected and full power came back … for a little while.

It then began to diminish again.

I tried switching computers, no change.

I disabled the injectors individually, first the secondarys then the primarys with no change.

I pulled be throttle back and power came up a bit but not much.

The engine was barely making enough power to stay aloft, but it was still making power, so I headed for my home airport about 18 miles away.

The air/fuel gauge was all over the place.

At some point I switched to both fuel pumps and power came up a bit more so I climbed up a bit.

I was looking for spots to land but there was not much inviting territory around.

That area is pretty desolate which is why it is used for a practice area.

The engine was still running smoothly just not producing much power.

At this power setting I was able to maintain level flight so I just left it there, not wanting to make it worse.

At 10 miles out I radioed the tower that I was inbound.

I was asked to report a right downwind for runway 2.

At this point I was mentally preparing for a one shot landing as I would not have sufficient power for a go- around.

Everything had to be just right.

I still had a cross wind to deal with, but was reasonably sure the plane and I could handle it, if we made it back that far.

The tower asked for a position report when we were 4 miles out.

At this point I was thinking that we just might make it back in one piece.

There was another aircraft entering the airspace at about the same time.

The tower asked for another position report a few minutes later and I responded with 2 miles after hearing that the other aircraft was 3 miles out. This way I got preference for sequence even though he was landing on the other runway. I entered a tight downwind and reported upon turning base. At that point I was cleared to land. I had to fight a gusty crosswind all the way down final approach but managed to put it down right on the first part of the runway. I was then asked by the tower to taxi all the way to the other end of the runway before exiting. But I didn’t mind.

I was just glad to be back on earth without incident.

The next day I went back to try to confirm my suspicions.

During the summer I had a similar encounter with my car while driving back from the airport. On the highway in 5^th gear the car would only do about 40MPH and about 2000RPM no matter how hard I pressed on the throttle. It turned out to be a partially clogged fuel filter.

So the first thing that I looked at on my Delta was the inside of the gascolator.

Sure enough there was lots of debris in the bottom and on the screen.

It looked sort of like little fragments of jello.

After removing the fuel filter it was found to be severely restricted.

I believe that the new auto fuel formulated with ethanol is causing my fiberglass fuel tank to slowly disintegrate.

When this fuel tank was first constructed in 2001 leftover pieces of fiberglass samples were submerged in fuel to test its long-term effects. Those pieces are still in tact, but that was the old fuel with MTBE.

The fuel tank is being used to test the new formulation and it appears that it is failing.

Next project … perhaps an aluminum fuel tank.

Well back to the drawing board.

Jim Maher

(Dyke Delta N11XD 13B 4.1 hrs)