I’m seeing tinges of a reddish-brown fluid near the underside of the right wing root. The landing gear seems to be operating OK, and I’m not seeing anything leaking when I look around under the plane (no drips or puddles). What can I do to check this out further? What other clues might there be, to help narrow it down?
For starters, a pair of tubes carrying hydraulic fluid for the retract system runs out through the root of each wing. There is also a brake line on each side, that contains the same fluid. If you can’t find any apparent leakage in the wheel well areas, that is seeping back inboard through the wing, then you’ll need to examine the wing root connections where the wing lines join the fuselage lines. Sometimes air duct spiral wire or other interference rubs a tiny hole through the hydraulic tubing (either brake or landing gear lines). You have to remove the floor boards and spar cover, as well as the belly panel, in order to inspect both main and nose gear lines, plus the brake lines.
Rigging problems and maintenance problems in the landing gear retract system can cause strange symptoms. Sometimes the gear light blinks on and off frequently in flight (more than a few blinks per hour). Sometimes the plane may seem to have buffeting, perhaps when turning in one direction or the other. Or perhaps the main gear door seals seem to flutter or come loose; or the plane seems to have lost some speed.
Even tiny fluid leaks, whether external or internal, will cause cycling on the gear pump. If this occurs too often, the pump motor’s brushes, and possibly the pressure switch, will have premature wear. Leaks can occur in all the components; they do show up a bit more often on the nose gear downlock actuator. This may be due to the constant load of heat that passes by it, coupled with the extra grit thrown around by the propwash on the ground. Fortunately it is easily repaired, provided that the shaft is not pitted, or does not have peeling chrome plating.
If the nose downlock is not properly rigged, the nosegear could collapse. If the main gear uplocks are not properly rigged and the stops are not in good condition, the main gear may bounce slightly in turbulence or turns. Especially if the main gear are not securely locked, or the travel stop is not in good shape, the nose gear can bounce or droop in flight. The plane needs to be put up on jacks, and the system thoroughly checked for leaks and proper operation and rigging.
I can tell you with certainty that one of the key drag items on the Sierra is the exposed (no gear doors) retracted nose-gear. Any protrusions around the nose area have a far larger drag effect, due in part to the higher-velocity propwash in that area. This is one of the reasons why Rutan put a retractable nose-gear on the Vari-Eze/Long Eze homebuilts (they had fixed main gear). It is also why some folks put the 500×5 nose-wheel/tire on the 19/23 aircraft. The smaller wheel and tire is also reported to slightly change the landing characteristics (less chance of a nose-gear arrival and porpoise). Prop clearance is normally far more than adequate with the 500×5 nose wheel (the Sierra, with its longer prop, came with the 500×5).
One more thing that can be done for slight drag reduction is to make a flat wheel cover for the leg side of the nose gear wheel, by laying out and cutting a round hole in the center of a standard flat 5″ wheel cover. The round hole must clear the axle spacer. With the gear retracted, the flat plate smoothes the airflow over the wheel and tire. You can also put a Cleveland domed cover on the nut side. While it doesn’t help with streamlining (it points up into the well), it looks much better; and in conjunction with the flat cover, it also helps to keep water and grit out of the nose wheel bearing.
Anything that results in the Sierra nose gear being more exposed in flight will reduce speed by a matter of knots (not fractions of a knot). Anything you can do to rig the nose-gear further into the well will improve cruise speed. This includes adjusting the stop bolt to the highest position that still keeps the hear leg from hitting the firewall cut-out. It also includes making sure that the nose wheel itself has the spacers configured so that the wheel is as close to the nut size of the axle as is practical.
Both of the first two actions get more of the tire up into the wheel-well. I have seen these actions make a three to five knot difference in cruise speed, depending on how far off they were to start with. That is a tremendous amount of difference in drag; it is roughly the equivalent of adding between fifteen and twenty horsepower.