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Saturday 19 Sept 2009
1.5 air time
1.5 flt time

Inter-flight activities:

  1. Chased down source of rattling noise heard during approach and landing on the previous flight. The rubber sealing strip at the left wing root fairing had come loose in a short section about 18 inches aft of the leading edge.
  2. Adjusted max rpm stop on the prop governor 1/3 turn.
  3. Traced standby alternator wiring. Found that the wire that supplies power from the control relay to the regulator had never been installed. Must obtain a suitable ring terminal, and then install the missing wire.

Purpose:

First in a planned series of flights to investigate aircraft handling at various CG positions. An exhaustive series of handling tests will be conducted at forward CG, mid CG, aerobatic aft CG and full aft CG. The tests include:

  1. Static longitudinal stability at all flap positions, with power at idle and max power, at low and high speed for each flap setting.
  2. Stick force per g at VH and VA.
  3. Static lateral and directional stability tests at all flap positions at idle and max power at low and high speed for each flap setting.
  4. Dynamic lateral and directional stability tests at all flap positions (aft CG flights only).
  5. Wings level, turning and accelerated stalls at idle and max power for each flap position.
  6. One turn spins at each flap position (six turn spins with flaps up will be done later, as part of the aerobatic evaluation).

This flight was at the most forward CG that will be seen in service - pilot, with no passenger or baggage. The CG was 79.79" aft of the datum. Van's recommended forward limit is 78.7", but there is no practical need for the CG to be that far forward on this example of the RV-8, so there is no point in testing there. If a passenger is carried, the CG is sure to be further aft. If a solo flight is flown with baggage, the baggage will be loaded in the aft baggage compartment. The forward baggage compartment will only be used if a passenger is carried.

Events:

  1. Static longitudinal stability at all flap positions, with power at idle and max power, at low and high speed for each flap setting.
  2. Static lateral and directional stability tests at all flap positions at idle and max power at low and high speed for each flap setting.
  3. Dynamic lateral and directional stability tests at all flap positions (aft CG flights only).
  4. Wings level, turning and accelerated stalls at idle and max power for each flap position.
  5. One turn spins at each flap position (six turn spins with flaps up will be done later, as part of the aerobatic evaluation).

Results:

  1. Engine speed for take-off was 2690 rpm - just about perfect. It came down to 2650 after the engine warmed up, but was found to have decreased to 2550 later in the flight. More investigation needed.
  2. Static longitudinal stability is fairly strong at all conditions (forward CG flight).
  3. Stick force was estimated at 10 lb per g up to 3 g.
  4. Static directional stability is strong at all conditions.
  5. Static lateral stability is weak at high speed conditions - i.e. there is very little roll response to sideslip, making it difficult to pick up a wing with rudder.
  6. Stall characteristics are excellent, with very little wing drop. Stall warning is marginal, with light buffet felt about 3 kt prior to the stall. There is not enough up elevator authority to fully stall the aircraft with idle power and flaps up or with one third flap.
  7. Spin - There is not enough up elevator authority to hold the aircraft in a spin. The angle and attack and rotation rate are oscillatory, and the airspeed continually increases, indicating the aircraft has transitioned to a full aft stick spiral dive. The one-third flap test point was aborted very quickly to prevent a flap overspeed. The full flap test point was not attempted.

Existing Snags:

  1. Max rpm still decreases late in the flight.
  2. SD-8 Alternator - must run power wire to regulator.
  3. Small amount of right rudder pedal force needed in cruise. Need to add a wedge on the left side of the rudder trailing edge.
  4. Pitch trim speed of movement is slow during a touch and go. Need to try it with the pitch trim speed governor removed.

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People in this conversation

  • Hi Kevin.

    I know you know this, but you might want to verify that your tachometer
    calibration isn't drifting as the instrument warms up. I had this exact issue, and
    it turned out that an optical tach didn't show the RPM drop. I spent a lot of
    time chasing it when the problem was in the EFIS electronics.

    --James Freeman

  • Hi James,

    Thanks for your comment. I always welcome constructive suggestions on
    things I may have missed. Even the seemingly most obvious things can be
    missed for various reasons.

    I've got two tachs - I mostly use the digital tach on the EIS 4000, but I've
    also got a round dial 2 1/4 analog tach. The two tachs get their signals from
    different sources - the EIS 4000 picks its speed signal from the magneto, and
    the round dial tach is fed from a tach generator on the accessory case.

    The two tachs never exactly agree on the engine speed, but the analog tach
    also shows a significant decrease in max selectable rpm whenever I note that
    condition on the EIS 4000.

    I'll adjust the prop control cable sheaf some more. I won't do any more than
    that until I switch to the final engine oil.

    ---
    Kevin Horton

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