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Sunday 20 Sept 2009
0.6 air time
0.6 flt time

Purpose:

Handling tests at mid CG. 75 lb of ballast was well secured in the aft baggage compartment to bring the CG to 82.34" aft of the datum at engine start.

Events:

  1. Static longitudinal stability tests with one-third flap and zero flap at low speed.
  2. Static lateral and directional stability tests with one third flap at low speed.

Results:

  1. The flight was cut short due a buzzing sound that started after one of the early test points. After landing, it was noted that the left wing intersection fairing rubber seal had come loose in a small area near the leading edge.
  2. An interesting event occurred while doing a right wing down, full rudder, steady heading sideslip test with the fuel supplied by the right fuel tank. The sideslip was sustained for longer than previous tests, with 30 degrees of bank required to hold heading - then suddenly the engine stopped, apparently due to fuel starvation - it was very quiet for a few seconds. The engine restarted immediately when the fuel was changed to the other tank. The fuel was left on the left tank for the remainder of the flight so it could be seen how much fuel it took to refill the right tank after landing. Only 4.6 USG of fuel was required to fill that tank. It is hard to fathom how a fuel pickup could unport on a tank that was almost 80% full but I can't come up with any other possible cause of the momentary engine stoppage.

Lessons of the day:#. Do all tests at a safe altitude, to allow recovery from unexpected events.#. Select fuel to high wing prior to sustained sideslips.

New Snags:

  1. Left wing intersection fairing rubber strip has come loose three times. It was planned to use glue to secure the rubber seal to the intersection fairing after the aircraft had been painted. Perhaps it will be necessary to do this now.

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

  • Kevin,

    Was the fuel starvation on the tank equiped with the Flop tube or with the fixed fuel pick up?

    I am also curious about your limited up elevator authority: eventhough you had W&B within limits, do you think this is a W&B issue given your relatively heavy engine, or an elevator design issue? If the second, any suggestions for someone building / installing the elevator?

    Good to see you flying again. I'm beavering away at my fuselage.....

    Normand RV8 fuse slo build

  • Norm,

    The fuel starvation occured on the tank with the fixed fuel pickup. I'll probably repeat this event, as I'm quite puzzled why there would be no fuel at the pickup with the tank 80% full, even with the sustained 30 degree wing down in the sideslip. I'll do this with my laptop recording data, so I can see if there are any other clues I missed. I didn't have the laptop on board for the original flight, as some of the planned events could lead to loss of control, and I wasn't completely certain that the way I was securing the laptop would stand up to that kind of abuse.

    The three blade MT prop seems to have quite a bit more prop discing drag at idle than I had with the two blade Hartzell prop. There is a noticeable nose down pitching moment as you pull the power back and the prop goes from creating thrust to creating drag. This nose down pitching moment at idle means you need more up elevator to hold the same AOA.

    I suspect that the aircraft may very well be quite happy to spin if I had a fixed pitch prop, or maybe with a two blade Hartzell prop. I also suspect that holding a touch of power through the spin entry may allow it to go into a spin, but it is hard to know whether it would stay in the spin once you pulled the power back to idle. I'll investigate these aspects once I get to the aerobatic approval phase, hopefully in October.

    ---
    Kevin Horton

  • Didn't realise that a CS or 3blade prop could have such an effect on
    elevator efficiency at slow speeds. I've never flown with CS prop, but
    was planning on installing a 2 blade Whirlwind or MT prop. Subsequent
    to your overspeed, I also thought an aerobatic prop would be wiser, but
    the guy at Whirlwind (@Oshkosh) counselled against it, but I can no
    longer recall what his reasons were. Are you satisfied with your MT?
    Any disadvantages with an aerobatic prop?

    Also, if I am going to install rear seat throttle control, should I also
    install the RPM control in the back or would a throttle lever be sufficient
    and safe enough in your opinion? The idea is that I would be in the
    back seat for check out purposes and would want to have sufficient
    engine control in case I need it.

    thanks,

    Normand

  • Norm,

    Sorry for the slow response - it was a crazy week.



    Yeah, so far I'm reasonably happy with this prop. My only beef to date is that the cruise performance seems to be slightly down compared to my original Hartzell. The older MTs were known to be about 10 kt slower than the older Hartzells. Then Hartzell came out with the Blended Airfoil props, that gave several knots more than the older Hartzells, like I had. Recently MT came out with a new blade design, and the info I had seemed to show that it offered performance very close to the Blended Airfoil Hartzells. But this testing had been done on Diamond DA-40s, which are a bit slower than RVs. Perhaps that lower speed was to the advantage of the MT more than the Hartzell.



    Not so much disadvantages as differences. Each prop (or more properly the prop governor) has a failure mode where it stops sending oil to the prop. With a conventional prop this puts the prop in full fine pitch. If you are at high speed, this leads to an overspeed, as happened to me. With an aerobatic prop, if the governor fails, the prop goes to full coarse pitch. If the coarse pitch stop is set too coarse, that could lead to a situation where the engine rpm is too low to allow level flight. I'm still planning to do some limited testing to see what happens on my aircraft. If need be, I'll have the coarse pitch stop adjusted to a position that would allow a continued climb if the governor fails after take-off.



    For my purposes, allowing other pilots to fly the aircraft while I am in the front seat, a rear seat throttle is enough. The only time you really, really need a prop control in the rear seat is during a touch and go or a go-around where the front seat pilot has not pushed the prop control forward, and you need it forward RIGHT NOW. For any other case, you have time to ask the front seater to move the prop control for you.

    If you really want to fly from the back seat for checkout purposes, you have many other issues to sort out too. You'll need proper rudder pedals and brakes. You'll need to be careful to place an ASI where you will have good view of it from the rear seat. It won't be easy to adequately equip the rear seat so you can do checkout flights from there.

    Kevin Horton

    Comment last edited on about 4 years ago by Kevin Horton