Narco AT150 CG for W&B Calc?

Discussion in 'Avionics and Upgrades' started by Eric Lehto, Mar 21, 2020.

  1. Eric Lehto

    Eric Lehto Pre-Flight

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    Hoping somebody can help me out. Recently had my Narco AT150 transponder replaced with a Garmin GTX330. The avionics shop didn't do a W&B update, and I'm pretty sure it needs to. With the current lockdown here in CA, I figured I'd spend some downtime getting everything together.

    Anyway, Looking at the specs for these units, the Narco weighs in at 2.3 lb and the Garmin comes in at 4.2 lb. The Garmin install manual shows its CG 4.9" fwd of the panel after installation. The Narco install manual doesn't show the CG position. Anyone know of an official spec for this?
     
  2. Doug Reid

    Doug Reid Pre-takeoff checklist

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    The CG position is generally the center of the unit.
     
  3. Bell206

    Bell206 En-Route

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    What was the total weight difference between the 150 and 330 installs, not just the radios? If the total difference is less than a pound then no empty weight/balance correction needed. Regardless, any correction to an aircraft empty w&b requires a AP signoff as it is considered a minor alteration. If you think it still does require one, call them up and they should be able to send you a signed corrected empty w&b record sheet covering the 330 install.
     
  4. Domenick

    Domenick Pre-takeoff checklist

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    If you still have the Narco see where it balances on a horizontal stick.
     
  5. Eric Lehto

    Eric Lehto Pre-Flight

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    Nice, simple. It'll do. Thanks.
     
  6. cgrab

    cgrab Pattern Altitude

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    Use the 4.9. At 1.1 pounds difference the most your be off is a couple of inch-pounds. You change more than that when you adjust your seat.
     
  7. Doug Reid

    Doug Reid Pre-takeoff checklist

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    You should have an equipment list showing install weight and balance for all your avionics. Look at that document if you can find it. Use that data to document the removal of the AT150. As trivial as it seems, you are supposed to recalculate weight and balance if the change exceeds one pound in our weight class. Larger aircraft fall under different rules.
     
  8. Domenick

    Domenick Pre-takeoff checklist

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    My equipment list for a 1979 Warrior II (PA-28-161 ) lists the Narco 150 transponder at:
    Weight: 3 lbs
    Arm: 57.3"
    Moment: 172

    The note indicates the weight includes the cable and antenna.
     
  9. Eric Lehto

    Eric Lehto Pre-Flight

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    Yeah, I've got an equipment list with the weight and arm, but obviously it references the aircraft datum. I don't have the arm for a known reference point such as the panel, so calculating the arm of the new transponder in reference to the the aircraft datum is tough.
     
  10. Domenick

    Domenick Pre-takeoff checklist

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    My Warrior's POH, Section 2, Limitations, states:
    "The datum used is 78.4 inches ahead of the wing leading edge at
    the inboard intersection of the straight and tapered section."

    Also, the Warrior MX manual, Section 2-3, Handling & Servicing/STATION REFERENCE LINES, states:
    So, for the Warrior, the station for the lower edge of the firewall is 44.5".
     
    Last edited: Mar 24, 2020
  11. kgruber

    kgruber En-Route

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    Do you own a tape measure?