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Thread: Help Smithcub W&B needed

  1. #1

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    Help Smithcub W&B needed

    Can anyone provide details on Weight and balance for a 180 hp smithcub.
    seeking the forward and reward limits.
    any information would be appreciated.

    thanks

  2. #2
    Bill Rusk's Avatar
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    Use the Cub Crafters Top Cub data

    https://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/bd617a52856a3758862582d30065366b/$FILE/A00053SE_Rev_3.pdf

    Hope this helps

    Bill
    Very Blessed.

  3. #3

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    Quote Originally Posted by Bill Rusk View Post
    Use the Cub Crafters Top Cub data

    https://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/bd617a52856a3758862582d30065366b/$FILE/A00053SE_Rev_3.pdf

    Hope this helps

    Bill

    Thanks Bill

    I’ll give that a try

  4. #4
    FdxLou's Avatar
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    I used the Top Cub W&B for my 180 Smith Cub.
    Lou

  5. #5
    C-GZUP
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    I was just looking at mine the other day. When I get back home in a couple of weeks I can copy it and send it to you if you still need it.
    The bad news is time flies. The good news is that your the pilot.
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  6. #6

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    Why not just weigh it and figure it out?
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  7. #7
    skywagon8a's Avatar
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    The forward and reward limits are whatever you determine them to be during your flight test phase. I used Piper's numbers but added 1/2" to the aft limit determined during flight testing. http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/ab203ab0e89895af862572090071f7cd/$FILE/1A2.pdf
    Piper's envelope is a bit longer than Cub Crafters.
    N1PA
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  9. #9

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    Quote Originally Posted by stewartb View Post
    Why not just weigh it and figure it out?
    I have weighed it

    I’m seeking the forward and aft limits and datum point in order to confirm I am safely within limits.

  10. #10
    skywagon8a's Avatar
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    Quote Originally Posted by Phil Sc View Post
    I have weighed it

    I’m seeking the forward and aft limits and datum point in order to confirm I am safely within limits.
    This makes me wonder how much you know about weight and balance? What did you use for a datum when you weighed the plane? What did you use for a reference when you leveled it for weighing?
    This is the FAA Type Certificate for a PA-18: http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/ab203ab0e89895af862572090071f7cd/$FILE/1A2.pdf

    Notice on page 6 that the datum is the wing leading edge. Some people use an arbitrary number ahead of the leading edge in order to not get confused with + & - arm numbers. If you use a spread sheet on your computer the + & - numbers are a non event. I use the wing leading edge because it is a known hard point from which I can measure rather than a point in space. The point in space just means more math which can be done wrong.
    The Leveling Means on page 6 says: "Plumb from PK screw in upper door frame channel to center punch mark on enclosure door rear hinge."
    We know that you do not have this on your plane. Alternatively you can refer to page 10 on the T.C. Landing Gear item 202: Tires are located at (+2) This means that when the plane is level you can drop a plumb bob from the wing leading edge and measure to the center of the axle 2". Another method of determining that the plane is level is to place your level on the firewall between the upper and lower engine mount fittings. The firewall should be plumb. We know this from the fuselage drawings. You may or may not have access to this drawing.

    This is the FAA's weight and balance handbook:
    https://www.faa.gov/regulations_poli...A-H-8083-1.pdf

    Some airplanes do have published empty CG limits. There are no published empty weight limits for a PA-18. The published limits are applied when the plane is loaded for any particular flight. You can refer to the T.C. for the seat, fuel, baggage and other moment arm locations.
    Last edited by skywagon8a; 01-14-2019 at 06:42 AM.
    N1PA
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  11. #11

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    W&B should have been provided prior to being issued an airworthiness cert. Phase 1 testing may have been used to amend it. How does this plane not have a W&B established already?
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  12. #12
    Eddie Foy's Avatar
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    Tough room!
    "Put out my hand and touched the face of God!"
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  13. #13

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    Quote Originally Posted by stewartb View Post
    W&B should have been provided prior to being issued an airworthiness cert. Phase 1 testing may have been used to amend it. How does this plane not have a W&B established already?
    Smith Cub was sold to Backcountry Cub and they have not been able to provide Weight and Balance information.

    Typically in a "Kit" aircraft weight and balance information is provided. This usually consists of a sample W&B indicating the datum point and arm measurements of pilot and passenger seats, fuel, baggage etc. This is to guide the builder with his own using measurements and weights obtained from the aircraft itself. The forward and aft limits should also be provided to ensure safe operation. I have built 5 previous kits (not my first rodeo) and each of the previous kit manufactures had these published figures. I used the leading edge for my measurements and properly leveled the aircraft but I need to confirm I am within safe limits and also satisfy Transport Canada paperwork prior to flight.

  14. #14

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    So are you doing the first flight?

    Cub clone? I'd start at standard Cub limits. My airframe is longer. BCSC provided me a sample W&B with fore and aft limits. Slats installed moves the aft limit back an inch. My testing says I need to move the forward limit back, too. PM me contact info and I can forward an excel spreadsheet. The column values can be edited. Pretty handy. Once established I entered my airplane info into Garmin Pilot's W&B page. That's very useful for changing sample loads to determine how the plane handles them.

  15. #15
    skywagon8a's Avatar
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    Quote Originally Posted by Phil Sc View Post
    Smith Cub was sold to Backcountry Cub and they have not been able to provide Weight and Balance information.

    .... I need to confirm I am within safe limits and also satisfy Transport Canada paperwork prior to flight.
    The Smith/Turbine Cubs of Wyoming/Backcountry Super Cub are all Piper PA-18 clones. As such in order to satisfy Transport Canada you should use Piper's limitations as published in the T.C. Mine is a TCOW 180 hp and I used Piper's numbers except as mentioned above I moved the aft limit aft. You will be safe using Piper's numbers.
    N1PA
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  16. #16
    C-GZUP
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    Phil sent me a pm with an email address and I’ll copy mine and send to you. You can use them if you want

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