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  • Weight and CG Calculations

    When MYRO has its permit inspection, it'll also have to be re-weighed. This will be necessary even though it was only weighed in August last year because several replacement parts have been used in the repair which may affect the weight. It'll also be complicated by the fact that I have added the second tank and want to put that mod through at the same time. The BMAA Weight and CG Report is quite complicated and has to be completed and sent in by the inspector but I want to be able to do my own calculations in parallel, as I did last time, and also get a feel for what flexibility I will have with seat weights and fuel load in the two tanks in order to stay legal (max weight no more than 390kg and centre of gravity within the prescribed min and max limits). So I've spent this evening creating an Excel spreadsheet that does all that for me. I've used it to check on the figures from last time and although I've made it primarily for my own use, it will in fact work for any 3-axis microlight - all that is needed is for an owner to 'plug in' the numbers from the relevant TADS/HADS for their aircraft into the red boxes and the spreadsheet, which is protected so no formulas etc can be changed or lost by mistake, and all the figures are updated automatically.

    It's very useful for older aircraft like the AX3 which have a low maximum weight and need to trade fuel for weight if, like me, you increase the tank capacity and need to know how much fuel you can add with any given passenger. Here's a pic of the top of the sheet with the main boxes showing the variables already entered for an AX3 with twin tanks.



    All I'll need to do is add the new weights in each wheel box and the spreadsheet will reproduce all the calculations that the BMAA need on their report, such as with min cabin weight (55kg) and no fuel, min cabin weight and max fuel, max weight in 1 seat with nil and max fuel etc etc. At the same time the spreadsheet then compares the results of the calculations with the parameters from the HADS (max permitted weight and min/max C of G limits) and indicates whether they are 'acceptable' or 'unacceptable', telling you immediately whether you're legal or not. There's a 'free' calculation section at the end of the spreadsheet which is especially useful when you are planning a real flight with a passenger to let you calculate the amount of fuel that it is legal for you to load and here is a pic of that.



    And finally, here's a shot of the bottom of the spreadsheet with the old weight figures plugged in for me flying MYRO with a 10 stone passenger that shows I could load full fuel (both tanks full) and still be legal. It also shows the figures for a couple of the other 'standard' calculations, both of which have 'unacceptable' results



    In case anyone would like to have the spreadsheet to either use or just play with, you can download it by clicking on the following link.

    DOWNLOAD SPREADSHEET

    If you do try it out let me know how you get on.

  • #2
    Weight and CG Calculations

    Nice spreadsheet (except it doesnt address baggage)

    But Roger, - whats wrong with the (mandatory) very simple fuel weight trade placard - for cockpit load X. max fuel = Y?

    CG is irrelevant as its a mandatory ' by design' Section S requirement that it cant go outside of Cg within its max weight under all configurations of loading.

    Paul

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    • #3
      Weight and CG Calculations

      PS Thinking some more, maybe you didnt realise the rules pertaining to trading fuel for weight, the requirement its idiot proof for balance, and the resulting simple placard etc - Til 26 explains what you have to do if you havent seen it.

      Paul

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      • #4
        Weight and CG Calculations

        You're dead right Paul. But the spreadsheet does all of the calcs that are on the BMAA weight and CG report when an aircraft is weighed plus I like to know and have a handle on the numbers myself. The placard is very broad brush - if/when I take a fat bugger for a ride I want to know exactly what the numbers are. Just me? Maybe.

        Cheers,

        Roger

        PS it's an easy enough matter to add baggage but I just didn't bother because it's not relevant for the AX3, that's all

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        • #5
          Weight and CG Calculations

          I could have sworn the AX3 had a baggage allowance on the floor tube. But looking at the TADS I cant find it. Looking at the AX2000 TADS at first glance to mention of baggage - and none on the weight and Cg info. However further down on the placard list there is a baggage placard shown of 12.5Kg on the floor tube... Mybe the AX3 was the same?? - I havent got my POH copy anymore - but it might be worth a look to see if you do indeed have a secret baggage allowance!

          As for the fat bugger - Basically I reckon if you can get them in through the blasted silly little door, then it ought to fly!

          Paul

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          • #6
            Weight and CG Calculations

            Paul, I know of a late model AX3 that has stickers on the cabin floor tubes just forward of the seats saying 'Baggage Here' but there's no mention AFAIK of any figures etc in any of the the AX3 paperwork. My guess is that with a max AUW of only 390 kg they figured that nobody would be stowing very much baggage anyway as it would have to come out of your max permitted seat weight of 2 x 97.5 kg. For calculation purposes as its so close to the seats you could easily just give it the same moment arm I reckon.

            Sorry, that's a bit garbled but you can probably understand what I'm getting at

            Roger

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            • #7
              Weight and CG Calculations

              I will look at the AX3 Docs I have for G-MYZC and I am sure G-MYZC has a placard on the floor tube with a baggage lable and weight on it. Will take a Shufty tomorrow.

              Regards
              Mark

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