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Weight and Balance Pre-planning

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  • Weight and Balance Pre-planning

    Good morning,

    I am curious how everyone's weight and balance is turning out. I'm building the LSA with an O-200 from Bob with lightweight prop, starter, alternator, oil reservoir, earthx battery, and have minimal weight instruments: Trig Com, Transponder, MGL Xtreme EFIS, an iPad, and ACK-04 ELT. I am putting in two landing lights (probably in the nose) and strobes, but that's about it.

    So, there isn't a whole lot I can move around. Battery location, Trig avionics remote modules can go under the boot cowl or aft of the baggage.

    Just wondering how I should be thinking/planning here.


    LSA QB started 2/6/2022, My Build Log, N67BH reserved.

  • #2
    You might consider certifying your airplane without the alternator, As a nonelectric there is no ADSB requirement and an EatrhX can easily carry the electrics for most flights.


    • jcowgar
      jcowgar commented
      Editing a comment
      What about the starter? Do I have to give it up too for inspection? I've never hand propped a plane in my life :-/

  • #3
    A starter is allowed in a nonelectric certifacation


    • #4
      I built mine as Jim described. Lightweight starter, no alternator, EarthX battery.

      No X ponder or ADSB required

      Not sure why landing lights are desired since (when operating as "Light sport") night flight is off the table.

      Works fine, flew from AZ to Oshkosh, charged there, returned back to AZ .

      Nominally 15 hours of flying between charges.

      Used some high current disconnects and made the battery easily removable to take somewhere and charge if not in my hanger.

      Look for the {"Minimalist panel" thread form a couple weeks ago for more discussion


      • jcowgar
        jcowgar commented
        Editing a comment
        I'm a private pilot and will be not be classifying my Bearhawk LSA as an E-AB. I do not do a lot of night flight, but coming home a but after dusk is something I want the ability to do.

      • Bcone1381
        Bcone1381 commented
        Editing a comment
        It seems prudent to research the amp draw of the items you will install (including the master solenoid's amp) and see if your battery can outlast your fuel supply. Landing lights are not a continuous draw and are not required for night flight. LED position and strobe lights are pretty frugal amp draw.

    • #5
      When completed, you will have an E-AB(Experimental - Amateur built) airplane.

      They key is if you have also set the limitations to meet the light sport category it can be operated by a pilot that meets the "Light Sport" criteria(drivers license medical, Sport Pilot) within associated operating limitations of the pilot certificate/medical..

      If you certify it to something that exceeds the restrictions of the category(for example, set the max allowable gross weight over 1320 lbs or install a "other than fixed pitch" propeller) it can never be "moved back" to being "LSA" and the operator will need to hold a PPL and at least Basic MED.

      Not a problem but worth keeping in mind, especially the "hard limit" on 1320 lbs gross weight.

      Every ounce you save is an ounce of legal useful load.

      Adding appropriate lights/electrical capacity will allow a PPL to fly it at night but there's no way around the extra weight impacting legal useful load when 1320 lbs is a hard limit.

      I started mine before Basic Med became an option and fly within the "light sport" boundaries(haven't renewed my third class medical for years now)

      With the availability of Basic MED, I likely would have built a Patrol instead of the LSA.
      Last edited by BTAZ; 02-27-2022, 10:38 PM.


      • #6
        The original question wasn't really about electrical system, LSA or not, or even equipment selection. It was simply how everyone's weight and balance is turning out. Are people finding the empty weight and balance being really close to the front, middle, rear... i.e. with the equipment I am installing, maybe I should think about mounting things behind the panel or behind the cargo area.

        I realize that everyone has different equipment, but I think that a lot are putting the O-200 w/light weight components, prop, etc... on their aircraft, but maybe I'm mistaken. I think the perfect scenario would be to have a CG right in the middle with my normal load. How to plan for that right now as I am building, that is where I am a bit sketchy on. My previous plane I built, I had an idea what others were doing and how their planes were turning out. So, I made a few decisions based on that and came out like the rest of the guys who have already been through their weight and balance.
        Last edited by jcowgar; 03-01-2022, 02:51 PM.
        LSA QB started 2/6/2022, My Build Log, N67BH reserved.


        • #7
          I don't have the actual number in front of me but mine(with no electrical system outside of the EarthX battery on the firewall and lightweight starter, Catto prop, 0-200 positioned on an engine mount built per the plans) ended up at 798 empty and that my moment arms came out very close to what Bob had in the LSA book.

          I leveled the plane and had my son(of known weight) get in the front and back seat and I put a couple boxes of drywall mix(again as an easy to handle known weight) in the baggage area and the resulting moment arms were within a half inch or so of Bob's numbers.

          So you are pretty safe to use the W&B example in the LSA Build book to see how things might change with options you select.


          • #8
            If I remember correctly the Factory LSA is a bit over 800lbs, 815 comes to mind. It has a basic panel with electrical system and radio. I don't know the actual C of G numbers but 2 of us on board and near full fuel it flew great. This was one of the first factory kits.
            I plan on a very similar build as the Factory plane except will have a GRT panel, Bob's O200, Stewart system. Running the numbers from the book puts it well within range


            • #9
              Originally posted by jcowgar View Post
              I think the perfect scenario would be to have a CG right in the middle with my normal load. How to plan for that right now as I am building, that is where I am a bit sketchy on. My previous plane I built, I had an idea what others were doing and how their planes were turning out. So, I made a few decisions based on that and came out like the rest of the guys who have already been through their weight and balance.
              My viewpoint on the perfect CG.......Everything that is loaded up in a typical Bearhawk, including fuel, shifts the CG aft. I believe this to be true for the LSA (but have never run the numbers). So it would seem to me that the ideal CG would allow Max baggage compartment weight, a big passenger, fuel to fly at MAX TOGW, and a comfortable CG inside of the aft limit. I bet that empty weight CG still lets you take everything out and climb in solo with a nice CG.

              Another viewpoint to consider on empty weight CG. I am not weighing anything. I am just building my Patrol. I trust that our wing's wide cord gives us a generous CG envelope. If not, then adding a bit of ballast will get the CG where I want it. Our Cords are the same as the Five.

              With that being said, you can get scientific about this if you desire. You will need to weigh everything and and obtain the fuselage and wing CG. That is easy to do with a hoist scale if your shop is properly equipped. It would be great info if we knew what our wing weight and CG's were running when the come out of the factory. I wonder if Mark has ever measured a set.

              Brooks Cone
              Southeast Michigan
              Patrol #303, Kit build


              • #10
                My two cents worth!. My LSA was scratch built and not directly as per plans but with the tandem built Bearhawk everything loaded is aft, it does not fly without the pilot. Upon preforming the empty W/B I was hoping for the most forward CG limit. I was lucky I got it. I loaded the plane with fue,l tie down kit, tools etc. She flys great. 270 hrs .My grandson now has 150 hrs not bad for a 15 yr old . STINGER
                Attached Files


                • #11
                  One of the best things I ever did, electrically speaking, was ditch the master switch on my RANS, replacing it at the same time I went to a EarthX. I now, for the last 5 years, use a Summit Racing mechanical disconnect, that performs, near as I can tell, the same function (killing all the energized wires and cables that are normally hot, or potentially so). Firewall mounted (inside) 8" from the battery, which is up against the firewall between the rudder pedals (oddly enough....totally out of the way there, surprised me too), and the big cable to the starter is about 14" long. I saved over 13 pounds by this mod plus putting the Odyssey battery in my ATV.


                  • jcowgar
                    jcowgar commented
                    Editing a comment
                    I'm not sure I understand. Typically a master switch on the panel is a Cessna style dual rocker switch or a simple toggle switch that simply provides power to the master solenoid. Are you saying that you removed that mechanism in place of a mechanical battery disconnect switch mounted on the firewall? Something like: ?

                • #12
                  I've been thinking for a few days about the premise of planning the w&b to fall in the mid range for a solo load. My first thought was that I don't think this is what you want, but I couldn't put my finger on why. I think what you want to do instead is to plan so that you can be forward of the aft limit when loaded to gross.

                  Here's what I'm thinking. If you have an occasion to take a full load, but you are aft of the limit, there's not really anything you can do about it. We don't have any place forward to add weight.
                  However, if you are flying solo and you want to move the cg aft, a 15-pound toolkit secured at the back of the cabin will make a big difference, and a 50-pound bag of chicken food will likely take you aft of the limit. These are made-up numbers but the point being that it's always easy to move the cg aft, because the arm is so long. Not to mention that pretty much anything you add to the plane also moves it aft.

                  Moving the cg aft has disadvantage of reducing pitch stability, but in moderation that can be a benefit if you like lighter pitch forces. Moving the cg aft will also reduce drag slightly, and make the plane less needing of pitch trim adjustments ad speed changes.


                  • jcowgar
                    jcowgar commented
                    Editing a comment
                    I believe that an aircraft flies best when it has a CG right in the middle of its range? I was thinking of trying to achieve this for my standard flight configuration which is an afternoon flight with friends or family, so a passenger and starting with full fuel, very limited baggage. If flying solo, and I was too far forward CG then I could add a standard weight in the baggage for example. But if I were flying around with some baggage and passenger, hopefully I'd be forward of the aft most CG.

                    Maybe that later example is what I am unsure of the most. For sure I don't want to wind up in a situation where I am within gross weight but unable to fly because of a too rear CG.

                • #13
                  I don't think I would agree with the idea that an aircraft flies best when it has a cg right in the middle of its range. When Bob designs a plane, he has a certain range of where he suspects the CG limits should be. Through flight testing, he establishes the forward limit based on criteria like elevator effectiveness at idle power. He establishes the rear limit based on factors like pitch stability. Each end of the envelope is located because of its own reason, and they don't have any relation to each other. "Right in the middle" is just halfway between those two unrelated points, making the halfway point rather arbitrary. The best point will certainly fall somewhere in the range limits, and it may even be near the middle, but I don't think we have any reason to think that it would necessarily fall at the 50% point. Maybe it would be 75% or 25%. Also, I think the ideal point is subject to pilot preference, as I've learned through discussions with other builders about the 4-place elevator effectiveness. Some folks seem to prefer more pickup truck handling than sports car handling, and naturally the first group would prefer a more forward CG.
                  If the limits were derived by taking the best point, and then expanding an envelope around that point, then I would agree that the half-way point is best, but that's not how it's done, at least not with Bob's planes.
                  I wish I could be more help with actual numbers, but my stick time in the LSA has not involved any CG limit testing. If I were in your situation, I could create a calculator for an excel spreadsheet or something similar, where you could quickly create several different load scenarios, and at several different empty weight and CG combinations. If this is something you'd like help with, let me know and I'll put something basic together and post it here.


                  • jcowgar
                    jcowgar commented
                    Editing a comment
                    You bring up a good point about pilot preference and my "best" was incorrect. I am not a designer by any means, but would the 50% point be a happy medium between a truck and sports car as you put it? I always thought that was the case but maybe I am mistaken about it.

                    I also am beginning to think I am thinking too deeply about this, as in reality, I have very little weight that I can actually shift around during my build. I am really wondering how much I can control the end game. I know Bob's designs have a wide CG range and I doubt I will wind up with an aircraft that is out of CG within its loading limits.

                  • Mark Goldberg
                    Mark Goldberg commented
                    Editing a comment
                    Jeremy, I would say you are over thinking this. The CG range of an LSA is quite large. On the LSA, me and some others who have flow it feel that the aft CG limit on the LSA is conservative. That the plane could likely be COMFORTABLY flown even further aft. Not like the four place which is not fun at aft CG. I would say just build your plane light, and put most weight as far forward as you can. Mark

                • #14
                  My Bearhawk LSA, N2227T, weight and balance sheet.
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                  This gallery has 2 photos.


                  • Chewie
                    Chewie commented
                    Editing a comment
                    Tim that's stunning!