f1rocket
Well Known Member
Well, it's winter time, the condition inspection is done, and I'm looking for a project. I am giving some thought to building an alternative fuel tank for the -12. I am just getting ready to dive into the engineering and CAD/CAM aspects of this, but before I do, I have a few questions for those of you smarter than me. First, let me say that I'm not convinced of either the need or the feasibility of doing this. This is more of a mind exercise at this point to see if something better might be possible.
First, my design thoughts. I'd like a tank that fits over the spar, behind the seats, and frees up baggage space. I guess the driving force behind this change is to get more room in the baggage area. While I can make the current limited space work, it's not altogether convenient and it is downright impossible for anything longer that a couple of feet. Capacity is also an issue. I would love to get 5 more gallons on board for those times when I fly by myself cross country. I fully admit this change, if made, appears to have marginal benefits. Like I said, I'm just looking at this at this point.
My initial concern is with the center of gravity shift forward of the weight of the fuel. Today, I fly mostly in the forward regions of the CG envelope. In fact, I find it impossible to get anywhere near the aft CG limit due to my weight, and the typical weight of any passenger. Moving the fuel CG forward is going to make this problem worse. I suspect, and will need to prove this once the engineering drawings are done, is that I will be forward of the forward limit at takeoff at gross weight.
So my question to those who have worked on this on the -12 before (both alternate tank design and wet wing design) is where did you calculate your fuel CG to be with your design? Do you have issues with the CG forward limit? Did you have to make other changes, like move the battery or add weight, to get the CG back in range?
If, and it's a big if, I can create a plug in tank to replace the current tank and not have to reengineer a bunch of other changes, then it might be worth putting together both kits and completed tanks for sale. I have free access on the weekends to an advanced machine shop so my primary investment is raw materials and time.
Comments and suggestions welcome.
First, my design thoughts. I'd like a tank that fits over the spar, behind the seats, and frees up baggage space. I guess the driving force behind this change is to get more room in the baggage area. While I can make the current limited space work, it's not altogether convenient and it is downright impossible for anything longer that a couple of feet. Capacity is also an issue. I would love to get 5 more gallons on board for those times when I fly by myself cross country. I fully admit this change, if made, appears to have marginal benefits. Like I said, I'm just looking at this at this point.
My initial concern is with the center of gravity shift forward of the weight of the fuel. Today, I fly mostly in the forward regions of the CG envelope. In fact, I find it impossible to get anywhere near the aft CG limit due to my weight, and the typical weight of any passenger. Moving the fuel CG forward is going to make this problem worse. I suspect, and will need to prove this once the engineering drawings are done, is that I will be forward of the forward limit at takeoff at gross weight.
So my question to those who have worked on this on the -12 before (both alternate tank design and wet wing design) is where did you calculate your fuel CG to be with your design? Do you have issues with the CG forward limit? Did you have to make other changes, like move the battery or add weight, to get the CG back in range?
If, and it's a big if, I can create a plug in tank to replace the current tank and not have to reengineer a bunch of other changes, then it might be worth putting together both kits and completed tanks for sale. I have free access on the weekends to an advanced machine shop so my primary investment is raw materials and time.
Comments and suggestions welcome.