Thanks Vance, I got the 6.0GPH from a supplier of aircraft prepped 2.2 subies and they advertise that at 75% power, they consume 6.0GPH with the EFI, Also the rotax 912 (carbed) (80HP) that i fly burns 4.0 GPH at 75% power, as an observation, at full slant she drinks about 5.2GPH.. ON the subie I bet I'll be about 7.0GPH, so you can see why I want 15 Gallons gas on board... cause I actually want to fly places more then 25NM miles away from home...
Anyway,
In the design of the Hollmann HA-2M (Hamster) because the cabin enclosure makes it look like a hamster with food packed into its cheeks… Anyway, the fuel tank centroid is essentially an aluminum box that is located 23 inches forward of the center of the operational range of the aircraft’s center of gravity. The tank is 12 gallons with only 10.5 usable. I intend on making a few tweaks of the tank bottom to increase the usable fuel level, and to increase the fuel level to 15 gallons. I have the room in around the tank to do so.
23 inches centroid to centroid seems pretty far forward of Aircraft CG for a fuel tank? What say you…
Because the tank is so far forward of aircraft CG I was not able to simply make a larger tank at the same location, because it puts my max weight takeoff CG forward of the operational CG limit by about 1 inch. Bummer!
I did my calculations last night on the original design and discovered that I can leave the tank exactly where it is in its same foot print, but instead of it being simply rectangle with a constant centroid at 23 inches fwd of CG, I can transform it into the shape of a parallelogram sloping in the direction of the rotor mast. By doing that, the tank now has a moving center of gravity. Full fuel moves the tank’s CG back toward the rotor mast by approximately 6 inches, ½ tank by 3 inches aft, and at ZF I’m right back to where I started. I verified that under all fuel and passenger loading configurations where the aircraft meets minimum and maximum operational weights, my aircraft CG falls with in design limits. And I am not over gross weight by increasing full fuel load from 12 to 15 gallons.
Actually it’s not a parallelogram, as the back side slopes more then the front does, so the sides are not parallel; therefore, it is not a parallelogram! That is how I got the increase from 12 to 15 gallons, the fact that it is not a parallelogram. I added this paragraph in as an after thought, because I figured someone here would catch this fact and taunt me
So how far forward or aft of aircraft CG range is your fuel tank?
Also with the additional fuel, I’m at 1070 pounds max gross flight weight assuming that my engine comes in at under 233 pounds.