RV-10 Auxillary Fuel Tank
I thought that I would talk a little bit about the axillary fuel tank I have installed in the forward part of the baggage compartment in my RV-10.
The RV-10 is a four place aircraft and as such is pretty nose heavy when you are flying with only the front seats occupied. As such, many owners fly with removable ballast in the baggage compartment. This ballast can take many forms such as a bag of sand, tool bag or in my case fuel.
I designed a fuel tank that fits in the forward co-pilot’s side of the baggage compartment. It occupies the triangular shaped cavity below the cross member at the front of the baggage compartment. It is mounted to the airframe using four AN4 bolts into the upper cross member and seven #8 screws through 2 mounting flanges. One to the forward side wall and one to the front center tunnel cross member.
The tank holds about 11.3 gallons of fuel. At 5.83 lbs/gal that works out to 65.9 lbs of fuel. The tank itself weighs in at approx. 14 lbs. The associated pumps, wiring and plumbing weigh in at about 10 lbs. Total weight of the system with full fuel is around 90 lbs.
This tank is directly connected to the right wing tank supply line that runs to the main fuel valve. The line to the aux. tank tees off of the Right wing tank feed line and runs through a 12v NC (normally closed) fuel shut-off valve that prevents fuel from flowing through the line when not energized.
Through a pair of wobble pumps I can either fill or drain the aux. tank from the right hand wing tank. There are both an electronic fuel gauge and a sight tube incorporated into the tank. The electronic sender is required if I want to directly supply the engine during takeoff. The site tube is there to aid in filling or emptying the tank as ballast.
There have been many trials and tribulations in the design, manufacture and installation of this tank. The process is not for the feint of heart. I have had some small leaks show up where the mounting brackets are welded to the tank body. I have also needed to add the fuel shut-off valve when I realized that the fuel in the aux. tank was gravity feeding back into the right wing tank. This oversight cost me a couple of days work in fabricating new plumbing in the pump bay to make room for the new valve.
What I do have now though, is a tool that will allow me to adjust the plane’s center of gravity depending on the mission. The plane flies much better with some additional weight in the back when the rear seats are unoccupied. I can now tailor the amount of ballast I carry and as a bonus I have an extra hour+ of fuel to be able to get into areas without fuel and the ability to be able to purchase a larger quantity of cheaper fuel.
I feel that this approach to the addition of extra fuel capacity in the RV-10 is much better option as compared to adding extra fuel to the outboard areas of the wing. By adding the weight to an area already designed to carry it I am not altering the wing in any way. I didn’t feel comfortable in adding the extra weight out at the end of the wing because I would not have been able to test it properly. The added outboard weight could have an adverse effect on the aircraft in the stall/spin envelope and I don’t play in that sand box.
Anyway, I have almost all of the kinks worked out of the design and have had fuel in the tank for calibration of the fuel level sender and sight tube. I have to determine the moment location of the tank and factor the weight of the fuel into the weight and balance calculations.
I will take some pictures if I think about it and post them later.
Dave