Hi Loukos,

Since you say you are slowly building your A-4, maybe I can also still provide some useful information as you may still be building. I still have my Tamjets A-4. I am using a Wren Supersport for power, appx. 18 pounds thrust. The Wren actually uses less fuel per minute than a P-60 but I wanted long flight times and had extra thrust to carry more fuel so I added a 16 ounce header tank in addition to the stock fuel.

My tank plumbing: I plumbed the saddle tanks to feed to the main in parallel, and then the main feeds to the aux and to the UAT in series. After a flight I never have any fuel left in the saddles, no fuel in the main, I've used about 5-7 ounces out of the AUX and there is absolutely no air in the UAT. It's good to keep the main tank full as long as you can if you are not running an aux tank (not stock - only a few guys I know are running aux tanks). The main tank form factor is long, wide and short so it's possible to uncover the klunk when it get's close to empty if you put some side load (yaw) tot he aircraft and that's always happening with RC planes. So I wanted to keep it full for as long as I could that's why I went with parallel saddle tanks and then series feed from the main onward.

So my fuel is parallel - series. Parallel feed from both saddle tanks at once - they draw air from the main vent line fed to the bottom of the fuse into a "T" fitting and then into the vents of each saddle tank - the fuel for the saddles each feed from their klunks to the individual vent fitting on the main tank vent lines (details 4 scale main tank has 2 vent tubes, 1 on each side). Then the main tank feeds from it's main klunk pickup, and up into the Aux tank that is mounted between the saddle tanks. My aux tank used to be 16 ounces. Now this season I changed to 12 ounces as I never used enough of the aux tank fuel and was landing "fat" on fuel all the time so I figured I would just save a few ounces of flight weight and keep my timer as it is - 7 minutes from full thrust application on takeoff to desired gear pass and landing when the beeper is going off. That's plenty. Anyhow, the "Aux" tank then feeds directly to the UAT. I have the UAT just aft of the equipment tray in the nose on the right side of the jet, just forward of the the right inlet. I consider the UAT to be unusable fuel and the A-4 is balanced with empty tanks and a full UAT. I don't need any lead in the nose at all as the UAT helps and also the equipment (2X 2300mah A123 packs for RX, fuel pump, 3200mah ECU pack, solenoids...) it's all mounted in the nose cone in a fixed equipment tray. It's actually a pretty light weight setup for a turbine with no lead ballast.

I've been extremely happy with the fuel feed performance this way and I appreciate the extra flight time. Compared to the stock fuel an extra aux tank can give you the extra time to clean out the main tank slowly in between air bubbles when it get's nearly empty while sucking off a nearly full aux tank and the UAT never ever get's close to having an air bubble in it so fuel delivery is guaranteed. Because I went down in weight a little with my updated aux tank and I have everything disassembled to change the fuel lines and such (annual inspection during the hot dry months as I don't fly turbines at home this time of year) - I'm using that as an excuse to finally install my smoke tank. It's a center line pylon tank with the pump and the smoke tank inside the "external tank fairing" and completely removable when not desired - so as to keep the jet as a clean, light sport jet when I'm not smoking.