EXTERNAL FUEL TANKS
ON A
RANS S7S
There are times when a little more fuel than the stock 18 gallons would be nice to have. I wanted the additional fuel but did not want it as far aft as a baggage tank would put it because we were planning a trip which would include some survival equipment and a rear seat passenger. I also wanted tanks that could be easily removed for the bulk of the time when I was flying locally.
This is the terrain that got me thinking about having lots of fuel:
Most of my flying is on floats but now that I have the 100hp engine, marina gas is not high enough octane so carrying extra fuel could be helpful. There is another advantage to having two separate fuel sources. High octane gas is only needed for full power operation. It is perfectly acceptable to cruise using lower octane gas. So now I could run with high octane in the wing tanks which would be used for takeoff but I could fill up the external tanks with lower octane marina gas which could then be used during cruise power settings (or visa versa).
These tanks
are available from dealers who stock parts for the Chinook and Beaver. I got my
pair from LEAF but they are available other places including the Chinook
manufacturer, ASAP, in
The tanks hold about 5 gallons each. The installed weight of the tanks total is 15 lbs. I estimate the cg to be at 42” which is well ahead of the wing tank arm of 52”
I made use of the existing spade/eye bolts at the jury struts to bolt on the SS brackets (.090 304 SS). Strictly speaking these bolts should be another dash number longer to get a few threads showing but they cost over $20 a piece. I plan to weld up some new ones from stainless.The Chinook uses a similar system but only clamps the brackets to their struts with 2 stainless clamps. I used the bolt and one clamp at the front and just the bolt at the rear. The aluminum channel is made from 040 6061 and takes a bit of fitting to clear the caps on the tank. The tanks come with two 1/4" aluminum lined holes for the mounting bolts. The horizontal bolt at the rear strut has a tube on it so that the aluminum, channel won’t be deformed when you tighten.
You cant make a simple U bracket at the front because the tank needs to be moved to the rear about 3/4" so the filler cap can clear the strut. That is why it is an odd shape.
This mounting feels pretty solid.
The filler
cap and fuel outlet cap are stock plumbing parts. The fuel line cap from the dealer
has a long barb going straight thru which I didn't like because it would result
in a big loop of fuel line above the tank. I bought new ones (3/4" MIP
plastic plugs) and made up barbs into a 90 degree path. You can buy the
screen/check valve pick up from the dealers. Most people get rid of the check
valve because they are unreliable. I just expanded mine to let the balls drop
out. That is a quick disconnect in the line. The lines are held on to the rear
strut leading edge with aluminum tape.
Below the flap handle I mounted a left/right/off valve. After the existing Rans fuel shut off, I put in a T to connect to this new valve output. The new valve moves pretty easily and once when I was poking around there I inadvertantly moved it to on. Without check valves and with the main valve open fuel will drop down from the main tanks into the selected outboard. To prevent this I’ll mount a plate with a slot in it to hold the valve handle in the off position. The plate will flex up to release the handle.
Here is the routing near the fuselage:
This is a link to Chinook ASAP who sell the tanks: http://www.ultralight.ca/Framesets/chinook/chfuelfr.htm
Probably the guys with show quality planes might not like the cosmetics of this especially when these lines would stay on even when the tanks are removed. Functionality suits me just fine however.
Peter
Peterc at pipcom dot com
2008/02/23
