On 12/19/2020 2:46 PM, Mark Langford via KRnet wrote:
There's nothing inherently wrong with stub wing tanks. They have the
advantage of being well protected between the spars, and more
importantly, outside of the cockpit. They are very close to the
aerodynamic center of the wing, which is essentially the point about
which the plane is balanced, although somewhat aft. Keeping the tanks
out of the wings eliminates a fuel connection between outer wing and
stub wing.
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I'm with Mark on this one. Don't read any of my post as "don't install
stub wing tanks". Most stub wing tanks are used as aux tanks and fuel
is pumped to header tank in forward deck. If you plan to eliminate the
header tank and go with stub wing tanks only you must take in to account
the shift in CG locations. Moving 90 pound of fuel from forward of the
CG to aft of the CG makes a considerable difference in an aircraft the
size of a KR. I eliminated the header tank and placed all fuel in the
outer wings but I also have a heavier 0-200 which to some extent moves
the CG forward of a location using a lighter VW. You can place your
tanks anywhere you want as long as you take in to account CG location.
Moving the engine as Mark indicated can be used to compensate tank
location. When moving weight outside the desired CG location make sure
to calculate the entire range from full to empty tanks, light weight to
heavy pilot / passenger/ baggage location, etc.. Consider the CG change
as fuel is burned off as this is really the only change in weight from
takeoff to landing.
Fuel line connection with my wing tanks was not a major issue for me. I
come out of my tanks with a 90 degree fitting facing aft, a length of
hose approx 10" long to another 90 degree fitting facing the fuselage.
This hose is located between the stub wing and the outer wing. From
that second 90 degree fitting I connect to aluminum line running to the
cockpit. I have 4"X9" hinged door on the bottom of my stub wing for
access to make all electrical and fuel line connections. With me as
pilot, 215 lbs, and full fuel, my CG falls almost dead center of the
design CG range and moves forward 1" from full to empty tanks. Adding
a passenger of any weight moves my CG aft noticeably. When I flew to
Oshkosh with Mark as passenger and all our baggage plus full fuel we
were extremely aft CG and pitch forces were extremely light and near
neutral stability. Not a comfortable way to fly and I'll not try that
again. My 24" fuselage stretch probably kept that flight from not
turning out well.
Put your plan on paper and see how it will turn out and adjust accordingly.
Good luck.......
Larry Flesner
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