Hi! Fergus and all.
I would venture to suggest that the purpose of the vent tube is also to
allow you to fill up to the neck of the filler cap which even for a tail
dragger will retrieve your 2.01 lost litres plus about another litre to
fill the filler tube.? All IMHO of course. With a trike most of this
problem is eliminated.
Regards
Bob Harrison kit337 G-PTAG.
-----Original Message-----
Behalf Of Fergus Kyle
Sent: 28 May 2000 23:30
Subject: Measured tank capacity
Today I measured my fuel tank, which was tagged as no. ,
dated . This tank goes in an XS cockpit, and was levelled at
its top to within 0.1deg of horizontal both laterally and fore/aft in
the presumption that what is wanted is Fuel Remaining in level flight,
which would be marked by a level headrest platform/tank top.
As by Tony Krzyzewski, I added vegetable colouring to each measured
litre of water and recorded its resulting depth in millimetres. I began
by filling the port side section through the filling inlet. When it was
full, the water began to fill the starboard section. When both were
replete, the combined level began to climb an increasingly wide common
volume, until the sides became virtually vertical. The filling ceased
when the bottom of the fill inlet was reached. From this I gleaned the
following facts:
(1) The two side sections join at approximately 153mm=22 l;
(2) Each side measured almost identically from top to 153mm.;
(3) The four sides of the tank became almost vertical at +/-190mm.=28.3
litres;
(4) From there upward, the curve became virtually linear to bottom of
filler inlet, 286mm.=45.4 l;
On the grounds that linearity (or nearly so) could be extrapolated, I
concluded that the Top of Filler would be reached at 326mm.=52.4 l and
that the Bottom of the Vent Boss would be reached at356mm.=56 l.
I then tipped the tank back to filling attitude (Noseup of assumed
7deg) and caught the outflow from the inlet boss. The loss of volume
amounted to about 2.0 l. From this I calculated, rightly or wrongly that
the max volume one would want on board at refuel would be 54 l. before
affecting the vent line.
If you wish to duplicate my graph of Fuel Remaining, and see the effect
of tank shape, follow the steps below:
A - Draw on a graph narrow side left to right, 60 - 0 squares (base is
litres), and up the left side, 0 - 400 units (depth of fluid);
B - Plot the following (litres - mm.): 54-354, 54-343*, 50-318, 46-300,
40-258, 32-200, 28-188, 26-180, 23-160, 22-153, 21-132, 17-95, 15-65,
13-35, 11-0, then go vertical to 11-153, 10-144, 8-120, 6-95, 4-65,
2-35, and 0-0 near the bottom right corner.
C - Join the points smoothly where required.
NOTE:
The curve represents Fuel Remaining in Level Flight. By playing with
the figures and assuming pessimistic errors, I cannot believe the curve
is anywhere in error by more than about one litre.
At about 153mm., the curve changes to reflect the depletion of Port side
only (about 11 litres) with 22 remaining. Thus the second cusp.
AT (OR BEFORE!) 11 litres remaining,THE STARBOARD (RESERVE) SIDE SHOULD
BE SELECTED, unless you have Nigel Charles' excellent scheme of backing
up with automatic-pump. That's why the vertical line at the 11 - litre
mark.
If you would rather have the raw measurements to acquire your own
graph, I can send same.
Bouquets or Brickbats,
happy landings,
Ferg A064
|