Posted Friday, April 23, 2010 @ 10:24 PM
Hi Guys,
This for Jorgen, although it seems pretty straightforward to me (but maybe because I've been doing the same thing in my aeroplanes and at work for years).
I refuell my aeroplanes from 20-litre jerry cans and/or 5-litre electrically conductive plastic fuel cans (older Americans can substitute 5-gallon & 1-gallon there) through a Mr Funnel, black, plastic, electrically conductive filter funnel.
Otherwise, I use a metal funnel with a chamois leather spread over it. This has such a fine mesh stucture that it will filter out water as well as any debris or specks. With a main jet only 1.25mm diameter, and an idle jet much finer, you don't want even the tiniest speck of dirt in your fuel (or any water - remember, you only have a 20cc float bowl).
Whenever I buy a new aeroplane, I calibrate the fuel gauge and make and calibrate a dip-stick -- both together.
First, I put a padded Jerry can or trestle under the tail to get it into the flying attitue (with Fourniers of course you also have to put something under the outrigger wheels to keep the wings level.
Then, siphon out most of the fuel.
Finally, put a container under the carburetor and remove the drain plug.
Once the fuel stops running out of the carburetor, you're down to 'minimum fuel'.
In a Fournier RF4D, that's zero fuel.
Of course, when calibrating the fuel float the airplane needs to be level, and when calibrating the dipstick it needs to be in the three-point (two-point really, in a Fournier) attitude, but that just means lifting and lowering the tail a few times during the process.
Now, fill the tank five or ten, or twenty litres at a time using precise amounts in your cans, as measured by the forecourt fuel pump at the gas station (which has to be accurate by law).
For the Maule, I use 20-litre graduations on the dipstick, the Champ has 10-litre graduations, and the Fourniers have 5-litre graduations, because those equate to half-an-hour's flying in each case.
On the Champ and Fournier fuel gauge wires I've filed 20-litre and 10-litre marks (one hour's fuel). For the Maule I've made up a conversion card, so when for instance the left main tank gauge reads 1/4, I know there's actually 22 litres left.
Because the tank's bottom is round, the Fournier dipsticks are calibrated with them held in finger and thumb at the front of the tank's filler neck, dangling vertically downwards till they touch the bottom, with the Fournier leaning on its left outrigger and me at the left of the aeroplane. This is probably far from vital, but ensures repeatability. On level ground of course, too.
In England I fly from a short airstrip and need maximum take-off performance for safety, so I never put in more fuel than I think I'm going to need. In the Maule or Champ that's probably 1½ hours worth (one hour for my planned sightseeing flight with half-an-hour reserve for getting lost, escaped cows on the strip, a passing shower etc). Having only the required amount of fuel gives me a shorter take-off, a better climb, a better glide, and less fuel to burn me when I crash.
With the Fourniers I mostly fly aerobatics. The manual says max aerobatic fuel is 15 litres (that's also one-and-a-half hour's flying at cruise power) so I virtually always fill the Fournier tanks to 17 litres -- a generous allowance for taxi, take-off and climb to a safe height, so I can start my aeros with exactly 15 litres.
Twenty minutes of full-throttle aerobatics burns slightly less than 5 litres, so when I land I usually need to refill with a little under 7 litres -- which just happens to be 5 litres of Mogas from a plastic can plus a couple of litres of Avgas drained from the Maule or the Champ to raise the fuel mix's octane.
I only very rarely siphon out fuel, but I do if I need to fly a passenger from my strip on a hot day, or if I've changed my mind from doing a cross-country in the Fournier to flying aerobatics.
When going to a display, it is vital to arrive overhead with precisely 15 litres for the aerobatics (or, at least, no less that 10 litres and no more than 15) So I fill appropriately before departure. More than 15 litres gives a C of G too far forwards and it won't fly the flicks/snaps cleanly, and doesn't perform too well (losing height too quickly), plus it's against the limitations. Less than 10 litres and the tank's exit keeps getting uncovered and the engine keeps spluttering, so I'm running out of height too quickly again.
Luckily, our Fourniers burn exactly ten litres per hour at cruise rpm (3,050 with our 1400 motors and Heliptera propellers), which makes the calculations nice and easy.
I fill to the dipstick, and then check with the fuel gauge if I'm going cross-country.
I hope that is of use to you all and not 'teaching Granny to suck eggs' -- a British expression that is probably incomprehensible to you all :-)
Yours, Bob
[Edit by Bob Grimstead on Thursday, April 29, 2010 @ 09:35 AM]
