Posted Friday, December 26, 2008 @ 11:06 AM  

Sorry for the slow reply, I hadn't seen your post.

I have had two of these made for me, both slightly different.

The fuel tank cap thread is apparently a standard thread that can be turned up by most folk with a lathe.
Take your current tank cap for them to see.
Best made out of aluminium, for lightness.

Into the centre I've fitted the needle valve from a Stromberg CD 150 carburettor. I used that because I happened to have a couple, but they are slightly more sophsticated than the average needle valve, with a couple of ball bearings of different sizes, completely enclosed in the brass fitting -- see the above photo.

That's threaded into an appropriately threaded hole tapped in the underside centre of the cap.
Use a small O-ring to seal it.
Into the top of the cap, with any thread you like goes a stainless steel bolt, with its head cut off.
I think mine were 1/4 inch BSF, but any appropriate-looking size should do.
Drill a hole from the threaded end into the bolt's shank all the way up to the top (1/8th inch I think -- whatever looks good), and then three or four holes (1/16th inch?) into the side of the bolt for the air to pressurise the tank.
Fit a locking nut, so you can turn the little holes to face forward however compressed your tank cap's O-ring becomes.

It's not hard.
It dribbles a tiny bit under -0.1g, but any more than that and it stops all flow.
Also sprays a bit if the tank's full and you taxi over bumpy ground, so don't open the canopy or you'll have an Avgas after-shave.

Good luck.

Posted Monday, September 14, 2009 @ 05:52 AM  

Here's a fuel float tip for everybody.

All RF4 floats tend to stick at the full mark, even when the tank is nearly empty and you checked it went up and down freely immediately before you closed your canopy. This problem is not so great if you take off with less than a full tank.

I've realised that the reason they stick is not due to any friction between the wire and its guide in the cap, but simply due to the high bending force imparted to the wire by the combined airflow and propwash.

An answer that works for me is to fit a tiny brass spring from a ball-point pen around the wire below the cap and above the float. This weighs nothing so it does not affect your fuel gauge reading, but it does help to push the float down from the cap. If your gauge is already assembled, you simply wind the spring around the wire until it's in place.

Then, if you are in flight, with this spring fitted, and you have been flying for some time but the wire isn't descending properly, merely close your throttle and slow down until you stall. The reduced airflow will allow the wire to straighten, and the spring will ping the float back down to its correct position.

If the idea of stalling frightens you, then you are definitely not practicing your stalling enough. Go and make a few stalls with an instructor in an RF5 or similar airplane, and then stall your own airplane regularly, and you'll find the fear goes away.

Yours, Bob

Posted Friday, January 15, 2010 @ 01:55 PM  

It is very stiff and springy and will flex rather than kink.

You can also solder it very easily as it has nickel or cadmium in its alloy I believe.

It is common in the US as any hobby shop will carry it in a multitude of diameters.

The next question is how can I put markers on it so it does not rub off in the guide tube?

I was thinking just sanding the bands where I want the tank level marks
so it would not be shiny in those areas.

Any ideas or comments on that?

Posted Saturday, January 16, 2010 @ 09:04 AM  

Yes, I have filed marks on all my fuel float wires (both Fourniers and the Champ -- I did it on my old Fly Baby, too).

Simply lift the tailwheel on to a jerry can and put both outriggers on to something to keep it wings-level and ensure you are in the 'omygod I don't have much fuel left so I'm throttled back and flying slowly' attitude, and put five litres of fuel into the tank (get it from the gas station in a five-litre can to be precise).
Then grab the wire where it comes out of the cap and bend it over at right-angles.
That's your 'when this kink starts tapping on the fuel cap I MUST LAND because I only have half an hour of fuel' mark.
When Bellanca built my Champ, they also painted this red.

Then put another five litres in to make ten litres and file a little groove all round the wire where it comes out of the cap.
Ditto for 15, 20, 25 and 30 litres. Full should be 36 litres.
Since the 1400 VW burns about 10 litres per hour at cruise, this gives you time left as well as fuel left.

We also made calibrated wooden dip-sticks at the same time.
Incidentally both these things are not only the law in Australia, but you must also by law re-calibrate your gauges and dipsticks every five (or is it three?) years
Like so many Austrlian laws, that's a good idea, but I reckon it's a bit anally-compulsive to make it a law!

My Champ and the Fly Baby have tiny, thin brass tubes for the gauges, rather than wire. By picking the right diameter of tube (from your local hobby/model shop) you can ensure the rod is a tight but movable fit in the cap, minimising the chance of it getting cocked over to one side by the airflow and jammed, and also minimising the amount of fuel you lose when you turn upside-down (or hit a big bump, either in the air or on the ground). Brass tubing is easy to solder too, of course, and lighter than wire of the same diameter.

Yes, I'm anally-compulsive about weight

Posted Saturday, February 20, 2010 @ 08:52 PM  

I used 3/32" music wire that the local hobby shop carried.

I believe the wire is a spring steel alloyed with some nickel and cadmium, so it is solderable and should not corrode.

The music wire is very springy and takes considerable force to bend or kink.

My float wire will never be bent again by an errant elbow or a canopy cover..

I also solved the wire marking problem (Paint rubs off quickly) by using solder to "tin" bands on the wire at 1/4 tank intervals.

I first masked the bands with painters tape, then used a dremel to rough up the bands slightly then soldered those areas and wiped off the excess solder.

I then heated the remaining thin layer of solder 1 last time to smooth it.

Upon measuring with the calipers I had deposited a layer of solder 1/500" thick so no worries on catching anything.

I think a little jewelers rouge on a buffing wheel and I will have very shiny makings.

The picture is before polishing the markings.