Originally Posted by
sj3cub
The only concern I have when mounting my four strokes inverted, is can I get the centerline of the fuel tank low enough in the fuse to line up in the correct relation to the needle valve/carb. Sometimes its possible, sometimes its not. This is where a lot of people run into problems when mounting inverted, and don't even realize it. If you had the pumped version, there would be no issue. Good flying!
The "problems" they run into is believing some of the hype about fuel tank height espoused around here.
MOST of it centers around "junk science" that has no basis in fact.
There is only a small issue of concern, which is not "junk science" and that is siphoning.
If the height of the fuel line ( top ) when the tank is FULL is higher than the spray bar, you can get siphoning.
Siphoning is of course bad, because you can flood the glow plug or even hydrolock the engine.
However once the engine is properly tuned, the spray bar oriface is quite small, and given the average 1 to 1.5" DIFFERENCE in height seen when inverting an engine, that leads to maybe a single DROP of fuel siphoning out evey minute or so with the engine throttle at idle.
If you shut down the throttle fully ( engine cut off ) you should see no siphoning, unless of course you have other plumbing problems.
So you set up your filling system so that fuel can not be pushed into the cab during fueling. You keep the throttle cut setting on once the tank is full, and you DO NOT prime the engine before you attempt to start it.
That is all you need to do...
Also remember that with most tail draggers, when the plane is on the ground the engine is lifted even higher than the thrust line. That often offsets the tank height difference enough to also stop siphoning.... either way it is not a big deal once you have everything dialed in and the pilot exercises a bit of care.
The rest of the nonsense about small tank height differences affecting engine performance is all speculative hype.
Some people will go as far as to talk about the difference of the thickness of a PLAYING CARD making a difference.... they are crazy.
Our planes would be cutting out when they fly inverted, change attitude or even when climbing were they to be correct.
Once running your four stroker engine sees no change if you raise the tank 3" or drop it 3". It takes a LOT more distance to cause the weight of the fuel in the line to affect things.