Hi Frans
I have a 914, not flying yet. I purchased a tool from the guy who makes
the lead scrubber additive (not TCP, the one not for use with certified
aeroplanes, but you can transport in cabin) that measures at what
altitude you can fly to with the brew in your fuel tank. It takes into
consideration temp, % of avgas, % of mogas and % of alcohol. It's a
syringe that you pull a specific vacuum on a scale, let it sit for a
short time and you can read then to what altitude you are safe to fly to.
It is very possible on a hot day at a high temperature, you get a stay on
the ground reading. I noticed he stopped selling them a while back
though.
That said, do you have a differential pressure gauge on your 914? Direct
fuel pressure reading does not provide very useful info unless you do the
calculations to see how you are doing. Did you do the math to determine
if you are in the differential limits?
It's worth it to do I think it's in Europas test, cheat your
fuel
pressure regulator to thinking you are at ~ 18K (I think that was the
approx. test), then do a fuel flow test, monitor differential fuel
pressure as well and make sure you are where you want to be. The thinner
the outside air and the thicker (inside your engine MP) air, the more
fuel pressure you will need. Something marginal will usually show itself
at this time. A restriction in your fuel system will also show. Do you
have a single point of failure or restriction in your system like a
gasculator? Or do you have a system when you turn on pump #2 it sucks
---From a separate fuel filter? What happened when you turned on pump two,
did it not make a change? Rotax recommends cleaning the fuel pump intake
side filter socks once a year, they say that this is the leading cause of
fuel pump failures.
On a 914 the float bowl gasket sealing is critical, differential fuel
pressure being positive only means you will be able to force the fuel
into the float bowls, if there is not airbox pressure that is maintained
in the float chamber (or higher than airbox pressure in the case you are
asking more than 108% power and the hand in the breeze is plumbed into)
your carbs with be providing a serious lean mixture condition.
If you are flying out of a tight field with a 914, if you are asking
more
than what a 912 can produce it's prudent to follow Rotax 914 users
manual and do a DO, I forget if it's a 178 or something in the 170s
take off. In other words turn off the TCU with the wastegate in the
closed position and adjust you MP with the throttle. Once you reach a
safe altitude then turn back on the TCU, this prevents the TCU for
whatever reason from turning the 914 into a straight 912 at just the
wrong moment.
For a short period of time using the throttle to control MP is not going
to cause much harm, but doing this trick for long periods of time is bad
for the turbo, the turbo is working overtime and you are now forcing
it's cool side output into a restriction.
I don't know if your mogas has alcohol in it, but flying up high and
into colder conditions can make the alcohol that has commingled with
water to precipitate out and cause problems. I for one will probably
follow my vapor pressure tools suggestion, and if I plan on flying high
will add 2 or 3% Isopropyl Alcohol to my mix in an attempt to keep water
in solution. The more alcohol you run the richer your mixture needs to
be. I will make sure when I do the required by Rotax (but not many folks
do this great test) CO test to make sure your leanest cylinder is running
rich enough at War Emergency power (I will also test between 85 and 100%
too), I will do this with 10% Ethanol and 5% Isopropyl. I am installing
the ability to lean along with an O2 sensor driven display to see how the
mixture is doing in addition to EGTs.
Ron P.
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