I have one comment on the subject of allowing the main to completely run out,
then
switching to the reserve. We did that once to check the procedure in a safe,
controlled, environment. The engine quit but was still wind milling. After
switching to reserve, the engine restarted and went to high RPMs because the
Airmaster CS prop had gone to full fine pitch when the engine cut out, and took
some time to recover once the engine restarted.
The lesson of the story is, pull the throttle back to idle before switching in
the reserve tank.
Regards,
Terry
-----Original Message-----
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com] On Behalf Of Sidsel & Svein
Johnsen
Sent: Sunday, June 23, 2013 2:29 PM
Subject: SV: Europa-List: Use of reserve tank
--> <sidsel.svein@oslo.online.no>
Graeme,
What we need to keep in mind is the following:
When we run off the main tank, about 28-30 liters of fuel goes out per hour at
cruise power (912ULS). Abt 10 of these liters return to the reserve tank (i.e.
abt 1/3 of the total flow out of the tank), and flow back over the saddle into
the main tank. This ensures that the reserve tank is always full, even if
we should fly a little uncoordinated once in while or experience some bumpy
turbulence,
and the net drain from the main tank is
18-20 liters (or whatever the cruise consumption may be).
What we should NOT do is switching to the reserve tank before we have decided
that
"OK, this is it for the main tank, from now on it's only the
reserve tank that will take me home." Take the following case: 9 liters
in the reserve, 11 liters in the main. If this were the case during the last
part
of a flight, we have 20 liters total, i.e. one hour's flying time.
If due to uncertainty about actual volume remaining in the main tank, we switch
to the reserve tank (9 liters), then we have a little under half an hour before
the engine tells you something. If we now switch back to the main tank, we
suddenly do not have 11 liters consumable fuel there anymore!
Why not? Because about 1/3 of that fuel is returned to the reserve tank, but
the
returned volume does not any more overflow into the main tank because the
reserve
tank first needs to be filled to its top. 10-15 minutes' flying time is
thus lost, which could be critical (unless we are conscious about this, and
switches back to reserve again).
What it all boils down to is knowing how much you have left in the main tank, so
we can confidently run this tank almost empty and switch to reserve just in
time before the engine tells you to, and then stay on the reserve tank.
I completely trust my fuel totalizer (feed and return flow senders) and the
sight
tube. By the way, I have connected the two vent tubes (the one from the top
of the sight tube and the one to the top of the filler neck) by a crossover
tube at their highest point. If one inlet should be blocked by an insect or
whatever,
the other will provide equal pressure on top of the tank and on top of
the fuel in the sight tube. It is amazing how erroneous the sight tube reading
gets even with a very small pressure difference in the standard tubing
arrangement
- just try it by blowing gently into one of the outlets.
/////////
About return flow: I mentioned early this spring that I would re-wire the fuel
flow system so that I could get temporary direct reading of the return flow
only.
I have the relay deck and the push button, but just have not had the time
to wire it in ........ Will do - will report!
Regards,
Svein
LN-SKJ
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