----- Original Message -----
Sent: Friday, February 11, 2005 11:36
PM
Subject: [FlyRotary] Vapor lock
One final thought.....my
aluminum sump tank in not vented. Seems we discussed this at length when I was
building this thing, and since the overflow is pumped into the sump tank, the
fuel might just be pumped right out of the vent. Take care. Paul
Conner
Paul, I think this is your problem. I brought this up on this
list once before. I nearly had the makings of a fatal accident a year ago when
I temporarily had my sump tank unvented. I had been flying for over four years
with a vented sump tank and never had a problem.
I flew to Puyallup WA for
the airfaire early in the morning. The plane sat out in the sun all day, with
temperatures rising. When I went out early afternoon to depart, I lifted the
nose, hopped in, started the engine, taxied to active runway. Very fortunately
there were several planes in the pattern and I had to wait for takeoff.
Finally, I took the active, pushed in full throttle - and the engine died.
This had never happened before. I got out and pushed it off the runway,
somewhat stumped. Finally I remembered the rubber cap I had put on the sump
tank vent. I popped it off and heard a "poof" sound, and then the sound of
fuel flowing into the sump tank. My sump tank is mounted low, fed from the
main tank by gravity. Apparently being parked nose down for several hours out
in the sun allowed vapor lock to form in the lines between the main tank and
the sump tank. If those planes had not been in the pattern, I would have
taken off from a relatively short field in a congested area and the engine
would have quit right after takeoff with no place to land safely.
My
sump tank vent is up at the top of the fuselage with the main tank vents, I
never have problems with fuel being pumped out the vent. I now maintain that
the sump tank must be vented - to do anything else may be fatal. I've brought
this up before on this list and more recently on Canard
Aviators.
Perry
Hi, Perrry....One question....Does your
unburned fuel (from the fuel rail) go back into your sump tank
also? Or do you return the unused fuel to one of your fuel
tanks? If I were returning fuel to one of the main tanks, I would think
that venting the sump would be appropriate, but since I am sending fuel undere
pressure back into the sump tank, I am concerned that once the sump tank is
full, the additional fuel pumped back into the sump tank would take the path
of least resistance....out the vent instead of back up the fuel line into the
tank? Thanks for your input. Paul
Conner
No virus found in this incoming message.
Checked by AVG
Anti-Virus.
Version: 7.0.300 / Virus Database: 265.8.7 - Release Date:
2/10/2005