[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

REFLECTOR: fuel lines, valves, and safety

 With all the current discussion, and my moderate reservations about the
fuel system as is, I've pasted together the last few bits of an offline
discussion I'm having on this subject with my former boss.  He is a Navy
physician, orthopedic surgeon, and is one of the lucky few qualified as a
dual designator (which is full Navy pilot training), has been through the
Navy's Test Pilot program (2 of the class of 5 died in their initial year in
TPS). Built and flew his Long EZ, while at Pax River (TPS site) with full
military flight test cards, chase planes, etc. Has 5000hours in A-6's and
other planes, active EAA'r, etc.
He takes flight safety seriously, and one of his favorite answers to my
questions is, "Yeah they tried that, it seemed to work for a while, then one
day it didn't and they're DEAD NOW! Just DON'T DO THAT!"
   I'm always prying information out of him that he has tucked away in his
brain somewhere: "tell me again why I shouldn't do ____"
  It's a bit lengthy. For the groups consideration and comment. If people
complain I'll not post things like it again.

Q:  What do you know about 'explosafe'; the spongelike material you put in a
gas tank (2% volume loss) which stops a fuel-air flamefront propagation, and
therefore prevents explosion of a tank? (not the burning of leaking fuel,
just an intank explosion. probably too rich a mixture anyway. oh well)

A: First of all, there was a lot of interest in Explosafe at about the time I
build my airplane.  The problem was there were no studies on the subject.  I
recall reading about some major problem with it, but I can't remember what
it was.  I think it had to do with static electricity and fire hazard or
something.  Anyway, Rutan (or probably Melville) didn't recommend it in a
Long Ez type simply because the gas tanks are in front of the engine and in
a crash there is very rarely a fire.
  Just was looking through a few back issues of the eaa magazine; they have an
article discussing a fuel tank material that has been in use for years.  It
isn't explosafe, but similar, and there have been problems with the material
breaking down and clogging fuel lines and filters.  They are into about the
eighth generation of this stuff and think they have about solved the problem
with breakdown, but unfortuneately all the studies are done with jet fuel
and there are no data for auto fuel or avgas.

Q:  Had a bunch of reflector (builder group) mail today regarding fuel shutoffs
and stuff. As i recall the Long EZ has fuel up to the pilot, a selector
valve, and then back to the engine. any history of fires during crashes?
fuel in cockpit problems?
  Velocity doesn't route fuel this way. I'm unsure about the Cozy. I'm at
the point of routing fuel lines, valves etc, so I'll have to decide soon.
  I'm also considering fitting  a 'low fuel sensor' about 1" above the fuel
ports, on the floor of the tank, in each tank. This will indicate a low
level due to unporting(yaw), or inattention if that occurs. It would also be
a bit earlier warning than the low fuel light in the sump, telling me I'm
about to have my engine quit. 
  By the way, why is it these reliable engines are quitting on short final?
any categorical problem or solution? ice? unporting?
  why isn't running the O-240's at 3200 rpm more damaging? whatever happened to
'redline'?  Can you do that with an O-540? (with a smaller diameter prop.
isn't that your EZ modus operandi?)

A:  Yes, the long ez and cozy both run fuel lines to the front cockpit where the
selector valve resides so that there is no linkage to deal with.  There have
been no fires in Long Ez crashes as a result. In fact, fires are very rare
in Long Ez crashes because the motor is behind the fuel and fuel doesn't
usually get all over the hot engine.  Rutan designed the fuel selector valve
the way he did to reduce parts count and eliminate the possibility of
linkage problems, such as happened with John Denver.  It's a nice, simple,
safe way to do it.  You never wonder which tank the valve is pointing to,
since you are looking right at it.  The plumbing is fairly easy.....one line
from each tank to somewhere in the front cockpit (down low), a selector
valve, and another line back to the gascolator. I imagine I would leave the
velocity fuel system as designed; the other alternative would be the Rutan
way, but I wouldn't deviate otherwise.
   The problem with a low level sensor is that it is affected by aircraft
attitude and you can get false alarms.  With the amount of fuel these
airplanes carry, fuel level isn't very much of a problem, particularly when
you switch tanks every hour for balance.
   I don't know why the engines are quitting on final, but there are several
likely culprits.  One is fuel starvation; when you're trying to stretch your
range, and realize you are in trouble fuel-wise, you tend to have the engine
quit just short of the nearest airport you could find.  Secondly, carb ice
is most likely to strike after prolonged periods of idle, such as in descent
on final.  Even having the carb heat on won't help if the engine is at idle.
So I presume a lot of them are due to carb ice, which may or may not leave
any trace. There have been several incidents of Ellison throttle body
injector-equipped engines quitting suddenly on final, but to my knowledge no
one has figured out why.  I don't think unporting is the usual culprit,
because most fuel systems are designed to feed at nose up attitudes.  There
could potentially be a problem with low fuel levels and sideslipping, but if
you're sideslipping making the runway isn't the problem. 
  I still see no viable alternative engines out there, and I watch pretty
closely.  There's some guy flying a Long Ez with a suburu conversion. He'll
probably die.  The powersport  motor never really panned out, and it is more
expensive than a Lycoming now.  Zoche continues to talk, but not much
happening. So:  buy an airplane engine; the race prepped engine sounds
reasonable, but you need to talk further with them about reliability and tbo
figures.  The main thing you are interested in is reliability, reliability
and reliability.  Everything else comes a distant second.  That's why we're
still using the 1930's technology motors.  They are not stressed much, are
simple, and pretty reliable. 

Q:  My concern with the Velocity is that it is indeed different from the
other canard designs.  It uses the simplest of k.i.s.s. philosophy; a simple
'y' from the fuel tanks, to the sump, to the engine. No shut off or tank
selector of any kind. after some uneven tank flows/emptying, they manifolded
the vent system for all three together to a single vent line, when
presumeably keeps pressure even for all and allows even fuel levels and
flows to the sump. (I do not have this in the BD-4, and do have uneven flows
from the tanks, and even fuel transfer from tank to tank via the sump, I
think, because my vents apparently create different pressures in flight.)
The current reflector discussion relates to inflight fires (none recorded in
Velocities, I believe Shirl Dickey had one in his E-racer during a race and
had to put it down, years ago) or impending crashes, and whether being able
to shut off the fuel flow to the engine is a safety factor or greater hazard
of mismanagement.
   It would seem that being able to select a tank in my Velocity would be
desireable, even if used infrequently.  A selector having an 'off' could be
used in case of fire, fuel filter changes, engine or carburetor work, etc,
as well as being a mismanagement hazard if inadvertently selected in flight.
Certainly a remote selector is going to have its problems with failure
modes, jamming, etc, and therefore would more likely be a hazard in routine
or infrequent operations.  This comes back to changing my designs fuel
system to reflect the more proven designs; should the fuel routing be like
EZ's and Cozy's, with a pilot selectable valve sitting within easy reach and
view, or be left in a 'too simple?' type system?
  In a prolonged decent from altitude, with low fuel,(stretching for home
scenario), or steep decent for more than a few minutes, (in flight problem
or other urgent need to get lower fast) the possibility of unporting my fuel
inlets appears to be quite high.  There is one outlet at the rear of the
tank. My tanks have a nearly flat floor for more than 60" of fore and aft
measurement (100gal option setup), leading to significant fuel shift forward
in a nosedown attitude, most significant at lowfuel levels. This could
definitely unport both fuel outlets. (In the BD-4 the wing is FLAT.  I
always use one tank down to minimal fuel, and leave the other with a higher
level for use during decent and approach work, so that when focusing on
other tasks, I am using the tank with the most fuel).
   My thought about placing a low fuel level sensor switch about 1" above
the fuel outlet is that it would give you a yellow light if you were in a
situation where your fuel outlet was no longer feeding your sump. If a
selector valve were in use, this would alert you that you were about to run
a tank dry (mismanagement), allowing you time to switch before your sump
light came on (red!) or change your pitch attitude for possible correction
of your fuel feed problem. (This is where the selector valve has created the
option of a pilot mismanagement of fuel, and the 'y' doesn't allow it.)
   This all may speak to an obvious solution, and one that was posted on the
net yesterday: keeping the simple 'y' setup and placing a single cutoff
valve just ahead of the firewall, lightly safetywired 'open', with a
mechanical pull cable allowing emergency pull shutoff of fuel to the engine
fuel line. It is my impression this would best be upstream of an inline
electric fuel boost pump (in series with the engine driven mechanical fuel
pump, for simplest plumbing).
   Another fuel line routing point. I'm hoping to route the lines in such a
way that any impact which might tear the gear loose, but be in itself
survivable, won't be in a place such that the gear folding back, (and upper
arm folding forward) won't break or rip loose the fuel lines in the cabin,
emptying my tanks into the fuselage interior, where I sit in a stunned or
injured state. In this scenario, routing them forward to a selector valve
and then down the keel would have likely kept them of of the way of the
folding gear.

A:  I think Rutan's design is the safest and best and least likely to fail.
Each fuel tank has a sump/blister at the rear inboard area of the tank that
is about four inches below the bottom of the fuel tank and against the
fuselage.  The fuel line runs from that sump to the front cockpit to a
t-valve and back to the gascolator.  You have one or the other tank
selected.  Then there is no need for a fuel level sensor because you only
drain from the selected tank regardless of attitude.  The small sump takes
care of fuel demand during unusual attitudes.  The fuel lines need to be
large enough in diameter for the engine in question, of course, but it's a
system which has never had any problems and never has caused a crash or a
post crash fire.  If you wish, I can scan in the appropriate Long Ez plans
and email them to you as attached files.  I don't see the Velocity fuel
system as improved.  Each tank has to have a vent, of course, with ram air,
and there is an electric boost pump that backs up the mechanical fuel pump.
The electric pump is in line after the gascolator on the firewall.  It's
very easy to build.
  One other thing...if you look at commercially built aircraft, all low wing
airplanes with which I am familiar use a fuel system exactly like the Long
Ez for exactly the same reasons.  Only high wing aircraft use a gravity feed
system where both can be selected because both tanks will drain, favoring
the more full tank.  In a low wing airplane, there is essentially no gravity
feed and you can suck one dry.  That's exactly why Rutan (and Beechcraft and
Piper) use a selector valve with either right or left, but not both.  It is
my opinion that the velocity system, while simple to build, is not the
safest or best way to go.  I would put in the Rutan and Piper and Beech
system which has been proven in low wing airplanes.  Then you don't need the
low fuel warning system, valves, etc.  If you're going to crash hard enough
to break your fuel lines, you are already in deep shit.  Remember, thought,
the engine is in the back and fuel carried forward is not the same magnitude
of risk as in a front engine airplane.  Also,  would consider the small fuel