REFLECTOR: Fw: [Canards] Pro Bolt Info & Gas Cap Anti Spark Device
Ronnie Brown
romott at adelphia.net
Thu Aug 5 14:15:37 CDT 2004
Forwarding a couple of notes from the Canard list.
The interesting one is about refueling. This has always been bothersome after reading about Melvin Ball's new V that burned to the ground while refueling in Colorado.
My vent lines are bonded by fuel cap rings. I added a 1 meg resistor to my vent line to aircraft ground connection. This bleeds any charge of at a slow rate rather than produce a spark (picked this up from an article in Sport Aviation a couple of years back). The next note suggests touching the fuel nozzle to the fuel cap/ring before opening the tank. That is probably the best thing to do.
Ronnie
----- Original Message -----
From: Flying Tiger
To: AAviators Canard ; AACanards
Sent: Wednesday, August 04, 2004 1:32 PM
Subject: [Canards] Pro Bolt Info & Gas Cap Anti Spark Device
I was browsing the Cozy Newsletters and found what I believe are two very good articles from Nat Puffer or at least I think that's who writes the newsletter? I know we have discussed both of these in lengthy detail but like the writer states it's good to go over these from time to time as a reminder. I especially like the braided gas cap cable and alligator clips and I'll add these to my VEZE later today.
Tim LoDolce
VEZE Truckee Tahoe
EAA TecCounslr/FltAdvsr
Propeller bolts. Propeller bolts are one of, if not the most
critical applications in an airplane. Less that the best bolts
may be okay for awhile if they are strong enough and properly
torqued. On the other hand, even the best bolts will fail if not
properly torqued. There are potential problems with either
AN bolts or industrial bolts, but fortunately, there are special
bolts made specifically for propeller installation. AN bolts are
made in accordance with military specifications for critical
aircraft use, using approved alloys, specified head treatment
to achieve the right combination of tensile strength and
ductility, and have rolled (not cut) threads to avoid stress
risers which could lead to fatigue failure at the threads.
Unfortunately, AN bolts are difficult to obtain in the lengths
required for propeller installation (particularly AN8), and the
thread length does not allow much room for error. For
example, the lugs for ½ in. bolts have a threaded length of .54
in, and in spite of the "book" value, we have measured the
thread length of AN8 bolts to be as short as .62 in. If AN bolt
are fully engaged in the lugs at initial installation, there would
be very little margin for retorquing, without bottoming out the
threads. If the threads bottom out, the bolts will soon fail in
shear. Industrial bolts are readily available in hardware
stores. They come in various grades, the most common being
grade 5 and grade 8. They have approximately 1-1/2 in. of
thread length, but unfortunately, the threads are cut rather than
rolled, which is against standard aircraft practice and more
likely to lead to fatigue failure. Grade 8 bolts have a tensile
strength of 150,000 psi (compared to 125,000 psi for AN
bolts), but because of their high strength, are too brittle. Grade
5 bolts have a tensile strength of 120,000 psi, and are closest
to AN bolts in properties, but have cut threads. The most
unfortunate thing about industrial bolts is the lack of
enforcement on quality. Our local ACE hardware store said
their bolts could come from any of 6 different countries,
based on price. Are you willing to risk whether they might be
made from inferior alloys and not have the properties they are
represented to have? Traceability of bolts to a reputable
source is the best protection against their being counterfeit.
Sensenich propeller bolts. Sensenich, the manufacturer of
propellers for the last 62 years, has been having one or more
reputable US manufacturers of AN bolts make special
propeller bolts to their specifications since 1956. These bolts
are traceable, made to mil specs similar to AN bolts, have
rolled threads (per aircraft practice), and have a longer thread
length. These bolts are made from approved AN alloys, are
heat treated to RWC-26-32 to obtain a minimum tensile
strength of 125,000 psi without sacrificing ductility, are
centerless ground to remove surface imperfections, have J-2
threads rolled on to a length of about 1.4 in., are then plated
and the heads are drilled for safety wiring. These bolts are
stocked by Sensenich in AN6, AN7, and AN8 sizes of various
lengths, and sold in kits of 6 with washers. They are slightly
more expensive than AN bolts of an equivalent size. We
purchased 6 AN8H-57AS bolts from Sensenich for $90
(some time ago). Contact either Ken DeGraph, or Ed Zircer at
(800) 462-3412. For reasons explained above, we do not
recommend either AN or industrial bolts.
FUELING FIRES
We have discussed this subject before, but it is so important that
it is worth reviewing over and over again.
For there to be a fire, three elements must be present: 1) fuel, 2)
oxygen, and 3) a source of ignition. When you are fueling your
airplane, fuel and oxygen will always be present. If you don't take
the necessary precautions, a source of ignition might also be
present.
In high-school physics, most people see a demonstration of a
Van de Graff electrostatic generator. It uses a moving, insulated
belt to generate potentials of millions of volts and sparks which
jump across huge gaps. The stream of fuel into your tank is the
same as the Van de Graff moving insulated belt. The fuel hose
nozzle is connected to ground, so it can move an unlimited number
of electrons into your tank. The fuel is non-conductive and the tank
is non-conductive, so these electrons collect on the surface of the
fuel with nowhere to go. The potential builds up, and when it
becomes great enough, a spark will jump from the fuel in the tank
back to the hose nozzle. That will be the last of your airplane, and
maybe you as well. There is a simple and effective solution.
The ground cable that all fuel trucks have is really worthless,
but I don't tell the driver that. I just tell him (or her) to hook it on
the exhaust pipes. This cable grounds the engine, but not the fuel
in the tank (my private joke). What I have is a braided cable
connected to my gas cap, which is long enough to dangle into the
fuel even when the cap is removed and laying on the top of the
strake, and of course it also lays on the tank nozzle when the cap is
removed. With a short electrical wire with alligator clamps on both
ends, which I carry in the side pocket of the front seat, I connect
the cable dangling into the tank and laying across the tank nozzle
with the fuel hose nozzle. This is called "bonding". It allows the
electrons collecting on the surface of the fuel to flow back to the
hose nozzle and to ground without generating a spark. The result is
that the fuel in the tank and the hose nozzle are at the same
electrical potential, so there is no way a spark could be generated.
This is probably even safer that fueling a spam can with metal
tanks.
Please do not be careless when fueling your airplane, even if
you fuel it from cans. Just a little precaution can prevent a huge
disaster!
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