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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