Tailwheel Shimmy and Spring Arch

[Gilbert Pierce]

My PA 18 spring camp took me about 20 minutes to make and bolted right up the Clipper. More recently they were supplying the Clamp.

[flynfish]

Also, the PA-18 spring would require a new spring hanger since it's 1.5" - the Husky comes with all the needed components.

First thing I did with my airplane when I got it was put the ABW PA-18 tailspring on it. Haven't had any shimmy since. Called them and ordered the pieces/parts they recommended. Went on with no issue.

[Short20]

Also, the PA-18 spring would require a new spring hanger since it's 1.5" - the Husky comes with all the needed components.

My spring just wouldn't hold an arch any more. Bought and installed the ABW PA-18 Spring. They supplied a new clamp that was a direct bolt on with no modifications needed. The wider spring still nests between the existing bolt holes. The bolts supplied with my kit were a hair to short though. I'm pretty happy but I could still use a bit of shim to increase the caster another couple of degrees.

[Shermanj1]

My spring just wouldn't hold an arch any more. Bought and installed the ABW PA-18 Spring. They supplied a new clamp that was a direct bolt on with no modifications needed. The wider spring still nests between the existing bolt holes. The bolts supplied with my kit were a hair to short though. I'm pretty happy but I could still use a bit of shim to increase the caster another couple of degrees.

I also had really bad shimmy with a maul tail wheel and original 1 1/4 springs that needed re-arching. Installed the ABW PA-18 spring, ABW 3200 tail wheel and replaced the bolts.
The spring bolted right up just make sure you have some extra washers and cotter pins for adjustments.
Bolt I used: AN6-26A spring to fuselage, AN7-21A spring to tail wheel. AN4-15A you may need a little longer lengths.
I took her up and no shimmy no matter how I bounced her in. Only thing that will take some getting used to is how stiff the spring is during take of
and landing.

[Jim Hann]

Folks,

Well, I’m tired of grinding the rubber off my tailwheel because my spring lost its arch again.

What is the current “best advice” for installing the ABI PA-18 tailspring on a 22/20? I see old posts saying it was approved but the website says it is a non-PMA part. Will 23-27 do the trick? What verbiage has been used in the logbook? My IA doesn’t like blazing new trails, following what others have done is good.

Thanks!


Sent from my iPad using Tapatalk

[Gilbert Pierce]

What is safer; a non PMA part proven to solve the problem or an approved part (Univar) that we know will shimmy right out of the box because of insufficient arch? No brainer to me.

Mine was an owner approved part. I approved the arch and stiffness and determined it met the requirements. You can do the same thing.

It was a great improvement over the new Univair part that I had to re-arch before it was usable.

[SMO22]

I don't know the answer, but I can tell you that a scott 3200 tailwheel with that 8" wheel combined with the taller ABI spring will raise your tail and increase your takeoff distance. I flew a Pacer that had the original 1 1/4 spring and an API 4" solid rubber tailwheel http://apitailwheels.com/wp-content/...18/03/6124.jpg and man did that get off the ground fast, at least 100' shorter takeoff roll than mine with the taller 8" scott 3200 tailwheel. Taxiing was more difficult because the tail is about 3 inches lower with the API 4" tailwheel so you can't see over the nose as you taxi or as you begin the takeoff roll or pull the tail down to rotate at a lower airspeed.

[Steve Pierce]

Jim, Call ABW and tell them you want a spring with more arch. Sign it off as owner produced part. You played a part in the design and meet the definition of owner produced.

[Gilbert Pierce]

Jim, a refresher on Owner Produced Parts.
Your IA may not be aware of this.


http://www1.faa.gov/avr/afs/news/arc...gust/IvsWe.htm

"I" versus "We"

by Bill O'Brien

Along with the pilot shortage and the mechanic shortage,
there is also a parts shortage that plagues the general
aviation industry. Because supply and demand are out of
balance the cost of new and used parts seem to increase
every day. Let's examine the reasons why this is so.

First, we have an old fleet. The average general aviation
(GA) single engine airplane is approximately 32 years old.
The average age of GA multi-engine reciprocating aircraft is
close to 27 years old. The average age for the turbine
powered multi-engine propeller driven aircraft average out
around 19 years of age. So because of long term wear and
tear the demand for replacement parts and large
sub-assemblies is much greater today than it was even 10
years ago.

The second reason is our general aviation fleet has been well
maintained over the years. So well maintained in fact, the
average GA aircraft with a mid-time engine and decent
avionics has appreciated to two or three times its original
purchase price and is still climbing. Yet even in that land of
many zeros the older aircraft are still substantially lower in
price than the cost of a brand new aircraft with similar
performance numbers and equipment. So the value of older
aircraft in good shape are proven investments that over time
have beaten the DOW JONES average. So we have an
economic imperative on the part of the owners to keep
maintaining older aircraft in flying condition which
increases the demand for replacement parts.

The third reason is the increasing production costs to make a
part. Today aircraft manufacturers are not making makes and
models of aircraft in the same quantity they made them back
in the Seventies. So the production runs for parts are not as
frequent and not as many parts are produced. In addition, it
is not cost effective for a manufacturer to make a lot of parts
even if the unit price for each part is out of this world
because taxes on maintaining a large inventory of parts
would eat all of the profits. This low parts production keeps
the supply of replacement parts low.

The fourth reason is that some manufacturers would prefer
that their older makes and model aircraft-made a million
years ago-would quietly disappear from the aircraft registry.
This retroactive birth control on the part of the
manufacturers may seem not to make any sense until you
look at aircraft market dynamics of creating demand and
reducing costs. First, each older aircraft that is no longer in
service creates a demand for a new, more expensive aircraft
to take its place. Second, despite some tort claim relief
granted to GA manufacturers in the early Nineties, the fewer
older aircraft there are in service, the manufacturers of those
aircraft enjoy reduced overall liability claims and ever
decreasing continuing airworthiness responsibilities.

So how are we going to maintain these older aircraft with an
ever dwindling parts supply when Part 21, section 21.303
Replacement and modification of parts, requires us to use
the Parts Manufactured Approval (PMA) parts on a type
certificated product? Well, the same rule grants four
exemptions to the PMA requirement.

[Gilbert Pierce]

Part II of the above:
1. You can use parts produced under a type or production
certificate such as a Piper, Cessna, or Mooney produced
part;

2. A owner or operator produced part to maintain or alter
their own product;

3. Parts produced under a Technical Standard Order (TSO)
such as radios, life vests and rafts, and GPS; or,

4. A standard aviation part such as fasteners, washers, or
safety wire.

Before I segue into the subject of "owner produced parts" as
called out in section 21.303, which is the purpose of this
article. I would like to create a small uproar with this
statement: "FAA Airframe and Powerplant rated mechanics
can maintain, repair, and modify parts, but they cannot make
a brand new part and call it a repair." Before you accuse me
of losing dendrites by the minute, check out section 65.81
General privileges and limitations. The section talks about
maintenance, preventive maintenance, and alterations, but
not the manufacturing of parts. Nor is it an implied privilege
in Part 65, because Part 21 section 21.303 says "no person"
may make a replacement part for a type certificated (TC)
product unless that person has a PMA, etc.

While I write this I can remember 25 pounds ago and when I
had hair, I worked in the real world and I specialized in
making engine baffles for Lycoming engines. Before
someone accuses me of bureaucratic ventriloquism which is
roughly translated as "talking out of both sides of my
mouth." My weak defense is, I made the parts because I
thought I could." It never dawned on me that I could not
legally make a part. Some of you may be astounded that I
make this confession freely. It's no big thing because I know
the statue of limitations has run out years ago and a jury of
my peers would never look me in the eye and convict me.

So here is our problem that we must solve. Since mechanics
cannot legally make parts for aircraft and aircraft need
replacement parts, how are we going to keep the fleet
flying? If we cannot find PMA, TSO, standard, or
production holder replacement parts, we are left to make the
part under the owner-produced option under section
21.303(b)(2). However, we must remember that the part is
for the owner/operator's aircraft only and is not
manufactured for sale to other TC aircraft.

To get through confusing regulatory policy with our pride
intact, let's try the question and answer routine. (Note: This
policy is taken from FAA 's AGC-200 policy memorandum
to AFS-300 on the definition of "Owner-Produced Parts"
dated August 5, 1993)

Question 1: Does the owner have to manufacture the part
him or herself in order to meet the intent of the rule?

Answer 1: No, the owner does not have to make the part him
or herself. However to be considered a producer of the part
he/she must have participated in controlling the design,
manufacturer, or quality of the part such as:

1. provide the manufacturer with the design or performance
data from which to make the part, or

2. provide the manufacturer with the materials to make the
part, or

3. provide the manufacturer with fabrication processes or
assembly methods to make the part, or

4. provide the quality control procedures to make the part,
or

5. personally supervised the manufacturer of the part.

Question 2: Can the owner contract out for the manufacture
of the part and still have a part that is considered
"owner-produced?"

Answer 2: Yes, as long as the owner participated in one of
the five functions listed in Answer 1.

Question 3: Can the owner contract out the manufacture of
the part to a non-certificated person and still have a part that
is considered "owner-produced?"

Answer 3: Yes, as long as the owner participated in one of
the five functions listed in Answer 1.

Question 4: If a mechanic manufactured parts for an owner,
is he/she considered in violation of section 21.303(b)(2)?

Answer 4: The answer would be no, if it was found that the
owner participated in controlling the design, manufacture, or
quality of the part. The mechanic would be considered the
producer and would not be in violation of section 21.303(a).
On the other hand, if the owner did not play a part in
controlling the design, manufacture, or quality of the part,
the mechanic runs a good chance of being in violation of
section 21.303 (b)(2).

Question 5: What kind of advice can you give on how a
mechanic can avoid even the appearance of violating section
21.303(b)(2)?

Answer 5: First, a mechanic should never make a logbook or
maintenance entry saying that he/she made a part under his
certificate number. This foopah will send up a flare and get
you undue attention from your local FAA inspector, which
you could do without. However, the mechanic can say on the
work order that he helped manufacture an owner-produced
part under section 21.303 (b)(2).

Second, the owner or operator should be encouraged to
make a log book entry that is similar to section 43.9
maintenance entry that states: The part is identified as an
owner produced part under section 21.303 (b)(2). The part
was manufactured in accordance with approved data. The
owner/operator's participation in the manufacturer of the
part is identified, such as quality control. The owner must
declare that the part is airworthy and sign and date the entry.

Question 6: Is there anything else a mechanic must do?

Answer 6: The mechanic must ensure that the
owner-produced part meets form, fit, and function, and,
within reasonable limits, ensure that the part does meet its
approved type design (e.g. like looking at the approved data
used to make the part). Then the mechanic installs the part
on the aircraft, makes an operational check if applicable,
and signs off the required section 43.9 maintenance entry.

Question 7: What is the owner responsible for and what is
the mechanic responsible for concerning owner-produced
parts?

Answer 7: The owner is responsible for the part meeting
type design and being in a condition for safe operation. The
mechanic is responsible for the installation of the
owner-produced part being correct and airworthy and for a
maintenance record of the installation of the part made.

Question 8: How does the owner or operator get the
approved data to make a part if the manufacturer and other
sources are no longer in business?

Answer 8: For aircraft that the manufacturer is no longer
supporting the continuing airworthiness of, the owner or
operator can petition the FAA Aircraft Certification
Directorate under the Freedom of Information Act for the
data on how the part was made. Or the owner or operator
can reverse engineer the part and have the data approved
under a FAA field approval or, if it is a really complicated
part, have the data approved by a FAA engineer or FAA
Designated Engineering Representative.

Question 9: What happens to the owner-produced part on
the aircraft if the original owner sells the aircraft?

Answer 9: Unless the part is no longer airworthy, the
original owner-produced part stays on the aircraft.

I hope that I spread some light on the murky subject of
owner-produced parts, so the next time instead of saying to
the owner of an broke aircraft: "Sure, 'I' can make that part,"
you will now say "Sure, 'WE' can make that part."


Bill O'Brien is an Airworthiness Aviation Safety Inspector
in FAA's Flight Standards Service. This article also
appeared in the Aircraft Maintenance Technology
magazine.