April 2015-
Q: Hi Steve,
I fly a Piper Cherokee 180 and want to install new stabilator tips and wingtips. Mine are original, and they are in pretty sorry shape.
My mechanic said he could remove them and use off-the-shelf fiberglass products to fix them up, but I don’t think that’s what I want.
I’ve seen other Cherokees with tips that are much better looking than the originals. What are my options for new tips?
—Bad Tip Terry
A: Dear Terry,
A long time ago Piper manufactured wingtips out of aluminum, but later changed to using ABS plastic because it was lightweight, easy to manufacture and economical. And as long as it was well protected by good paint, ABS was pretty durable.
However, I wouldn’t recommend attempting a repair of your original ABS plastic wingtips or stabilizer tips with fiberglass. ABS plastic is a much more flexible product; although fiberglass can be repaired, in this case you’d be mixing a rigid product (fiberglass) with a flexible product (ABS). It’s better to use ABS repair products on ABS tips, and ABS repair components are available from various vendors.
When it comes to purchasing new, you have a lot of options. While there’s still one company producing ABS products, two others make their products of fiberglass.
Is fiberglass better? Well, it’s tougher and stronger—but while that rigidity might seem like a plus, it’s not without a few liabilities.
Texas Aero Plastics argues for using ABS parts. One point made on the company’s website is that flexible ABS plastic will transfer much lower stresses to the wing or stabilator in the event of any impact such as “hangar rash” which is a catchall term for inadvertently contacting an immovable structure or another vehicle.
The company claims ABS has a life span of 15 to 20 years—longer than most owners will own their airplane. According to the site the only time fiberglass is better is under hard service, in extreme heat or cold and for extended service life. ABS parts are also less costly than fiberglass parts.
There’s more than one point of view, however.
Met-Co-Aire has published a discussion on its website stating that ABS plastic is a markedly inferior product for aircraft parts such as wing and stabilator tips; in fact, Met-Co-Aire says ABS was never intended to be used for exterior parts.
Met-Co-Aire has been manufacturing and selling FAA-approved (STC) replacement fiberglass wingtips and other parts since the 1950s. Its wingtips are specially shaped to utilize what is known as the Hoerner shape, so named for Dr. Sighard Hoerner. Met-Co-Aire claims the Hoerner shape reduces drag and provides performance improvements in speed and climb rate, increases stability and lowers stall speed.
Met-Co-Aire argues that it offers the best replacement tips, and backs this up by offering a “three-star” guarantee: lowest price, best quality and increased performance. Met-Co-Aire, a PFA supporter, also sells other fiberglass parts for your Cherokee including stabilator tips, a dorsal fin and a tailcone.
Other vendors that sell fiberglass replacement parts include Knots 2U and RMD. Knots 2U, a supporter of the Piper Flyer Association, sells a wide range of performance enhancement products as well as wingtips and stabilator tips from its Burlington, Wis. factory.
Fiberglass wingtip options include swept-up fiberglass wingtips by RMD that include the internal structure and a streamlined lens to mount a landing light in each tip. They also sell a swept-up tip sans landing light, also by RMD.
In addition to these, the company markets a standard-shape replacement tip design by Globe Fiberglass, a division of Knots 2U. All these tips are fiberglass and need to be painted after installation.
RMD Aircraft Lighting was the first company to sell FAA approved (by STC and FAA-PMA) fiberglass wingtips that incorporated structure and a lens for installation of a full-sized landing light. These products are still the company’s mainstay, although it has responded to buyers’ requests by developing approved tips without the landing light provision.
In summary, ABS tips are lighter, cost less and are more bendable. Fiberglass tips weigh a little more, are a little more costly and are more rigid—but are available in a wider variety of shapes and options.
Happy flying.
Q: Hi Steve,
I fly a Piper Cherokee 235 and my mechanic has told me that there’s a government bulletin that needs to be complied with to get through my annual inspection. I think he said it’s about control cables.
He told me that best thing to do is replace all the cables, and that sounds expensive. Can you shed some light on this?
—Cable Cal
A: Hi Cal,
Your mechanic is advising you on one way to comply with AD 2013-02-13. The AD applies to all serial numbers on a bunch of Piper airplanes, including the entire PA-28 Cherokee line (including retractables), the PA-32 Cherokee Six line (including retractables), the PA-34 Seneca line and all PA-44 models.
The AD was written following reports of control cable assembly failures that resulted in loss of stabilator control. Nobody wants that.
This AD, along with Piper Mandatory Service Bulletin 1245A published in November of 2012, provide detailed instructions on when the inspection is due, how to conduct the inspection and how often to conduct the inspection.
An initial inspection is required at the next annual inspection or within 12 months of March 11, 2013 if the age of the airplane is at or exceeds 15 years. If the airplane is less than 15 years of age, the initial inspection is due at the next annual inspection or within 12 months of the date the airplane reaches 15 years of age.
This inspection focuses on the turnbuckles and the cable terminals of the stabilator control system. Turnbuckles (sometimes called turnbarrels) look like bronze tubes. One end has a left-handed thread and the other a right-handed thread.
Turnbuckles are the adjustment mechanism used to tension control cables. Rotating the turnbuckle in a clockwise direction causes the cables to be drawn into the turnbuckle; rotating the barrel of the turnbuckle counterclockwise causes the cables to extend from the barrel.
During the inspection, each turnbuckle must be removed. The turnbuckles, both cable terminals and the adjacent portion of each cable must be cleaned and closely inspected (visually) for cracks, corrosion or broken strands.
The parts may be cleaned with a solvent such as methyl ethyl ketone (MEK) or acetone and an abrasive cleaning pad (e.g., Scotch-Brite). Any corrosion, cracks or evidence of cable fraying—however minute—is cause for cable replacement.
Flight surface control cables are beginning to attract the attention of regulatory agencies as the cause of more than one accident. In my experience it’s rare for these cables to be inspected, let alone changed.
Fortunately, McFarlane Aviation sells control cable kits for most of the airplanes affected by this AD. Each kit includes the left and right forward stabilator cables, the left and right aft stabilator cables, two new turnbuckles and two locking pins. Costs range from $285 to $537.
The FAA estimates that the inspection will take five man-hours for the inspection (about right, since the system has to be tensioned and re-rigged for travel after the inspection) and 10 hours to replace, rig and tension the four cables if replaced. (The 10-hour estimate is low, in my opinion.)
This is an important AD. Control system failure is no joke.
Happy flying.
Know your FAR/AIM and check with your mechanic before starting any work.
Steve Ells has been an A&P/IA for 43 years and is a commercial pilot with instrument and multi-engine ratings. Ells also loves utility and bush-style airplanes and operations. He’s a former tech rep and editor for Cessna Pilots Association and served as associate editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation (EllsAviation.com) and the proud owner of a 1960 Piper Comanche. He lives in Paso Robles, Calif. with his wife Audrey. Send questions and comments to editor@www.piperflyer.com.
RESOURCES >>>>>
ABS plastic replacement wingtips
Texas Aero Plastics
buyplaneparts.com
Fiberglass replacement parts
– PFA supporters
Met-Co-Aire
metcoaire.com
Knots2U
knots2u.com
Fiberglass replacement parts
RMD Aircraft Lighting Inc.
rmdaircraft.com
Control cable inspection documents
AD 2013-02-13
www.piperflyer.com/AD2013-0213
Piper Mandatory
Service Bulletin 1245A
www.piperflyer.com/SB1245A
Control cable kits – PFA supporter
McFarlane Aviation
mcfarlane-aviation.com
