I recalled from my days as a tech rep that the most common failure of a light airplane fuel bladder is age-related deterioration of the top surface due to long-term exposure to heat. So my first thought was to dig back into the airplane records to find out if the airplane’s right bladder had ever been changed.
Then I remembered—I’d bought my Piper Comanche, Papa, at below market value because the maintenance records only covered the preceding three years.
Being an experienced A&P mechanic, I figured I would be able to determine through inspection if there were any maintenance deal breakers, so I was willing to buy Papa in spite of the severe shortage of logs.
During my due diligence prior to putting down my money, I contacted the FAA Registry office and asked for copies of the aircraft registration and aircraft maintenance records. Two CDs at a total cost of $10 arrived in a few days.
The registration records showed that Papa had been based in Albuquerque, N.M. for at least 20 years. That hot, dry climate—and the fact that Piper applied paint to its parts prior to assembly— eliminated my concerns about corrosion in the Comanche.
The registration data provided a starting point in my search for Papa’s records. A maintenance shop owner in the Albuquerque area told me that he suspected that an unscrupulous business owner had concealed the aircraft logs in an effort to swindle the widow of Papa’s owner into selling for a low price.
I wasn’t able to accurately determine the age of the bladders. But the right one was leaking and it did have to be changed.
Repair, refurbish, or replace
One of the resources I use for my aircraft is a type club-generated tips manual. In it is a description of how some club members repaired a leaking bladder by removing it, cleaning it thoroughly inside and out, and resealing it and patching leaks using 3M™ Scotch-Weld™ EC-776.
EC-776 is a brushable fuel resistant coating, and is still available. A one quart can cost over $60. One of the writers describes how he checked his patch/reseal work by pressure testing the bladder for leaks by inflating it with compressed air.
It’s physically and materially possible to field repair a bladder given enough time, diligence and discipline. The Comanche Service Manual does describe repair procedures but prohibits repairs in the radius of a cell and in the fitting areas.
Before you choose the option to repair or refurbish, thoroughly inspect your leaking bladder to determine if it’s worth the time and effort. Check with the A&P mechanic overseeing the maintenance on your Comanche to determine if he or she is agreeable as to the suitability and approvability of a field repair.
After pulling the bladder in my Comanche, I determined that it was the original bladder from 1959. It was built by U.S. Rubber in Mishawaka, Ind., and had lasted over 40 years.
The three biggest light aircraft fuel bladder companies today are Aero-Tech Services in Santa Fe Springs, Calif., Eagle Fuel Cells in Eagle River, Wis., and Floats & Fuel Cells (FFC) in Memphis, Tenn. Eagle Fuel Cells and Floats & Fuel Cells are PFA supporters. According to information on both Eagle’s and FFC’s websites, there were three different bladder types built by U.S. Rubber between 1959 and 1961. Some are repairable and some aren’t.
My bladder, a U.S. 584, was one that wasn’t a candidate for repair, but repair can be an affordable option for some leaking bladders. All of the major bladder repair companies offer a “test and advise” option that clarifies the repair/new decision.
I spoke with Aaron McCloskey, the senior sales representative at FFC who said that the repair cost for most tanks is between $200 and $400. McCloskey said that repair is a good option since even the most extensive repair is less than half the cost of buying a new tank.
During repair new nipples are installed and repaired tanks are guaranteed for two years. If time is critical, providers offer repaired bladders on an exchange basis.
The bladder I ordered was much smoother and a much more flexible tank than the old U.S. 584 tank. Included with it was an installation kit that included all new clips, a roll of bay tape—applied inside the tank bay prior to tank installation to cushion any wear points—cork gaskets and nipple clamps. All of the providers include installation kits.
Tank removal and installation
After draining all the fuel from the right tank I started preparing the bladder for removal. Eagle Fuel Cells’ notes recommend grounding the airframe to lessen the possibility of generating a static electricity-generated fire.
I did have some difficulty loosening the nipples connecting the tank to the fuel outlet and the fuel cell vent. The Hints page of the Eagle Fuel Cells website suggests loosening all clamps and waiting to let the rubber relax. Then the rubber of each nipple can be softened by wrapping it in a towel or rag that’s been dipped in hot water.
Since I was installing a new bladder I cut one side of each nipple on the old bladder and shot a little bit of LPS-1 into the cut; that helped release the tubing. (Any penetrant type lubricant will do.)
After removing the screws holding the filler neck plate in place and setting it aside, I used a mirror and flashlight to make sure I had freed all the clips holding the top—and the bottom—corners of the tank in position before removing the bladder.
Cushioning the edges of the access hole with tape lessens the chances of damaging the bladder during removal (and installation) and reduces the amount of skin rubbed raw while working through the hole.
After all the nipples were free and all the hangar clips were removed, I rolled the tank into a tube and slid it out the hole in the top of the wing. During tank removal I discovered a gap on one side of the metal mesh covering the end of the fuel pickup tube and repaired it.
Prior to installing the new tank I cleaned the bay to remove any fuel stains and dirt. Then I renewed the bay tape where necessary.
Installation of the tank was pretty easy. The only real glitch involved sliding the vent tube onto its nipple. Next time, I’ll polish the outside surface of each tube with a scouring pad and lube the tube with a little light oil to lessen friction.
I used a small block of wood as a pusher to get enough push to drive home one of the snaps located at the end of my reach. Long, strong arms are required.
The Eagle website contains a long list of hints to make installation and removal easier, and I can tell you that making the bladder more flexible by heating it is a help. Flipping the bladder to expose the top and bottom surfaces while it’s spread out in sunlight on the top of the wing is an easy, safe, no-cost—and “green”—heating method.
McCloskey said that some installers tape a pad onto the end of a broomstick or dowel and use it to push the bladder into position in the corners of the tank bay.
The torque specs for the 10-32 and ¼-28 screws and bolts used to complete the installation were printed on the bladder and are on the suppliers’ websites.
NACA-type fuel tank vents
My 1960 Comanche has pretty rudimentary fuel tank vents. These are nothing more than an aluminum tube that is connected through a nipple to the top of the tank, is routed back and down behind the rear of the tank and before exiting out the bottom of the wing. It’s very simple—and not good in icing conditions since it hangs out in the airstream, just itching to get clogged with ice.
Piper issued a couple of Service Bulletins regarding these vents. SB 180 requires that the tube be shortened until the leading edge is only half an inch long before cutting it at a 45 degree angle. Service Bulletin 193 requires that a 0.098 inch hole be drilled in the tube approximately halfway up the trailing edge of the tube to provide venting in case the opening became blocked. Manufacturer’s Service Bulletins are not mandatory.
Collapsed fuel tanks have caused many incidents and a few accidents because a partially collapsed tank appears from the opening and on the gauge to be full of fuel, but in reality contains much less.
One simple tool that every Comanche owner should use before every flight is a fuel quantity dipstick—it’s a surefire way to determine the actual fuel level in bladder tanks. When fuel starvation shuts down an engine, the silence is mighty loud. I hope you never hear that silence.
In 1968 the FAA issued AD 68-13-03 aimed at solving the Comanche fuel tank vent icing problem. The AD mandated certain fuel system inspections on PA-24 and PA-24-250 aircraft be conducted every 100 hours.
The bladder tanks must be inspected visually for indications of bladder collapse. The “thermos” type fuel filler caps must be inspected for proper part number and condition; fuel quantity indicators must be checked for operation and the fuel tank vent system must be tested to make sure there’s no blockage.
Blockage of the fuel tank vent will cause the tank to collapse inward as fuel is pulled out of the tank by the fuel pump(s). Anecdotal information includes a number of reports of inaccurate fuel gauges; this condition also results if the bladders collapse due to blocked vents.
The only surefire solution to vent icing is to install fuel tank vents that don’t project into the airstream. These are called NACA-style vents. Piper started doing this on serial number 3530 and later aircraft. Piper also developed fuel tank vent conversion kits (part number 760-277 for each main tank and 760-281 for each aux tank), and the installation of these kits is a terminating action for the AD.
Unfortunately for those that still have the tube-type fuel tank vents, these kits are as scarce as $2 Avgas—as in, good luck finding one. Sometimes it’s possible to get the parts (23464-00 vent assembly and 23478-00 vent splash plate for the left side and 23464-01 and 23478-01 for the right) from a Comanche fuselage in one of the larger U.S. salvage yards. Piper Flyer Association’s parts locating service is also a resource to try—and it’s free for members.
Cool bladder tanks live longer
The keys to getting great bladder service life start with the installation. Experienced and diligent first time installers should strive to achieve a tank installation where the tank bay is clean and prepped to provide an abrasion-free home for the bladder; where steps are taken to insure that any wrinkles in the bladder’s bottom surface are minimized and where the nipples aren’t pulled out of position or stretched during installation.
After the bladder is in and is deemed ready, I like to fill the tank in five-gallon steps—with the airplane on level ground and the landing gear struts and tires at normal inflation—for two reasons. This is the perfect time to make up a fuel tank quantity dipstick (I know I sound like a dipstick salesman, but they work and they are a simple safety tool) and to make sure you know exactly how much fuel your new bladder holds.
A new bladder should provide good service for at least 20 years and much longer if you take steps to keep the top surface of the bladder cool. Do this by shading the top surface of the wings whenever possible and by striving to top off the fuel tanks after each flight since the fuel will moderate bladder surface temperatures by acting as a heat sink. Hangaring an aircraft is the most effective method for preserving its fuel bladders.
When you smell fuel outside the airplane for an hour or two after topping off a Comanche fuel tank but not when the fuel level is down, the most likely cause is age-related deterioration of the top of your bladder. If replacing the gaskets on the filler plate and quantity transmitter don’t solve the problem, it’s bladder time.
New bladders cost between $800 and $1,000 apiece; refurbishing costs one-quarter to half as much as new. Removal and replacement labor usually runs between 10 and 12 hours.
Removing and replacing a bladder is not a difficult process. It can be a way to cut back on labor costs if an owner/pilot is comfortable in their technical abilities and savvy about working on one of the most important systems on a Comanche. Check with your mechanic to see if he or she is willing to supervise as you take on the through-the-hole job of bladder R&R.
Fuel Bladder Suppliers
Aero-Tech Services, Inc.
Eagle Fuel Cells-ETC, Inc.
Floats & Fuel Cells, Inc.
Piper Comanche Service Bulletins and Letters
Refurbish, Repair or Replace: What do to when your fuel bladder fails