Maintenance Matters

How much does your airplane really weigh? Our bet is that the last POH weight is wrong and probably not in your favor.

When was the last time your airplane got weighed?

Back when Ike was golfing, when it left Lock Haven or Wichita, right? Meanwhile radios have come and gone, engines have been overhauled, changed and re-accessorized, seats have been replaced-or maybe removed entirely. Its probably been painted two or three times, at least.

Perhaps youve had a couple of things 337d aboard with some quick arithmetic to recalculate weight and balance. Who knows what your airplane really weighs in 1998? Certainly not you.

Surprise, Surprise
I didnt know either, it turns out, although my homemade Falco was carefully weighed as recently as 1991, just after I finished building it.

In time-honored homebuilder manner, I borrowed half a dozen bathroom scales from friends, spanned pairs of them with planks out on the relatively flat ramp (gee, thats interesting, look how the numbers fluctuate when the breeze comes up…) and lifted the airplanes three wheels onto the boards: 1231 pounds. Sounded right. I was delighted that Id done such a good job building that the airplane weighed what the worlds more carefully constructed Falcos generally do.

Well, I was 94 pounds low and about an inch too far forward on N747SWs CG. I discovered that last spring by flying the Falco to Reeves Air (401-596-8559), a Westerly, Rhode Island shop that has sophisticated, biennially recalibrated electronic scales and advertises its aircraft-weighing services. For a flat singles-and-twins fee of $250, Reeves put the Falco inside its hangar sheltered from the wind, totally defueled it, emptied the cockpit of nonessentials, carefully leveled the airplane laterally and longitudinally (which ultimately involved strapping down the nosegear scissors and partially deflating the nosegear tire-certainly something Id never considered doing) and used $5400 electronic truck scales to come up with a wheel-by-wheel total weight of 1311 pounds.

The entire process took three men about two hours-much of it consumed by laborious defueling and refueling of my nearly full tanks-and left me officially signed off with a computer-generated sheet listing the Falcos new weight and CG and defining the calculations used to compute the CG.

Thats a bargain in the airplane world, especially since the job usually takes about an hour longer on a more complex airplane. If I were on the verge of selling my airplane, it would be money we’ll spent. Any potential owner will want to know about weight and balance, or should. As it is, Im confident knowing my airplanes actual to-the-pound weight and, more important, its balance.

Homebuilts have no gross-weight limitations. The requirement is simply that the airplane is loaded within its balance envelope and that safe climb performance for the mission being flown is retained.

As a certificated, factory-built Italian design in the 1960s, the Falco had an official maximum gross weight of 1800 pounds. But homebuilt versions have flown considerably heavier than that. Indeed, the well-known Italian Falco modifier and racer Nustrini once lofted his entire family-four small children, bambino, wife and himself-in the two-seater. don’t believe it? He took an in-flight wide-angle photo to document it, which you can see on the Falco website,

Part 135 airplanes require re-weighing every 36 months, but Part 91 operators can get away with having new weights and CGs calculated arithmetically and signed off as a continuing revision of the airplanes original factory empty weight. Thats what most owners do. For years.

You do have to get your airplane reweighed, however, after a major STC installation such as a different engine. And we homebuilders can, for better or worse, do it all ourselves.

To have a professional do the job correctly requires either defueling the airplane or determining the specific gravity of the fuel aboard. Only then should they do the arithmetic to figure exactly how much to subtract from the indicated scale weight.

Michael Reeves, who with his father, Ed, operates Reeves Air, says, On something like a Cessna 402 with full tanks, you can be as much as 20 pounds off if you just assume six pounds per gallon and get the specific gravity wrong. Also, whos to say whats full tanks? One guys full might not be as topped off as another pilot likes them.

Planning ahead to arrive for the job with minimal fuel makes sense, particularly if, as in the case of the Falco, the operator uses the airplanes on-board electric fuel pump to empty the tanks, flowing the gasoline into a plastic drum about as fast as a half-open bathroom tap.

Even using the quick drains is far from quick. The worst was a guy with a 310 who came in from Groton [an 11-mile flight from Westerly] with every tank topped-wing tanks, locker tanks, tip tanks…and hed had the appointment with us for two weeks, Ed Reeves recalls.

Reeves puts the drained fuel back into the tanks by using a small aircraft electric pump driven by an old battery and some jumper cables, the whole horrifying process taking place amid spilled gas and fumes, atop the half-filled fuel barrel. My little wooden airplane never looked so much like a tinderbox. Even an old-fashioned hand-cranked centrifugal pump of the type my local hardware store sells would be far faster and safer, guys.

Circuit Riders
Although Reeves Airs scales are good for a total of 12,000 pounds, they don’t get customers in that empty-weight range because its uneconomical to take a large Part 135 airplane out of revenue work long enough to fly it to a weighing site. Its cheaper for an operator to own a set of scales or pay somebody to bring the scales to the customer.

Thats what Chester, Connecticut weighing specialist Eric Propper (203-269-9634) does. He flies his scales and equipment hither and yon throughout the Northeast in a Cherokee Six.

Propper uses not flatbed scales but highly accurate strain-gauge load cells that fit between an aircrafts jacks and its jacking points, which allows him to easily weigh aircraft as heavy as small commuter airliners and Gulfstream IVs.

Proppers GA rates run from about $250 to $500, depending on gross weight, plus $75 an hour for the Cherokee flight time. Propper is leery of doing homebuilt aircraft, however, for many of them don’t have well-defined jackpads that will interface cleanly with his load cells.

The Reeveses have, of course, seen a variety of object lessons in the efficacy of updating aircraft weights.

One of the worst we ever got was a plain old 172, in fact, says Ed Reeves. It left the factory 35 years ago, and whenever anybody did any work on it, they apparently just pulled numbers out of the air. The owner brought it to us expecting to gain some useful load, what with the more modern equipment that had been installed over the years. He ended up losing 70 pounds.

Worst of all, though, was a Riley Rocket 310 conversion, says son Michael. Somebody had screwed up the weight and balance after the big engines were installed. When we redid it, the owner was shocked to discover that he had a six-seat airplane with a 500-pound useful load with full fuel.

Mike Reeves considers the salient parts of a good job to be getting the airplane into a clean, dry hangar and taking your time to level it perfectly, especially longitudinally. don’t ever say close enough. Misleveling wont throw off your empty weight, but it can foul up your CG calculation. If youre going to bother to do this job at all, might as we’ll take the time to be accurate about it.

Aircraft weighing isn’t a service that every shop provides, but any good local FBO will know the location of the nearest facility with scales. I highly recommend it as a useful undertaking for EAA chapters hangaring a bunch of airplanes weighed on bathroom scales.

-by Stephan Wilkinson
Stephan Wilkinson is an Aviation Consumer contributing editor.