Striking New Technology

It's a knotty problem that all airframe makers working with composites must ultimately face: lightning protection. For all its advantages, composite construction holds one prime disadvantage, that of being electrically inert. You could have no better chances passing electricity easily and effectively through fiberglass than Newt Gingrich has of remaining on Hillary's Christmas card list. By their very nature, composites are dielectric, characteristically incapable of passing meaningful voltage.

In normal flying this really isn't a serious concern. Sure, it means that far-flung electrical devices — lights on the wing tips and tail, for example — need separate ground paths where in metal airplanes the airframe itself suffices. But for homebuilt airplanes in particular, the ease of working with composites, the ability to make compound curves and complex surfaces, and the potential for great structural rigidity all make the medium desirable. Widely used in aerospace, composites will likely be more and more a part of new-design light aircraft in the coming years.

But something tremendously undesirable happens when lightning strikes a conventional composite airplane. With astonishing energy — the textbook lightning bolt carries 1.5 million volts and 250,000 amps — an encounter with God's own flash bulb threatens to literally blow a composite structure apart.

Stoddard-Hamilton, maker of the Glasair and GlaStar kit aircraft, in concert with the funding of a Small Business Innovation Research grant and the assistance of NASA, sought the answers to making a fiberglass airplane survivable in the event of a lightning strike. The result is the Glasair IIILP, an otherwise normal 300-horsepower, two-place speedster that happens to have some of the latest thinking in lightning protection in its very skin. The findings of the research program embody technologies used in the Ruschmeyer R 90, a fiberglass four-placer certified for IFR, and those that will likely be employed by Diamond aircraft if it wants the Katana line to be approved for flight in the clouds.

Bob Gavinsky, formerly an engineer for Boeing, headed the team for Stoddard-Hamilton. Although the company realized from the start that a lightning-protected kit airplane might not be a flaming sales success, it decided nonetheless to invest the necessary resources. Gavinsky is one of the first to defend the outlay: "We learned a lot about lightning and composites in this program." The bottom line is a fully lightning hardened kit that you can buy today, and significant trails blazed for the rest of the industry that will surely be well trodden upon in the future.

What, then, does it take to turn an ordinary composite airplane into a lightning-hardened design? It starts with testing. According to Gavinsky, the company produced whole pieces of the airplane in both standard and prototype hardened and took them to Lightning Technologies in Pittsfield, Massachusetts. What they discovered about a composite airplane's behavior to a lightning strike will just about curl your hair.

"When a lightning bolt hits, the voltage potential is really high, with the bolt trying to arc from the cloud to the ground," explains Gavinsky. "There's not a lot of current initially, but a lot of voltage. Say it hits the airplane...as the bolt connects to [the Earth] it suddenly has this nice current path. With that the lightning bolt expands." When it does so — with incredible force — it tears into the fiberglass structure, blowing holes in skins and sizzling cores to a fine crisp in the matter of a few milliseconds. It's like ice forming in a sealed container full of water, only much more exciting to watch.

What's more, the electrical energy constantly seeks the path of least resistance back out of the airplane. In the case of the Glasair (and many other designs, for that matter) that path might be through metal control rods or cables, or through the electrical system of the airplane itself. In either event, the pilot will likely experience some of nature's free energy, as will the avionics suite. Chances aren't good for the survival of delicate electronics when hit with 375 billion watts. What has kept lightning strikes from being instantly lethal is the short duration of the event, says Gavinsky.

Stoddard-Hamilton's response to the lightning issue took several paths, although one of the chief concerns was for weight and cost. According to Gavinsky, "We asked ourselves — can we do this on a small general aviation aircraft and make it cost and weight effective? Lightning protection is a smaller percentage of the total weight in larger aircraft..." but can become significant in something as compact as a Glasair.

First came protection of the airplane's skins themselves. Sandwiched near the outer plies of fiberglass is an extruded aluminum mesh, described as similar to the type used on your average industrial stair step. In the Glasair IIILP, the mesh ranges from 5 to 10 mils thick, in densities of 0.015 to 0.06 pounds per square foot. Pretty light material, but plenty conductive just the same. In total, the company estimates the protection adds some 60 to 70 pounds to the bare airframe. (Stoddard-Hamilton's lightning protection arrangement differs from that used in the Beech Starship, incidentally, which is mostly graphite and already somewhat conductive; still, the turboprop needed additional conductive materials to pass lightning tests during certification.)

This mesh covers the entire airplane, throughout the fuselage, wings, and cowlings. One of the most difficult challenges in the project centered on joining these pieces of conductive material to create a cohesive whole. It does no good to have panels of conductive material if they're not joined; the lightning will arc across the joint and do nearly as much damage as if the parts were not treated. Stoddard-Hamilton staff spent many hours determining how to best mate the material during the building process, and the result is said to increase building time only slightly. (Constructing the basic airframe of a homebuilt is only a small part of the project.)

With the skins protected and mated electrically, the testing showed that parts of the interior and individual systems need to be mated to the main ground plane of the airplane, or, for those items that may be in contact with humans, isolated from it. Emerging from this need is what Stoddard-Hamilton calls an equiplane. It's an aluminum ground plane that spans the length of the fuselage, connecting all the electrical components from the firewall on back.

Coupling the airplane's subsystems electrically helps prevent arcing from circuits of different voltage potentials. If the electrical energy is allowed to flow continuously through the structure, from point of first contact to the exit location, damage can be limited and the chances for human injury dramatically reduced.

Some of the details needing attention in the Glasair IIILP demonstrator include providing ground straps around the rubber engine mounts and locating the antennas on the outside of the airframe. (No longer can the builder hide the antennas inside the normally electrically transparent structure.) Control surfaces had to be electrically bonded to their mounts by means other than the hinge, lest the surface become fused after the lightning strike.

Conventional protection for the fuel system in the form of grounded caps and isolated vents and lines also followed from the research. The more trying modifications included mating the major metal parts of the airplane — like the engine and landing gear system — to the equiplane without incurring greater complexity or undue weight.

Eventually, Stoddard-Hamilton arrived at an airplane that is far more lightning-hardened than most production airplanes. That's in part because the vast majority of light aircraft flying today were certified under old regulations, which didn't have provisions for lightning protection. The company points out that in many respects a standard composite airplane isn't much worse off than a metal airplane certified under the old rules, because surface bonding and electrical cohesion were not big concerns at the time in the heyday of so-called Spam can production. It's worth noting, too, that the myriad steps and cabinets full of paperwork generated by the research project have essentially laid the groundwork for conventional certification under FAR Part 23 rules, though Stoddard-Hamilton says flat-out it has no such intentions.

Aside from the lightning-protection equipment aboard N540LP, this Glasair III represents pretty much the norm of the type. It's very well equipped and carries the latest-specification slotted flaps — both characteristics that seem to be hallmarks of customer-built IIIs. We did not fly the airplane with the optional extended wing tips, which are said to reduce approach and stall speeds appreciably.

In flight, the IIILP remains familiar to anyone with standard Glasair III time. With 300 hp on tap from an IO-540 Lycoming and a maximum gross weight of just 2,500 pounds (with the extended wingtips; 100 fewer without), the III is what you might call a sprightly performer. Claimed climb rate at maximum weight for the standard III is 2,400 fpm, and top cruise (75-percent power, 8000 feet) is listed as 224 knots. Extended-tip IIIs can hold as much as 72 gallons of fuel normally, although builders have been known to add substantially to that number by extending the wing fuel tanks into normally dry bays.

With full normal fuel (61 gallons) and two aboard on a slightly colder-than-standard day, the factory's IIILP climbed at better than 1,500 fpm from near sea level. The rate decreased to 1,400 fpm at 4,500 feet and 1,000 fpm by 9,500 feet. This was using full throttle, 2,500 rpm, and 140 knots indicated, well in excess of the normal best-rate speed of 113 knots but one that offered a decent forward view.

Leveled at 11,500 feet (13,730 feet density altitude), the IIILP accelerated up to 168 knots indicated at just under 65-percent power. True airspeed settled on 208 knots consuming 15 gph, a setting slightly leaner than best-power mixture. Though we didn't check it, company pilots say the IIILP is a few knots slower than a normal III at its optimum altitude, partly because of its exposed antennae.

Compared to the last III we flew, the IIILP seemed a bit more docile, as though the slight additional avoirdupois were helping to slow the airplane's normally quick reflexes. (It could also be that we're becoming more familiar with airplanes of the III's ilk, and so the light control forces, high wing loading and low power loading are not as foreign as they once were.)

In any event, the IIILP's slotted flaps return the investment in extra building complexity by being far more effective than the original plain, bottom-hinged affairs. Now the airplane can be flown down final at a reasonable 80 knots with more than just the long snout in view. Moreover, there will be sufficient energy left for a leisurely roundout. Stoddard-Hamilton's newer slotted flaps make the IIILP easier to become familiar with than was true of the original circa-1987 Glasair III prototype, N540RG. Unfortunately, pitifully low gear- and flap-extension speeds mean that large power reductions will be part of every pattern entry in the III.

While those limitations can create awkward moments in the cockpit, they are nothing compared to how the Stoddard-Hamilton staff felt when the III suffered a rash of accidents in the early 1990s. After a number of mishaps, it quickly became apparent to Glasair III owners that insurance, if even available, would be expensive beyond reason. Stoddard-Hamilton stepped up and helped pen a training syllabus (mated to an airplane- inspection program) that is now executed in the field by Professional Instrument Courses (PIC). Though it's possible to get insurance without taking the annual PIC training, many owners have gone through the course and come out praising it. We had a sample of the PIC course some time ago and were impressed by the thorough syllabus and rigorous in-the-airplane training. Partly as a result of the training, Glasair III accidents and incidents have declined dramatically.

What hasn't changed in the world of Glasairs is the method of construction. As always, the III (including the IIILP) is made of room- temperature-curing fiberglass bonded with vinylester resin. Other common kitplane materials include oven-cured, pre-impregnated fiberglass bonded with epoxy. Which is best? This has come to be the high wing/low wing argument in the kit world, but the materials have worked in Glasairs for more than 15 years. In addition, Stoddard-Hamilton and a vast cadre of builders are familiar with it and know the material's properties intimately.

These days, a basic Glasair III kit will set you back $37,700. (At press time, the company was continuing a 15-year anniversary pricing special that includes a raft of desirable options — including electric slotted flaps, dual brakes, electric elevator trim, canted instrument panel, and wing tip extensions — for $35,699.) Add your own engine, prop, electrical system, avionics, paint, and interior. The additional lightning-protection hardware adds $11,500 to the basic kit cost and add a bit to the estimated 1,800-hour build time. Lightning hardening is available for any of Stoddard-Hamilton's Glasair kits.

So far no hardy, all-weather flyers have stepped up to the IIILP. That doesn't surprise Stoddard-Hamilton. Ultimately, the value of the IIILP comes as an exercise of what can be done, a flashlight shone into the murky future of composite aircraft. Better that, goes the company reasoning, than to be shown the way by a bolt from the blue.