HP AT Review by Dennis Pagen

HP AT Review by Dennis Pagen

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Pilot Report: Wills Wing HP AT 158

By Dennis Pagen
Originally published in Hang Gliding Magazine, January 1990. © 1990 United States Hang Gliding Association. Reproduced with permission.

This review reflects the author's personal experience and assessment at the time of publication.

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We have learned to live with DDT in our food chain, PCBs in our water, THC in our brains and STP in our cars, so why not WW-HP-AT 158s in our atmosphere? At least this was my reaction when I first heard of the alphabetic acronym for Wills Wing's latest offering to the world of unfettered flight.

Then I got to see six early examples at the World Meet in July and thought, "Well, they sure look purty." Then I heard the results of the Nationals in September and thought, "Well, they must fly right nice." Then I got a call from Rob Kells of Wills Wing with an invitation to come to California and fly some ATs for a flight report and thought, "Hot damn!"

When I arrived at the Wills Wing complex in Santa Ana, California in early November, I was handed a folio of maps, the keys to a car, a box of tapes and a new glider. I was in hawk heaven. They pointed me in the right direction and I flew to the point of satiation. In eight flying days I logged nine flights (two towing) at eight sites for a total of almost ten hours. I flew four different gliders in conditions ranging from ridge lift with light drifting thermals to scratching in yo-yo air bashing around in elusive lee-side boomers.

When I had finished this orgy of airtime, I had enough notes and impressions to write an article. My standard policy on equipment reviews is simple: if I like it, I write it up; if I don't like it, I send it back. The presence of this article testifies to my regard for the WW-HP-AT 158.

Design Concepts

It is every designer's desire to improve on his previous model. His success depends on his ingenuity, his understanding and his abundance of good fortune. When Wills Wing set out to make a new high-performance glider, they had to rely on all of these factors plus a fancy array of computer components to get the job done. They had a formidable task, for their previous glider, the HP II, was a well-proven performer and they had only eight months to produce a certifiable glider in time for the 1989 World Meet.

The HP first appeared in 1984 and turned out to be a potent competition glider. Its main drawbacks were less than perfect handling, adequate, but not overwhelming sink rate, and less than docile landing characteristics. The HP II also posted an impressive competition record and seemed to improve on the earlier model, with better handling and sink rate at perhaps the expense of a little top end. Finally, the HP AT takes over to offer even better sink rate and improved handling. As the culmination of a gradual progression, the HP AT can be declared a success.

Here is a partial list of some of the changes incorporated in the new AT. A smaller sail, greater span, higher aspect ratio, a new airfoil, a new luff curve, new hardware, a VG system and a new airframe.

The area of the AT is 158 square feet compared to 162 square feet on the HP II. This factor, coupled with three inches greater span, to 34' 7", results in an increase in aspect ratio from 7.2 to over 7.5. Now, the equations say that increasing effective aspect ratio improves glide ratio and sink rate. However, the key word is effective. Just increasing the numbers does nothing if wing twist (washout) is increased or the lift distribution strays from the elliptical ideal. So the jury is still deliberating about the benefits of the increased aspect ratio, and the verdict will only come after a year or so of comparative flying in a multitude of conditions.

You can be sure of one thing: Wills Wing has made these design decisions carefully, with the goal of improving overall performance while maintaining the necessary safety. We will look at performance below while mentioning that the HP AT exceeds the required HGMA testing for strength and stability.

The Airframe

We must make mention of the airframe, for it is what the Church Lady would call "special." Chief designer, Steve Pearson, explained to me the technicalities of his leading edge. "The ideal leading edge would be tapered," he mused, "it would be larger diameter in the place of maximum stress at the crossbar junction and have a smaller diameter toward the ends where there is little bending force." Unfortunately, tapered aluminum tubes are about as rare as a brainwave in a hairdresser's salon. So what must be done to maximize strength and bending pattern while minimizing weight is to step the tubing down by inserting a smaller piece inside a larger. Normally this can only be done in 1/8" steps or the slop is too great. However, Wills Wing devised an ingenious method whereby two crescent-shaped inserts mate a large tube to an inner tube that is much smaller. The front part of the AT is 60mm (2.36 inches) and the rear part is 50mm (1.97 inches), about .4" difference. This arrangement resulted in a stiffer leading edge compared to the HP II with a reduction of weight of several pounds per side.

The entire airframe, except for the control bar, is made of 7075 tubing. The advantages of this alloy is its greater yield-strength-to-weight ratio compared to the most common alloy, 6061. With 7075 tubing, wall thicknesses as thin as .028 inches can be used without worrying about undue denting. This feature allows a designer to optimize strength while minimizing weight. Witness this: the HP AT is five pounds lighter than the HP II and that includes the addition of the VG system.

The disadvantages of 7075 tubing are its greater cost, the need to order a year in advance in mega-quantities, and its tendency to corrode. Wills Wing helps combat the latter problem by using aluminum bushings and coating the inside of every tube with LPS-3, a standard procedure in the aircraft industry. They have also performed tests to assure the reliability of 7075 airframes by putting a new sail on a 2-1/2 year old glider that spent at least one year at the beach wearing jams and Vuarnet sunglasses. The glider passed the HGMA strength requirements with aplomb, despite its trying time in the salt spray.

In sum, Wills Wing must be given high marks for the AT's new hardware. It must be realized that without their high sales volume (close to 1,000 per year), such a fabrication of unique parts would not be feasible, for the tooling and development of the AT cost close to $100,000.

Purely out of curiosity, I asked Mike Meier to list the number of parts in the AT in order to get an idea of the complexity of the design. He was able to oblige this request easily by virtue of his position as overseer of design specifications and manufacturing processes.

If nothing else, this chart serves to indicate the amount of manufacturing that goes into a modern glider, and why you have to spend so much of your hard cash to fly higher and further.

Hardware

One of the goals of the AT design project was to develop new hardware for improved aesthetics, function and aerodynamics, with strength at least equal to the former gizmos. With the aid of AutoCAD, Wills Wing has come up with some fine fittings indeed. Here are some highlights:

The control bar corners and top fitting are made from extruded and machined aluminum that allow a quick erection of the control bar and an easy folding back to drop the glider on the ground in an emergency situation (this can be a life saver in a surprise high wind). These fittings are small and functional.

One of the best hardware items on all Wills Wing gliders, in this writer's opinion, is their unique keyhole tang cable attachments at the nose (lower front wires) and tail (upper rear wire). This tang fits over a grooved bolt and the whole system is quick, easy and light.

The control bar itself is one of the most comfortable I have used, with 68" faired downtubes and a medium-bulge belly bar. The downtubes are of fairly small cross-section with a boundary layer trip ridge and a good feel in the hand. The basetube is practically perfect due to its well-placed padded foam grip. No muscular handshake required here.

The two items I am not totally in awe of are the crossbar hold-back pin and the lower side wire tangs. The former must be inserted when the crossbar is pulled back. Because it is only a ball pin, the holes in the tang it attaches have a very close tolerance, which often requires a bit of jimmying to get the pin in and out. Perhaps I'm ham-handed, but I think a PIP pin would make life easier.

The control bar tang is only a problem when storing the glider. It is not long enough to allow the side wires to fold neatly against the downtubes. As a result, careless packing can cause the cable to bend at the Nicopress fitting. One of the gliders I flew had a permanent bend at that location. Knowing this problem will prevent it if a pilot exercises care. A quarter-inch longer tang and a shorter side wire would be the ideal fix.

The rest of the AT's unique hardware consists of several special fittings for the VG system (which we review below), plastic bushings for all moving parts, and neat kingpost brackets, top and bottom. The bottom bracket consists of a series of slots that allow an instant no-tool positioning of the hang point to adjust trim speed.

The VG System

Wills Wing has long resisted the clamor to create variable geometry gliders. Be that as it may, when they finally decided to join the bandwagon, they answered to a different tune. The VG on the AT is not a dainty little string, but a hearty man-sized lever reminiscent of the switch Dr. Frankenstein threw to animate his monster.

The rest of the VG system is elegant enough. From the lever a motorcycle-like cable is routed up the downtube to a block on top of the keel, where the inner cable extends to engage the crossbar. There is no string or pulleys to get entangled. Another cable extends from the crossbar into the base of the kingpost to activate a reflex bridle compensator at the kingpost top. In my view this is a much better way to change reflex bridle lengths (necessary when activating a VG system) than the standard method of shifting the kingpost back and forth.

There are two positions on the VG lever: full on and full off. At first I thought this was limiting, but after using the system and reflecting on my general habits, I realized that full on or full off is how I fly with any VG system 95% of the time. Normally I put a VG half on for takeoff, but with the AT I was comfortable taking off full tight as well as full loose. (Taking off with a VG system tightened somewhat reduces side-wire looseness which makes matters easier in gusty launch conditions.)

So in conclusion, I can live with the two-position VG and I like its clean engineering. According to the factory, the VG was designed with a range to give adequate handling in the tight mode and good performance in the loose mode. In fact, the glider is intended to be flown most of the time loose, for the handling in this mode allows an adept pilot to maximize climb rate.

The AT Sail

All HP ATs come with the same sail, including competition editions. This sail has a leading edge of Profile coarse-weave cloth which has an open weave coated on both sides with mylar. This material is very tough and very unstretchable, which is the main reason why it adorns the HP leading edge. However, we must note that this Profile cloth is dimpled like a golf ball. Now ask yourself: "Why does a dimpled golf ball travel much further than a smooth golf ball?"

The rear of the sail — the area of highest stress — is made from 5.6 ounce HTP 240 cloth. This cloth has high resilience, durability and stretch resistance. Former owners of Wills Wing products should not be fooled: despite this cloth's resemblance to the metal cloth used previously (the stuff with the square pattern), it is not the same. The new cloth has a 1,000 denier thread thrown in at intervals, whereas the old cloth simply had a doubling of the 180 denier thread. A careful inspection of the cloth will reveal the difference.

The rest of the sail top and bottom is made of 4.0 ounce standard cloth in a variety of non-standard colors — your choice. Finally, we should mention the special reinforcing material at the batten pocket ends. This touch is intended to cure a common problem: batten pocket blowout.

Performance

Most pilots wade through the technical details or skip them entirely in their rush to learn of a glider's hard-core performance. This is a natural tendency, for the reason a pilot buys a top-of-the-line glider is for performance. However, we must mention a few caveats.

First, we are probably close to the limits of performance of portable, swept and twisted, weight-shift control flying wings. A designer can trade sink rate, maximum glide, glide at speed, handling and landing sweetness, but to wring out superior overall performance is a task of Augean proportions. In fact, there is probably a greater difference in gliders of the same design that are tuned differently than there is in high performance gliders of different design.

Second, we must realize that pilots have different requirements according to the type of flying they do. For example, someone who spends most of his time boating around the local site trying to top out the pack will probably want a design different from that of the guy who scoots along the ridge in high winds or covers vast distances in strong inter-thermal conditions.

Third, a glider that may be a potent weapon in the hands of a top-drawer pilot may be too much to handle for the average aerial cowboy. Finally, the absolute useable performance of a glider generally varies with conditions, and only a year or two of comparison flying at local sites and in competition will tell the true tale of a glider's performance.

However, with all the above in mind, and considering the newness of the glider, I will try to make a tentative assessment. The pure (straight-ahead) sink rate of the AT appears to be quite good. I attribute this to the glider's ability to slow down a remarkable amount before stall begins. Straight-ahead sink rate is fine for floating in magic air or coastal buoyancy, but the real test is thermaling climb rate. Because of the AT's ease of handling (see below) and leading edge construction, it will probably excel in this mode of flight (a stiffer leading edge maintains sail shape better during the increased loading of turning flight). In my experience I found I could climb with the best gliders at the sites I visited, but unfortunately only a few of these gliders were other than ATs! The HP in general seems to do well in booming conditions, and there is no reason to believe that this new version will not do the same.

The high-speed glide of the AT is undoubtedly good. It appears that the AT is a bit better than the HP II in this department, perhaps due to the very clean tip fairings and the slightly smaller size. Wing loading plays a great part in high-speed performance with greater weight on a glider allowing a better glide at a given speed above best glide speed. Only comparison tests or accurate performance maps (polars) will tell.

Before any reader draws conclusions from my musings, note that the AT can be tightened or loosened by changing shims in the leading edges or adjusting the VG range. The gliders I had to test were set as they come from the factory — tuned for the average Hang IV pilot. In general, I believe the AT is a formidable all-around performer and will not disappoint the buyer in that department. Note that at the last U.S. Nationals, four out of six ATs in the meet placed in the top ten. The AT took the top two highest places for Class I gliders.

Flying Characteristics

First, the bad news: The AT is not for everyone. In fact, the glider is rated for advanced (Hang IV) pilots only. The main reason for this is its extra dollop of glide in ground effect that complicates landing (this trait is common to all high-performance gliders).

Handling is a big item on everyone's wish list. Perfect handling is probably only achievable with soft recreation gliders. But as high performance rides go, the AT is nice. With the VG loose the AT supposedly handles at least as easy as a Sport (I haven't flown a Sport for two years, so I cannot judge). My feeling is that the glider is quite pleasant in loose mode.

As mentioned, the factory recommends flying with the glider loose most of the time. I can attest to the fact that the glider thermals well loose, because I was climbed through in a light thermal by a pilot in another AT. My VG was tightened and I noticed his was loose as he left me floundering and foundering in the lift.

In the spirit of perversity, I didn't listen to the factory and flew the glider with the VG full on about 50% of the time. It felt like most tightened high-performance gliders. There was additional initiation required, more delay in the turn and an occasional tendency to lock out when lift bullied one wing more than the other. However, I found this behavior pattern to be quite normal, quite predictable and easy to live with. I could initiate a turn in a variety of ways in the tight mode — with a bump and push-out to the side or a pull-in and side movement. In the loose mode I found the best way to turn was the classic "J" stroke, perhaps because the inside wing doesn't approach a stall as it does in the tight mode with a push-out initiation.

I found I had to do a bit of high-siding (moving to the outside of a turn) in variable thermals. This is typical of spanny gliders and the only way to avoid this characteristic is to loosen the glider, which adds dihedral. The occasional need to high-side was only apparent with the VG tight, and was less than that of many other gliders in the AT class. The AT's overall thermal behavior was benign, with easy coordination and a willingness to adjust the turn readily. The thermal capabilities plus the good glide at faster speeds should make the AT a worthy X-C ship.

Leaping into the sky strapped to an AT is not particularly difficult. The static balance and control bar configuration are fine. The glider is light enough, solid enough and slow enough to facilitate any normal takeoff.

Landing characteristics are equally benign. The biggest problem I had at first was flaring a bit too soon. This was because the AT seems to slow more than I had expected, so waiting an extra second allowed me to stick the landing. The flare timing is not too critical as long as a full flare is applied.

I am used to controlling altitude during landing setup with diving turns. My first trial at these turns resulted in a small bit of wing walking (Dutch roll). Later I knew what to expect and eliminated this extraneous motion. I'm thinking now that the glider's facile handling in the loose mode, coupled with its slow stall speed, will allow additional turning on landing and thus a slower approach. I expect the glider may open up new possibilities in the landing phase of flight in the hands of a competent pilot.

Setup and Breakdown

The AT is a full-blown, state-of-the-art glider. As such, it sports a full complement of battens, VG system, faired tips, reflex bridles and shifting crossbar — all of which need to be inserted, attached, applied, hooked up or otherwise fiddled with. At least one Sport owner I spoke to was chagrined at the extent of the AT's setup procedure upon first exposure. However, it doesn't seem to me that there are any more steps to setting up the AT than with any high performance glider. When you learn the system you get more efficient. It's just a fact of life that you have to live with batten mania in order to gain that extra 100 feet or go that extra mile.

As with most gliders, the breakdown of the AT is simply the reverse of the setup. The one difference is, however, that you must put the multiple protection devices in place. There are kingpost pads, control bar covers, keel socks and a major water-repellent cover. Most pilots welcome all these protection items, for they certainly increase the longevity of the glider.

It should be noted that the owner's manual does a fine job of guiding the unfamiliar pilot in the setup and breakdown procedures. The manual is indeed a complete and useful document and Wills Wing quite justifiably points out that their batten pattern is the clearest and the most informative in the business.

AT Availability

Of course, you can get an AT from your friendly AT dealer. In fact, that's the only place you can get one, for Wills Wing staunchly supports their dealers by steadfastly refusing to sell factory direct. This policy guarantees dealer service and pilot qualification.

The factory tracks inventory control with their computer system and can tell a customer when a particular glider will be shipped at all times. Linda Meier in the front office keeps the record on customer information, production scheduling, special instructions, inventory control and test flying. If you call the factory with a problem (or solution), chances are you'll talk to Linda.

If you are over in Europe, you can buy your AT from Marcus Villinger of Fly International in Austria. As it stands, 40% of Wills Wing gliders are sold in Europe and about 12% go to Japan. Fly International is the only agent other than Wills Wing licensed to assemble and test fly Wills Wing gliders. Wills Wing provides sails, wires, battens and hardware, and Fly International fabricates the airframes.

When searching for a new glider a pilot is wise to consider customer service as part of the package, especially when all the manufacturers are producing fine gliders with similar performance at the top-of-the-line. Wills Wing has long had a strong dealer program geared to customer-support. From the little bag of goodies (shims, bolts, nuts, ties, safeties, a hat and a hug) that comes with each glider, to their excellent parts delivery, Wills Wing has tried to lead the way in service. I'll let the reader heed the rumors to see if they have succeeded.

We have tried to provide as much information as possible for the prospective buyer or the merely curious. Although some of the discussion is technical, it should be noted that all pertinent data should be considered when one prepares to lay down close to four big ones (that's four with three little zeros tagging along) on a toy. Of course, we always recommend that an interested pilot test fly any glider he intends to buy.

I wish to thank Wills Wing for their help in gathering all the proffered information. Hopefully future glider reviews can be as complete. By the way, no glider expose is, in fact, complete without an explanation of the name and model derivation. In this case it is simple. WW-HP-AT 158 = Wills Wing-High Performance-Advanced Technology with 158 square feet of sail. Indeed, the name is apropos, for in the guise of this glider, high performance and advanced technology run rampant. I recommend this glider to anyone who appreciates such qualities and this includes myself.

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Specifications