"Soaring with Sonex" Xenos Article (1.2mb )

Soaringwith

SonexDesigner John Monnett returns to the motorglider scene with the two-place Xenos. BY MURRY ROZANSKY

W W W . K I T P L A N E S . C O M8 K I T P L A N E S A P R I L 2 0 0 5

PHOTOS: RICHARD VANDER MEULEN

The long-wing Xenos motorglider (front) and Y-tail Waiex are the latest designs from Sonex, Ltd.

A little yellow slot car withwings. That’s how one visitorto Sonex engineer Pete Buck’s

hangar described the company’s Xenosmotorglider. That’s a strange thing tosay about an airplane with a 45-footwingspan and a length of 19 feet 9inches. But on closer inspection (andfollowing a flight in the new design), Ithink that visitor may well have cap-tured its spirit.

Why? Well, the bright yellowpaint job is the obvious reason, andthe fact that the Xenos sits close to theground. But this aircraft is no groundhugger—it wants to fly.

The Xenos and its short-wingbrothers—the Sonex and the Waiex (seePage 19)—did not burst onto thehomebuilt scene from nowhere. Sonex,Ltd., the company that designed andproduces kits for the Xenos, is the creation of designer John Monnett, whoruns the company with his wife, Betty,son, Jeremy, Pete Buck and a few otheremployees.

Genesis of the XenosIn 1971, Monnett debuted his first commercial homebuilt design—the Son-erai, a Formula V, VW-powered racer—

and he quickly followed with a two-seatversion. Both were of mixed construc-tion, featuring an aluminum wing and asteel-tube fuselage covered with cloth.Their longevity speaks to the popularityof the designs; plans for both are stillavailable today from Great Plains Air-craft Supply (www.greatplainsas.com).

Monnett’s interest in soaring led tothe design of the Monerai, a compactsteel-tube sailplane with a fiberglass pod,aluminum wing and a V-tail. The Monimotorglider followed and helped to establish the basic architecture for thecurrent line of all-aluminum aircraft.

The Xenos evolved as an idea for atwo-seat version of the Moni. Demandfrom Europe and the impending Light-Sport Aircraft (LSA) category in the U.S.led Monnett to release the short-wing,speedier Sonex design first. That design,with a low price tag, sporty perform-ance and an easy-to-build kit, took off.Today, there are 83 flying and nearly700 more under construction just 7 yearsafter the design was introduced.

Even as the industry concentratedon the LSA rule for the past few years,Monnett and Buck believed in thepotential of the motorglider. While themajority of potential LSA consumers

SONEX LTD. XENOS

Price (excluding quickbuild options) . . . . . . . . . . .$18,995

Estimated completed price . . . . . . . . . . . . . . . . . .$30,500

Estimated build time . . . . . . . . . . . . . . . . . . . . .1000 hours

Number flying (at press time) . . . . . . . . . . . . . . . . . . . . . .2

Powerplant . . . . . . . . . . . . . . . . . . . . . . . . . .AeroVee 2180

80 hp @ 3300 rpm

Propeller . . . . . . . . . . . . .Sensenich two-blade fixed-pitch

Powerplant options . . . . . . . . . . . . . . .Jabiru 3300, 120 hp

AirframeWingspan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45 ft 9 in

Wing loading . . . . . . . . . . . . . . . . . . . . . . . . . .8.07 lb/sq ft

Fuel capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16 gal

Maximum gross weight . . . . . . . . . . . . . . . . . . . . .1275 lb

Typical empty weight . . . . . . . . . . . . . . . . . . . . . . . .750 lb

Typical useful load . . . . . . . . . . . . . . . . . . . . . . . . . .525 lb

Full-fuel payload . . . . . . . . . . . . . . . . . . . . . . . . . . . .429 lb

Seating capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

Cabin width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40 in

Baggage capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . .50 lb

PerformanceCruise speed . . . . . . . . . . . . . . . . . . . . . .120 mph (104 kt)

8000 feet @ 75% power, 4 gph

Maximum rate of climb . . . . . . . .600 fpm (at max. gross)

1200 fpm (at aerobatic weight)

Stall speed (landing configuration) . . . .44 mph (38 knots)

Stall speed (clean) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .n/a

Takeoff distance . . . . . . . . . . . . . . . . . . . . . . . . . . . .300 ft

Landing distance . . . . . . . . . . . . . . . . . . . . . . . . . . . .300 ft

Specifications are manufacturer’s estimates and are

based on the configuration of the demonstrator aircraft.

As they say, your mileage may vary.

The Xenos’s 45-foot wingspan results in agenerous 24:1 glide ratio, an engine-out safe-ty margin most powered pilots aren’t used to.

might not be interested in a motor-glider, I think a close examination ofthe Xenos will change their minds.

“But why,” you ask, “should I paymore for a slower, harder-to-store long-wing Xenos when all three currentSonex designs are LSA compliant?” Afew reasons:

•You can shut the engine off andenjoy the wonders of soaring. It mayhave a motor up front, but this aircrafttruly is a glider. For powered aircraftpilots, think of the safety benefits ofhaving a 24:1 glide ratio with theengine off. From 8000 feet, your still-airglide is more than 35 miles. It’s a lotquieter with the engine off. And withpractice soaring you might enjoy thechallenge of flying using as little fuel aspossible. A motorglider provides achance to enjoy engine-out flight; in ashort-wing speedster, that qualifies as asituation to avoid.

•An additional plus for some isthat the medical requirements formotorgliders are even less restrictivethan for the new Sport Pilot license. Ifyou have a glider license with a motor-glider endorsement (or if you decideto earn one), you can self certify yourmedical. The time and cost of dealingwith the FAA on medical issues has putmany healthy pilots out of the air—the motorglider route is a legal way tofly over the red tape.

Strapping InFor this article, my mission was to visitwith Buck for a chance to sample theXenos in flight. Buck’s motorglider,N212XS, is based at Mountain ValleyAirport in Tehachapi, California. Situated in a pass where the southernend of the Sierra Mountains bumpsinto the Tehachapi Mountains, it is oneof Southern California’s best soaringsites. The air from the San Joaquin Val-ley battles with the Mojave Desert air.Windmills farm the air for electricity.

The Sailplane Homebuilders Association holds its western workshopin Tehachapi once a year. It was duringthat event that I hooked up with RogerTanner, a CFI-Glider, to fly Buck’sXenos. Tanner, like Buck, has a real jobbesides playing with cool kit airplanes.Tanner flies for the test pilot school at

K I T P L A N E S A P R I L 2 0 0 5 11

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Edwards Air Force Base, and Buck is an engineer at Lock-heed Martin. Buck’s day job is why his six-cylinder, 120-hp Jabiru-powered Xenos is not back in Oshkosh at theSonex factory with its four-cylinder, 80-hp AeroVee-powered brother.

The Xenos sits low to the ground on its titanium-rod taildragger landing gear, and it’s quite easy to get intounder the side-hinged canopy. The Y tail is the onlyobviously unusual feature on the airframe. The normal Vtail with ruddervators is supplemented by a small rudderhinged to the rear of the fuselage. When you can’t see it,the tail seems completely normal. Given the restraints ofsingle plane curves, where compound curves are restrict-ed to the extremities—the tips, cowling and canopy, forexample—it is an attractive aircraft. It looks especiallygood in yellow, and I think the color was an inspiredchoice (more on that later).

Taxi and TakeoffReaching for the Xenos checklist, Tanner reminded methat the use of a checklist is essential, even in the simplestglider. Twenty seconds later, we were fired up with the dual


Xenos MotorgliderCONTINUED

The author says the Xenos cockpit is a bit tight for two people, but itcould be built as a great single-place for an XXXL pilot.

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The two-place Xenos evolved from the single-seat Moni motorglider, an early John Monnett design.

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ignition checked and ready to taxi. Getting my headset on was about themost difficult part of the pre-takeoffchecks. Those are needed under power, asthe Xenos is a sheet aluminum airplanewith an unmuffled, air-cooled engine.

Taxiing was a piece of cake. Thelow c.g., low wings, light weight anddirect steering make ground handlingsimple even to a newcomer. And takeoffwas just as straightforward. It required alittle effort with the feet to keep thenose straight, and we were off the run-way and climbing after 3-4 seconds. Weset up for a cruise climb to 10,000 feet atabout 70 mph and headed for themountains south of the airport where wewould have a 2000-foot clearance toshut the engine down and look for lift.

Soaring and StallingWe had encountered bumps during theclimb and pulled the throttle back ataltitude to bring the engine tempera-tures down from the climb conditions.After less than a minute, we shut theengine down and stopped the prop. The60x52 fixed-pitch Sensenich prop, whichis so small it would not look out of placeon a giant scale RC model, did not seemto cause much drag. That saves theexpense of a feathering prop. After afew minutes, Tanner remembered: “Wecan take our headsets off.”

The thermals seemed quite smalland I (a bit out of practice) had troublecentering and getting full turns in lift.What was more interesting was that I didnot have to think about flying the air-plane. It felt so natural and comfortablethat after only flying it for 10 or 12 min-utes I was able to concentrate whollyon catching thermals.

We held our own for a while andthen did some stalls. A soft but distinctburble occurs as the wing starts to stall.With the wings level it seems to hang ina mush with the ailerons still effective.With a large bank angle, the nose final-ly dropped, but getting the stick off therear stop got us flying again.

Tanner did the stall and spin testingof the Xenos, and there is a link to hisreport on the Sonex web site. My impres-sion is that it would take an exceptionallydumb or determined pilot to get intostall/spin trouble with the Xenos.

I used to own an HP-18, a high-performance sailplane built from a kit.It was designed for the 15-meter racingclass. On one flight, I was thermaling at14,000 feet and the top wing let go. Iwas flying with a forward c.g. and wasable to recover normally; I re-enteredthe thermal and stalled it again. I wasnot on oxygen and therefore no doubtslower and dumber than usual, but therewas no warning of those stalls. I askedmyself, “Is it the airplane or is it you?”

As I burned off some altitude, Imade the decision to sell the HP-18to someone who would fly it moreoften and was a more skilled pilot. It isone thing to fall out of a thermal at14,000 feet, quite another to do thesame at 200 or 300 feet above a moun-tain while scratching for lift. In a purehigh-speed aircraft, you would onlyget near a stall in the landing flare.But in a glider, the slower and tighteryou can turn, the better you will climb.You’re often racked over at the edge ofa stall trying to ride a boiling, rollingand turbulent mass of hot air heading for a cloud base. The Xenosscores a big plus with me on its low-speed handling qualities.


To keep build times reasonable, Sonex incorporates a number of advancements into its kits includ-ing preformed parts and laser-cut starter holes.

The spoilers, shown here fully extended, areset at half extension for Xenos landings.

14 K I T P L A N E S A P R I L 2 0 0 5

Cruise and LandingTo take a look at cruise flight we head-ed north over the mountains north-bound to Lake Isabella at 10,500 feet.We were running 130 mph true atabout 6.5 gph. According to Tanner,it’s possible to knock about 1 gph offthe fuel burn by leaning. Company-provided specs for the Xenos show theaircraft as 20-30 mph slower comparedto the Sonex and Waiex, depending onengine and flight conditions.

I let the Xenos fly itself hands-offfor a while. The air was still quitebumpy, and I was impressed by its sta-bility. We felt the bumps, the airplanewent up and down with the air, but thenose stayed pointed where I wanted it.No wandering, wobbling or tail wag-ging. Like a slot car with wings.

On the way back to the field Itried some of what I call power assistedsoaring. I set the engine for level flightat about 70 mph, slow down and climbin lift and push the nose down and gofast through sink. It’s called dolphiningin sailplanes; when conditions arestrong, remarkably high cross-countryspeeds (125 mph plus) can be achievedwith no engine at all. I know it offendsthe soaring purists, but the Xenos canmimic pure sailplane performance byrunning its engine a bit above idle. It isalso a much less expensive and a moreversatile aircraft than a pure sailplane,if not as sexy.

As we approached the airport, Tan-ner instructed me to set up for a power-off landing on the power runway. (Mountain Valley Airport has two run-ways and patterns, one for power onthe south side and the other for gliderson the north.) This apparent contradic-tion confused me long enough to spot atow plane ahead of us. We were engineoff, ready to turn base with half spoilersout. But in the space of about 1.5 sec-onds, Tanner closed the spoilers, pushedthe start button and we were in a climb-ing turn to get more space between usand the tow plane. Try that in a pureglider or a self-launching sailplane thathas to unfold its propulsion system fromits back before the prop can turn.

Landing was another non-event.“Half spoiler and keep lined up andtouch down at about 55 mph,” Tanner

K I T P L A N E S A P R I L 2 0 0 5 15

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told me. That’s about 10 mph abovethe listed stall speed. I think it is a func-tion of the low deck angle of the Xenoson its landing gear. That low anglemakes visibility and handling on theground easier but does increase the min-imum takeoff and touchdown speeds.The takeoff performance is so good thatit is a non-issue, and if you really had toland at minimum speed you couldtouch tailwheel first. As it was, we didnot have to use brakes and as we rolledto the turn off, Tanner re-started theengine to taxi back to Buck’s hangar.

I did not want to leave that littleyellow bird.

The KitSimplicity of construction and efficientperformance—through lightweight,compact design—seem to have beengiven equal emphasis during thedevelopment of the Xenos. The use offlat-wrap skins is an example, evenextending to the Lexan windshield

portion of the canopy. This is typical ofthe company’s desire to make the buildprocess easier and less expensive.

The Xenos is available in kit formand comes with construction plans thatare regarded as among the best in theindustry. The kit costs $17,985. Or, youcan opt to build the Xenos from scratchby purchasing plans only ($600). If youchoose the 80-hp AeroVee engine kit($5695) from Sonex, it’s reasonable toaim for completing the aircraft for lessthan $30,000, depending on paint andinstrument choices. The 120-hp Jabiruengine will add approximately $10,000to the build cost.

A weekend builder’s workshop atSonex’s facility in Oshkosh is includedin the kit price to help get you started.I would recommend that anyone seri-ously interested in any of the Sonexaircraft attend the workshop.

The kit appears to be unusuallycomplete—most of the more difficultoperations are completed for thebuilder. The welded parts are completeand powder coated. The skins are lasercut, ribs, bulkheads and channels are

formed and pilot holes marked. Thebuilder has to trim, fit, drill and rivetand otherwise assemble the airframe.The factory claims less than 1000 hoursbuild time from the kit, an estimatebased on experience with Sonex kitbuilders. As ever, build time is highlyelastic and depends on the skill andorganization of the builder.

“We try to make our kits easy andeconomical to build for the first timebuilder,” Monnett said. “They are alsoeconomical to own and give good per-formance while being suitable for low-time pilots.”

Final ImpressionsI think John Monnett and companyhave nailed it with this aircraft design.Most sport pilots end up back at theirhome airport after a typical flight anddo the occasional long cross-country.For many of those pilots, giving upsome cruise speed for the flexibility,economy and added safety of an air-craft that can glide so far may be theright choice.

Is it a perfect airplane? No. All


K I T P L A N E S A P R I L 2 0 0 5 17

Want to know what a kit airplane looks like before it’s built? This is what to expect on your doorstep.

airplanes are compromises flying inclose formation. It is not an airplanefor two really large people, although itcan be built as a heck of a single placefor the XXXL pilot. It could be quieterunder power.

The only serious competition forthe Xenos is the Europa motorglider,which went off the market whenEuropa closed its doors a few monthsago. The Europa features a bigger cabinbut is more expensive to build (the kitalone costs $33,300) being a moldedcomposite kit based on four-strokeRotax engines and requiring a full-feathering prop to get its best per-formance. It remains to be seenwhether it reappears on the market.

If I could work out the details, Iwould be building a Xenos right now. Itis a near perfect aircraft for me. I couldbase it at an airport 20 minutes frommy house instead of driving an hourand a half to the glider port. No towplanes to wait or pay for. I could exploresoaring the Sierras with little fear of anout landing while visiting friends inLake Tahoe.

But why that bright yellow paintjob? It is a good color for staying visible,but I think that’s only part of it. I thinkthe Xenos could be the J-3 Cub of the21st century. Not the number flying,but in terms of cost and ease of con-struction for the homebuilder and good,honest handling qualities.

With good speed on modest-sizeengines for economy of operation,Sonex has produced the right plane forthe time. Most of the company’s cus-tomers will be seduced by the biggercruise speed numbers of the shorter-wing members of the tribe as they sharemany of the same good qualities of theXenos. But some may tire of boringholes in the sky and will want to try anaircraft where they can shut the engineoff in flight—intentionally.

For more information on the Xenos motor-glider, AeroVee engine or any other ofSonex’s products, visit www.sonex-ltd.comor call 920/231-8297.

W W W . K I T P L A N E S . C O M


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"Soaring with Sonex" Xenos Article (1.2mb )