Kolb Mark III experimental amateurbuilt light sport aircraft.

Experimental Aircraft News Magazine - The Kolb Aircraft Company Mark III Xtra side-by-side 2-seater. It literally offers extra in several ways pilots will like. The venerable Mark III has been through a series of changes since original company founder Homer Kolb first brought out a 2-seater called the TwinStar. The latest change does a lot to alter the appearance of the older design. 

Kolb designs have narrow noses like a lot of other designs. The new Xtra presents a clean edge cutting through the air, but it now has a wider look – at least from head-on – that imparts a new feel to the occupants. Some will say the “Xtra” comes from “Extra-Wide.” With its bulging doors, the new cabin is 45 inches wide (42.5 at the hips). Although the design will look bigger and heavier to some, the new shape is one you’ll come to like… if you have a seat. So, let’s do that.

Kolb Wide Body
If it works for Boeing and Airbus, why not The Kolb Aircraft Company? The Kentucky-based company opted for a wider fuselage, and the creature comfort benefits are instantly obvious.
When you sit in the Xtra, each occupant has a side to him- or herself. In the older Mark III version, both occupants had to angle their legs toward the center and then operate rudder pedals causing your ankles to angle back. You can get used to it, but I found it distracting. I tended not to operate the rudder pedals with equal force as I would if they were straight in front of me. The wide-bodied Xtra cured that problem.
For those wondering about the pointier-nosed Mark III, the company now calls this the “Classic,” and, yes, you can still order it. Some may still prefer the “nostalgic” look, but I think most will opt for the newer Xtra. Many will be built to support the 81-hp 4-stroke Rotax 912 as well.
Although TNKAC talks about a significant increase in speed, and although the 4-stroke engine attracts general aviation-trained pilots, the real story in my mind is the increased comfort, which adds enjoyment in flight.
The Xtra with Rotax 912 engine as flown for this report can be equipped with the optional 19-gallon fuel supply, giving the model almost a 400-mile range. With a pilot’s certificate tucked in your wallet, you can cover some ground in the Mark III Xtra.
The company is understandably proud of the changes made to the Mark III. And they feel the newer Xtra adds value in various ways. “You can still expect to get the most desired features: STOL performance, roomy cabin, superior visibility, sturdy construction, quick-folding wings and tail, superb handling, and the ability to carry large people and pay loads. What you get in addition is increased speed, more cabin room, and more visibility,” states the company.

The company hired well-known aerodynamicist Barnaby Wainfan to do the redesign work on the Mark III. Wainfan is known to the light-flight set for creating a cool-looking machine called the Facetmobile, which gets near the weight range of ultralight aircraft. And he has another project, building off his “Junk Yard Wars” TV effort against competitor Chuck Slusarczyk, that he says will qualify for the Part 103 ultralight rule. Though his expertise is employed for larger aircraft, Wainfan is also a fan of ultralight flight.

Wainfan’s shape-changing work for New Kolb included creating a new nose pod for the existing Mark III welded fuselage structure. By the time the new nose was developed, a few structural alterations made, and slick new paint was applied, the older airframe gained 75 pounds, says former New Kolb CEO Norm Labhart. However, this was the prototype while production Xtras have shed a majority of this extra weight.

While it has other benefits, Wainfan’s new nose shape adds hugely to visibility. In fact, it’s surprising just how much some extra width will help. On whole, the broader cabin that came with the new fiberglass nose created a helicopter-like viewing platform.

Homer Kolb’s more conventionally shaped nose fairing followed the common ultralight design pattern of providing a flange to form an instrument panel just above your legs. Yet in the Xtra, an instrument pod now seems to mushroom up out of the floor, also in the style of helicopter designs. Not only did this prove to be an efficient way to mount instruments closer to you, it also leaves lots of open space in the cockpit. I noted a similarity to RANS with their suspended instrument panels. However, I like this implementation even better. Instantly you feel less cramped and long-legged pilots will no longer be bumping their shins into the instrument panel’s lower edge.

Creative and functional as the new instrument pod is, it cramped interior space in one way, at least in this first iteration. As I used full stick deflection and shifted my leg to allow this movement, my leg bumped into the pod. For this reason, the company plans to move the panel about 6 inches forward. But a better idea may be to merely invert the pod, placing the wider section at the top in a move that should free up more legroom. Kit builders have this option and many may see how it fits.

With the new front end, doors now hinge forward, which proved to offer easier entry than the older gull wing doors that had to be held open during entry. Here’s a pilot-friendly idea facilitated by the new nose fairing. I congratulate Wainfan for bringing innovation to ultralight interiors and for New Kolb in reaching out to an independent designer for new ideas.

Back In The Saddle
As I’d done once before, I flew with Kolb representative Norm Labhart. He was Kolb’s CEO for a while but was glad to relinquish those duties and is now back in the satellite television business.

From that earlier Xtra, one notable change is that big “barn-door flaps” on the previous aircraft have given way to flaperons on the newer one. This brings a noticeable change in control operation that I’ll touch on later in this article. The new flaperon lever has a 2-notch position, but successive kits will remove the second notch because it limits control motions too much, says Labhart. The company is concerned about limiting control authority at slow speeds.
The Xtra’s elevator trim remains the same as older models using a multiple-detent configuration. This notched hardware provides about 10 trim positions rather than the more customary infinitely adjustable trim.

The control is only available to the occupant of the left seat, making the design a bit less student-friendly, though an instructing builder might be able to create a second lever.

As Labhart and I flew at somewhere around the FAA weight of 170 pounds per occupant (he’s a very light fellow), I trimmed the Xtra at one notch short of full-back and even that did not satisfactorily hold up the nose. Of course your personal Xtra could and should be adjusted to your flying weight (see “Propwash – Getting Ready for Sport Pilot Part VII: Weight and Balance,” this issue), and you can make the trim adjustments more to your personal needs as well.

A Mark III Classic I flew about 3 years ago had been fitted with dual joysticks that replaced the center joystick of the older version. This permitted a more natural grip for pilots in each seat. New Kolb supplies a Y-stick as standard but offers the dual joystick arrangement as I experienced in the test Xtra. Y-sticks are quite good for instructional use, but I much prefer the joystick at the front and center of my seat. It allows a valuable armrest and provides more leverage while permitting finer control movements.

The decked-out Mark III Classic also eliminated the center throttle arrangement of the early Mark III’s that forced the left-seat occupant to reach across his body with his outside left hand to make power adjustments. Most pilots will be able to make finer power adjustments with a more convenient throttle position.

In the Wainfan-redesigned original Xtra, this arrangement again changed. All the power controls were located along a center console that, when covered and padded, gave a restful location for your arm that permits precise changes in power, trim, and gives an easy location for choke application.
In the Xtra flown in 2003, that changed again to throttles located outside of each seat in a very accessible position. The choke lever went overhead above the parachute handle seen in the photos. A flap lever remains in the center, albeit adjacent to the seat backs.

In the Mark III Classic the instruments seem farther away. They may be easy enough to read but are less convenient for changes like altimeter settings or switch operation. Using the Xtra’s helicopter-like panel, these switches and instruments are placed comfortably close to both occupants. I liked it a lot better.

The best news of the wide nose pod and centralized instruments is that your legs and feet now have plenty of room for posture changes during longer flights, and you no longer have to adapt your leg and foot movements to the narrow nose of the older model. I found this allowed not only a more natural control of the aircraft, but transition from another ultralight should be swifter. It was also more comfortable and a relaxed pilot should be a better pilot.

Some things didn’t change much on the Mark III Xtra. The design is still a noisy aircraft. Labhart says this is because the cockpit is open at the rear. Even though the 912 has a throaty roar compared with the whine of any 2-stroke, the Xtra was quite loud and seemed much more so than ultralights with fully enclosed engine compartments. However, even unfaired 912-powered ultralights that I’ve flown seem quieter than the Xtra. Get a good headset or helmet and the problem is muted.
The Xtra’s door latch mechanism, while secure, is a little far back and therefore a little hard to reach. I also found the door opening to be rather narrow. Doors on the test Xtra were restrained by a small chain to prevent them from blowing open in stronger winds and possibly damaging parts. However, this made it slightly harder to enter the Xtra as the pointed trailing edge of the door is near the wing’s leading edge. Without the added chain, the Xtra doors can swing forward, but you’ll want to watch the wind.
Most pilots will like the new Xtra enclosure. The Mark III Classic’s tapered nose – with doors removed for more comfortable flying in warm times of the year – allows a considerable windblast to enter the cabin. This can be quite fatiguing. The Xtra’s wider nose will lessen this effect and the bulging doors allow enough room that you may never remove them.
Looking around the cockpit you’ll find a few other items of interest. The black knob just ahead of the pilot’s seat is the handle to a throttle friction lever. Throttles were installed on both sides on the outside edge of the seats. The flaperon lever is not a button detent, but rather a simple lever arrangement that the left-seat pilot pulls to his side and then moves up or down to the next notch. Located above the parachute activation handle is a choke.
Get The Air Moving
New Kolb was only able to find the small, 1.5-inch air vents so we had to taxi with the doors held ajar in the warm April heat of Florida.
While taxiing, you can slow or stop the Xtra through its powerful, optional, hydraulic brakes.
As with most lightweight aircraft powered by a Rotax 912 engine, takeoff was swift; the sensation of power dominates the takeoff roll. Kolb designs have always been fast to leave the ground. Bolt on a 912 and tighten your seat belts because it’ll feel as if you’re blasting off on a Mars mission.
Coming around in the pattern, I made approaches at 55 to 60 mph based on Labhart’s recommendations. Later efforts worked well at 50 mph and experienced Xtra flyers like Labhart say they can get down to 45 mph on approach. At those speeds, landings will be quite short.
“The Mark III Xtra is designed primarily as a STOL-class aircraft – it has generous wing area, big flaperons, and powerful engine options, so that short takeoffs and landings are possible from short fields,” says New Kolb.
Using those flaperons will help but not as dramatically as the big barn-door flaps of older models. Since the plane can fly slowly, this isn’t the negative it might otherwise be.
Kolb designs have long impressed me and many other pilots with their very fluid controls. Not only are the movements light and easy, but the response has been quick yet secure. Such characteristics have defined the Kolb fleet for years.
The Xtra changes the game a bit and this change may please those pilots with experience in general aviation aircraft or larger homebuilt designs. Gone is the superlight touch that comes with the prior Mark III’s. Instead the controls are now a little heavier but this exchanges for less total control movement that makes it easy to fly while resting your joystick arm on your leg.
The change comes with some control linkage adaptations that reduce the chance of hitting your leg as you fully deflect the joystick. In the older Mark III, the center-mounted joystick stood up from the middle of the aircraft and although it had a delightfully light feel, you
also had to move the stick more to achieve the desired result.
A change was necessary as the dual joysticks don’t have the stick range as the old single lever. Had the company not redesigned the linkage, you might run out of stick range if you tried to achieve maximum lateral control; your legs might prevent the stick from moving as far as you like. Not only does the update keep the stick in a better ergonomic position, pilots of larger aircraft may find movements closer to that which they have previously flown. Pilots of general aviation aircraft or heavier homebuilts should find a quicker transition of skills to the ultralight-like realm occupied by the Xtra.
Production Xtra ailerons were on the stiff side. Adding spades to the ailerons didn’t help much, Labhart said. Technicians had mounted the spades to the mass balances near the wingtips, causing Labhart to speculate that the airflow at this location might be turbulent, making the control enhancement surface less effective. Structural reasons prevented their installation at mid-span as is more common. The good news is that lots of pilots prefer more feedback in handling.
Those true-blue ultralight enthusiasts who yearn for the light touch controls, slower speed flight, and exceptional agility long associated with Kolb aircraft still have choices from The New Kolb Aircraft Company. The Kentucky-based outfit continues to manufacture the FireStar II jump seat 2-place model. And for the genuine Part 103 adherent, the superlight FireFly remains one of America’s fine ultralight choices. Nearly 100 FireFly kits have taken to the air since it was introduced, while nearly 600 FireStar models are in operation.

Kolb Mark III Experimental Amateurbuilt Aircraft Video

Xtra Performance
Wainfan’s Mark III redesign effort brought another popular benefit – in a word, speed. According to Labhart, the Xtra picks up 10 mph in cruise, perhaps even more, though the company limits its claim to 10 extra miles per hour. This alone will be enough to encourage many buyers.

As the years have passed for the Mark III, the plane has departed from a standard 50-hp 2-stroke Rotax 503 that was once sufficient to propel the plane through the air with two people aboard. Now New Kolb lists the 65-hp 2-stroke Rotax 582 as standard and the 81-hp 4-stroke Rotax 912 as an option that they expect to become commonplace.
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Adding this kind of power certainly should shove the Xtra through air more quickly, what with power leaping from 50 horses (dual carb Rotax 503 engine) to 81 hp. Kolb gained experience with this sort of power on their tiny 22-foot wingspan SlingShot model, which was first fitted with the Rotax 912.
With the 503 Mark III, Kolb listed cruise speed at 65 mph, a figure that increased to 77 mph if you installed the 65-hp Rotax 582. Powered by the 912 and its 81 horses, New Kolb says you can cruise at 90 mph, for a total gain of 25 mph (or 40%). No wonder the flight sensation is different.

My experience with the 912 Xtra corroborated the claims of 90 mph high cruise and 75 mph easy cruise. Having flown the 2-seat Kolb over several of its design iterations, I can verify that it has become a faster, more comfortable plane that remains essentially true to its fast takeoff ultralight roots.
One note for those who examine photos carefully. I’ve been saying all through this article that the Xtra had an 81-horse Rotax 912 engine, yet the valve covers are green, the same color Rotax uses for their 100-hp 912 SUL model. Kolb repainted the valve covers merely to match the paint job on the aircraft.

Xtra Personal
The Xtra will cost you $11,058 (as of January ’04) for the two airframe kits needed to complete it, before optional extras, covering fabric, and your choice of paint and other finish items.
If you elect the older model, you can save more than $1,300 as the Mark III Classic is priced at only $9,690. But add the 81-horse Rotax 912 engine for around $11,600 (price subject to exchange rate fluctuations) plus fabric covering kit, paint and instruments, and you’ll invest around $25,000 to $27,000 in your Xtra. Of course, you’ll need to spend about 500 hours of your own time assembling it.
The same Xtra airframe with standard 65-hp Rotax 582 and mounting kit costs about $17,000 (before covering, paint, and interior), a significant savings with plenty of reserve power. Even if you bid the price higher with options, you can still get a lot of aircraft for about $20,000 that is below the average price of a new car today. Let’s see, in which one are you likely to have more fun?
Over the years, Kolb has sold well over 300 Mark III designs. The 2-seater is second only to the FireStar line. Between all models, Kolb is closing in on 1,000 aircraft flying, a fine achievement of which all employees and builders can be proud.
When you can put it together as well as The New Kolb Aircraft Company and designer Barnaby Wainfan did, a winner should result. You may love all the extras on the Xtra as I did.

Seating 2, side-by-side
Empty weight 490 pounds
Gross weight 1,000 pounds
Wingspan 30 feet
Wing area 160 square feet
Wing loading 6.25 pounds/square foot
Length 24 feet
Height 6 feet 4 inches
Kit type Construction kit
Build time 450-550 hours

Standard engine Rotax 912
Power 81 hp
Power loading 12.5 pounds per hp
Cruise speed 75 mph
Never exceed speed 100 mph
Rate of climb at gross 1,100 fpm
Takeoff distance at gross 175 feet
Landing distance at gross 250 feet

Standard Features Rotax 582 (tested with Rotax 912), mostly enclosed cabin with wide seating area, instrument pod, folding wings, shared Y-stick, in-flight trim and remote choke (as tested), steerable tailwheel.

Options Hydraulic brakes, engines up to 81-hp Rotax 912, dual controls, covering kit, upholstery package, starter kit, quick-build kit, ballistic parachute.
Construction Welded 4130 chromoly steel fuselage, aluminum wings and boom, fiberglass fairing, steel landing gear, dope-and-fabric wing coverings. Made in the USA by American-owned company.

Design
Cosmetic appearance, structural integrity, achievement of design goals, effectiveness of aerodynamics, ergonomics.
Pros – Wholly new design made from the familiar Mark III 2-seater originally designed by ultralight legend Homer Kolb. Widened nose pod makes for a more comfortable aircraft but performance was also enhanced. Distinctive aircraft that will be recognized by most light-sport pilots. Quick-folding wings and tail have long been Kolb strong points.
Cons – Character has changed with the wider nose and flaperons replacing discreet flaps; aircraft flies faster. With Rotax 912 engine, price rises beyond $25,000. Builders have often said Kolb designs are quite labor-intensive.
Systems
Subsystems available to pilot such as: Flaps; Fuel sources; Electric start; In-air restart; Brakes; Engine controls; Navigations; Radio; (items covered may be optional).
Pros – Dual throttles are a great replacement to the center throttle; no more reaching across. Trim is easily used (by left-seat occupant only) and secure as to position with detents. Choke is handy just to the right of the pilot’s head; can be reached by either occupant. Powerful hydraulic brakes installed in test Xtra.
Cons – Trim cannot be reached by the right-seat occupant. No easy way to determine fuel in flight (unless gauges installed by builder). Hydraulic toe brakes are optional (though they are differential and use nice hardware). Flaperon handle is rather far aft and is somewhat awkward to reach.
Cockpit/Cabin
Instrumentation; Ergonomics of controls; Creature comforts; (items covered may be optional).
Pros – Major improvement to cockpit with the wider nose; your legs no longer have to angle to the center. Much more open inside with enormous visibility. Seats are well padded, not just Kolb’s once common sling-type seat. Four-point seat belts were installed in tested Xtra. Full enclosure effectively blocked windblast.
Cons – Fuel tanks have to be filled inside the aircraft; fumes result (though the aft of the cabin is open and fumes are pulled out when the engine starts). Doors restrained by chains, as on test Xtra, don’t open far enough for the easiest entry. Open aft cabin makes for a noisier environment.
Ground Handling
Taxi visibility; Steering; Turn radius; Shock absorption; Stance/Stability; Braking.
Pros – Though the Xtra sits low, it still has good ground clearance, and prop is protected by main tail boom. Wide-open visibility is a real plus before takeoff. Full-swiveling tailwheel makes for tight turning capability. Directional hydraulic brakes assured good ramp maneuverability and offered substantial stopping power.
Cons – All Kolbs tend to have a noisy cable “slap” as they are routed inside the tail boom; no problems reported but sound can be distracting if you hear it over your ear protection. Suspension is limited to gear leg flex. If gear leg is damaged, labor is significant for replacement according to factory workers.
Takeoff/Landing
Qualities; Efficiency; Ease; Comparative values.
Pros – Great launch enthusiasm comes with the 81-hp Rotax 912 engine. Ground break is well under 200 feet. Visibility out of the helicopter-like cockpit is huge; very helpful for landing at crowded airports. Excellent crosswind control capability.
Cons – Heavier airplane (with 912) makes for slightly longer landing roll (though still only about 250 feet). At its weight with the big engine, landing with a little power seems to help a lot. Design tends to lose energy quickly in ground effect; be ready for the round-out phase.
Control
Quality and quantity for: Coordination; Authority; Pressures; Response; and Coupling.
Pros – Handling has always been a strong point of Kolb designs; still great in crosswinds or rowdy air. Control harmony is quite good (though see negative). The Xtra was easy to control in formation with photo plane. Adverse yaw is less than many designs. The Xtra’s somewhat heavier flaperons may give some pilots the feedback they want.
Cons – Flaperons are on the stiff side (even according to New Kolb’s owner). This also suggests control harmony cannot be as good as the older models. While the deck angle is very shallow, the Xtra is still a taildragger and some pilots don’t feel ready for such gear.
Performance
Climb; Glide; Sink; Cruise/stall/max speeds; Endurance; Range; Maneuverability.
Pros – The 81-hp Rotax 912 assures excellent performance even at full gross (tested well below). Cruises easily at 75 mph and can hold 90 mph, quite a bit faster than older Mark IIIs. Climb is more than 1,000 fpm. Performance with 65-hp Rotax 582 is also quite strong. Good payload; can nearly carry its empty weight in occupants.
Cons – Not everyone is seeking higher speed (though those buyers can select the Rotax 582 while saving around $6,000). The Xtra with the big 4-stroke, 4-cylinder engine becomes a heavier plane that loses some of the agility long associated with more minimalist Kolb designs.
Stability
Stall recovery and characteristics; Dampening; Spiral stability; Adverse yaw qualities.
Pros – Secure seat restraint was appreciated, as was the BRS parachute system installed in the wing cavity with pull handle in aft of cabin. Stalls were reasonably slow, at around 40 mph. Stall responses were normal and uneventful. Controls remain effective right down to stall break; allows slower speed approaches.
Cons – Power-on stalls put the Xtra at a very high deck angle; it will surprise most new Mark III pilots. A parachute handle you have to turn to reach might not be optimal in a violent upset situation. With the higher thrust line, added power will push the nose over slightly (though backing off slightly stops this).
Overall
Addresses the questions: “Will a buyer get what he/she expects to buy, and did the designer/builder achieve the chosen goal?”
Pros – Proven design with years of history in the ultralight arena and many aircraft flying successfully. Redesign by Barnaby Wainfan comes with many extras (as its name implies). Company offers quick-build options for those who want to get in the air faster. Once-new ownership is now well established and has continued the solid reputation of Homer Kolb’s original company.

Cons – Most Kolb designs are considered rather build-intensive; company estimates 500+ hours to complete the Xtra (though optional quick-build kit can lower this substantially). Priced with 81-hp Rotax 912 engine, the Xtra will run more than $25,000 before owner customization or more options. Taildraggers aren’t for everyone, which may affect resale.

by Dan Johnson

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