Zenith transforms its angular and chunky STOL bruiser into a ‘cruzer’ that retains much of the short-field capability of the original
Words: Dave Unwin; Photos: Jim Lawrence
Thump! With a resounding whack I deal the ground a mighty blow. Mortified, I turn to test pilot Roger Dubbert and mumble an apology. “Don’t worry about it, Dave,” he laughs. “Zeniths are well designed, I doubt anything fell off!”
Before flying the CH750 Cruzer at Florida’s 2015 Sebring LSA expo, I had the opportunity to discuss the thinking behind it with Zenith Aircraft Company president Sebastien Heintz. Seb explained it had become apparent to the company that although few Zenith STOL owners were using the aircraft’s full capabilities – it’s an amazing machine, able to get airborne in around thirty metres – many prospective 750 purchasers had indicated that what they really wanted was a faster cruise speed.
This led the company to develop the Cruzer. Although similar to the STOL in many ways, it has been optimised to be an economical touring aircraft with a large comfortable cockpit and plenty of baggage capacity, with the emphasis on operations from paved runways.
Quickly and easily
As with the rest of Zenith’s all-metal kits, the Cruzer has been designed to be built quickly and easily. The accurately-made skinning and frames are of the ‘matched hole’ type, produced using ultra-modern CNC machines and the company claims a typical build takes less than 400 hours.
Constructed mostly from 6061-T6 aluminium sheets (composites are only used for the wingtips, cowling, fairings and wheel spats) the customer assembled parts of the semi-monocoque airframe are fastened together using Zenair blind rivets. These are similar to Avex brand ‘pop rivets’, but Zenith sources and tests its own.
The wing spars and lower cabin frame are supplied completely factory riveted with conventional ‘AD’ solid rivets. The wings, tailplane, elevators, fin and rudder use stamped aluminium ribs covered with anodised sheets of 6061-T6. Chrome-moly steel components, such as the control system, nose leg and top cabin frame are welded at the factory and supplied ready for assembly.
Although the CH750 Cruzer does look similar to its STOL sibling from a distance, as soon as you draw closer the differences quickly become apparent.
Probably the most obvious change is to the strut-braced wing, for the STOL’s full-span fixed leading-edge slats are not fitted to the Cruzer, which also uses a different aerofoil. Of course, once Zenith decided the Cruzer didn’t need the STOL’s incredible slow-speed performance and impressive ‘off-piste’ capabilities, other changes soon followed. These included replacing the STOL’s large, unspatted tundra tyres with 5.00 x 5 wheels covered with close-fitting spats, and a significant redesign of the tail unit.
Whereas the STOL features the characteristically Zenith arrangement of a small dorsal fin and swept back all-flying rudder, the Cruzer has a traditional fixed fin and separate rudder. The tailplane is also different: the STOL uses an inverted aerofoil, as it can fly at high alpha and requires more downforce on the tail, while the Cruzer has a smaller, symmetrical-section tailplane.
Firewall-forward
Cleverly, the Cruzer uses the same ‘firewall-forward’ arrangement as the CH650 and STOL, thus the prospective builder has a wide range of engine options, including Continental, Jabiru, Lycoming, Rotax and UL Power aero-engines and auto conversions such as Corvair and Viking.
I tested two different Cruzers and, unsurprisingly, the different cooling requirements of an air-cooled engine as opposed to a liquid-cooled mean the cowlings are different. The composite cowling covering the ULPower engine features big, bulged ‘cheeks’ for adequate airflow over the cylinders, but although it provides adequate access to the engine bay (it splits horizontally) it would be better if Camlock or Dzus fasteners were used for the top half, instead of screws. The oil dipstick can be reached through a small hatch in the top of the cowling.
N750ZW was powered by a ULPower 350iS air-cooled flat four that produces 130hp at 3,3000rpm, turning a two-blade, ground-adjustable Sensenich propeller. The nosewheel uses a bungee for shock absorption and steers through the rudder pedals, while the mainwheels are carried by a single-piece, cantilever aluminium leaf-spring bolted directly to the underside of the boxy fuselage.
The strut-braced wing carries the fuel (114 litres total) in a pair of welded aluminium fuel tanks, located in the leading edge near the wing roots. The wing has no wash-out, instead the full-span flaperons are made in two parts joined with splice plates, the outer sections being set at a lower angle of incidence than the inners. There is a sizeable slot between the trailing edge of the wing and the leading edge of these surfaces, which allows them to function like Fowler flaps when they are lowered.
The flap setting is infinitely variable between zero and fifteen degrees, actuated electrically. Cables are used for the elevator and rudder, with pushrods and torque tubes for the flaperons. Pitch trim is provided by an electrically driven tab that covers the entire trailing edge of the port elevator.
Cockpit access is excellent, with large gull-wing doors that open wide over low sills, while Zenith’s signature Y-shaped centre-stick helps. The doors are supported by powerful gas struts, although as the Cruzer is approved for flight with the doors off they can be removed readily and stowed in the baggage bay.
The cabin is abnormally wide ? it’s about the same size as a Cessna 182’s, although the extensive glazing makes it seem even bigger. Bulged doors are an option. The rudder pedals are not adjustable but the rail-mounted seats move over a good range.
Using the Y-shaped control column (a traditional dual-stick arrangement is an option) means each pilot has their own plunger-type throttle. PICs also has the trim and flap switches next to it. It seemed to me the panel was wider and deeper than the STOL’s and Roger explained this is because that model’s panel is deliberately narrow to enhance the forward view in a nosehigh (slow flight) attitude.
Any way you want
Roger bore my usual complaints about the three-point harness and the flap switch not being flap-shaped with an “I knew you’d say that” although the classic combination of a key-operated rotary switch for the mags and starter, and the master consisting of split rockers for ALT/ BAT won my approval, as did the use of colour to delineate the switches.
I liked the way all the switches and circuit-breakers are built into a neat RSP1 unit. And of course, as it’s a kit aircraft, you’re free to arrange the panel and engine controls any way you want, within reason.
Of the built-in features, I liked the air vents and that simplest but most useful of things ? a large glovebox, directly in front of the P2. However, I was completely taken by surprise by the electric toggle switch fuel tank selector, particularly as the STOL had a simple on/off fuel valve, with the tanks in that model feeding simultaneously. The Cruzer’s selector seemed unnecessarily complex to me, but Roger explained the fuel-injected UL350iS uses electric high-pressure pumps that return fuel to the tank in use, requiring a selector.
The cockpit heater controls, mags/ starter switch, headset sockets and twelve-volt power outlet are in a stack extendsing down from the centre of the instrument panel and connecting with a centre console, while behind the seats is a big baggage bay which can hold up to 22kg.
As the seats, fuel tanks and baggage bay are all closely concentrated around the C of G, weight and balance issues are unlikely to be a problem. The instrumentation is completely digital and consists of a single, ten-inch Dynon Skyview MFD (multi-function display) that incorporates a transponder. The other avionics are a Garmin GMA350 audio panel and SL40 transceiver. Flap and trim positions are shown on the SkyView.
Just turn the key and it starts
With Roger in the right-hand seat, I start the engine and taxi out. Although it uses the classic GA aero-engine arrangement of being a direct-drive, air-cooled flat-four, the ULPower 350iS is one of the newest engines on the market and features FADEC, multi-point fuel injection and an electronic ignition system.
It is considerably lighter than ‘legacy’ engines of similar horsepower, while being thirty per cent more powerful than the contemporary Rotax 912S. It being a modern motor, starting is simple. Forget all that nonsense about primers, mixtures or chokes – just turn the key and it starts.
The Cruzer is a delight to handle on the ground. The combination of a tricycle undercarriage, precise nosewheel steering, powerful toe-operated hydraulic disc brakes and a fine field of view make it an extremely easy aircraft to taxi.
With Roger and I, plus full tanks, we’re still some way below the 600kg MAUW, while the OAT of +20°C is giving a density altitude of barely 100 feet.
Although not as impressive as the STOL’s take-off performance, which is truly remarkable, the Cruzer still uses less than ten per cent of Runway 01’s 1,595 metres, while the initial climb rate is well over 1,400fpm.
As always around show time, the Sebring sky is buzzing with visiting aircraft and I was grateful that ? for a high-wing design ? the field of view is exceptional. Due to the proximity of the wingroots to the windscreen, many high-wing designs are cursed with a blind spot in the turn, but the CH750 has a sort of ‘gull-wing’ feature at the wingroots, as well as a good-sized windscreen.
Unexpectedly agile
As soon as we find a quiet bit of sky, I begin an examination of the handling. Just as I found with the STOL, the Cruzer’s boxy appearance is misleading.
It’s unexpectedly agile, with a respectable roll rate and good control authority around all three axes. Breakout forces are agreeably low and control harmony ideal as the flaperons are just a little lighter than the elevator. Slow flight is straightforward, and although it doesn’t have the truly remarkable performance of the STOL in this regime, the Cruzer is still very benign.
I honestly don’t know how slow we get with the flaperons lowered to 15° (the Dynon’s speed tape had, I think, quit in disgust) but it’s somewhere south of 35kt. There is no artificial stall warning device and as the stall is approached the buffet is quite subtle, but the steep deck angle is hard to ignore. Even rather brutal, full-power departure stalls are benign, while when stalled in a turn the aircraft always rolls wings level.
In fact, the stick-free checks confirm the Cruzer is a stable machine, being strongly positive longitudinally and directionally, and neutral laterally. Moving on to the cruise performance reveals that, as I’d expected, deleting the fixed slats has greatly improved things. A practical cruise speed in the STOL is around 70-75kt, but in the Cruzer you can either cruise some 15kt faster or use the same speed as the STOL but burn around twenty per cent less fuel (everything else being equal).
The engine certainly sounds happy at around 2,500rpm – although maximum power is produced at 3,300rpm this is a bit fast for good propeller efficiency, due to high tip speeds – while peak torque is produced at 2,400rpm. Anyway, at 2,500rpm and 8,000ft the TAS is just over 100kt, for a fuel burn of less than 20 lph. Maximum range (including VFR reserve) is over 400 nautical miles.
Back in the circuit I note that, in common with too many LSAs, at only 65kt Vfe is lower than I like, but on the other hand it’s easy to just leave the flaps up when mixing with faster traffic. On final, 55 is a good speed, with a Vref (aka ‘over the hedge speed’) of fifty. You can come in slower, but need to be aware that, just like its STOL sibling, the Cruzer does bleed energy rapidly in the flare, particularly if you’re not carrying any power.
Safe stick
How do I know? While at Sebring, I was lucky enough to fly the famous OneWeekWonder. N140WW is a 750 Cruzer built during the course of the 2014 AirVenture at Oshkosh, and is owned by the EAA. As it only has one set of brakes, Roger had to seek specific approval from the EAA for me to fly it from the left seat, but as he and I have flown together several times he managed to convince them I was a ‘safe stick’.
N140WW is powered by a 100hp Rotax 912iS Sport and features a pair of the new, touchscreen Dynon Skyviews, which incorporate a neat AoA indicator. The switches for the electrical services were different, and I found the flap and trim switches were more logically arranged (‘whiskey whiskey’ has the rocker switch for pitch trim above the left seated command pilot’s throttle, with the flaps to the right, while ‘zulu whiskey’ has the flap switch above the throttle and the trim on the right).
Whiskey whiskey has a more conventional mechanical fuel valve, although this has its own foibles as it has two on and two off positions. Although the Rotax’s 100 horses can’t compete in the climb against the ULPower’s 130, there’s little in it in the cruise. It really does fly very nicely. In fact, it’s beautifully rigged, which speaks volumes for the accuracy of the ‘matched hole’ kit, bearing in mind hundreds of pairs of hands helped build from scratch in a week.
Anyway, after a pleasant evening flight through Florida’s tranquil skies, I turn final at Sebring, intent on showing Roger his faith in talking the EAA into letting me fly their unique machine was well placed. But guess what – despite the fact we are slap into wind on a runway long enough to take a B737, on my first landing I run out of airspeed, altitude and ideas all too early, and absolutely plant the aircraft!
Honestly, it speaks volumes for the build quality nothing fell off, and I wouldn’t have been surprised if the airport authority hadn’t billed me for a huge dent in the runway.
I suppose it was a good test of the CH750 Cruzer’s ability to cope with ‘real world’ landings, but it really was a shocker. Roger laughed like a drain.
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