Speed Freak

As we roll to a stop after my landing, the guy in the right seat has a question. “OK, so do you want me to show you how to get a really short take-off?” That guy is Jean-Marie Guisset, managing director of JMB Aircraft. “Wasn’t it short enough for you?” I ask back. “Well…” Jean-Marie grins and suggests changing places.

OK, so with him in the left seat and me in the right, we roll back to the start of Runway 33 in Choceň. Jean-Marie sets the flaps to position 2 (37°), holds the Beringer brakes, which are only mounted on the left side of our machine, opens the throttle and lets the engine reach 5,750rpm, then releases the brakes. It’s a real kick in the back and we’re airborne a few seconds later. Was that 200 metres? A quick circuit, and when landing, the VL-3 ends roughly at the same place where it took off, Jean-Marie keenly using those brakes again. 

• Update December 2023: BMAA partners with JMB to bring rocketship to UK

The Cirrus that we’ve flown to the Czech Republic to visit JMB Aircraft’s home base, feels smoother at the start. Sure, with a normal take-off, we don’t hold the aeroplane against the brakes until the engine has reached its maximum power, but a look at the numbers reveals that both aircraft are equally dynamic regardless of their class: The SR22-G3 Turbo has a weight-to-power ratio of 4.9kg per horsepower at max weight, while the VL-3 Evolution with its Rotax 915 iS manages 4.3kg per horsepower. 1,548kg and 315hp versus 600kg  and 141hp. 

I’d first seen this Rotax engine, with its characteristic blue rocker and manifold covers when visiting the same factory in mid-February 2020. The project to fit the Rotax 915 iS to the VL-3 had not long begun and the aircraft still looked very unfinished. My question of when we could fly was met with a typical manufacturer’s answer – ‘as soon as it’s ready’. And now, at the end of June, I find myself looking at the second prototype, parked outside the hangar. “It’s not completely fine-tuned yet,” admits the JMB boss.

It is quite a sight though. On our photo flight above the clouds, I feel like putting the camera away and simply just looking at it. The composite form, painted in a racer-like colours, flies in wide circles, as if circling with the pace-plane, Reno Air Race-style, in readiness to go racing. Mustang! Lancair! Glasair! With its new radiator under the wing, the VL-3 looks like a combination of those types.

As many aircraft manufacturers have found, it was not a trivial task to fit the newest Rotax aircraft engine in the VL-3. Like the most powerful VL-3 engine to date, the 115hp Rotax 914, the 915 iS is turbocharged, but the 915’s turbo also has an intercooler. This increases both the space requirement and the weight in front of the firewall. The nose of the VL-3TE-915 is eight centimetres longer than that of the other versions.

“All in all, the new engine weighs around 30kg more,” says Petr Kábrt, who designed the VL-3 with his brother Miroslav and oversees their latest development. The additional weight would be even greater if they had not been satisfied with a simple version of the belly scoop holding the cooler, through which the coolant for the cylinder heads is pumped. An adjustable solution would have been preferred by Jean-Marie Guisset, just like the P-51 Mustang, but it would have weighed more. As it is, a large part of the undercarriage hydraulics had to be relocated from the engine compartment to behind the cabin. The aircraft we’re flying today weighs around 380kg when empty. This is too much for Jean-Marie. “We definitely want to be under 370kg in the production aircraft.”

With the increase in performance, JMB completely reevaluated and retested the aircraft’s structure. The airframe has been tested and found flutter-free to 242kt, Vne was increased from 170 to 184kt. Max speed in turbulent air is up from 135 to 150kt, while the manoeuvring speed remains 102kt. The VL-3’s Galaxy ballistic parachute rescue system has a maximum deployment speed of 180kt at 600kg – just below Vne.

On my first flight with this new VL-3, before Jean-Marie’s short take-off demonstration, the runway was not so important to me. Flaps to position 1 (15°), feet off the brakes and accelerate, but not abruptly. My right foot is ready to respond if the aircraft decides to turn strongly to the left, but it doesn’t. I later learn that a little offset to the thrust line of the engine has been added to help compensate for any swing.

In the vicinity of Choceň we remain low, underneath the military airspace until we get further east when we climb, full throttle at 5,500rpm and 80kt at over 1,500fpm.

All about performance

Every difference on this new VL-3 with the Rotax 915 iS, compared to the earlier 100 and 115hp models, boils down to performance. So what does the new engine deliver? Obviously, True Air Speed ​​increases with altitude, and this is where the intercooled turbo shows its prowess, with its ability to develop full take-off power up to 15,000ft. This aircraft is fitted with oxygen so you can take advantage of flight above 10,000ft should you so desire. In the Czech Republic, microlights are rarely approved for heights above 10,000ft, so on our flight we make do with 9,500ft. The constant speed Woodcomp composite propeller stays at 5,500rpm as I push the throttle fully forward. As we accelerate, I try to keep the nervous needle of the VSI at zero. The ASI comes to rest – 185ktas – wow! OK, the SEA Risen (tested in FLYER April 2017) might be faster with 26hp less, but is a far different overall concept with its very small airframe. But as a microlight that was designed primarily for fast travel and never intended to set speed records, the VL-3TE-915 enters into a performance range where few microlights have been before.

Pulling the throttle back gradually, applying 90 per cent power and the speed of the constant-speed prop falls from 5,500 to 5,000 rpm and the speed to 150ktas. In Germany, Jean-Marie says that with ATC clearance he climbs 2,500ft higher to 12,000ft when he’s making the trip back and forth between the factory and his Belgian hometown of Amougies. He has made the trip three times in this particular aircraft and can cover the 485nm in two hours and 50 minutes. In a hurry, 90 per cent power, 5,400rpm, at 12,000ft givres a True Air Speed of190kt and a fuel burn of 35 litres per hour. A more economical cruise at the same altitude, is 50 per cent power, 150kt and 18 litres per hour. Theoretically, with this power setting you can travel 1,084nm with a 30 minute reserve from full tanks. In practice, a typical pilot’s flight will be shorter, as not many of us are comfortable spending over seven hours in the cockpit in one go…

Landing configuration

It takes a while for us to be slow enough to approach the stall in landing configuration. Undercarriage at 80kt, we slow more and gradually add flaps. At 49kt a warning tone sounds. It was not programmed but comes from the angle of attack indicator. “If you want to fly stalls, you have to do it with my test pilot,” says Jean-Marie. At 43kt, the aircraft begins to buffet. I release the back pressure, the stall speed is sufficient for the approval of 600kg ULs in Germany, where 45kt must be demonstrated. With the flaps retracted, we are warned acoustically at 58kt, the stall stops at 55kt. That is still too high for Jean-Marie – he says the angle of the pitot tube is not yet perfected, the aim is 50kt. To improve the stall behaviour with the bigger engine with power on, the 915-powered VL-3 has been fitted with boundary layer wing fences. I’m told the VL-3 with the 115hp Rotax 914, has power-on stall behaviour without boundary layer fences that is routine.

Handling, operation, the view (excellent by the way) and cabin comfort is unchanged from the smaller-engined VL-3 models. Unfortunately, our prototype does not have the optionally available electrically operated landing flaps, but mechanical ones. The muscle power that you need to extend them is high, especially as you near the lever position needed for full flaps. I find this a bit of the distraction to the light touch that’s otherwise needed with power during take-off and landing. The pitch trim is effective, and even at maximum power in level flight the aircraft can be trimmed hands-off. However the substantial angle at which the tab deflects alarms me. Not just because it increases drag, but also because of the the considerable mechanical load it imposes on the trim tab and the control surface at high cruise speeds. When I raise it with designer Petr Kábrt, he defends the solution and says he is less keen to use the alternative of having a spring trim, that is used in the control system on some other microlight types. JMB is currently testing electrical actuation of the trim tab.

Warning horn

Landing holds no particular challenges for the pilot. At Jean-Marie’s suggestion I turn downwind at just under 80kt and extend the undercarriage, fly crosswind at 70kt and extend 15° of flap, turning onto final at 65kt, and extending 37° then 55° of flap. You should plan to cross the threshold at 54kt. If somehow you set the flaps with the undercarriage retracted, a warning horn sounds to remind you to lower the gear.

As I mentioned at the start, just how steeply the VL-3 can be flown on the approach is shown to me by Jean-Marie in his short take-off and landing demonstration. When the huge slotted flaps are fully extended and the aircraft is throttled right back to idle, at 67kt the aircraft will descend comfortably at nearly 1,500fpm.

Next project to follow the Rotax 915 iS is to fit the VL-3 with the fuel-injected 100hp 912 iS, which is in response to customer demand. Interestingly, hardly anyone opts for the fixed undercarriage version that JMB offers. At the moment however, the most powerful Rotax excites the most new customers. Over half of new orders for the VL-3 are to include the 915, says Jean-Marie. At over €200,000, for over 180kt, is it worth it? What a question! Would you ask the same about a Mustang…?