BRISTELL

Climbing back up into a flawless Florida sky from another effortless touch-and-go, I felt slightly uneasy. The speed, rate of climb, temperatures and pressures and so on were all good − yet the nagging sense of disquiet continued. There had to be something about the Bristell that wasn’t spot-on: I just wished I could find it!

 

The first time I flew a Light Sport Aircraft (LSA) was way back in 2005, when the FAA’s idea of Sport Pilot Certificates and LSA was beginning to gather momentum. It soon became apparent that for many private pilots, the LSA was the future. By using new design techniques, allied with CNC manufacturing machinery, modern materials and innovative ideas, these new aircraft were superior in just about every respect to the traditional GA two-seater. Since then, I’ve flown a considerable number of LSAs, and they just keep getting better.

 

I was intrigued as soon as I spotted a BRISTELL at Sebring. From a distance, it looks a bit like the SportCruiser − which is not surprising, because Milan Bristela also designed that, along with the high-wing Parrot (see Pilot, May 2011) and Mermaid amphibian. In fact, Milan was on the BRISTELL stand at the show, which gave me the ideal opportunity to quiz him about the aircraft as I inspected it.

 

Well-thought-out design

Close study revealed that a great deal of thought had gone into the design. For example, the BRISTELL has wing-root lockers (an idea I’ve always thought highly of) but on the BRISTELL they’re waterproof. Furthermore, each aircraft comes complete with a comprehensive emergency kit − including an electric compressor − in one of the lockers. Other neat ideas are that the voltage regulator is mounted upside - down to prevent water ingressing and causing corrosion, and the coolant reservoir has a blow-off valve.

 

The only tool required to change the oil is a screwdriver to remove the top cowl. Access to the filter is outstanding, and the oil tank has an integral drain valve.

 

A particularly interesting aspect of the BRISTELL is that unlike most metal LSAs, which are made from 2024 aluminium, the BRISTELL is built from 6061-T6 aluminium. Although this material is considered to be harder to work with than 2024 (which is why there are no compound curves on the aircraft) using 6061-T6 does have its advantages. For example, it doesn’t require the use of Emfimastic sealant between the sheets for corrosion protection, nor does it need to be anodised. Both of these factors save weight; indeed, BRISTELL claim that the empty weight is 60kg below that of a similarly equipped SportCruiser. Interesting factoid: the famous aluminium plaques on the Pioneer spacecraft were made out of 6061-T6.

 

Power is provided by a 100hp Rotax 912S (ULS option) which turns a three-blade, fixed-pitch Fiti prop. As mentioned earlier, access to the engine is extremely good with the upper cowl off, while the oil and coolant levels can be checked through a small hatch on the top.

 

An inspection of the rugged-looking tricycle undercarriage revealed that the nose wheel is carried by a heavy-duty pneumatic shock absorber, while the mains are mounted on a composite spring arrangement. The nosewheel (a weak point on some LSAs) looked particularly robust, and I noted with interest that not only are the wheels relatively big for an LSA at 15.00-6.00 x 6, but all three are the same size. This is an excellent feature for flight schools, as they need only carry one size of wheel, tyre and tube. All the wheels are covered by snug-fitting spats, although the nosewheel’s looked quite large. Now, having a lot of keel area in front of the pivot point can have a detrimental effect on the directional stability for a variety of reasons, so I made a mental note to check this carefully.

 

Another good feature is the external power socket, on the right side of the cowling just forward of the wing. NACA ducts on either side of the fuselage feed air into the cockpit. The straight-taper, cantilever wings carry the two 65-litre fuel tanks and use an MS316 aerofoil section at the root, changing to MS313 at the tip. As mentioned earlier, wing-root lockers are an option. As they’re located almost right on the centre of pressure, they can carry up to 20kg each without affecting the C of G. Recessed into the leading-edge are large LED taxi and landing lights, while the upswept wingtips carry strobe and position lights. The slotted flaps extend over about two-thirds of the trailing edge and have four settings: 0º, 10º, 20º and 30º.

 

Moving towards the tail, I couldn’t quite shake the feeling that the BRISTELL just seemed a little bigger than many LSAs: Milan confirmed that it is both wider and longer than most. A small dorsal strake blends smoothly into the elegantly swept-back fin. This carries a large, broad-chord rudder while the tailplane mounts a big, constant-chord elevator that is fitted with a Flettner-type trim tab. The elevator and ailerons are actuated by pushrods, with cables for the rudder and electric motors for the flaps and elevator trim system. Aileron trim is an option − albeit an unnecessary one, in my view.

 

Eager to get beneath the skin of the aircraft (it is quite unusual to actually meet an aircraft’s designer at a show) I questioned Milan about the design, materials and construction of the BRISTELL. He explained that the wing attach points are some 50 percent larger than they need to be to ensure a long fatigue life, and that the metal parts are machined using CNC techniques wherever practical. This ensures close tolerances, and allows many of the sub-assemblies to be interchangeable for ease of production. However, neither the flaps nor ailerons can be swopped over, as the wing is trapezoidal in plan form.

 

Composites are also used quite widely - for example, the canopy frame is carbon-fibre and the rudder skin a vacuum-glass sandwich, while the seats and engine cowl are a Kevlar sandwich. A great deal of attention has been paid to keeping the empty weight down, which allows an impressive payload of 270kg. (Even with full fuel, there is still 177kg left for occupants and baggage.)

 

Factory-built and kitplane available

BRISTELL had two versions of the aircraft at the show, the E-LSA and the S-LSA, and I flew them both. (An S-LSA is a factory-built, ready-to-fly machine, designed and constructed in accordance with ASTM ‘consensus’ standards for LSA, while an E-LSA is a kitplane based on an aircraft that has received an S-LSA airworthiness certificate.)

 

Access to the cockpit is excellent. This is especially important for LSAs, as many potential customers are older-generation pilots who are, shall we say, neither as young nor as thin as they used to be. In this respect, high-wing aircraft will always have an advantage−but the BRISTELL is extremely good for a low-wing design: to unlatch the canopy, simply press the big black button below the port cockpit sill and lift it by the two recessed handles. It swings forward, opens wide and is well supported by gas struts, while the steps aft of the trailing edge are sensibly sited and the non-slip wing-root walkway is wide. Two handholds built into the glareshield and a third between the seats make ingress and egress easy, while behind the seats is a large baggage bay. This can carry up to 15kg and is accessible in flight. Observant readers may have just worked out that this means the total baggage capacity is an impressive 55kg!

 

The cockpit is truly huge. It’s pretty deep and an astonishing 1.3m wide at the shoulders, which is of course where you need maximum width. (For comparison, a Cirrus SR22 is 1.24m.) The seats are comfortable and also very strong, which is a great safety feature. However, the downside to strong seats is that they have to be fixed, and although the pedals adjust over a good range, I felt that perhaps I could also have used a cushion behind me. Shutting the canopy is easy−simply lower until the gas struts no longer support it and let go, and as it drops into position it latches automatically. I’d prefer to have a sliding direct-vision panel on the pilot’s side, but am aware of the argument that this does make the canopy more prone to cracking.

 

With such a huge panel there are acres of space for just about every possible permutation of instrumentation. The S-LSA version I flew first, N922BL, was fitted with a Tru-Trak EFIS SG with an autopilot, while in the centre of the panel was a Garmin 696, a SL40 Comms unit and GTX 327 Mode S transponder. Engine data are shown on a neat little Gemini EMS to the right of the avionics centre stack, while most of the electrical services (switches and fuses) are directly below the EFIS. The guarded ‘mag switches’ − strictly speaking, they control electronic ignition packs − are above the split BATT/ALT master, with the start button quite high up on the panel, just to the right of the LED strip that shows pitch trim position. The key is only used to lock the canopy. Below the transponder are four small round plungers, which operate the park brake, cabin heat, demist and carb heat. These were a little bit samey for me − I’d be minded to make the heater controls triangular, swap the positions of the carb heat and park-brake plungers (so that the carb heat is nearest the pilot) or even better, make the choke a plunger and relocate the carb heat next to the throttle. I’d also make the park brake square or chock-shaped.

 

Beneath the plungers are the fuel valve and rotary flap selector. Again, I’d like the flap selector to be aerofoil shaped, and marking the flap limiting speeds for each setting adjacent to the relevant position indicator wouldn’t do any harm either. (You may think I’m anal about these things: I just like controls that have different functions to look different. If it’s possible to give some sort of hint regarding whatever it is that they do as well, so much the better.)

 

A centre console extends aft between the seats and carries the big T-handled throttle, choke lever and rocker switch for the electric pitch trim. I particularly liked the location of the pitch-trim rocker switch, and found that both stick and throttle fell agreeably to hand. However, as mentioned earlier, I would swap the choke and carb heat positions. Furthermore, the choke lever looks exactly like a mixture control, which is poor ergonomics. Using the choke lever to operate the carb heat would be much better, particularly if these two levers were arranged so that application of full power − such as during a go-around − automatically turned the carb heat off. (BRISTELL has since said it may make changes along the lines of Dave’s suggestions − Ed.)

 

Proper brakes and good ground handling

Thus far I’d been favourably impressed with the BRISTELL, and before I’d even taxied it a hundred metres I’d warmed to it further. Many, if not most LSAs have either differential toe brakes and a castoring nosewheel, or a steerable nosewheel and non-differential, hand-operated brakes. Not so the BRISTELL, which has a nosewheel that steers through the pedals and toe-operated hydraulic disc brakes. I think that pilots who’ve learned on ‘legacy’ types, such as the C152 or PA-28, will certainly appreciate these aspects of the BRISTELL. With the steerable nose-wheel and differential brakes, there was no difficulty tracking the centre line as the aircraft accelerated, while the initial rate of climb was very good at around 1,000fpm. Ambient conditions were several degrees above ISA, while with 60 litres of fuel, BRISTELL USA’s John Rathmell in the other seat and no baggage, we were around 60kg below the 600kg MAUW.

 

With lots of show traffic inbound to Sebring, I was very grateful that the big canopy provides an excellent field of view, although I think that − as good as it is − it could still be improved. The sunshade on the top of the canopy should be extended with a tinted area and/or a fabric concertina-type blind.

 

Almost as soon as we were clear of the circuit I was moved to say to John, “This thing doesn’t feel like an LSA.” “That’s what they all say,” he replied with a grin. And it’s true: the L in LSA stands for ‘light’, and it’s irrefutable that some of them really do feel−and fly−as if they’re… well, a little flimsy. The BRISTELL just feels more solid, and this is also how it flies. When we were well clear of Sebring’s busy airspace, I commenced my initial assessment of the control and stability. The controls are powerful, nicely balanced and well harmonised, with the rudder being the heaviest and the ailerons lightest. Break-out forces were agreeably low and with little ‘stiction’, despite the fact that this was a relatively new machine, with less than 100 hours on the airframe. Only small amounts of rudder were required to keep the slip-ball centred, while the elevator trim is nicely geared. The BRISTELL really is a fine-handling machine, which will appeal to both students and instructors.

 

A look at the stick-free stability revealed, as I’d suspected, that aerodynamic forces working on the connected nosewheel spat prevented the rudder from returning to neutral. (BRISTELL says that this has since been corrected by the inclusion of a centring spring−Ed.) Laterally, stability is barely positive−almost bordering on neutral− while it is strongly positive longitudinally, the aircraft returning to the trimmed speed from a 10kt displacement via two long-wavelength, low-amplitude phugoids.

 

Prior to entering the pattern at Avon Park for some circuit work, I examined the low-speed and stall characteristics. Slow flight is very benign and flap-limiting speed; Vfe is usefully high at 75kt (some LSAs can be found lacking here, with very low Vfes). The BRISTELL remained fully controllable even post-stall, although one slight criticism is that the natural pre-stall buffet is very subtle, and there is no artificial stall warner.

 

On the other hand, as it stalled at around 30kt with full flap at our weight, no pilot worthy of the name should ever inadvertently stall this aeroplane. Even with the flaps retracted, it stalls below 40, and is reluctant to drop a wing.

 

As we were now near Avon Park, I took the opportunity to try a few touch-and-goes. As with every other aspect of the BRISTELL’s flight envelope, it is a delight to fly in the circuit. The field of view is good, the flaps powerful and the aircraft nicely speed-stable. I tried a number of different flap settings, side-slips and glide approaches, and they were all only notable for how easy they were to execute. This really is a fine airplane!

 

For the brief transit back to Sebring I pushed the power right up, trimmed forward and saw the speed tape settle on 118kt IAS at 3,000ft. This is only two knots below the LSA limit of 120kt, although of course running the engine at its ‘max continuous’ of 5,500rpm means that it is guzzling the gas. A more frugal power setting is 4,800rpm, and at 3,000ft the TAS was 108kt for a fuel flow of around 18 litres per hour. In fact, the limiting factors regarding range and endurance are buttocks and bladder, as with up to 130 litres available the maximum range is around 700 nautical miles, while if you pull the power right back, the endurance could be as much as ten hours.

 

By now the thermals were just starting to pop, and we were starting to punch through some light, choppy turbulence. However, the ride quality really is very good and there was none of the ‘up-against-your-harness-down-in-your-seat’ sensation that some light aircraft provide when cruising in conditions that are less than smooth.

 

Back at Sebring, show traffic was landing on the taxiway that had been turned into a runway for the duration. Despite the fact that it really was quite short, I feel confident that, with less than two hours on type, I could have comfortably landed, stopped and then taken off on the remaining runway!

 

Kit-built version quicker?

A few days later I flew N405BL, the E-LSA version, for an air-to-air sortie. The only notable difference is that the E-LSA doesn’t have the wing-root lockers. I’ve often said that there are few finer tests of an aircraft’s overall handling than a close formation session with a demanding photographer, and the BRISTELL revealed itself to be more than up to the task. A curious anomaly was that ‘Five Bravo Lima’ seemed to be slightly quicker than ‘Two Bravo Lima’, and I wondered if perhaps the S-LSA’s wing-root lockers weren’t as well sealed at they could be and were generating a bit of drag.

 

Back on the ground, I admitted to the BRISTELL USA people and designer Milan that I was somewhat perturbed, as apart from my observations about the ergonomics, I hadn’t found any significant flaws or made any real criticisms. Determined to find something else, I got extra picky, but every point I raised they countered effortlessly.

 

Finally − and in desperation − I said, “You know, using cable ties to hold the hydraulic brake hoses to the main-wheel legs isn’t very neat.” “We know,” replied John. “These two are fairly early models. All the new ones use aluminium clips, we just haven’t got around to fitting them to the two demo aircraft yet.”