The Robin 400 design dates back to 1972, and well over 1,300 variants of the aircraft have been produced by the manufacturer at its factory in Darois, just northwest of Dijon in France.
The new Robin 400 production versions are now all designated DR401 and continue to share the same fuselage layout and dimensions coupled with the distinctive Robin low set, cranked wing (of various wing chords and developed from an earlier Jodel design with washout on the outer wing sections). It also retains the same classic large, full cabin length, bubble-type canopy with a forward sliding front section for pilot and passenger entry. All DR401 versions have a fixed, faired tricycle gear.
The DR401 range features four different petrol (avgas) types. However, since 2014, that engine range has been supplemented by the DR401 CDI type: a two-litre turbo diesel engine (using Jet A-1 fuel) and rated at 135bhp (2.0 version) or 155 bhp (2.0S version).
The diesel engine used on the DR401 is based on a design originally produced by Thielert Aircraft Engines. Thielert went into bankruptcy and was bought by Continental Motors (US) in July 2013. Continental Motors had itself been sold to the China-based AVIC International in December 2010. The two diesel engine versions on the DR401 are now marketed as Continental “Centurion” engines.
The vision to equip the DR401 range with turbo-diesel engines was, to a large part, driven by an individual: Steve Bailey, the owner of Mistral Aviation and the sole UK distributor of Robin Aircraft. Bailey lent his own DR401 (G-JSMH) to the Robin Company to facilitate the development programme for fitting the Centurion engines, which led to the issuing of an EASA Supplemental Type Certificate (STC) in 2014. Additional STCs for the DR401 now cover the Garmin digital avionics and the new Oratex paint-impregnated fabric wing covering – developed from German model aircraft technology – which eliminates the historical problem of surface cracking that is common in over-painted plain fabric.
The DR401 CDI 2.0 and CDI 2.0S versions, with the above STCs incorporated, are now produced as a production standard by Robin. Additionally, with the standard upgraded engine exhaust fitted to meet stringent German noise regulations, it means that the DR401 CDI 2.0 and CDI 2.0S are also certified as glider tugs.
New Robin 400 production versions shares the distinctive low set, cracked wing
BillyPix
Specification
The aircraft I would evaluate would be Mistral Aviation’s own DR401 CDI 2.0S, which is registered G-JSMH. The CDI 2.0 version is primarily aimed at flying schools, and the CDI 2.0S is marketed as a true four-seat touring aircraft.
The Continental CDI 2.0 and CDI 2.0S are both fuel-injected, water-cooled turbo-diesels using Jet A-1 fuel (now widely available at most general aviation airfields), using full authority digital engine control (FADEC) and requiring no mechanical back-up control. The engines drive a three-bladed, variable pitch propeller produced by MT. It has no reverse pitch.
The true single power lever now automatically controls power and propeller pitch combined, and power is indicated to the pilot as a simple percentage. The FADEC removes the need to monitor and separately control boost, mixture, propeller RPM or carburettor heat at varying airspeeds, altitudes or outside air temperatures (OATs). The engine block of the Centurion is made from aluminium rather than the cast iron used in the original Thielert engines, which grants significant weight saving.
The digital avionics feature the two-screen Garmin G500 electronic flight information system (EFIS) on the left side of the instrument console, and the touch-screen Garmin GTN 750 navigation and radio display on the right side. The depth of the instrument console of the DR401 is not big enough to accommodate the larger Garmin 1000-type displays. Two small standby digital displays for artificial horizon (AH) and altitude/airspeed separate the main display sides. The EFIS is supplemented by a two-axis S-Tec autopilot as well as a traffic collision avoidance system (TCAS), and ADF and DME navigation aid receivers. In this configuration the aircraft was fully EASA instrument flight rules (IFR)-certificated. The DR401 family has no anti-ice system.
Normal fuel capacity is 110 litres (29USgal), but G-JSMH was fitted with the optional long-range fuel tank that adds an extra 50 litres. 160 litres of Jet A-1 grants the aircraft a still air maximum range of 850nm (1,570km), which allows for 7h of flight with 1h reserve. This is based on starting from the maximum take-off weight (MTOW) of 1,100kg when flying at 10,000ft/3,000m at 65% power, with 20 litres/hour of fuel consumption and an economical cruise speed of 111kt (206km/h) indicated air speed (IAS). The diesel engine can also be run at up to 100% power without time limitations. Mistral claims a cost saving in fuel of approximately £60 ($92) per flight hour in comparison to an avgas-powered aircraft of similar configuration, and this reduction in direct operating costs represents a very significant saving to the owner/operator over the life of the aircraft.
Time between overhauls (TBO) of the engine is 1,200 flight hours/12 years, but Robin expects this TBO to be extended to 1,800 flight hours in 2015. Engine overhaul cost is £31,000. Propeller reduction gearbox time between exchange is 600h (as a replacement part swop-out) and a new gearbox unit cost is £4,000. These engine/gearbox costs must then be balanced against the significant savings made in fuel.
The MTOW of the DR401 CDI 2.0S is 1,100 kg. The basic operating weight (BOW = no fuel, cargo or pilot/passengers) of G-JSMH was 670kg, giving a useful load of 430kg. Two adults and two children at an assumed weight of 260kg, 40kg (maximum) of baggage and 130kg fuel (equalling the maximum long-range fuel of 160 litres) means that the aircraft is a true four-seater, while at the same time retaining true maximum range.
The aircraft has conventional, unpowered flying controls with ailerons on the outboard wing section, an all-flying horizontal stabiliser with balance tab and electric trim, and two-stage electrically driven flaps (100kt deployment limit). The rudder is also electrically trimmed. Best angle of climb is obtained at 65kt and best rate of climb (700ft/min at MTOW) is at 75kt. Take-off distance to clear a 15m obstacle is 492m (273m ground-roll) and landing distance over a 15m obstacle is 415m (175m ground roll). Typical rotate speed is 60kt with flap at setting 1, and typical final approach speed is 65kt with flap 2 into a 60kt flare. Maximum ceiling is 16,000ft; never-exceed airspeed (Vne) is 146kt; the maximum demonstrated crosswind is 22kt. The aircraft has no aerobatic or deliberate spinning capability.
The aerostructure (all Robins are made entirely from wood) has a warranty of 20 years and the Oratex wing fabric warranty is 10 years. The new price for the DR401 CDI 2.0S in its basic version is €203,500 ($228,000), but at the upgraded, full-specification production standard represented by G-JSMH, including a full leather interior, the quoted new price is €325,000.
What the Robin lacks in speed, it makes up for in range, comfort and field of view
BillyPix
Evaluation
The evaluation was flown from Elstree Aerodrome (EGTR) using runway 26 (tarmac). Wind was 300/10 gusting 15kt, OAT +6˚C, and visibility was greater than 10km. Aircraft all up weight (AUW) with three adults and 80 litres of fuel was approximately 970kg.
The first noticeable thing about the DR401 CDI from the outside was the incredibly smooth fuselage surface that replicates carbon fibre in its finish. Entry to the cockpit can be made from either side, with passenger entry to the rear cockpit facilitated by folding the backs of the front seats forward. The baggage compartment, accessed on the left-hand side of the aircraft, was not voluminous but looked as if it had space for two medium-sized holdalls.
Field of view from the cockpit was outstanding, with the canopy coming below elbow level at the side. With the EFIS console, the single ‘tee handle’ shaped power lever and the central, dual control columns, the cockpit felt wonderfully uncluttered.
Pre-start checks were minimal and the key start was identical to that of a car, with no need for priming or mixture lever gymnastics. The FADEC integrity check was the essential element post-start. Ground-handling was precise, with nosewheel steering allied to excellent brakes.
Prior to take-off the aircraft was held on the brakes momentarily at 100% power to check that the propeller reached and stabilised at 2,300rpm. Take-off acceleration with the variable-pitch propeller was noticeably faster than with a fixed prop. After rotate, and in chase with the photo ship, the controls felt light and well harmonised. The electric flap travel is designed to be slow (approximately 10s from flap 2 to up and 4s from flap 1 to up) so there were virtually no out-of-trim forces felt as the flaps were moved in either up or down. Control breakout and freeplay were small but centring laterally was not that strong. However, this was not a distracting feature.
No adverse yaw was discernible and the aircraft exhibited no Dutch-roll tendency. Roll rate at full lateral deflection was typical of a GA-type aircraft at around 40-45˚/s. The aircraft rolled moderately with rudder and, at 75kt, a steady heading sideslip showed it could generate 25˚+ of sideslip for a kick-off-drift crosswind landing. A 60˚/2g level turn at 120kt showed no wing buffet.
Longitudinal stability away from trim speed was distinct but moderate in force and quickly negated by the pitch trim. The control column ‘stick top’ was my only dislike. It had two prominent buttons: red for autopilot disconnect and black for autopilot control steering, but then had five very small and recessed buttons: one black radio transmit button and four grey ones for pitch trim (up/down) and rudder trim (left/right). These recessed buttons were not always easy to feel and I would have preferred them to be more prominent.
At 75% power and 2,000ft altitude in level flight, the aircraft stabilised at 118 KIAS (knots indicated airspeed). The combined engine instrument does not show fuel flow. The aircraft was placed into a slight dive and at 140kt the control forces, while slightly heavier in pitch and roll, remained light and perfectly acceptable. Two level stalls with idle power and flap 2 gave a stall-warning horn at 55kt and a defined nose drop at 46kt. Each stall was accompanied by a very small left wing drop but that may have been in part generated by me not having ensured perfect trim in yaw.
In formation around the photo ship I worked the engine/propeller combination hard, but the power response always remained smooth, rapid and effective. In the cruise at 2,000ft, the AP functions were easy to manage, the level ride was very comfortable and the superb field of view continued to delight me.
On recovery to Elstree, three visual circuits were flown in gusty crosswind conditions. The variable pitch propeller allows for speed to be shed quickly if fast on approach. In the gusty conditions the aircraft felt stable and I elected for a decelerating approach from 90kt into a 65kt flare. Precise touchdowns to the selected touchdown point were easy to make while still coping with kicking off drift in the crosswind. The DR401 CDI retains the Robin’s trademark short take-off and landing (STOL) capabilities.
Owner Steve Bailey (left) and Collins with Mistral Aviation's own DR401 at Elstree
BillyPix
Conclusion
Without doubt I believe the future of modern GA aircraft now lies with the economy of diesel engines; the efficiency of variable pitch propellers; the flyability granted by FADEC; and the survivability afforded by EFIS when flying in and through increasingly complex GPS-based airspace. The Robin DR401 CDI now has these options in place, certified and combined into an impressive package.
The aircraft, with its fixed gear, is not particularly fast, but its STOL ability on to grass surfaces, allied to its very long maximum range with four people on board, gives it some significant advantages over its closest rivals.
The final part in the equation is cost. No new GA aircraft, at this level of specification, is cheap, and especially so in comparison with pre-owned aircraft. However, the new Robin DR401 CDI 2.0S is a superb touring aircraft and one that I would be proud to own.
Source: Flight International
