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Flight Test: refurbished Socata TB-10 Tobago

PUBLISHED: 11:02 09 November 2016 | UPDATED: 11:02 09 November 2016

Socata TB-10 Tobago

Socata TB-10 Tobago

keith wilson (c) PIL OCT16 FLIGHT TEST Socata TB-10 SINGLE USE PILOT MAG ONLY

Can a thirty-year-old airframe refurbished by Cavendish Aviation compete with today’s four-seat tourers?

Words: Dave Unwin; Photos: Keith Wilson

Humming smoothly towards the inviting waters of the Channel at two miles a minute, I turn to Cavendish Aviation’s MD, Steve Allen, and nod in agreement. “You’re not wrong, Steve − this is the perfect Le Touquet aircraft!”

The French have always had a reputation for designing fine flying machines, but my initial thought as I walk toward the gleaming TB-10 Tobago is that I simply can’t believe this is a 33-year-old airframe. Built in 1983 by Socata, then part of the European Aeronautic Defence Space Company (the largest aerospace company in Europe), it has been extensively refurbished by Earls Colne-based Cavendish Aviation and really does look practically new.

Speed and economySpeed and economy

It is an attractive aeroplane and, from the tip of the spinner to the apex of the rakishly swept fin, it looks fast even when standing still. The pre-flight reveals it is also extremely well made.

The TB line (TB for Tarbes, where the aircraft were built) was designed during the late 1970s as a faster-flying replacement for the well-known Rallye series. Socata was originally a subsidiary of the French aerospace giant Aérospatiale and − as one of the main contractors for the production of a large number of Airbus components − had the use of highly sophisticated CNC (computer numerically controlled) machine tools. Although more common today, their use for light aircraft production was unusual 36 years ago.

"This is the perfect Le Touquet aircraft!

Something common in the TB range is that the main spar is milled from a single piece of metal, meaning it is free of any kind of join, which greatly increases its structural integrity. The TB-10’s fin and rudder are set forward of the tailplane (actually a stabilator or all-flying tailplane) and there are a pair of ventral strakes mounted under the fuselage. Ventral strakes and dorsal fillets always make me think ‘Hmm, aerodynamic fudge’ as their addition is usually to improve directional stability. However, Steve tells me in the Tb-10’s case, Socata fitted the strakes to assist in spin recovery. “Although, in practice, they do assist greatly in hands-off directional stability − as you will discover.”

Anyway, despite my initial scepticism about both the fin and those strakes, there was little about the Tobago I didn’t like. Wherever possible, the aeroplane’s skin has been flush-riveted and the entire airframe appears to be especially well made. As the engineers who originally built the aircraft probably worked on Falcon business jets and Mirage fighters, the high build quality is unsurprising.

As delivered from the factory, its 180hp Lycoming O-360 drove a two-blade Hartzell constant-speed prop, but Cavendish Aviation is now upgrading the aircraft by fitting three-blade McCauley units with ‘Scimitar’ blades. Steve was extremely enthusiastic about the difference these new McCauley props make, as they are much quieter than the original two-blade Hartzell.

Can't believe this is a 33-year-old airframeCan't believe this is a 33-year-old airframe

Starting with the next aircraft to be refurbished, the company plans to replace the original exhaust with a four-into-one merged-collector manifold produced by Atelier Chabord. With this arrangement, the Inconel manifold connects to an extender pipe that carries a large silencer mounted under the fuselage, reducing noise still further. Access to the engine is reasonable (there are quite a few fasteners to undo) but the oil can be checked via a small hatch on the top of the cowling.

It’s quite obvious Socata made a determined effort to reduce drag, so it’s a little surprising that, despite all three undercarriage wheels being enclosed with tight-fitting spats, the nosewheel’s drag links are exposed. This must add a considerable amount of drag.

It flew well in formationIt flew well in formation

The fuel is contained in a pair of 102 litre tanks located in the wing’s leading edge. The wings feature a small amount of dihedral, but are aligned chordwise with the longitudinal axis, having zero angle of incidence at the root. The trailing edge consists of balanced ailerons and electrically-actuated slotted flaps, with a ground-adjustable trim tab in the starboard aileron. The wingtips are fibreglass. Another aerodynamic anomaly is that the stabilator appears to have little down movement. It features a full-span anti-balance trim tab, while the rudder has a ground-adjustable trim tab.

Overall, the TB-10 is thoughtfully designed and well-made, an impression reinforced when entering the cabin as access to the cockpit is excellent. There are small steps mounted either side just aft of the trailing edge and, with the large gull-wing doors unlocked and opened, it is easy to step up onto the wing and then down into the cockpit.

The non-slip wingroot walkway is sensibly-sized, unlike some aircraft where you are always aware how easy it would be for someone to step where they shouldn’t.

The gull-wing doors nicely match the new Scimitar propThe gull-wing doors nicely match the new Scimitar prop

Settling into the comfortable seat, I was struck by how roomy the cockpit is. The cabin is about 125cm wide at shoulder height, generous for an aircraft in this class, and combined with the large windows extending up into the roof, it really does make the cabin feel part of a larger aircraft. The rear seat is of the bench type used in later models certified for three occupants in the back, although I imagine they would all need to be significantly slimmer than me!

The test aircraft is s/n0058, and a four-seater. Apart from the two gull-wing doors, there is a separate baggage bay hatch on the port side of the fuselage aft of the wing. The baggage bay can carry up to 45kg, is quite capacious and accessible in flight, although the baggage bay door could have been bigger.

Accessible in flight, the cavernous baggage bay will take 45kgAccessible in flight, the cavernous baggage bay will take 45kg

The cockpit may have been spacious, but there are some ergonomic areas I found less than satisfactory, such as the power control levers. At the base of the avionics stack is a large centre console extending back between the front seats. This carries the throttle, prop, mixture and carb heat levers, and although they’re correctly shaped and ordered, the colours aren’t entirely right (the carb heat is blue, the colour correctly used for the propeller). Not an issue for the private owner, but the sort of ‘gotcha’ that just might confuse a low-houred renter under stress.

Conversely, the pitch trim wheel is perfect – large, nicely geared and exactly where you want it (just behind the throttle lever) with the pitch trim indicator adjacent.

Just in front of the power control levers are the buttons for the electrics, an aerofoil-shaped switch for selecting the flaps and a flap position indicator. Unless you’ve flown other Socata aircraft (such as the Rallye) you’ll find the system used for selecting the electrical services to be unusual as they favoured using thermal overload buttons.

The manufacturer's original aerodynamic tweaks include strakes under the rear fuselageThe manufacturer's original aerodynamic tweaks include strakes under the rear fuselage

Consequently each service has two push buttons, a now rather yellowed white one for on and a red one for off. Unfortunately, these aren’t labelled either, and they really should be. The circuit breakers are located in a neat stepped panel close to the pilot’s left knee, and the cockpit has some useful stowage areas for airways manuals and the Pilot’s Operating Handbook.

The comfortable control yokes are nicely trimmed in leather, while the beefy rudder pedals are suspended from below the instrument panel. Other good features are that the fuel tank selector and park brake are both under the pilot’s yoke – easy to see and reach – while a small panel in the roof contains useful operating limitations.

You can fit three in the back, but they must be slimmer than me!You can fit three in the back, but they must be slimmer than me!

I’ve already mentioned the Tobago gives the impression of being a larger aircraft than it actually is, and this illusion is enhanced by the instrument panel. Consisting of three padded ‘boxes’, the one in front of the pilot carries all the primary flight instruments and a comprehensive annunciator panel, while the one on the right contains the power gauges and additional flight instruments.

In the centre of the panel is a large vertical stack crammed with avionics, including a GPS and autopilot, and topped with unusual vertical-reading gauges that show oil pressure and temperature, fuel quantity and pressure and volts. H

However, I have two fairly major beefs. First, the annunciator panel is not labelled but simply marked with vague symbols. Second, the gauges in the middle (with the exception of fuel quantity) are only colour-coded. Now, I’d rather know when I’m cruising at ‘23 squared’ on an ISA day that the oil is at a specific pressure and temperature and the fuel at a specific pressure, so I can track trends. This arrangement is far too nebulous for my taste, particularly when allied with the not-easily interpreted annunciator lights.

Cockpit dominated by the distinctive 'three box' panelCockpit dominated by the distinctive 'three box' panel

By now you’re probably wondering, ‘Why didn’t they go glass during the refurb?’ Well, a pair of Garmin G1000s isn’t cheap and it is irrefutable many pilots prefer nice round analogue dials, arranged in the classic ‘sacred six’. Having a reasonable amount of time in glass cockpits but having earned my Instrument Rating on steam gauges, I can see both arguments − although on balance I do feel a fully integrated digital cockpit is a superior solution.

That said, Cavendish does offer a bespoke service (Steve was adamant any avionics suite should be “pilot-inspired”) so you pays your money and takes your choice!

Hooray! A properly engineered, manual elevator trimmerHooray! A properly engineered, manual elevator trimmer

The seats have been re-upholstered, the leather-covered yoke is hand-stitched and the interior smells like a new car. Steve told me about a recent customer whose wife had commented how nice it was to go from their Aston Martin into an equally sumptuous aeroplane, and I knew exactly what she was getting at. I’ve often wondered how many people have been turned off GA when they arrived at the airfield in a brand new luxury car, and then got into something with an interior reminiscent of a 1975 Austin Allegro.

The seats adjust over a respectable range and, in common with many other modern aircraft, inertia-reel seat belts are fitted. Fine for the passengers, but I always believe the pilot should have a four-point harness. An oddity is that the seats really aren’t that comfortable when you first sit down, (I actually thought I was sitting on some object!) It’s quite obtrusive, but goes away after a few minutes.

The doors are well supported by gas struts and it is easy to swing them gently shut. Pulling the locking handle to ‘closed’ draws the door snugly into its seal. The Lycoming starts readily – once I remember the French foible of pushing in the rotary mag switch to start up – and, with Steve in the other seat, I taxi out to Earls Colne’s Runway 24.

What happened to Socata's colour coding?What happened to Socata's colour coding?

The Tobago is, like most modern aircraft with a tricycle undercarriage, easy to taxi, although the nosewheel only steers through a relatively narrow arc so a dab of differential braking is required for a tighter turn. The toe-operated hydraulic disc brakes have a nice progressive feel and the field of view is good.

Pre-takeoff checks are pretty standard for this class of aircraft, so with the prop set fully fine, fuel pump on, takeoff flap set (ten degrees) and the elevator trim neutral, I line up with the centreline. It is quite warm with just a gentle zephyr blowing, so I take Steve’s advice to stand on the brakes and run the engine up to 2,700rpm with as much manifold pressure as we can get.

Good ergonomicsGood ergonomics

With full fuel, no baggage and only two adults aboard we are around 170kg below the maximum all-up weight of 1,150kg and the acceleration is adequate. A fairly hefty pull on the yoke is required to rotate the Tobago into the takeoff attitude at just over 65kt, but as we have a fairly forward C of G, this must be taken into consideration. Anyway, having used about half of the 840m available, the Tobago is off the ground at around seventy knots and soon settles into a good climb of almost 1,000fpm.

Passing rapidly through 500 feet I press the flap switch to up, turn off the fuel pump, pull throttle and prop back to 25/25, nudge the pitch trim wheel forward and set off in pursuit of the camera ship. The Tobago’s Vy (best rate of climb speed) is eighty knots but I deliberately trim for ninety in order to improve the forward visibility.

This is not to say the field of view is substandard though, far from it with such large windows and a generous windscreen. The subtle tint (part of the refurbishment) is another nice touch.

C'est ouvert!C'est ouvert!

It is a beautiful summer’s day and heading straight towards France in a French aircraft seems entirely appropriate.

When assessing an aircraft’s overall control characteristics I always feel an excellent indicator is how easy it is to fly in formation, and Keith’s fine photographs from the Cessna 172 clearly show that. I am both confident and competent enough with the Tobago to hold a perfectly rock-steady formation on the camera ship.

Overhead panel mounts speaker, fresh air vents and airliner-style individual reading lightsOverhead panel mounts speaker, fresh air vents and airliner-style individual reading lights

The Tobago doesn’t just feel bigger than it really is, it flies bigger. This is almost certainly due to the relatively low wing area and consequently high wing loading. The net result is a much firmer ride.

I break away from the Cessna and begin to experiment further with the Tobago’s handling and performance characteristics. Setting the aircraft up for the cruise at 3,000 feet, I draw the throttle and propeller levers back to ‘23 squared’ and the needle of the ASI eventually settles just over the 115kt mark, for a true airspeed of around 120kt.

I have to estimate the actual TAS as, although the ASI is of the type that can be corrected for temperature, there isn’t an OAT gauge! Anyway, 120 is a really good ‘going places’ speed, and at two miles a minute in still air the time/distance calculations are a breeze.

Cavendish's next TB, ready for refurbishmentCavendish's next TB, ready for refurbishment

It can go faster of course, but at the expense of fuel consumption, while at 23/23 the fuel flow of around thirty litres per hour is perfectly acceptable. In fact, I was pleasantly surprised by its cruise performance as the TB series is fitted with a constant chord wing, a design not known for conferring commendable cruise characteristics. This TB-10 is very smooth and quiet.

An exploration of the stick-free stability reveals the aircraft has strong longitudinal stability and weak lateral stability. The former is probably a function of our forward C of G, while the latter (just barely positive) is shared by many modern light tourers. Directional stability is good, helped no doubt by those ventral strakes.

Wish we could have just kept goingWish we could have just kept going

Slowing down to explore the stall regime takes a while, as the aircraft is quite slippery, so I experiment with some steep turns to shed some energy. The flight controls are powerful and nicely coordinated, but the ailerons do seem a trifle on the heavy side. Unusually, all the primary flight controls, including the rudder, are driven by push-rods.

The stall is perfectly innocuous, both flaps up and flaps down. With full flap the stall occurs at 49kt, and is preceded by aerodynamic buffet and a warning bell, activated by a small vane in the left wing. Cleaned up, it stalls at about sixty and, as expected, there is markedly less aerodynamic buffet. This is slightly faster than I’d anticipated, but the C of G is well forward.

Incidentally, the stall warner is almost musical, and while it would make a fine doorbell, it’s a little too genteel and subtle for warning you of approaching critical alpha. Behaviour at the stall is benign – initially, it begins to mush and then gently breaks straight ahead with absolutely no tendency to drop a wing.

Its relatively small wing area/high wing loading gives a smooth rideIts relatively small wing area/high wing loading gives a smooth ride

Back at Earls Colne, a good speed to start from in the circuit at our weight seems to be 90kt, with 80 on base leg, bleeding back to 75 on final with a ‘last-look’ speed of just under 70. Vfe is 95.

The TB-10 is speed-stable and easy to land, although it does seem to like a hint of power left on all the way down and the stick forces do feel quite high in the flare. Again, probably a function of our forward C of G.

The all-pushrod control system confers nice control responseThe all-pushrod control system confers nice control response

You can learn more about an aircraft during a few ‘circuits and bumps’, and with each touch-and-go I feel increasingly at home. None of the landings are bad, but I eventually get a real squeaker, and then call it a day.

Conclusions? Well, the TB-10 offers a good combination of speed and economy, allied with nice handling and a fine balance between control and stability, all wrapped up in a large, comfortable cabin with a graceful, Gallic appearance. Paint the prop and carb heat levers the right colours, spend half an hour with a Dymo label writer and you’d own an aircraft that really represents exceptional value for money.

____________________

More Flight Tests:

Aeroprakt A-22 Foxbat

DHC-1 Chipmunk

Diamond DA40 NG

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