FLIGHT TEST

Vive la difference!

Clive Davidson flies the amusingly quirky Nord NC856A Norvigie 1950s French Army observation aircraft…

Pictures: Neil Wilson

Above The Norvigie definitely has a bucket load of Je ne sais quoi!

Flight Test

The subject of this month’s flight test is a Nord NC856A Norvigie, a characterful tenth iteration of no less than 15 variations of the marque. The type was developed in the late 1940s as an entry in the same competition that was won by the SIPA S90, and which the Jodel D11 that was also entered. The competition was launched by SALS – Service de l’Aviation Légère et Sportive, a DGAC (French CAA) sponsored organisation, which was formed in 1946 to encourage the growth of flying clubs and the availability of French designs for their use.

The manufacturer, SNCAC, Société Nationale de Constructions Aéronautiques du Centre, at Bourges (which became Nord Aviation in 1954), developed the prototype NC850 from its unsuccessful 1946 NC840, a four-seat tricycle machine powered by a 140hp (104 kW) Renault 4Pei engine, which did not go into production. The prototype NC850 had a single fin and rudder, was a two-seater and was powered by a 100hp (75 kW) Mathis G4F engine and flew in April 1947. The type finished second in the competition and, like the SIPA, received a government order for 100 aircraft. The production version became the 75hp (52 kW) Minié 4. DA.28 powered NC853, which featured the twin fin and rudder tail that became synonymous with the type, and here in the UK we have a number of 65hp Continental converted examples, which are designated as NC854S. The idea of placing the fins and rudders out in free air, with near double the area of the standard tail set, removes most of the slipstream’s rotational force, making for less required response from a lazy-footed pilot. This twin fin on a single prop driven airframe is not very common and although SNCAC’s idea is pretty distinctive among single engine airframes, it is not unique. The pre-war Swiss C3603 fighter bomber used this set-up, and it was used for the 1950s French Armée de l’Air communications Broussard. Very few others followed this concept, however, the reason for such isolated use may perhaps be laid at the door of it being more expensive to construct and its negative impact on ground handling. Which brings us to our flight test aircraft, Richard Ellingworth’s NC856A Norvigie, G-CGWR, which is unique in the UK. The Norvigie is a highly modified variant of the NC850 series carried out in 1951, specifically as an observation aircraft for the French Army, which went on to take delivery of 112 examples. It features a longer rear fuselage to accommodate a third occupant, extensive cockpit glazing and a more powerful engine, the 140hp (104 kW) inverted inline four-cylinder Regnier 4LO-4. Some idea of the ‘growth’ of the design can be garnered from the fact that the max all up weight was increased from the typical 1345lb / 610kg of the NC854S to the Norvigie’s 2436lb /1,105kg.

A trip to Spanhoe

Rebecca Tiers, under the auspices of her father Carl’s company, Windmill Aviation. We flew up to Spanhoe with David Frasier in his Piper Pacer and the Norvigie, serial number 54 built in 1955, was already sitting out on the grass waiting for us. It would have been rude to have assumed that Richard wouldn’t have minded us crawling all over her, so I walked around her, in ever smaller circles, being reeled in. With a 40ft wingspan and an obvious presence, her military unit and national markings on a khaki green camouflage base sets her apart from our normal civilian fare. The khaki is complemented by the contrasting forward to aft blue, white and red (even the way this is spoken is in reverse) of the rudders’ display of France’s national insignia. But then again, to differentiate between French and British Allied machines during WWI, the roundels and rudder flashes alternated for this distinction.

She seemed to have so many obvious external aerodynamic oddities that it wasn’t long before I was leaning over the tailplane taking a closer look at her. I have to admit to expecting a few contrasting features to the norm as having read of aircraft produced in France, principally before and during WWII, the standard French operation of the throttle worked in reverse to the world’s, now uniform, agreement. To reduce power both you and I would pull the throttle back, and to open the throttle and increase power we would ease the throttle forward. However, the early French machines reduced power by easing the throttle forward and increased power, ‘pouring the sauce’ as Capt W E Johns might have said, by bringing the throttle fully back. You just cannot believe it, can you?

Interesting features

The aircraft has elevator mass balances supported by huge, slightly S shaped rods leaning far forward quite high over the tailplane, a sort of cosh shaped head of a sea serpent rising from the waves. The elevator also has trimmers on its extremities, as do both rudder trailing edges. The rudders are of a generous size and the trimmers have their lower edge clipped at an angle so that a fully up elevator is not snagged.

The wings are slightly swept forward and true to this breed’s form, shoulder mounted, so sitting forward of the wing gives an excellent field of view. The inboard trailing edge has generously sized five position flaps, operated by a high and centrally mounted handbrake style lever with a squeeze up ‘trigger’ locking mechanism to unlock and locate the flap lever to its next slot. The first notch of flap sees the stalling speed reduced from 55kt clean to 53, second stage to 45kt, third to 42, but there is now an imposed operational restriction of not being able to use the last two stages. Would you credit that, under test conditions, the last stage of flap induced a slightly higher stall speed of 45kt? When Dan Griffith, the LAA test pilot, flew the aircraft and noted the rather ineffective last two stages of flap, he surmised that the steeper approach angle afforded by their use may have been a military requirement to help limit the time the aircraft

Above The ailerons are heavy, but this aeroplane is stable and handles very predictably.

Left The ‘double decker’ ailerons with flaps deployed. Note also the enormous spades to help flap deployment.

Below The twin fins and aerodynamically balanced rudders, note the enormous ‘sea serpent’ elevator mass balances.

might be vulnerable to small arms fire, but commented that rapid speed drop off in the flair was a serious issue. The pull down force on the lever whilst on the ground is much like an Auster, of no real strain, and broad flat ‘spades’ have been mounted outboard from the fuselage and forward of the flap hinges to counterbalance the force required to lower the flap when airborne. It works well and of course being flat plates presented to the oncoming air, the spades act as speed brakes as well.

‘Double-decker’ ailerons

If you took only a cursory look at the ailerons, there appears to be a number of mass balances hanging down to prevent our old enemy, flutter. However, you will have missed a quirk that is so unusual, go back and look, it has ‘doubled up’ ailerons. The ailerons run from the flap edge to the curve of the wingtip and are ‘spooned’ on top of each other. Going into the cockpit and lowering the flaps sees the underside portion of the aileron droop as well as the flap. This is no doubt to improve low speed handling, the same angle aligning the flaps and lower half of the aileron together. Sideways movement of the stick for roll has the ailerons react in the normal and expected manner. But how effective might this be, I would soon find out I am very sure. To help reduce the force for deflecting the ailerons, the lower set have servo tabs.

Power plant

The SNECMA Regnier 4LO4 engine of 6.3 litres produces its max continuous power of 135hp at 2,280rpm. with a consumption of 36.3 litres an hour. At take-off 2,340rpm may be expected with 140hp. It drives a two-metre diameter Legere EF.10A wooden propeller that is inflight adjustable by an instrument panel mounted rotating car-type window winder, probably purloined from a Citroën, Simca or Renault (which were going through their own government directed construction from 1946).

Wind the white triangular indicator to the right with a clockwise action and the prop coarsens from 23.30° to 30° for an efficient cruise, and backwards to fine pitch for better take-off at 15° to 30°. The prop extension and the blue spinner gives the aircraft quite a prominent nose, a rather apt caricature of the French President at the time of its inception – General Charles de Gaulle.

Below Low and slow, as it may well have spent much of its service career.

The cockpit

The cockpit area is extensively glazed, revealing its exposed metal tubed construction – the wing incidentally is of skeletal metal construction, and like the fuselage, is fabric covered. There are two front seats and a single rear, and two front doors that open forward. The rear seat has ‘floor to ceiling’ and overhead perspex too – it’s single door on the port side folds down for entrance and exit. Both the P1, front left seat, and the rear seat have rigid backs, but the right-hand seat, soon to be occupied by me, fortunately has a firm base, but unfortunately a deck chair canvas back, which is not so good for posture. I assume this is so the rear occupant might exit through the right-hand front door in an emergency should the left fuselage be blocked or damaged. There are full harnesses to secure the crew.

The 120-litre fuel tank is just behind and below the front seat and its yellow colour filler and neck is located by the port-side rear door filler. Its usable amount is 110 litres, and the maximum oil tank capacity is 15 litres but there should be an ullage space of two litres. The minimum level is six

Above The cockpit certainly has an old style military feel. Not fuel filler to single tank behind strut.

Left This view forward from the rear seat superbly illustrates the enormity of the perspex transparencies.

Below A side view with the rear seat passenger’s door hinged down. litres, while normal is around the 10-litre mark. The oil used is a mineral detergent and being the warmer season, 100 rather than 80 was in use.

Unfamiliar environs

Seated, but not strapped in, it was certainly worth taking time to spot all of the necessary controls, levers and instruments soon to be called upon – progressing from the known and then trying to decipher the unknown.

The stick could be circled all around the box without any restrictions and showed no signs of slackness or play. The flap lever and its locking trigger could be reached above my left shoulder and activated without fuss, and the rudder pedals could be easily moved back and forth but, dipping my head down into the well regretfully confirmed I had no toe brakes on my side. A shame, as I wouldn’t be able to gauge ground handling, other than allowing the castoring tailwheel it’s freedom to wander where it might wish. The usual directional control of deflecting a rudder with a blast of propwash would be useless, as already mentioned it misses both rudders. The elevator trimmer is on the left of the panel, a vertical sliding lever – slide up for nose up, and down to for nose down.

This left-hand panel also houses the already mentioned winder for prop pitch, the fuel pressure gauge, an rpm dial and an obviously more recent boost gauge because it measures manifold pressure in inches. Adjacent is a vertical placard of recommended manifold pressure settings for height in thousands of feet with a prop set for cruise at 2,180rpm.

The centre section of the panel has the standard six instruments and a small Becker 8.33 above the artificial horizon – and the ASI is in knots and not in kms as I was expecting. Its white flap arc, allowing for my offset angle, displays a stalling speed of 40kt and a limiting upper speed of 76kt. The green arc for normal operation extends to 120kt and there is a brief cautionary orange range of a further five knots before the red line continues up to 140kt.

Shifting my gaze directly beneath this central panel to the supporting lip, there are a lot of French labels, all helpfully indicating each switch and lever. The yellow colour coded ‘essence’ fuel knob is pulled back for on, the fuel pump flicked to the right for pressure. Fortunately, there are orange, green and red bands painted on the outer edge of the fuel pressure gauge dial, although the pressure is measured in ‘pz’. A little research later led me to discover that it is a metric measurement also once used by the Soviets, although it was dropped in the mid-1950s. Its full name is piezes (which I am tempted to pronounce as ‘pizzas’) and fortunately conversion from pzs to our more familiar mbs is by simply multiplying by 10, hence the international standard atmosphere, for example, is 101.3pz or 1013 mb – or hectopascals to use the current idiom.

Underneath the centrally mounted black knobbed throttle are the mag’ switches, actually a pair of side by side up and down sliders. Again, this type is new to me, but they are similar to examples fitted to the Jungmann except their sliders are keys and may be taken out of their slide and then left hanging on their lightweight chains. Up is ‘ON’, and the push to start button is directly to the left of the throttle, all conveniently sited and well thought out. And finally, the right-hand panel has the vacuum gauge, a newly installed CHT, a clock with a tiny inset second hand and, rather surprisingly, a G meter (with a limiting red band from 2.85G).

Prep, then start

The propeller is first set in low pitch by winding the ‘car window winder’ clockwise. Then, having checked the mags are both hanging down disconnected and off, the prop can be pulled through five to 10 blades. Remember, although unlikely, this is an inverted engine whose cylinders might possibly partially fill with oil, so turning the prop is not the ‘sucking in’ process.

Back in the cockpit with brakes on, the electric fuel pump is switched on – checking the pressure is above Below The instrument with its mix of quirky and regular gauges and switchgear. 16hpz, and then switched off; mag switches are slid in and up for ON, two full pumps on the throttle then crack it open 1cm, a shout of ‘clear prop’ and pull the starter lever back. She fires and settles at a tad under 1,000rpm, and the oil pressure gauge shows it is flowing above the minimum of 2.5pz. We sit and wait for her to warm up.

The power check is conducted at 1,800rpm, and we wind back and forth two pitch changes. Richard confides that the prop pitch doesn’t, in reality, make a great deal of difference! The acceptable mag drop is a difference of 50rpm. Carburettor ‘frosting’ (the check list’s charming translation) is checked, and tick over rpm restored. Idle is fine, so back to 1,000.

Taxy, take-off and climb

Taxying by myself in the right-hand deckchair backed seat is a forlorn attempt. Having been given control with a judiciously safe and large open area in front of the Nord’s nose, all attempts at S turning with only rudder pedals and no brakes had absolutely no effect, other than promoting slight anxiety for me. A burst of power can usually vitalise the rudders to swing a castoring tailwheel, but no, as I assumed, the twin rudders were not affected by the slipstream. I closed the throttle, rolled to a stop and handed control back to Richard. Perhaps with a strong wind flowing over the rudders then the right seater might have a modicum of control, but otherwise no way. The book figures for the take-off roll to 40kt, with flaps on the second notch, is around the 200-metre mark, bearing in mind we were operating from grass, with its greater drag. Then accelerate in ground effect and climb away at 60kt. To clear a 15m object ahead we need a further 150m. We are burning fuel at a prodigious rate of 57 litres an hour at 2,500rpm, time to throttle back, cut the corner, and catch the camera ship. The best rate of climb with full power and the optimum speed of 60kt is 984ft per min, or as stated, 5 m/s. In general, and slightly optimistic, just multiply

metres per second by 20, which in this example gives 1,000ft per min. Not too far adrift.

General handling

Set in the recommended cruise of 75pz manifold pressure and 2,180rpm we are trimmed out showing an indicated speed of 90kt while burning 36 lph. We have a marvellous view of the world, both ahead and to the side, and above and below the shoulder wing. And had we a radio operator in the third, back seat, although he couldn't see quite as much as us, the rear perspex comes right to the base of the fuselage.

Richard had previously warned me that the ailerons are slightly heavier than one might expect, otherwise I would have thought we had a lot of ‘stiction’ within the circuitry. Admittedly there is little or no aileron drag, but the ailerons are definitely heavy. In relation to the other controls the pitch functions well, and yaw with rudders in free air which would normally be of a higher value, is less than the force needed for rolling with ailerons. So, what is usual in harmony terms for values of aileron:elevator:rudder of the ideal values of 1:2:4, the Norvigie has an order of elevator:rudder:ailerons – but I would struggle to place values on them. However, this unusual trait doesn’t take long to overcome and internalise, you accept the force and live with it. It is what it is, it’s just different. Something else that is different was to find a G meter on the panel for an aircraft specifically intended for the observation role. However, it limits the stick force to 2.89G, and when you consider that to sustain a 60° balanced turn the aircraft is experiencing 2G, in effect this limitation prevents the pilot from bank angles exceeding 69° (3G is felt at 70.6°). So, overly steep turns are not on the agenda today.

A stable aeroplane

It probably comes as no surprise that Whisky Romeo is stable in all three axes, after all she is a spotter aeroplane. She responds well to starting points for the phugoid hunt of either nose up or down, swapping speed for height and height for speed as the trimmed speed is recaught and she is settled again in stable, level flight. Releasing from a steady heading side-slip with crossed controls, first those double deckered ailerons show lateral stability and a return to wings level, and the nose swings back into alignment with the Below No, proud owner Richard Ellingworth isn’t 5ft 2in, this is one big aeroplane. twin rudders being released. It is all gratifyingly textbook.

Those ailerons work right up to the stall, at which just at the beginning edge, the incipient hint, there is a shudder and then a goodly rate of sink, all very predictable behaviour. The standard stall recovery works splendidly, both clean and in the approach configuration. The upper flap limiting speed is 75kt and the stall is in the mid 40s so there is plenty of time to apply and balance power with accurate anticipatory footwork and then retract that drag flap.

I later read, unsurprisingly, that intentional spinning is prohibited, but it was obviously part of its original test flying as the pilot’s operating handbook advises a nonstandard recovery technique. After closing the throttle, apply the opposite rudder to the direction of rotation (good so far) but then just centralise the stick without pushing it forward and waiting. The standard is to ease the stick forward, with neutral ailerons, until the spin stops, then exit the steep dive. I am also intrigued by the prospect of twin unmasked fins and twin working rudders engulfed in free air without the hindrance of a shielding tailplane. Unfortunately I can only wonder.

Landing

Richard generously allowed me the landing, brave fellow. The approach was made with three stages of flap at 55kt (just above 1.3 of the stall speed), with the prop wound anti-clockwise to fine. Should we have experienced an engine failure during the detail, then the glide speed is at 55kt with coarse pitch wound on clockwise. Book figures to clear that 15m tree, or any other obstruction coming in and landing, is 350m with a ground roll the same as the take-off run. Crosswind limit is high at 20kt, but we had no real wind to speak of, although I am sure a pair of feet were hovering over the brakes in the left-hand seat. She paid out nicely and the flare height is just a tad higher than an Auster or Cub, seeing our seats are that little bit higher in this Nord. She ran straight and true. To say I enjoyed flying this rare bird is an understatement. I enjoyed discovering so many little idiosyncratic features and, when airborne, to be able to hover around David’s Pacer over such scenic countryside, with Neil capturing our antics and then to be let free to see how she behaved, was a real treat. Thankyou Richard for your time and generosity. ■

Bulldog Model 120 Nord NC856A Norvigie

General characteristics

Crew: Two +1 Length: 7.3m (24ft 0in) Wingspan: 12.2m (40ft 0in) Height: 2.1m (7ft 0in) Wing area: 17.0 m2 (183 sq ft) Empty weight: 651kg (1,432lb) Gross weight: 902kg (1,984lb) Powerplant: 1 × Regnier 4L.O4 four-cylinder air cooled inverted inline engine, 104 kW (140 hp)

Performance

Maximum speed: 189km/h (118mph, 103kn) Cruise speed: 170km/h (106mph, 92kn) Stall speed: 7 km/h (43.5mph, 37.8kn) Endurance: Three hours Rate of climb: 5.0m/s (984ft/min)