Airtest – Aerospatiale AS355F Twin Squirrel

Rex’s GM went so far as to say, during a handover ceremony in Sydney, that helicopter utilisation by private companies and government authorities in Australia is expected to significantly increase in the next three to five years.

His justification is beyond fault; we in Australia are reaching saturation point in the fixed-wing light aircraft field. There is an indefinable but undeniable tendency to go for light/medium twins these days, in times of selective investment by consumers.

The proliferation of airfields, strips, and landing areas, are sufficient to take care of fixed-wing needs for years to come, as lighting becomes more sophisticated and performance improves in the landing/take-off footage demands.

AUSTRALIAN AVIATION predicts that the helicopter will come more into its own in this decade. It ·will be a long-term pull; there will be no overnight miracle. It will have to go as far back as constructing buildings in cities with a genuine rooftop helipad capability.

For example, most of Sydney’s existing buildings haven’t got the pavement strength to take a chopper – even one as light as this new Gallic export which boasts a couple of Allison 250 C 20 F turbines.

David Irons forecasts that the Aerospatial range will really shine in relatively short flight capability and flexibility, using the 100-150 nm range envelope from a point of departure.

‘Helo operations around Sydney and Melbourne, and other major decentralised locations, by private companies, will increase as service time from conventional transport becomes uneconomically longer,’ says Irons.

‘It’s simply too inefficient. . . ‘ And those companies that operate corporate aircraft and don’t provide a time factor for transport to and from airfields will bear that out.

Following up this line of thought would indicate that many companies will go for a double-header – a corporate twin in the medium/heavy turbine range, plus a helicopter such as Rex’s new Ecureuil AS 355 F. It isn’t as fanciful as one might think for operations within a nation such as Australia, although there could be minor positioning problems to overcome.

Back to the new Twin Squirrel. (The French translation, Ecureui/, is pronounced ‘E-cue-ray’ . ) The first one has already been sold to New World Aviation, a division of New World Properties. New World has already ordered a second Twin Squirrel, for development as a corporate/charter machine based in Sydney.

The first aircraft has already arrived – and it’s a stunning progression from the single-engine Squirrel AUSTRALIAN AVIATION evaluated in 1979. The second AS 355 arrived in August, and the third in November this year.

Helicopter Manager for Rex Aviation, ex-Army QFI Ian Paull, is enthusiastic about this new Twin Squirrel, as are his Rex helicopter division colleagues Terry Summers and Leon Kippin, also ex-Army helicopter instructors with numerous qualifications to their names.

His pre-evaluation briefing brought to light the fact that ·Rex don’t bother about containerising their choppers from Marignane these days – a wise move, alas, because of the uncertainty of assured dockside unloading dates in Australian ports. They airfreight them out. . .

A lead time of only two days is needed to get the Twin Squirrels (and the smaller single-engined Ecureuil) to the other side of the world. Lead time on actual delivery after order placement remains a respectable six months – such is the demand for Aerospatiale’s products.

To back up their product marketing, Rex have instituted a special school for training customers or their corporate pilots on type, on-site. The establishment is compact, set up in a portable building alongside Rex’s already well-known fixed-wing school.

The rotary wing conversion school doesn’t set out to produce qualified helicopter pilots overnight; if a rotary wing pilot is already conversant and proven on helicopters, has a minimum of 1000 hours – 500 of them on turbines, he would be put through the wringer before he would be deemed competent.

‘To be anywhere near competent, he would go through 30 hours in our ground school,’ says Rex chief helicopter instructor Terry Summers (see Interview, page 92). And integrated within this budding ‘twin’ pilot would go through thorough operational flight training.

Good insurance when one considers the sophistication and dual systems (plus two Allisons) packed into what is basically a Squirrel airframe. As we mentioned, the helicopter division personnel are ex-service pilots, trained and qualified to instruct in what could be considered the hardest school of all – military operations.

Ian Paull, who heads up the division as Manager and chief helicopter pilot, has ten years of Army experience behind him, in Kiowas, Iroquois and Sioux, plus the title of QFI (Qualified Flying Instructor). Terry Summers has a Kiowa/Sioux background, plus a stint on Gazelles whilst at the Central Flying School in Shawbury, England, during attachment to the British Army. He is also a QFI.

Additionally, over recent years, all three instructors have gained a great deal of experience with regard to helicopter training requirements and operational applications, within the industry.

Rex helicopter personnel have themselves a detailed and very searching checkout at Aerospatiale’s Marignane base, flying the Twin Squirrel to the uttermost limits of its performance envelope.

Between them, they also cover demonstration work, with Terry heading the flying training side of the operation as an extra ‘hat’.

Terry Summers also has another task – that of customising helicopter training courses to individual client requirements.

It is thus apparent that between the three helicopter division pilots (Ian Paull trained with the US Army, and Terry and Leon both trained in the UK as part of their Army experience), Rex Aviation has a wealth of experience and knowledge on which to call, to sell and prove this new addition to Rex’s Aerospatiale range of rotary wing types.

The aircraft they are marketing, the AS 355 F, represents perhaps the known limit of twin-engine light helicopter development and design, which can still fall into the light helicopter bracket. (The Twin Squirrel has an all-up weight of 2300 kg. )

With most of the already-proven AS 350 Ecureuil design features built into its construction, the twin-Allison AS 355 is an all-around winner in terms of performance, range and downright economy.

General characteristics include (when considering a Twin Squirrel as a working investment), passenger/transport (single pilot and five passengers in the standard version, single pilot and four passengers in what the French with typical wit call the comfort version), casevac (single pilot plus one/two stretcher patients with one/two medics); and cargo-carrying (single pilot plus 2. 16 cubic metres load in the cabin).

The main rotor transmission limits twin engine (max. continuous) operations to 73% torque per engine. This adds up to a 643 SHP capability. The max. Continuous torque with one engine inoperative is 100%, which corresponds to 439 SHP per engine at a rotor speed of 394 rpm. In addition, a transient limit of 112% is available for 16 seconds with one engine inoperative.

As ambient temperature and altitude increase, exhaust gas temperature (T4) becomes the limiting factor. Maximum T4 on takeoff (two engines) is 810°C for 5 minutes and the max continuous limit is 738°C. Max. Continuous with one engine inoperative is 810°C and 899°C is available for a max. Transient of 12 seconds.

What this all means is that in normal twin-engine operations the Allisons are not working very hard and more significantly the Twin Squirrel is not power limited at a max. takeoff weight of 2500 kg (for external loads), up to 40°C and 2000 feet pressure altitude.

In addition, the aircraft’s performance margins allows single engine accountability (i. e. guaranteed safety if one engine should fail) during the takeoff and approach phase at its maximum (internal load) takeoff weight of 2300 kg with mean sea level air temperatures up to 38°C!

While the Twin Squirrel shows many identical characteristics to its smaller brother, the Single Squirrel, the twin-engine version exhibits what one would expect in terms of empty weight – 1300 kg as against the smaller Squirrel’s 1130. But the benefits of IFR flight, enhanced performance and range (and that includes about 150 more pounds of fuel than the little Squirrel) speak for themselves . . .

General performance figures are a revelation, wedded to internal cabin comfort, lack of noise and general ease of pilot handling.

The Twin Squirrel shows no vices of any significance, and in fact has remarkable stability in all levels of its normal performance envelope. The French design experts have balanced this desirable characteristic against the need for high manoeuvrability (control power), which has been attained through the latest technology incorporated in its ‘Starflex’ main rotor hub design.

One built-in asset AUSTRALIAN AVIATION explored fully during the 1979 AS 350 evaluation was the efficient way in which the vertical fin design reduced the tail rotor’s workload in damping out torque reaction.

In the Twin Squirrel, the camber on the vertical fin has been increased, further enhancing this feature.

With all these innovations and working features, it’s little wonder that the Australian Department of Aviation had something of a head-scratching job to slot the Twin Squirrel into Australia’s existing legislation. Apparently, Transport Australia had never had to fit a type like this into the legalities of single-engine operations in this country – a light helicopter with two engines . . .

And remember the Twin Squirrel entered Australia already certified to FAR 27 (below 2750 kg) requirements, as laid down by the FAA.

Performance figures checked out during the AUSTRALIAN AVIATION evaluation were in most cases better than the Manual.

VNE (never exceed speed) was steady on 147 knots in the midweight category (about 2100 kg). Fast cruise speed with remarkably low noise level and lack of vibration read-out at 131 knots — Ian Paull claims just over an hour from Canberra to Sydney under fast cruise readings.

Fuel consumption at fast cruise checked out at around 3. 31 pounds/nm. The recommended cruise is listed as 3. 205 lbs/nm.

Rate of climb under ISA conditions is given as a healthy 1830 fpm, thanks to the two powerful Allisons.

The maximum range without reserve and at recommended cruise speed settings is given as 416 nm at mid-weight.

In ISA, with a 17-knot crosswind coming from the left, the Twin Squirrel has a hover ceiling in ground effect at takeoff power of 9850 ft. In ISA plus 20, that figure is still a respectable 7550 ft. Out of ground effect (nil crosswind), the hover ceiling at takeoff power is pegged at 10,700 ft, and in ISA plus 20 it still comes out at a comfortable 8200 ft. Which is probably why Rex is marketing the AS 355 F with such confidence, and why customer interest is so marked even at this relatively early stage of the Australian marketing campaign. (Incidentally, the 350 and Big Brother 355 are the first French helicopters from Aerospatiale to be sold through a conventional distributor/dealer network – another pointer to growing interest by France in Australasian sales. )

Service ceiling of the 355 F is 16,000 ft with a 200 ft/min gain margin.

Usable fuel is given as 193 galls/US in standard tankage, plus an optional 126 galls/US in a ferry tank.

Before the evaluation sortie, AUSTRALIAN AVIATION was given more clues on why the Aerospatiale product is such a natural winner:

Basically, it’s the result of a welding together of two main assets – Ecureuil technology and reliable powerplants.

The technology: first, the airframe uses a heap of new, lightweight and corrosion-proof materials. The 355’s rotor blades are of a wider chord than its little brother, otherwise one is looking at the same basic airframe.

The Starflex rotor head – which we featured in the earlier Squirrel evaluation and detailed the cut-down of working parts made possible by advanced technology. This in turn made for almost. Continuous maintenance-free hours. The Starflex system, as is well known, features pitch, drag and flap movements provided by what Aerospatiale in a somewhat laboured fashion call wholly constitutive composite materials.

Modularity – although we hated the translation – is another feature of Aerospatiale’s brilliant design follow-up. So is the addition of an intermediate combining gearbox between the twin Allisons and the MGB (main gearbox).

Reliable powerplants: A combination of power, lightness and trouble-free operation, the Allison 250 20 F have up to 20 million hours’ experience on engine type behind them. It’s pretty basic to point out that this type of powerplant is eminently suited to the ever-changing needs of business aviation, also that it has that little extra up its sleeve in times of emergency. In fact, with one engine out, it’s perfectly permissible to keep the ‘live’ engine going at full 100% torque to the nearest alighting area.

Cabin layout is typically French – carried out with flair and design brilliance echoing that ‘something different’ we saw during an evaluation of yet another Aerospatiale product – the delightful little fixed-wing Tobago, some years back.

The instrumentation on the standard aircraft is full enough to satisfy even the most fastidious pilot. The Allisons mounted aft of the cabin are fitted with four chip detectors with a tell-tale on the warning panel, torque measurement pickups, air intake screens.

The transmission system is anti-vibration mounted with great efficiency and effect. Drive includes two engine-to-main-gearbox coupling shafts. The tail drive is carried by no less than six antifriction bearings.

Other specifications on your standard Twin Squirrel include that famous Starflex head with three composite material blades of wide chord and tested to work efficiently even if one has a notion to fire a bullet through a blade or two. The tail rotor is also built of composites.

The actual cabin is floored in light alloy sheet metal, and features pilot and co-pilot seats with height and reach adjustability, and behind them are a brace of two-place bench seats – depending on whether you go for the increased seating options.

Pilot and co-pilot doors are jettisonable and boast sliding windows. A polycarbonate double wall forms the ventilation and air conditioning ducts and also double as a ceiling to the main cabin.

As we mentioned, the options are legion . . .

The exchange value of the French franc at the time of our evaluation made the Twin Squirrel a really good buy; although Rex was reasonably cagey about quoting exact figures, it appeared at that time the price of a VFR to Australian standards Twin Squirrel, airfreighted to Australia, would be around the $650,000 mark. Equipped to IFR standards, the price is expected rises to around $840,000. And that is with the cabin equipped to VIP interior configuration.

Options also include a two- or three-axis autopilot; emergency flotation gear; skis; a sand-prevention filter fitted to each air intake; left and/or right sliding doors; and an exterior mirror for those pilots who don’t follow the technique of flying the load on the sling by looking out of the window or flying by r/t directions from the ground.

In operating, the drills are near enough to standard for turbines; booster pump on, pressure correct; Ng increase observed after operating the starter, and when Ng (gas generator rotational speed) increases to 15 per cent put the fuel flow lever into the Start gate, monitoring Ng, exhaust gas temperature (T4), engine oil temperature NR/Nf, torque.

Let the Start button go when Ng reaches 60 per cent and slowly advance fuel flow lever into Flight gate mode. Generators and alternators on after starting each engine.

Noise levels and vibration were low in all phases of ground and flight operation. On takeoff after checks, the drill is to initially hover in ground effect and synchronise engines by using trim. Forward flight was initiated in a slight climb, according to Manual recommendations, with IAS rising to about 55 kts.

Visibility, ease of control access and instrumentation layout got top marks from AUSTRALIAN AVIATION’S team. As we put the Twin Squirrel into cruise, we followed the Manual’s recommendations by going for maximum range, i. e. 120 knots TAS at MSL at MTOW (reducing max. continuous by about 10 per cent). If one goes for max. endurance, it means a healthy slice out of the IAS bracket- reducing to the optimum climbing speed of 55 on the clock.

Engine failure- this is a breeze with the power in hand from the Allisons.

After determining which is the ‘dead’ engine you shut off the relevant systems, rest assured that the remaining Allison is equal to the load; it carries on as if the other engine wasn’t wanted anyway . . .

It’s best to make sure you don’t go past the 100 knots mark on one engine, just to prevent the turbine from turning when the engine is shut down.

Tail rotor malfunctions are serious, but the camber on the Twin Squirrel’s vertical tail fin reduces rotation to a marked degree.

Normal landings are standard procedure – on the intermediate approach do your checks, then on finals fly about 45 kts IAS, and from the hover reduce pitch slowly and control your landing until the skids contact ground. Then get the collective to full low and other controls to neutral.

The ease of overall operation, pilot and passenger comfort plus low noise and vibration levels, made AUSTRALIAN AVIATION give the Twin Squirrel a standing ovation, plus a pat on the back for price and economical operation when one considers this type is aimed at the Long Ranger bracket.

Before we end this, it’s worth noting that the Twin Squirrel’s single0engine performance is given as a rate of climb at 4630 lb, of 630 fpm, and a service ceiling of 6600 ft while still notching 200 fpm at takeoff power.

And we endorse Rex Aviation’s claim that the 355, Twin Squirrel or Twinstar depending on your fancy for nomenclature, extends the versatility of the original Squirrel, with reserve power and safety for all types of demands under commercial or charter operations.

It is now up to Australia’s flying businessmen, and commercial and charter operators to recognise the value of this machine in terms of economical intra-city and suburban operations, its real slot in the scheme of business, commerce, heavy-lift, offshore work, government department work. . .

It is a sad commentary but a realistic comment to say that Australia is several years behind the rest of the Western world in terms of advancement when it comes to the proper use of aircraft – fixed or rotary wing- but there are signs of a very real awakening Down Under when it comes to serious consideration of rotary-wing usage, both for business and private flying.