Airtest – Mooney 231 Turbo

One of the most impressive things about the new 231 is its potential in duration and range, flexibility almost throughout the flight spectrum.

With 72 usable galls US on board, the 231 can spend up to eight hours at economy cruise, and speed can notch up to 160kts if you’re venturing into the FL 180-FL 220 envelope. The 231 is new in terms of a longer fuselage than the 201, a longer nose, revamped ventilation and undercarriage cosmetics.

The aircraft’s mechanical heart, a 210hp Teledyne­ Continental TS10-360 motor, is the new Dash-G version made only for Mooney. It features a specially-tuned induction and exhaust system for improved power output, linked with Mooney installation providing even cooling in all flight regimes with minimum drag penalty.

In airframe updating, the people at Kerrville have gone in for control surface tuning in a big way. We were warned before the test flight that the 231 has some nice surprises in store in terms of handling characteristics.

Mooney’s claim that the 231’s controls have been specially tuned and balanced like a fine sports car wasn’t an idle boast. A balanced pitch system with a bigger elevator gave positive and precise rotation on take-off, and from then on gave out a definitely crisp and sporty response without ever giving the impression that the aircraft wanted to get the bit between its teeth and run away with the rider.

Aerodynamically sculptured wingtips help to iron out vortex drag in operation, plus minimising aileron back­ pressure.

The wings themselves are contoured to NACA 632-215 at the wing roots, going out to a NACA 64′-412 at the tips. This combination gives the 231 a delightfully light yet comfortable feel in all sections of its flight envelope.

Airtrame in Mooney’s latest single is the usual robust welded tube steel in the cabin region, covered with an aluminium skin. Push-pull tubes are standard for control surfaces, as usual, and a spring-loaded interconnect indirectly joins ailerons and rudder systems to help lateral control during flight manoeuvres.

A variable downspring in the tail cone plus a bobweight give control force at rest or low speed, to keep a balance of forces.

Other significant parts of the new 231 include chrome/ molybdenum tubular steel main undercarriage legs retracted by an electrical gear operating mechanism.

One of the biggest surprises on opening the lid in the test aircraft was to behold the diminutive size of the turbo­ charger. The complete works – turbine and compressor assembly, waste-gate hose and ducting are just about as compact as human engineering can devise.

Although Mooney hasn’t come right out and said so in bald, unequivocal terms, the 231 and all its assets are aimed quite obviously at the Bonanza and Turbo Arrow family.

But to balance any mud-throwing, Kerrville’s PR Division urges buyers to consult a Mooney-made guide to speeds, roe readings, cabin width, base prices and other factors.

From the data, it appears that the 231 has the edge on or equals most of the Turbo Arrow, Arrow Ill, Skylane RG and Bonanza F33A figures in many departments.

For some unknown reason, Mooney has included the magnificent Turbo Centurion which, to be fair, is in a class of its own in many respects . . .

Be all this as it may, the 231 stands proud in many respects and is indeed an aircraft for all seasons and reasons for many Australian consumers.

Once again, the Mooney 231’s actual cabin width (43. Sin) was belied by the slim lines outside. There’s plenty of room inside the beast, verified by our back-seat crew. The two front-seat occupants have the same room, Mooney having again provided that sports-car design where one sits closer to the panel than in other types, with most of the person underneath the panel than in front of it.

The aircraft under test, the first of its type in Australia at the time of testing, bore a serial number indicating that it was the 154th to roll out of Kerrville and was pegged at the time of evaluation at $A75,000, full IFR and on Australian register.

There was about a three-month lead time on orders at the time of AADR’s test evaluation, according to Adams Aviation’s Ron Murn who flew the right-hand seat for our check.

Mooney’s superlative finish and engineering were immediately apparent during the walkaround. Among numerous cosmetic treatments was the 231’s new-type fuel locking cap with a spring-loaded flap underneath to prevent siphoning in flight should one be unfortunate enough to lose a fuel cap while airborne.

Inside the test aircraft, more surprises . . . the usual contoured seating, finished in a wide choice of either genuine leather, fabrics or vinyl, was set off by innovations for both pilot and passengers.

Airline-style overhead ventilation for passengers is both quieter and more efficient than earlier systems, fed from ram air inlets set on the vertical stabiliser fillet.

Front-seat occupants are faced with what Mooney call their New Dimension panel, featuring a wrap-around design placing all priority flight controls and instruments with easy eyeball range and reach.

One new thing we liked was the refacing of the tacho, combined with a re-alignment of the manifold pressure gauge and fuel flow indicator. All indicators align straight up and down when MP, fuel flow and rpm are normal on take-off to allow the pilot to monitor at a glance.

Pre-start evaluation in terms of external and internal finish, accessibility, visibility, legroom, air and actual seating was either Above Average or Excellent on our checklist. Emplaning and deplaning physical acrobatics got Average . . .

Starting the 1400hrs TBO Continental was a standard fuel­ injection drill. Throttle quarter open, prop pitch fine, rich mixture, Master ON, prime for three to five seconds.

With a very low noise factor filtering in, the throttle was initially set at 1000rpm while we took in more data.

Maximum continuous rating is 210bhp at 2700rpm, 40 in manifold pressure, driving a McCauley 74in constant speed prop. Vne Is carded at 225kts IAS, Vno at 200, Va (manoeuvring) 137, Vfe 128, Vie 152, Vlo 152.

Weight on leaving the ramp at Adams Aviation threading our way through smaller Money, Lakes and assorted aircraft on the life, was just about max AUW of 2900Ib. The only thing missing was the 120Ib baggage component.

Foot loads were moderate, becoming less as ground speed increased and making it possible to initiate the publicised 41ft turning radius thanks to the nose wheel’s + 14 degrees travel on each side of the centreline scope.

En route to the holding point, Ron Mum mentioned that one can peg fuel consumption back to an incredible 8 galls US/hr with 65 per cent settings of 30/2300 at 4000ft, with turbine inlet temperature (TIT) sitting halfway up the scale.

This was actually achieved during the evaluation, without undue juggling or wizardry.

Checks over, including cycling the 33-degree maximum flaps, we lined up with OAT hitting the + 20C mark.

The take-off run was marked by a lack of significant torque, a working example of that easy-scan panel, and crisp acceleration which quickly built up to Yr of 65kts IAS.

The test aircraft left the ground smoothly under quiet back-pressure at 67 indicated, rocketing up into an initial 1500fpm rate of climb while the undercard was cycled up.

Settings were eased back from max continuous to 30/2500 during a left turn and roe settled on 1100fpm, slightly above the manual’s 1080fpm at. sea level. At this stage, our passengers began commenting on low noise levels and excellent visibility in the test Mooney, with front-seat occupants doing the same.

Checking our test report form, we initiated “Negligible” in the pitch change section for undercarriage, and noted that wheels should be up before 104 knots indicated.

The climb rate remained constant while manual settings of 40/2700 were applied, to check roe. The figure of 96-113 knots was bettered while the rate of climb likewise was topped despite the check aircraft being as near gross as could be calculated.

Getting the test aircraft on the step at 75 per cent settings proved a no-height-loss exercise, and she sat there at knots better than the carded 182 knots IAS, with 4000ft of patchily turbulent fresh air under her 174. 8sq ft of wing area.

Fuel flow at those settings worked out to about 11. 3gph US. Bringing back the settings to 55 per cent gave us the booked 156 knots IAS, with fuel flow coming back to 8. 7gph US. At that combination, nil reserve, we could have spanned fully 1182 nautical miles – more, if a flight plan took advantage of upper air winds and the occupants of trade-plate Foxtrot India X-ray had oxygen equipment on board.

These facts immediately lent solid proof to Mooney’s claim for a long-legged beastie with almost an airborne camel’s capability to do without liquid fuel for considerable periods.

Stalls were performed as a matter of manoeuvre. A stall in landing configuration brought about a fore-and-aft pitch at SSkts IAS without a definite break or wing drop. Mooney’s manual lists a dirty stall occurring at just above 57kts.

Normal manoeuvres proved things of minimum pilot input, with the aileron-rudder interconnect proving its worth in all but tight turns.

The old, old man that Mooney has a tail wag just doesn’t wash any more with this Supe:~Mooney – in fact, it hasn’t been valid for years. Point the 231 at a given datum, trim it for hands-off flight and sit back and relax, do your nav, knitting or whatever; the 231 will do the rest.

With a service/operational ceiling of 24,000ft, the 231 is a natural for longer flights, and could even give some of the jets a run for their money when it comes to distance.

Maximum speed is listed as 201 knots, and with the test flight’s OAT and height, was right on the money at max gross.

Sample readings and settings at various heights include:

18,000ft, best economy (26/2500), 20mpg/US, and IAS of 170kts, under!SA conditions.

Come down to 12,000ft set up the best economy and you should get an IAS of 172kts and a fuel consumption of 17. 7mpg/US.

At 8000ft, the best economy looks for 17. 4mpg/US and an indicated air speed of around 166 knots.

Mind you, the 231 comes out relatively poorly in the payload stakes on a sample 95-mile trip at, say, 12,000ft. The payload figure is 685Ib, compared with the Turbo Arrow’s 744Ib and the Skylane RG’s 948Ib.

While on comparisons, Mooney claims their 231 and 201 have a wider cabin than any comparable single bar the 182RG and Bonanza. The only serious competitor in November ’78 prices in the pocket-book department are the Arrow 111 and its Turbo-sister.

Circuit work in the test aircraft was approached cautiously, but we needn’t have worried. Unless speed is lowered to the point where a sink rate sets in, the 231 is joss itself to operate in and around the circuit.

In the Hoxton Park touch-and gos, downwind was negotiated at 80 knots IAS, with the undercarriage hung out early to help slow for circuit entry (Vie and Vlo are identical at 152 knots).

First-stage flap produced moderate pitch change, easily corrected with wheel-mounted trim. Base and the turn to finals were also made at 80 on the clock, with speed coming back to the 70 mark as the 231 settled into rock-steady finals.

With the flap coming down progressively, controls delightfully responsive and everything in the green, indicated airspeed came back to 65 over the fence, with a touch made at 60 indicated.

Go-round power application produced the expected instant response.

Back at Bankstown after a full workout, a further conference with passengers produced the repeated response that this is an aircraft in which one could spend all day – or at least, as long as the fuel lasted.

And with 72 galls/US usable, that’s likely to be quite some time with proper flight planning and in-flight housekeeping.

As a high-performance retractable, the Mooney 231/M20K is in many respects the ultimate for long-distance pilots. In fact, Kerrville’s PR Department make the claim that in terms of speed, performance and economy no other turbo comes close to matching the 231.

AADR endorses that claim and adds that although the 231 is a pilot’s aircraft there’s a lot to be said for passenger comfort in the structure.

We expect one of the mods soon to be available for Australian pilots will be radar; many singles are being offered with this innovation and AADR can’t see Mooney or Adams Aviation lagging behind the rest of the field in this department.

The lead build-up by Mooney in fuel efficiency is too valuable to be wasted . . .

Data Box

Mooney 231 M20K:

Single engine four-place turbo­ charged low wing type, retractable undercarriage, medium/long range performance. Private/small corporate type.

Price

of aircraft tested, with extensive avionics, $75,000 at the time of evaluation. Aircraft evaluated supplied by Adams Aviation, Bankstown, NSW. Telephone (02) 707 2770.

Specifications:

Gross weight 2900Ib; empty 1800Ib. Useful load, 1100Ib. Baggage capacity 120Ib. Wing area 174. 8ft. Wing loading 16. 6lb/sq ft. Aspect ratio 7:558. Power loading 13. 8Ib/hp. Wingspan 36ft 1in. Length 25ft Sin. Height 8ft 3in.

Engine: Teledyne-Continental TS10-360-GB fuel-injected turbocharged six-cylinder horizontally opposed. Recommended TBO 1400hrs. Max continuous rating 210 bhp/2700rpm/40in manifold. Usable fuel 73 galls/US. Total 80 galls/US.

Propeller:

McCauley 74in constant speed with hydraulics by engine oil.

Cabin:

width 43. Sin; length 114in; max height 44. Sin.

Limiting data:

Vne 225kts IAS; VNO 220; Va (manoeuvring) 137; Vfe 128; Vie 152; Vlo 152 (white arc on ASI, full flap operating range 58-109; green arc 63-174 normal operating range).

Performance:

(figures for ISA conditions, plus/minus three per cent): max speed 201kts. Cruise 75 per cent power, 182kts. Range 75 per cent power, nil reserve, 1063nm. Fuel flow/mpg, 75 per cent power, 18. 6 mpg/US. Cruise at 55 per cent, 156kts IAS. Fuel flow/mpg, 55 per cent, 21 mpg/US. Range 55 per cent, nil reserve, 1182nm. Rate of climb, sea level 1080fpm. Stall in dirty condition, power off, 66mph/57. Skts. Operational ceiling 24,000ft.