Pilot report - Piper Aztec

[Reprinted from Fliteguide / Imperial Aviation]


Those who take an interest in light aircraft history will know that the industry was formed by a collection of perverse and idiosyncratic characters. Each one was to stamp their personal ethos onto the aircraft we fly today. Walter and Olive Beech were just as comfortable with the cut and thrust of post-depression business as they were mixing it with high society. When Walter died in 1950, the slim, attractive and astute Olive took over the company's helm to steer it successfully into the booming sixties and seventies. Dwane Cessna, who had studied aeronautical engineering at Wichita University, reactivated his uncle Clyde's aircraft factory in 1934. He then gave the company a strong engineering core by employing two of his class mates; Tom Salter and Jerry Gerteis who became largely responsible for Cessna's wide and diverse range of light planes. It was this engineering strength that led Cessna into developing structurally innovative aeroplanes, in particular the 337 Skymaster, and cantilever wing 210.

Piper was led by the unprepossessing and homespun 'W.T.' Piper who happened to produce five sons, one of whom, Howard, was to be responsible for moving a reluctant company into the modern age. If it had not been for Howard 'Pug' Piper, the company would probably have died producing antiquated Cubs and Tri-Pacers. It was Howard who recognized the huge advances made in all metal construction methods by the end World War Two. With a wary eye on the celebrated 'V-tail' Bonanza, Pug could not persuade his old man to develop the company's four-seat PA-6 Sky Sedan beyond two prototypes and the project was cancelled in 1947. Pug's next opportunity to drag the company away from tube and fabric aircraft came in the early fifties when it became clear that a more sophisticated market was demanding business aircraft - preferably with two engine safety.

Piper's conservative engineering standards came from WT Piper's disinterest in the subject. Pug too was not an engineer but he was a great conceptual thinker and doer. Moreover, the company, unlike Beech and Cessna, had no previous experience in building twins. In fact Piper thought it a good idea to buy in a design, especially as Beech had just launched their Model-50 Twin Bonanza. If WT was a reluctant engineer, he was extremely adept with figures and quickly realized that his bought-in design would be too expensive to produce for the customers he had in mind. The company resolved to begin with a clean sheet design and in 1952 flew their prototype model 23-01 Apache. It was to be the first of Piper's Indians.

By industry standards, the Apache was not a technological leap. The fuselage was constructed of steel tubing and initially covered with fabric. It also had twin fins similar to those on the Beech 18. High single-engine rudder forces quickly forced a change to a single vertical stabiliser taken straight from the cancelled Sky Sedan. Despite a dealer network that was reluctant to sell a Piper for so much money, the Apache was launched in 1953, selling for an unprecedented (for Piper) US$32,500. The aircraft began to sell immediately, especially as Cessna's 310 cost US$17,000 more and the Twin Bonanza a huge US$38,000 more. In fact, Piper struggled to keep up with demand. Although the Apache was a great deal slower than a 310, it did benefit from extremely benign handling and quickly established a reputation for safety Thus, when customers began to clamour for more power, speed and payload, the Apache's replacement, the Aztec, proved just as popular.

So successful was the Apache that Piper's basic design was almost entirely carried over to the new twin and early examples are difficult to identify from a distance. The most noticeable change was the modestly swept back vertical stabiliser, larger fuselage and longer engine nacelles which housed a pair of 250 horsepower IO-540 six-cylinder Lycomings. Piper continued marketing the Apache which in 1962 adopted the Aztec airframe but used a pair of 235 horsepower O-540 Lycomings. The Apache was finally dropped in 1965.

First Aztec deliveries took place in 1959. These early models shared the Apache's short nose but its bigger fuselage carried space for six occupants and the larger engines boosted speed to 205 mph in the cruise. A number of variants followed beginning with long-nose B models in 1961 and it was in this shape that Aztec production finally came to an end with the F model in 1981. From the 1964 model C, turbocharging was offered.

Flying the Aztec

Although production had only stopped less than a decade earlier, by the late eighties, Aztec's were already considered old and expensive and were often to be found derelict around various Gauteng airfields. Many South African aircraft had led tough lives as charter aircraft and by the time their useful life had expired, some were to be found providing a seemingly cheap step into the heady realms of multi-engine flying. Pristine examples were rare and many of the aircraft still flying were showing signs of their age. It was in one of the latter aircraft that I completed my multi-engine rating and whoever owns ZS-MBG nowadays is welcome to call me - I have some interesting tales to tell, especially concerning an adventurous holiday to Malawi which tested the very limits of my patience and ingenuity.

I will never forget staring at the decrepit innards of the valve technology avionics scattered across the bench of Air Malawi's radio repair shop! So it was with great affection that I settled into Daniel Coetzer's pristine E-model Aztec, ZS-OFR, which he had rescued from almost certain dereliction after a hard life as a Kenyan charter hack. Like many Aztecs, Daniel's aircraft was bought cheap and has had a great deal of care lavished on the engines, airframe and interior to bring the aircraft back to its former glory. Both OFR's hefty Lycoming engines were fresh out of a top quality Alton Engineering overhaul with less than ten hours running time on them. IO-540 overhauls are not cheap but Daniel had spared no expense in having them worked on and even ordered a full set of Millennium Cylinders. The IO-540 should be worthy of its 2000 hour TBO and indeed the engine has a good record for easily reaching this limit.

However, over the years, with many engines on their second, third and sometimes fourth overhaul, and often suffering on-condition component replacement, these engines often need a top overhaul at midlife. Thus, Daniel approached his overhauls with a clean-sheet wish to have the best available.

Being a perfectionist, it wasn't only the engines that received Daniel's attention. OFR's interior was completely refurbished along with the panel. Sitting proudly in the centre avionics stack is a shiny new Garmin 430 combined VHF and GPS. The Aztec's panel was never a masterpiece of ergonomic purity and the Garmin does clash somewhat with an ancient King Analogue ADF, a remote DME and various other items which in the sixties were considered state of the art. However, in Daniel's aircraft, all of it works including the Altimatic-5 autopilot and a more modern King slaved HSI. There is further evidence of Piper's old hodge-podge approach to panel design. The system switches are lined up on the lower left, above the pilot's knees and the engine start buttons as well as magneto rocker switches are attached to the left side of the cabin, this time just above the pilot's left knee. The gauges are all lined up along the top of the right panel in a way that manages to destroy any semblance of aesthetic symmetry. Below the power lever quadrant is the flap and undercarriage lever with two cowl flap levers in between - behind which sits the all important hydraulic power pack driven by a pump on the left engine. The primary emergency pump lever snuggles below. I'm not sure of Piper's thinking at the time but would hazard a guess that this layout helped to create a flat floor making it easy for the pilot to slide across to his seat. The most glaring omission is the absence of any rudder or elevator trim controls. These are mounted horizontally on the roof and until the early eighties remained a quaint if slightly illogical feature of early Pipers.

Make no mistake; the Aztec's cabin is big. Early publicity photographs showed be-hatted pilots beaming languidly from behind the panel. Settling in must be like getting into your old family Chev during the sixties.

A tubular airframe is never easy to hide behind cabin trimming without having a great deal of space between the interior trim and exterior aluminium skin. The Aztec is typical of this as evidenced by the window sills and airframe tubing that protrudes from the cabin roof into the top of the instrument panel.

The fuel selectors are located between the front seats and the system is simplicity itself. There are two tanks per wing, though an optional long range system was sometimes installed in the wing tips. OFR has standard tankage with a capacity of 144 gallons. The entire contents are available for crossfeed in the event of an engine shut down.

The two Lycomings start easily from cold with the left hand engine being started first so that hydraulic power is available soonest. Pre-takeoff checks are entirely conventional save for Piper's unusual recommendation that the mixture is not leaned off below 5,000 feet. In most light aircraft, this procedure is carried out above 3,000 feet. A glance at the two roof-mounted trim indicators is amongst the last 'full-and-free' final checks before lining up on the runway. At this point, a wise twin pilot will be thinking of the all important critical takeoff speeds so that he is ready to make some fast decisions in the event of an engine failure. Like the Apache, the Aztec is a kindly aircraft, but like all twins requires decisive handling under asymmetric conditions. The aircraft responds quickly to full power application and accelerates to its rotation speed with a firm and reassuring push in the back. With a constant backpressure on the control column the aircraft lifts off at just over 70 miles per hour and as soon as an aborted takeoff is no longer an option the gear is retracted as well as any flap. The minimum single engine speed is an extremely low 80 mph and the Aztec accelerates quickly through this speed to its best two engine climb speed of 120 mph (104 knots). With a maximum one-engine ceiling of 5,000 feet at gross weight, any engine failure in this configuration is likely to result in a downward trend at South Africa's inland airfields.

Some of my previous Aztec time involved some gross weight flights and I found the aircraft to be weight sensitive in the cruise regime. This also affected endurance but under normal circumstances an Aztec should return a consistent 160 knots in the cruise. Piper claim substantially more but in my experience Piper's claimed speeds rarely match reality. Gross weight is 5200 lbs and empty weight 3042 lbs leaving a maximum payload of 2158 lbs. The aircraft is thus able to carry full fuel and fill the seats with a small baggage allowance for each passenger - a great combination and a major reason behind the Aztec's tremendous sales success. Indeed, the aircraft is truly versatile with huge luggage bays behind the rear row of seats and inside the nose. Despite its respectable load carrying ability, these vast caverns are an invitation to overload.conditions.

The big Piper twin also has a reputation for being a gas guzzler. This is hardly surprising considering the two thirsty 230hp Lycomings. The operators manual claims a cruise fuel consumption of 27 gallons per hour - enough for a tanks dry endurance of five hours and giving a no reserve range of 940 nautical miles - plenty to get from Johannesburg to Maun and almost all the way back again. It's no wonder the aircraft was so popular with charter companies throughout Africa.

The Aztec is pleasant to fly though few twins, with the exception of the Baron could be described as having responsive handling. It is extremely unlikely that Aztec owners will buy their aircraft with the object of performing mild aerobatics; therefore any discussion regarding the finer points of handling is purely academic. As an IFR platform, the aircraft is immensely stable though it does suffer from the unusual characteristic of raising its nose with the application of flap - a thing to remember on approach for unfamiliar pilots.

There is no better way of sampling an aeroplane's handling qualities whilst flying formation. We were tasked to team up with a Cessna 172 - such a dissimilar mix is nothing unusual in the magazine world of air-to-air photography. I found the Aztec easy to hold and change position behind and too the right of the Cessna, especially in a left bank as we circled over the busy flying area west of Pretoria. A right turn where we were or the inside of the 172 and thus slower, encouraged the beginnings of a buffet from the powerful elevator. The Aztec was gently telling us that we were nibbling at the edge of its stall envelope. I rolled out wings level and allowed the Cessna to continue its turn before rejoining. This was an ideal demonstration of the Piper's gentle handling.

Returning to the circuit, I slowed to 150 mph on an early base to bring the gear down - double checked by a handy mirror stuck to the inside left engine cowling. Although many pilots might distrust these highly engineered hydraulic power packs, especially if they have flown Cessna 210's, I've yet to hear of an Aztec having to endure a wheels up landing following a system failure. As a last resort though, Piper thought fir to install a secondary emergency system which blows the wheels down with a blast of COČ. Much like a hand grenade, this is activated by pulling a firing pin under the pilot's seat. First stage flap can be lowered at under 160 mph but the speed needs to be below 125 mph for full flap. As I lowered flap in stages during the approach it was slightly peculiar to have to apply nose down trim. The aircraft is easy to land and requires no funny control inputs at the flare - unlike the Aztec's earlier sister, the Apache. Moreover there is little tendency to float if the speed isn't just right like trying to place a Twin Comanche onto the runway. Lovely!

It was a profound pleasure to fly an Aztec once again and sample its kindly flying qualities; especially one is such fine condition as Daniel's. Owning one that isn't in top condition might be a more frustrating experience though. Despite its obvious robustness, there are a number of items to look for when appraising the Piper twin. I'm told that a fuel tank mod is required that involves inserting a wedge between the rubber bladder and wing skin. The purpose of this is to prevent fuel from collecting behind any folds or ridges in the tank thus preventing all the fuel from feeding into the engines. This mod costs over US$1,000 to install. I can't imagine any sensible pilot allowing the fuel state to get anywhere low enough to benefit from these wedges but regulations is regulations I suppose. With so many Aztec's leading a hard charter existence in a previous life it also pays to see if the step attach point has been beefed up. Piper mandated a reinforcement as the attach point is mounted on the same piece of tubular airframe as the rudder pulleys. The implication here is obvious. Lastly, the flaps are relatively large and there is considerable strain on the flap spars. An experienced Aztec engineer would look closely at this area as it is not uncommon to find cracks.

The Aztec remains an intriguing choice for the used aircraft buyer. Whilst it is fairly heavy on fuel, the initial purchase prices are usually low enough to make up for this. These aircraft also allow a potential owner to source a well used example and have it refurbished to a high standard for much less than the cost of a Baron or late model Cessna 310.

Specification

Engines:
2 x Lycoming 250hp IO-540 C4B5. 2000 hr TBO
Propellors:
2 x Hartzell two-blade
Seats:
6
Wing span:
37.2 feet
Length:
31.2 feet
Height:
10.3 feet
Gross weight:
5200 lbs
Empty weight:
3042 lbs
Payload:
2158 lbs
Fuel capacity:
144 gallons
Fuel consumption:
Between 21 and 34 depending on cruise settings
Max speed:
210 mph (180 knots)
Max range:
1210 miles (long range cruise)
Takeoff distance:
820 feet
Min single eng control speed:
80 mph
Stall speed dirty:
70 mph
Ceiling:
21,000 feet
Single engine ceiling:
5,000 feet

[END OF REPORT]

Note: PlaneCheck often has some nice Piper Aztecs for sale