Mooney M20
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The Mooney M20 is a family of high performance, piston-powered, propeller-driven general aviation aircraft, all featuring a low-wing and tricycle gear.
Overview
The 20th design from Al Mooney was his most successful. This design was fittingly designated as the "M20." The M20 series was (and is) produced in many variations over the last 50 years, from the wooden wing M20 and M20A models of the 1950s to the fastest Mooney ever, the M20TN Acclaim, that debuted in the 21st century and is currently in production.
Model Synopsis
The Mooney M20 series has been produced in three fuselage lengths: the "short body," "medium body" (including M20J), and "long body" types. Only the long body Mooneys are in current production. Although all M20s have four seats, the fuselage length increase provided more passenger legroom but with a slight performance decrease. Other airplane improvements over the years more than compensated for the effects of a longer fuselage.
The original M20 (1955-1958) and the M20A (1958-1960) had wooden wing spars but were otherwise similar, with the M20A enjoying an increase in power (to 180 hp, up from the M20's 150 hp). Some unfortunate owners of these early examples quickly discovered that the wooden wing spar was prone to inflight breakup if overstressed, especially if the spar was water damaged or rotted. Careful, frequent inspection of the wing spar is required to keep these aircraft airworthy.
Mooney addressed this problem by switching to an all metal design in 1961 with the M20B. The all metal design added some weight, but the change was well received and has resulted in an extremely sturdy aircraft. Corrosion can reduce the strength of the aircraft, but this has proved much less of a problem in the field than the wooden spar. There have been no reported inflight breakups of all metal M20s.
In 1962 Mooney made further incremental improvements in the M20C (1962-1978). The M20C was the last short body Mooney to end production. More M20Cs were produced than any other Mooney model to date. In 1963 Mooney introduced the M20D, essentially an M20C with fixed gear intended primarily for flight training and for owners desiring lower insurance rates. The M20D lasted only until 1966, and most have been converted to M20Cs for increased cruise speed and climb performance.
The first Mooney "hot rod," the M20E, was produced from 1964 to 1975. The M20E was essentially an M20C with a more powerful (200 hp) fuel injected engine. This short body Mooney still has the distinction of using the least amount of runway for takeoff, at least at lower elevations. (Turbocharging, which would maintain this performance at higher elevations, is available as an aftermarket option.) It is the most highly sought after short body Mooney.
Mooney stretched the fuselage for the first time with the M20F (1966-1977). The M20F is otherwise basically identical to the M20E. Likewise, the M20G (1968-1970) was a stretched M20C.
In 1969 Mooney made electrically operated landing gear and flaps standard across all its aircraft. Prior to that, pilots extended and retracted the standard landing gear using a heavy metal Johnson bar (Electric gear was an option). There are still arguments among Mooney enthusiasts whether this change was wise.
Mooney hired Roy LoPresti to undertake an aerodynamic cleanup of the M20F, resulting in the 1977 model year debut of the M20J. Many pilots consider the M20J to be the ultimate balance between speed and efficiency. The Mooney M20J is also known as the 201 because of its 201 mi:h[convert: unknown unit] top speed in level flight. The M20J first flew in September, 1976. The improved aerodynamic shape and updated 200 hp engine made the M20J the second most popular variant of the M20 series, after the M20C. It is often used as a training aircraft for commercial pilots. It was originally designed as a private/commercial touring aircraft because of the high cruising speed and relatively low operational cost. The J model had an impressive production run, lasting until 1998, thus ending the medium body M20s.
Up through the M20J all Mooney M20s had four cylinder Lycoming engines. After designing the M20J, Mooney modified the basic design to include a variety of more powerful six cylinder engines, including some models with turbocharged engines. The first such design was the turbocharged M20K (1979-1998). The M20K's first engine was more difficult to operate at acceptable engine temperatures, so by 1986 the "252" variant featured a more compliant engine and various speed improvements. In 1988 Mooney went to even greater lengths, partnering with Porsche to include their geared engine and stretching the fuselage the last time to produce the first long body M20. Most M20Ls no longer use this unique engine. M20L production ended in 1990.
The M20M (1989-) boosted output initially to 270 hp and was also turbocharged. The M20R (1994-) started at 280 hp and did not have turbocharging. With minor changes in engine output (e.g. the M20S "Eagle") and various performance tweaks, these two basic models (both high power, both with long bodies, one with turbocharging) remain in production today as the "Bravo" and "Ovation." The latest and fastest of the M20 series is the M20TN Acclaim.
Mooney and Cessna (formerly Columbia Aircraft) have been frequently trading positions as producer of the fastest production single engine piston aircraft. Currently, the Acclaim's 242 knot cruise speed at FL250[1][2] puts it ahead of the Cessna 400 and the turbo-charged version of the Cirrus SR22 GTS (Cessna advertises a 235KT cruise, the Cirrus advertises a 220KT cruise, both at FL250). The Acclaim has retractable gear, while the Cessna and Cirrus both have fixed gears. This latest M20 is extremely fast, strong, efficient and still based on the well proven M20 airframe, a basic design which predates Cessna's design by decades.
Airframe
With the exception of the wooden wing spars of the original M20 and M20A, M20s are all metal, low wing aircraft. The wings are of cantilever construction, consisting of a main spar and an auxiliary spar that extends from the fuselage to the mid position of the flaps. The wing skin is a wrap-around light sheet metal alloy and is flush riveted in many areas to reduce parasite drag. Slotted flaps are alloy surfaces that cover 70% of the trailing edge. Early models use a hydraulic hand pump to control the flaps while later models use electrically operated flaps. The fuselage consists of a steel, tubular cabin, with an alloy skin, similar to that of the wings. The aft fuselage is of semi-monocoque design. The stress load is distributed between the skin, stringers and metal bulkheads. The aft fuselage is connected to the empennage at a pivot. The entire empennage can be pivoted for pitch trimming. All surfaces of the stabilator and rudder are constructed with wrap around light alloy flush-riveted skin.
Undercarriage
The tricycle undercarriage legs of the Mooney M20 models are made of heat treated chrome-molybdenum steel. The main gears are attached to the main wing spar, while the nose gear is mounted onto the steel cabin frame. Rubber discs, as well as spring steel, around the legs allow for compression and shock absorption on landing. Except for an unmodified M20D, the nose wheel retracts rearward and the main wheels towards the fuselage. Early models use a clever hand operated and nearly fail-safe "Johnson Bar" system to raise and lower the gear. Later models use an electrically operated landing gear retraction system with a backup crank-operated or wire-pull gear extender.
Brakes
The brakes are fitted to the main wheels and can be applied separately to assist in sharper turns on the ground. The brakes are of the hydraulically operated disc type. Toe pressure on the rudder pedals causes hydraulic fluid from the master cylinder to be delivered under pressure to the brake pads, which close in on either side of the rotating brake discs.
The toe-brakes were standard on the pilot (left seat) and an option on the co-pilot seat in later years.
Aerodynamic Features
The Mooney M20 is a stable and highly efficient aircraft. This is attributed to the aerodynamic design. The efficiency of the original design, although superior to other designs of its day, was compromised by a large cooling air inlet that stayed with the M20 until the introduction of the M20J. The J model reduced this opening, added a more aerodynamic windshield, and made numerous aerodynamic enhancements that gave it a substantial speed increase without adding power to the existing M20F design. All M20s after the "J" have benefited from the aerodynamic cleanup.
Wings
To increase aerodynamic efficiency, the wings of the M20 are designed to minimize induced and parasite drag. In flight, the high pressure underneath the wings will 'leak' to the lower pressure above in a span wise flow at the wingtips. This form of induced drag is called a wingtip vortex. To minimize the effect, the Mooney M20 is designed with medium aspect ratio, and tapered wings. Consequently, the smaller wingtips create weaker vortices. Furthermore the wings are constructed with washout; the angle of incidence at the roots is 2 ° 30’, and becomes 1 ° at the tip. The pressure differential between the bottom and top of the wing tip is considerably lower than that of the root; this further reduces the magnitude of the vortices. Parasite drag is reduced by the simple, streamlined shape of the wing, and the smooth surface. On the M20J navigation and anti-collision lights are located inside an aerodynamically designed cover at the wingtips to further eliminate drag.
Lateral Stability
The wings of the Mooney M20 are low and have 5° 30’ of dihedral. This configuration assists in the positive lateral stability of the aircraft.
Stall Strips
Later M20s are equipped with stall strips to improve the stall characteristics. There are 2 wedge shaped lengths of metal that are located on and run parallel to the leading edge of the wings. At high angles of attack the strips will disrupt the boundary layer of airflow, inducing a stall. This is beneficial because it forces the wing roots to stall first, instead of across the entire wing where it is more probable that loss of control and an unrecoverable spin, will occur. The stall strips also accentuate control buffeting by sending turbulent air over the empennage at the onset of the stall. This gives the pilot ample warning to take corrective action before the aircraft stalls.
Empennage
The empennage of the Mooney M20 is easily recognisable by its unique tailplane with a vertical leading edge. (The tail looks like it is "leaning forward," but it is actually straight vertical.) The horizontal tailplane consists of a fixed stabilizer and trailing elevator, and does not include any trim tabs. The entire tail assembly pivots at the rear of the fuselage to provide for pitch trim. The simple aerofoil is consequently very streamlined and produces minimal drag.
Propulsion
Fuel System
All M20s store fuel in two separate tanks (left and right) which are located in the inboard sections of the wings. There are no fuel tanks per se. Instead, the "wet wing" design consists of sealed internal wing sections. The sealant normally lasts about 20 years, requiring repair to keep the wings from leaking. The unusable fuel exits at the lowest point in each tank, below the outgoing fuel line, so that sediment, contamination or water will not be pumped and also can be tested through the sump drains. One tank can be selected at a time. Fuel is driven from the tank to the injectors or carburetor by an engine driven pump. In the event of failure of this primary pump, a secondary electric boost pump also exists.
Piston Engine
The piston engine installed in the Mooney 201 is a 200 bhp TEXTRON-Lycoming IO-360-A3B6D, with four horizontally opposed cylinders. The engine runs on a modified Otto cycle, where in a full cycle, the crankshaft, in two revolutions receives power from each of the four cylinders alternately. The engine model's D suffix refers to its dual magneto ignition system contained in a single housing. The single housing has been controversial since improperly maintained or repaired magnetos could work loose from the engine, resulting in loss of ignition. Other M20s have dual magnetos in separate housings.
Ram Air
For increased power many M20s also have a ram air system called the Mooney "Power Boost". For normal operations the intake air is filtered before it enters the induction system. When ram air is on, partially unfiltered air will enter the induction system with a higher pressure and consequently the manifold pressure will increase, giving a greater power output. The ram air is only used in clear, dust-free air to guard against engine damage. For obvious reasons, the turbocharged variants omit this feature as they have their own "power boost" that provides far more increase in manifold pressure.
Cooling and Lubrication
Oil system
The engine has a wet sump oil system with 7.6L capacity. The oil is deposited in a sump underneath the engine. It is pumped first through a filter and then an air cooler at 60-100psi before lubricating, cooling and cleaning the engine through a series of small tunnels in the engine casing. The pilot can monitor oil pressure and temperature through instrumentation in the cockpit. If oil temperature is low, an automatic bypass valve reroutes the oil around the cooler.
Cooling System
The engine is predominantly air cooled. Air is routed evenly over the cylinders and engine components by the use of baffles. After cooling the air exits the cowling through the adjustable cowl flap. The pilot can monitor CHT from the cockpit and open/close this flap as required to maintain a recommended temperature. The engine can also be cooled by increasing the fuel mixture. More fuel will be evaporated in the cylinders and hence the cooling effect of evaporation will be increased. An increase in airspeed or decrease in angle of attack also has a cooling effect. The Mooney Aircraft Company suggests that cowl flaps should usually be closed during cruise and descent to avoid excessive or shock cooling of the engine.
Constant Speed Propeller
All M20s are single engine aircraft. The power created by the engine is first transferred into torque by engine components, and then into thrust by the constant speed propeller.
The propeller has both forward velocity and rotational velocity, giving a resultant relative airflow. As the forward velocity increases, the angle of attack decreases. To maximize thrust output efficiency, the constant speed propeller is able to maintain an optimum angle of attack of approximately 4°, giving the best lift/drag ratio, by changing the blade angle in flight. In all M20s, the CSU governing system is hydraulically controlled by engine oil and automatically adjusts the blade angle to maintain a specified RPM.
Oil pressure is applied to a piston in the hub of the propeller. As more oil enters the hub, the blades are mechanically (sliding rod and fork arrangement) caused to coarsen, and as oil exits the hub the blade angle progressively becomes finer. In the event of total loss of oil pressure, the blades will become fully fine, and maximum thrust is available. The constant RPM is maintained by the use of a fly-weight assembly. The pilot sets a certain manifold pressure and a corresponding RPM using his controls in the cockpit, and the governor works to maintain that RPM. The fly-weights spin at a speed directly proportional to the engine and are attached to and control the position of the pilot valve. The position of the pilot valve determines whether oil will be entering or exiting the hub, or neither.
Operational Requirements
Crew and Runway
The Mooney 201 is equipped with dual controls. If necessary, 2 pilots can take shifts on longer flights or training can be conducted in the aircraft.
The runway length required to take-off or come to a full stop will depend on many factors. These include runway surface, temperature, barometric pressure, weight, wind, runway slope and aircraft configuration and speed. The length required can be calculated using performance charts distributed by the Mooney Company. The aircraft's Pilot Operating Handbook advises against takeoffs in conditions where the wind conditions, relative to the active departure runway, presents a crosswind greater than 11 knots or a tailwind greater than 5 knots.
Ground Equipment
Towing
While on the ground, it may not always be economical to taxi the Mooney 201 short distances using the engine. A tow bar can be attached to the nose wheel leg and pulled by hand. Safety markers are located on the leg to indicate the maximum degree that the nose wheel can be rotated to avoid damage (14°).
Tie Down
The Mooney 201 should be tied down when not in use, especially in windy conditions. The equipment required is 3 ropes and a nose chock. The aircraft is faced into the wind and the nose chock is put into place. 2 metallic eyebolts are located on the wings, and one on the tail. Ground anchored ropes are tied to these to minimize movement due to wind.
Fuel Requirements
Refueling of the Mooney 201 is done on the ground. Both tanks must be refueled alternately. The minimum grade fuel for operation is AVGAS 100/100LL octane (blue). Refueling can be done using a drum or pump. For the aircraft to operate legally and in balance, weight and loading charts can be consulted to ensure the Mooney remains in the ‘normal’ loading category throughout the flight. The Mooney 201 typically burns 10.5 gallons (41 liters) of fuel per hour at cruise speed. The Mooney comes with a cup actuator which is used to drain fuel from the bottom of the tanks and lines to test for contaminants and water.
Safety
Safety Record
A comprehensive safety review of Mooney aircraft was conducted by the AOPA Air Safety Foundation from 1982-1991. It was found that in this time 392 Mooney related accidents had occurred, and 75% of these were due to human error. Approximately 6 Mooney aircraft out of every 100 registered in the USA is involved in an accident. According to the review, the most common cause of fatal and serious accidents involving the Mooney aircraft is poor weather judgment. Situations such as inadvertent cloud entry are the cause of 26% of Mooney accidents. Mooney aircraft are involved in twice as many overshoot landings than other aircraft in the same class. This is due to pilot error; approaching the runway faster than the recommended speed of 70 knots. Airspeed cannot be quickly reduced in the Mooney 201 because of the low drag, aerodynamically efficient wings. When airspeed is not sufficiently reduced before the round out, the Mooney 201 tends to stay afloat in ground effect and will balloon. As a result much of the usable runway is wasted and an overshoot is possible. The 3 most recent accidents involving the Mooney 201 in Australia are published in the ATSB archives. These include a mid-air collision due to unauthorized CTA entrance, engine failure resulting in a stall and spin during go around and loss of control at night with unknown causes.
Safety Features
Landing gear
To avoid an inadvertent retraction of the undercarriage while on the ground, an air switch exists behind the ASI for some production years. Below 65 knots, the air switch opens the gear actuator circuit, preventing gear retraction. Above 65 knots, dynamic pressure is sufficient to close this circuit allowing the gear to retract. This system, however, can be bypassed in the case of a required take-off and climb below 65 knots. The ‘wheel up’ belly landing is not uncommon in the Mooney 201, be it due to an electrical/mechanical failure or due to pilot error. An aural warning is set to activate whenever the gear is not fully extended and power is set at below 12”MP. This is generally the power configuration on the base leg of landing. An electrical light will advise the pilot whether the gear is up, down or in transit. This can be confirmed by a visual gear position indicator between the co-pilot and pilot seats. The landing gear can also be extended manually in the case of electrical failure by a spring retracted pull cable in the cockpit.
Flight systems
In case of an auto-pilot malfunction, such as auto-pilot or trim run-away, autopilot can be switched off in 3 separate ways. The Autopilot on/off switch, use of the electric trim or by pulling the trim circuit breaker. The aircraft can then be trimmed manually using the trim wheel. The normal static ports on the 201 fuselage that are used to calibrate the altimeter, VSI and ASI may become blocked and give incorrect readings. Therefore an alternate static source exists and can be selected. This is positioned inside the cockpit and gives slightly erroneous readings because of the difference in pressure between the cockpit and outside air.
Cabin
The baggage door doubles as an auxiliary emergency exit. If required, a light plastic covering situated on the inside of the door can be pulled off to reveal a pin. Pulling this pin disables the locking system and the baggage door can be opened from the inside. Seatbelts consist of a lap strap and shoulder harness and must be worn during take-off and landing.
Famous aircraft
The Mooney Super M20E is the aircraft most closely associated with Robin Miller, a famous Australian female pilot known as the "Sugar Bird Lady" for her work in distributing the polio vaccine across Australia. Her aircraft is preserved at Jandakot Airport near Perth, Australia.
Specifications (M20J)
General characteristics Performance
Bibliography
Sources
- ^ Russ Niles (October 2, 2007). "Mooney Expands the Acclaim's Speed Envelope". Retrieved 2007-10-04.
- ^ Mary Grady (October 4, 2007). "Mooney Acclaim Type S: "Unquestionably the Fastest"". Retrieved 2007-10-05.
- Robson D, Aircraft General Knowledge and Aerodynamics, Aviation Theory Centre, Victoria, 2001
- Eric Broumand Nesbit Evans, Dynamics of flight, stability and control-McGraw 2005
- Mooney 201 Handbook, Mooney Aircraft Company, Texas, 1981
- Mooney M20J Pilots Operating Handbook, Mooney Aircraft Company, Texas, 1983
- Frawley, G, International directory of Civil Aircraft, Aerospace Publications, ACT, 1999
- Jane’s All the World’s aircraft 1981-1982, Jane's Information Group, U.S.A., 1981
- AOPA Air Safety Foundation, Mooney aircraft Safety review, AOPA, U.S.A., 1991
- Bonds, R, A Century of Flight, Salmander Books Ltd, London, 2003
- Professor Munib Kirdoggy Sagpur, "Flight dynamics", East Fremantle AOPA Publishing, 1995
- Selkirk Professional Aviation College, Aerodynamic centre, http://selair.selkirk.bc.ca/aerodynamics1/Stability/Page7.html, 2005
- History of Mooney models
- The Al Mooney Story: They All Fly Through the Same Air
- FAA type certificate for all M20 models