Aircraft Evaluation:
Mooney M20M

by Trey Hughes

 

When most people think of Mooney, they think of speed, lots of speed.  It was this premise that in 1989 brought the aviation world the Mooney M20M – TLS.  Introduced during the French ownership era, the M20M was one of the “one new model each year for five years” program initiated by Alexandre Couvelaire during the mid-eighties.  The M20J – 205, the M20J – Lean Machine, The M20L – PFM and the Advanced Trainer System (ATS) were the first 4 aircraft with the M20M completing the package at the end of the eighties.

 

The TLS was a big departure for Mooney Aircraft engineers who were known for their “performance through efficiency” approach to aircraft design.  Not since the M22 Mustang, had such a combination of airframe and big engine been considered in Kerrville .

 

Using an airframe based on the one-foot longer M20L fuselage stuffed with a turbocharged and intercooled 270-horspower Textron Lycoming TIO-540-AF1A engine, the M-model was to be the most powerful Mooney produced since the 1967 – 1970 pressuri ze d Mustang.  The original goal was for 214 KTAS at 25,000 feet – the designed maximum operating altitude.  However, the airplane would actually do closer to 220 KTAS!  Some people, myself included, think this longer body airplane was the best-looking Mooney ever built.  With it’s stretched nose, long sleek fuselage and the longer side windows, the TLS looks fast sitting still.

 

And fast it is.  The engine is a version of Lycoming’s parallel-valve; 540-cubic-inch opposed six with a single AiResearch Turbocharger and carries a maximum power rating of 38 inches manifold pressure and 2575 RPM.  Two controllers operate the single wastegate to regulate pressuri ze d air to the induction system.  With this system, the engine is capable of maintaining its full 270 hp up to FL210 under standard conditions.  With this high 21,000-foot critical altitude, the TLS is able to achieve very high cruise airspeeds.  At FL250, as high as you can legally fly in the M20M, it’s still possible to utili ze maximum continuous power – 34” and 2400 RPM, which is about 240 hp or 89%!

 

Of course all this speed comes at a cost - about 18 gallons of Avgas per hour of cost to be specific.  And that is if you lean aggressively to the 1750-degrees-Fahrenheit turbine-inlet temperature (TIT) maximum, one of the highest certified TIT's in piston aircraft.  We will discuss leaning in detail again later in this report.

 

One thing did become evident during the first few years of production.  With the airplane delivering such high cruise airspeeds, at high altitude with high power settings, many TLS owners discovered that their airplanes needed engine work at 400 to 500 hours.

 

In retrospect, this could be a predictable situation.  Here we have a large-bore engine producing 270-horsepower and in the hanger next door may be another variation of the TIO-540 in, say a Navajo Chieftain, producing 350-horsepower.  It would be easy for the average TLS operator to think his engine was a de-rated version of the 350-hp monster.  At 270 hp it’s not working as hard as the engine in the Piper, and using nearly 90% of that number for cruise should pose no major problems.  Unfortunately, this premise is incorrect.  The two engines have little in common.  The engine used in the TLS is rated at 260 hp without the turbocharger – at a higher compression ratio and RPM – and is really a lightweight version of the Navajo’s 540.  As a result, exhaust valve guides bore the brunt of the wear from these operations.

 

There was a predictable rise in oil consumption and dropping compression readings during as little as 300 hours of operation.  Fortunately, these excessive wear indicators did not lead to any catastrophic failures.  But many owners discovered that a quarter of the way to overhaul, top-end engine work was necessary.  One of the factors in this increased need for unexpected maintenance could have been the high TIT red line.  Most turbocharged Lycoming engines of that day had a more conservative limit of 1650 degrees F, and they had a better maintenance picture than the early TLS’s.

 

Mooney and Lycoming came up with a solution for the TLS top-end wear problems.  A process that Lycoming used successfully to cure similar problems on the TIO-541 Beech Duke engines – oil cooled exhaust valve guides – was accomplished on the TLS.  The illustrative name “wet head” was given to the conversion that was accomplished on all production engines that resulted in a designation change to TIO-540-AF1B.  The change from the AF1A to the AF1B brought about the nickname for the engine, the “Bravo mod”, and in fact the TLS became the TLSBravo and has since been shortened to just the Mooney Bravo.

 

In this conversion (and on subsequent production engines) oil is fed under pressure to a gallery in each cylinder head adjacent to the exhaust-valve guide.  The guide it self has a small groove cut into the outer diameter allowing oil flow to surround the guide and draw away heat.  From the valve guide, this additional oil flow is routed through the rocker boxes where it helps to draw away additional heat and then through the normal drains back to the sump.  The modification is easily seen as a bunch of snaking external oil lines leading to each cylinder head.  Our information is that all US airplanes have been modified (Mooney paid a substantial part of the Service Bulletin), however some foreign TLS’s may have been missed.

 

To date, 314 M20M TLS and TLSBravos have been manufactured with the last one (27-0316) rolling off the Kerrville production line in 2001 just prior to the factory shutdown.  By the way, the TLS designation came from the engineering department who referred to the airplane during testing as the Turbo-Lycoming-Saber.  Marketing had at one time thought of naming the new model the Mooney “Saber” as they were trying to get away from using the maximum airspeed for the model name as on previous Mooneys.

 

Let’s take a look at some statistics on the M20M:

 

Engine                                                            Textron Lycoming TIO-540-AF1A (AF1B)

Recommended TBO                                                                                       2000 hours

Length                                                                                                                 26.75 feet

Height                                                                                                                    8.33 feet

Wingspan                                                                                                              36.1 feet

Wing area                                                                                                        174.8 sq. ft.

Wing loading                                                                                               19.26 lb./sq. ft.

Power loading                                                                                               11.85 lbs./hp

Seats                                                                                                                                  4

Cabin length                                                                                                          10.5 feet

Cabin width                                                                                                             3.6 feet

Cabin height                                                                                                            3.7 feet

Empty weight                                                                                                       2012 lbs.

Average equipped empty weight                                                                       2400 lbs.

Max. Gross takeoff weight                                                                                  3368 lbs.

Average useful load                                                                                               968 lbs.

Fuel capacity – standard tanks                                     89 gallons useable/517.98 lbs.

Average Payload w/full fuel                                                                             450.02 lbs.

Max. Baggage capacity                                                                                        120 lbs.

Max. Landing weight                                                                                           3200 lbs.

 

Let’s Take A Test Flight

 

In order to find an airplane to fly, I made a call to David McGee and Jimmy Garrison at All American Aircraft (1-800-777-1491) here in San Antonio .  They have a beautiful Metallic Maroon and White with Gold accent strips 1999 Bravo, and were kind enough to offer it for this evaluation.  N765LM is s/n 27-0269 and has only 333 hours total time on the airframe and engine since new.  Equipped with a full stack of Bendix King avionics including dual KX-155A Navcoms, a KLN-94 IFR enroute and approach certified GPS navigator, a KMD540 color multi-function moving map display and a KFC-150 Flight Director/Autopilot complete with Altitude Pre-select, it appeared it would be difficult for me to get lost during this flight.  Also in the panel of 765LM was a BFG-950 Stormscope and a JP Instruments EDM-800 Graphic Engine Monitor showing individual cylinder EGT and CHT as well as OAT.  The EDM-800 also includes a fuel computer and aircraft bus voltage monitor.

 

M20M TLS – long and sleek

 

 

As I was preflighting 5LM, a quick check of the logs proved something that I had thought.  I had flown this airplane at FlightSafety when it was new. Then, it carried the registration number of N21278.  This was going to be fun to reacquaint myself with an old friend.

 

Like all other Mooneys, the pre-flight inspection is straightforward.  There are some things however, that should be done in a specific sequence.  Because the gascolator drain is lower than the wing sumps, it is very important to drain the wings before draining the gascolator.  This way, if any water is in the fuel tanks, it isn’t introduced into the fuel system during the draining process at the gascolator.  At FlightSafety we taught new pilots transitioning into any Mooney to first drain the wing tank sumps and check the oil quantity prior to conducting the cockpit check.  This is easily accomplished and will allow any water collected in the tank sump area to be drained before being drawn into the aircraft fuel lines.  It will also give you time to get a quart of oil into the engine should the quantity be below the recommended 8 quarts minimum for flight.

 

A TIO-540-ARIE under the long nose.

A complete stack of IFR avionics.

 

 

After these early exterior checks, it’s time to enter the cockpit to begin the pre-flight inspection.  Like most late-model Mooneys, the M20M has two batteries instead of one.  This was done by the engineers in Kerrville to add weight to the aft end of the airplane, but it makes a great addition to electrical redundancy.  Cockpit checks then should include the charge-state of both batteries.  Even though there is a second battery, both are required to be installed and serviceable for flight.  A switch on the circuit breaker panel controls the battery that is selected for use, and the one with the highest voltage should be used for engine starting.  However, if both batteries are of equal voltage, we suggest alternating their use each flight.  You will be happy to know that the battery that is not selected for flight is constantly kept charged through a “trickle-charge” circuit, so it is fully charged should it be needed.  With two, 28-volt seventy amp-hour alternators and two 24-volt batteries included, as standard equipment there shouldn’t be a shortage of electrical power.

 

One of the real nice changes to the later year Bravos is the addition of the Moritz engine gauges.  These gauges are arranged horizontally across the top of the instrument panel right below the glareshield.  The indicators have both digital and analog presentations, and make setting very precise values of Manifold Pressure, RPM, and TIT very easy.  It is also a benefit to be able to read CHT, Oil Pressure and Temperature accurately using the digital display.

 

After the cockpit pre-flight is complete, including draining the gascolator from each tank position, it’s time to look at 5LM from the outside.  Again, a straightforward external inspection except for paying close attention to the empennage security and free-play as well as control movement and attachment.  During the walkaround inspection, the external fuel indicators on the top of each wing tank make partial fuel loading and checking very easy.  These are magnetic indicators and require no electrical power.  Operators should note however, because of the attitude at which the TLS sits, these mechanical fuel gauges are only accurate on the ground.  Once airborne, at cruise attitude, they are no longer reliable for indicating fuel quantity.  Also, the digital fuel quantity indicators on the LCD panel in the cockpit are only accurate in flight and not on the ground.  This fact could make enroute refueling interesting if the pilot were to order fuel based on the value displayed on the cockpit gauges after landing.

 

Now that the “dirty” work is done, it’s time to go flying!  Starting the big Lycoming is very easy.  Following the checklist, the boost pump is used for 8 seconds, and after engaging the high-speed 24-volt starter, the engine is soon giving forth that wonder 6-cylinder rumble.  One thing to remember when starting the TIO-540, boost pump priming time is dependent on outside air temperature.  It was warm in San Antonio this day, with the IOAT at +21 C so 8 seconds was just the right amount of fuel to get the beast running.  Had it been winter (something we only allow a little of in Texas ) an IOAT of 0-degrees would have required 15 seconds of fuel.  Any warmer than 20-degrees C and priming time could be as short at 5 seconds.

 

Moritz engine instruments

At 17,500 the view is terrific.

Bravo logo on the flagship of the Mooney fleet.

 

 

 

Engine start and taxi were normal, and I was soon at the end of 12R at San Antonio International.  The 540 is a heavy engine, so there is a little effort necessary to turn the nose wheel with the rudder pedals.  You can make life easier however, it you keep the standard rudder trim system set to the neutral or centered position until just before takeoff.  This way, you don’t try to taxi against the right turning tendency and rudder/nose wheel angle that would be present if takeoff rudder trim were selected.  The rudder trim is very useful however when it comes to relieving the effort needed by the right leg in compensating for all the torque and P-factor produced by the big Lycoming turning that 3-blade 75” McCauley propeller.  On the way to the runway, I always switch fuel to the fullest tank.  This way, I can do the run-up and then takeoff on the same tank (always a good idea) and I have also checked that both feed the engine properly.  I’d hate to discover this during flight over hostile terrain.

 

With the oil temperature comfortably above the 750 F minimum for run-up, a check of the magnetos and propeller governor are made at 2000 RPM.  A quick check of the digital volt/amp meter shows that both alternators are supplying the correct outputs.  Wing flaps and trims are checked for operation and set for takeoff, a last check of instruments, radios and clearance along with the last checklist items and we are ready to go.

 

Cleared for takeoff, and a last check of the engine instruments, controls and trims, it’s time to make the Lycoming “rock and roll”.  Since we are departing VFR, I plan an unrestricted cruise climb to 10,500 feet MSL to do some speed and power checks.  As the throttle is slowly and carefully pushed in, allowing the turbo compressor to spin-up, a check of the annunciator panel shows that the boost pump light is illuminated indicating that the pump was automatically activated by a throttle position switch.  With takeoff power set and a rolling takeoff (unless the runway is very short, I don’t like to make static power takeoffs – too hard on the brakes and propeller) we are rapidly down the runway.  With the conditions at KSAT at; IOAT +20 C, wind variable at 10 kts, density altitude of 3100 feet, and our gross takeoff weight at just a shade over 3100 pounds, we are off the runway in a little over 900 feet and only need an additional 1000 feet to gain the magical 50 foot altitude.  Less than 2000 feet total takeoff distance on a warm day from a 1000’ MSL airport – what a performer.

 

While we are looking at takeoff performance, I guess I should talk about our weight today.  The TLSBravo is not a light airplane.  Most came from the factory or were later equipped by their owners with most of the “bells and whistles” available on a single-engine piston airplane.  The M20M has a maximum gross takeoff weight limit of 3368 pounds.  Unlike earlier Mooneys, it also has a 3200 pound maximum landing weight, so fuel and weight at the destination is now a consideration if we takeoff above 3200 pounds.  N765LM had a rather conservative equipped empty weight of 2379.4 pounds.  I have seen Bravos with TKS and/or air conditioning top out at over 2440 pounds.  This can be a very heavy airplane, and operators need to pay close attention to fuel and cabin loading to remain within the certified envelope.

 

At 2379 pounds, I could carry full fuel and 469 pounds of people and bags.  However, by reducing the fuel load to a more reasonable 70 gallons (still leaving 3.5 hours of flight available), the payload is now 518 pounds.  That’s enough for 2 larger than FAA standard adults and maximum baggage.  Put 3 standard 170-pound people and no baggage and you are still in the envelope.  Or, two 150-pound folks, a couple of small kids and 100 pounds of bags in back and you are still good to go.  There is a great flexibility to fuel and passenger loading in the biggest Mooney.

 

VR for our weight today is 64 KIAS.  As the airspeed is passing through 60 kts, begin a slight pull on the control wheel to reduce the weight on the nose.  Waiting too long to apply back-pressure can leave the wing flying while the nose wheel remains firmly planted on the runway.  In order to takeoff and climb, you must change the angle of attack of the wing; otherwise it will begin flying while the airplane remains a tractor on the runway - not a good thing for the propeller.  On the long bodied Mooneys (M20M, M20R and M20S) the airplane sits with a positive pitch attitude of about 4.5-degrees.  This means that the attitude to rotate and fly away from the runway is going to be about 8 to 10 degrees of positive pitch, and this is the pitch attitude to achieve for lift-off.  One point to consider here, with a Flight Director system for a reduced visibility takeoff, set the pitch reference to about 10 degrees prior to takeoff.  This would be the same attitude as that used for a go-around, so if your system has a GA button, use it to set the proper pitch attitude for takeoff.  When you can’t see an adequate horizon, the Flight Director command bars work real nice.  This also works at night.

 

With our takeoff weight about 225 pounds below maximum, you can imagine that 5LM could climb.  After takeoff, I maintained power at the authori ze d maximum of Full throttle (38” MP), 2575 RPM.  After cleaning the airplane up, and establishing a 120 KIAS climb speed I set cruise climb power (34” & 2400 RPM), closed the cowl flaps and saw the VSI nailed at 1100 FPM.  This power setting and airspeed did two things.  It shut-off the automatic operation of the boost pump activated with all full throttle operations, and it allowed a more traffic observing deck attitude.  At 120 knots, there is enough cooling air going through the engine compartment that, on all but the hottest days, engine temperature is not an issue.  Rates of climb were as follows:

 

Altitude

IOAT

MP/RPM

Fuel Flow

IAS

Rate of climb

2000

+21

34/2400

29.5

120

1100

3000

+20

34/2400

29.5

120

1000

4000

+ 18

34/2400

29.5

120

980

5000

+17

34/2400

29.5

120

900

6000

+15

34/2400

29.5

120

900

7000

+13

34/2400

29.5

120

900

8000

+12

34/2400

29.5

120

900

9000

+10

34/2400

29.5

120

800

10000

+9

34/2400

29.5

120

800

 

These rate of climb values are slightly better than book numbers even though the conditions weren’t standard day.  This illustrates the positive effect of not always operating at maximum weight.

 

The first set of speed and power checks was accomplished at an altitude of 10,500 feet.  I set up Maximum Cruise Power (34”/2400 RPM) which was the same as that used for climb, so after the KFC-150 executed a precise level off, I just sat back and let the airspeed build.  Once the speed had stabili ze d, I could adjust the mixture for the Best Economy setting of a maximum of 1750-degrees F or peak Turbine Inlet Temperature (TIT) whichever comes first.  At altitudes below 22,000 feet, this power/TIT combination is allowed and yields Best Economy cruise.  Above FL220 and above 32”/2400 RPM, the maximum TIT is 1650 F.  The TIT did not peak prior to 1750-degrees, so leaning stopped at that point and the resultant fuel flow was 19.5 gallons of avgas per hour.  However, being the conservative pilot that I am, after taking note that the fuel consumption was slightly higher than the 18.1 value from the performance charts, I re-adjusted the mixture to 1650-degrees TIT.  This yields Best Power cruise and the fuel flow stabili ze d at 21.3 GPH.  After doing some TAS checks at 10,500, I took the TLS up to the maximum VFR altitude that nasal cannulas are authori ze d at of 17,500 feet and repeated the checks.

 

Cruise True Airspeed

 

Altitude

IOAT

MP/RPM

Fuel Flow

Direction

KIAS

GPS GS (KTS)

10,500

+9

34/2400

21.6

N

157

192

 

 

 

 

E

157

206

 

 

 

 

S

157

196

 

 

 

 

W

157

177

 

 

 

 

 

TAS

193

 

 

 

 

 

 

 

Altitude

IOAT

MP/RPM

Fuel Flow

Direction

KIAS

GPS GS (KTS)

17,500

-7

34/2400

21.3

N

150

215

 

 

 

 

E

150

229

 

 

 

 

S

150

202

 

 

 

 

W

150

184

 

 

 

 

 

TAS

208

 

 

During all the above operations, Cylinder Head Temperature (CHT) was consistently 3950 F, and Oil Temperature was 1920.

 

An operational note here.  Using 34” MP at 2400 RPM represents the maximum recommended cruise power setting.  As I said before, I’m a conservative guy, and while the M20M and the TIO-540-AF1B are certified for operation at 34/2400, I would operate my TLS at the lower setting of 32”/2400 RPM.  This setting gives a TAS of 194 knots at 17,500 feet and would reduce the fuel consumption to 17.3 GPH at peak TIT or 19.1 GPH at the Best Power 1650-degree F temperature.  For a further look at some operational aspects to be considered when operating the TLS, please refer to “M20M Operations Revisited” located elsewhere in this magazine.

 

After spending some time just enjoying the smooth cool air at seventeen-five, and doing a little sightseeing, it was soon time to take the Bravo to the traffic pattern to see how it lands.  Dropping the nose slightly, I let the airspeed build-up to the bottom of the yellow arc on the airspeed indicator.  174 KIAS with a slight reduction in MP and we are coming down comfortably at 500 FPM.  Here is where I really like the JPI EDM700/800 Engine Monitor.  I will change the display to show the rate of cylinder cooling to help reduce the possibility of doing damage to the engine cylinder heads.  As I reduce manifold pressure or enrichen the mixture, I keep an eye on the JPI.  By keeping the rate of cylinder cooling in the –10 to –20 degree range, I completely avoid shock cooling.  This is a great aid in controlling power and airspeed safely.  As an additional note, the mixture should be adjusted to keep the TIT in the warm range of about 15000 F.  This helps keep some heat in the heads and further helps avoid damage due to too much cooling.  If I want to increase the rate of descent without massive power reductions, I just need to deploy the speed brakes.  As in most Mooneys, using speed brakes during a descent will approximately double the descent rate for the same airspeed and power setting.

 

Into the traffic pattern and I slow the TLS to the Maximum Gear Extension Airspeed of 140 KIAS by setting the power to about 18” MP and 2400 RPM.  We prefer to fly the downwind at between 120 KIAS and 140 KIAS in the long body Mooney.  This keeps us within the normal airspeed of a majority of the other light aircraft that might be sharing the pattern and allows us to extend the landing gear at any time.  Abeam the touchdown point and down comes the landing gear and after a slight power reduction to about 17” the airspeed will be into the white arc so that the first setting of flaps is available.  The TLS has flaps set with a 3-position paddle switch on the center console.  With the switch up, the flaps go to the full “Up” or Zero-degree position.  The middle position is the “Takeoff” setting or 10-degrees and is used as an approach flaps setting as well.  With the switch moved to the down setting, the flaps will extend to “Landing” and the full 33-degrees is available allowing for the slowest landing approach speed.

 

Once the gear is down and 10-degrees of flaps are selected, another slight power reduction will help establish a 500-FPM descent and the targeted airspeed is between 90 and 100 KIAS.  This is the speed and rate that we recommend on base-leg.  At this point I like to do the first pre-landing or GUMPS check.  Once we are on final approach, the rest of the flaps are extended and power is again reduced for the target VREF for the approach.  This approach VREF is based on 1.3 VSO for the landing weight of the airplane.  A good target is to be established at the correct VREF by between 50 and 100 feet above the runway.  For a maximum landing weight condition in the M20M, this means 75 KIAS on short final.  At the target point, I like to have the airplane configured, trimmed and on speed so that the remainder of the descent to the runway is very easy.  As we continue to the runway, the power is slowly reduced once the threshold is past, and the landing VREF of 1.2 VSO is the target.  Again, at 3200 pounds maximum landing weight, the landing reference speed is 68 KIAS.  If we were landing at a weight of 3000 pounds, these two VREF speeds would be 71 KIAS and 66 KIAS respectively.  One sure way to have difficulty in making good landings in the TLS or any Mooney is to be too fast on approach and landing.  The second way to make landing interesting is to fail to adequately trim off the pressure on the control wheel caused by the extension of the flaps and the reduction in airspeed throughout the final phase of the landing.

 

In my opinion, the long body Mooney, especially the M20M with its three-blade propeller, is the nicest and easiest Mooney to land.  It’s something about the length of the elevator arm, combined with the weight and rotational inertia up front that make for a very solid feel during landing.  And flown correctly, the TLS has very respectable landing distance numbers.  On this day, with a Density Altitude of 3500 feet at just below 3000 pounds weight, the total distance from 50-feet to stop was 2600 feet.  Not bad for an airplane that will also give better than 210-knot true airspeeds and this distance didn’t abuse the airplane one bit.

 

After some trips around the traffic pattern to once again get landing current, too soon it was time to return 765LM to David and Jimmy so that they could find it a good home.  After the final landing it is necessary to let the engine and turbocharger cool before shutdown.  A minimum of 3 minutes is recommended and I usually try for 5.  Since landing rollout and taxi count, most normal operations at controlled airports will allow for shutdown once at the FBO ramp.  However, I would not hesitate to wait the requisite amount of time on the ramp until I was sure all the oil had cycled through the turbo and oil cooler, and the turbo bearings had sufficiently cooled before pulling the mixture to cut-off.

 

Any pilot purchasing the M20M TLS/Bravo should consider a very thorough, model specific transition course prior to solo.  Although it’s a Mooney, systems like the turbocharger, fuel, and advanced avionics should be completely understood before venturing out into the potentially “wild” blue yonder.  In addition, this airplane can operate at altitudes that are not suitable for support of human life, and a detailed understanding of the effects of this is critical.  Training should be from a knowledgeable and qualified M20M instructor, and should include a thorough systems review as well as emergency procedures and high altitude physiology.  An ounce of preparation and prevention here can not only save costly maintenance but possibly a life.

 

I enjoyed my time in the flagship of the Mooney fleet.  This high flying model has been promoted in the past as Mooney’s “Personal Airliner” which it truly is.  With a maximum altitude of 25,000 feet, the Bravo can top all but the severest weather and will do that while giving the choice of “blindingly fast” airspeeds with average range or very fast airspeeds and excellent range.  It can be equipped with TKS Known Icing Systems, air conditioning, Electronic Flight Information System (EFIS), Flight Management (FMS) and GPS systems and just about anything that a personal jet might have except for a potty.  All American Aircraft has this and several fine TLS’s to choose from.  Give them a call if you are interested in the fastest production non-pressuri ze d piston engine airplane in the sky today.