{Note:  photographs will be added to this evaluation shortly}

 

Flying the M20K 252

 

Not only one of the best Mooneys ever built; one of the best airplanes ever built.  Let’s fly one and see why this is one of Mooney’s all time favorites.

 

 

Improving Upon the Model 231

In 1985, Mooney’s engineering department was tasked with making as many improvements as possible to the M20K 231 and bringing to the market a vastly improved airplane.  Not an easy task – the 231 is a pretty darn good airplane.  But there was room for improvement.  I was Mooney’s engineering test pilot at the time and was given the responsibility for development and certification flight testing on the 252. 

 

Mooney’s engineering department knew the 231 was a good airplane, but there were several things about the engine installation that we wanted to improve upon.  We also wanted to update some of the airplane’s systems.  Primarily, the 252 is a 231 with a refined engine, but there are other airframe and systems changes that make the 252 one of the best Mooneys ever built.

 

A Better Engine and A Better Engine Installation

First on the list of desired improvements to the 231 was engine cooling.  The Continental TSIO-360 in the 231 ran pretty hot, especially the –GB version installed from 1979 through 1983.  The –LB version incorporated for the 1984 model change ran cooler (20 degrees cooler cylinder heads and oil), but still was a pretty hot running engine.  The goal was to make the engine in the 252 operate much cooler.

 

Engine cooling was attacked in two ways.  First, larger cooling air inlets were cut into the front of the cowl.  Second, the outlet area was increased at the bottom of the cowl for all this added cooling airflow to exit.  The dual, horribly inefficient cowl flaps on the 231 were replaced with a single, infinitely adjustable electric cowl flap on the 252.  These two changes (inlet area and cowl flap) resulted in a lot more cooling air entering and exiting the cowling.  An added benefit was a slight reduction in cooling air drag, as a result of the larger, more efficient cowl flap on the 252.  These changes worked wonders.  The 252 is one of the coolest running turbocharged airplanes ever.

 

The next big change with the engine installation was a redesign of the 231’s primary induction system.  The 231 has a complex and relatively inefficient duct arrangement mounted on the copilot side of the engine.  From flight testing, we knew it was inefficient, choking air being delivered to the compressor.  Second, it was prone to allowing ice particles to enter the inlet duct and collect on the face of the induction air filter.  A side mounted NACA duct and filter can arrangement was designed and tested that was non-icing and that delivered lots of induction air to the compressor.  What a great change!  The TSIO-360 in the Mooney now had plenty of induction air to breath and use for combustion.

 

So in actuality, these were the two powerplant  changes made at the factory to make the 252.  They don’t sound like much, but we spent 250 flight test hours fine tuning these changes.  We now had a great installation for the TSIO-360 engine.  Now, if TCM would just give us an improved version of the engine to use in the 252.

 

Along Comes the TSIO-360-MB Engine

And they did.  TCM listened to customers and made big improvements to the TSIO-360 engine that resulted in the –MB version used in the 252.  The changes were many.  Most important on the list were a tuned induction system for more even induction airflow to the cylinders, a larger Airesearch TAO4 turbocharger, a manifold pressure controlling system allowing full throttle operations for takeoff and the incorporation of an  intercooler that cooled induction air temperatures by as much as 100 degrees F.

 

These changes were monumental.  Now, the TSIO-360-MB engine was one that ran cool, smooth and clean.  Where the –GB and –LB versions needed 40 inches of manifold pressure to develop 210 horsepower, the –MB needed only 36”.  That’s huge reduction in manifold pressure for the same horsepower output.  Another major improvement to the engine was a change in the fuel flows and fuel pressures at both the upper end and lower end of the power envelope.  The –GB and the –LB always seemed to be flooding in fuel flow.  The –MB ran clean and lean, from takeoff to idle power.

 

Other Changes and Certification to 28,000 Feet

Other changes for the 252 included the incorporation of a 28 volt electrical system, the option of a dual 70 amp alternator installation (most were so equipped) and a tailcone counted standby vacuum system that was quickly made standard equipment for redundancy in IFR conditions.  We also installed inboard main gear doors, which added 3 KTAS to the airplane.  These changes along with the powerplant improvements made the 252 a very reliable and capable airplane.

 

One additional change that I found ill advised - the maximum operating altitude was increased to 28,000 feet.  I spent lots of hours way up there deriving cruise performance and engine cooling data.  I can tell you that above 23,000 feet, the environment becomes pretty hostile.  After an hour or so of flying at FL280 with the standard oxygen masks in the airplane, I was washed out. 

 

We certified to 28,000 feet for only one reason – to obtain a maximum publishable cruise speed of 252 mph (210 KTAS) for the marketing department.  252 MPH was the number they wanted to promote the airplane.  We got it, but while flying unpressurized airplanes at 28,000 may be legal, in my opinion it’s not advisable.  A minor problem with the oxygen system can result in unconsciousness in 30 seconds – or less.  And, if you have a mechanical problem with the airplane this high, you’ll find you’re a long way from the ground and safety.

 

The First M20K 252 Delivered in 1986

The very first 252’s were ready for customer delivery in early 1986.  I was the first to fly the airplane on demonstration flights.  I can’t tell you how impressed everyone was who flew in the 252, especially 231 owners.  They couldn’t believe the new ability with the 252 to climb at full power, averaging 1000 feet per minute all the way to 20,000 feet.  They couldn’t believe the ability to climb and cruise without worrying about over-temping the engine.  And they really liked the smoothness of the engine in the 252 compared to the snorting common to the 231.

 

These first retail customers were a sign of things to come.  The 252 caught on and sold very well.  1986, 1987 and 1988 were good years to be at Mooney.  We sold 144 airplanes per year during those years and the majority was the model 252.  Very well equipped, the airplanes sold in the neighborhood of $180,000 to $220,000 – a heck of a bargain.  Almost all were equipped with dual alternators, a standby vacuum pump and speed brakes.  They also came with an excellent stack of digital Bendix/King avionics.  KAP or KFC 150 autopilots were the norm and almost every airplane had an HSI.  Loran C was big in the late 1980’s and many model 252 airplanes had them installed at the factory.

 

Shortcomings of the Airplane

There aren’t many with the 252.  Probably the biggest shortfall with the airplane is cabin payload with full fuel.  As well equipped as they are, most model 252’s have a 550-650 lb payload with full fuel – not much for a four-place airplane.  But this limitation isn’t really a factor since most Mooneys are flown with one or two people on board. 

 

There were some early problems with cracking engine induction air tubes, but TCM did a good job of taking care of this nuisance.  The solution was a beefed up induction tube design.  For the most part, this solved the cracking tube problem.

 

During the first 18 months of production, the airplane suffered from lots of engine driven vacuum pump failures.  We were so thankful in Kerrville for the decision early in the production run to equip every model 252 with a tailcone mounted standby vacuum system.  They were used quite often.  Sigma-Tek did a good job of correcting these early vacuum pump problems and we saw a dramatic improvement in the number of engine driven vacuum pump failures after the first 18 months or so of production.

 

Mooney’s Bread and Butter Airplane in the Late 1980’s

The model 252 was a home run in the marketplace.  I was at the factory during this period and I can tell you that the 252 was our “bread and butter” airplane.  252 sales covered many a payroll in Kerrville during the late 1980’s.  And the aviation press loved the airplane.  One of the best pieces of publicity was an article Flying magazine did in their June 1986 issue, comparing the 252 to the bigger and more powerful Cessna T210R.  To everyone’s surprise, the Mooney was faster.  To quote the article, “Little guy smites big fella”.  That one piece of publicity sold us countless airplanes.

 

Production Ends – The Reason

Model 252 production continued through 1990.  The market didn’t kill the 252 – demand remained strong for the airplane.  In 1989, the Model M20M TLS was introduced.  The French owners of Mooney did not want to build two turbocharged models at one time, thinking the factory would be building it’s own worst competition.  The 252 would have been really tough competition for the TLS.  So, just like that, one of the best to ever come off the assembly line in Kerrville was terminated in a split second decision.

 

A summary of model 252 production is shown below.  These are all great airplanes, built by people who cared about their jobs and about their workmanship.  No model year is better than the other – the same people built the 1986 models with the same care and concern they built the 1990 models.

 

       Summary of Model M20K 252 Production

Year          Serial Numbers           Total Number Built

1986         25-1000 to 25-1066                67

1987         25-1067 to 25-1157                91

1988         25-1158 to 25-1198                41

1989         25-1199 to 25-1220                22

1990         25-1221 to 25-1230                10

                                              Total         231

 

Finding an Example to Fly

Model 252’s are highly sought after today on the used market.  So much so that it’s difficult to find a good one to fly for an evaluation report.  As usual, David McGee and Jimmy Garrison at All American Aircraft in San Antonio (1-800-777-1491) came up with a great airplane for MAPA to fly.  It was a super nice 1986 model, serial number 25-1031, N252WG.  I remembered N252WG on the assembly line in Kerrville in 1986.  If I remember correctly, the airplane served as our factory demonstrator for a while.  It was good to see an old friend again.  The airplane has been kept perfectly by several owners.  The original paint and interior looked really good, a tribute to the wonderful factory personnel who applied it in 1986.  The airplane had amassed 2440 total flight hours and had a major overhaul by Mattituck only 212 hours ago.  Dual alternators were installed as well as a JPI engine analyzer.  The airplane was (and is) priced at $199,000, probably $15,000 to $20,000 more than it sold for new back in 1986.

 

The Cabin and Instrument Panel

With flight bag in hand, we approached N252WG for an evaluation flight.  Talk about feeling like saying hello to an old friend!  I spent many flight test hours in the 252 prototype.  Of all the airplanes I’ve flown in my engineering flight test career, I feel like I know the 252 the best.  It felt really good to be flying one again.

 

N252WG looked really good, almost like it did on the factory floor in Kerrville 16 years ago.  Up onto the wing and peering inside, it was good to see the lower instrument panel installed in all J and K models.  You can really see well over the nose in these two airplanes compared to the current production models with their too-tall panels.  In the J and K you can actually crank your seat all the way down and still see over the panel.  Doing this really improves your headroom.  In the current production airplanes, your seat has to be cranked up for adequate over-the-nose visibility.  Problem is, when you do that, there goes your headroom.

 

The instrument panel is pretty full on these earlier airplanes.  With less area to put stuff, every square inch of panel space in most J and K models is taken.  N252WG had something stuck in just about every empty space – flight instruments on the left, avionics in the middle and engine instruments on the right.  Engine power controls are located lower center and are positioned just right for comfort.  The lower center console contains the flap and cowl flap controls and indicators.  Cabin ventilation and heat controls are also located there. 

 

One thing I really like on these late 1980s airplanes is the color of the instrument panel.  The factory started painting them white beginning in 1986.  I really liked this change then and I still like it now.  Black panels tend to blend the instruments into one.  With a lighter colored panel, the instruments seem to be much more visible and prominent.  I really notice this when flying IFR.  It’s probably a psychological thing, but I still believe that flying behind a lighter colored panel is easier on the eyes and brain than a dark one.

 

External Inspection and Engine Accessibility

The M20K 252 is very similar to the 231 externally.  Firewall aft, it really is the same airplane.  The side windows on a 252 have rounded corners, the 231 square ones.  This was a cosmetic change only.  But firewall forward, the external differences between a 231 and a 252 are significant.  The 252 has larger (40% more) cowl inlets for added cooling air, a larger area electrically actuated cowl flap to exit more of that air and a  side-mounted NACA duct for engine induction air.  These are all major improvement items over a 231 that we spent lots of flight test time fine tuning back in 1985 and 1986.  These changes may seem minor, but along with the installation of the TSIO-360-MB engine, they make up the heart and soul of the 252. 

 

One thing we didn’t improve upon was engine accessibility for preflight inspection.  There is a little door in the top of the cowling for checking and adding oil, but that’s it.  If you want to inspect the engine carefully, bring a screwdriver with you and lots of patience.  It takes 10-15 minutes to remove and reinstall the upper cowling, which gives you a partial view of the upper portion of the engine compartment.  Give yourself at least 30-45 minutes to remove both the upper and lower cowlings.  And neither job is really doable by one person.  You will need a second pair of hands, especially for the lower cowl.  The best way around this design limitation is to make sure you are on hand when the airplane is in the shop for an oil and filter change.  That’s a great opportunity for you to step in and carefully inspect the engine, accessories and exhaust system for any problems that might have developed over the past 25-50 hours.  All Mooneys fail miserably in the area of engine accessibility for preflight.  The only way around this is to make the effort to do it yourself occasionally or to make it a habit to look over the engine anytime the airplane is in the shop with the cowling removed.      

 

Cabin Comfort and Shoulder Harnesses

Let’s get settled into the airplane.  One door on all Mooneys makes it a little awkward for boarding passengers.  It generally works best if the pilot is the first to enter, followed by any rear seat passengers.  The last in is the copilot/ right seat passenger.  The cabin is cozy for four, but that’s a subjective opinion.  I personally think four works quite well in a J or K model.  There’s not the feeling of spaciousness one gets in a Bonanza, and I think that comes from the lower ceiling in the Mooney.  But all things considered, a J or K model can carry four occupants just fine.  Not four 250 pound guys, but four average sized adults.  For four 250 pound guys, buy a six-place airplane.

 

You’ll like your seat – the left front one.  You’ll especially like the ability to adjust the seat all the way down and still see over the panel.  And if you’re like me, you’ll find yourself flying with the seat positioned at or very near the most forward position to reach the rudder pedals.  This puts your face pretty close to the panel, so get those reading glasses out of your pocket.  If you wear them like me, you’ll really need them in the Mooney to see the panel clearly.

 

Shoulder harnesses are standard for all four seats in the 252, a huge safety consideration.  All Mooneys, regardless of make and model, should have shoulder harnesses, at least for the two front seat passengers.  MAPA members ask me all the time what the most important safety feature is they could add in their airplanes.  Without a doubt, it’s front seat shoulder harnesses.  Rear seat harnesses aren’t quite as important, but they would certainly help as well. 

 

I can’t emphasize enough that serious injuries to front seat occupants without shoulder harnesses happen in Mooneys quite often.  And it doesn’t take much of an impact for the front seat occupants to pivot around a single lap belt and hit the panel with their heads or face.  A sudden stop from 20 knots will do it.  We sit awfully close to the panels in the Mooneys we fly.  Installing shoulder harnesses is the single most important thing you can do to improve the safety of your airplane.

 

Let’s Start the Engine and Taxi to the Runway

The TSIO-360-MB engine in the 252 has to be the easiest engine to start in the entire Mooney fleet.  There are a number of reasons for this.  First is the tuned induction system.  All cylinders receive almost equal amounts of induction air for combustion, resulting in much easier initial combustion for engine starts.  Another reason for easy engine starts in the 252 is the overall leaning of fuel flows and fuel pressures with the

–MB engine compared to the –GB and –LB.  Where the 231 is generally always set up too rich, the 252 is running a fuel flow and pressure that is just right.  You’ll see this in smoothness of operation and especially in ease of starting.

 

So, to start a 252, open the throttle one-quarter of an inch, prop control full forward, mixture full rich, primer on 3-5 seconds (8 seconds if it’s really cold) and engage the starter.  You’ll get a start.  The only negative you’ll encounter is the tendency for the engine to begin stumbling immediately after firing.  The trick here is to be ready with your finger on the primer.  Immediately when the engine begins stumbling, give it a short (2 seconds) shot of primer.  That should catch the engine and keep it operating until it smoothes out.

 

After the engine settles down, try leaning the mixture control for the taxi to the runway.  Again, the –MB engine in the 252 is set up to operate leaner at low power, so leaning on the ground is not so important as the overly rich –GB and –LB in the 231.  But you’ll still be helping keep those expensive plugs cleaner in the 252 if you aggressively lean for taxi.

 

You’ll like the ground handling of the 252.  Rudder pedal forces are just about right, much less than the current production airplanes with so much more weight on the nose gear.  And the turn radius of the 252 is less than the newer airplanes.  Ride quality is typical of the airplanes we fly - stiff.  Smooth pavement is okay, but you’ll feel all the bumps and joints.  Operations on grass or soft fields are questionable.  It’s my opinion that J Model and higher Mooneys don’t make good soft field airplanes.  Not enough prop and gear door clearance.

 

Takeoff - Power Settings and Technique

Onto the runway now for takeoff and we see the real advantage of the engine controlling system in the 252 – full throttle takeoffs.  With the 231, you have to carefully set a part throttle condition for takeoff to avoid overboosting the –GB or –LB engine.  This puts lots of responsibility on the pilot not to harm the engine.  With the 252, you can smoothly push the throttle to the full open position and let the controlling system regulate the manifold pressure.  Certainly, you need to watch carefully for a controlling system malfunction, but generally you put the throttle to the full open position in the 252 and leave it there.

 

Takeoff parameters in the 252 are 36 inches (+ or - 1 inch) manifold pressure at full throttle, 2700 prop RPM, and 1400-1500 degrees TIT.  Indicated fuel flow at takeoff power should be in the range of 22.0-24.0 gallons per hour.  If you see these parameters, your engine is operating perfectly and full power is being developed.  Don’t sweat an inch or so of manifold pressure off of 36 inches at full throttle.  That’s well within the controlling systems ability to regulate power, so don’t worry about it.

 

Most Mooney pilots know the trick for smooth takeoff rolls.  It’s that 5 pounds or so of slight pull aft on the control wheel as the airplane is accelerating down the runway.  This puts the weight of the airplane more on the main gear instead of the nose gear.  I’ve actually seen Mooneys get up on the nose gear during the later stages of the takeoff roll.  Not good.  You can keep this from happening if you apply that a steady pull of 5 pounds or so on the wheel as the airplane is accelerating down the runway.

 

I like to lift off the runway somewhere near 65-70 KIAS in the 252, accelerate to 80 KIAS once airborne, then retract the gear and takeoff flaps (if used).  On the subject of takeoff flaps, use them if the field is short or soft or if obstacles after takeoff are a factor.  But on long runways, try a few takeoffs without flaps.  In most Mooneys, takeoff flaps really don’t do much for performance and you’ll hardly notice a difference without them.  And it’s one less thing to remember to retract after takeoff if you don’t use them.

 

Climb Power, Performance and Engine Cooling in the Climb

Once off, cleaned up and climbing, it’s time to transition to enroute climb.  Try climbing a 252 to altitude at a power setting of full throttle (36 inches manifold pressure + or – an inch), 2700 RPM, mixture set for 1450-1500 TIT fuel flow at 22.0-24.0 GPH.  Full power climbs are the way to climb a 252 (and all other Mooneys) to altitude efficiently and in a way the airplane was designed to be flown.  We’ve gone over it many times in the past, but partial power climbs give everything away (performance when you need it the most) for nothing.  You won’t hurt the engine climbing at full power.  All the engines installed in Mooneys are rated for continuous takeoff power settings.  TBO is not magically increased by climbing at reduced power.  Fly the airplane to altitude at takeoff power.  It’s the way to fly your Mooney.

 

Concerning mixture settings in climb, the TSIO-360-MB engine in the 252 is properly developing takeoff power at a TIT (turbine inlet temperature) value of 1450-1500 TIT.  The corresponding fuel flow in that TIT range is 22.0-24.0 GPH.  Anything over 24.0 GPH and the engine is flooding in fuel and horsepower is down.  So it is perfectly okay to lean the mixture in the full power climb.  Most engines are set up too rich.  Get the mixture setting proper for climb by setting a TIT reading of 1450-1500 and note a corresponding fuel flow in the range of 22.0-24.0 GPH.

 

I like to climb a 252 at 120 KIAS.  Day in and day out, regardless of aircraft weight, 120 KIAS works the best for me.  Climb rates are very good and engine cooling is superb at the higher speed.  And you’re covering the ground in the climb at a very good clip.  Certainly, if obstacles are in the way or terrain dictates, I'll climb at best rate (Vy) or best angle of climb (Vx) airspeeds.  But climbing this slowly for sustained periods is not the way to fly the airplane.  Get the speed up to 120 KIAS and watch the airplane fly as it was designed.

 

I took a look at the climb performance in our evaluation airplane, N252WG.  The data below shows the observed rate of climb performance obtained during a continuous climb from shortly after takeoff to 18,000 feet:

 

Climb Performance Data

1986 Model M20K 252, N252WG

Full fuel, one on board, 30 pounds of equipment

Climb performed at full throttle, 2700 RPM, mixture leaned to 1450 degrees TIT, cowl flaps full open and constant 120 KIAS.

Time        Pressure Altitude       OAT        Man Press.     Fuel Flow          Calculated

Min.                 Ft.                         C             in. Hg.            GPH         Rate of Climb - FPM

0                    1000                       30              35.9               22.3                  ---

1                    1900                       30              35.6               22.1                 900

2                    2800                       28              35.2               22.0                 900

3                    3740                       25              35.5               22.1                 960

4                    4640                       22              35.1               22.4                 900

5                    5520                       21              35.1               22.4                 880

6                    6460                       19              35.2               22.9                 940

7                    7350                       18              35.1               22.8                 890

8                    8340                       17              35.1               22.9                 990

9                    9250                       12              35.1               22.9                 910

10                 10150                      10              35.1               23.0                 900

11                 10820                      10              35.1               23.0                 670

12                 11680                        9              35.1               23.0                 860

13                 12480                        9              35.1               23.0                 800

14                 13280                        7              35.1               23.0                 800

15                 13960                        5              35.1               23.0                 680

16                 14650                        3              35.1               23.0                 690

17                 15460                        2              35.0               23.0                 810

18                 16210                        2              35.0               23.0                 750

19                 16800                        1              35.0               23.0                 590

20                 17400                        0              34.9               23.0                 600

 

That’s excellent climb performance for a 210 horsepower airplane, even if it is turbocharged and even if we were about 300 pounds under gross weight.  The average rate of climb from 1000 feet to 17,400 feet was 820 feet per minute.  And that was at a constant 120 KIAS, well above the best rate of climb airspeed.

 

Our test airplane was equipped with a multi-probe JPI instrument that monitored engine temperatures in the climb.  I jotted down the readings just as I pushed over from the climb at 17,400 feet.  Here is what they read:

 

Observed Engine Temperatures in the Climb

1986 Model M20K 252, N252WG

Full power climb, 120 KIAS, cowl flaps full open

CHT 1     CHT 2     CHT 3     CHT 4     CHT 5      CHT 6       OIL TEMP

  371          381          395          370          360           352                189

 

These readings are far below maximum allowable values (460 CHT, 240 Oil).  For a turbocharged engine, they are remarkably cool.

 

So remember, a suggestion is to climb your 252 at full throttle, 2700 RPM, mixture leaned to 1450 TIT (about 23 GPH), cowl flaps open and 120 KIAS.  You’ll like the way the airplane carries you to altitude using this technique.

 

A Suggested Cruise Power Setting and Measured Cruise Performance

The engine and propeller in the 252 were designed and configured to be at their optimum at a certain power setting for sustained cruise flight.  We spent many flight test hours at altitude finding that setting.  If you fly a 252, here is the suggested power setting to use all the time, regardless of altitude and OAT:

 

Suggested Cruise Power Setting – Model M20K 252

Any Altitude and OAT

Manifold Pressure     RPM         Mixture Setting        Cowl Flaps        Approx. Fuel Flow

        28” Hg               2500            Peak TIT               Full Closed           12.8-13.8 GPH

                                                  + 50 deg. Rich

There are reasons for this setting.  28” is where the tuned induction system was designed for optimum air distribution to the cylinders.  2500 RPM is where the propeller was designed to be the most efficient.  And 50 degrees rich of peak TIT is the optimum compromise between best economy (peak) and best power (125 degrees rich of peak) TIT values.  And operating with this setting will always keep you within operating limits of the engine, regardless of altitude and OAT.        

 

We buy Mooneys to travel, and travel the 252 does.  We took a look at three different altitudes in our test airplane to measure actual, real world cruise speeds.  We used the four-way GPS groundspeed method to determine true airspeed.  The procedure has been discussed in previous articles.  At any altitude you want to evaluate, set a fixed power setting.  Stabilize airspeed and altitude and fly North, South, East and West on the compass (use the DG or HSI).  Write down the GPS groundspeed on each of the four headings.  Average those four.  The result is the aircraft’s true airspeed for the particular altitude and power setting being flown.  And it’s very accurate.  Airspeed indicators are not very accurate in the airplanes we fly, especially as the airplanes get older.   By using the GPS for determining performance, we are eliminating the airspeed instrument and obtaining much more reliable and accurate data.  Here is what we found on our test airplane, N252WG:

 

Level Flight Cruise Performance

1986 Model 252, N252WG

28” MP, 2500 RPM, leaned to Peak TIT+50 degrees rich, indicated fuel flow between 13.5 and 13.7 GPH, cowl flaps closed.

Pressure Altitude    OAT – deg. C      Direction       GPS Groundspeed - KTS

          5500                     21                       N                            188

          5500                     21                       E                             165

          5500                     21                       S                             147

          5500                     21                      W                            174

                                                             Average GS/KTAS     168.5

 

         12500                    8                        N                             194

         12500                    8                        E                              190

         12500                    8                        S                              174

         12500                    8                       W                             178

                                                             Average GS/KTAS     184

 

         17500                    0                       N                              203

         17500                    0                       E                               203

         17500                    0                       S                               181

         17500                    0                      W                              178

                                                             Average GS/KTAS     191.25

 

Those are excellent numbers, exhibiting cruise performance only other manufacturers can dream about.  They also demonstrate the performance advantages over the 231.  In our evaluation of the 231 in the August 2001 issue, we did the same cruise performance test on our test 231 airplane.  Here is how the 252 and 231 test airplanes compared in level cruise performance:

 

Comparative Cruise Performance   Model 231 versus Model 252

Data derived using the four-way GPS method

Model         Test Altitude     True Airspeed – KTS

  231                8500                       162.75

  231               17500                      180.75

  252               5500                        168.5

  252               12500                      184

  252               17500                      191.25

 

Looking at this data, you’ll find that the 252 averages about 10-12 KTAS faster than the 231.  That’s what most of the airplanes exhibited at the factory.  That’s a pretty good increase in cruise speed for the same basic engine and airframe.  It’s a big reason why the 252 is such an improvement over the 231.  The 231 is a fast airplane.  The 252 is faster.

 

How About Engine Temperatures in Cruise?

The other area where the 252 is head and shoulders above the 231 is in engine cooling.  The –GB and –LB variants of the TSIO-360 engine used in the 231 run pretty warm in cruise.  Sometimes, it is necessary to crack open the cowl flaps to keep comfortably in the green arc.  But not so with the –MB in the 252.  This installation runs cool all the time.  It’s just about impossible to over temp the –MB in any phase of flight, certainly not in cruise.  Here is some observed engine data taken from the JPI instrument in our test 252 in level cruise flight.

 

Observed Engine Operating Temperatures    Level Cruise Flight

1986 Model M20K 252   N252WG

28”MP, 2500 RPM, Peak TIT+50 rich, Cowl Flaps Closed

Altitude     OAT - C    CHT1     CHT2     CHT3    CHT4    CHT5     CHT6    OIL

  17500           0             385         420         415        404        411         394      204

  12500           8             370         409         404        394        391         374      199

  5500            21            366         387         395        378        378         361      203

 

Those are excellent numbers, especially for a turbocharged airplane.  Plenty of cooling margins.  It’s the number one reason why most model 252’s make it to engine TBO.  They run smooth and they run cool.  Therefore, they generally make TBO with few problems.

 

A Descent Profile That Will Keep the Engine Warm

Time to descend from altitude and the magic power setting that works for every Mooney will work with the 252.  When coming down, try using the following power setting:

 

Suggested Enroute Descent Power Setting

20” manifold pressure, 2500 RPM, peak TIT or EGT, cowl flaps closed

 

In the 252 (as in all other Mooneys), this power setting will keep the engine warm and will result in excellent descent profile airspeeds and descent rates.  And you can make the manifold pressure reduction from the cruise setting of 28 inches to 20 inches at one time.  I’ve heard pilots tell me that they use some formula of reducing manifold pressure every 1000 feet or wait 2 minutes before reducing manifold pressure in one inch increments.  I guess this won’t hurt anything, but where do these rules come from?  Just make one reduction to 20 inches and leave it there for the descent.

 

I took a look at some descent rates at the above power settings in the descent from altitude.  Here is what I got in the test airplane:

 

Observed Rates of Descent

20” manifold pressure, 2500 RPM, peak TIT cowl flaps closed

Airspeed KIAS             Rate of Descent FPM

140                                                                              500    

      150                                      1200             

160                                                                            1500

 

Speed Brakes                               

Most model 252 airplanes are equipped with speed brakes.  Our test airplane was no exception.  Speed brakes can do one of two things for you in descent.  First, for a given airspeed, their use will just about double the descent rate.  So if you’re coming down at 500 feet per minute at 140 KIAS clean, deploying the speed brakes will increase your descent rate to 1000 feet per minute.  The other thing they can do is for a given descent rate, they will slow you down about 20 KIAS.  In other words, if you’re coming down at 500 feet per minute at 140 KIAS clean, deploying the speed brakes will slow you down to 120 KIAS while still maintaining a 500 feet per minute descent.                     

 

An Absolute Minimum Power Setting for Descent

Many people ask what is the absolute minimum power setting that can be used in descent without shock cooling the engine.  Flight testing showed in the airplanes we fly that 15 inches of manifold pressure is the point where the propeller begins to power the engine instead of the other way around.  When the propeller begins to power the engine, shock cooling is the result.  So, keep in mind that in a pinch, you can reduce the power back to 15 inches in the descent if you have to without getting into a shock cooling mode.

 

Landing Pattern Procedures

Into the traffic pattern now with the 252, and it’s time to slow down for landing.  I like enter the downwind at 120 KIAS or so, then put the gear down somewhere near mid field.  The gear in a Mooney produces very little pitch change but certainly is an effective speed brake.  Opposite the touchdown point on downwind is where I like to place the flaps to the takeoff position (15 degrees).  Like all Mooneys ever built, expect a big nose down pitch change with flap defection.  Experienced Mooney pilots help offset this pitch change by always running the electric trim in the nose up direction anytime the flaps are deploying.  It helps a lot to smooth out the nose up force required on the control wheel as the flaps deploy.

 

On base leg, I put the remainder of the landing flaps down and slow to 80 KIAS.  Remember the big nose down pitch change with flap deflection – running the trim in the nose-up direction as the flaps deploy will help to eliminate that big pull required on the control wheel.  Turning final, I like to fly final approach in the 252 at 80 KIAS.  At this point, I usually go through the GUMP (Gas, Undercarriage, Mixture and Prop) check.  But one thing to keep in mind - don’t just blindly push the mixture control to full rich, especially at higher density altitudes.  Even though the 252 is set up to run leaner fuel flows at lower power, blindly pushing the mixture control to full rich on final approach could flood the engine with too much fuel.  So what I do is to increase the mixture control towards full rich, but not all the way to the full forward position.  On most airplanes, you’ll find that about one inch of travel on the mixture control will remain for the correct mixture setting on final approach.                                                    

               

Proper Landing Flare Speeds

So here we are on short final with at 80 KIAS with everything done in preparation to land.  The gear is down and the mixture control is properly positioned.  Now it’s time to begin slowing down so we will be at the correct speed for entering the landing flare.

 

We’ve discussed the subject at length, but the MAPA community’s number one area of mistake and mishap is trying to land with the airspeed too high.  Arrows and Lances and 210’s and even Bonanzas will all take care of a pilot who tries to land going too fast.  Those airplanes dissipate speed quicker in the landing flare due to their higher overall drag and more effective flap systems.  Not so with Mooneys.  We fly clean airframes with fairly ineffective flaps.  In other words, the Mooney is a floater.  And excessive airspeed in the landing flare in a Mooney makes an already clean airframe even more difficult to get on the ground.  This is where a Mooney pilot can get into trouble - excessive speed, floating down the runway with the end of the runway approaching. 

 

Mooneys have few vices, but one of them is this - never, ever try to force a Mooney onto the runway with forward pressure on the control wheel.  You might get away with it a few times, but sooner or later here’s what’s going to happen: 1) the airplane’s nose gear will strike the runway, 2) the airplane will rebound back into the air, 3) at the top of this bounce, the pilot will again push forward on the wheel again, 3) the airplane will strike the runway again on the nose gear, 4) the airplane will rebound back into the air a second time, 5) at the top of this second bounce, the pilot again pushes forward on the control wheel, 6) this time, the airplane strikes the runway in such a nose low condition that the prop strikes the ground, curling back the propeller tips, 7) the airplane will stay on the ground this time, but the pilot faces a $15,000 repair job for an engine teardown and prop replacement.

 

The above landing incident happens much too often in the MAPA community.  It’s our number one area of accidents and insurance claims.  But the solution is simple – begin the landing flare at the proper landing flare speed.  You won’t float and you won’t bounce if the airspeed is correct as the airplane enters the landing flare.  Many people ask me what the correct speed is to fly in the landing pattern.  My answer is “whatever you’re comfortable with”.  The speed in the pattern isn’t that important.  But what is of critical importance is the speed at which you enter the landing flare about 10 feet above the runway.  It better be close to being right on target in a Mooney.

 

So what is that proper landing flare speed?  It’s 1.2 times the stall speed for the flap configuration you are using.  And the way to determine what that proper indicated airspeed is to do a series of power off stalls in your airplane with various flap configurations with the gear down.  Write those indicated stall speeds down.  Multiply them times 1.2.  The resulting number is the correct indicated airspeed for entering the landing flare at the various flap settings.

 

So what are these speeds in the 252?  We took our test airplane to altitude and did a number of power-off stalls at with the flaps both full up and full down.  Here’s the data.

 

Stall Speeds and Calculated Landing Flare Speeds

Model M20K 252, N252WG

Power         Gear        Flaps         Indicated Stall Speed      Landing Flare Speed - KIAS

                                                               KIAS                             1.2 X Stall Speed

Off            Down         Up                        54                                          65

Off            Down     Full Down                50                                          60

 

I know these speeds sound low.  But they worked perfectly.  My technique was to “cross the fence” at 80 KIAS, then decelerate to the proper flare speed as the airplane got within 10 feet of the runway.  Beginning the flare at 65 KIAS flaps up and 60 KIAS flaps down resulted in just the right amount of energy for a good flare, a little bit of float and a smooth touchdown.  And the landing distances were short.  Very little braking action was needed to stop the airplane within 1000 feet of the touchdown point.

 

The secret to good landings in a Mooney is to have the airplane at the proper speed as the landing flare is initiated.  Too slow and the airplane will plop on the runway.  Too fast and the potential is set up for the airplane to float and the pilot to push.  Sooner or later, this will result in a nose wheel first touchdown, a series of bounces and a propeller strike. 

 

Taxi and Engine Shutdown

After clearing the runway, retract the flaps, open the cowl flaps and lean the mixture for the trip back to the hangar.  Leaning for ground operations is perfectly okay and will save your plugs from fouling, especially on an engine that is set up with the idle mixture too rich.

    

There is a note in the POH about letting the engine idle for 5 minutes before shutting it down.  This has to do with the turbocharger bearings cooling down sufficiently and not baking or coking the oil when the oil supply is stopped as a result of stopping the engine.  Don’t sweat this too much.  Certainly, it wouldn’t be a good idea to stop the engine immediately after landing.  But remember that you’re not using much engine power in the landing approach, so the turbocharger has been cooling since you reduced power on final approach to land.  What I do is to consider the 5 minute cool down time to include the time I spent at low power on the approach and the taxi back to the ramp.  For the airports I fly into, it takes me about 5 minutes from the time I reduced power to land until the time I taxi into the parking space, so I normally don’t need any more cool down time than that.

 

Summary

The 252 is simply one of the top Mooneys ever built.  Because the engine installation is engineered correctly to run cool and smooth and at the proper fuel flows, most 252 airplanes make the published 1800 hour TBO.  The airplane delivers excellent cruise speeds along with very good fuel economy.  The current production Mooneys deliver more performance, but at the cost of higher horsepower, fuel flow and maintenance costs.

 

A Model 252 is simply a best buy in the pre-owned marketplace.  If you can find one, buy it.  Prices are escalating sharply.  A 252 is an investment that you’ll make money with.  Buy the airplane, fly it for a few years and sell it for more than you paid.  Add a Garmin 430 or 530 to the panel and you’ve got just as much instrument and airplane capability as a current production Mooney….at one-half the price.  175-185 knots on 13.5 gallons per hour is hard to beat.  As a matter of fact, it’s impossible to beat.  No other Mooney can do this.  You’re in an elite club if you fly a 252.  Get one if you can.