{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.
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.
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.
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 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
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.
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
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
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
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
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
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
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.
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.
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.
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.
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.
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:
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:
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.
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:
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:
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:
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.
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.
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.
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:
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:
20”
manifold pressure, 2500 RPM, peak TIT cowl flaps closed
Airspeed
KIAS Rate of Descent FPM
140
500
150 1200
160
1500
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.
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.
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.
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.
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.
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.
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.