Operational hints and tips for the M20K

SHOP TALK – March 2000

by Kerry McIntyre

This month's column is very special to me. I get to write about the type of airplane I have (rebuilt and) operated for the last four years and some 250 hours - the TLS (M20M). The Mooney TLS is the fastest, single-engine, piston-powered aircraft in production today (March 2000). For many MAPA members, the possibility of owning a TLS might only be a dream at this time because the purchase price (new or used) is so high. But who knows what the future holds. For those members who might someday own an M20M, let me give you a little insight into what flying this airplane is like from a recent trip I made with my dad.

Just after Christmas 1999, my dad and I flew to Mt. Vernon, Illinois, 75 miles east of St. Louis. The first leg of the trip from Evanston, Wyoming (90 miles east of Salt Lake City), was against some headwinds, so we stopped in North Platte, Nebraska, to top off the fuel. We left North Platte and filed for FL230 to St. Louis. Climbing at 115 knots IAS at 1000' per minute, we were at 17500' in just under 18 minutes. Waiting a few minutes for ATC to allow us higher, we finally began to see the headwinds change to tailwinds.

With 199 knots TAS, the GPS was showing 229 knots ground speed and ATC gave us the okay to climb to FL230. Trimming the nose up for a 750' per minute climb to FL230 yielded a 170 knot TAS climb speed and a 20.7 GPH fuel burn. Once level at FL230, the TIT is 1625°, the CHT is 460° (a little on the high side) and the oil temp is 190° after we reduce power to 32" and 2400 RPM for cruise. This yields 17.6 GPH fuel burn at 206 knots TAS, now the GPS showing a ground speed of 260 knots. After a few minutes at cruise, the CHT is at 450°.

Flying over St. Louis at FL230, the OAT is -30° Celsius. The TLS cabin heater is marginal at best under these conditions. ATC allowed us to let down to FL190, but our destination is now less than forty-five miles away. I'm beginning to wonder if we will be able to get down in time for landing at our destination, Mt. Vernon. As a matter of fact, at this distance and altitude, I'm beginning to wonder if we will be able to land anywhere in the state of Illinois!

ATC finally cleared us to descend below FL190, only 42 miles out. The field elevation is 480' MSL. We have been slowly reducing power to 30" while waiting for ATC to let us down. We pop out the speed brakes and push the nose over. The VSI needle quickly disappears behind the 2000' mark. The altimeter is fast unwinding like something out of an old 12 O'clock High episode. The CHT is kept at 425° during the descent (aren't speed brakes great!). With the airspeed indicator in the yellow at 181 knots (smooth air), the GPS registers 305 knots ground speed.

It's late Sunday afternoon and nobody is in the pattern at Mt. Vernon. We cross the field at pattern altitude doing 170 knots. The turn to downwind scrubs off a bunch of speed and down comes the gear and 10° of flaps. A gentle turn to base leg and another gentle turn to final approach. We land with the speed brakes still out and full flaps at 70 knots with plenty of runway to spare.

That's what flying this magnificent airplane is like. Now that you've gotten an idea of the performance and energy management that's required in flying the TLS, let's get into a little history of the airplane.

Mooney originally took a Porsche airframe (M20J PFM) and installed a one-of-a-kind Lycoming TIO-540 under the cowling. The first three years (1989, '90, and '91) were development years and there were many changes. The early airplanes had gross weight (3200 lbs.) and a different angle on the dynafocal engine mount. By mid-1990 (serial #69 and up) the engine mount angle had been changed to reduce vibration and the gross weight was up to 3368 lbs.

In 1991, an inner gear door stop kit solved the problem of broken gear door linkage parts and loose gear doors that would hang open and vibrate against the airframe at higher airspeeds. A fresh-air kit was added in 1991 to properly evacuate smoke in the cockpit if an electrical fire were to occur. Most TLS airplanes came loaded with top‑of-the-line Bendix/King avionics. In 1991, an option for EFIS was added to the panel. As far as I can tell, all TLS airplanes came with dual alternators, dual vacuum pumps, dual 24-volt batteries, speed brakes, built-in oxygen, and vertical adjustable articulating lumbar front seats.

When the TLS is being flown at high, cold altitudes, it exhibits some very interesting quirks. It is typical for the fuel flow to drop a half-gallon per hour after about one hour of flight. Most everyone agrees that this is because the fuel is cooling, becoming denser, and the density altitude controller is compensating to maintain the same BHP that the pilot set the engine controls for. Because the TIO-540-AFlA and -AFIB are equipped with a density altitude controller, it makes little difference to the engine what the atmospheric conditions are. The controller adjusts the manifold pressure to compensate for air density so you can maintain 100 percent BHP to 22000'. Unlike the 231 or 252, this will give you a consistent TIT at the same altitude regardless of OAT and air density.

We have found that a good way to set the proper fuel flow at higher power settings (70% and above) is to watch the manifold pressure gauge. The manifold pressure gauge is more accurate than the TIT. The reason for this is as you get close to peak TIT the TIT needle moves very little and responds slowly. Most engines have a steep initial leaning curve, but as you get close to peak this curve flattens out and the actual peak point is very easy to miss.  By watching the manifold pressure gauge as you slowly lean the engine you will see the manifold pressure jump up one-half to one inch right at peak TIT. This is because the engine is now burning every drop of fuel with all cylinders operating at their maximum.

When that manifold pressure peaks, note the temperature on the TIT gauge. That's the accurate peak TIT value for your flight conditions. Then, my recommendation is to reduce it by 100°F (max continuous 1600°F) by enriching the mixture. I advise using caution running economy cruise (25°F rich of peak) at any power setting higher than 70% BHP. Variations in fuel flow among the cylinders may have one or more cylinders too lean and too hot. A per-cylinder engine monitor would spot this. Try to remember that fuel is a coolant in an air-cooled engine and fuel is the cheapest thing you will ever put in your airplane. By running 100°F rich of peak TIT, it is my opinion that you are adding life to your turbocharger and cylinders. The amount of extra fuel burned at 100°F rich-of-peak will vary with altitude but will be well worth it in longer engine life and lower maintenance expense. The bottom line here is, in cruise, make 1600°F TIT a limit.

The Lycoming engine in the TLS has nitride-hardened steel cylinders that can handle heat a lot better than the 231/252 TCM cylinders. As a result, 100° rich of peak TIT is just fine as long as you don't exceed the 1750° maximum for one minute and 1600° degrees continuous TIT Lycoming has set for the TIO‑540‑AFIA and -AFIB. The 500° CHT never-exceed-limit for the TLS is, in my opinion, too high to operate near or at for any length of time. When operating in the flight levels, it is not uncommon to see the CHT one or two needle widths from the red line. Your engine will last a lot longer if you open the cowl flaps just a little to bring the CHT down to below 450°. Remember that high TIT and CHT temperatures are only going to damage your engine.

In the flight levels, the oil pressure on my TLS drops one needle width (top of the yellow, bottom of the green) but the oil temp shows no change. The oil pressure drop is a gradual one and I believe it is an indicator problem, possibly caused by the low ambient pressure at altitude. Another strange item is the fuel pressure needle will quiver gently on and off. I used to think that ice crystals were forming in the fuel but after running IPA in the fuel for an entire winter, it made no difference. Flying at the flight levels at -30°C causes piston engines to do strange things.

Another problem that some TLS engines had was some surging during takeoff. When the atmospheric conditions were just right, the density altitude controller and the pressure controller would fight for control of the manifold pressure at full throttle. Remember, the TLS will not always pull redline manifold pressure at full throttle. But it should always produce 270 BHP at full throttle regardless of conditions. Lycoming issued Service Letter #1473 to readjust the setting on the pressure controller. This solved all the surging problems.

The TLS engine has been plagued with exhaust valve guide problems since day one and I will attempt to explain why and how this problem was solved. In my opinion, when compared to the TCM engine, Lycoming engines have a somewhat inferior oiling system from the camshaft to the valve guides. Couple that with an aggressive leaning power chart and you have the recipe for cooking that engine. In 1995, Lycoming developed the Bravo kit for the TIO-540-AFlA by taking an idea from the Beech Duke engine - an injection of oil directly to the exhaust valve guides to keep them cool and lubricated during high power operations. However, like most new things, the Bravo kit had its development problems. Early kits had small oil drain-back lines; oil would collect under the valve covers and flood the intake valves causing high oil consumption and excessive blow-by on the belly of the aircraft. Also, in 1997, the FAA issued an airworthiness directive against piston pins in TIO-540 engines. By mid-1997, the Bravo kit was starting to prove its worth, the exhaust valve guide problem having been solved.

From my experience in operating my TLS, if you use a little common sense and not use the fuel flow numbers provided by the power chart, the TLS engine will give its owner plenty of trouble-free hours. I can't say this enough - always find peak TIT by using the manifold pressure gauge and then enrich the mixture 100° rich of peak TIT (never exceed 1600° continuous). This procedure will give you the correct fuel flow for proper cooling.

Just because your POH says it's okay to run 500° CHT temperatures does not mean that this is the best practice when it comes to the proper long term care for your engine. My opinion is that if you operate hot (CHT above 450° and TIT above 50° rich of peak), the TLS engine and turbo system will cost you a fortune to repair. My TLS typically costs me about $250 to $550 in parts during the annual. Typical items are brake pads, a new air filter, oil, oil filter, oil sample kit, spark plug gaskets, and fuel injection 0-rings. There are only two airworthiness directives against the TLS and both are one-time occurrences (provided you replace the required parts).

For a high-performance turbocharged airplane, the TLS should be a very inexpensive airplane to maintain provided you don't abuse the engine. My TLS is typically flown on 2-3.5 hour flights and about 75 hours per year. About 40 percent of the time, these flights are made in the flight levels. At the last annual, reinforced aileron links were installed and during the next annual I will install new main gear doughnuts. I am budgeting an additional five hundred dollars for those doughnuts.

I have not had any engine problems at all (one alternator failed 3 years ago), but I have seen others having the problems caused by using overly lean fuel flows from the power chart while operating in the flight levels.

The real beauty of the TLS is that it is like owning a 201, 231, 252 and a TLS. It can be flown at 7500' on 10.5 gallons per hour at 160 knots like the 201. It can be flown at l3.5 gallons per hour at 170 knots like a 231. The TLS has a similar performance curve as all Mooneys; it just has a much larger performance envelope than any other Mooney ever built. I tell people all the time that "If you don't need more than 4 seats you will never outgrow this plane." Let's think about that statement for a moment: The TLS flies higher and faster than almost every twin-engine piston powered plane and it costs 2/3 less money to own and operate. With the TKS anti-ice system installed, you now have an all-weather airplane that will get you through and above many icing conditions, although I personally believe that flying in known ice in a single-engine airplane is not the smartest thing to do. I can't help but remember the Cessna P210-T210 and -T206 fuel systems icing up causing engine failures at altitude or the Mooney 231 engine air filter icing problems.

I hope you've come to know the TLS a little better by now. If you ever get the chance to upgrade to a TLS, take it. I'm sure you will never regret it. I really enjoy my Turbo Lycoming Sabre and will never be able to replace it. Nothing flies higher or faster on so little money. If I can answer any of your questions about the TLS, you may contact me via e-mail: shoptalk@knr-inc.com or by the old‑fashioned telephone at our aircraft repair facility: 307-789-6866. As always, I hope you enjoy flying your Mooney.