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Breathing…It’s The Difference in Engine Performance

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The PT6 engine that’s found on the Jetprop and Meridian is designated a -21, -34,-35, or a -42A.  The Continental engine on a Malibu is either a TSIO 520 or a 550.  What’s the difference? Why should I care? Most pilots don’t understand the difference, but it’s pretty easy to understand…and it’s all about breathing.

Whether a piston or a turbine, the engine has a ratio of fuel/air that works best.  For a piston model, we can make adjustments to this ratio by adjusting the mixture.  In climb we use a richer ratio to help cool the engine, and in cruise we lean the mixture to save fuel since we don’t need the extra fuel for cooling (due to higher speeds which cools the engine). In the turbine, the ratio is set and there’s nothing that can be done about it…except climb to a higher altitude.  But, more about that in a second..let’s go back to the piston discussion…

Piston: A Continental 520 engine and the 550 engine are flown exactly the same.  On takeoff, both will develop 310HP (38″MP with the 520, 35.5″MP with the 550).  So, why would a pilot want a 550 in his airplane as opposed to a 520?  The answer is breathing.

A 520 is named appropriately because the engine displaces 520 cubic inches of air with each complete cycle of all 6 cylinders.  To determine the displacement, just figure the bore (diameter of the cylinder) and the Stroke (how far the piston travels in the cylinder) and plug the numbers into this formula:

CID = Bore X Bore X 0.8754 X Stroke X # of Cyl.

Here’s the bore and stroke of the Continental 520 and 550 engine:

TSIO 520:  Bore = 5.25″ and Stroke = 4″
TSIO 550: Bore = 5.25″ and Stroke = 4.25″

So, you can see the two engines are exactly the same except the 550 has a little longer stroke, and therefore displaces a little more air.  Said another way…it the sucks the air into the engine a little better.

So, with this knowledge, the ability for the engine to breathe becomes a little more clear.  Both a 520 and a 550 will perform exactly the same until the point that a 520 simply cannot suck enough air and begins to develop less MP as a result.  For most 520 engines, this will happen somewhere around 18,000 ft.  But, it is dependent upon a myriad of factors including: health of the engine, altitude, temperature, and atmospheric pressure. When the 520 hits this point, the throttle can be full-forward, but the engine will not develop full MP, but some number that is less.  I’ve seen a max MP at FL250 in a 520 Malibu to be about 31″MP.  So, you can probably guess that the rate of climb will correspondingly suffer as the engine develops less MP.  How do we fix this problem?  Enter the 550…

Since the 550 displaces more air, the engine will maintain max MP to a higher altitude.  When the 520 begins to develop less power at about FL180, the 550 engine will be able to continue to maintain 35″ at a higher altitude.  Make no mistake…the 550 will also hit an altitude where is cannot develop 35″MP, but this altitude will probably be nearly FL220.  So, the 550-powered Malibu will reach cruising altitude faster than the 520.

But, at cruise both engines are pulled back to 30″MP.  So, either engine will deliver the same cruise speed because they are both able to develop 30″MP at any altitude.  Does it really matter if you’ve got a 520 or a 550 engine?  Answer: not much.  Both are excellent engines and both will deliver the airplane to the destination, but if the chosen altitude is above FL180, the 550-powered airframe will probably arrive a few minutes earlier.  Which would I want if I were purchasing an airplane?  It’s not a big enough deal, IMHO.  I’d select the best airframe/engine/prop combination and not put much weight into the 520 vs. the 550.

Turbine world: So, how about the -21, -34/35, and -42A compare?  Here, there’s  big difference, but it’s still all about the breathing.  A -21, -34/35, and -42A are all derivatives of the famous PT6 family of engines, and all are designed to be 1000+SHP engines de-rated to fit the airframe.  For instance, the -42A engine is 750SHP when mounted on a King Air 200, but the same engine is derated to 500SHP when mounted on the Meridian.  Ditto with the -21 and -34/35 engines…all are de-rated.  So what’s the difference? Breathing…

At the lower altitudes all will develop their maximum rated SHP, meaning they will all develop maximum torque.  And, down low there’s plenty of air to breathe so the engine has no problem developing that torque at a low ITT.  But, as altitude is gained, the engine must suck more air to develop the same torque, and the ITT goes up.  At some point in the climb (depending upon altitude, temperature, pressure, and IAS) the engine will not be able to produce max torque without exceeding Max ITT.  At this point, the engine cannot breathe any more (suck in anymore air), and the power (torque) developed falls off.  With the -21 engine, the power falls off quite dramatically because the engine simply cannot breathe well.  It is a smaller engine and more air cannot be forced into the compressor section.  For the rest of the climb the engine is “ITT limited” and the performance will suffer.

The -34/35 engine is a little bigger and will develop maximum power (torque) to a higher altitude.  And, when the torque does drop off (as altitude is increased), the rate of decrease is less because it can breathe easier due to it’s larger size.  Guess what? The -42A will beat out the others and develop max torque to an even higher altitude.  With this decrease  in torque available also comes a welcome friend…less fuel burn.  Altitude is the friend of any turbine pilot, and he/she will climb to the highest altitude possible to save on fuel.

The end result is the -21 powered Jetprop will cruise at 238 KTAS (in the summer) with a fuel burn of only 28gph.  The -34 will have higher torque than the -21 and will develop more SHP and will have a higher cruise (260 KTAS in the summer) with a correspondingly higher fuel burn (32gph).  The -42A will be breathing easily at higher altitudes, and will develop the most torque, but with a fuel flow of 39gph.  The Meridian (with the -42A) will not out-perform the -34/35 Jetprop in cruise purely because the Meridian is much heavier.

Just remember…fuel flow in a turbine is always commensurate with its ability to breathe and a turbine’s ability to breathe is a function of the engine’s ability to breathe.

With this knowledge…let’s check your understanding.  Answer this question: Will a Jetprop cruise faster in the summer or winter?  Remember, cold air is more dense than warm air, and an engine will develop power according to it’s ability to suck in air.  More air available, more power available.  Answer: Winter.

A good analogy: I’m a Cross-fitter (meaning I do crossfit workouts a lot).  In the gym we have various workouts that test a person’s ability to perform.  Guess who usually does the best?  Right…the guy who can breathe the best.  A person is nothing more than an engine…we intake air and combine it fuel and burn it to develop energy.  In Crossfit, the person with the biggest engine (muscles that can develop power) that can sustain power (good aerobic capability) will win almost every time.  The only variables then are genetics (how well-made is the engine), flexibility (you’ve got to be able to get into the position), and skills (there are more efficient movements).  A good Crossfitter will work hard on mobility, skill, and try to increase the bodies ability to increase capacity through a tough workout.

To get maximum performance, the pilot cannot change the engines skill or mobility (at  least not without an engine change!), but a thorough understanding of the how the engine breathes will help him/her use the power that is available to the fullest.

Joe Casey’s aviation story began in 1990 with his first flight near Nacogdoches, TX in a Cessna 172. From lift-off, Joe knew he would have a lifetime passion flying just about anything that will leave the ground…He was completely hooked.

Along with being an FAA Designated Pilot Examiner (DPE), Joe is an ATP/CFI-AHMG and Commercial Rotorcraft/Glider Pilot in the civilian world and also a UH-60/AH-64 Pilot-in-Command/Instructor/Examiner Pilot in the US Army Reserves.  His passion for the last 19 years, however, has been the PA-46 Malibu/Mirage/Matrix/Jetprop/Meridian. Has has amassed over 6,500 hours in various PA-46 airframes and believe it to be one of the finest flying machines available for the serious cross-country pilot with an eye for efficiency.

Now, Joe has flown more than 12,200 hours in just about every imaginable environment. Whether providing initial/recurrent training in the PA-46’s, TBM’s, instructing in NVG’s in a UH-60 Blackhawk, flying the King Air series of airplanes, giving tailwheel endorsements, or taking kids flying for the first time, he simply loves flying machines and the people who fly them.

Garmin GFC 700 Autopilot

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The Garmin GFC 700 Autopilot is an amazing machine.  Fully digital and fully integrated with the Garmin G1000 glass panel, it makes a pilot’s workload a lot easier, especially in busy airspace.

I train a lot of pilots in airplanes that have the Garmin GFC 700 autopilot.  The Cirrus SR22, the Columbia 350 & 400, the G36 Bonanza, and the Piper Mirage and M350 to name a few.  The most common problem I see for pilots transitioning into the Garmin GFC 700 equipped aircraft is that it doesn’t act like other autopilots.

STECs and DFC 90 Autopilots function like this:  you push the button for the mode you want on the autopilot controller and that turns the autopilot on.

Not so on the Garmin GFC 700.  If you push the button for the mode on the GFC 700, then the flight director engages, but not the autopilot.  This confuses folks a lot who move up from different autopilots because their autopilot primacy side of their brain is telling them the autopilot is on whenever they push one of the buttons on the GFC 700 controller.

Here’s an example:  A pilot has just departed and is ready to turn on course.  In his old airplane with an STEC 55x autopilot, the pilot pushes the direct to key to go to his first waypoint, then pushes NAV on the autopilot controller and the STEC 55x comes on and starts flying on course.  Then he presses VS and ALT to initiate a climb.

With the same scenario and a Garmin GFC 700 autopilot, the same pilot (who is used to a 55x), pushes the direct to key, then pushes NAV on the autopilot controller and pushes IAS or FLC to initiate the climb.  He lets go of the flight controls thinking the autopilot is engaged.  The airplane starts nosing over and he starts panicking.

Why did this happen?  The pilot in the second scenario never pushed the AP button on the Garmin GFC 700 so the autopilot never engaged.  All he did by pressing the NAV button and IAS button was to turn the flight director on.

How to remedy this?  Get in the habit of checking your scoreboard.  On the top of the G1000 or Garmin Perspective PFD, there is an autopilot annunciation strip (or scoreboard as I like to call it).  In the very middle of the scoreboard is an area to show if the autopilot or flight director is engaged.  AP means the autopilot is on; FD means the flight director is engaged but the autopilot is not.

I teach pilots to be in the habit of checking your scoreboard each time you get done pressing buttons on the autopilot controller to ensure the Garmin GFC 700 is in the proper mode.  This saves some of those panic moments when it is supposed the AP is engaged, but it’s only the FD.

Shock Cooling in a PA46

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We’ve all heard it said…”reduce the throttle by no more than 1-inch every minutes to ensure you don’t shock-cool your engine”. Does this advice apply to a PA46 engine? Can a PA46 engine (Lycoming 540 or Continental 520/550) really be shock-cooled? How should the engine temperature be managed?

Metals expand and contract with temperature, and the various metals in an air-cooled aviation engine expand and contract at a different rates. Shock-cooling supposedly occurs when the engine changes temperature quickly and the different metals in the engine cool (and therefore change shape) at different rates. When the change occurs dramatically supposed scoring, rubbing, and marking of the metal can occur, which can cause catastrophic results.

So, let’s back to the original question…can a PA46 engine suffer shock-cooling and should a pilot operate the engine so as to avoid shock cooling? Simply put, I’ve never seen nor heard of any piston PA46 engine suffer shock-cooling. In 5000+ hours flying the piston PA46 and 16 years of flying/managing/training in the Malibu/Mirage/Matrix, it simply has not happened to me nor anyone I know. Does it mean that it cannot happen or has never happened? No. But, it is certainly not a prolific threat to our fleet.

Should the owner/pilot operate the engine with a cautious eye cast toward the potential of shock cooling? Well, sort of…but, let’s flesh this out. My suggestion is that a pilot should operate the engine with conservatism in movement of temperature, but only because this is a good operating practice with any machine, and any flying machine is (by definition) not “overbuilt”. And, there are many ways to change the temperature of the engine…not just by reducing power. Here’s a partial list of ways to cool your PA46 engine:

  • Reduce power: Obvious…yes. When the engine produces less power, less heat is generated. Reducing power in a piston engine will almost always result in less temperature.
  • Lower the nose: By descending (and leaving power in a cruise setting) the airspeed will increase and cool the engine.
  • Enrichen the mixture: Fuel has a cooling effect on the engine, so the richer the mixture the cooler the engine.
  • Lower the landing gear: Yes…you read that right…engine cooling will occur when you lower the landing gear because more air will flow over the cylinders. Notice the landing gear doors on the PA46 have air louvers. Air flows into the engine nacelle on the front, passes down through the cylinders (along with the oil cooler, intercoolers, and other components) and then out the louvers of the closed gear doors. When the landing gear is lowered the “back door is opened” and a LOT more airflows over the cylinders.

My suggestion is that a pilot only perform ONE of these actions at a time when beginning a descent. This suggestion was presented to me by Chad Menne (Owner, Malibu Aerospace) some time ago and I’ve operated engines this way ever since. If you are at a higher altitude and simultaneously reduced the power, lowered the landing gear, started a big descent, and enrichened the mixture in one flail swoop, I think there’s a chance that your engine would suffer some negative effects that could be called “shock cooling”. So, when you do start a descent, pick one “cooling action” to accomplish at a time. I’m sure you’ll not hurt your engine.

Simply put, shock cooling is not a huge factor in the PA46 community, and a PA46 pilot does not need to be overly cautious. The “one inch per minute” rule may apply in some other airframes, but in the PA46 world it is not applicable.

Joe Casey’s aviation story began in 1990 with his first flight near Nacogdoches, TX in a Cessna 172. From lift-off, Joe knew he would have a lifetime passion flying just about anything that will leave the ground…He was completely hooked.

Along with being an FAA Designated Pilot Examiner (DPE), Joe is an ATP/CFI-AHMG and Commercial Rotorcraft/Glider Pilot in the civilian world and also a UH-60/AH-64 Pilot-in-Command/Instructor/Examiner Pilot in the US Army Reserves.  His passion for the last 19 years, however, has been the PA-46 Malibu/Mirage/Matrix/Jetprop/Meridian. Has has amassed over 6,500 hours in various PA-46 airframes and believe it to be one of the finest flying machines available for the serious cross-country pilot with an eye for efficiency.

Now, Joe has flown more than 12,200 hours in just about every imaginable environment. Whether providing initial/recurrent training in the PA-46’s, TBM’s, instructing in NVG’s in a UH-60 Blackhawk, flying the King Air series of airplanes, giving tailwheel endorsements, or taking kids flying for the first time, he simply loves flying machines and the people who fly them.

Night Flying

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Ah, fall is finally here.  In Texas, it arrived about a month late, but showed up with a vengeance.  A strong cold front caused a 40 degree temperature drop in 12 hours earlier this week, bringing rain, lower freezing levels, and lots of wind.

Fall means cooler temps, but fall also means less light.  The sun begins to set sooner, plus the fall back time change in November cause darkness to spring upon an unaware pilot.

Before getting in to too many night landings tips, just a friendly reminder, passengers can only be carried at night if the PIC has completed 3 takeoffs and landings to a full stop in the last 90 days during the time period of 1 hour after sunset to 1 hour before sunrise.

Lots of us have been landing long before sunset for most of the past couple of months, so those night flying skills might be a little rusty.  The best way to remedy night flying rustiness?  Call an instructor and go get some practice.

In the meantime, here are some tips as to what to expect for your next night flying experience.

  1. Your Eyes Are Very Important.  This may seem like an obvious statement, but night vision can be affected by many things.  Before you takeoff, you want to make sure you can see in the dark.  The FAA recommends no bright lights 30 minutes prior to takeoff.  They also recommend using oxygen at night as this greatly improves night vision, even at low altitudes.  Use off center viewing to help spot traffic or other objects in the air.  Finally, when preflighting, use a red flashlight as much as possible, but if you do have to use a white light, close one eye to keep one eye from being blinded.
  2. Utilize Approach Lights on Landing.  Night landings are very different then day landings.  It is very difficult to get the proper depth perception, not too mention see obstacles below you on your final approach to a runway.  PAPI’s, VASI’s, and instrument approach glide slope’s become very important.  If you are VFR only pilot, if your airport has a PAPI or a VASI, keep 2 white and 2 red (or 1 white and 1 red) lights.  If you see 3 red (or 2 red), climb.  If you see 4 red, definitely climb.  If you are an IFR pilot, I highly recommend always flying an approach at night.  What if your airport doesn’t have a PAPI, VASI, or approach with a glide slope?  You might not want to utilize it at night.  One side note on VFR flight: Clouds are nearly invisible at night.  If you do fly into a cloud (a clue is your strobe lights start reflecting back at you), don’t panic.  If you have an autopilot, turn it on and execute a 180 degree level turn.  If you don’t have an autopilot, start scanning your instruments, keep your attitude indicator blue side up, and make a shallow 180 degree while maintaining altitude.  Then call ATC, advise them what happened, and ask for help.  One more note:  I highly recommend that if a pilot finds that he/she will fly at night at lot, get an instrument rating and fly IFR at night.  It’s much safer.
  3. Practice Landings Before Carrying Passengers.  The tendency when landing at night is to level off too high before flaring, causing the airplane to bleed off speed and energy too high above the runway.  This can lead to a stall, a hard landing, and/or too high of a pitch attitude at touch down causing a tail strike. A good tip is start your level off when you can see the tire marks on the runway.  Make sure you practice night landings, preferably with an experienced instructor who is night current and proficient, before carrying any passengers on board, even if you are night current, but haven’t landed at night in a while.
  4. Night Emergencies.  For engine failures at night, you are very limited on options.  Unless you have a Cirrus equipped with a CAPS parachute system, you really have two options if an airport isn’t within gliding distance.  Find a wide, lighted road that appears to be lightly trafficked.  A word of caution, though:  be careful of light poles, fences, concrete medians, cars, and buildings.  The LA freeway would not be a good option (though there are exceptions to this rule as is evidenced by the picture below).  The second option is find a dark spot and pray it’s a field (or the Hudson River).  As you get closer, you can turn your landing light on to see what the ground looks like.  If it looks good, keep the light on and continue.  If you don’t like what you see, turn your landing light off and continue….

Flying at night can be the best time of day to fly.  It’s usually smoother, cooler, and you get to see all the city lights.  It is a very different environment, however, so make sure to get some training before darkness settles in on your next trip.

2018 Houston, TX CPPP

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The Cirrus Pilot Proficiency Program is once again returning to Houston, TX the first weekend in November. Henrickson Jet Center at the Houston Executive Airport (KTME) will be the host FBO this year.  If you are a Cirrus owner in the South Central US, the Houston CPPP weekend is definitely worth your while.

What is it?  The Houston CPPP is a combination ground and flight training weekend.  With ground classes ranging from engine management, to loss of control prevention, to avionics best practices, an attendee will not lack a better Cirrus education by the time he or she leaves.

The flight training side of the weekend gives an attendee several options.  A Houston CPPP attendee can do 1 or 2 flights with a highly qualified Cirrus Standardized Instructor Pilot (CSIP), one on Saturday and one on Sunday (if the 2 flight option is selected).  The Cirrus Owner’s and Pilot’s Association (COPA) brings in exceptional instructors for each of the CPPP events, so the training is top notch.  Folks who want to take in more ground school, but still want to fly a little bit have the option of just doing 1 flight, either Saturday or Sunday, in order to increase their Cirrus knowledge.

The Houston CPPP event will be November 2nd, 2018-November 4th, 2018, a Friday through a Sunday.  The weekend kicks off with a welcome dinner Friday night, then ground sessions and flying on Saturday and Sunday, plus a dinner on Saturday night.

For those who want to challenge themselves, there are simulator sessions available with a challenging instrument approach that doesn’t quite meet up with the normal, ho-hum type of approach.

The Houston CPPP also provides a Partner in Command course for those right seaters out there wanting to learn more about what to do in an emergency situation.

Hank Gibson of Texas Top Aviation will be at the Houston CPPP as a flight instructor.  For more information and to sign up, please click here.

Hope to see you there!