GarKenyon vs. Parker-Hannifin Hydraulics

I get lots of questions about the differences in the two hydraulic systems on the early Continental-powered Malibu’s, so it seems logical for me to leap into the gap and provide my thoughts in writing.  I fly both versions regularly and believe I’ve got a good understanding of the benefits and detriments of both.

The earliest Malibu’s have the GarKenyon (GK) Hydraulic Systems.  All 1984 through 1985 Malibu’s have GK, and the earliest of the 1986’s do too.  Basically, Piper decided to go to the Parker-Hannifin (PH) system in 1986, but they used up the remaining GarKenyon systems they had in stock.  So, some of the earlier 1986 models have Garkenyon.  From 1986 1/2 and beyond, all PA46’s have Parker-Hannifin (until the Frisby System, which is nearly identical to the Parker-Hannifin in design and operation, became the source around year 2000).

Bottom line forward…I’m OK with either system in the PA46 Malibu, although I prefer the Parker Hannifin System.  If I were in the market to consider an early Malibu, would I avoid the GarKenyon aircraft? No! The early GarKenyon Malibu’s can be a great value.  To me, I’d pursue value, mechanical history, engine type, propeller type, aesthetics, and avionics before the hydraulic system would be a differentiator in a purchase decision. But let there be no misunderstanding…the type of hydraulic system in a Malibu is a differentiator to the market in general and the PH-equipped Malibu’s should draw a premium because they are better. Let’s break the two systems down…

What’s the difference? The big difference is that GarKenyon uses a “one-direction” pump and Parker-Hannifin is a “reversible pump”.  Although this may not sound like a big deal, it is.

The GK system uses a pump that only moves in one direction.  The electric motor turns only one direction which turns the hydraulic pump which can only turn one direction.  So, plumbing is provided and a series of valves are used to move the hydraulic fluid to make the various actuators move.  When the pilot raises the landing gear handle, he/she is moving a hydraulic valve, and this requires a good amount of force (we call it the “knuckle-buster”).  The pressure is applied from the pump and the pilot merely moves the pressure to the side of the actuator that does the desired work (moving the gear either up or down).  So, the pilot’s hand is actually on a lever that is actually moving mechanical devices (valves), not simply moving electrons. For GK-installed airplanes, the hydraulic system usually moves the flaps too.

The PH system uses a “reversible pump” that is turned by an electric motor that can turn both clockwise and counter-clockwise.  It turns one direction to move the gear up and another to move the gear down.  The pilot is therefore not moving a hydraulic valve, he/she is moving an electrical switch that commands the direction of the electric motor on the reversible pump.  The force required to move the landing gear handle is “finger-tip pressures”, and MUCH less than the GK system.  It is a much more simple system with fewer moving parts.

Advantage PH: Protection. There’s one other major benefit with the PH system…protection while on the ground. Since the landing gear switch on a PH is simply an electric switch, it is much simpler to route the action of that switch through the Landing Gear Squat Switch (on the Left MLG).  So, inadvertent gear retraction while on the ground is provided in a robust manner. On the GK system, the landing gear handle moves a hydraulic valve, so if the Landing Gear Handle is moved up while on the ground, the gear will collapse since the hydraulic pressure holding the gear locked down is released. To keep inadvertent retraction from occurring on the ground, Piper added a small guard that moves out of the way (to the right) electrically by the Squat Switch (see video below). This small guard is the only protection that exists, and this guard is (IMO) rather weak. I’ve seen MANY early Malibu’s that had faulty guard’s. Just to be clear…moving the GK “knuckle-buster” Landing Gear Handle takes a good amount of force, and this is not going to happen by simply “bumping” the handle…but, if the gear lever is raised on the ground, the airplane will experience a gear collapse.

Advantage PH: Strength. The PH actuators are physically bigger (larger diameter) than the GK actuators. With this additional beefiness comes added strength. The actual landing gear itself is identical across the PA46 fleet, but the PH actuators are larger than GK actuators. This translates into more strength with side loads on the main gear and with fore/aft movements on the nose gear. To be fair, I’ve not seen a greater propensity of side load problems (improper crosswind landing, improper ground operating technique, etc) in the field on the main gear actuators, but the weaker nose gear actuator does translate into more problems. For instance, if the parking brake were left ON (and NO pilot should leave any PA46 with the parking brake ON…ever!) and the Malibu were towed by a nose-mounted device, a gear collapse could occur more easily with the GK system because the GK actuator is simply smaller than the PH actuator.  I know of one GK Malibu that had a nose gear collapse while being towed, and another had a nose gear collapse after landing on a grass runway that had not been mowed recently (idiot pilot…I know…but still the GK failed when the PH might have withstood the trial).  Bottom line…both the PH and the GK systems are plenty strong enough for use, but neither will allow for abuse.

Another drawback to the GK: Hydraulic Flaps. Except for a minority of 1986 Malibu’s, all GK Malibu’s also have hydraulic flaps. In 1986 Piper moved to electric flaps and there are a few 1986 models that have GK gear and electric flaps. And…the hydraulic flaps need an experienced technician to perform maintenance. The rigging of the flaps is critical and a novice can spend a BUNCH of your dollars trying get it right. If you’ve got GK flaps, be sure to let one of the premium PA46 shops (Malibu Aerospace and Midwest Malibu are the two premium shops, IMO) do that work. GK hydraulic flaps don’t break often (they are very reliable), but when they do require adjustment, take it to a shop that knows exactly what to do. You don’t want to fund the education of your mechanic while he fumbles the job.

Mucho Dinero: Expense. The GK systems is (now) fully supported and the PH System, while fully supported, is getting more and more expensive to support. GK had a bad problem a few years back when replacement nose gear actuators were virtually non-existent. That problem has been rectified by Arizona Aircraft Accessories (a really good company that rebuilds hydraulic parts) obtaining authority to repair the nose GK actuator. A GK-equipped airplane at my airport sat for about a year awaiting the FAA to grant authority to repair the GK nose actuator, and that owner (along with about 6-8 other owners around the country) was not happy. But…that situation has been rectified and the GK system is now fully supported and parts are available. On the flip side, there are LOTS of PH PA46’s out there, and they enjoyed a long history of support. But, PH replacement parts can be a bit pricey.  One trusted mechanic stated, “If you need a PH actuator, and there’s not a good rebuilt one available on the market, you’ll have to go to Piper…and going to Piper for anything will set you back financially.”

Talking with mechanics that are “in the know”, I get the impression that they like the sturdiness of the PH system, and like the fact that the GK system requires more (billable) maintenance.  One mechanic stated that the GK system will, “nickel and dime you to death” (smaller nagging problems), but the PH system will, “work well for many years and then slam you for a high maintenance bill when something goes wrong”.  All mechanics I spoke with felt that the actuators on either the PH or the GK should be overhauled every 2,000 hours, regardless of their apparent functionality.

Parker-Hannifin Benefits:
* Much easier to move the gear switch up and down
* More protection from an inadvertent gear collapse
* More desirable in the marketplace
* Stronger actuators

Gar-Kenyon Benefits:
* Cheaper replacement parts
* Possible “deal” can be made on a 1984-1985 Malibu. They are less desirable in the marketplace, but they are still quite functional and quite safe.

With all of this information, you can see that the 1986.5 to 1988 model PA46’s (equipped with PH hydraulics) are truly special airplanes. There’s not a lot of them available on the market at any one time and they should demand a premium. To me, they are the creme-de-la-creme of the PA46 piston fleet for a sub-$400k value buyer because of the electric flaps and PH gear. But…don’t snub the early Malibu’s with GK gear! If you find a nice example configured as you like with great avionics, great logbooks, and nice P/I…buy it. GK-equipped airplanes are still robust and strong and serve their owners well. Both are good, but the PH is best.

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Airport skateboard (It’s very Unique…)

I’ve found a very Yuneec way of getting around an airport! Brint is a PA46 pilot that I recently trained and he showed me his Yuneec Skateboard. I instantly fell in love with the board and bought one myself. Here’s a quick video that tells more:

Interested?  I bought mine through Don Barthlow, and he can be reached at 512/633-6877.

You can find more information at: https://vimeo.com/channels/yuneecego/page:2

Thanks Brint!  I appreciate you showing me cool stuff!

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SLD Icing demonstration

I’ve studied SLD (Super-cooled Large Droplet) Icing on aircraft, but the study always left me with more questions than answers.  I simply understood that SLD meant that there could be “big drops of water” that stick to the airplane and create a more dastardly result.  But, exactly how does it work?

I had a breakthrough in my understanding of the phenomenon when I was taught that water does not always freeze at 32F.  For it to freeze at the 32F, the pressure must also be correct.   So, water can exist in liquid form in an atmosphere when the pressures exerted on the droplet are less.  When the pressure changes, the water will instantly freeze.  And…it doesn’t have to be a tiny water droplet…it can be a VERY large droplet…and, as Dr. Thomason demonstrates, even a full bottle of water can freeze instantly.

A good friend of mine (and PA46 owner/pilot), Dr. Thomason made a really cool video that shows how water can be super-cooled and remain in liquid form until the pressure changes.

So, the super-cooled liquid water is present in a cloud or as falling precipitation.  When the airplane goes through the air and hits the super-cooled water, it freezes instantly because the pressure increases dramatically.  The icing in SLD on the airplane will be clear icing (the worst kind) and because of the large size of the droplets (see the Advisory Circular below) the airplane becomes heavily ladened with ice quickly.

The same phenomenon happens in a non-aviation environment with freezing precipitation.  A few years ago we had a terrible power outage in the area that I live because of freezing precipitation.  The temperature was freezing at the surface, but due to a temperature inversion, the temperatures aloft were above freezing.  So, the rain fell from the warm clouds, entered the cold airmass, but didn’t freeze.  When the rain hit the local trees and power lines, it froze instantly due to the change in pressure and stuck.  When the weight became too great, the power lines and trees fell causing huge power outages.

Here’s a cool pic that shows the effects of SLD (Freezing Rain) on power lines.

Bottom line…water doesn’t always freeze at 32F, but it will when it receives a pressure increase.  Pilots can apply this knowledge to icing aloft and gain a firmer understanding of how severe icing can occur in aviation.

For more discussion, here’s a good link to FAA AC91-74A that discusses aircraft icing:  Link to FAA Icing A/C

 

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Avoiding a Hot Start…

Let there be no doubt about it…the greatest danger that faces your PT6 engine (and consequently, your wallet size) is the potential of a hot start.  So, knowing exactly how to start your PT6 is critical.  Here’s the noteworthy points of an engine start that I recommend you consider when starting your PT6-powered PA-46:

1.) Check battery voltage: If the battery voltage is below 23.5v, stop the sequence and either charge your batteries or get a ground start. On the Jetprop, make sure to check both batteries, ensuring both the individual and collective voltage is over 23.5v.  The Meridian has only one airframe battery.
Possible problems if voltage is below 23.5v:
– Battery Minder inoperative?
– A possible drain on the battery with the battery switch OFF?
– If one battery is low in the Jetprop, someone (possibly maintenance?) used one battery too long for ground checks?
– Loose connections?

2.) Ice deflector – OFF: (Jetprop only) This is generally a minor consideration, but you want to eliminate all variables during the start sequence.

3.) Fuel pump(s) and Ignition – ON: One of the WORST things you can do to your engine is leave the Ignition switch OFF during start, and then engage the Ignition Switch after the Condition Lever is advanced.  The volume of fuel that is dumped into the engine (but not ignited due to the igniters being OFF) will set off a DEFINITE hot start when the ignition is added late.  Think of the PT6 like it is a propane BBQ grill.  If the propane is turned ON your grill with the hood closed and propane fills the grill, the chef will get a “boom!” if he hits the igniter and will probably lose his eyebrows.  Same with the PT6…if the condition lever is advanced, fuel is entering the combustion chamber.  If the ignition is OFF, this fuel is not ignited.  If this excessive fuel meets ignition late in the sequence, the only result will be the same “boom!”, except that a PT6 will cost a LOT more than a BBQ grill.

4.) MOR lever – OFF: A Hot Start will DEFINITELY occur if the MOR lever is in any other position than OFF.

5.) Press the starter switch and notice the voltage drop:  If the battery voltage drops below 17v immediately after pressing the start switch, then the condition of your battery should be suspect.  Usually a drop below 17v indicates the battery(s) will soon need replacement.  If the battery voltage drop goes below 16.5v, I would abort the start.
Possible problems if voltage drops below 18v:
– Battery(s) getting old, possibly needing replacement
– Connection problems?

6.) Allow the Ng to stabilize: Before advancing the Condition Lever, allow the Ng to stabilize and note the speed.  The speed should be above 15% and should not fluctuate much from start to start if the battery voltage is normal.  Most engines will settle at about 16.5 Ng (or so), but the more important factor is noticing a change in speed from start to start, especially notice if the speed decreases. If the engine is hot from being operated recently, allow the Ng to spool and watch the ITT decrease.  When the ITT decreases below 120, then it is safe to advance the Condition Lever.  I’ll often allow the Ng to stabilize for 10+ seconds before advancing the Condition Lever.
Possible problems if Ng is slower than normal:
– Rubbing inside the engine: Extremely expensive…have this checked soon if no other abnormalities are noted
– Starter approaching end-of-life:  The PT6 starter should be overhauled every 1000 hours.
– Starter brushes need replacement: This is a cheap and easy fix, and starter brushes can wear quickly.
– Connection problems?

7.) Watch for Max ITT: Once the Condition Lever is advanced (and you should keep your right hand on the Condition Lever in case you need to shut the engine down), the ITT should dramatically rise and peak before declining sharply to a steady state.  Note the Max ITT.  If the ITT goes above 875F, instantly retard the Condition lever to OFF.  Usually the Max ITT value (if all else is equal) will vary with OAT.  The higher the OAT, the higher the Max ITT.  The lower the OAT, the lower the Max ITT (unless bitter cold weather is present, and then the Max ITT can go up slightly as temps decrease).

On any start sequence, you are looking for any deviation from what is normally seen.  If you see a change, abort the start sequence and troubleshoot.  Make no mistake…the costs of a hot start can be over $100k.  It simply is not worth the risk to “see what happens” or “hope for the best” if a “deviation from normal” is observed.  Solidify in your mind now that you will not let the urgency of the mission coax you into continuing a start that is “not normal”.  It’s simply not worth it.

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-21 Jetprop Conversion

Bottom line forward…I really like the -21 Jetprop Conversion!  There are usually not very many of these conversions on the market, but one does show up every now and then.  When it does, I get a lot of questions from prospective buyers, most wanting to know if the -21 is “worth owning”.  My usual response is, “Absolutely!”  But, as is true with most aircraft purchase decisions, “he with the most information usually wins.”  With three variants of Rocket Engineering’s popular Jetprop Conversion, there seems to be a lot of confusion amongst the uninitiated and the -21 Conversion is certainly the most misunderstood of the Jetprop conversion.  So, it seems appropriate for me to leap into the gap and post my thoughts on the -21.

A little history…the -34 was the first Jetprop conversion in the late 1990’s and when it became available it was the best of the best.  It performed well and was popular and was a really good conversion.  But, since the -34 is an engine designed for the lower altitudes (originally developed for the helicopter market and crop-duster market), some of the -34 conversions did not perform as-advertised at high altitude (the late Lyn Amestoy, a great salesman at Rocket Engineering who regrettably passed away in an accident in mid-2015, told me that about 10% of the -34’s performed “less than ideally at high altitude”, suffering a slightly lesser cruise speed).  The compressor section was deemed the culprit of the lack of power at altitude, so the -35 engine was offered (the -35 is generally the same as the -34 except the -35 has better aerodynamics in the compressor section). The -35 became the benchmark for the Jetprop conversion, replacing the -34.  The -21 was introduced in the early 2000’s as a cheaper option for those that wanted a Jetprop, but were interested in preserving cashflow.  So, today you can only purchase a -21 Conversion or a -35 Conversion from the factory in Spokane.  Without a doubt, the -35 Conversion is the most popular of the conversions offered today.  Effectively, the -34 and -35 Conversions provide the same performance, so I will contrast the -34/35 collectively with the -21 in this discussion.

The “dash number” for a PT6 engine relates generally to the size of the engine and the amount of air that can be forced through the compressor section.  That may be a bit of an over-simplification, but it’s a general good rule of thumb.  The fuel/air ratio that is burned in a PT6 engine is the same at any altitude. So, the more air that can be forced through the compressor the more fuel can be burned and more power is generated.  All of these engines perform well at lower altitudes since there’s plenty of available air density, but that changes as altitude is increased.  Effectively, the -21 performs nearly identically to the -34/35 at low altitude.  But, at high altitude (with the less dense air), the smaller -21’s power drops off quickly.

Comparatively, the -21 and the -34 will climb from sea level through 12,000 MSL at about the same time since both are “torque limited” through 12,000 MSL…the -34/35 will beat the -21 in most instances, but not significantly.  But, as the climb continues (and it almost always does continue in the Jetprop since the airplane performs so well at high altitude), the -34/35 will outpace the -21.  A turbine engine is normally “torque limited” at lower altitudes and “temp limited” at higher altitudes.  During takeoff, a turbine pilot will keep a keen eye on the torque gauge, with little care for the ITT knowing that the ITT (temp) will be low (usually, unless there’s an anomaly).  But, as the climb continues, the ITT increases and the torque decreases.  Where this switch occurs is usually observed by the pilot so he monitors the correct limiting factor.  Here’s the point…the -21 becomes “temp limited” (meaning the torque is now decreasing for the rest of the flight) at about 12,000 MSL (in most situations) and the -34/35 becomes “temp limited” at about 15,000 MSL.  So, the -34/35 will comparatively produce more power than the -21 as the altitude is increased, and this results in a better climb rate and faster cruise, but it also results in higher fuel consumption.

As the -34/35 goes through FL180, the average rate of climb (ROC) is about 1,200 FPM; as the -21 goes through FL180, the average ROC will be about 900 FPM.  As the climb continues, the -34/35 will average about 1,000 FPM ROC through FL230 and the -21 will be at about 700 FPM.  At the very top of the climb (near FL270), the -34/35 will still be climbing at 800 FPM, and the -21 will eek out 500 FPM.  So…the -34/35 should beat the -21 to FL270 by a 2-3 minutes, easy.  Is that a big deal?  Not in my book.  In fact, the -34/35 has a STELLAR climb rate throughout the climb, and the -21 has a very acceptable ROC throughout the climb.  In the grand scheme of things, the ROC is just not a huge deal with either the -34/35 or the -21.

The additional horsepower available that was used for the climb is turned into forward speed in cruising flight.  The -34/35 will cruise at 260KTAS (average) at FL270, and the -21 will cruise at about 243 KTAS (average) at the same altitude.   But, the -34/35 will burn between 32-33 Gallons Per Hour (GPH) at FL270 and the -21 will burn about 28 GPH at the same altitude.  Does the additional speed of the -34/35 translate into a meaningful lessening of flight time?  To answer that question, I turn to www.fltplan.com which has templates for both the -21 and -34/35 conversions (incidentally, I use fltplan.com for all of my flight planning, mainly because they have SUPER-accurate fuel-burn calculations as they use ACTUAL forecast winds in the flight time/fuel burn analysis).  I planned a flight from Dallas, TX (DFW) to Nashville, TN (BNA) and found the following results on this 549NM flight (using current weather on the day of writing this article):

  • -21 = 2’24” burning 76.9 gallons of Jet-A
  • -34/35 = 2’15” burning 75.8 gallons of Jet-A

So, the fuel burn is nearly identical, and the -34/35 arrives 9 minutes earlier.  To my way of thinking, 9 minutes doesn’t move the needle very far on a flight of that length.  That’s just not enough of a time consideration to make a huge difference.  Is there a big difference on a shorter flight?  Here’s the calculations for a flight from DFW to HOU (Houston, TX) on the same day using the same weather:

  • -21 = 1’12” burning 43.3 gallons of Jet-A
  • -34/35 = 1’09” burning 40.5 gallons of Jet-A

On this shorter flight, the -21 arrives only 3 minutes later than the -34/35 and burns a comparatively equal amount of fuel.  My point…the slightly slower speed of the -21 translates into only a nominal flight time penalty.  To me, the -21 is just as solid a cross-country machine as the -34/35.

Concerning comparative costs, there are two variables to consider: initial acquisition costs and engine reserve costs.

  • Initial acquisition costs: The -21 conversion costs about $70k less than a -35 conversion when initially installed, so it inherently will demand a lesser price at sale later in the airplane’s life.  Sometimes an early Malibu will be converted to a -21 Jetprop, and these airplanes can be real values on the marketplace (low purchase price and high useful load).  If you want to buy a Jetprop and want to limit the cash flow, the -21 can be a real contender for your dollars.
  • Engine Reserve Costs: The -21 (3,600 hour TBO) will cost the least to overhaul as compared to the -34 or -35, especially the -35.  The -34 has a 4,000 hour TBO, so it arguably could be comparative to the -21 engine reserve costs, but the -35 (with it’s extra stage of axial-flow compressor blades and 3,600 hour TBO) will cost more.  What’s the true engine reserve on these engines?  Well, your guess is as good as the next guy’s…as there has not been a Jetprop that has hit TBO yet.  But, almost assuredly the -21 will be the cheapest to overhaul, and consequently have the lowest engine reserve costs.  Also, with the -21 engine being found on thousands upon thousands of King Air C90 airplanes (2 engines per airplane) being built over the last 4 decades, there’s plenty of shops that have vast experience with the -21 and parts are simply not a problem.  The -21 engine is considered to be bulletproof and easy to manage/maintain.

There’s is one disadvantage to the -21…the market does not favor the -21.  I think it is simply “numerical prejudice”, but the -21 is less popular.  What is “numerical prejudice”?  Most buyers don’t understand the differences between the Jetprop variants, but they do know that 35 is a bigger number than 21, and therefore it must be better, right?  Well, not always.  Buyers of a Jetprop value speed and many simply don’t understand buying anything that is “slower”.  And, remember…”power is always popular”.  Most Jetprop buyers are previous owners of piston PA-46’s and love their piston steed, but they always dream of the day they can afford a turbine, and want the “most power they can buy”.  So, although there are fewer -21 Jetprops on the market, there are certainly fewer buyers for the -21 than for the -35.  Is this appropriate?  Probably not, but it is reality.

Buyers of the -21 become aware of the lack of any consequential differences in performance and are therefore happy to buy a – 21 if it is available.  They tend to know what they are looking for and will pounce when they see the right -21 with the right “desirable” characteristics (good maintenance lineage, avionics, paint/interior, useful load).  -21 Jetprop owners tend to become some of the most vociferous supporters of their purchase decision to own one of these incredible airplanes, and tend to own them a LONG time.  The -21 is certainly the cheapest turbine to acquire/operate, and owners become rightfully passionate.  But, it sometimes takes a low price or a knowledgable buyer to jump into the -21 market, especially if other -34/35 offerings are available.

Care to join the -21 owners club?  I fly all of the Jetprop variants frequently and I’d CERTAINLY buy a -21 if I were shopping for a Jetprop.  To me, the biggest consideration when buying a Jetprop…any Jetprop…is the purchase price, maintenance history, avionics, interior/paint quality, and engine time…not the engine type.  I’d take a nice, well-maintained -21 any day over a less-than-stellar -34/-35.  In today’s market, good Jetprop’s tend to sell VERY quickly, often never being advertised on Controller or TAP.  So, don’t hesitate if you find a good -21 on the market. These airplanes are still Jetprops and are fabulous airplanes for the pilot that values efficiency.

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