Continental 520 with a 2-blade prop

Do lower numbers really mean a lesser product?  Is an iPhone 6 really better than an iPhone 5? Is a PT6-35 really better than a PT6-34? Is a 4-blade prop better than a 3-blade prop or a 2-blade prop?  And is a Continental 550 really better than a Continental 520?  The answer is to all these questions is, “It depends”.  What does it depend upon?  To answer that question as it relates to the 520/2-blade combination, a broader understanding is required.

There’s several engine/prop combinations that get a “bad rap” in the PA-46 market, some justifiable and some not.  The Continental 520/2-blade prop combination on the Malibu is one of the engine/prop combinations that gets a “bad rap”.   But in my opinion it only gets a “bad rap” because of the market’s perception that a “lesser number” translates into a “lesser product”.  When the market learns that a 550 conversion exists, then the 520 must be “lesser” and “not as good”.  There’s absolutely nothing unsafe, wrong, or improper about a Continental 520, or a 2-blade prop, or the combination together.  As John Mariani has told me several times, “We originally designed the Malibu with the 520/2-blade in mind…they are a great match!”  He is absolutely right, it is a great pairing with no skeletons in the closet.  Both the 520 engine and the 2-blade prop are considered to be older, but well-proven designs.  So, if it is such a good combination, why did the 550/3-blade conversion come about?  Is the 550/3-blade (Malibu Aerospace M-5 Conversion) better?  In my opinion the 550/3-blade combination is better in most regimes of flight, but is it enough better to pay for the conversion?  Let’s now break the engine and prop combinations apart for greater clarity.

Engine: The 550 has a slightly longer stroke that the 520. This means that the piston travels slightly farther during one revolution of the crankshaft.  Although the 550 piston and rod are different aesthetically than the 520, they are of the same dimensions.  The crankshaft in the 550 is where the difference is found that creates the longer stroke.  The longer stroke translates into 30 more cubic inches of fuel/air mixture being compressed into the cylinders for each two turns of the crankshaft.  This allows the engine to breathe better when less air is available (at high altitude, for example,  Read this article for greater discussion).  So the 550 will maintain climb power slightly better at the upper altitudes, and this is a benefit…although a small benefit only.

During takeoff with either the 520 or the 550, the pilot advances the throttle to max FORWARD position and achieves 38” MP (if properly set/maintained) for the 520 and 35”MP for the 550.  Both achieve nearly the same amount of power at those settings, but the 550 will generate slightly more torque due to the longer stroke.  And, the longer stroke will provide one more benefit…a slightly better climb rate.

Any bicyclers out there?  I love to ride my road bike for a workout, and think there’s a good analogy when comparing the two.  The distance between the bike pedal shaft and the crankshaft on a bike (pedal arm) is no mere coincidence.  For professional bikers, they will use different bike configurations for different races, and they will use bikes with longer pedal arms on races where climbs are important (think Tour deFrance time trials).  The longer pedal arm translates into more torque being applied, and helps the biker climb slightly better.  It won’t do much for the top-end speeds for a biker, but it will help in the climb when torque is needed.  Don’t believe me?  Ride a nice road bike for 10+ miles and then jump on a Huffy for another 10 miles.  Huffy’s always have a shorter pedal arm, and the shorter arm is very noticeable.  Seconds count in bike races, and additional feet-per-minute climb rates count with airplanes.  So the 550 engine will produce better torque at lower airspeeds in the climb.  When the speeds are low and the power fully applied (every takeoff and climb), the 550 engine will create slightly more power and, as every pilot has been taught, excess power available translates directly into additional rate of climb.

Propeller: The 3-blade prop on the M-5 conversion is the best propeller for the PA-46 piston airframes.  I was going to write that it is “arguably” better, but I really don’t think there’s much argument from anyone that is “in the know”.  It is sleek, looks super, has a great abrasion strip on the leading edge, lasts a long time, is slightly quieter, slightly smoother, and does a super job of translating engine power to performance.  But, the 2-blade prop…is it a “bad” propeller?  Answer…no! The 2-blade propeller is a good propeller that is not nearly as sexy (far less ramp-appeal), but does a great job, especially in cruise. The 2-blade has a couple of other advantages too…when towing the Malibu, the 2-blade provides the most clearance, and an overhaul on the 2-blade is by far the cheapest.

To answer the original question about a 520 or a 550 and a 2-blade vs. a 3-blade prop, here’s my summation and advice:

  • Don’t let the smaller numbers fool you…the 520/2-blade is a nice pairing on the Malibu with good performance and good overhaul costs.
  • The climb rate is slightly better with the 550/3-blade combination, but not tremendously so.  There’ll be some difference, but it is not a “game-changer”.
  • If a Malibu is stretching your aviation budget, but you’d really like to get into the pressurized/turbocharged world, the 520/2-blade combination (original configuration) Malibu’s can be a super value, packing a lot of performance with a cheaper purchase price tag.  There’s absolutely nothing wrong with an early (1984-1985) Malibu that has the original engine/prop combination.  They can be bought very reasonably and are great airplanes.
  • If you have a 2-blade prop on an existing 550 conversion, I’d consider an upgrade to a 3-blade with the M5 conversion (upgrade to a 550 engine) simply to compete the conversion and add the most value to the airplane.
  • If you have a 520 engine, I’d consider an upgrade to the M-5 conversion when the engine is due overhaul.  It’ll cost a little more than overhauling your 520, but you’ll get a great “firewall-forward” and the market will love your airplane when you sell your Malibu
  • I’d not remove a 520/2-blade combination that is not near overhaul to install the M-5 conversion unless you had a solid buyer for your existing 520/2-blade combination (trade-in).
  • The market really likes the M-5 Conversion, and you should expect to pay more for an airplane with the installation, and you should expect to receive more if selling an airplane with the conversion.  It’s one of the best Malibu conversions when considering “return on investment”.
  • There are some buyers that will not consider buying an airplane with a 520/2-blade combination unless the engine/prop are due overhaul and an M-5 conversion can be purchased after the purchase of the airplane
  • If you want a “best-of-the-breed” Malibu with all the best options (1986.5-1988 airframe, great avionics, spoilers, additional range fuel, upgraded interior, etc.), then you’ll need the 550/3-blade conversion to “complete the package”.  A “best-of-the-breed” Malibu will fetch nearly $400k in the marketplace, and the M-5 Conversion is a “must-have” to truly be a “best of breed”.

About Joe Casey

ATP, CFI, CFII, MEI, CFI-G Commercial Pilot - SE, ME, Rotorcraft, Glider US Army AH-64 Pilot and UH-60 Instructor Pilot and Instrument Flight Examiner
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