Okay, many people may think that I may be a little biased on this subject and they would be right, but that doesn’t mean that I can’t perform a factual comparison of the 3-blade and 4-blade propellers with some subjective observations. So, at the risk of coming across as too much of a “salesman”,(I prefer that the products speak for themselves), I thought I would post the results of a recent test we conducted. I recently had the opportunity to do a back-to-back comparison of the 3-blade Hartzell and 4-blade MT propellers on a standard PA46-350P Mirage. Both flights were performed with the same fuel load, cabin load, weight, C.G. and the OATs were within a couple degrees of each other, to minimize correction errors.
Let’s start at the beginning; weight and balance, pre-flight, taxi and take-off. The 4-blade does weigh about 10 pounds less, but during the pre-flight I noticed several small dents and dings in the leading edge of the blades, which seems to be common with the 4-blade and yet I have never seen a single dent or ding in the leading edge of a 3-blade propeller, since it uses a much stronger and thicker electro-formed Nickel leading edge. Next, when we went to pull the plane out of the hangar, it was immediately apparent that it is much easier to contact the propeller blades during handling and movement with the towbar and the 4-blade, due to the reduced distance between the blades thanks to the 90° angle vs. the 120° angle between the blades, potentially causing blade damage. Once I started the engine and began to taxi, there was a definite difference in the sound of the two propellers from inside the cockpit that was difficult to quantify and would definitely be a personal preference, mine being for the 3-blade,(of course). I would describe the 4-blade as a “whispy” sound and the 3-blade as a more “throaty” sound that just seemed right to me,(this is where it gets a little subjective as I am certainly more accustomed to the sound of the 3-blade). Now we get to the best part; the takeoff! For both takeoffs the wind was calm and by my measurements, the 3-blade took about 6-7% less runway to get the plane off the ground, but the biggest difference was once the plane was airborne, the 3-blade seemed to accelerate to Vy much better than the 4-blade and completely removed that feeling of “underpoweredness” that the PA46 often has during takeoff. For me, the takeoff performance alone is enough to “sell” me on the 3-blade; it seems to completely change the demeanor of the plane from a lazy land-lover to tiger that is clawing its way into the sky.
Now let’s look at the climb and cruise performance differences between the propellers. In a stable Vy climb,(110kts), to 17,500′ the 3-blade propeller averaged 71FPM,(7%, -this is a Mirage), better climb rates than the 4-blade, however the 4-blade kept the engine about 10-20°F cooler than the 3-blade,(we have a cooling mod to fix that). During climb, it was very difficult to notice any difference in noise and vibration; although they did sound “different” from each other, I would maybe have to give a very slight edge in overall smoothness to the 4-blade, but with its extremely light and flexible blades, this wasn’t a huge surprise. This could also be considered subjective, as I do like the sound of the 3-blade and it just feels like it’s doing more,(and it is!). Once level at 17,500′, the most impressive comparison yet showed itself; a very repeatable 4-6 knot speed advantage for the 3-blade! With the OATs within 1° and MAP, RPM, FF and TIT all a near perfect match, the 3-blade was a solid 5-6kts faster with just one reading coming in at only 4kts faster than the 4-blade and one reading at 7kts faster than the 4-blade. That is really significant, considering the engine is producing the same power and using the same amount of fuel; adding 2.5 t0 3% more speed is noteworthy. I know the 3-blade is efficient and all of our customers have said that it is either equal to, or slightly faster than the 2-blade on the Malibu, but I did not expect up to a 6 or 7kt difference against the 4-blade!
Now that I have finally had the opportunity to do a real back-to-back comparison and although these tests were performed with a Mirage, the results will also apply directly to the Malibu as the airframes are essentially identical. I hope it answers that age-old question; which is better, the 3-blade or the 4-blade? From a performance perspective, the answer is clear and from a reliability and durability perspective, as more and more 4-blade propellers are removed from service due to grease leaks, delamination, leading edge damage and poor field service, history is proving that the “bullet-proof” Kevlar construction of the Hartzell 3-blade is standing up to meet the demands of the PA46 fleet.
Chad Menne
