2 Blade vs 3 blade for Mooney M20C

[Weston]

Hey guys.  We are in Florida with a 65’ M20C and looks like we are on last overhaul for the Hartzell.  We use shorter soft fields quite often, so was considering going for a 3-blade.  For the guys that have gone 3-blade, does the takeoff performance convincingly make-up for the added initial cost and reduced cruise?  Would much appreciate any thoughts, comparative performance indices, and/or specific props that you guys have experience with!  Many thanks in advance.  W 

[Hank]

I have a 3-blade Hartzell, but can't offer comparison because it was already on the plane when I bought it. My normal takeoff recently in early-summer weather had me 300-350' agl at the end of a 3200' runway--no flaps, rotate at 70 mph, positive rate then gear up, climb at Vy = 100 mph. Initial climb to 500 agl at Vx = 85 mph would be a different matter. 

I also visit a 3500' grass strip at the beach in NC in late July, leaving hot, humid and heavy with Takeoff Flaps. [My wife has forgotten what I initially taught her about packing light!] Sorry I don't have any climb data for you.

As for slow cruise, you've been listening too many old wives' tales. Granted, I have a 201-style windshield and the guppy mouth closure, but above 7500 msl I regularly see 145-148 KTAS, which is faster than book speed. Power is WOT- / 2500, 50° Rich. WOT- means level off, accelerate then pull back the throttle until the MP needle wiggles, then set RPM and lean. Cocking the throttle plate is intended to create turbulence inside the carburetor for better fuel atomization and more uniform distribution.  Done right, possibly with a little carb heat, can allow running LOP if you don't mind the speed loss.

[Weston]

31 minutes ago, Hank said:

I have a 3-blade Hartzell, but can't offer comparison because it was already on the plane when I bought it. My normal takeoff recently in early-summer weather had me 300-350' agl at the end of a 3200' runway--no flaps, rotate at 70 mph, positive rate then gear up, climb at Vy = 100 mph. Initial climb to 500 agl at Vx = 85 mph would be a different matter. 

I also visit a 3500' grass strip at the beach in NC in late July, leaving hot, humid and heavy with Takeoff Flaps. [My wife has forgotten what I initially taught her about packing light!] Sorry I don't have any climb data for you.

As for slow cruise, you've been listening too many old wives' tales. Granted, I have a 201-style windshield and the guppy mouth closure, but above 7500 msl I regularly see 145-148 KTAS, which is faster than book speed. Power is WOT- / 2500, 50° Rich. WOT- means level off, accelerate then pull back the throttle until the MP needle wiggles, then set RPM and lean. Cooking the throttle plate is intended to create turbulence inside the carburetor for better fuel atomization and more uniform distribution.  Done right, possibly with a little carb heat, can allow running LOP if you don't mind the speed loss.

Thank you Hank, sounds like a nice takeoff and cruise.  I read one of your other threads and it was very helpful as well.  

[KSMooniac]

I would choose my MT again... It's the only 3 blade option that is smaller diameter (more ground clearance) than other Mooney props. It is also far lighter and much, much smoother than any metal option, especially 3 blade metal. Takeoff and climb is improved and cruise is about the same as stock as far as I could tell. I think the 2 blade Top Prop is the fastest cruise option, but I'm not a Hartzell fan with their AD's and cracking spinners.

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[Z W]

Had a '68 M20C with a three-blade Hartzell for several years.  It took off very short, and more importantly, it slowed down really well at idle.  Never flew it with a 2-blade to compare directly on the C, but compared to a M20K with a 2-blade, the 3-blade was a great short-field performer.  Still cruised 140-ish.

[A64Pilot]

Since you’re in Fl, MT is in Deland, might be worth going over to them and talking. I think our problem is sand erosion, and I’m not sure how well an MT is for that.

I know they have a leading edge wear strip, hopefully Nickel and not SS, but I don’t know.

I do know the owner, a little German guy named Gerd or something similar is a pain, but you won’t have to deal with him.

I think the MT is the less expensive option

[pirate]

I added my Hartzell 3 blade a while back during overhaul and also added the flap gap seals.

I like you wanted better takeoff / climb performance. 

For me it was worth it performance wise.

 It did make me me a bit nose heavy but I installed a light weight starter to off set. 

[philiplane]

23 hours ago, Weston said:

Hey guys.  We are in Florida with a 65’ M20C and looks like we are on last overhaul for the Hartzell.  We use shorter soft fields quite often, so was considering going for a 3-blade.  For the guys that have gone 3-blade, does the takeoff performance convincingly make-up for the added initial cost and reduced cruise?  Would much appreciate any thoughts, comparative performance indices, and/or specific props that you guys have experience with!  Many thanks in advance.  W 

a good 2 blade will always yield the greatest speed on a 180 HP engine. Every blade you add, adds weight, and also adds some drag. That said, you might gain some climb with a 3 blade prop, and it would probably be equal in cruise speed to the original 2 blade. The new Hartzell composite 2 blade props are very efficient, giving the best of both world. They are also a true composite, using advanced materials to achieve better performance than an aluminum prop, while still being just as durable. 

You can ask around about MT propellers and get many different opinions. MT uses a wood core for the blades, with a fiberglass jacket and a glued on stainless or nickel leading edge. They are prone to cracks, erosion, and grease leaks. And there is substantial data on engine case cracks appearing on engines equipped with MT propellers. On the Cirrus Pilots forum, you would find extensive discussion of this problem. While lightweight sounds good, it can cause other problems because you lose quite a bit of the flywheel effect you get from a standard prop. MT's need more maintenance like repaints, filler around the leading edges, and sometimes, early removal to fix grease leaks. The Hartzell composites don't suffer from these problems. Nor do their aluminum blade props. 

[philiplane]

On 6/7/2023 at 5:16 PM, A64Pilot said:

Since you’re in Fl, MT is in Deland, might be worth going over to them and talking. I think our problem is sand erosion, and I’m not sure how well an MT is for that.

I know they have a leading edge wear strip, hopefully Nickel and not SS, but I don’t know.

I do know the owner, a little German guy named Gerd or something similar is a pain, but you won’t have to deal with him.

I think the MT is the less expensive option

Sand erosion of the MT is a huge problem since the blade coatings are less durable than others. I maintain a lot of planes that go to the Bahamas on a regular basis. And those runways are full of sand, loose bits of gravel, etc. The MT's don't do well. And the leading edges dent more easily than an aluminum blade. You file out a small ding in an aluminum blade. But the MT leading edge requires replacement. $$$$

MT's used to be less expensive to buy. Not anymore. And they are more expensive to maintain.