Mooney Propellers

July 2000

ShopTalk this month discusses that device that connects the power of the engine to the airframe, propelling your Mooney through the air. Let’s call it the propeller.

We’ll begin with proper maintenance and care of your current prop and how to recognize when you have a problem. At the end of this article, we will discuss some options available to upgrade your aircraft.

Probably the most common prop used on the bulk of the Mooney fleet is the two-bladed Hartzell C2YK series. This 74-inch diameter two-bladed prop has a 2000 hour/5 year TBO and can have a diameter reduction of up to 72.5 inches. The FAA issued a serious AD (77-12-06) against this propeller some years ago. This has cost owners of this prop a lot of money. AD 77-12-06 required all C2YK series props to have the blade shanks cold rolled and shot peened every five years. Eventually the blade shanks became undersized and you had to purchase new prop blades. Needless to say, Hartzell C2YK series props cost their owners a lot of money and it was questionable if this expense was warranted. Fortunately, the AD notice was later modified extending the time, providing relief for those operating only under Part 91 of the FARs.

The Hartzell C2YK propeller hub has two zerk fittings per blade. A problem occurs when the hub is serviced. If grease is pumped into the forward zerk fitting without removing the aft fitting then the pressure will blow the blade seal out and the prop will throw grease. Improper servicing and seal damage will be evident by the grease streaks on the backside of the prop. The only remedy once this occurs is to have the prop removed and the blade resealed. I service these propellers with Aeroshell-5 grease but any Hartzell recommended grease will do.

Most C2YK series props and McCauley props can be clipped when needed. This can save you a bunch of money during overhaul. If the prop can't have any diameter reduction and the blade does not pass inspection because of a tip problem, then you will have to purchase a new blade. Some Mooney props can’t be clipped. The C2YK Q-tip and the factory installed McCauley on the M20K are two examples.

When caring for your prop, your mechanic should file all nicks out of the blades and lightly sand the backside of the blades so they can be repainted flat black to keep the glare down to a minimum. If the prop has been dynamically balanced, don't remove more material or add excessive paint to just one blade. Try to keep them as equal as possible. Always remember to install the spinner and screws just as they came off. Installing the spinner 180° off will throw the balance out.

A typical 74 inch diameter propeller on a Mooney provides marginal tip to ground clearance. Keep your nose tire properly inflated to the proper air pressure. Old compressed gear doughnuts are another factor. Maintaining proper clearance helps prevent your prop from picking up small rocks and pebbles. Rolling takeoffs will also help.

To avoid water collecting and corroding the propeller base and the hub, park two-bladed props at a 45° angle and three-bladed props with one blade down. This will also minimize damage from bird droppings.

McCauley is the other manufacturer supplying propellers for Mooney aircraft. The 201 has two different styles and 180 HP Mooneys came with props from both manufacturers.

Some of the more common problems with McCauley props are:

1. Loose blades in the hub.
2. Oil speckles on the nose bowl or on the back of the blades.
3. No diameter reduction on all two-bladed M20K series props.

The loose blade can be repaired on the airplane by the installation of oversized o-rings and just reshimming that blade. This may also solve the oil speck problem.

Some McCauley prop hubs are filled with red dye oil. This provides easy detection of hairline cracks in the hub. McCauley prop hubs don't require servicing between overhauls.

Most of the two-blade props have a five year/1200-2000 hour recommended TBO. If you operate only FAR Part 91, this overhaul time is just a recommendation. When the time comes to replace or overhaul the prop you may want to consider upgrading. If your two-bladed prop needs new blades then a three-bladed won’t cost that much more. Currently Hartzell and McCauley are offering their three-bladed prop kits at not much more then a new two-bladed prop.

McCauley currently offers three-blade Blackmac propeller kits for M2OC-K aircraft. These prop kits all come with Scimitar blade technology (see below) with polished spinners. The Blackmac kits are all about $7200.00 list price and have a six-year/2000 hour (2400 hour for the M20K) recommended TBO. I have installed the M20F kit on a customer's plane and I believe it was worth every penny. The airplane is not only quieter but it climbs better and has even gained about three knots in cruise. The red zone on the tachometer has been eliminated by this conversion. For M20C-J, the new placard states “Avoid continuous operation below 15” between 1650 and 2200 RPM above 85 KIAS”.

Hartzell currently offers their Top Prop three-bladed conversions for M20C-K also. These kits also eliminate the tachometer red zone and come with polished spinners. The blades on these props are not the Scimitar design (with the exemption of the Mooney Missile). These kits will also provide a smoother ride and quieter cabin. The Top Prop kits are also priced around $7200.00 list price. The red zone on the tachometer has been eliminated by this conversion. For M20C-J, the new placard states “Avoid continuous operation below 15” between 1950 and 2350 RPM”.

Almost any three-bladed prop will give you less vibration and noise than any two-bladed prop. Because of greater efficiency (each blade has to provide 66% less lift or thrust than a two-bladed prop), take-off, climb and cruise performance is enhanced.

The Scimitar blade is the latest in advanced prop technology and offers better thrust with less exterior and interior noise. At 16,000 feet and 150 KTAS, a 74-inch diameter propeller rotating at 2500 RPM has a blade tip traveling near the speed of sound. The Scimitar design provides a swept-back wing section at the tip to improve efficiency at these near-supersonic speeds.

A last item of consideration in upgrading to a three-bladed prop is the appearance of the aircraft. I believe that the performance difference is worth the extra cost in weight and money, but when you add the appearance aspect (especially the Scimitar blade look) then the upgrade is obvious. With a three-bladed prop conversion, the weight penalty is fifteen to twenty pounds.

For those of you hooked up to the web, check out Hartzell at www.hartzell.com and McCauley at www.mccauley.textron.com. Both sites contain a large amount of product support and general information.

An additional note for TLS owners: New propeller blades may not meet the manufacturer’s (McCauley) original published specifications for blade tip thickness. This has been corrected in recent issues of the specification by eliminating the requirement for measurement at the blade tip station.

As always, if you have a question about this article, you may contact me at my aircraft repair shop, 307-789-6866 or via e-mail. Until the next ShopTalk, enjoy flying your Mooney.