SENSENICH PROPELLER MANUFACTURING COMPANY, INC.
A) Basically yes. A wooden propeller has two rudimentary maintenance problems.
You must check the bolt torque every 50 hours, during a seasonal change, or
during a trip to a climate which is different then normal. You must always be
conscious of rain and moisture. Wood will rot. It must be treated when
subjected to moisture. Cost to recondition a wooden propeller is usually $200.
All aluminum propellers must be kept free of nicks and cuts; but our fixed pitch propeller doesn't have o-rings and sealants that can go bad. Our 70CM series propeller should not have to be serviced unless it receives a strike. If a constant speed propeller receives a strike, not only does it need serviced, but a service bulletin recommends that the hub be replaced!
Due to metal fatigue, both fixed pitch and constant speed propellers should be reconditioned every 2000 hours. This normally costs between $250 and $350 for a fixed pitch and $1750 to $1850 for a constant speed/governor overhaul at most prop shops.
Q) Is an aluminum propeller really more efficient?
A) Normally, it will be. Due to the physical characteristics of an aluminum
propeller, we are better able to achieve the ideal blade shape and thickness than a wooden propeller manufacturer. Tolerances can also be much tighter without fear of expansion and contraction.
A constant speed propeller will give you 100% rated horsepower on climb out. This is the constant speed's strength. At sea level, our 70CM series propeller produces about 83% of rated horsepower. Due to the tremendous climb capabilities of the aircraft, this is where we compromise. Guess where the constant speed prop compromises? On the top end you will find the Sensenich propeller will give you better cruising speeds at a given RPM!
Q) Aluminum propellers are a lot more expensive, right?
A) Not our fixed pitch propeller! When you purchase our fixed pitch aluminum propeller the price includes the
extension and the mounting hardware. Wooden propellers are priced as a
propeller only. When you factor in the cost of the extension, hardware, and
crush plate, our 70CM propeller system is only about $400 more.
A constant speed propeller and governor will cost you about $4000 more. Yes, that is three zeros next to that four!
Q) What are the weight differences?
A) A complete wooden propeller setup will come in around 20 pounds, our 70CM propeller system weighs 38.75 pounds, and a constant speed/governor will weigh about 60 pounds.
Q) How important is the 2600 RPM restriction?
A) Extremely important! The propeller has a tenth order, third mode vibration when operated above 2600 RPM.
Q) What if I accidentally exceed the 2600 RPM restriction?
A) You absolutely must not exceed the 2600 RPM restriction! We have pitched the propeller so that at altitude, you will max out at 2600 full throtle level. Every aircraft and engine will be a little different; so a slight pitch adjustment at the local prop shop may be in order.
Q) I heard a rumor that you are going to remove the 2600 RPM restriction. Any truth to that?
A) You should assume that the placard will always be there!
Q) The O-320 comes with 3/8 or 7/16 bolt diameter bushings, do I have to switch from one to the other?
A) No, you may order the propeller with either bolt diameter. Simply order a 70CM6 for 6/16 (3/8) or 70CM7 for 7/16 inch hardware.
Q) I understand arbitrary diameter reductions can be dangerous in metal propellers. Can this propeller's diameter be reduced?
A) Yes! The 70CM has a minimum diameter of 68 inches. This will allow the repair of tip damage due to ground strikes and foreign objects. Reducing the diameter below 68 inches can lead to a failure because the blade becomes stiffer and this changes the vibration characteristics of the propeller. Extensive vibration testing was completed to determine the minimum diameter at which the propeller is safe to operate.
Q) I have been told that this propeller is Type Certified, what does this mean to me?
A) If your aircraft is using a type certified engine and propeller, you should be able to reduce the fly-off time to twenty-five (25) hours.
Q) Product support is very important to me. Is this a factor?
A) It certainly is. With a wooden propeller, you are generally at the mercy of the manufacturer. With a Sensenich metal propeller, you will be able to get your propeller repitched and serviced at any authorized Sensenich repair center, world-wide.
Q) My wood prop manufacturer can always repitch the propeller if it's not quite right, can't he?
A) Absolutely not! A wood prop can not be repitched and maintain it's original design efficiency.
Q) I already have a wood prop extension. Can I use the metal propeller with this extension?
A) No. Due to the high polar moment of inertia with a metal propeller, a spool type spacer should never be used.
Q) What have I learned from all of this?
$400 is not a lot more to pay for an aluminum propeller over a wooden propeller. $4000 is a lot to pay for an extra 17% horsepower on climb out. Heck, for an extra $1500 you can buy a new O-360 and get an extra 20 more horsepower. You can buy a new 70CM series propeller every time you have to recondition your constant speed prop and governor.
70CM Propeller Update (O-320 Engine) |
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