Apples and Cumquats
As an observer of the obvious: D
You can throw out the Hartzell because that goes under the C/S vs. fixed pitch prop debate. It is an animal of a different fur.
I have a Hartzell by the way on my last RV and current RV and love it. The blended airfoil is the best performance you can get, and it has been documented (in the RVator). If you have an engine that can run a Hyd prop, at approx $5500 plus gov it is a bargain in my opinion. C/S props provide the best overall performance and efficiency (gas mileage, less noise with lower cruise RPM and wear and tear on engine). Not to mention doing aerobatics is a joy with no throttle jockeying.
If you don't want, need or can use a C/S prop, for what ever the reason, cost or engine capability,
there are two other choices, both fixed, one is metal and the other is wood or wood with fiberglass skin (Catto).
The metal Sensenich is a known quantity. It has known performance and known material properties (aluminum). For the O-360, the Sensenich has documented known performance. The nice thing is the prop was designed for RV's and is well tested on RV's. You can't get much more durable and low maintenance than a fixed aluminum prop. We build aluminum RV's for are reason and not Glasair's, right.
Catto, I have heard good things, people like them and they are sexy. I think the painted finish attracts people, however you can get a metal prop custom painted.
Custom Prop Paint (click the aircraft links on the bottom of page)
The debate now becomes wood vs. metal. Both props have pros and cons. I guess it's a matter of choice at this point. Things I do know are
metal will be less maintenance, hands down. Minor repair like a rock ding will be less with metal. The only negative I have heard of regarding Catto, is one guy in another forum had one break or throw a piece off. To be fair he was racing at Reno or something like that in a formula racer, but the wood failed, which is always a concern. Let's face it, wood is a natural material and subject to small imperfections. Go to your favorite home-supply mega-store and look for good pieces of wood. It's hard to fine sometimes. Now add the fiberglass wrap and bonded erosion shield and you have a complex built-up bonded structure. Any bonded structure is very process depended, meaning any small variation or error in making it can cause serious defects.
Wood will be hands down lighter and feel a little smoother because wood dampens vibration very well. For solid wood props with no cover the biggest Con in my opinion is constant checking and re-torquing of the prop bolts. Wood expands and contracts with moisture content, which it will do year round with the sessions. The Catto fiberglass wood wrapped blades may or may not be subject to this also, but I don't know? They have an aluminum plate bonded in the hub area, so this may help.
Sensenich performance is well known, and
a metal prop should out perform a wood prop. Why? Well metal prop blades can be made thinner than wood. It would be interesting to have a fly off between the Catto and Sensenich, where the props where switched out on one or two planes. The Sensenich was flown against several C/S props and did very well as shown in the RVator. There are no well documented fly off between a Sensenich and Catto I know of. However I looked at their site and they note that the top 3 Biplanes at race had Catto props.
Why was they?re so many wood props in the 80's and early 90's. Well they?re where no fixed pitch metal props available, period. Using metal props for slow planes cut down and re-pitched was not a good thing and even tragic. Metal props unlike wood is made of a similar material as the crankshaft, metal. So harmonic vibration and fatigue is of concern. (Wood by the way has good fatigue life and will die from decay not fatigue like metal can.) To make sure it's not an issue, metal props need to be well engineered and tested, that requires complex equipment and analysis. Sensenich stepped up and tested their line of RV metal props, which in a way made wood props obsolete for a large population of average RV builders. The price is also very good. A well-tested metal prop is very safe and fatigue not an issue. An experimental un-test metal prop is dangerous. Wood is so forgiving you can whittle a wood prop out and not worry about it, however there have been some wood prop experiments gone wrong in the past. The most popular wood props have a good safe record overall. However things like leading edge erosion strips do and have come off wood props, and it is not uncommon. If this happens it can shake the plane quite vigorously. I think the Catto does not use bonded leading edge strips like may wood or wood/fiberglass props do. This is a good thing.
Wood still has appeal, but it is a special appeal in the RV world. Many homebuilt planes are better suited for the Catto because frankly Sensenich does not make a prop for their application (Long-EZ). Also some homebuilts are very weight sensitive, which the RV is not. With the use of light alternators, starters and batteries and placing equipment aft when given the choice, the extra weight is not an issue for the RV. I know the RV-7 needs weight on the nose to allow full baggage and remain in the aft CG limit. Weight on the nose is good for the dash 7.
In the end it depends on
how the company will support you. Hartzell will be there but will cost the most. In return have the best overall performance and efficiency (fuel economy), and that is not a debate but fact. To get this will cost weight on the nose (which is need on some RV's) and money. The Sensenich will be there down the road, and like Hartzell has tested their product on RV's and supports RV's specifically. The Sench is a known quantity and a unique feature wood does not have. If you make your plane a little faster with some drag reduction, like a fairing mod or the like, you can re-pitched the Sensenich fixed pitch prop. Wood has the advantage of smoother operation and lightweight. I would also add lower cost to the plus column of wood props, but the hybrid wood/composite props are not cheap and actually cost almost the same a metal props.
Also you have to think of maintenance. If there is some small damage who will repair it?
Hartzell and Sensenich can be repaired at any prop shop. The custom wood prop will most likely need to be shipped to the manufacture. The last point is a toss up. Wood props tend to be totaled when they are hit on the ground, while metal may be able to be repaired. However if the "strike" is bad the wood prop will break and save the engine while a metal prop may cause damage to the engine crank in a hard strike condition. This of course is not something you want to happen in any form, but it is a small factor. Last and may be most important is what engine do you have (solid/hollow crank) and how much money do you have to spend on it.
George
