Where did he say that?
martinkh said:
Why does Van's say a fixed pitch prop is not appropriate for a 180hp engine?
Where did Van say that?
History wise most RV's had fixed pitch props and engines with 160 hp or less (over 15 years ago). Than the 180 hp became more popular. The fixed wood props of the time started to show problems on the 180 hp engines. The props they where using on the 180 hp engines where made like 160 hp props but with more pitch. The hub area was taking a beating, burning in some cases. The 360 Lyc has a strong power pulse which plays havoc on the wood props. The solution was to make larger, thicker hub and crush plate, among other changes. The wood prop than where OK on the 180 HP, as long as you kept on re-torquing the prop bolts. So they overcame the issues and beefed it up.
Than Sensenich came along and made a metal prop just for the RV. It happens to have great performance, low maintenance and is a bargain. Sensenich makes a 180 HP prop, which Van sells. I am not aware of where Van said "a fixed pitch prop is not appropriate". Now he may have said that; I don't know? I know for a fact Van said, way back, long ago, that he was not in favor of constant speed props, he just felt they cost too much. Well obviously he changed his mind and recognized the advantage them on RV's. He also understood that builders had the desire and cash to put them on for gain in performance. So he does change his mind, but still recognizes the trade offs and the pros and cons of each. Now Van's individual employee's may have OPINIONS, and I have heard this fixed on a 180 or even 200 HP engine is not ....... (fill in the blank - GOOD). However what is the data on that. My personal prefrence is for a constant speed prop on my O360, Hartzell in particular. However the aerodynamics and economics of props , 150 HP or 180 HP are the same. Let me explain below.
Fixed pitch props do have an overall compromise in performance from a constant speed prop, however in trade they cost less, are simpler, a little lighter and are a little less maintenance. It does not matter if it's on a 150 hp or 200 hp, the compromises are the same. However in the case of real high HP engines, +200HP, they just don't make fixed pitch props. I am not sure why Sensenich does not make a metal prop for the IO360 angle valve 200HP Lyc. It could be market, since there are way less RV's with this engine. It could be for technical reasons. You would have to call them. There is a limit of how much HP a wood hub can take I suppose, as was inadvertently found when the 180 hp engines started to become more popular in the 80's and early 90's.