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Why no fixed pitch in big engines?

Where does it say that? There are a lot of 180hp powered RVs with fixed pitch props and they fly just fine.
 
props

A fixed pitch prop is like having a car with only one gear. You have to compromise something - takeoff/climb performance, cruise performance, or most typically, a little of both.
A C/S prop allows you to 'shift' in flight - which allows you to operate at high rpm & high MP for takeoff and then for cruise use lower rpms (better prop & engine efficiency) but keep the power up with higher MP (than you'd get with a FP prop at that same RPM). With a FP, you have to keep the RPMS high to get the same HP.
Hope that helps...
 
I don't see it

martinkh said:
When you do the cost estimator. I was checking out the rv7 and 9
I tried the cost estimator and didn't see them say that the fixed pitch was inappropriate for the 180HP engine. There is a message that says that the RV-9/9A will not accept the 180HP engine. Are you thinking of this?
 
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.
 
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At Oshkosh this year I saw AN RV-10 with an advertised 325hp turning a 3 bladed CATO fixed pitch prop. He said it worked fine and didn't want to spend the money on a constant speed.
Go figure.
 
FP Wood Props :)

gmcjetpilot said:
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.

The standard for the 0360 is 1/2" bolts with a 1/2" crush plate. I've seen 0320's with 7/16" bolts and even one with 3/8". That will not work with the 0360, as George points out.

Lots of guys are flying with FP props and 180-200 HP Lycomings. I like them of wood, as I like wood. They are light weight, can be manufactured to any pitch, and are reasonably priced. My experience with them has been good. Three blades run smoother than two - don't ask me why, but it is true.

Naked wood is out these days. Catto and MT are examples of wood core props with a glass/epoxy finish, very beautiful.

Metal is also in, but would not be my first choice because of weight and if a blade ever lets go, say good-by to the engine due to vibration, it will literally leave the airplane. I know of a Mooney that lost a blade during a ground run up and before the engine could be shut down, the engine was on the ramp.

That's not necessarily so with a light weight wood prop. I had a piece of an exhaust pipe leave a pusher and on its way through the prop, and took 2/3's of one blade with it. The ensuing vibation scared the dickens out of me, but some subliminal part of the brain saved the day by directing my right hand to pull the mixture and things got real quiet and calm in just a few seconds. The flight ended with a glide to a hard surface runway at Auburn, Alabama. A subsequent inspection of the engine revealed no damage whatever. The primary crank drive key was normal as was flange run out on the other end.

That's why I like wood props. :)

If I had a Lycoming engine, it would have a Catto prop, hands down. It is light weight, inexpensive, beautiful, and works very well according to anyone who has one.

dd
RV-7A N707DD
Subby H6 MT

 
There are aircraft with >200 hp with fixed pitch props.

A couple of examples that use the same engine (the 235 hp version) as the RV-10 are the Cherokee 235 and Pathfinders (same thing) which can be found with either fixed pitch or constant speed units.

Of course, the speed range for that aircraft isn't as wide as say, an RV-10, so the performance compromise isn't as severe.

In pre-WWII days, Gladiators and Hurricanes, both of which had 900 hp or more were fitted with fixed pitch props. Later, the Hurricanes were all retrofitted with variable pitch props... Dunno about the Gladiators.
 
Kyle Boatright said:
There are aircraft with >200 hp with fixed pitch props.

A couple of examples that use the same engine (the 235 hp version) as the RV-10 are the Cherokee 235 and Pathfinders (same thing) which can be found with either fixed pitch or constant speed units.

Of course, the speed range for that aircraft isn't as wide as say, an RV-10, so the performance compromise isn't as severe.

In pre-WWII days, Gladiators and Hurricanes, both of which had 900 hp or more were fitted with fixed pitch props. Later, the Hurricanes were all retrofitted with variable pitch props... Dunno about the Gladiators.

Kyle, I believe the early ME-109's had a FP wood prop also with 700-800 HP.

dd
 
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