danielhv

danielhv

Well Known Member
So, are the only advantages to a CS over FP seen during climb & decent? Will they both cruise the same if you have a cruise prop? (assuming two identical airplanes.)
 
Dan,

It really depends on the pitch of the FP prop. Some FP props are optimized for cruise and can actually out run a CS prop in level flight. To do that they give up some climb performance.

In the RV's that "degraded climb performance may still be around 1500 FPM depending on the plane, engine, and prop.

One advantage of a FP prop is they are lighter, unless you go with a composite CS prop, then the weight may be a wash.

To toss out some numbers, my old wood prop was around 9 pounds, a FP metal prop can be as much as 40 pounds, and a metal CS prop will be more than that.

Maybe someone who has switch their props can talk about the numbers they have seen with the same airplane/engine combination and list the make, diameter, and pitch of the FP prop involved.
 
I like the lower sound levels when pulling back to 2300 rpms. Even at full throttle.

I don't have to add some kind of weight at the nose to have decent baggage capacity.

As is known,.... takeoffs are faster, as the engine is allowed to develop full horsepower. The C/S is great for managing deceleration. I even hear it's great for formation flight.............according to some recent threads.

I'd never put an F/P on a 6,7,8,9,10. Perhaps a wooden F/P on a 3. Just a simple lightweight machine. If I wanted an F/P, I'd be flying a Cessna 172. :D

L.Adamson --- RV6A / Lyc 180 / Hartzell CS
 
All other things being equal, for a given HP, fuel consumption will be less at lower rpm (higher MP). So you can bring the revs back on the CS prop to say, 2,000 to 2,200 rpm in the cruise and achieve worthwhile fuel savings compared to a FP prop which will most likely need to operate at higher rpm in the cruise. Plus its great to have another knob to play with!

Fin
9A
 
Oh yeah, this is an easy question to answer.

I think that it boils down to:
FP - you decide what type of performance you want when you buy the prop.
CS - you decide what type of performance you want while you fly. At a small cost in weight.

Kent
 
Another advantage of C/S -- you don't have to worry about overspeeding the prop (unless you're Kevin Horton, of course). Point the nose down for a quick descent and just watch your airspeed. In a FP you'll be watching your airspeed AND your RPM.

One thing that's seldom mentioned and that I was sort of naive about before I made my prop decision -- overhaul cost. Yes, you will pay 2K every five years to overhaul your hartzell. That must be considered into the equation if you plan on keeping your airplane for a while.
 
there are so many advantages of a C/s over a f/p prop. for me a max RPM take off with max pull up is one. When I feel a light head I know I've hit it right. Feels great, only way to fly.
 
formation

Another slight advantage is the braking affect you get from a constant speed prop. Can be great for joining up on someone's wing so you don't overtake - should not be a crutch for good technique however.
Also, on landings you get some braking as the prop flattens out.

Plus it's cool!;)
 
cost of prop after 10 years.........

c/s ................ fixed

prop $6649 $2135
gov 1200
2 oh 4000
__________ _____
total $11,849 $2135


* 2009 prices

It's like a stuffed panel............... What are you going to use the aircraft for?
 
other choices....ground adjustable?

Haven't I seen some adjustable/not CS somewhere?
If I were on a long x-country, I wouldn't mind speed over climb, if I know where I'll be landing. If I know I'm going into a short grass strip on a hot day with a full load of camping gear, I'd put up with less speed for the climb I need.
I'm not sure though that I trust, 100%, the various types of blade clamps I've seen. Seems there are always failures.

and just for reference, not everyone gets 1500 fpm climb as a tradeoff for their 'cruise' prop.
I have an 0-320 rv-9a with a -79 pitch Sensenich, which is a mild climb prop, and rarely see 1000 fpm at any speed, top speed is about 140 IAS...sorry don't have a whole bunch of 'official' numbers.
YMMV
 
Let me throw a little more shxxxx considerations in the game. The FP is lighter, so the weight difference gives a little more payload. It is much, much cheaper, both in the short run and in the long run, because not only does it cost more for the CS prop but also for the regulator and for the periodic overhauls, especially relative to a sexy three-blade or boss four-blade FP. There are probably a lot more failures of CS props than FP props, although I don't have any specs to back that up, it's only my opinion. We used to fly four people in a high drag, 135 HP Tri-Pacer, and now we're flying two people around in a 150HP-200HP low drag RV. Just compare the difference in ROC between these two! The planes these days have so much excess power that even with the lower take-off and ROC power available with the lower rpm of a FP, the take-off and ROC of these hot-rods is still phenomenal. And if you have a high efficiency design prop, you'll get not only faster cruise with the FP than the CS because of the CS's higher drag hub and tip, you'll still have really good ROC. I get over 1500 fpm at 105 mph and 2400 rpm on a 2800 rpm rated, 125 HP engine so it's not that big of an ROC difference especially since the extra weight and higher hub and tip drag of the CS lowers the ROC a little. So what it boils down to is that as in a lot of other decisions, its best to set up a table of pros and cons of each and then, if possible, reach an intelligent rather than an emotional decision. Whichever way you decide, it's OK!
 
flyboy1963 said:
Haven't I seen some adjustable/not CS somewhere?
If I were on a long x-country, I wouldn't mind speed over climb, if I know where I'll be landing. If I know I'm going into a short grass strip on a hot day with a full load of camping gear, I'd put up with less speed for the climb I need.
I'm not sure though that I trust, 100%, the various types of blade clamps I've seen. Seems there are always failures.
Click to expand...

I've seen them, but the idea of pulling all the screws out of spinner, let alone a few for the prop............sure doesn't sound too appealing.

FWIW, since a lot of our RV's are flying out of high altitude airports in mountain country, the majority are C/S props. I've never heard of anyone around here wishing they had a F/P instead. But I've heard of numerous RV owners wishing they had went with a C/S or had an engine that didn't have a solid crank.

L.Adamson --- RV6A
 
danielhv said:
So, are the only advantages to a CS over FP seen during climb & decent? Will they both cruise the same if you have a cruise prop? (assuming two identical airplanes.)
Click to expand...

If you plan on doing serious formation work or competative aerobatics you had best go with a CS prop. If you are just doing sport aerobatics and the occasional cross country formation maybe the added expense of a CS is not worth it.
 
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