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-   -   Fixed vs CS prop (https://vansairforce.net/community/showthread.php?t=177744)

wbhammack 12-14-2019 12:34 PM

Fixed vs CS prop
 
I'm about to pull the trigger on my first RV. I'm military / airline guy so my GA experience is limited at best. If anyone has any advice on a CS prop vs a Fixed pitch I'd be interested to hear your opinions. I've narrowed my search to a 7 or 8 (14 if I could find one) because I will doing some acrobatics. Nothing crazy but I want to keep that option open.

74-07 12-14-2019 12:58 PM

My son and I (both ex-militery pilots) have owned two RV-8s, one with a Catto three blade fixed pitch prop and one with a Hartzell CS prop. Both fly well but the CS just performs better especially during takeoff. We've also owned a RV-7 with a Whirlwind CS and it was awesome also.

Scott Hersha 12-14-2019 02:19 PM

With a constant speed prop you will get full, or nearly full, power at takeoff and early in the first segment of climb. With a fixed pitch prop, you most likely won?t - unless you have a fixed climb prop, which will negatively affect cruise speed. A fixed pitch prop is like driving your car with only one gear. Most of us chose a cruise type pitch if using a fixed pitch prop for speed reasons, at the expense of takeoff/climb performance. That isn?t as great of a penalty in an RV as it is with some airplanes, because RV?s still have excellent takeoff performance with fixed pitch props - just not as good as their constant speed brothers. My fixed pitch RV4 still gets airborne in well under 1000? and by the time I?m at the end of the runway on climb out, I?m out climbing my constant speed buddies. I?ve owned 5 RV?s. The 3 I built had constant speed props. The 2 I?ve bought, including my current RV4 have fixed props. Which is better? The constant speed is better for performance reasons. My fixed pitch RV4?s are/were better in terms of cost, weight, and simplicity. If you are routinely flying out of hot/high, or short airports, the constant speed RV will be significantly better. I?m a flat lander using mostly long (3000?+) runways, and my fixed pitch prop is not that much of a detriment, but it is a detriment. Formation takes a little more ?finesse? than my constant speed RV?s, but that is easily learned. All things being equal in your search (build quality, cosmetics, condition, instrument equipment) the constant speed RV?s are more valuable than their fixed pitch clone, both in terms of your overall performance, and in resale value. To me, build quality and condition trumps the constant speed/fixed pitch question, but that?s my opinion based on the type flying I do. Your requirements are probably different.

B Cunningham 12-14-2019 03:33 PM

C'mon Skip, do you really have to ask? CS all the way... welcome aboard.

clam 12-14-2019 07:28 PM

Ditto...
 
Quote:

Originally Posted by B Cunningham (Post 1392967)
C'mon Skip, do you really have to ask? CS all the way... welcome aboard.

Exackry what he said... and make it an RV-8 with a Whirlwind CS when you pull that trigger. Happy RV hunting!

Flash 12-14-2019 07:44 PM

PM sent.

Scott

plehrke 12-15-2019 04:19 AM

Like others have said, depends on your flying. I did not see a benefit having constant speed prop as take off performance is already outstanding with fix pitch on my 180 hp RV6A. Flying almost exclusively in middle America at cruise speeds, a fixed pitch is perfect for my flying. I think a big swinger in prop decision is HP. With 160 HP I would have gone constant speed, with 180 HP I think a cruise fixed pitch is a good choice.

FlyinTiger 12-15-2019 05:00 AM

Final Approach and Landing
 
I've had the pleasure of flying my fixed pitch Catto and O-320 RV-4 at all altitudes from sea level to mountain airfields at over 9000 feet MSL.

Now I'm flying an RV-7 sporting an IO-360 and Hartzell constant speed prop and have landed at airfields from sea level to mountainous high altitude runways.

Without a doubt the biggest difference I notice between the two types of propellers is approach and landing. A fixed pitch prop is going to remain at the same pitch used for takeoff, which provided a static RPM significantly less than maximum RPM. A constant speed equipped aircraft produces rated horsepower on takeoff, so it is when the propeller control is at "high RPM" or "fine pitch."

With a constant speed prop I need to add a little power above idle on final approach to maintain desired speed as opposed to pulling the fixed pitch RV to idle on downwind and leaving it there, even slipping to keep approach speed with full flaps on final. RV-4s are more slippery than RV-7s by a little, yes. I've flown a little in a fixed pitch RV-7 and RV-7A, they both were at idle on short final to maintain a normal glide path.

Enjoy the search! Its a fun and challenging endeavor to find a flying aircraft that you like, has the equipment you like and is in a place where you can adequately look it over before buying. This is why many build their own. I found one flying that checked all my boxes, so I know it can be done!

BCP Boys 12-15-2019 09:41 AM

Obviously CS is best but if you do find a nicely built plane but it has Fixed pitch, I would certainly not turn my nose at it. I bought a beautiful RV7 exactly 5 years ago and over the past five years I have not only put the panel that I wanted, but I added a CS prop and WOW :eek: what a difference!!! I absolutely love it.

Toobuilder 12-15-2019 09:55 AM

This question comes up all the time and there are plenty of opinions. The reality is, it's not an opinion question, it's something that can be solved with simple analysis.

But it requires solid input data, starting with "what are your mission requirements". Many people choke right there.

I do long cross country work at max gross weight and that is the overiding consideration for me. I'm in and out of short strips, climb mountain ranges and run WOT, LOP for hours on end. Simply put, I "require" 2750 RPM for takeoff/climb as well as the ability to pull the prop back to 2300 in cruise with the throttle against the stop (WOT). That makes it a pretty simple choice for me.

What are your requirements?


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