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Need Advice on Prop Pitch RV-9A, 160HP

Av8torTom

Well Known Member
I'm trying to decide on a fixed pitch propeller for my RV-9A, 160HP.

I know the 9 tends to be a little tail heavy, so an aluminum prop might be advantageous there. However, the Sensenich props are RPM limited to 2600.

My other choice is a Whirlwind ground adjustable. I believe the composite props have a higher RPM rating, but are significantly lighter.
I have 3/8" bolts, and the Sensenich ground adjustable apparently only comes 7/16" bolt compatible.

Please chime-in with thoughts and experiences for the 9A.

Thanks,

Tom
 
Steve,

So you're saying the higher RPM limit is more important than the extra weight up front?

Thanks
 
Whirlwind 100%. Fantastic props with better performance than the Sensenich. I would not add extra weight just for the **** of it unless you have already calculated that you need to, and in that case only add what is necessary - far better to move the battery a little forward over having all of that extra spinning weight. Pluss, with the ground adjustable feature you can tune the prop in to your exact plane and flying.
 
I have a Sensenich fixed pitch 70CM7S9-0 (79), which is limited to 2600 RPM, on my RV-9A that has an O-320.

I have never seen 2600 RPM and think I would have to be in a very purposeful dive at full throttle to hit that. 75% power in cruise is something like 2450 RPM and 160 knts TAS. Climb is >1500 fpm.

I do not experience CG problems within MTOW.

I was not the builder and therefore did not choose this prop. Some of the composite 3 bladed props would be tempting if this one wasn't performing so well!
 
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I'd be tempted to get the metal Sensi. No rain worries, no degradation worries, probably a more useful CG. Having a thinner blade section should lead to the metal prop being more efficient, so what you give up in ultimate RPM, you get back in efficiency.
 
Correct me if I'm wrong, but the metal Sensenich prop is pitched so you cannot exceed (at least not easily) the 2600 RPM limit. With a composite prop you can select a pitch that will allow you to use the full RPM range of the engine. That's a advantage of a composite prop as I see it.
 
I have the whirlwind ground adjustable on my 9 and have no cg issues. I for one would not use a rpm limited prop. I personally don’t understand why anyone would but maybe I’m missing something. My empty weight was 1087 I believe. My weight and balance info is in the plane but I could get you numbers if that would help. Whirlwind lists 3/8, 7/16 or 1/2 bolts for the 0320 or 0360.
 
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Keep in mind that all the prop manufacturers calculate their pitch slightly differently. This makes comparison by pitch number alone very difficult.

I have had a Catto on both my engines and wouldn't run anything else!
 
I had a Sensenich for 200+ hours and it was basically fine, no rain problems. However, as with any fixed pitch prop, going cross country in up- and downdrafts, you're always adjusting the power, adding power in the downdrafts and pulling it back in the updrafts (with the autopilot flying). 2600 RPM limit was for me a so-what, as I never flew that high or wanted to burn more gas.

That said, I now have a Hartzell constant speed and the plane can climb more steeply than I like, so I climb at higher airspeeds. The big advantage of the /cs prop is that it has more drag, power off, so you can slow down more easily, especially on landing rollout.

The RV-9A has a huge c.g. range, so that's basically a non-issue. But go run some numbers on a spreadsheet and see for yourself.
 
Can?t go wrong with a whirlwind GA, Sensenich GA, or Catto two or three blade. With those options, all available with Nickel leading edges, I would not bother with a metal prop.
 
My experience

Hi Tom. You may recall I had 3 different props on my -9A. When you flew with me I had a WW ground adjustable. I really liked that prop. Great performance and no issues with rain, CG, etc. I started with the metal sensenich and I felt I never got the performance I expected out of that. The WW was much better in my option. I ended up with a WW 151 which was a real game changer but $$. So given a choice id definitely consider the WW GA prop. I only hear great things about Catto but have no experience. Ask Vlad. He put 4000 hrs on his😮
 
Another reason for a ground adjustable???

Maybe give you some versatility to find your sweet spot. The more aggressive cruise prop is good for what it is but lacks when the engine has to work harder, creating more heat on climb. Just remember your climbing the hill in 5th gear.
 
Because

why would you consider a prop limited to 2600 RPM?

Because its a very good performing propellor even with the rpm restriction

Because Its vitually maintenance free

Because it might provide a CG that make the airplane more useful

Because it might be less expensive than other options

Because even as a cruise prop it will give excellent climb performance if you climb at correct speed.

I had one on my 160hp RV4 for 600 hours and it was a very good choice for me.

Cm
 
Because its a very good performing propellor even with the rpm restriction

Because Its vitually maintenance free

Because it might provide a CG that make the airplane more useful

Because it might be less expensive than other options

Because even as a cruise prop it will give excellent climb performance if you climb at correct speed.

I had one on my 160hp RV4 for 600 hours and it was a very good choice for me.

Cm

got it. thx
 
Not all metal Sensenich propellers recommended for use on Vans airplanes have that 2600 RPM limit. For instance, my O-360 powered RV4 has a Sensenich 72FM prop and doesn?t have that restriction.. In fact none of the 72? metal props have that restriction.

http://www.sensenich.com/wp-content...luminum_Propeller_Applications_1349891787.pdf

They call the 72FM props 72 inch props, but they are actually 71?. Mine is actually a 72FMS9-1-85, which is 85? pitch. My RV4 climbs very well, but at 2700 RPM in level flight, I?m not at full throttle yet - at any breathable altitude. At full throttle in level flight I?ll see about 2900 RPM. I?ve only run it this way to gather data for Nicole at Catto. A new Catto, or Sensenich repitch is in the plans.
 
Here is the issue with a 2,600 rpm limited prop: RV9's are intended to be cross country machines. Generally this means higher altitudes to take advantage of fuel efficiencies. Above 8,000 ft you can not get to 75% power and you cant hurt your engine running it at 2,700 rpm, so if you have a prop that can not exceed 2,600 rpm you are giving up almost 4% of your speed.
Secondly, if your prop i pitched so that you can not exceed 2,600 it is putting a tremendous strain on your engine on take-off. You are going to have higher peak pressures VS the same operation with a plane pitched for 2,7000.
 
Most people running fixed pitch props on RV’s do not cruise them at 2700 rpm.
For those people the 2600 rpm limit is not going to be an issue. In fact, the pitch is a pretty good matched for most people with O-320 powered RV’s. Is a bit more performance available? Sure, but you have to run the engine pretty hard to achieve it.
Regarding the rpm in a climb, it is no different than what the climb rpm is on a C-172 or Cherokee Warrior, so it is not lugging the engine any more than has been typical for decades. It is not a problem.

I do agree that for best performance with a fixed pitch you should have to pull the throttle to limit RPM to 2700 if you are below 11,000 - 12,000 ft.
 
Secondly, if your prop i pitched so that you can not exceed 2,600 it is putting a tremendous strain on your engine on take-off. You are going to have higher peak pressures VS the same operation with a plane pitched for 2,7000.


Guess all those 172's and Cherokees with fixed-pitch props are putting a tremendous strain on their engines.....

Actually, the engines aren't being hurt. Lower rpm just means the engine is producing less than rated power. My RV-6 with O-320 and fixed Sensenich has had a "tremendous strain" ;) on the engine every takeoff for twenty years now. The 2350 rpm climbout just means the engine is producing much less than rated horsepower, probably ~120 hp in my case. The rpm is lower at full throttle but the lower power output keeps CHTs in range so the engine is happy.
 
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Most people running fixed pitch props on RV’s do not cruise them at 2700 rpm.
For those people the 2600 rpm limit is not going to be an issue. In fact, the pitch is a pretty good matched for most people with O-320 powered RV’s. Is a bit more performance available? Sure, but you have to run the engine pretty hard to achieve it.
Regarding the rpm in a climb, it is no different than what the climb rpm is on a C-172 or Cherokee Warrior, so it is not lugging the engine any more than has been typical for decades. It is not a problem.

I do agree that for best performance with a fixed pitch you should have to pull the throttle to limit RPM to 2700 if you are below 11,000 - 12,000 ft.

I have a slightly under pitched prop on my 6A and really like it. It gives me a better climb (typically 2500 RPM) and more options. At 13K, I turn 2700 at peak EGT and at 8-10K I turn 2700-2730 at around 30-50 LOP. Without turning 2800+, I cannot run ROP at 8-10K, but I am really too cheap to throw the extra gas at it to do so anyways. I am in the camp that the 320's can easily handle 2800 in cruise, so I still have options for extra speed if I feel it necessary.

Its all about compromise. Optimize the pitch for your most common cruising regime and preference for climb performance. I agree with others that the lugging involved with more course pitched props has negligable affects on longevity.

Larry
 
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I have a slightly under pitched prop on my 6A and really like it. It gives me a better climb (typically 2500 RPM) and more options. At 13K, I turn 2700 at peak EGT and at 8-10K I turn 2700-2730 at around 30-50 LOP. Without turning 2800+, I cannot run ROP at 8-10K, but I am really too cheap to throw the extra gas at it to do so anyways. I am in the camp that the 320's can easily handle 2800 in cruise, so I still have options for extra speed if I feel it necessary.

Its all about compromise. Optimize the pitch for your most common cruising regime and preference for climb performance. I agree with others that the lugging involved with more course pitched props has negligable affects on longevity.

Larry

I have always told people that for an RV that is typically cruised at higher altitudes, there is no such thing as a climb prop and a cruise prop. They are both the same prop.
There is really only a difference if your desired max cruise performance is around 8000 ft. In that case, the prop that gives the best overall performance will seem under pitched.
 
Adjusting power

However, as with any fixed pitch prop, going cross country in up- and downdrafts, you're always adjusting the power, adding power in the downdrafts and pulling it back in the updrafts (with the autopilot flying).

I end up doing this with the Hartzell as well, though probably less than I would with fixed-pitch I suppose.

That said, I now have a Hartzell constant speed and the plane can climb more steeply than I like, so I climb at higher airspeeds.

Same here. Climbing in my Hartzell-equipped -9A at Vy usually generates a deck angle that is not conducive to cooling, or to seeing and avoiding the copious buzzards that frequent New Kent International Aerodrome. :)

The big advantage of the /cs prop is that it has more drag, power off, so you can slow down more easily, especially on landing rollout.

I like this added ability to slow the otherwise fairly slick -9. Very handy for instrument work.

The RV-9A has a huge c.g. range, so that's basically a non-issue. But go run some numbers on a spreadsheet and see for yourself.

Indeed. From what I can tell, it's practically impossible to load mine out of CG if you observe the 100-pound limit for the baggage area.
 
Here is the issue with a 2,600 rpm limited prop: RV9's are intended to be cross country machines. Generally this means higher altitudes to take advantage of fuel efficiencies. Above 8,000 ft you can not get to 75% power and you cant hurt your engine running it at 2,700 rpm, so if you have a prop that can not exceed 2,600 rpm you are giving up almost 4% of your speed...
I suppose people running CS props at 2400 RPM in cruise are also giving up power then?
 
Keep in mind that all the prop manufacturers calculate their pitch slightly differently. This makes comparison by pitch number alone very difficult.

Another reason for a ground adjustable???

Not necessary. The prop makers, such as Catto, know what their pitch number and diameters of their prop style(s) work best with each engine and airframe combination.

Catto will ask what engine, compression, igntion, fuel system, and model airplane (RV3, 4, 6, 7, 8, 9, Longzy, etc.), and what configuration (taildragger or tricycle), etc. He will then custom fabricate a prop to match your unique configuration that will be spot on.

I haven't mentioned any of the other very good prop manufactures out there simply because I don't have experience with them.

I did order a WW GAP and when it arrived and I found out it was setup only for the small hub bolts, I returned it and ordered my Catto.

As for the Sensenich GAP, my neighbor had one on his OTRV (Other than RV) and his mags wouldn't last 30 hours. After three mag failures he bought a Catto and the problem went away. It turns out the Sensenich was so stiff the harmonics were destroying his mags. Once he switched to the Catto, the problem went away. (Yes, the blades were set the same, the prop was balanced, etc. He went through everything his IA could think of to solve it and nothing helped.)
 
As for the Sensenich GAP, my neighbor had one on his OTRV (Other than RV) and his mags wouldn't last 30 hours. After three mag failures he bought a Catto and the problem went away. It turns out the Sensenich was so stiff the harmonics were destroying his mags. Once he switched to the Catto, the problem went away. (Yes, the blades were set the same, the prop was balanced, etc. He went through everything his IA could think of to solve it and nothing helped.)

Without a LOT of supporting data, I?d be reluctant to jump to that conclusion. There are a bunch of metal Sensi?s out there and if ?eating mags? was a problem, it would have surfaced long before now and impacted hundreds, maybe thousands of aircraft.
 
I suppose people running CS props at 2400 RPM in cruise are also giving up power then?

No, because they are increasing their pitch accordingly to maintain power at lower RPM's. With a FP prop, RPM is your only speed knob.
 
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