Van's Air Force
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Catto 68x74
- Thread starter rph142
- Start date
I second what Mel says.......
My RV-6 has a 160 hp engine with a two blade 68-74 Catto Propeller. When I ordered the propeller, I ordered it assuming I would be swapping the magnetos for electronic ignition, which never happened. My static RPM with the magneto ignition was insufficient. The take off performance was poor. I sent the propeller back after flying it for a few months, and Catto adjusted it in some manner. I'm not sure what he did, but I have 100 more static RPM now. Take off performance is better. At full throttle at 8000' the engine will turn almost 2800 RPM.
An RV-3 will be faster than my RV-6. I would think that prop might be a little bit too fine for it, but Catto will adjust for you one time without cost if you find it needs it.
The wonderful speed range in these airplanes really does put a constant speed propeller to good use. I like the flying qualities of my RV-6, and wonder how it would be with the weight of a constant speed propeller up front. I recently flew an RV-6 with 180 hp and a constant speed propeller. Take off performance was in a different world than I fly in with my airplane.
In the air, it was the same as mine.
An RV-3 will be faster than my RV-6. I would think that prop might be a little bit too fine for it, but Catto will adjust for you one time without cost if you find it needs it.
The wonderful speed range in these airplanes really does put a constant speed propeller to good use. I like the flying qualities of my RV-6, and wonder how it would be with the weight of a constant speed propeller up front. I recently flew an RV-6 with 180 hp and a constant speed propeller. Take off performance was in a different world than I fly in with my airplane.
In the air, it was the same as mine.
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Prop
Your prop is already underpitched for your RV-6- it should only turn 2700 at full throttle. It will be way underpitched for your -3. Catto is slightly reshaping the prop to get your results. This can only be done a couple of times before too much material is taken off. Metal props are bent at various stations to get the pitch. Van's has some calcs you can do to get to the desired top speed at 2700rpm for each airplane.
Your prop is already underpitched for your RV-6- it should only turn 2700 at full throttle. It will be way underpitched for your -3. Catto is slightly reshaping the prop to get your results. This can only be done a couple of times before too much material is taken off. Metal props are bent at various stations to get the pitch. Van's has some calcs you can do to get to the desired top speed at 2700rpm for each airplane.
Aden is Mistaken'
We had a great talk by Craig last night at our fly-in near his home. You should be able to turn more than 2700 RPM at WOT. There is no magic to that number. A local Pitts flew 2500 hours on a Lycoming at 3000 RPM. Our fastest guys turn upwards of 2900 and can really make some speed. It can also twist off the shaft of your old vacuum pump if you still use one....
I got the impression from the talk that good rules of thumb are a static of around 2300 and a top of 2850 or so means you have a good all around prop for your installation.
Constant speed props are great for take off and climb. His prop, properly suited to the installation will outrun one every day.
We had a great talk by Craig last night at our fly-in near his home. You should be able to turn more than 2700 RPM at WOT. There is no magic to that number. A local Pitts flew 2500 hours on a Lycoming at 3000 RPM. Our fastest guys turn upwards of 2900 and can really make some speed. It can also twist off the shaft of your old vacuum pump if you still use one....
I got the impression from the talk that good rules of thumb are a static of around 2300 and a top of 2850 or so means you have a good all around prop for your installation.
Constant speed props are great for take off and climb. His prop, properly suited to the installation will outrun one every day.
rph142
Well Known Member
Thanks for the input everyone. Im still torn between a 68x74 and a 68x76. Catto recommends the 68x74 for the RV-4, but since my 3 will be smaller and lighter I would think a 68x76 would be a better fit. Tony Spicer has a 68x76 and reported the following numbers:
static- 2200 rpm
takeoff roll- 2320
climb at 115mph ias- 2380
wot at 1000' density alt- 2980 and 220 mph tas
wot at 8000' density alt- 2890 and 210 mph tas
These numbers look pretty good to me. On the other hand, I plan to fly mostly acro (big round loops, cuban 8's, clover leafs, etc.), which would be better suited for the 68x74. So I guess I have some thinking to do.
static- 2200 rpm
takeoff roll- 2320
climb at 115mph ias- 2380
wot at 1000' density alt- 2980 and 220 mph tas
wot at 8000' density alt- 2890 and 210 mph tas
These numbers look pretty good to me. On the other hand, I plan to fly mostly acro (big round loops, cuban 8's, clover leafs, etc.), which would be better suited for the 68x74. So I guess I have some thinking to do.
smokyray
Well Known Member
RPM=HP...
I was always asked by my 180 C/S RV4 buddies how I could keep up with (and pass) them so well with only 150HP/Catto running MoGas.
RPM my brother, RPM!
Rob Ray
RV4ormerly
HR2
BTW, JAARS operates Helio Couriers in the Mission field worldwide. It uses a Geared Lycoming GO-480 which turns 3000 RPM continuous at 2400 prop rpm. They routinely see 2000 hours with no worries. Also the 0-290GPU ran at 3000 continuous, the forerunner of the 0-320.
http://www.youtube.com/watch?v=gDunPCisZWw
I was always asked by my 180 C/S RV4 buddies how I could keep up with (and pass) them so well with only 150HP/Catto running MoGas.
RPM my brother, RPM!
Rob Ray
RV4ormerly
HR2
BTW, JAARS operates Helio Couriers in the Mission field worldwide. It uses a Geared Lycoming GO-480 which turns 3000 RPM continuous at 2400 prop rpm. They routinely see 2000 hours with no worries. Also the 0-290GPU ran at 3000 continuous, the forerunner of the 0-320.
http://www.youtube.com/watch?v=gDunPCisZWw
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