Do I have the right pitch

[lr172]

I have a 6A (160 HP) with a Catto 2 blade set up for a 160 HP 9A. I went up to 8K DA yesterday (cold air) and got around 2800 RPM at Peak or a bit ROP. I was getting close to 2750 in the summer, which makes sense given the lower density of the warm air. I then went LOP and the RPM dropped down to 2700 and gave me 190-192 TAS @ 8 GPH. I think that I am happy with this. Furhter, my EGT spread shrinks a bit at WOT. Being a bit finer pitched than optimum would seem to give me better climb performance and the ability for a bit more TAS at higher altitudes (I have O2 and plan x-country travel).

At 8K, 2800 RPM and ROP, my Dynon was showing 79% power. I am guessing that by going LOP to reduce RPM to 2700 should leave me safe for LOP operation. I assuming that once LOP and 2700 RPM I am under 75%.

I was hoping others could chime in and help to validate my thinking here. Could I get a higher TAS cruise speed with a bit of a coarser pitch?

Thanks,

Larry

[jrs14855]

I am not an RV person but lots of experience with props on EAB Aircraft. For an airplane that is mostly a go fast airplane you are almost exactly where I would want to be on pitch. Slightly less pitch would give slightly better acceleration and climb. To maintain the same cruise you would have to be willing to turn the flatter prop 50 or 100 r/m higher.
The racers are most likely running props that will turn 3000 rpm at full throttle. Whether this number is valid at low altitude or at high altitude seems to be somewhat of a secret. In the early cross country racing probably low altitude. For the races such as ND to WI a few years ago some were flying quite high, sometimes with some help from the wind, sometimes no help and a costly decision to fly high.
For the Pitts or similar aircraft that were used 90% for aerobatics I wanted a prop that would turn 3300 r/m at full throttle at Vne.
So it boils down to what r/m you are personally comfortable with. The aerobatic airplanes have a long history of running as high as 3500 r/m with both the 360 and 320 Lycoming. The average person will not live long enough to wear out one of those engines. Of course there are the rare exceptions such as Rutan, Melville and Rosie, some have worn out two engines.

[Dbro172]

Sounds about perfect to me. What pitch and diameter Catto?

[rightrudder]

I think that's spot on. I haven't flown my -9A yet, but I've got a Catto 70x70 2-blader with an IO-320 D1A 160-horse engine, and my invoice says the target speed is 189-193 mph at 2750 rpm.

[Christopher Murphy]

I dont know much about the -9 but 192kts true airspeed is pretty darn fast for any 160hp RV. I have to assume that is statute mph.

Id say you have the right pitch

Cm

[WA85]

I have an IO-320 with Catto 70/70 and I get 2780 RPM at 8000 feet, leaned to max power, 173 ktas.

[lr172]

Originally Posted by Dbro172

Sounds about perfect to me. What pitch and diameter Catto?

It is a 68 X 72 2007 vintage. I know he has had several iterations and not sure which generation it is. I understand that the dia/pitch sizings don't compare across different generations.

Larry