New Catto prop test results

[Steve Brown]

I ordered a finer pitch prop from Catto.
Old Prop 66x72 3 blade
New prop 68x66 3 blade

Primary design goals:
-2700 RPM at full throttle @ 17,500 on a warm day. That's about 19,500 DA.
-2700 RPM cruise at low altitudes at or above 150kts.
-Improved climb performance, especially up high

The following at 2700 RPM and appropriate throttle:
_MSL_ _PA_. _DA_. OAT KIAS. KTAS .MP. ~%power
05500 na___ na___ 021 138.5 155_ 22.2 72.7 (data taken different day)
09500 na___ 11680 013 129.5 155_ 19.8 66.6 (data taken different day)
14500 14500 16800 006 117.5 153_ 16.0 55.2
15500 15430 17656 004 116.0 153_ 15.5 53.9
16500 16460 18583 001 115.0 154_ 15.2 53.4
17500 17400 19630 -01 113.0 154_ 15.0 53.1

Speed ranged are 153-to-155 kts. The differences are probably related to my accurate reading of 2700 RPM on a vibrating tach needle. The TAS crossover with the old prop is about 16,000 DA, and I was getting about mid 140s TAS at 19,500 with the old prop. So, I gained close to 10 kts at my maximum operational altitude.

At 19630 DA I was running approximately full throttle for a while. I got into some different air mass after a while (I think rising air) and my speed went up to above 157 so I pulled the throttle a nick to get back down to 2700 RPM.

At all lower altitudes I had to decrease throttle to keep 2700 RPM.

On a hot day close to 20C above standard:
I got 1539 FPM for the first 1700' GPS at KIAS above Vy. 10:55 to climb from 281' GPS to 12,000' GPS. This was solo, starting with full fuel.

I don't have good climb data from the previous prop, but my perception is that I'm getting an extra 200FPM. My perception is also that takeoff roll is shorter.

Glide ratio went from 11.5 with the old prop down to 10.8:1 with the new one. My glide testing location was less than optimum because of my test box limitations so I may have been in slight downdrafts resulting in lower than real glide ratio. Nevertheless, reduced glide was an expected negative. However, it's not all bad because landing is just a bit easier now.

I gave Catto my design goals and performance numbers of my old prop. Obviously, he nailed the goals perfectly and slightly exceeded them.

I'm impressed, and a happy customer!

I haven't decided whether to sell my old prop of not. If my daughter moved to this side of the rockies, I might put it back on since at low and mid altitudes, its got more speed. Its ideal up to low teens for my engine, with an O360 probably higher. If anyone is interested in that prop it might help me to make up my mind so send me a message.

[turneraero]

Steve, PM sent

Thanks Jerry