hevansrv7a
Well Known Member
Why write this? First, there is very little direct comparison data on FP props on the same airplane in similar conditions. Second, I'm not aware of any data comparing these two well reputed props. Third, I hope to learn from the other members of the forum by presenting this information.
I started with a Prince P-Tip and recently bought a Catto. The P-Tip is a 2-blade and the Catto is a 3-blade. I did some testing under almost identical climate conditions. In both cases, a mild high with haze layer below and clear above. On warmer days I've had higher speeds from the P-Tip by about 6 kts and I don't know why the difference, but at least these two runs were under very similar conditions.
Both props were pitched by their makers after thorough discussion about my engine, cowl, fairings, etc. but still ended up too finely pitched. This may be evidence that my engine is stronger than expected. However, the airplane is not going as fast as it should, so that's an unsolved mystery for now. The Catto is on its way back to Craig for adjustment.
Both prop makers are excellent people to work with and I'd have no hesitation in recommending either one.
The instrument is a GRT Horizon & EIS and the EFIS is calibrated for TAS as per manufacturer's directions. Based on how it computes hw/xw and on the GPS speeds, I believe the TAS is accurate to within 1 knot. The OAT is below the wing in the first inspection panel and seems to agree with the ASOS once it stabilizes after leaving the heated hangar.The EFIS altimeter is IFR certified and tested to a max error of 20' all the way to 20K. The MAP was calibrated when the IFR check was done.
Cruise Data
P-Tip
Start with full tanks
OAT -6 deg C at altitude
Density Alt 9130
Power (per EFIS) 76%
WOT, best power mixture by ear
10.2 gph (maybe higher)
2750 rpm
168 KTAS
Catto
Start with -19 gallons = 114 pounds approx.
OAT -3 deg C at altitude
Density Alt 9472
Power (per EFIS) 78%
WOT, best power mixture by ear
10.8 gph
2810 rpm
173 KTAS
Climb Observations
Catto climbs better but at lower RPM: 2200 vs 2400, roughly, with about >200 fpm difference for Catto. Takeoff quicker by a few feet and accelleration subjectively better. The P-Tip climbed at about 1500 FPM using 16.4 GPH at 2440 rpm. I did not write down the climb numbers for the Catto, but I remember seeing 1800 or more on the VSI and lower GPH.Test was done about 100 pounds lighter but this seems to me a difference beyond the weight difference. In other flights I thought the Catto was doing this, even with a passenger and the FPM was higher.
Noise observations
If there's a difference, the P-Tip is quieter, but the difference could be how I inserted my HALO earplugs that day.
Other factors
The Catto is significantly out of balance and thus could be expected to perform a little better if balanced better.
Side Note #1
Prince says his prop self adjusts by as much as 3" of pitch based on load and rpm and until now I could not test that. The RPM range of the P-tip is about 200-250 less than that of the Catto and this is evidence that Prince is correct. Range here means from climb/static to top power at altitude. It's interesting that while the prop does seem to self adjust, the 3-blade Catto is climbing better and going faster anyhow. While the difference in cruise is not great and can be attributed to higher RPM (higher power), the climb difference is clear. Conventional wisdom says the 3-blade will climb better and cruise slower.
Side Note #2
Power percentage is, as I've noted before, a slippery concept. These numbers show that. In both cases I moved the red knob to where the airplane flew the fastest but I don't know how much ROP that was. The BSFC's should have been very close to equal. The Density Altitudes were quite close and should not matter anyhow. Superior says that at peak EGT BSFC is .43 and at 75 degrees ROP it's .50. So best power is likely at something between .43 and .50. (a quick Google of "best power EGT" gets answers from 25 to 125 ROP.) If we arbitrarily use an optimistic .45, then 10.2 gph is about 75% but if we use .50, then 10.2 gph is 68%. For 10.8 gph, it's 80% and 72%. The ratio of 10.2 to 10.8 does not equal that of 76 to 78. It's possible my 10.2 number is wrong. It's also interesting to note that the traditional 8000 Density Altitude would, in my airplane, give well above 75%. On the Catto flight, I tried it and WOT at 8000 yielded 82%. I think that's the result of the ram air in the intake snout, but I have no direct proof other than in other tests with this airplane, the MAP values were higher than the DA would account for and the MAP has been calibrated.
I started with a Prince P-Tip and recently bought a Catto. The P-Tip is a 2-blade and the Catto is a 3-blade. I did some testing under almost identical climate conditions. In both cases, a mild high with haze layer below and clear above. On warmer days I've had higher speeds from the P-Tip by about 6 kts and I don't know why the difference, but at least these two runs were under very similar conditions.
Both props were pitched by their makers after thorough discussion about my engine, cowl, fairings, etc. but still ended up too finely pitched. This may be evidence that my engine is stronger than expected. However, the airplane is not going as fast as it should, so that's an unsolved mystery for now. The Catto is on its way back to Craig for adjustment.
Both prop makers are excellent people to work with and I'd have no hesitation in recommending either one.
The instrument is a GRT Horizon & EIS and the EFIS is calibrated for TAS as per manufacturer's directions. Based on how it computes hw/xw and on the GPS speeds, I believe the TAS is accurate to within 1 knot. The OAT is below the wing in the first inspection panel and seems to agree with the ASOS once it stabilizes after leaving the heated hangar.The EFIS altimeter is IFR certified and tested to a max error of 20' all the way to 20K. The MAP was calibrated when the IFR check was done.
Cruise Data
P-Tip
Start with full tanks
OAT -6 deg C at altitude
Density Alt 9130
Power (per EFIS) 76%
WOT, best power mixture by ear
10.2 gph (maybe higher)
2750 rpm
168 KTAS
Catto
Start with -19 gallons = 114 pounds approx.
OAT -3 deg C at altitude
Density Alt 9472
Power (per EFIS) 78%
WOT, best power mixture by ear
10.8 gph
2810 rpm
173 KTAS
Climb Observations
Catto climbs better but at lower RPM: 2200 vs 2400, roughly, with about >200 fpm difference for Catto. Takeoff quicker by a few feet and accelleration subjectively better. The P-Tip climbed at about 1500 FPM using 16.4 GPH at 2440 rpm. I did not write down the climb numbers for the Catto, but I remember seeing 1800 or more on the VSI and lower GPH.Test was done about 100 pounds lighter but this seems to me a difference beyond the weight difference. In other flights I thought the Catto was doing this, even with a passenger and the FPM was higher.
Noise observations
If there's a difference, the P-Tip is quieter, but the difference could be how I inserted my HALO earplugs that day.
Other factors
The Catto is significantly out of balance and thus could be expected to perform a little better if balanced better.
Side Note #1
Prince says his prop self adjusts by as much as 3" of pitch based on load and rpm and until now I could not test that. The RPM range of the P-tip is about 200-250 less than that of the Catto and this is evidence that Prince is correct. Range here means from climb/static to top power at altitude. It's interesting that while the prop does seem to self adjust, the 3-blade Catto is climbing better and going faster anyhow. While the difference in cruise is not great and can be attributed to higher RPM (higher power), the climb difference is clear. Conventional wisdom says the 3-blade will climb better and cruise slower.
Side Note #2
Power percentage is, as I've noted before, a slippery concept. These numbers show that. In both cases I moved the red knob to where the airplane flew the fastest but I don't know how much ROP that was. The BSFC's should have been very close to equal. The Density Altitudes were quite close and should not matter anyhow. Superior says that at peak EGT BSFC is .43 and at 75 degrees ROP it's .50. So best power is likely at something between .43 and .50. (a quick Google of "best power EGT" gets answers from 25 to 125 ROP.) If we arbitrarily use an optimistic .45, then 10.2 gph is about 75% but if we use .50, then 10.2 gph is 68%. For 10.8 gph, it's 80% and 72%. The ratio of 10.2 to 10.8 does not equal that of 76 to 78. It's possible my 10.2 number is wrong. It's also interesting to note that the traditional 8000 Density Altitude would, in my airplane, give well above 75%. On the Catto flight, I tried it and WOT at 8000 yielded 82%. I think that's the result of the ram air in the intake snout, but I have no direct proof other than in other tests with this airplane, the MAP values were higher than the DA would account for and the MAP has been calibrated.
