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Catto 3 blades performance with O320 on a 7A

herve-RV7

herve-RV7

Active Member
I intend to have a Catto 3 blades on my 7A, with a O320. I have no clue on which pitch to order, I didn't even start to discuss with Craig at Catto. For those with similar configuration, can you please give me performances acheived (top speed, speed at 75%, climb solo and gross weight) for which pitch.
Thanks in advance.
 
Talk to Craig. He is the expert on which prop to use on any given plane, engine and mission configuration. I told him I just wanted my plane to be 2 kts. faster than my hanger mates RV-7 :)

Steve Eberhart
RV-7A, just riveted on the last major piece of aluminum. It really looks like an airplane now.
 
I have an IO360 using a 3 blade Catto 66x76.
Originally, I suspected an overpitch but after engine break-in and adding the fairings along with airframe cleanup, Craig was right on the money.
I asked him to pitch to achieve Van's specs.

I have found the prop to be draggy in that with a headwind, I lose rpms.
Otherwise, I'm very happy with the prop.

Tell Craig what you want in performance and he will deliver.
 
n5lp said:
I don't understand what you mean. Could you expand? What does a head or tail wind have to do with RPM?
Click to expand...

I should say the prop is very subject to drag.
During 3 & 4 way speed tests, same throttle setting, depending on the headwinds encountered on that leg, I would see a loss in rpm of about 20-50rpm. RPMs would recover once turning back into a neutral or tailwind situation.

RPMs also suffered when non-faired.
 
Last edited:
I still don't get it

DanLandry said:
During 3 & 4 way speed tests, same throttle setting, depending on the headwinds encountered on that leg, I would see a loss in rpm of about 20-50rpm. RPMs would recover once turning back into a neutral or tailwind situation.
Click to expand...

Hmmm...could there be something else to account for the loss of RPM when going upwind? The prop cares about airspeed, not groundspeed. Otherwise, I think you may have to patent this idea: the tachometer as a wind speed detector.:)

DanLandry said:
RPMs also suffered when non-faired.
Click to expand...

Now that I do believe. Fixed pitch props do react to changes in load, so when you reduce drag it makes sense that it speeds up a bit.
 
DanLandry said:
I should say the prop is very subject to drag.
During 3 & 4 way speed tests, same throttle setting, depending on the headwinds encountered on that leg, I would see a loss in rpm of about 20-50rpm. RPMs would recover once turning back into a neutral or tailwind situation.
Click to expand...
With a fixed-pitch prop, you need pretty much perfectly smooth air, and a perfectly constant altitude in order to have a constant rpm. Otherwise every time the altitude changes a bit, the true airspeed changes, which changes the load on the prop, and this leads to a change in rpm. Is it possible that you are being misled by some of the transient rpm changes you see if conditions or the flying are less than perfect?

None of the conventional laws of physics explain why the stabilized full throttle rpm at full throttle in level flight should depend on the wind. If this is truly a repeatable effect, you should contact an aeronautical engineering school and ask them if they want to investigate it - there could be a Nobel Prize hiding in there somewhere.
 
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