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Catto prop

D

dan carley

Well Known Member
I’ve recently purchased a Rv6 180 hp
It has a catto prop 68-76 pitch
I kinda lugging on take off and only get 2580
At top end. Would this have something to do with the engine getting hot
What would be the correct pitch for the 180 hp
Thanks
Danny carley
 
For comparison purposes: I have a 3-blade Catto, 68X75 on my 210hp O-375, 7A.
Static rpm : 2250-2300.
Climb out at 110-120mph : 1500- 1800 fpm
At cruise I’ve seen 2750 rpm with alittle throttle left to go.
True airspeed at 2750 around 190-195 mph.
 
Test Conditions?

Is the max rpm measured at 7500' Density Altitude? Was the engine leaned to peak power? 7500' DA is going to be about optimal speed as wide open throttle should be about 75% power.

What true ground speed are you getting? [At a minimum fly a heading, and then the reverse heading and give us the GPS ground speed.] It may be that there are things slowing the plane down and hence the prop appears to be over pitched.

Could also be down on power. Ignition timing checked recently? Air filter serviced?
 
If you can't get past 2600 at any altitude, you are definately over pitched and your climb rates lower than optimum.
 
blaplante said:
Is the max rpm measured at 7500' Density Altitude? Was the engine leaned to peak power? 7500' DA is going to be about optimal speed as wide open throttle should be about 75% power.

What true ground speed are you getting? [At a minimum fly a heading, and then the reverse heading and give us the GPS ground speed.] It may be that there are things slowing the plane down and hence the prop appears to be over pitched.

Could also be down on power. Ignition timing checked recently? Air filter serviced?
Click to expand...
Yeah, what he said. We need more information.
 
Just to pile on here. If you don't have wheel pants and fairings you will also not get good speed/ RPM.
 
So, 68x76 is Catto's recommended "best All-around" configuration for 180hp.

Like mentioned before, if you are missing fairings, you will be slow and may have CHT issues.

Overall, it sounds like you are down on power though. Check compressions, check timing...
 
gasman said:
Manifold pressure and RPM will show you power output.
Click to expand...

Well, not really. But static RPM alone is a pretty good test dyno. (free)
As was pointed out, late timing, low compression and I might add, flat cam, rich mixture can reduce power all with normal MP. Rule of thumb - 1% RPM variation = 2% torque variation. Density altitude is compensated but not humidity.

Max cruise RPM mostly linear with TAS. So, wheel pants etc a plus and increased induced drag with altitude a minus.
ron
 
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FWIW I was taught the following for a fixed pitch propeller:

Go to 8,000ft Density Altitude.
Best power mixture.
Wide open throttle.

Let the speed stabilize and your propeller RPM should be between 2,700 - 2750 RPM's. Optimum is 2,725RPM's. If below that range, your propeller is over pitched. If above that range, your propeller is under pitched.

Obviously this assumes you engine is working correctly and can provide 75% power.

:cool:
 
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Sorry for the maybe stupid question but my pperating manual of the engine states 2700rpm as max continous RPM but nothing about absolute max. RPM.. So if you fly at 2725-2750... you would be above?

Cheers Yves
 
YvesCH said:
Sorry for the maybe stupid question but my pperating manual of the engine states 2700rpm as max continous RPM but nothing about absolute max. RPM.. So if you fly at 2725-2750... you would be above?

Cheers Yves
Click to expand...
You don't operate continuously at those speeds, only for the short time needed for testing. Most CP propellers are rated for an absolute max of around 3,000 RPMs but verify this with your propeller manufacturer.

:cool:
 
Yes I know that this will only happen very seldom and if then for a short period of time. Yes I have also a Catto with a redline of 3100 RPM..

I was just not sure if I once would spin up the Engine up to this if I would have to perform a overspeed inspection or if something like this even exists.. I flew a Aircraft with a Rotax in the past and there was a max cont. and a absolute redline. I just could`t find a absolute redline in my operatings handbook of the engine...
 
Cumulo said:
Well, not really. But static RPM alone is a pretty good test dyno. (free)
As was pointed out, late timing, low compression and I might add, flat cam, rich mixture can reduce power all with normal MP. Rule of thumb - 1% RPM variation = 2% torque variation. Density altitude is compensated but not humidity.

Max cruise RPM mostly linear with TAS. So, wheel pants etc a plus and increased induced drag with altitude a minus.
ron
Click to expand...

https://www.kitplanes.com/determining-engine-power/
 
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