[jimevison]

I have a new Lycoming 0-320, Catto three bladed prop (specified for my 9a with 160 hp engine) one Slick Mag and one P_Mag. The engine reaches a maximum of 2410 rpm full rich while burning 11gph. TAS is less than 140 knots without pants and fairings. (About 20 knots less than I'd expect)... I've checked throttle and mixture linkages for full range of travel. I plan to call Catto to ask about the pitch of the propeller but is there anything else I should be looking at?

 

[LifeofReiley]

You will be very surprised what correctly installed fairing and pants will do. What Gen prop do you have and what is the pitch?

 

[sailvi767]

Between pants and fairings and leaning to best power I suspect your numbers will improve quite a bit.

George

 

[scard]

Sounds just about right to me. Please don't bother Craig before you are in the final configuration that you are going to fly with, including pants and fairings.

 

[jimevison]

Leaning

Adjusting the mixture yields no higher rpm. Would you expect the addition of pants and fairings to bring rpm up by 300 - 400?

 

[Mike S]

What Scott said.

Please don't bother Craig before you are in the final configuration that you are going to fly with, including pants and fairings.

Quite right, get it all finished before looking at changing the prop.

 

[Neal@F14]

Double check the ignition timing on both mags. Also check your tach accuracy against a handheld digital tach.

 

[RV10inOz]

Check your static is correct by running a GPS box and copare the TAS indicated to TAS from the GPS box. You could have a big error.

If your RPM is definitely right you might have a dog of a prop. I wonder about Jamie Lee's RV7A, it is slow too with a 3 blade Cato.

Others get a good result? So who knows. I have had timber laminate props that measure the same for pitch on a jig, yet one to the other are daylight and dark. We could never work out why.

 

[N941WR]

The rule of thumb is 10 knots for the gear leg fairings and another five for the wheel pants.

Fairings and other tweeks may add another five.

 

[hydroguy2]

Would you expect the addition of pants and fairings to bring rpm up by 300 - 400?

Quite possibly. Your prop is designed for a 160hp RV9. With no fairings or pants you have significantly more drag. ie...you're not flying a RV-9 profile.

 

[jimevison]

Confirmation of TAS

Check your static is correct by running a GPS box and copare the TAS indicated to TAS from the GPS box. You could have a big error.

Flying a box yields a TAS of 138 while GPS ground speed measures 136 Knots. This indicates that I'm looking at valid TAS values.

The normal expectation is that addition of leg fairings and pants contribute 15 knots. That allows me to expect a top speed of 153 Knots once those items are in place.

I believe my engine /prop combination should be producing a top speed of around 198 mph or 172 Knots. I'd like to understand where I'm losing 19 Knots and the very low rpm at the top end seems unusual.

I'll check ignition timing which was set by Lycoming at the factory. I'll also measure tach speeds at several points to confirm what the EFIS is measuring.

 

[aerhed]

Note to everybody with a new engine from anywhere: Always, always check your timing.

 

[RV10inOz]

Note to everybody with a new engine from anywhere: Always, always check your timing.

x 100

Good advice.

 

[woodmanrog]

Read my article

on speed mods. I gained over 30 knots over the ground by simply eliminating parasitic drag. Wheel pants and fairings are good for 10-12 extra knots. Catto props are the best and Craig can tweak a prop if needed. I installed two of them and they were right on the money right out of the box. Two bladed props do perform a little better IMHO.

 

[David-aviator]

Check your static is correct by running a GPS box and copare the TAS indicated to TAS from the GPS box. You could have a big error.

If your RPM is definitely right you might have a dog of a prop. I wonder about Jamie Lee's RV7A, it is slow too with a 3 blade Cato.

Others get a good result? So who knows. I have had timber laminate props that measure the same for pitch on a jig, yet one to the other are daylight and dark. We could never work out why.

I do believe Catto props are NOT one of a kind. They are carved with CNC precision.

The prop may not be pitched properly but that can be verified by carefully checking static rpm. If it is in the 2100-2200 range it is most likely correctly pitched. Top end performance then becomes a drag issue. Cleaning up the aircraft will improve performance.

It is most inadvisable to make a prop pitch change before the fairings are installed. I don't think Catto would do it.

 

[Don Jones]

I have a new Lycoming 0-320, Catto three bladed prop (specified for my 9a with 160 hp engine) one Slick Mag and one P_Mag. The engine reaches a maximum of 2410 rpm full rich while burning 11gph. TAS is less than 140 knots without pants and fairings. (About 20 knots less than I'd expect)... I've checked throttle and mixture linkages for full range of travel. I plan to call Catto to ask about the pitch of the propeller but is there anything else I should be looking at?

Identical setup to mine and identical numbers before pants and fairings. It now runs 169kts at 2700. Only change wheel pants and fairings. Keep on flying.

 

[MarkW]

Jim,
Keep in mind that as you decrease your drag your speed will increase. As you increase speed you RPM's will increase. As your RPM's increase your HP will increase.
Put your pants on.

 

[apkp777]

Have you checked your static RPM (brakes set max throttle)?


Once, you get your pants on (the airplane) Craig will want to know that, also your RPM during normal climb and then WOT level at 8500 DA.

 

[Mike S]

Read my article on speed mods.

And where might that be found??

 

[RV10inOz]

I do believe Catto props are NOT one of a kind. They are carved with CNC precision.

So were the ones I refer to above. Allegedly the same. One was a dog, it never pulled the same RPM as if it was coarse in pitch but it never went quicker either. It just did everything worse.

Even at the factory and measured on the jig it was within spec.

 

[Toobuilder]

...I believe my engine /prop combination should be producing a top speed of around 198 mph or 172 Knots. I'd like to understand where I'm losing 19 Knots and the very low rpm at the top end seems unusual...

Next time you fly, push the nose over until you attain a steady 172 knots and see where your RPM ends up. It's a quick and dirty way to overcome the airframe drag with gravity. Unless this takes thousands of feet of altitude change, your prop won't know the difference between a descent and a major airframe drag reduction.