Pitch settings and cruise speed

Hi all,

I'm wondering what others are using for your prop pitch and what cruise speeds/climb rates you're seeing.

I have a 120hp Corvair with a Warp Drive 66" prop (10.0deg) in my 601xlb, and am seeing ~92knots cruise (at 2600rpm) and ~900 ft climb rate.

Thanks

Dale

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Permalink Reply by Ernest Christley on April 3, 2021 at 1:49pm

That sounds almost exactly what I'm getting out of a 3100 using a Sensinich prop.  I don't think you're going to get much better than that.  You can turn the prop faster, but the 601 seems to hit a wall and get real draggy just above 100kts.  

Permalink Reply by Dale Walters on April 3, 2021 at 2:08pm

Sigh, I was afraid of that

Thanks Ernest

Permalink Reply by christopher fryatt on April 4, 2021 at 12:49pm

Not to start a fight but after removing2700 corvair and small prop, (rated 100 hp) to a O-200D (rated 100hp) with a 70 " prop i cruise at 109 Knots true at 75% power.   To go fast and climb great the corvair needed more rpm for sure.

If drag is the issue .............is the cowling slicker ? or less cooling drag ?

Permalink Reply by Dale Walters on April 4, 2021 at 3:31pm

You won't get an argument out of me Christopher.

I do believe the cowling is at least part of my problem... I have a WW style cowling; 2 piece aluminum with a separate nosebowl. 

Cooling drag... does that mean the cooling air going into the engine area?  Any idea what would be causing cooling drag, or what I could do to fix it?

Thanks

Dale

Permalink Reply by Ernest Christley on April 4, 2021 at 6:15pm

What was the installed weight difference?

The Corvair is heavy, with many people running out of nose up trim for everything but cruise flight.  Constantly having to pick the nose up results in lots of drag.  

Permalink Reply by Patrick Hoyt on April 5, 2021 at 11:16am

Christopher is onto something here, regarding the RPM's. I too originally ran a Corvair on my 601, and in hindsight I would have liked to have done some more testing with higher RPM's. I don't think I turned higher than about 3050 rpms in mine, but it sure would have been fun to have set that pitch finer for greater RPM and then got some data....

Reason I never explored that was because the performance that I was getting was about the same as what everyone else with the same engine/airframe/prop combination was getting, so I just left it at that without ever really considering that maybe some performance was being left on the table.

Testing of prop pitch vs RPM - and plotting the results on a chart - can identify where the sweet spot for prop pitch is for any particular airplane.

Then drag reduction. That "601 drag wall" exists if you're flying in a nose-high attitude.

Tuft testing can be used to explore different areas for drag reduction (like drag under the fuselage behind the gear, and drag on the side of the fuselage near the flaps).  Also consider that there is a lot of cooling drag under the cowl. Make it easy for the air to go in, go through the fins, and then go out.

While the Zodiac is never going to be known as a "fast" airplane there's no reason you should be stuck flying 120mph either. The Zodiac is entirely capable of flying faster than what is comfortable and prudent.

https://www.youtube.com/watch?v=ppSnp8qfKzs

The horsepower differences are not THAT much, and drag reduction plays a large role anyway.

Permalink Reply by Dale Walters on April 5, 2021 at 12:12pm

Heh.  I could only wish for 120mph.  I barely get 102mph in cruise

Permalink Reply by David Krakowsky on April 17, 2021 at 6:48pm

Me too!

Permalink Reply by Dave Gardea on April 9, 2021 at 12:59pm

Hi Dale,

I usually get about 115 mph indicated at WOT and 3130 RPM with my 2700 Corvair on my CH 650. I think my 66 inch Warp Drive prop is pitched at about 10 degrees also.


Regards,

Dave

Permalink Reply by Dale Walters on April 10, 2021 at 3:21pm

Thanks Dave.  That's similar to mine.

What do you cruise at?

Permalink Reply by Dave Gardea on April 10, 2021 at 3:36pm

Dale, if I'm flying to breakfast or lunch with my buddy who has an RV7A, that's usually my cruise. If I'm flying alone, I'll throttle back to 105-110 MPH to enjoy the scenery and burn less fuel.

Dave

Permalink Reply by Peter Eiberger on April 26, 2021 at 9:12pm

What is your fuel burn at that speed/rpm/altitude? 

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