McCauley Props on RVs

I've just read some of the postings on McCauley props and feel compelled to post this message. I flew a Mc prop and engine from a '91 Mooney 20J for over three years on an RV6 and strongly recommend anyone considering using this prop to reconsider. The prop has a harmonic while not very prevalent on the Mooney seems to resonate with the RV. This only occurs when operating below 15in MP and between 1500 & 1950 rpm, unfortunately the RV needs to pass through this power range when landing, some times more than once if you add power. The airplane will literally almost shake like a wet dog. Very unsettling to say the least and you will scare the heck out of your passengers, even when forewarned the look of panic will appear on their face. This resonance can be minimized by flying a very careful and planned approach to reduce your airspeed below 100mph before passing through this power band, a very difficult thing to do in the RV.

This prop , in my opinion, is not safe to use on the RV because of the extra attention and distraction it creates for the pilot in the cockpit during landing. I spent many hours and many phone conversations with the McCauley people and Lycoming. There is no fix for this prop on the RV and for those of you that feel it is OK to cut the prop below the minimum diameter or adding an extension you are playing ?Russian Roulette?. You could be moving a harmonic along the length of the blade or the crankshaft with catastrophic results. Many prop blade failures resulting in separation from the aircraft have occurred over the years as a consequence of these actions. If you have already set up your plane for the prop the easiest fix would be to change the Mc blades out with one of the manufactures making blades for the McCauley hub.

You will be much happier with your airplane and enjoy flying more if you select a better suited prop for the RV. I finally gave up trying to make the McCauley work and modified the cowl to accept the Hartzell (74in), the result is that I no longer had to manage my approach to land and I could pull the power back at any speed and enjoy flying again.

The Mooney 201 McCauley prop that I have on my RV6 does experience a slightly rough resonant zone between 1400-1900 RPM when operated between 10"-12" MP that makes landing a bit tricky, but it doesn't shake like a wet dog as you mentioned that yours did. The values you quoted to avoid below 15" MP between 1500-1950 RPM is the factory placarded range that all the Mooney M20 series are supposed to avoid according to McCauley, but that is when the prop is used behind an angle valve IO-360 with the counterweighted crank and a prop blade length between 73"-74" (anything less than 73" is not allowed on the Mooney).

On my RV6 application I have a parallel valve O-360 that has the same type of counterweighted crank (it is an A1F6D-O-360 from out of a fixed gear Cessna 177 Cardinal), and the Mooney prop blades have been rounded off to create a 72" diameter prop (the original blades had an elliptical tip on them that when cut to form a circular tip resulted in a perfect 72" diameter prop with round tips without the need to remove any material from the blade leading or trailing edge). On my application the resonant zone has been shifted to a slightly lower RPM and lower MP when compared to the Mooney. I do also have a 1 5/8" long extension on my prop, but it appears to make no difference in the harmonics from what I can tell (who knows for sure). I have tried numerous methods to avoid the 10"-12" MP @ 1400-1900 RPM resonant zone during landing in order to limit the roughness (for example pulling the power back to idle & landing without power on approach, landing with power above 12" MP @ 1500 RPM with full flaps and an 80 mph approach speed, etc.), and have now settled into a routine of simply blazing at 200 mph all the way up to the center of the airport at 1300' above the runway, cutting the power all the way back to idle with the prop pulled into minimum pitch (climb pitch) for maximum braking action, and then peel off into a turn to the downwind leg and continuing to base & then final leg with flaps being dropped to full position at 100 mph on short final. By doing this type of approach I always have enough airspeed to make the runway without power (including if the engine were to quit running during the approach), and I avoid having to plan a long extended slow approach for landing with all of the problems of going thru the rough running resonant zone (not to mention that I get to my destination a whole lot faster!!).

It would be nice to change out to the composite blades that ACI or Whirlwind makes for the McCauley hub, but those sure are expensive (over $6500 more than what I already have in my current Mooney prop...which isn't such a great deal at all since a brand new Hartzell prop only costs about $6500 or so!). The real question is do those composite blades really eliminate all the resonant problems associated with the McCauley hub and the Mooney type blades? And who's to say that they too might not have future failure problems once they have been in service for about 10 years or so, not to mention all the rain errosion problems that such designs have! In the long term the original aluminum blades may well be more durable even though they have strange resonant zones that need to be avoided during continuous running. I have flown behind an O-360 in a Bellanca Scout that had a fixed pitch aluminum prop that was rougher than the Mooney prop I have on my O-360 right now, so it isn't all that bad all things considered. Maybe your setup just didn't work as well for whatever reason?

More on McCauley

I never flew my -8 with the McCauley blades. I had Whirl Wind install the 200C blades on my McCauley hub prior to my first flight. The cost of that swap was about $5k. Pretty expensive but certainly less than a new prop. Anyway, I have a counterweighted IO360 from a Mooney 201. I have not experienced any noticable vibration at any power/rpm settings. Whirl Wind does restrict continuous operation for some RPM settings (I can't remember the specifics off the top of my head). However, I have operated the airplane at the lower settings referred to in the earlier posts again with no noticable vibrations.

Rick McBride

McCauley prop on RV-8

Here is a picture of the Mooney 201 prop on my RV-8. (click on the thumbnail and it should go to the "big" picture) I have 5 hours on it now, it does have a noticable harmonic vibration when the power is chopped and it comes down through 1900 RPM, but can I still hold power on approach up to 1750 RPM or so if needed and avoiding that range is not a problem. I am trying to make my base and final approaches without using much power. I can get a better flare dropping in power off with a steep sink rate than I can dragging it in on the prop. I have not had it harmonically balanced yet either.
NOTE: no wet dogs were harmed during flight testing of this aircraft


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