72" or 70" Prop

[Sleepy]

I'm in the process of ordering a Whirlwind 300 series 3 blade propeller for my RV-4 (1990, standard length gear). When I bought 15 years ago and it had a cutdown 73" Hartzell (HC-M2YR-1BF-F7666) propeller. It was big, but I never had an issue with it. In 2018, it went for a reseal/repack and the Hartzell authorized service center suggested taking it down to 72"s which they did.

In talking to Hector at WW, he recommended a 72" 300 series based on my engine (Lycoming IO-360-B1E). He said a 70" would work, but might be pushing the limits of the propeller. The largest engine they recommend for the 70" is a IO-340 (9.6:1) which is right at 180hp like my Lycoming.

Not being an engineer I have no way to know whether 72" or 70" really makes a difference. Is there a noticeable performance difference? Is the extra 1" of prop/ground clearance significant enough to warrant the smaller prop? Probably the simplest question is what are other RV-4 owner's with the original length land gear flying? And why.

Any advice would be greatly appreciated.

Scott

 

[Rv6mike]

I used a rebuilt 70 inch Hartzell on my 6a. It flew great and climbed nice.. but the tips were very thin so I bought a new hartzell a72 inch and noticed no difference in performance . I flew to Mexico at the time often and did not want to take a risk at a chip.

 

[Rv6mike]

I used a rebuilt 70 inch Hartzell on my 6a. It flew great and climbed nice.. but the tips were very thin so I bought a new hartzell a72 inch and noticed no difference in performance . I flew to Mexico at the time often and did not want to take a risk at a chip.

 

[andoman]

I acquired a short gear -4 with a 2 blade 72 in. Hartzell constant speed. IO-320 160 hp. The lack of ground clearance was concerning but I got used to it.
At prop overhaul the shop cut it down to 70 in. I notice no change in performance and the extra margin of ground clearance is nice.

 

[Roadjunkie1]

Not being an engineer I have no way to know whether 72" or 70" really makes a difference. Is there a noticeable performance difference? Is the extra 1" of prop/ground clearance significant enough to warrant the smaller prop? Probably the simplest question is what are other RV-4 owner's with the original length land gear flying? And why.

SuzieQ (short gear, O-320 160 hp) had a Bernie Warnke prop carved up by The Master before his passing that is a 68-74. That was his standard prop for the speed and versatility of the RV-4. Great performance for both climbing and cruise. He called this his "Almost Constant Speed" prop. It has been an amazing piece of art that makes SuzieQ GO! I can actually feel the prop 'grip' more as the speed increases. She easily cruises at 152kt at 2400/19 sipping 7-7.2 gph. Full throttle will make for 172kts but 10gph is not what my wallet likes. I have been in some funky places and the prop and prop tips look as good as the day I put it on. A little Sun-faded, perhaps....

So: 68 inch (at least this one) does an amazing job of pulling her/us through the Sky. Not sure regarding constant speed or metal/composite props but this was a question about the length.