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  #1  
Old 12-16-2020, 08:38 AM
Karetaker's Avatar
Karetaker Karetaker is offline
 
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Default Propeller Selection Assistance

Howdy Everyone. I need some assistance in regard to propeller choice from people more experienced than I am on the subject. (Mostly everyone.)

I am building a -7 and just acquired an Aero Sport Power IO375-M1S engine. 8.5-1 compression, non-counterbalance crank, 200 HP @ 2700 RPM. Mounted on the rear case is a PCU5000X prop governor.

I want a CS propeller with focus on long cruise performance. I am building the plane as light as I can build it and understand CG can be an issue with this airframe and composite propellers. Still, I would consider a composite if the advantage was worthy.

What say you?
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  #2  
Old 12-16-2020, 08:55 AM
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Carl Froehlich Carl Froehlich is offline
 
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All the data Iíve seen on propeller cruise efficiency point to the standard Hartzell BA CS prop from Vanís sat the best option.

I build my RVs with a heavy tilt toward high efficiency cruise - and fly with this prop.

Carl
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  #3  
Old 12-16-2020, 09:47 AM
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Thanks. Are you using the 72" or 74"?
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  #4  
Old 12-16-2020, 10:05 AM
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Carl Froehlich Carl Froehlich is offline
 
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I installed the 74Ē on both the 8A and the 8. I used the 80Ē for the RV-10.

Note - Vanís recommends the 72Ē for the RV-8. Iím using Grove gear and noted the prop to ground clearance was a little more than a neighborís RV-8 using stock gear, so Iím comfortable with the 74Ē prop.

For an RV-7 I recommend calling Vanís and asking for their recommendation. As a practical matter, I suspect there is not much performance difference between the two.

Carl
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  #5  
Old 12-16-2020, 10:12 AM
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I have talked to Vans about the 72" -V- 74" and did not receive any intel. on performance differences. They did say that either could be used on a -7 but the owner needs to be aware of the potential ground clearance issues and except the risk. I find it odd that a 1" difference is so critical.

Anyhoo, another variable in the mix: my engine has dual P-mags installed. I believe I have read about concerns with non-weighted cranks, pulse/shock stresses from electronic mags and composite props not playing nice. Anyone have some insight on this?
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  #6  
Old 12-16-2020, 08:12 PM
David Z David Z is offline
 
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Quote:
Originally Posted by Karetaker View Post
I am building a -7 and just acquired an Aero Sport Power IO375-M1S engine. 8.5-1 compression, non-counterbalance crank, 200 HP @ 2700 RPM. Mounted on the rear case is a PCU5000X prop governor.

I want a CS propeller with focus on long cruise performance. I am building the plane as light as I can build it and understand CG can be an issue with this airframe and composite propellers. Still, I would consider a composite if the advantage was worthy.
You pretty much described me, but I'm hoping to put that on my -8. I've also considered the Hartzell BA prop from Van's, but wonder about the RPM restrictions. I don't have an answer, just the knowledge that the question needs an answer.

Whirlwind recently restricted their props from 370/375 engines without counterweights, so that rules them out. I don't have an engine yet, so I need to look into a counterweighted crank (cost/weight penalties). The other thought is an MT Prop. Some say they're a few knots slower in top speed, others say cruise is the same as the Hartzell BA. I've never heard about restrictions, yay or nay, about mounting one on a 370/375.

The composite blade MT prop will be lighter, not sure how much though. For $4300 difference in price, that will all have to be considered.
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  #7  
Old 12-17-2020, 01:25 AM
tgmillso tgmillso is offline
 
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If you haven't already bought the engine mount, there's the possibility of using the 320 mount to push the CG a little further forward than it would be otherwise if you end up using a composite propeller, which should probably be your choice if there isn't a tested/certified aluminum propeller available for your your specific engine build (fatigue/torsional vibration risks). I too am all for keeping it light. These aircraft are just amazing to fly when there isn't a lot of weight onboard. Less stress on everything and amazing response rates.
Tom.
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  #8  
Old 12-17-2020, 08:08 AM
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Howdy David. I was looking at the 300 series Whirl Wind propellers last night. They cost more than the Hartzell aluminum 2 blade deal that Vans sells and as you noted, not recommended for non-weighted cranks on the 370-375 engines. The MT props are more expensive than the WW plus they ship only to a build center. On top of the prop price, you then need to pay for a US shop to do the assembly; then shipping to your place of choice. Because of cost, MT is off my list, so is WW because my engine is not supported.

Hartzell has RPM/manifold pressure restrictions that I need to look into further.

Running out of options quick, what other choices are there? Doesn't seem to be many CS prop companies available.


Tom, I already have my engine mount and cowling in hand. You mention a composite prop should be my choice; can you explain? I was thinking the opposite; that an aluminum prop would be better suited in an untested engine/prop/RPM situation.

Thanks guys; keep the suggestions/discussions coming!
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  #9  
Old 12-17-2020, 08:18 AM
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Carl Froehlich Carl Froehlich is offline
 
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Quote:
Originally Posted by Karetaker View Post
Hartzell has RPM/manifold pressure restrictions that I need to look into further.
If memory serves, the EI RPM restrictions were for an earlier Vanís prop offerings. I suspect however that if you ask Hartzell about the BA prop you will get the standard lawyer response of ďwe have not tested that combinationĒ.

Iíve run dual pMags with the Hartzell BA prop for ~1000 hours.

Carl
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  #10  
Old 12-17-2020, 09:28 AM
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Thanks Carl. Curious if during those 1000 hrs. if you abided by the restrictions as stated by Hartzell? I am hoping those restrictions are in an operational area of the power curve that is never really used continuously. My luck, they will be right where I want to cruise...

I would actually consider installing a weighted crank in my engine if it was a simple swap I could do in my home shop.

I suppose I will further look into the characteristics of composite -V- aluminum propellers and vibration/ignition pulses/RPM etc. I just don't understand what is actually happening with these engines>
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