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Propeller Selection Assistance

Karetaker

Well Known Member
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?
 
All the data I’ve seen on propeller cruise efficiency point to the standard Hartzell BA CS prop from Van’s sat the best option.

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

Carl
 
I installed the 74” on both the 8A and the 8. I used the 80” for the RV-10.

Note - Van’s recommends the 72” for the RV-8. I’m using Grove gear and noted the prop to ground clearance was a little more than a neighbor’s RV-8 using stock gear, so I’m comfortable with the 74” prop.

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

Carl
 
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?
 
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.
 
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.
RV-7
 
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!
 
Hartzell has RPM/manifold pressure restrictions that I need to look into further.

If memory serves, the EI RPM restrictions were for an earlier Van’s prop offerings. I suspect however that if you ask Hartzell about the BA prop you will get the standard lawyer response of “we have not tested that combination”.

I’ve run dual pMags with the Hartzell BA prop for ~1000 hours.

Carl
 
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>
 
Not an issue for as I have a parallel valve (180hp) engine. Also I’m rarely above 24” in cruise as I’m typically WOT at altitude - or when above 24” I’m at 2700 RPM (for take off) and 2600 RPM for climb.

Carl
 
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Howdy Carl. I get what you are saying. I am seriously looking at the Hartzell BA aluminum props now. For those curious, here is the restriction from Hartzell:

For undamped 200 HP IO-360: Continuous
operation is prohibited above 24 Inches
manifold pressure between 2350 and 2550
RPM.
 
One more thing...for those wondering...I received an email from Aero Sport Power today stating that switching from a non-weighted to a weighted crank is a simple swap. Consumables such as bearings, nuts, bolts, etc. need to be replaced as well, of course. This is a task I would consider doing however, the new crank is expensive! Plus, having done the swap, I would be looking at all types of 3 blade composite fancy props further driving up my costs! I believe I will work with what I have;for now. :)
 
Weight

Did they say how much more the counterweighted crank weighs? I ask to compare the whole "power plant" package.

Non-CW IO-375 and Hartzell vs a CW IO-375 and WW prop. One having a lighter engine and heavier prop while the other has a heavier engine and lighter prop. If it turns out to be very similar in weight and quite a bit more expensive, that's an easy decision. Well unless you really want 3 blades, composite prop and the smoothness of operation that has to offer.

These operating restrictions seem pretty easy to live with:
For undamped 200 HP IO-360: Continuous
operation is prohibited above 24 Inches
manifold pressure between 2350 and 2550
RPM.

Take-off at normal 2700rpm full throttle. Climb at 2550-2600. Cruise at 2100-2300rpm
 
I have no information on weight differences between engine/prop. combos, David. I do agree the restrictions are livable and will look further into the Hartzell blended airfoil propeller. I am hoping I may be able to pick the prop up from Hartzell as I live in the area...ish.
 
Mike, don't discount operating restrictions, in particular from Hartzell. They have a huge body of experience actually measuring vibratory propeller strain. Flip side is high confidence; if they say you can run in some particular range, you really can. Unfortunately, that's not always been true with all.
 
Howdy everyone. Here is what I just received from Hartzell, if interested:

"The vibrational testing that Hartzell performed with the 375 undamped engine resulted in higher stress loading on the propeller than was seen with comparable engines. As a result, Hartzell would not recommend installing an aluminum or composite bladed propeller application with this engine configuration. If the engine was equipped with a damped crankshaft, aluminum and composite blade combinations could be recommended with no placards. Dual P-mags have not been tested at this time."


Answer from my follow up question was this:


"Unfortunately that engine (without dampers) is very hard on our propellers – so much so that we cannot recommend our installations.

Unless you change the crankshaft, or go with a different engine, wood is probably the only option."
 
Hartzell G2YR/N7605W-2X carbon fiber prop

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?

I went with the Hartzell G2YR/N7605W-2X carbon fiber prop. It was around 16lbs lighter than the the BA prop, has no operating restrictions, amazing climb performance, but may cost 1-2kts on the top end.

https://hartzellprop.com/owner-of-composite-propeller-for-rv8-shares-his-story/
 
Composite is fine

On my first 7 I had a parallel valve 360 with Whirlwind RV200 composite prop. It was no problem at all. You will still be well within CG range. The back side of the CG range makes the elevator sensitive but not at all dangerous.

Another data point. Another guy on our airport had a RV 7 with the exact engine as mine built by the same guy. He went with the Hartzell BA prop because of discussed GG concerns. We flew side by side at 6000 feet and set the power to 24/24. I flew away from him. Probably a 5 knot difference. I should point out, his plane was 50lbs lighter and the pilot weight difference was probably another 40.
 
What I'm reading in this is that there is no suitable constant speed prop for a non-counterweighted -375?

If true, that's really unfortunate, I'm hoping to avoid the weight and cost of a counterweighted crank. I'm still curious about how much heavier and how much more expensive. The extra power is great, and I'm sure the counterweighted -375 is still lighter and cheaper than an angle valve engine.
 
Howdy Everyone. Howdy David. I can't answer your weight questions but I will share what I know as of today. As stated in an earlier post of mine down the page here, I have confirmed with Hartzell that they do not sell a CS propeller suitable for an IO-375, 200 HP with a non counterweighted crank. Perhaps with lower compression and lower HP, but I did not look into those engines. They confirmed twice via email and it is also stated on their website when looking at their propeller charts. Harzell stated that a wood prop may be my only option. So, I started looking into replacing the crankshaft. I spoke directly with Aero Sport Power, whom made my engine and confirmed a weighted crank CAN be installed with new bearings, seals, nuts, etc.etc. The new crank is a drop in replacement...no machining required. Cool. Went to the Vans propeller order form and looked at the price for the Hartzell CS prop for my RV-7. The new weighted crank from Aero Sport Power, bearings, nuts, etc., shipped, added to the cost of a new Hartzell from Vans, shipped, cost more than a 3 bladed MT prop.

Looking at the Vans website, MT order form, I found:

"MTV-9-B/183-50a propeller must be used with 4-cylinder engines 195hp and above if 6th order crankshaft counterweights are not installed or electronic ignitions are installed that are operated outside the engine manufactures timing specifications."

I asked directly from MT and they also confirmed that the above propeller is suitable for my engine and there are no restrictions. This is a wood composite propeller. (Fiberglass/carbon fiber/kevlar...don't recall.)

Anyhoo, this is the propeller I will be purchasing.
 
Congrats

I'm glad you found a propeller, although a quite expensive one. Your prop selection adventure has given me a lot of insight and a lot to think about. Thanks for sharing your progress.
 
This thread has really got my attention being that I have an IO375, 8.3:1, dual P-Mags, a Hartzell HC-C2YR-1BFP/F7497-2 prop and 204 hrs on it.

When I bought my engine from AeroSport in 2013 this prop was on their list of propeller options for this engine so I assumed it was OK. I checked with Hartzell in 2017 before first flight and they indicated that since they hadn’t tested this combination to use their most restrictive operating limit, namely “Continuous operation is prohibited above 24”MP between 2350 and 2550 RPM.

My engine has a “balanced” crankshaft per AeroSport’s quote. What does balanced mean? What exactly is a dampened vs a counterweighted crank? I’ve emailed AeroSport on this but have not yet received a reply.

VAF threads back in 2009 & 2014 had posts regarding counterweight problems/damage resulting from abrupt throttle movements and not to use it for aerobatic flight.

Mike - your post (#18) refers to Hartzell’s test on a 375 with an “undamped” crank with bad results but post 22 refers to counterweights. So I’m confused on the damped vs counterweighted crank and not sure my “balanced” crank is in the clear.

I will contact Hartzell since it appears they have done testing on the 375 since I contacted them in 2017.

If anyone can educate me on this I’d appreciate it.
 
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My engine has a “balanced” crankshaft per AeroSport’s quote. What does balanced mean? What exactly is a dampened vs a counterweighted crank?

Fundamentally, the the assembled crank is spun on a dynamic balance machine. The photos below illustrate an old school Schenck balancer. Mass is removed as necessary to move the balance markers to the center of the circle.

Look close at the crank. This one, a 550 Continental 6-cyl, has two sets of bifilar pendulum absorbers. The typical 4-cyl has one set. "Dampened" and "counterweighted" are both poor terminology; pendulum absorbers don't act as dampers, and don't counterweight anything but their own own opposing masses. However, they are the common terms. The goal is a reduction in torsional vibration, which beats **** out of the prop and the accessory case components.

I've attached an illustration from a Lycoming parts catalog, and a drawing from a popular paper on the development of the R-2800. The large masses swing on rollers (12 and 13). The pendulum and crank bushings (7 and 11) are of equal ID. The relative OD of the roller and the ID of the bushings determines the tuned order of the absorber. Remember pendulum theory? The length of the pendulum sets frequency.

VAF threads back in 2009 & 2014 had posts regarding counterweight problems/damage resulting from abrupt throttle movements and not to use it for aerobatic flight.

That would be a huge surprise to every serious aerobatic performer, as all the 540 and 580 cranks have pendulums. Yes, theory says it is possible to dent the bushings and detune the pendulum, but hey, some folks can break a bowling ball in a rubber room.
 

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Agree with Dan on "dampened" and "counterweighted". Balanced crank is a different term again explained by Dan.

Yes, I was surprised and concerned when I started getting intel on the IO375 and the lack of propeller support; but it made sense as I dove into it. The propeller is stupid expensive as are new engines in my opinion. I hate it, but knew what I might be getting into when I decided to build an airplane. Financially I come out ahead with the MT prop and newly acquired engine as opposed to installing a counter weighted crank and Hartzell. Personally, I am pleased with the combination and I should get the performance I want out of it.
 
Warning...pure opinion...

It is better to reduce the damaging force, rather than bolt on something claimed to withstand that force.

The EAB industry has been far too cavalier about propellers.

Engineers add pendulums to cranks when they have a good reason to do so. It wasn't a whim.
 
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Nailed it. It is always better to attenuate the forcing function than to design around it (or dampen a response if talking A or D control systems). If anyone can think of an exception to that logic, would love to hear it.
 
Harzell stated that a wood prop may be my only option.

https://whirlwindaviation.com/props/HRTseries-3_Blade.asp
TheWhirl Wind Aviation 3 blade HRT 73" propeller is suitable for the non-counterweighted O-370/375.
This hub platform is very robust, wt=55 lb

Any confusion that we might not support this engine probably stems from discussion about the 300 series which was designed to be as lightweight (wt=36) and compact as possible for the less aggressive engines. https://whirlwindaviation.com/props/300series.asp

There is a significant wt. difference between the propellers. This represents the required structure to safely take the additional loads imposed from the 370 power pulses.
 
Contradiction

https://whirlwindaviation.com/props/HRTseries-3_Blade.asp
TheWhirl Wind Aviation 3 blade HRT 73" propeller is suitable for the non-counterweighted O-370/375.
This hub platform is very robust, wt=55 lb

Any confusion that we might not support this engine probably stems from discussion about the 300 series which was designed to be as lightweight (wt=36) and compact as possible for the less aggressive engines. https://whirlwindaviation.com/props/300series.asp

There is a significant wt. difference between the propellers. This represents the required structure to safely take the additional loads imposed from the 370 power pulses.

One of the sources of confusion is the WW aviation website. I'm in a similar but different boat. The subject Aerosport has a listed rating of 200HP. The Titan IO370 (9.6:1) engine that's getting built for me would probably need the extra weight up front of the HRT series for CG reasons; however, the NP rating will be 195HP but should be around 210HP based on Titan's previous builds. Both of these engines expected outputs are below listed min HP rating for the HRT series prop; 220.

Some OEM explanation/clarification is obviously needed, IMO.
 
I'm happy to be wrong, and please tell me if I am.

It's looking like the 370/375 engines are similar in propeller needs to the angle valve 360/390 engines. Basically meaning that an un-dampened (counterweights) 370/375 is equally hard on equipment as an un-dampened angle valve engine. It makes sense to me because a ~200hp 4 cyl engine probably makes very similar power pulses regardless of crankshaft stroke or cylinder head design. It's still the same size power pulses.

Un-dampened angle valve engines aren't common but they are around. Whereas un-dampened 370/375 engines are a lot more common.

Basically, if you want 200hp, get a dampened crank or one of the robust (expensive) props. MTV-9 or WW HRT.

The one thing I don't get, and may help out Champ with his engine/prop combo is this quote from the Hartzell Application Guide (link) for the the RV 4,6,7,8,14 with the prop C2YR-1BFP/F7497 (page 1557) "For undamped 200 HP IO-360: Continuous operation is prohibited above 24 inches manifold pressure between 2350 and 2550 RPM". It's an approved combination with the restriction. Why would it matter if it's an un-dampened 200hp IO-360 or an un-dampened 200hp IO-370/375? They're both 200hp 4 cylinder engines. What am I missing?
 
I'm happy to be wrong, and please tell me if I am.

It's looking like the 370/375 engines are similar in propeller needs to the angle valve 360/390 engines. Basically meaning that an un-dampened (counterweights) 370/375 is equally hard on equipment as an un-dampened angle valve engine. It makes sense to me because a ~200hp 4 cyl engine probably makes very similar power pulses regardless of crankshaft stroke or cylinder head design. It's still the same size power pulses.

Un-dampened angle valve engines aren't common but they are around. Whereas un-dampened 370/375 engines are a lot more common.

Basically, if you want 200hp, get a dampened crank or one of the robust (expensive) props. MTV-9 or WW HRT.

The one thing I don't get, and may help out Champ with his engine/prop combo is this quote from the Hartzell Application Guide (link) for the the RV 4,6,7,8,14 with the prop C2YR-1BFP/F7497 (page 1557) "For undamped 200 HP IO-360: Continuous operation is prohibited above 24 inches manifold pressure between 2350 and 2550 RPM". It's an approved combination with the restriction. Why would it matter if it's an un-dampened 200hp IO-360 or an un-dampened 200hp IO-370/375? They're both 200hp 4 cylinder engines. What am I missing?

With hat in hand, I'll offer this to the bright group of people on this thread regarding torsional vibration. Higher compression ratios or advanced timing will make "peakier" power pulses. Though the average of the power pulses may be the same to get, say, 200 HP, there will be more energy at the higher order frequencies to resonate the crank/propeller system as compression ratio is increased. Another factor is rod/stroke ratio. A stroker usually has a smaller rod/stroke ratio, and that will increase secondaries 2, 4, 6, etc. as well do to piston/crank geometry. So, these are two factors that could intensify a TV concern in comparing two equal horsepower engines and may be relevant to David Z's question.

By the way, and according to Den Hartog as well , much of the TV energy is dissipated by the prop. Props with heavy blades tend to dissipate less, so resonances will be more intense. Relatively light wood blades DO have advantages and will be easier on crankshafts as well.

Here is a very easy reading source on the subject of torsional vibration which reads a bit like a good novel. It is framed in the development of the P&W R-2800, and the subsequent R-2800-CB16 - maybe the best round engine of its era: http://www.enginehistory.org/NoShortDays/TV.pdf

Ron
 
Theres a few things going on with this thread, and I actually have recent, personal experience with some of it.

First off - propeller "cruise performance"... Better define what that is because some props are better than others in certain RPM ranges. For instance, I bought the Hartzel BA 2 blade for my Rocket because data suggests its the "fastest" out there. That has indeed been demonstated to be the case compared to the MT 3 blade. But thats at 2700 RPM. At 2300, where I spend 99% of my time, the MT handily crushes me. Been there, done that. Should have bought the MT.

Also, dynamic counterwights do break in service. I had one overspeed event crack the ears. 4.7 hours earlier, the crank was installed and good. 3 seconds of overspeed and it was junk.
 
Howdy everyone. I have made my decision, but am glad to see this thread continue down this road of discovery!

Toobuilder makes a good point about cruise performance. My personal cruise settings I plan to use in my (hopefully light weight) RV-7 and IO375-M1S engine should play very nicely with this MT prop. Others may cruise with different setting, different engine, different aircraft and find the 3 blade MT unsuitable.
 
I spoke with AeroSport on this. They’ve had no reports of problems with 375/prop combos. They did suggest to dynamically balance the prop at CIs and do frequent tap tests. Also putting in a cw crank would add 12lb to my engine. Haven’t heard from Hartzell yet. I will start looking into an MT or WW HRT replacement though. One concern is resale value with my Hartzell prop. Anyone need a low time Hartzell BA?
 
Research

I compiled the data from this thread and some research. The prop weight and prices are accurate as of today. The engine weights are approximate and 12lbs apart for a counterweight/dampened crank based on the post above. The engine prices (except for Van's) is a wild inaccurate guess. I'm happy to update if numbers are provided.

I take no liability for incorrect information. Verify everything for yourself, it's merely meant as a discussion point.

Looks like the the extra 15 cubic inches and ~20hp is worth about 7-9 grand with insignificant weight difference. The biggest variance was 8lbs. They all seem like good options to me, and it's really up to personal preference.
 

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Theres a few things going on with this thread, and I actually have recent, personal experience with some of it.

First off - propeller "cruise performance"... Better define what that is because some props are better than others in certain RPM ranges. For instance, I bought the Hartzel BA 2 blade for my Rocket because data suggests its the "fastest" out there. That has indeed been demonstated to be the case compared to the MT 3 blade. But thats at 2700 RPM. At 2300, where I spend 99% of my time, the MT handily crushes me.

Interesting that you mention this. I delivered an angle valve IO-360 RV-7 that had the 3 blade MT prop. It was slower than I expected, but I noticed something interesting. While cruising, I experimented with rpm from 2500 down to 2200, leaned each to 75 ROP for each setting. (MP was wide open at 11,500) and I found NO speed loss at the lower rpm settings! The more I pulled the rpm down, the egt got cooler, allowing me to lean more, helping fuel economy..
 
I spoke with AeroSport on this. They’ve had no reports of problems with 375/prop combos.

If you're new to this game, note EAB's classic Catch 22. Owners tend to keep issues between themselves and the vendor (in this instance, the prop guy), usually fearing loss of support. The community at large doesn't hear about the issues until the support stops, or patience and checkbook run dry.

They did suggest to dynamically balance the prop at CIs and do frequent tap tests.

Dynamic balance has nothing to do with blade vibration. And a tap test tells nothing about fatigue and fretting of the aluminum ferrule at the root of the composite blade, which requires a teardown to detect.
 
For all those interested. With the -375, the counterweighted crank is 6 lbs heavier and costs a bit over $2300. This is of course on a new build engine, and not a retrofit to an existing engine.
 
One more datapoint to add, as of March 2021:

As of very recently, Whirl Wind Aviation has now designated ALL of their props except for the 300 series into a LEGACY product line, meaning they are supported but no longer available.

Those of us with Aerosport IO-375 "non-counterweighted crank" engines awaiting the purchase of a prop can currently no longer buy anything from them... until the 330 officially comes out.

Grrrrr.
 
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Not long ago I was talking to Whirlwind about that exact engine. The 330 series with 3 blades can handle the non-counterweighted IO-370/375 cranks. Having said that it's a beefy prop and ~53lbs.

Since I haven't bought an engine, and still at the "thinking stage", I'm leaning towards the 330 series 2 blade, but then I'm limited to an (I)O-360 or a counterweighted crank on the (I)O-370/375. The 2 blade is ~40lbs

With a -370/375, the options are basically add 6lbs for a counterweighted crank, or add 13 lbs for the additional prop blade. The price difference between the two combinations was insignificant, $100 or so. More expensive crank, or a more expensive prop, so it basically balanced out on purchase price.

As always, verify all info with the manufacturers before deciding.
 
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