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Whirl Wind compatibility with IO-370/375

N546RV

Well Known Member
So this is just an informational post for anyone who might be interested in this information now or in the future.

In another post about the HRT props and James cowl, it was pointed out that WW now has wording on their site about how they no longer support the IO-370 and -375 engines. This is of interest to me since that's exactly the combination I've been planning on for my build.

Anyway, I reached out to them to try and find out the reasoning behind this decision, and got this reply today:

Hello Mr. Clifton,

Yes, since [last summer] Whirl Wind Aviation has decided not to support the IO-370 and the IO-375 engines.

Because of higher torsional vibrations of the IO-370 and IO-375 engines there is a strong possibility that they will need more frequent tear down inspections due to blade grease leaks. The grease leaks are not a safety issue but just a nuisance for the owner and we will not be pro-rating early tear down fees on the props on -370 and -375’s.

Additionally, there could be premature wear of the blade bearing races, retainers and possibly even the hub sockets that could lead to earlier, higher maintenance costs.

We have no objective data defining if or when such things will happen. They may never, but we know based on our vibration studies of these engines that the possibility exists.

So, long story short, there's no "ticking time bomb" thing going on here, they just strongly suspect that longevity of their props will suffer in front of thee engines, and they won't be responsible for shorter overhaul/maintenance intervals resulting from this combination.

So just an FYI for anyone else considering this combination and wondering what's up.
 
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So, since composite props handle torsional vibrations better than aluminum, where does that leave you in the search for a prop? Has Hartzel given an opinion on that engine?
 
I don't believe Hartzell has given any sort of opinion, though this is based on what I've read while doing generic WW vs Hartzell research and is far from extensive. I had the same thought about composite + vibration, but in this case it sounds like their concerns are related more to the hub design than the composite blades.

The way I figure it, I have a few choices:

  • Go with my original plan (370+WW 74HRT) and deal with whatever happens down the road. Doesn't seem like there's a safety-of-flight issue, but possibly some wallet pain
  • Stick with the 370 and go with the Hartzell composite prop. More expensive up front but general consensus seems to be that things might even out in the long run thanks to longer teardown intervals with the Hartzell.
  • Stick with the 74HRT but go to an angle valve 360. Also more expensive up front, but less than the Hartzell option. I'm currently working on evaluating possible effects of going with the heavier engine.
  • Go with a regular old 180-horse 360 and maybe a 200RV prop from WW

Right now I'm leaning towards options 2 & 3, dependent on what my W&B analysis yields. Probably slightly more towards #2.

I'd like to be flying by the end of this year, so I'm looking to try and place FWF orders around the time of SnF to hopefully take advantage of discounts. The clock is ticking...
 
We were contacted by GT Propellers, an Italian company. They make composite blades and use Harzel hubs. No endorsement here, not enough info but perhaps another option to explore. The owner is an RV guy.
 
Cut/paste from Hartzell application guide:

Aircraft T.C./STC: Experimental
Engine Model: Titan 370
Power: 210 HP @ 2700 RPM
Propeller Model: HC-M2YR-1BFPX (M is extended hub)
Notes: Remove TC and PC markings from Hub
and Blades, and Remove S/N from Hub.
Placard/Restr: With counterweighted crankshaft and 9.6:1
(or less) compression ratio: no placards
Blade:
F7497*3X
F7497X

I spoke with Les Dowd at Hartzell and he had no concerns using the HC-C2YR-1BFP (available from Van's) with my IO-370 high comp CW crank with stock mags.
 
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I don't believe Hartzell has given any sort of opinion, though this is based on what I've read while doing generic WW vs Hartzell research and is far from extensive. I had the same thought about composite + vibration, but in this case it sounds like their concerns are related more to the hub design than the composite blades.

The way I figure it, I have a few choices:

  • Go with my original plan (370+WW 74HRT) and deal with whatever happens down the road. Doesn't seem like there's a safety-of-flight issue, but possibly some wallet pain
  • Stick with the 370 and go with the Hartzell composite prop. More expensive up front but general consensus seems to be that things might even out in the long run thanks to longer teardown intervals with the Hartzell.
  • Stick with the 74HRT but go to an angle valve 360. Also more expensive up front, but less than the Hartzell option. I'm currently working on evaluating possible effects of going with the heavier engine.
  • Go with a regular old 180-horse 360 and maybe a 200RV prop from WW

Right now I'm leaning towards options 2 & 3, dependent on what my W&B analysis yields. Probably slightly more towards #2.

I'd like to be flying by the end of this year, so I'm looking to try and place FWF orders around the time of SnF to hopefully take advantage of discounts. The clock is ticking...
There's nothing wrong with IOX-370 and the 200RV prop. It's what I run. My engine supposedly puts out about 191hp.
 
No measurable data leads to opinion

Since the manufacturer's response was...
"Quote:

Hello Mr. Clifton,

Yes, since [last summer] Whirl Wind Aviation has decided not to support the IO-370 and the IO-375 engines.

Because of higher torsional vibrations of the IO-370 and IO-375 engines there is a strong possibility that they will need more frequent tear down inspections due to blade grease leaks. The grease leaks are not a safety issue but just a nuisance for the owner and we will not be pro-rating early tear down fees on the props on -370 and -375?s.

Additionally, there could be premature wear of the blade bearing races, retainers and possibly even the hub sockets that could lead to earlier, higher maintenance costs.

We have no objective data defining if or when such things will happen. They may never, but we know based on our vibration studies of these engines that the possibility exists. "

? not sure how anyone can make a data-driven, fact-based determination. Certainly, the manufacturer isn't able or willing.

Sounds like you just have to use your research thus far and make the best decision you can.

I fly the WW200RV turned by an IOX-360 and all is good in 130 hours. Of course, this isn't the combination you're looking for, so maybe some folks with 370/375 & WW with hours nearing the overhaul schedule can chime in with their experience. I'm interested in hearing their experience.
 
Been happy with the combo

I have a WW 74RV on an IO-375. No issues in 560 hours over 4 years. Very happy with the setup.
Update- Looks like I spoke to soon. On a post flight inspection a couple of weeks ago, I found some surface cracks in one blade. I've contacted Whirlwind for their opinion on my options. At this point I would just encourage anyone thinking of this combination to be sure to do their own research.
 
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You don't want to bet against the ticking time bomb when considering any prop selected without the benefit of a blade vibration survey.

When Les Dowd says he has no concerns about a specific engine/engine accessory/propeller combination (see Walt's post), it's because Hartzell outfitted a test subject with strain gauges and a many-channel telemetry transmitter, then flew a specific series of flight tests. MT does similar. Best I know, Whirlwind does not, and there have been serious blade root issues with some combinations.

Which brings us to the notion of composite blades negating vibration concerns. There is some truth, apparently based on blade fatigue comparison with aluminum blades. However, that's a narrow area; overall the statement is far too general. "Composite" describes a wide variety of materials and methods, and even if the blade itself is highly fatigue resistant, there can still be blade shank, blade retention, hub, flange, and crank issues.

Trust but verify....
 
Another point to consider....

I remember years ago, after Sensenich had just introduced the (I)O-320 fixed pitch metal prop for RV's, everyone was asking for an (I)O-360 version.

At that time, they expressed doubt that they would be able to design one that had good performance #'s and no interactive vibration problems.

They eventually (obviously) were able to do it, but it shows that the "people that know", consider small changes in displacement, stroke, and/or compression to be very influential in potential interacting issues between an engine and a propeller.
 
We've been looking for a 3 blade for our build for a while now on a planned 9:1 CR 375(200 hp). The only one I've been able to get an absolute yes on was an MT MTV9B. Vans sells the MTV12 through the builders program which is a midsized hub, the mtv9 is a full size hub to help deal with the increased torsional forces. Both the engine builder and the prop manufacturer have said running the 2.5" extension for the Sam James long cowl will not put any restrictions on operations.

The only other 3 blade that comes close is a hartzell HC-M3YR-1RFX for an f4 raider. Rated for 200 hp with a counterweighted crank and already comes on the extended hub so no spacer is required with the Sam James long cowl. I've asked hartzell about putting this on an RV7 with the 375 and got no response.
 
74 HRT compatibility issues

Hi Guys,

I just came across this information. I am in my final assembly stage and have a Aerosport Power IO-375-M1S (Non CW & 200 HP) and the Whirl Wind 74 HRT. This is the combination that now says Not Supported in Red on the Whirl Wind Website.:eek:

This is the prop they(Whirl Wind) recommended when I placed my order. The propeller has been installed and looks great, but the engine has not been run.

Anybody in the same boat, if so what have you done?

FB (Mark)
 
74 HRT UPDATE

Hi Guys,

I contacted Nichole at Whirl Wind Aviation, she sent me a very candid email explaining that IO-370/IO-375 engines are rough- their torsional vibrations are significantly higher and this could lead to premature wear.

This is why they choose not to support this engine prop combo going forward.

To date: they have had no problems with propellers, nothing has broken, no reports of excessive wear, etc.

She also said: We will not abandon our customers due to specification changes, Will support our existing -370 and -375 propeller owners for as long as they own the our product.

I am happy with the quick response and will continue forward to my first fight soon.
 
Whirl Wind Engineering

You don't want to bet against the ticking time bomb when considering any prop selected without the benefit of a blade vibration survey.

When Les Dowd says he has no concerns about a specific engine/engine accessory/propeller combination (see Walt's post), it's because Hartzell outfitted a test subject with strain gauges and a many-channel telemetry transmitter, then flew a specific series of flight tests. MT does similar. Best I know, Whirlwind does not, and there have been serious blade root issues with some combinations...

Just noticed this post and wanted to assure everyone that we absolutely do perform all the necessary testing and analysis on our propellers and to my knowledge, every major propeller manufacturer has run into issues with fatigue cracks in the past. Our cracks were not at the root, but at the transition to the nickel leading edge. We refined our FEA model and determined what modifications were needed to prevent the cracking and it has not been an issue since.

Whirl Wind 200HRT series and 300 series ARE suitable with O-370/375 engines IF they have a counter weighted crank shaft. The “not supported” warning only applies to 370/375 engines with NON-COUNTER WEIGHTED crank shafts.
Below are examples of generic data we've collected on another engine.
• WW performs propeller vibration surveys using wireless telemetry and strategically placed strain gages.
ACtC-3cYgQeV5EA8b-jEyPPgt_lSW6iR8qJeKkXDP5t1ct3H8ym7eYkkz5p5qrt7ONK6NfxhProB2XK2QRyN9NY37XWZRXq7atJIjP-umwF4y_H8_2x5QgTXmmojIhOJRWzbjzGMfbgLZk4SI1W4oE_nXVVG=w500-no
ACtC-3fZFtxB6hFiQcWw6dRRJvWMdFn-r4wgKqPapuAweFlIQGQgXnewwmBUdR9FuG0NL6NTPoCPAn018wdvuGpk6QVNrB6NI0TIbVhEfd-7sABY1wrrivkD88QESGEZZJL2elQrz7zWa9fivIhDy__DhDku=w637-h381-no

• In the design process we use previously collected engine torque data and FEA tools to estimate stresses. These stresses are later verified with the strain gage testing of the propeller operated on the engine.
ACtC-3dIM-gKD3Ocb79lGwzYQzW2RMq7-EWPkpSW77te8hLVIH4700_FpFS9tLKLM1MfXprm4yexTibZB1uG23PpOuwV79NUyGBJlNATzZbVBKs19IqdJl6BBwnwEfjQhBkmcPNqclgqdyOlrQ1VOTj33fQ2=w884-h524-no
ACtC-3etIEdgvYU_RZZV_6YWiqMc1n4-nwcN72QJrLy1LR0VtfbeuVP9c6EjdZJwrnrcl2vC0f7fH1f0c4ovDYtZQcdNbGSO7inoL0SIA74oCiwStV6tCp4ka4Lc_oG2dTqdQiMmoBcyeFngU4vxXQH3uMsj=w646-h735-no

• The issues of the non-counter weighted 370/375 engines is the peak torques from the ignition and compression strokes (positive and negative torque) are so high it moves the blade back and fourth in the hub. This can lead to grease leak, premature hub wear, and possible surface cracking of lower leading edge of the blade. The counter weighted crank shaft reduces the magnitude of the peak torques.
 
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Whirl Wind 200HRT series and 300 series ARE suitable with O-370/375 engines IF they have a counter weighted crank shaft. The “not supported” warning only applies to 370/375 engines with NON-COUNTER WEIGHTED crank shafts.

Oh reeeealllly...well this is very interesting info to me, since the Titan IO-375 I'm going with is a counterweighted engine.

Maybe I'll end up with a 74HRT hanging off the front of my plane after all. Good info!
 
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