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  #21  
Old 12-18-2020, 08:16 PM
David Z David Z is online now
 
Join Date: Aug 2010
Location: Thunder Bay Ontario
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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.
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  #22  
Old 12-22-2020, 01:47 PM
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Karetaker Karetaker is offline
 
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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.
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  #23  
Old 12-22-2020, 07:48 PM
David Z David Z is online now
 
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Default 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.
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  #24  
Old 12-22-2020, 10:06 PM
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Champ Champ is offline
 
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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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Last edited by Champ : 12-23-2020 at 04:52 PM.
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  #25  
Old 12-23-2020, 07:34 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by Champ View Post
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.

Quote:
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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Last edited by DanH : 12-23-2020 at 07:38 AM.
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  #26  
Old 12-23-2020, 08:09 AM
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Karetaker Karetaker is offline
 
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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.
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  #27  
Old 12-23-2020, 08:59 AM
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DanH DanH is offline
 
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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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Last edited by DanH : 12-23-2020 at 09:09 AM.
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  #28  
Old 12-23-2020, 09:39 AM
Freemasm Freemasm is online now
 
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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.
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  #29  
Old 12-23-2020, 03:34 PM
Whirl Wind Propellers Whirl Wind Propellers is offline
 
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Quote:
Originally Posted by Karetaker View Post
Harzell stated that a wood prop may be my only option.
https://whirlwindaviation.com/props/...es-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.
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  #30  
Old 12-23-2020, 06:14 PM
Freemasm Freemasm is online now
 
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Quote:
Originally Posted by Whirl Wind Propellers View Post
https://whirlwindaviation.com/props/...es-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.
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