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- Reddevil556
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4 blade vs 8 blade C130H
Any been near the H model with the 8 blade props vs the old 4 blades? Is there is a noticeable decibel difference?
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- aumaverick
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Re: 4 blade vs 8 blade C130H
I'm not sure about decibel levels but there is a noticeable difference in pitch, with the old 4-bladed Hs having that familiar thrum sound vs the new 8-bladed props.
Re: 4 blade vs 8 blade C130H
If both provide a specific power level, the logic would say then acoustic amplitude from each of the 8 blades would be lower than each of the 4 blades.
There would also be a potential complication of increase natural frequency vibration mode of the 8 blades vs 4 blades which could impact the fatigue life if near by structure.
It gets complicated and is not my strong suit.
bt
There would also be a potential complication of increase natural frequency vibration mode of the 8 blades vs 4 blades which could impact the fatigue life if near by structure.
It gets complicated and is not my strong suit.
bt
Re: 4 blade vs 8 blade C130H
Reddevil556 wrote:Any been near the H model with the 8 blade props vs the old 4 blades? Is there is a noticeable decibel difference?
Collins Aerospace claims its NP2000 eight-bladed propellers reduce noise by 50% (20 decibels) compared with the old 4-bladed propellers.
https://www.collinsaerospace.com/-/media/project/collinsaerospace/collinsaerospace-website/product-assets/marketing/n/np2000/np2000-brochure.pdf
Re: 4 blade vs 8 blade C130H
CowAnon wrote:Reddevil556 wrote:Any been near the H model with the 8 blade props vs the old 4 blades? Is there is a noticeable decibel difference?
Collins Aerospace claims its NP2000 eight-bladed propellers reduce noise by 50% (20 decibels) compared with the old 4-bladed propellers.
https://www.collinsaerospace.com/-/media/project/collinsaerospace/collinsaerospace-website/product-assets/marketing/n/np2000/np2000-brochure.pdf
20db is a lot more than a 50% reduction. Somebody needs better proof readers for their handouts.
Re: 4 blade vs 8 blade C130H
CowAnon wrote:Reddevil556 wrote:Any been near the H model with the 8 blade props vs the old 4 blades? Is there is a noticeable decibel difference?
Collins Aerospace claims its NP2000 eight-bladed propellers reduce noise by 50% (20 decibels) compared with the old 4-bladed propellers.
https://www.collinsaerospace.com/-/media/project/collinsaerospace/collinsaerospace-website/product-assets/marketing/n/np2000/np2000-brochure.pdf
20db is huge. If it's only half truth, a big difference.
Re: 4 blade vs 8 blade C130H
Just a guess, but they may be referring to decibel reduction in terms of power (sound intensity), and percentage in terms of perceived loudness. 20db would be a factor of 4 in terms of loudness. Not sure how they reconcile 20db to 50%, but possibly the 20db is a peak value, vs average for loudness. If so, then the average reduction would be more like 10db, which is consistent with the range of reasonably expected improvement.
Re: 4 blade vs 8 blade C130H
If you look at the civil certification for the commercial freighter version of the Hercules, a 20-decibel drop seems plausible. The LM-100J was certified in 2019 and meets the Stage 5 noise requirement that went into effect in 2017. The E and G models meet the Stage 3 requirement, while the other models don't meet any of the noise regulations. Stage 4 is a 10 dB reduction from Stage 3, and Stage 5 is 7 dB lower than Stage 4. That's a 17-decibel difference between the E/G aircraft model (with 4-bladed, square-shaped props) and the J model, which has the Dowty R391 scimitar propellers of the same 13-1/2 feet diameter. I would assume that the Collins NP2000 8-blade propeller has similar or better noise performance than the 6-bladed Dowty R391.
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