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heaysr(at)telus.net
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 Posted: Sat Aug 13, 2022 11:27 am Post subject: Yak 55M - Change in vibration when swapping props |
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I changed from the Russian 2 blade prop to the 3 blade MTV 250 diameter prop.
With the 2 blade, general engine to airframe vibration as perceived in flight from the cockpit was proportional to engine RPM as expected. The prop was dynamically balanced. Albeit, vibration is a lot more than sitting behind a Lycoming in a Decathlon. I have never flown any other Yak 55M so have nothing to gauge. Engine mounts were new.
With the 3 blade and stock M14P governor, vibration was very different from the 2 blade in the 70% to 85% RPM range. The vibration becomes harmonic in that range akin to a twin with RPM out of sync. The beat frequency is, I guess, around 3 or 4 cycles per second (Hz) and increases as PRM approaches 85% at which point it becomes imperceptible. After a dynamic balance there was no change.
I wonder if it is the governor? I have read from Richard's website that the stock Russian governor is somehow underpowered for the MTV 3 blade. But I don't know the symptoms.
Any comments. Have others had this problem?? Maybe this is just a feature of changing to an MTV, whether on a Sukhoi or Yak 18T?
Royden Heays
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richard.goode(at)russiana
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| Posted: Sun Aug 14, 2022 2:13 am Post subject: Yak 55M - Change in vibration when swapping props |
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Hello Royden,
The three blade MT propeller is intrinsically much smoother than the Russian V-530 propeller, but you do need to dynamically balance a propeller after installation, which you seem to have done. But was the MT a new propeller, or new after overhaul? The point is that in either case, it will have the static balance weights bolted to the back plate of the propeller and I'm wondering if this had not been done correctly. And, I would also ask if the people doing the dynamic balance know their equipment well. A lot of organisations, particularly those who normally balance helicopter rotors aren't that good with fixed wing propellers!
But I can say that the prop MT should be extremely smooth!
With best wishes
Richard
RICHARD GOODE AEROBATICS
Rhodds Farm, Lyonshall, Hereford, HR5 3LW, UK
Tel: +44 (0)1544 340120 Fax: +44 (0)1544 340129
e-mail: richard.goode(at)russianaeros.com (richard.goode(at)russianaeros.com)
www.russianaeros.com
WORLD LEADERS IN SOVIET & CHINESE RADIAL AIRCRAFT ENGINES
In partnership with Aerometal Kft, Hungary.
From: owner-yak-list-server(at)matronics.com <owner-yak-list-server(at)matronics.com> On Behalf Of Royden Heays
Sent: 13 August 2022 20:27
To: yak-list(at)matronics.com
Subject: Yak 55M - Change in vibration when swapping props
I changed from the Russian 2 blade prop to the 3 blade MTV 250 diameter prop.
With the 2 blade, general engine to airframe vibration as perceived in flight from the cockpit was proportional to engine RPM as expected. The prop was dynamically balanced. Albeit, vibration is a lot more than sitting behind a Lycoming in a Decathlon. I have never flown any other Yak 55M so have nothing to gauge. Engine mounts were new.
With the 3 blade and stock M14P governor, vibration was very different from the 2 blade in the 70% to 85% RPM range. The vibration becomes harmonic in that range akin to a twin with RPM out of sync. The beat frequency is, I guess, around 3 or 4 cycles per second (Hz) and increases as PRM approaches 85% at which point it becomes imperceptible. After a dynamic balance there was no change.
I wonder if it is the governor? I have read from Richard's website that the stock Russian governor is somehow underpowered for the MTV 3 blade. But I don't know the symptoms.
Any comments. Have others had this problem?? Maybe this is just a feature of changing to an MTV, whether on a Sukhoi or Yak 18T?
Royden Heays
| | - The Matronics Yak-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Yak-List |
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