Return-Path: Received: from mxsf29.cluster1.charter.net ([209.225.28.229] verified) by logan.com (CommuniGate Pro SMTP 4.2b2) with ESMTP id 3209621 for flyrotary@lancaironline.net; Thu, 06 May 2004 20:02:59 -0400 Received: from office (68.116.253.147.ts46v-02.dntn.tx.charter.com [68.116.253.147] (may be forged)) by mxsf29.cluster1.charter.net (8.12.11/8.12.11) with ESMTP id i46NpQ4Y098119 for ; Thu, 6 May 2004 19:51:39 -0400 (EDT) From: "marc" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] 20B - torsional vibration Date: Thu, 6 May 2004 18:51:28 -0500 Message-ID: <000701c433c5$0da97600$6502a8c0@office> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0008_01C4339B.24D36E00" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.3416 Importance: Normal X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1409 In-Reply-To: This is a multi-part message in MIME format. ------=_NextPart_000_0008_01C4339B.24D36E00 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Powersport tests were found to be faulty by dint of the fact that they used a piston engine coupling to the dyno. The shaft excited itself and busted several times, and they blamed the engine. Torsional reversals are not a problem on a rotary-there aren't any, but there is some harmonic vibrations, easily tamed. Completely different animal. Mazda did have some flexing problems on the early 20 shafts, they were all recalled or replaced. The forgings, metallurgy, and some details were changed. Marc Wiese -----Original Message----- From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Al Gietzen Sent: Wednesday, May 05, 2004 11:00 AM To: Rotary motors in aircraft Subject: [FlyRotary] 20B - torsional vibration Subject: [FlyRotary] Re: 20B Al, Same here on my 20b. Out of a 94 Cosmo. It has the counter weight under the accessory cover, no harmonic damper in the front or back. Barny The reason I had asked this question is because in doing some development testing on a 20B, Powersport determined the need for a harmonic damper on the shaft at the front to reduce a torsional vibration. The test were done with the Powersport re-drive, which, if you are not familiar with it, is a tight tolerance spur gear arrangement which is designed to be "stiff" in order to keep any resonance frequencies above the top end of the operating range. I have been looking (again) at the torsional vibration issue, and wondered in Mazda had determined there may be a problem with the 3-rotor, either regarding the engine internals, or the driven accessories. Upon further thought, I realized that Mazda only used this engine with a torque converter coupling to an auto trans; and the torque converter is about the best vibration damper you could find. Putting a stiff drive on the output end changes the picture entirely. Tracy's re-drive design takes the opposite approach; i.e., a flexible coupling with some play in the gears which lowers the resonance frequency to keep it below the low end of the operating range. This obviously has been quite successful in using with the 2 rotor rotary. Use with the 3-rotor is not yet proven. Going to a 6-planet system obviously can handle more continuous torque, but if you do have a resonance in the operating range; 6 vs 4 doesn't really make much difference, because you can get torque amplifications of 10 or more. On first cut, it seems to me likely that picture with the RD-1B on the 3-rotor may be even better than on the 2-rotor because of a further separation of the driving frequency (higher because of more pulses/rev) and the natural frequency of the re-drive system (which stays roughly the same). Unfortunately, until you test, you don't know, because the entire (geared) rotational system from front pulley to prop is extremely complex analytically. Now; if you are not asleep yet, I will tell you that I was concerned about the amount of belt vibration (alt and pump drive) I observed on my 20B during the dyno runs. This could be caused by some non-uniformity in the pulleys, but there seems to be no measurable runout. It is likely that it was the result of torsional vibration. This could result in reduced belt life, or a failed alternator mount, or nothing. One thing is pretty certain, a harmonic damper on the front would reduce the risk of a problem. The torsional vibration characteristics of the system will be different for the engine, with the re-drive and the prop, than it was on the dyno. It won't be long (crossed fingers and toes) before I can observe what happens on the airplane. If I could find a harmonic damper that will mount to the front end of the 20B e-shaft, I'd look at putting it on (especially a viscous damper). It could reduce the torsional vibration for the entire system. (Anybody know of one?) BTW; I'm not trying to be an alarmist, it's just that torsional vibration in pulsed drive engines is a fact of life - auto engines, airplane engines; whatever. Any torsional vibration resonance, which is what can get you, is something manufactures have always had to deal with. People have in the past wrecked dynos and broken drive shafts when unknowingly running into a torsional vibrations resonce, and one topic-du-jour example is the MT prop on 4-cylinder Lycomings. Seems that there is mysterious cracking of prop blades, and MT has restrictions on ceratin RPM ranges. I find evidence (although limited and may just be my interpretation) of problems with a 3-rotor and the Ross drive. So we need to be observant when going into uncharted territory. Al ------=_NextPart_000_0008_01C4339B.24D36E00 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

Powersport tests were found to be = faulty by dint of the fact that they used a piston engine coupling to the dyno. = The shaft excited = itself and busted several times, and they blamed the engine. Torsional reversals = are not a problem on a rotary-there aren’t any, but there is some harmonic vibrations, easily tamed. Completely different animal. Mazda did = have some flexing = problems on the early 20 shafts, they were all recalled or replaced. The forgings, metallurgy, and some details were changed.

 

Marc Wiese

 

-----Original Message-----
From: Rotary motors in = aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Al Gietzen
Sent: Wednesday, May 05, = 2004 11:00 AM
To: Rotary motors in = aircraft
Subject: [FlyRotary] 20B = - torsional vibration

 

Subject: [FlyRotary] Re: 20B

 

Al,

 

Same here on my 20b. Out of a 94 Cosmo.  It has the counter weight under = the

accessory cover, no harmonic damper in the front or back.

 

Barny

 

The reason I = had asked this question is because in doing some development testing on a 20B, = Powersport determined the need for a harmonic damper on the shaft at the front to = reduce a torsional vibration.  The test were done with the Powersport = re-drive, which, if you are not familiar with it, is a tight tolerance spur gear arrangement which is designed to be “stiff” in order to keep = any resonance frequencies above the top end of the operating = range.

 <= /font>

I have been = looking (again) at the torsional vibration issue, and wondered in Mazda had = determined there may be a problem with the 3-rotor, either regarding the engine = internals, or the driven accessories.  Upon further thought, I realized that = Mazda only used this engine with a torque converter coupling to an auto trans; = and the torque converter is about the best vibration damper you could find.  Putting a stiff drive on the output end changes the picture = entirely.

 <= /font>

Tracy’s = re-drive design takes the opposite approach; i.e., a flexible coupling with some = play in the gears which lowers the resonance frequency to keep it below the low = end of the operating range.  This obviously has been quite successful in = using with the 2 rotor rotary.  Use with the 3-rotor is not yet proven. = Going to a 6-planet system obviously can handle more continuous torque, but if = you do have a resonance in the operating range; 6 vs 4 doesn’t really = make much difference, because you can get torque amplifications of 10 or = more.

 <= /font>

On first cut, = it seems to me likely that picture with the RD-1B on the 3-rotor may be even = better than on the 2-rotor because of a further separation of the driving frequency = (higher because of more pulses/rev) and the natural frequency of the re-drive = system (which stays roughly the same).  Unfortunately, until you test, you = don’t know, because the entire (geared) rotational system from front pulley to = prop is extremely complex analytically.

 <= /font>

Now; if you = are not asleep yet, I will tell you that I was concerned about the amount of = belt vibration (alt and pump drive) I observed on my 20B during the dyno = runs.  This could be caused by some non-uniformity in the pulleys, but there = seems to be no measurable runout.  It is likely that it was the result of = torsional vibration.  This could result in reduced belt life, or a failed = alternator mount, or nothing.  One thing is pretty certain, a harmonic damper = on the front would reduce the risk of a problem.

 <= /font>

The torsional vibration characteristics of the system will be different for the = engine, with the re-drive and the prop, than it was on the dyno.  It won’t = be long (crossed fingers and toes) before I can observe what happens on the airplane.

 <= /font>

If I could = find a harmonic damper that will mount to the front end of the 20B e-shaft, = I’d look at putting it on (especially a viscous damper).  It could = reduce the torsional vibration for the entire system.  (Anybody know of = one?)

 <= /font>

BTW; = I’m not trying to be an alarmist, it’s just that torsional vibration in = pulsed drive engines is a fact of life – auto engines, airplane engines; whatever.  Any torsional vibration resonance, which is what can get = you, is something manufactures have always had to deal with.  People = have in the past wrecked dynos and broken drive shafts when unknowingly running = into a torsional vibrations resonce, and one topic-du-jour example is the MT = prop on 4-cylinder Lycomings.  Seems that there is mysterious cracking of = prop blades, and MT has restrictions on ceratin RPM ranges.  I find = evidence (although limited and may just be my interpretation) of problems with a = 3-rotor and the Ross drive.  So we need to be observant when going into = uncharted territory.

 <= /font>

Al

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