Return-Path: Received: from mail4.mx.voyager.net ([216.93.66.203] verified) by logan.com (CommuniGate Pro SMTP 4.2b2) with ESMTP id 3209671 for flyrotary@lancaironline.net; Thu, 06 May 2004 20:42:08 -0400 Received: from u036fr3za011 (d83.as0.wtma.wi.voyager.net [64.77.139.149]) by mail4.mx.voyager.net (8.12.9/8.10.2) with SMTP id i470g36d079569 for ; Thu, 6 May 2004 20:42:04 -0400 (EDT) Message-ID: <006201c433cd$34b4e880$3c40fea9@u036fr3za011> From: "Barnhart" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: 20B - torsional vibration Date: Thu, 6 May 2004 19:49:50 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_005F_01C433A3.4AE31B60" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 5.00.2615.200 X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2615.200 This is a multi-part message in MIME format. ------=_NextPart_000_005F_01C433A3.4AE31B60 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Al, I talked to the people at Powersport about using one of their harmonic = balancers on someone else's drive. They said it was only good for their = drive only. I may be wrong, but I'm not interested in having anything = extra in weight, complexity, a possible maybe problem. I plan on = keeping it in the back of head as something to look out for. There isn't = enough data one way or the other to deal with it. After looking at the = set up on their engines, I decided to go without it. Barny MGDQ 20bt ----- Original Message -----=20 From: marc=20 To: Rotary motors in aircraft=20 Sent: Thursday, May 06, 2004 6:51 PM Subject: [FlyRotary] Re: 20B - torsional vibration 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 -------------------------------------------------------------------------= ----- This message scanned for viruses by CoreComm=20 ------=_NextPart_000_005F_01C433A3.4AE31B60 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Al,
 
I talked to the people at Powersport = about using=20 one of their harmonic balancers on someone else's drive. They said it = was only=20 good for their drive only. I may be wrong, but I'm = not interested=20 in having anything extra in weight, complexity, a possible maybe  = problem.=20 I plan on keeping it in the back of head as something to look out for. = There=20 isn't enough data one way or the other to deal with it.  After = looking at=20 the set up on their engines, I decided to go without it.
 
Barny
MGDQ 20bt
 
 
----- Original Message -----
From:=20 marc=20
Sent: Thursday, May 06, 2004 = 6:51=20 PM
Subject: [FlyRotary] Re: 20B - = torsional=20 vibration

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

 

Marc = Wiese

 

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

 

Subject: [FlyRotary] Re: = 20B

 

Al,

 

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

accessory cover, no harmonic damper in the = front or=20 back.

 

Barny

 

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

 

I have = been=20 looking (again) at the torsional vibration issue, and wondered in = Mazda had=20 determined there may be a problem with the 3-rotor, either regarding = the=20 engine internals, or the driven accessories.  Upon further = thought, I=20 realized that Mazda only used this engine with a torque converter = coupling to=20 an auto trans; and the torque converter is about the best vibration = damper you=20 could find.  Putting a stiff drive on the output end changes the = picture=20 entirely.

 

Tracy’s re-drive=20 design takes the opposite approach; i.e., a flexible coupling with = some play=20 in the gears which lowers the resonance frequency to keep it below the = low end=20 of the operating range.  This obviously has been quite successful = in=20 using with the 2 rotor rotary.  Use with the 3-rotor is not yet = proven.=20 Going to a 6-planet system obviously can handle more continuous = torque, but if=20 you do have a resonance in the operating range; 6 vs 4 doesn’t = really make=20 much difference, because you can get torque amplifications of 10 or=20 more.

 

On first = cut, it=20 seems to me likely that picture with the RD-1B on the 3-rotor may be = even=20 better than on the 2-rotor because of a further separation of the = driving=20 frequency (higher because of more pulses/rev) and the natural = frequency of the=20 re-drive system (which stays roughly the same).  Unfortunately, = until you=20 test, you don’t know, because the entire (geared) rotational = system from front=20 pulley to prop is extremely complex analytically.

 

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

 

The = torsional=20 vibration characteristics of the system will be different for the = engine, with=20 the re-drive and the prop, than it was on the dyno.  It = won’t be long=20 (crossed fingers and toes) before I can observe what happens on the=20 airplane.

 

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

 

BTW; = I’m not=20 trying to be an alarmist, it’s just that torsional vibration in = pulsed drive=20 engines is a fact of life – auto engines, airplane engines; = whatever. =20 Any torsional vibration resonance, which is what can get you, is = something=20 manufactures have always had to deal with.  People have in the = past=20 wrecked dynos and broken drive shafts when unknowingly running into a=20 torsional vibrations resonce, and one topic-du-jour example is the MT = prop on=20 4-cylinder Lycomings.  Seems that there is mysterious cracking of = prop=20 blades, and MT has restrictions on ceratin RPM ranges.  I find = evidence=20 (although limited and may just be my interpretation) of problems with = a=20 3-rotor and the Ross drive.  So we need to be observant when = going into=20 uncharted territory.

 

Al

 
This message scanned = for viruses by=20 CoreComm=20
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