X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from [24.25.9.100] (HELO ms-smtp-01-eri0.southeast.rr.com) by logan.com (CommuniGate Pro SMTP 5.0.8) with ESMTP id 1035792 for flyrotary@lancaironline.net; Thu, 16 Mar 2006 00:21:53 -0500 Received-SPF: pass receiver=logan.com; client-ip=24.25.9.100; envelope-from=eanderson@carolina.rr.com Received: from edward2 (cpe-024-074-025-165.carolina.res.rr.com [24.74.25.165]) by ms-smtp-01-eri0.southeast.rr.com (8.13.4/8.13.4) with SMTP id k2G5L4Qf001743 for ; Thu, 16 Mar 2006 00:21:06 -0500 (EST) Message-ID: <001701c648b9$7061e010$2402a8c0@edward2> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Motor teardown results Date: Thu, 16 Mar 2006 00:21:11 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0014_01C6488F.872A0900" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2180 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 X-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. ------=_NextPart_000_0014_01C6488F.872A0900 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MessageThe chatter marks are certainly apparent, Chuck. Whoa! 150 = hours is certainly not much out of a brand new housing. It could be as = you suggest that the two piece seal played a role. However, I have = another suggestion. Measure the apex seal slot at the top (across the = gap) and see what the distance is. Do it both on the good rotor and the = damaged one if you can find an undamaged spot. If like my rotor, the = slots are worn, I believe they may contribute to the chatter and = breaking of the apex seal. Here's the theory. As the slot "V"s there is less support for the seal = near its top, the bottom is still fairly well constrained. As a = consequence, the top portion of the seal is more able to be swayed back = and forth by combustion and friction forces. In other words, instead of = just rubbing on the rotor housing wall with the smooth top of the seal, = the edge of the seal starts to drag along the wall. The seal (with = less support at the top) acts like a stiff spring (up to a limit) and = "vibrates" as it slides along the housing wall leaving the chatter = marks. At some point the forces become too much and the seal breaks. =20 It might be interesting to determine the vibration frequency of a seal ( = given its dimensions and composition) and then measure the average = distance between the peaks (or valleys) of the chatter. Then given the = resonant frequency of the seal determine at what rotor rpm it would = leave chatter marks of the measured distance. {:>). No, I don't have a = clue about how to do this, but I'll bet some mechanical engineer could = come up with something. Just a theory, of course, but if your apex slot tops are within the = specifications called for by Mazda then that would discredit the theory. = If they are worn then it might tend to give it support. When my seal broke it also caught the next seal down in is slot and = smeared the top of the slot such that it could not come back up. You and I are apparently the only ones (that I know of ) that seem to = have had this failure mode of an apex seal disintegrating for no = apparent reason. Thanks for sharing the photos and information. Are you going to try for Sun & Fun? Ed=20 Ed Anderson Rv-6A N494BW Rotary Powered Matthews, NC eanderson@carolina.rr.com Ed =20 ----- Original Message -----=20 From: Chuck Dunlap=20 To: Rotary motors in aircraft=20 Sent: Wednesday, March 15, 2006 10:44 PM Subject: [FlyRotary] Motor teardown results I finally got time to get my failed 13b apart. The rear rotor was = missing one apex seal, the other 2 were intact but jammed due to the = fragments of the broken one. The rotor housing has the classic chatter = marks all around. Doing a Google of "13B apex seal chatter" results in = plenty of examples of this failure mode. Apparently the chatter is from = the natural resonant frequency of the seal, it eventually fatigues the = seal causing failure. The front rotor was in good shape, but the housing had the same = chatter marks, but not as severe as the rear rotor. The front rotor = housing was brand new 150 hours ago when I rebuilt this motor after the = Grand Canyon forced landing. At that time the good rotor housing had = slight chatter marks but I reused it. The front rotor was destroyed at = that time due to foreign object entering the rotor. Both rotors were missing the corner seal rubber plugs on the side = with the short apex seal segment. Perhaps the small segment vibrated = more, disintegrating the rubber seals? The first 260 hours of flying my rotary bird was with stock 3-piece = seals, and I never saw any chatter marks. The last 250 hours has been = flown with 2 piece seals and now I have chatter marks . I now have Tracy's 2 piece apex seals and I wonder how they will = perform, it appears that the heavier weight of the 2 piece seals puts = the resonant frequency in the cruising range of 6000RPM? Chuck Dunlap RV6 13B -------------------------------------------------------------------------= ----- -- Homepage: http://www.flyrotary.com/ Archive and UnSub: http://mail.lancaironline.net/lists/flyrotary/ ------=_NextPart_000_0014_01C6488F.872A0900 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Message
The chatter marks are certainly apparent, = Chuck. =20 Whoa!  150 hours is certainly not much out of a brand new = housing.  It=20 could be as you suggest that the two piece seal played a role.  = However, I=20 have another suggestion.  Measure the apex seal slot at the top = (across the=20 gap) and see what the distance is. Do it both on the good rotor and=20 the damaged one if you can find an undamaged spot.  =   If=20 like my rotor, the slots are worn, I believe they may contribute to the = chatter=20 and breaking of the apex seal.
 
Here's the theory.   As the slot "V"s = there is=20 less support for the seal near its top, the bottom is still fairly well=20 constrained.  As a consequence, the top portion of the seal is more = able to=20 be swayed  back and forth by combustion and friction = forces.  In=20 other words, instead of just rubbing on the rotor housing wall with = the=20 smooth top of the seal, the edge of the seal starts to drag along the=20 wall.   The seal (with less support at the top) acts like a = stiff=20 spring (up to a limit) and "vibrates" as it slides along the housing = wall=20 leaving the chatter marks.  At some point the forces become too = much and=20 the seal breaks.  
 
It might be interesting to determine the = vibration=20 frequency of a seal ( given its dimensions and composition) and then = measure the=20 average distance between the peaks (or valleys) of the chatter.  = Then given=20 the resonant frequency of the seal determine  at what rotor rpm it = would=20 leave chatter marks of the measured distance. {:>).  No, I don't = have a=20 clue about how to do this, but I'll bet some mechanical engineer could = come up=20 with something.
 
Just a theory, of course, but if your apex = slot tops=20 are within the specifications called for by Mazda then that would = discredit the=20 theory.  If they are worn then it might tend to give it=20 support.
 
 
When my seal broke it also caught the next seal = down in is=20 slot and smeared the top of the slot such that it could not come back=20 up.
 
You and I are apparently the only ones (that I = know of )=20 that seem to have had this failure mode of an apex seal disintegrating = for no=20 apparent reason.
 
Thanks for sharing the photos and=20 information.
 
Are you going to try for Sun & = Fun?
 
Ed
 
 
Ed Anderson
Rv-6A N494BW Rotary = Powered
Matthews,=20 NC
eanderson@carolina.rr.com
 
Ed
 
 
 
----- Original Message -----
From:=20 Chuck = Dunlap=20
Sent: Wednesday, March 15, 2006 = 10:44=20 PM
Subject: [FlyRotary] Motor = teardown=20 results

 
 
I = finally got time=20 to get my failed 13b apart. The rear rotor was missing one apex seal, = the=20 other 2 were intact but jammed due to the fragments of the broken one. = The=20 rotor housing has the classic chatter marks all around. Doing a Google = of "13B=20 apex seal chatter" results in plenty of examples of this failure mode. = Apparently the chatter is from the natural resonant frequency of the = seal, it=20 eventually fatigues the seal causing failure.
The = front rotor=20 was in good shape, but the housing had the same chatter marks, but not = as=20 severe as the rear rotor. The front rotor housing was brand new 150 = hours ago=20 when I rebuilt this motor after the Grand Canyon forced landing. At = that time=20 the good rotor housing had slight chatter marks but I reused it. The = front=20 rotor was destroyed at that time due to foreign object entering the=20 rotor.
Both = rotors were=20 missing the  corner seal rubber plugs on the side with the short = apex=20 seal segment. Perhaps the small segment vibrated more, disintegrating = the=20 rubber seals?
The = first 260=20 hours of flying my rotary bird was with stock 3-piece seals, and I = never saw=20 any chatter marks. The last 250 hours has been flown with 2 piece = seals and=20 now I have chatter marks .
I = now have Tracy's=20 2 piece apex seals and I wonder how they will perform, it appears that = the=20 heavier weight of the 2 piece seals puts the resonant frequency in the = cruising range of 6000RPM?
 
Chuck=20 Dunlap
RV6=20 13B

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