X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Tue, 06 Aug 2013 11:42:57 -0400 Message-ID: X-Original-Return-Path: Received: from nm1-vm0.bullet.mail.ne1.yahoo.com ([98.138.91.74] verified) by logan.com (CommuniGate Pro SMTP 6.0.5) with ESMTPS id 6405449 for lml@lancaironline.net; Tue, 06 Aug 2013 10:35:46 -0400 Received-SPF: none receiver=logan.com; client-ip=98.138.91.74; envelope-from=casey.gary@yahoo.com Received: from [98.138.90.53] by nm1.bullet.mail.ne1.yahoo.com with NNFMP; 06 Aug 2013 14:35:11 -0000 Received: from [98.138.101.163] by tm6.bullet.mail.ne1.yahoo.com with NNFMP; 06 Aug 2013 14:35:11 -0000 Received: from [127.0.0.1] by omp1074.mail.ne1.yahoo.com with NNFMP; 06 Aug 2013 14:35:11 -0000 X-Yahoo-Newman-Property: ymail-3 X-Yahoo-Newman-Id: 619513.980.bm@omp1074.mail.ne1.yahoo.com Received: (qmail 70413 invoked by uid 60001); 6 Aug 2013 14:35:11 -0000 DomainKey-Signature:a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=X-YMail-OSG:Received:X-Rocket-MIMEInfo:X-Mailer:References:Message-ID:Date:From:Reply-To:Subject:To:In-Reply-To:MIME-Version:Content-Type; b=h/KPiFUUiJ9We6R6gHvkQeOBiRTdqbkQq/8XrYq0loztaLMM07qKXag7lP3IjCIby6zIfBPYsaoST6abiNmojmJMUyHhf05vqTp0g6SyTFarJwAt8QJ8yRRke7F6l1WShw3wmecDRPtsY6vt5jrZa9kqhyZc6YnY+EFhScU1AEM=; X-YMail-OSG: 1IR5rdcVM1mOkDZkI.CNFZrZY8UfvOKMmBmNsdXbUTskLai efC_Mzl4fgPZzdXPqXdrGi2KAsZjFw60m0aekESfKyE9dCj_i8LTkli2Ff8p mYDGkpr8PJVUIzsDnnPaueGRgbw1T7y2T.bo4Fcftslz2vCUjHjKw7br0rbv o_D3pn5HUJQCImTEiTQTgjzAC_ZDWJ1HU_hCt5zt0hdfbHnaOZKCxQXQLi2V nc_yp5bR1e3CnDa.BBgURw4o8n4tTTiAWpSKKRst49Et8xvZ8gBGkn572DKU JkBQN2kPoBASmgqgxL68mNCDgtbM8oHjUgaowzjOO5rp.x6gzHIpepFPT6JI MwZr3iHo3mLNQlf.uvzOorWsvfjY9GKl7iyXvwzRMklA.9PhJyTDAPGCEr8K YgYabkyh691Cyv2bXPpGUIEcMQL79vCapVvKK.1dHEBB9gaciBLxPuzKSjYj OD_G3.61deAKVIzEG2nHRydN6VpcR0gpWrbADltGgWpJPX74BKGvYSkQPBoZ jqBNDolTkDxOUbtG_oMsjavUPauPGI7yVEOR9vC93YNqIqEFlsoARti2fFiI yH0eKMP27JwK_0k0x9g-- Received: from [97.92.63.83] by web120101.mail.ne1.yahoo.com via HTTP; Tue, 06 Aug 2013 07:35:11 PDT X-Rocket-MIMEInfo: 002.001,VGhhbmtzLCAiQ2F1ZGV0dCdzIGh1c2JhbmQiIGZvciB0aGUgaW5mb3JtYXRpdmUgcG9zdC4gwqBJIGhhdmUgc29tZSBjb21tZW50cyBvbiBoaXMgZmluZGluZ3MsIGluIFticmFja2V0cyBiZWxvd10uIMKgTm8gYW5zd2Vycywgc28ganVzdCBza2lwIHJlYWRpbmcgaXQgaWYgeW91IGxpa2UgOi0pCkdhcnkgQ2FzZXkKCk9zaGtvc2gvVmlicmF0aW9uLCBvciB3aGF0IEkgbGVhcm5lZCBvbiBteSBzdW1tZXIgdmFjYXRpb246CgpGaXJzdCwgYWxsIDU1MCBDb250aW5lbnRhbCBjcmFua3NoYWZ0IHNlcGFyYXRpb24BMAEBAQE- X-Mailer: YahooMailWebService/0.8.152.567 References: X-Original-Message-ID: <1375799711.69225.YahooMailNeo@web120101.mail.ne1.yahoo.com> X-Original-Date: Tue, 6 Aug 2013 07:35:11 -0700 (PDT) From: Gary Casey Reply-To: Gary Casey Subject: Re: Potential Problem-Engine Vibration X-Original-To: Lancair Mailing List In-Reply-To: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="1072509510-1747390383-1375799711=:69225" --1072509510-1747390383-1375799711=:69225 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Thanks, "Caudett's husband" for the informative post. =A0I have some commen= ts on his findings, in [brackets below]. =A0No answers, so just skip readin= g it if you like :-)=0AGary Casey=0A=0AOshkosh/Vibration, or what I learned= on my summer vacation:=0A=0AFirst, all 550 Continental crankshaft separati= ons and cracks have been=0Atraced to prop strikes or likely prop strikes.= =A0 We are back on flight status=0Awith 15SC.=A0=A0[Were the crankshafts in= spected after the strikes? =A0If so, the inspection method might be suspect= .]=0A=0ALes Doud (Applications Engineer) of Hartzell, spoke at Jeff Edwards= Forum=0Aand spent 30+ minutes with me later discussing our Vibrations.=A0 = The most=0Ainteresting point was the weight of a metal 3 blade prop causes = it to act as=0Aa gyroscope. [Of course. =A0All props have more inertia than= the engine itself, I think even the composite ones] =A0The engine and all = moving parts can create a=0A harmonic more=0Aeasily as a result.[A "harmoni= c" is a vibration double or half in frequency as the base vibration. =A0A h= armonic of what? =A0The torsional excitation frequency? =A0An engine vibrat= ion frequency? =A0Just saying "a harmonic" doesn't say anything.] =A0Lighte= r weight composite props have much less gyro=0Aeffect and therefore are inh= erently smoother.[Well, I don't know if they are "inherently" smoother. =A0= They tend to exhibit resonant frequencies higher than heavier aluminum prop= s, but is that good or bad? =A0I don't know.] =A0Our stiff composite airfra= mes [Composite materials are somewhat LESS stiff than metal structures - ca= rbon-based structures being stiffer than ons based on glass fibers. =A0That= 's why composite airframes are typcially on the heavy side - to get the sti= ffness high enough. =A0On my ES I can see the wings flex and I was never ab= le to do that on any metal airplane.]=0Aare more susceptible=0A than an alu= minum one with "every rivet acting as a=0Adamper".[I'm not sure I buy that.= =A0Sure, every joint in a metal plane is a source of damping, but then eve= ry fiber-to-epoxy joint in a composite is a source of damping. =A0I don't k= now whether metal or composite planes absorb vibrations better, but I think= composite planes have the edge here] =A0 I previously thought the main rea= son was composite blades had less=0Aresonance than metal. [Everything has a= "resonance", it's just a matter of the frequency and the damping inherent = in the structure. =A0Aluminum blades, being a homogenous structure, certain= ly have less damping that composite. =A0They will probably have a higher re= sonant frequency. =A0But then there is the question of the mode of vibratio= n, but that's another discussion.] =A0=0A=0AAfter all the obvious sources h= ave been checked and fixed, the best=0Adiagnosis tool is a in flight Spectr= um Analysis and Plot=0A with the top of the=0Aline DynaVibe (tool cost $300= 0+).=A0 At least that is what the DynaVibe rep.=0Asaid in a forum and Les a= greed.=A0 Mount the sensor tightly on something solid=0Alike a spar cap, ho= rizontal and parallel to the spar (not on anything like=0Athe panel dust co= ver). [I certainly agree with that.] =A0Determining increased first, second= or third order=0Avibrations(crank rotation speed, twice crank speed, firin= g frequency] narrows down the source.=A0 Les thought in my case of unpredic= table=0Avibration, the free iPhone ap "Vibration" could be accurate enough = to find=0Athe major shake.=A0=A0[That almost makes me want to go out and bu= y an iPhone! =A0I think maybe I will]=0A=0ALes advised checking prop orient= ation for parallel alignment of one of the=0Ablades with #6 cylinder at Top= Dead Center on compression.=A0 This is best for=0Asmoothness. [I fail to s= ee a connection between the prop orientation and vibration, not that there = couldn't be. =A0In the case of a 4-cylinder engine and=0A 2-blade prop I ca= n see it.]=0A=0APaul Snyder, an Engineer with Lord Mounts, thinks he may be= able to help.=0AHe cited the Mooney Ovation with a vibration problem that = was improved by a=0Asingle stiffer mount on the left front (probably airfra= me-specific].=A0 Early Cirrus with 550's and 3 blade=0AHartzell's vibrated,= later versions have 6 mounts with 4 near the front to=0Abetter balance the= static weight of the prop and engine[Yes, in a Continental with metal prop= the CG is very close to the front mount, so it has to support all the engi= ne weight].=A0 He may have=0Asuggestions when he knows the part number of t= he brown (silicone) mounts=0Asupplied to me by Lancair.=0A=0AOshkosh is a e= xcellent resource for all things aviation[ain't that the truth!].=A0 You ca= n button=0Ahole the engineer/designer/owner and get a lot closer to answers= .=A0 I was=0Aimpressed with their willingness to help us and the lack of de= fensiveness on=0Atheir part.=A0=A0=0A --1072509510-1747390383-1375799711=:69225 Content-Type: text/html; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable
Thanks= , "Caudett's husband" for the informative post.  I have some comments = on his findings, in [brackets below].  No answers, so just skip readin= g it if you like :-)
Gary Casey

Oshkosh/Vibration, or what= I learned on my summer vacation:

First, all 550 Continental cranksh= aft separations and cracks have been
traced to prop strikes or likely pr= op strikes.  We are back on flight status
with 15SC.  [We= re the crankshafts inspected after the strikes?  If so, the inspection= method might be suspect.]

Les Doud (Applications Engineer) of Hartz= ell, spoke at Jeff Edwards Forum
and spent 30+ minutes with me later dis= cussing our Vibrations.  The most
interesting point was the weight = of a metal 3 blade prop causes it to act as
a gyroscope. [Of course. &nb= sp;All props have more inertia than the engine itself, I think even the composite ones]  The engine and all moving parts can create a=0A harm= onic more
easily as a result.[A "harmonic" is a vibration double or half= in frequency as the base vibration.  A harmonic of what?  The to= rsional excitation frequency?  An engine vibration frequency?  Ju= st saying "a harmonic" doesn't say anything.]  Lighter weight composit= e props have much less gyro
effect and therefore are inherently smoother= .[Well, I don't know if they are "inherently" smoother.  They tend to = exhibit resonant frequencies higher than heavier aluminum props, but is tha= t good or bad?  I don't know.]  Our stiff composite airframes [Co= mposite materials are somewhat LESS stiff than metal structures - carbon-ba= sed structures being stiffer than ons based on glass fibers.  That's w= hy composite airframes are typcially on the heavy side - to get the stiffne= ss high enough.  On my ES I can see the wings flex and I was never abl= e to do that on any metal airplane.]
are more susceptible=0A than an alu= minum one with "every rivet acting as a
damper".[I'm not sure I buy that= .  Sure, every joint in a metal plane is a source of damping, but then= every fiber-to-epoxy joint in a composite is a source of damping.  I = don't know whether metal or composite planes absorb vibrations better, but = I think composite planes have the edge here]   I previously thought th= e main reason was composite blades had less
resonance than metal. [Every= thing has a "resonance", it's just a matter of the frequency and the dampin= g inherent in the structure.  Aluminum blades, being a homogenous stru= cture, certainly have less damping that composite.  They will probably= have a higher resonant frequency.  But then there is the question of = the mode of vibration, but that's another discussion.]  

After = all the obvious sources have been checked and fixed, the best
diagnosis = tool is a in flight Spectrum Analysis and Plot=0A with the top of the
li= ne DynaVibe (tool cost $3000+).  At least that is what the DynaVibe re= p.
said in a forum and Les agreed.  Mount the sensor tightly on som= ething solid
like a spar cap, horizontal and parallel to the spar (not o= n anything like
the panel dust cover). [I certainly agree with that.] &n= bsp;Determining increased first, second or third order
vibrations(crank = rotation speed, twice crank speed, firing frequency] narrows down the sourc= e.  Les thought in my case of unpredictable
vibration, the free iPh= one ap "Vibration" could be accurate enough to find
the major shake.&nbs= p; [That almost makes me want to go out and buy an iPhone!  I thi= nk maybe I will]

Les advised checking prop orientation for parallel = alignment of one of the
blades with #6 cylinder at Top Dead Center on co= mpression.  This is best for
smoothness. [I fail to see a connectio= n between the prop orientation and vibration, not that there couldn't be.  In the case of a 4-cylinder e= ngine and=0A 2-blade prop I can see it.]

Paul Snyder, an Engineer wi= th Lord Mounts, thinks he may be able to help.
He cited the Mooney Ovati= on with a vibration problem that was improved by a
single stiffer mount = on the left front (probably airframe-specific].  Early Cirrus with 550= 's and 3 blade
Hartzell's vibrated, later versions have 6 mounts with 4 = near the front to
better balance the static weight of the prop and engin= e[Yes, in a Continental with metal prop the CG is very close to the front m= ount, so it has to support all the engine weight].  He may have
sug= gestions when he knows the part number of the brown (silicone) mounts
su= pplied to me by Lancair.

Oshkosh is a excellent resource for all thi= ngs aviation[ain't that the truth!].  You can button
hole the engin= eer/designer/owner and get a lot closer to answers.  I was
impresse= d with their willingness to help us and the lack of defensiveness on
the= ir part.  
--1072509510-1747390383-1375799711=:69225--