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Wed, 17 Mar 2021 19:16:15 +0000 Date: Wed, 17 Mar 2021 19:16:13 +0000 (UTC) To: "Finn Lassen finn.lassen@verizon.net" Message-ID: <1466914501.1533397.1616008573040@mail.yahoo.com> In-Reply-To: References: Subject: Re: [FlyRotary] Re: Balance prop MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_1533396_78905038.1616008573038" X-Mailer: WebService/1.1.17936 YMailNorrin Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/88.0.4324.192 Safari/537.36 Content-Length: 13840 ------=_Part_1533396_78905038.1616008573038 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Seems like you're over thinking it.Take a reading with nothing added.Add a= nut and take a reading at each of the four points.=C2=A0Two of the points = should show improvement (less vibration), and two of them should show degra= dation.=C2=A0 Each set should be adjacent.=C2=A0 If this is not the case, y= ou're done, because your motor is balanced better than your hardware can de= tect.=C2=A0 The one exception is if all readings got worse.=C2=A0 In that c= ase, repeat the operation with a half sized nut, like maybe jam nut. If you did get improvement in two adjacent points, you've identified the po= int of imbalance.=C2=A0 Now you just have to determine how much weight to r= emove it. I'd try another weight scaled to the nut you used and the amount = of improvement it produced.=C2=A0 For instance, if position A cut the ips i= n half, and an adjacent position B by 75%, the imbalance is going to be bet= ween those two.=C2=A0 I'd try the nut and a washer on A, and a washer on B.= =C2=A0 Keep doing that until you find it to tedious to contine. This process also works to balance a treadmill motor that you add to a benc= h top mill, btw. On Wednesday, March 17, 2021, 01:23:56 PM EDT, Finn Lassen finn.lassen@= verizon.net wrote: =20 =20 I'm now on day 5 (newly) trying to balance the engine with prop removed. After a trip chasing a wild goose into the weeds with FFT, I'm now trying = the spreadsheet method: measure amplitude at these four points: Unbalanced Adding a 7.9g weight (nut) at one of the four bolts (reference) Move the nut +90 deg from the reference bolt Move the nut -90 deg from the reference bolt =20 Tried it at 3000 RPM. Plugged the numbers into the spreadsheet, it told me to add 28g at 4.5 deg= . Seemed like a lot. The result was a lot worse vibration that I could actu= ally feel. =20 Tried again at 4,500 RPM, this time using P-P voltages. Now wants me to add 183g at -143 deg. =20 Very hard to get consistent readings. =20 Really doesn't make any sense that the addition of a 8g weight influences = the amplitude of the scope curve so little. The big washers on each side of the rubber donuts are 30g each. =20 I'm getting a good trigger signal from a piece of alum tape near rim of fl= ywheel. Using a ADLX335 accelerometer=C2=A0 followed by a 100Hz low pass filter an= d 300x amp. ADXL335 has sensitivity of 300mV/G. With 300x amp, that's 90V/G= . 0.7Vp is about 0.008 Gs or 0.005 ips at 6000 RPM if my math and circuit is= correct. V (ips) =3D A (Gs) * 3690 / RPM =20 Is it possible that the near-sine curve I see on the scope is actually the= reaction (acceleration/de-acceleration of the rotor) to the combustion eve= nt? =20 Steve,=C2=A0 how did you balance your engine? =20 Finn=20 =20 On 1/28/2021 12:39 AM, Sboese sboese@uwyo.edu wrote: =20 Matt,=20 One cannot balance the prop by placing the balance weights on the flywhee= l due to the gear ratio of the psru. =C2=A0I chose to dynamically balance a= t the flywheel with the prop removed, then install the prop, and finally dy= namically balance at the prop. =C2=A0That appears to have given good result= s for me.=20 Steve Boese =20 =20 =20 =20 On Jan 27, 2021, at 6:09 PM, Matt Boiteau mattboiteau@gmail.com wrote: =20 =20 =20 =EF=BB=BF =20 =E2=97=86 This message was sent from a non-UWYO address. Please exercise ca= ution when clicking links or opening attachments from external sources. =20 How does everyone balance their prop, do they gain access to the flywheel= and add bolts/washers there like a standard aircraft engine? I'm looking t= o balance the prop around X60 (Williston, FL), and I forget who, but someon= e=C2=A0said we could rent one nearby? =20 =20 Had a 301 ss slip joint bellow for the exhaust and it cracked, which set m= e back a few months. The end of my exhaust must have too much vibration, I= =C2=A0will figure out more rubber mounts with the welder to stop the end vi= brating. Bought a 2.75" inconel split joint bellow from SPD exhaust that sh= ould handle the heat. http://www.spdexhaust.com/pdfs/AccPDFs/Bellows.pdf =20 =20 - Matt Boiteau =20 =20 =20 =20 =20 | | =20 This email has been checked for viruses by Avast antivirus software.=20 www.avast.com=20 | -- Homepage:=C2=A0 http://www.flyrotary.com/ Archive and UnSub:=C2=A0 http://mail.lancaironline.net:81/lists/flyrotary/L= ist.html =20 ------=_Part_1533396_78905038.1616008573038 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
=
Seems like you're over think= ing it.
Take a reading with not= hing added.
Add a nut and take = a reading at each of the four points. 
Two of the points should show improvement (less vibration), an= d two of them should show degradation.  Each set should be adjacent.&n= bsp; If this is not the case, you're done, because your motor is balanced b= etter than your hardware can detect.  The one exception is if all read= ings got worse.  In that case, repeat the operation with a half sized = nut, like maybe jam nut.

If you did get improvement in tw= o adjacent points, you've identified the point of imbalance.  Now you = just have to determine how much weight to remove it. I'd try another weight= scaled to the nut you used and the amount of improvement it produced. = ; For instance, if position A cut the ips in half, and an adjacent position= B by 75%, the imbalance is going to be between those two.  I'd try th= e nut and a washer on A, and a washer on B.  Keep doing that until you= find it to tedious to contine.

This process also works t= o balance a treadmill motor that you add to a bench top mill, btw.


=20
=20
On Wednesday, March 17, 2021, 01:23:56 PM EDT, Finn Las= sen finn.lassen@verizon.net <flyrotary@lancaironline.net> wrote:


=20 =20 =20
I'm now on day 5 (newly) tr= ying to balance the engine with prop removed.
After a trip chasing a wild goose into the weeds with FFT, I'm now trying the spreadsheet method: measure amplitude at these four points:
Unbalanced
Adding a 7.9g weight (nut) at one of the four bolts (reference)
Move the nut +90 deg from the reference bolt
Move the nut -90 deg from the reference bolt

Tried it at 3000 RPM.
Plugged the numbers into the spreadsheet, it told me to add 28g at 4.5 deg. Seemed like a lot. The result was a lot worse vibration that I could actually feel.

Tried again at 4,500 RPM, this time using P-P voltages.
Now wants me to add 183g at -143 deg.

Very hard to get consistent readings.

Really doesn't make any sense that the addition of a 8g weight influences the amplitude of the scope curve so little.
The big washers on each side of the rubber donuts are 30g each.

I'm getting a good trigger signal from a piece of alum tape near rim of flywheel.
Using a ADLX335 accelerometer  followed by a 100Hz low pass filt= er and 300x amp. ADXL335 has sensitivity of 300mV/G. With 300x amp, that's 90V/G.
0.7Vp is about 0.008 Gs or 0.005 ips at 6000 RPM if my math and circuit is correct.
V (ips) =3D A (Gs) * 3690 / RPM

Is it possible that the near-sine curve I see on the scope is actually the reaction (acceleration/de-acceleration of the rotor) to the combustion event?

Steve,  how did you balance your engine?

Finn

On 1/28/2021 12:39 AM, Sboese sboese@uwyo.edu wrote= :
=20 Matt,

One cannot balance the prop by placing the balance weights on the flywheel due to the gear ratio of the psru.  I chose to dynamically balance at the flywheel with the prop removed, then install the prop, and finally dynamically balance at the prop.  That appears to have given good results for me.

Steve Boese



On Jan 27, 2021, at 6:09 PM, Matt Boiteau mattboiteau@gmail.com <flyrotary@lancaironline.= net> wrote:

=EF=BB=BF

=E2=97=86 This message was sent from a non-UWYO address. Please exercise caution when clicking links or opening attachments from external sources.


How does everyone balance their prop, do they gain access to the flywheel and add bolts/washers there like a standard aircraft engine? I'm looking to balance the prop around X60 (Williston, FL), and I forget who, but someone said we could rent one nearby?=


Had a 301 ss slip joint bellow for the exhaust and it cracked, which set me back a few months. The end of my exhaust must have too much vibration, I will figure ou= t more rubber mounts with the welder to stop the end vibrating. Bought a 2.75" inconel split joint bellow from SPD exhaust that should handle the heat.
http://www.spdexhaust.com= /pdfs/AccPDFs/Bellows.pdf


- Matt Boiteau




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