From: "Stephen Izett stephen.izett@gmail.com" <flyrotary@lancaironline.net>
Received-SPF: pass
 receiver=logan.com; client-ip=209.85.210.172; envelope-from=stephen.izett@gmail.com
Content-Type: text/plain;
	charset=utf-8
Content-Transfer-Encoding: quoted-printable
Mime-Version: 1.0 (Mac OS X Mail 14.0 \(3654.60.0.2.21\))
Subject: Re: [FlyRotary] dynamic balance
Date: Fri, 19 Mar 2021 14:52:29 +0800
References: <list-1323830@logan.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
In-Reply-To: <list-1323830@logan.com>
Message-Id: <B91892EC-D647-4924-A047-D960CEF99828@gmail.com>

Thanks Steve B.
Do you recall how much weight was required to balance the engine at the =
flex plate?
Steve Izett

> On 19 Mar 2021, at 9:40 am, Steven W. Boese SBoese@uwyo.edu =
<flyrotary@lancaironline.net> wrote:
>=20
> I did not try the procedure described by Finn where a weight was =
attached at the four cardinal locations.
>=20
> I used a Freescale MMA7260Q eval board as the 3 axis accelerometer, a =
USB 6009 as an A to D unit and Signalexpress software both from National =
Instruments, and a laptop computer to collect and process the data.
>=20
> The photo shows the setup for balancing the prop.  The position =
reference Hall effect sensor was installed on the red mount and clamped =
to redrive.  The sensor and mount were covered in modeling clay to =
dampen resonance vibrations possible in this mount.  The Hall effect =
trigger was attached to the prop flange with double sided tape along =
with an equal weight attached in the same way 180 degrees from the =
trigger.  The accelerometer is seen behind the red clamp and was =
installed in a 1/4=E2=80=9D aluminum plate.  This was screwed to a =
second 1/4=E2=80=9D aluminum plate which was bonded to the redrive with =
epoxy putty.  Before the engine was started, a  =E2=80=9Cthump test=E2=80=9D=
 was performed by striking the accelerometer lightly with a rubber =
hammer and recording the results in order to verify the stiffness of the =
accelerometer mount.  The balance was adjusted by adding washers under =
the screws which attach the spinner to the aft bulkhead and at the =
angular location indicated by the processed data.  The final balancing =
weight was in the form of washers, nut, and bolt installed in the aft =
spinner bulkhead.  This weight took into account the difference in the =
radius from the center of the prop shaft to the test washers under the =
spinner screws compared to the radius to the location of the balancing =
bolt, nut, and washers.
>=20
> The engine was balanced by locating the Hall effect position sensor =
where it would see a trigger attached to one of the damper plate to flex =
plate bolts with an equal weight attached to the opposite bolt.  Washers =
of various weights were installed under two of the bolts until the =
unbalance phase angle was aligned with one of the four bolts.  Then the =
weight under that bolt was adjusted until the balance was acceptable.
>=20
> Steve Boese
> <prop balance setup c.jpg>--
> Homepage:  http://www.flyrotary.com/
> Archive and UnSub:   =
http://mail.lancaironline.net:81/lists/flyrotary/List.html