From: "Stephen Izett stephen.izett@gmail.com" <flyrotary@lancaironline.net>
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Subject: Re: [FlyRotary] Balance prop
Date: Thu, 18 Mar 2021 10:30:38 +0800
References: <list-1320093@logan.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
In-Reply-To: <list-1320093@logan.com>
Message-Id: <8F58DD75-F2D0-4F35-AA03-02144BB6BAA9@gmail.com>

Hi Steve B and Finn

Appreciate learning from your minds.
I=E2=80=99m trying to understand your process.
I have a new prop and plan to balance engine at ring gear prior to =
balancing prop as you are doing.
I=E2=80=99m fortunate to have access to a prop balancer but would like =
to understand your process.

I have some questions:
What device are you using to get your trigger sig from the aluminium =
tape reference point?
Should the cro image look sinusoidal, period being equal to rpm and =
amplitude proportional to imbalance at the particular angle of rotation =
relative to the trigger position?
Should the X and Y signals from the ADLX335 (breakout board mounted on =
its edge) be the same but 90deg out of phase?
I'm trying to remember my filter theory! Won=E2=80=99t a 100hz filter =
attenuate your signal at 6000rpm by some 3db, so your higher rpm =
readings may look better/more balanced than lower rpm readings?

Steve B. I=E2=80=99m trying to follow your logic.
Having taken 4 readings with a nut moved around the 4 cardinal =
positions, if the nut is not way to small or large, and the system was =
not initially at best balance, then 2 of the readings (adjacent =
positions) will show less amplitude than initial reading, and the other =
2 higher amplitude.

So after the 4 test readings, if the 4 signals are equal and higher =
amplitude, wouldn=E2=80=99t this point to the initial balance being =
better, and so suggesting a smaller nut be used and retested? Is this =
what you are saying?
Sorry if I=E2=80=99m confused.

Could you measure the required angular position of a correction weight =
directly from the cro image? That being the angular distance between the =
trigger position and the maximum amplitude of the signal minus 180deg?

Appreciate you guys and the mental stimulation.

Steve Izett


> On 18 Mar 2021, at 1:23 am, Finn Lassen finn.lassen@verizon.net =
<flyrotary@lancaironline.net> wrote:
>=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 actually 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 flywheel.
> Using a ADLX335 accelerometer  followed by a 100Hz low pass filter 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
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> 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?
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> Steve,  how did you balance your engine?
>=20
> Finn=20
>=20
> On 1/28/2021 12:39 AM, Sboese sboese@uwyo.edu wrote:
>> Matt,
>>=20
>> 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.
>>=20
>> Steve Boese
>>=20
>>=20
>>=20
>>> On Jan 27, 2021, at 6:09 PM, Matt Boiteau mattboiteau@gmail.com =
<flyrotary@lancaironline.net> wrote:
>>>=20
>>> =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.
>>>=20
>>>=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 to balance the prop around X60 (Williston, FL), and I forget =
who, but someone said we could rent one nearby?
>>>=20
>>>=20
>>> 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 out 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
>>>=20
>>>=20
>>> - Matt Boiteau
>=20
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>  =09
> This email has been checked for viruses by Avast antivirus software.=20=

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