From: "Stephen Izett stephen.izett@gmail.com" <flyrotary@lancaironline.net>
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Subject: Re: [FlyRotary] RD1-C damper
Date: Tue, 8 Dec 2020 15:29:37 +0800
References: <list-1019087@logan.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
In-Reply-To: <list-1019087@logan.com>
Message-Id: <1E6A34BC-4F0A-45A3-B60B-CB7C5F7F45AA@gmail.com>

Thanks Steve.
Can I pm you to discuss the MT ?

Steve Izett

> On 8 Dec 2020, at 3:23 pm, Steven W. Boese SBoese@uwyo.edu =
<flyrotary@lancaironline.net> wrote:
>=20
> Steve,
>=20
> When I installed an MT 3-blade electric constant speed prop, I =
dynamically balanced the flywheel end of the engine with the damper =
plate installed but without the reduction drive installed.  This was =
accomplished by changing the weight of the damper plate attachment =
washers in two adjacent positions.  The result was 0.018"/sec at 4000 =
RPM.  This could not be improved further due to the angular location of =
the imbalance changing from one run up to the next.  My guess is that =
this was a result of about 0.020" of radial clearance between the =
corners of the square damper plate and the flex plate.  The damper plate =
may shift until there is no radial clearance at some location and this =
angular location is not consistent.
>=20
> After installing the reduction drive and prop, dynamically balancing =
the system with the sensor on the reduction drive as close to the prop =
as possible resulted in a one per prop revolution signal of 0.035"/sec.  =
There was a three per prop revolution signal on the ground that =
disappeared in flight.
>=20
> In flight at 2100 prop RPM (~6000 engine RPM) and above, the system =
seemed to be vibration free.  At prop RPM less than 2100 and greater =
than 1800, there was a definite vibration felt in the control stick but =
not noticeable when placing a hand on the instrument panel.  If the =
plane was oriented such that the reflection of the outer prop disk was =
visible, the arc of the blade tips was very clear when there was no =
vibration felt in the control stick.  This arc reflection became less =
distinct when the stick vibration was present.  My guess is that one or =
more prop blades was fluttering slightly fore and aft or all three =
blades were not tracking as closely to each other when the vibration =
occurred.
>=20
> After placing the prop controller in manual mode in flight thus =
allowing no subsequent pitch change and then landing, it was found that =
the pitch of one of the blades as measured at the tip was different from =
the other two by one degree while the other two were consistent within =
less than 0.2 degrees.
>=20
> Repositioning the pitch change blocks within the prop hub allowed the =
pitch of all three blades to be consistent within less than 0.2 degrees =
at the blade tips.  In flight, the RPM dependent vibration in the =
control stick was essentially eliminated.
>=20
> There is about one degree of slack in the pitch change mechanism for =
each of the blades.  When in flight in constant speed mode, a slight =
pitch change causes that control stick vibration to momentarily return =
and then disappear. One of the blade's seals causes more resistance to =
pitch change rotation than the other two.  It appears that the =
aerodynamic twist in addition to the blade counterweight generated =
torque is insufficient to allow that blade to follow its pitch change =
block as rapidly as the other two.  This doesn't seem to me to be a =
safety of flight problem and the issue can be avoided by operating in =
manual mode if it is too annoying.  That behavior may also be resolved =
upon prop overhaul.  The overhaul interval is specified at 100 hr which =
seems unreasonably short to me, possibly determined by lawyers as =
opposed to engineers.
>=20
> This may or may not have any bearing on what you are seeing.
>=20
> Steve Boese
>=20
>> On Dec 6, 2020, at 6:08 PM, Stephen Izett stephen.izett@gmail.com =
<flyrotary@lancaironline.net> wrote:
>>=20
>> =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
>> Thanks Dave
>>=20
>> That makes sense, particularly for those of us with the damper =
already.
>>=20
>> I suppose I=E2=80=99m also questioning our own vibration and noise =
from our fwf. I=E2=80=99d be interested to know what others have found.
>> Our prop is an electric adjustable.
>> We balanced each blade pretty precisely and then dynamic balanced it =
at 6000rpm, and according to the equipment we used we got it was right =
down in the noise at <0.05 inches/sec.
>> It did require quite a bit of weight to get it balanced and Ive =
always wondered why that was. ~8 X 3/4 inch washers and the nuts and =
bolts that hold them to the spinner backplate at a radius of about 5 =
inches.
>> I=E2=80=99ve pondered:
>>       1. The Engines Rear counterbalance being wrong. But I thought =
it was on the back of the Eccentric Shaft when I got the engine =
originally, and then I purchased and bolted on the flex plate.
>>       2. The Damper itself, but all the bolts, washers and nuts =
appear symmetrical.
>>       3. The Prop Hub and Spinner - all appears symmetrical.
>>=20
>> I wish I had checked the balance dynamically without the blades and =
spinner to isolate what is causing the need for the weights.
>>=20
>> We can certainly hear/feel the difference in flight when we adjust =
the rpm=E2=80=99s between say 6K and 7K rpm.
>> Its really smooth at 7K but rougher at 6K.  Though I=E2=80=99d prefer =
to run her at around 6K.
>> There doesn=E2=80=99t seem to be a significant change in the fuel =
flow/IAS from using 6K vs 7K. I suppose the equivalent of driving in 3rd =
or 4th gear.
>> I=E2=80=99d just prefer to lower the wear in case that is =
significant!
>>=20
>> I suppose it's this vibration difference that makes me want to get =
rid of the damper if others have found its not necessary.
>>=20
>> Cheers
>>=20
>> Steve
> 	=20
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