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Message-ID: <1b4b137c0804301726u364b60ccjbad291ea751ee3a1@mail.gmail.com>
Date: Wed, 30 Apr 2008 20:26:16 -0400
From: "Tracy Crook" <tracy@rotaryaviation.com>
Sender: rwstracy@gmail.com
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Post Mortum on RD-1B
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Hi Dave,
  You might expect the hub or engine to freewheel at some point but this can
manifest itself in several ways.  The sungear is a Ford part and the amount
of interference fit varies a lot due to the tolerances in the sungear ID.
The original design of the input shaft used just an interference
/ heat-shrink fit until I learned that the gear ID was not consistent enough
for a reliable fit.
  At the low end of the interference fit the engine and/or prop might
freewheel but the most likely scenarioo is a momentary slip followed by the
shaft friction welding itself to the sun gear.  This can happen with amazing
suddenness.  I experienced this in-flight during initial development of the
drive before the gear was mechanically pinned to the input shaft.  It took
several flights during which I was sure that the engine had a sudden severe
'miss' at full throttle before I concluded that the engine was not at
fault.  Inspection of the drive revealed the sun gear had spun on the input
shaft.

Tracy

On Sun, Apr 27, 2008 at 9:09 PM, David Staten <Dastaten@earthlink.net>
wrote:

> Tracy,
>   Thanks for the comprehensive write up.
>
>   Given the lack of other similar failures being discussed in the past, I
> am dismayed to know this is likely an assembly error on our part. I
> performed the original assembly and mating, but the oil seal leak developed
> at some point in the first couple hours, at which point the assembly was
> demated, seal replaced, and assembly remated.
>
>   The "shearing then welding on shaft" event, wouldnt this at some point
> been associated with a motionless or freewheeling hub? I never saw any
> episodes of this during the engine testing sessions in which i was present.
> Granted I was not present for a significant portion of the engine runs,
> including none after the reassembly.
>
> Dave Staten
>
>

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<div>Hi Dave,</div>
<div>&nbsp; You might expect the hub or engine to freewheel at some point but this can manifest itself in several ways.&nbsp; The sungear is a Ford part and the amount of interference fit varies a lot due to the tolerances in the sungear ID.&nbsp; The original design of the input shaft used just an interference /&nbsp;heat-shrink fit until I learned that the gear ID was not consistent enough for&nbsp;a reliable fit.</div>

<div>&nbsp; At the low end of the interference fit&nbsp;the engine and/or prop might freewheel but the most likely scenarioo is a momentary slip followed by the shaft&nbsp;friction welding&nbsp;itself to the sun gear.&nbsp; This can happen with amazing suddenness.&nbsp; I experienced this in-flight&nbsp;during initial development of the drive before the gear was mechanically pinned to the input shaft.&nbsp; It took several flights during which I was sure that the engine had a sudden severe &#39;miss&#39; at full throttle before I concluded that the engine was not at fault.&nbsp; Inspection of the drive revealed the sun gear had spun on the input shaft.&nbsp; </div>

<div>&nbsp;</div>
<div>Tracy<br><br></div>
<div class="gmail_quote">On Sun, Apr 27, 2008 at 9:09 PM, David Staten &lt;<a href="mailto:Dastaten@earthlink.net">Dastaten@earthlink.net</a>&gt; wrote:<br>
<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">Tracy,<br>&nbsp; Thanks for the comprehensive write up.<br><br>&nbsp; Given the lack of other similar failures being discussed in the past, I am dismayed to know this is likely an assembly error on our part. I performed the original assembly and mating, but the oil seal leak developed at some point in the first couple hours, at which point the assembly was demated, seal replaced, and assembly remated.<br>
<br>&nbsp; The &quot;shearing then welding on shaft&quot; event, wouldnt this at some point been associated with a motionless or freewheeling hub? I never saw any episodes of this during the engine testing sessions in which i was present. Granted I was not present for a significant portion of the engine runs, including none after the reassembly.<br>
<br>Dave Staten<br><br></blockquote></div>

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