REFLECTOR:CG Test

John Dibble reflector@tvbf.org
Sat, 24 Jan 2004 22:27:35 -0600


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Keith,
I completely agree with you and plan on using my new data to modify my 
W&B calculations.  Jim S. points out that the factory published pilot 
arm may be off a bit. (A 2" change in the pilot seat location changes my 
cg by 0.2")  Perhaps the calculation can be simplified for the standard 
Velocity (I'm not familiar with the XL) because both the rear seat and 
the fuel are close to aft cg.  Therefore changes in the reat seat weight 
and fuel weight will not change the cg much when you are near aft cg and 
that is the only time to be concerned about balance (with the exception 
of too much weight in the front seat which is a forward cg issue).  Only 
changes in the front seat weight make a big difference.  So what it 
boils down to is to determine how much front seat weight is needed to 
avoid being aft cg.  From my test it appears that my weight is 
sufficient for this purpose and that makes it a no-brainer as long as 
the plane doesn't leave without me or I don't become anorexic and lose 
50 lbs.  My only remaining concern is how much the fuel can change cg by 
shifting back during a climb with the tanks 1/2 full.  Moving the fuel 
arm back 2" moves the cg back 0.2".  However if I move myself forward 2" 
I can cancel out the fuel shift, so I think I'm covered.  I know there 
are ballfes, but over several minutes the fuel will get past them.  
Again I appreciate all comments lest I have overlooked something.

John

KeithHallsten wrote:

> John,
>  
> I think the point of doing the weight and balance measurements and 
> calculations is to have documentation of the acceptable C.G. range.  
> Then some proposed loading can be checked before flight to assure that 
> is within the acceptable range.  This is both good practice and 
> required by regulation: it's the "W" in the "AROW" required documents 
> list.
>  
> Maybe because of my engineering background, calculating the center of 
> gravity location seems like a very logical thing to do.  I plan to 
> calculate W&B for all of my proposed loading configurations, then 
> compare those numbers to the flight characteristics experienced.  That 
> way I will know what flight characteristics to expect when I'm 
> proposing to fly at some different loading configuration for which I 
> calculate the W&B numbers.
>  
> Keith Hallsten
>  
>
>     ----- Original Message -----
>     From: John Dibble <mailto:aminetech@bluefrog.com>
>     To: reflector@tvbf.org <mailto:reflector@tvbf.org>
>     Sent: Saturday, January 24, 2004 10:50 AM
>     Subject: Re: REFLECTOR:CG Test
>
>     Jim,
>     I appreciate your comments.  I suspect a weight/balance would
>     confirm an aft cg loading according to the numbers that Velocity
>     provides.  What I am trying to do here is establish a limit
>     specific to my plane which may be different from the standard
>     assuming there are small differences in how each plane is built. 
>     Scott S told me that, for a standard Velocity, typically 170 lbs
>     in the front seat is enough to put you within the aft cg limit. 
>     So perhaps my plane is different, or maybe the original cg
>     measurements are off.  In any case I think an actual flying stall
>     test is more meaningful than measurements on the ground.  Of
>     course with flying there is  risk involved and the weight/balance
>     measurement is essential before first flight when you know nothing
>     about how it will fly.  My plane has 280 hours (75 of which are
>     mine), so I know it flies ok and I'm looking to fine tune
>     (determine with more certainty) my aft cg limit and hopefully 
>     avoid adding weight to the nose.  From recent reflector
>     discussions I felt I understood the causes and onset indicators of
>     a deep stall as well as how to recover from it (altitude, prop
>     pitched for power, moveable weights) and felt sufficiently
>     comfortable to stall the canard near the aft cg limit.  I think
>     doing a weight and balance measurement now is like measuring the
>     length of the bungee cord after having already jumped off the
>     bridge.  If anyone disagrees, please tell me.
>
>     John
>
>     Jim Sower wrote:
>
>>Having done what you have done, I would be inclined to muster up some friends and do a
>>weight/balance with the fuel load you tested with, you *personally* sitting in the
>>pilot's seat, and the weights you used just as close as you can place them to where
>>they were in the back seat.
>>Just to be sure .... Jim S.
>>
>>John Dibble wrote:
>>
>>  
>>
>>>I decided to do a test to determine my aft cg limit as suggested by
>>>Scott B.  My balance calculations for my SRG indicate I will be aft cg
>>>with less than 250 lbs in the front seats.  I weigh 170 so this needs to
>>>be resolved and nose weight added if needed.  I put 8 x 10lb weights in
>>>the copilot seat.  At 7500' I trimmed for 75-80kn and pulled back until
>>>the canard stalled at 60kn.  It took all the aft stick and I had to trim
>>>to about 70kn in order to stall the canard.  The canard motion was
>>>gentile and the plane was a bit wobbly, but stable.  One-by-one I moved
>>>the weights to the rear seat and repeated the stall.  Each time the
>>>canard motion was less pronounced.  With all the weights in the back
>>>seat the canard just kind of mushed down at 58kn.  In all cases I had to
>>>maintain aft stick pressure to get slow enough to stall and never had to
>>>push the stick forward.  I should add that I have 3 leading edge
>>>vortilons and one trailing edge fence inboard of the aileron on each
>>>wing.  So it appears that I do not need to add any nose weight.  Anyone
>>>agree/disagree?
>>>
>>>John
>>>    
>>>
>>
>>_______________________________________________
>>To change your email address, visit http://www.tvbf.org/mailman/listinfo/reflector
>>
>>Visit the gallery!  www.tvbf.org/gallery
>>user:pw = tvbf:jamaicangoose
>>Check new archives: www.tvbf.org/pipermail
>>Check old archives: http://www.tvbf.org/archives/velocity/maillist.html
>>
>>
>>  
>>

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Keith,<br>
I completely agree with you and plan on using my new data to modify my
W&amp;B calculations.&nbsp; Jim S. points out that the factory published
pilot arm may be off a bit. (A 2" change in the pilot seat location
changes my cg by 0.2")&nbsp; Perhaps the calculation can be simplified for
the standard Velocity (I'm not familiar with the XL) because both the
rear seat and the fuel are close to aft cg.&nbsp; Therefore changes in the
reat seat weight and fuel weight will not change the cg much when you
are near aft cg and that is the only time to be concerned about balance
(with the exception of too much weight in the front seat which is a
forward cg issue).&nbsp; Only changes in the front seat weight make a big
difference.&nbsp; So what it boils down to is to determine how much front
seat weight is needed to avoid being aft cg.&nbsp; From my test it appears
that my weight is sufficient for this purpose and that makes it a
no-brainer as long as the plane doesn't leave without me or I don't
become anorexic and lose 50 lbs.&nbsp; My only remaining concern is how much
the fuel can change cg by shifting back during a climb with the tanks
1/2 full.&nbsp; Moving the fuel arm back 2" moves the cg back 0.2".&nbsp; However
if I move myself forward 2" I can cancel out the fuel shift, so I think
I'm covered.&nbsp; I know there are ballfes, but over several minutes the
fuel will get past them.&nbsp; Again I appreciate all comments lest I have
overlooked something.<br>
<br>
John<br>
<br>
KeithHallsten wrote:<br>
<blockquote type="cite"
 cite="mid001b01c3e2b4$ecedbd60$1da33c42@quiknet.com">
  <title></title>
  <meta http-equiv="Content-Type" content="text/html;charset=ISO-8859-1">
  <meta content="MSHTML 6.00.2800.1276" name="GENERATOR">
  <style></style>
  <div><font face="Arial" size="2">John,</font></div>
  <div>&nbsp;</div>
  <div><font face="Arial" size="2">I think the point of doing the
weight and balance measurements and calculations is to have
documentation of the acceptable C.G. range.&nbsp; Then some proposed loading
can be checked before flight to assure that is within the acceptable
range.&nbsp; This is both good practice and required by regulation: it's the
"W" in the "AROW"&nbsp;required documents list.</font></div>
  <div>&nbsp;</div>
  <div><font face="Arial" size="2">Maybe because of my engineering
background, calculating the center of gravity location seems like a
very logical thing to do.&nbsp; I plan to calculate W&amp;B for all of my
proposed loading configurations, then compare those numbers to the
flight characteristics experienced.&nbsp; That way I will know what flight
characteristics to expect when I'm proposing to fly at some different
loading configuration for which I calculate the W&amp;B numbers.</font></div>
  <div>&nbsp;</div>
  <div><font face="Arial" size="2">Keith Hallsten</font></div>
  <div>&nbsp;</div>
  <blockquote dir="ltr"
 style="border-left: 2px solid rgb(0, 0, 0); padding-right: 0px; padding-left: 5px; margin-left: 5px; margin-right: 0px;">
    <div
 style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-stretch: normal; font-size-adjust: none;">-----
Original Message ----- </div>
    <div
 style="background: rgb(228, 228, 228) none repeat scroll 0%; -moz-background-clip: initial; -moz-background-inline-policy: initial; -moz-background-origin: initial; font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-stretch: normal; font-size-adjust: none;"><b>From:</b>
    <a title="aminetech@bluefrog.com"
 href="mailto:aminetech@bluefrog.com">John Dibble</a> </div>
    <div
 style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-stretch: normal; font-size-adjust: none;"><b>To:</b>
    <a title="reflector@tvbf.org" href="mailto:reflector@tvbf.org">reflector@tvbf.org</a>
    </div>
    <div
 style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-stretch: normal; font-size-adjust: none;"><b>Sent:</b>
Saturday, January 24, 2004 10:50 AM</div>
    <div
 style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-stretch: normal; font-size-adjust: none;"><b>Subject:</b>
Re: REFLECTOR:CG Test</div>
    <div><br>
    </div>
Jim,<br>
I appreciate your comments.&nbsp; I suspect a weight/balance would confirm
an aft cg loading according to the numbers that Velocity provides.&nbsp;
What I am trying to do here is establish a limit specific to my plane
which may be different from the standard assuming there are small
differences in how each plane is built.&nbsp; Scott S told me that, for a
standard Velocity, typically 170 lbs in the front seat is enough to put
you within the aft cg limit.&nbsp; So perhaps my plane is different, or
maybe the original cg measurements are off.&nbsp; In any case I think an
actual flying stall test is more meaningful than measurements on the
ground.&nbsp; Of course with flying there is&nbsp; risk involved and the
weight/balance measurement is essential before first flight when you
know nothing about how it will fly.&nbsp; My plane has 280 hours (75 of
which are mine), so I know it flies ok and I'm looking to fine tune
(determine with more certainty) my aft cg limit and hopefully&nbsp; avoid
adding weight to the nose.&nbsp; From recent reflector discussions I felt I
understood the causes and onset indicators of a deep stall as well as
how to recover from it (altitude, prop pitched for power, moveable
weights) and felt sufficiently comfortable to stall the canard near the
aft cg limit.&nbsp; I think doing a weight and balance measurement now is
like measuring the length of the bungee cord after having already
jumped off the bridge.&nbsp; If anyone disagrees, please tell me.<br>
    <br>
John<br>
    <br>
Jim Sower wrote:<br>
    <blockquote cite="mid4011F9AF.FCFC2173@frontiernet.net" type="cite">
      <pre wrap="">Having done what you have done, I would be inclined to muster up some friends and do a
weight/balance with the fuel load you tested with, you *personally* sitting in the
pilot's seat, and the weights you used just as close as you can place them to where
they were in the back seat.
Just to be sure .... Jim S.

John Dibble wrote:

  </pre>
      <blockquote type="cite">
        <pre wrap="">I decided to do a test to determine my aft cg limit as suggested by
Scott B.  My balance calculations for my SRG indicate I will be aft cg
with less than 250 lbs in the front seats.  I weigh 170 so this needs to
be resolved and nose weight added if needed.  I put 8 x 10lb weights in
the copilot seat.  At 7500' I trimmed for 75-80kn and pulled back until
the canard stalled at 60kn.  It took all the aft stick and I had to trim
to about 70kn in order to stall the canard.  The canard motion was
gentile and the plane was a bit wobbly, but stable.  One-by-one I moved
the weights to the rear seat and repeated the stall.  Each time the
canard motion was less pronounced.  With all the weights in the back
seat the canard just kind of mushed down at 58kn.  In all cases I had to
maintain aft stick pressure to get slow enough to stall and never had to
push the stick forward.  I should add that I have 3 leading edge
vortilons and one trailing edge fence inboard of the aileron on each
wing.  So it appears that I do not need to add any nose weight.  Anyone
agree/disagree?

John
    </pre>
      </blockquote>
      <pre wrap=""><!---->
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