REFLECTOR:CG Test
John Dibble
reflector@tvbf.org
Sat, 24 Jan 2004 12:50:02 -0600
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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
>>
>>
>
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Jim,<br>
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.<br>
<br>
John<br>
<br>
Jim Sower wrote:<br>
<blockquote type="cite" cite="mid4011F9AF.FCFC2173@frontiernet.net">
<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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