REFLECTOR:Determining AFT CG Limit
John Dibble
reflector@tvbf.org
Wed, 10 Dec 2003 13:06:54 -0600
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Scott Baker wrote:
> Lack of pitch stability is certainly a clue.
> Set out a detailed, conservative flight test program to determine the
> aft cg limit of your aircraft.
> Step 1. would be to calculate the loading conditions to achieve a
> rear-most cg (as shown in the POH).
> Step 2. would be to load the aircraft so that the cg of the aircraft
> is ... say 2" forward of the rear most suggested limit and go fly the
> aircraft. At a safe altitude and at a safe location - enter slow
> flight (75-80 knots) and raise the nose (about 7-10 degrees pitch up
> attitude) into a low power climb (about 16" map or around 1800 rpm)
Do you recommend leaving the pitch trim at the 75-80 kn setting or
triming for the low power climb? I think it should stay at the 75-80 kn
setting to allow more forward stick room if the canard begins rising.
> and wait for the onset of the canard stall.
Can you describe the onset of canard stall?
> Try to hold the pitch attitude during the stall. If the nose is
> dropping and (in order to maintain the constant climb attitude) you
> are pulling "nose up" stick force, this is good. Land, calculate what
> it will take to shift the cg aft another 0.5" and go do it again.
> VERY IMPORTANT NOTE> If, on the other hand, at the onset of the stall
> you find the canard rising - and you are pushing on the stick to
> maintain the constant climb attitude
How fast does the rising occur? Is it similar to the canard rise
following rotation?
> - you are in the dreaded "too far aft" cg range ... immediately apply
> full forward elevator and full power, lean forward, and take thyself
> back to the airport and (while adding 5 knots to your normal approach
> speed) ... land and shift some weight forward ... and then go do it again.
I'm thinking of putting several 10 lb weights in the co-pilot seat to
get within the aft cg limit, do the canard stall, and then repeat,
putting the weights in the back seat one-by-one until I find the exact
cg limit.
John
> SB
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Scott Baker wrote:<br>
<blockquote type="cite" cite="mid001201c3bc21$e05315f0$0200a8c0@DAD">
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<div><font face="Arial" size="2">Lack of pitch stability is certainly
a clue.</font></div>
<div><font face="Arial" size="2">Set out a detailed, conservative
flight test program to determine the aft cg limit of your aircraft.</font></div>
<div><font face="Arial" size="2">Step 1. would be to calculate the
loading conditions to achieve a rear-most cg (as shown in the POH).</font></div>
<div><font face="Arial" size="2">Step 2. would be to load the
aircraft so that the cg of the aircraft is ... say 2" forward of the
rear most suggested limit and go fly the aircraft. At a safe altitude
and at a safe location - enter slow flight (75-80 knots) and raise the
nose (about 7-10 degrees pitch up attitude) into a low power climb
(about 16" map or around 1800 rpm)</font></div>
</blockquote>
Do you recommend leaving the pitch trim at the 75-80 kn setting or
triming for the low power climb? I think it should stay at the 75-80
kn setting to allow more forward stick room if the canard begins rising.<br>
<blockquote type="cite" cite="mid001201c3bc21$e05315f0$0200a8c0@DAD">
<div><font face="Arial" size="2"> and wait for the onset of the
canard stall.</font></div>
</blockquote>
Can you describe the onset of canard stall?<br>
<blockquote type="cite" cite="mid001201c3bc21$e05315f0$0200a8c0@DAD">
<div><font face="Arial" size="2"> Try to hold the pitch attitude
during the stall. If the nose is dropping and (in order to maintain
the constant climb attitude) you are pulling "nose up" stick force,
this is good. Land, calculate what it will take to shift the cg aft
another 0.5" and go do it again.</font></div>
<div><font face="Arial" size="2">VERY IMPORTANT NOTE> If, on the
other hand, at the onset of the stall you find the canard <em>rising</em>
- and you are pushing on the stick to maintain the constant climb
attitude</font></div>
</blockquote>
How fast does the rising occur? Is it similar to the canard rise
following rotation?<br>
<blockquote type="cite" cite="mid001201c3bc21$e05315f0$0200a8c0@DAD">
<div><font face="Arial" size="2"> - you are in the dreaded "too far
aft" cg range ... immediately apply full forward elevator and full
power, lean forward, and take thyself back to the airport and (while
adding 5 knots to your normal approach speed) ... land and shift some
weight forward ... and then go do it again.</font></div>
</blockquote>
I'm thinking of putting several 10 lb weights in the co-pilot seat to
get within the aft cg limit, do the canard stall, and then repeat,
putting the weights in the back seat one-by-one until I find the exact
cg limit.<br>
<br>
John<br>
<blockquote type="cite" cite="mid001201c3bc21$e05315f0$0200a8c0@DAD">
<div><font face="Arial" size="2">SB</font></div>
</blockquote>
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