REFLECTOR: MODIFICATIONS - Aft cg limit

[Douglas Holub]

Thanks, everyone. Great info.
----- Original Message -----
From: "John Dibble" <aminetech at bluefrog.com>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Sent: Wednesday, January 05, 2005 3:13 PM
Subject: Re: REFLECTOR: MODIFICATIONS - Aft cg limit


>
>
> Douglas Holub wrote:
>
> > I wish there was a way to determine by testing where the aft c.g. limit
is
> > on a Velocity, the c.g. at which a deep stall occurs.
>
> I believe there is a way.  At least I have done so with my SERG because I
wanted to
> know for sure where the aft cg limit is for my plane.  The factory numbers
are general
> ones and I expect they are a bit conservative for liabiity if for no other
reason.
> The thing is, if you are going to perform stalls where you may be aft of
the true cg
> limit for your plane, you have to understand the deep stall issue and how
to
> avoid/deal with it.  Last year Scott B gave an excellent description of
how to perform
> a stall test and how to be aware of when you are about to enter a deep
stall.  Here is
> what he wrote:
>
> 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) and wait for the onset of the 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 -
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.
> SB
>
> To better understand the aft cg situation, I think it helps to consider
the
> following.  The moment arms for the rear seats and the fuel tanks are both
close to
> the aft cg limit.  Therefore when the plane is loaded near aft cg, fuel
and weight in
> the rear seats have little affect on the cg location.  The only thing that
matters is
> the weight in the front seats.  Of course weight in the nose matters, but
I'm assuming
> that does not change.  So as long as you have sufficient weight in the
front seats,
> you will be within the aft cg limit for your plane.  If you can stall the
canard, then
> you are within the aft cg limit.  If you can stall the canard when flying
solo with no
> other weight in the front, then you never have to do an aft cg calculation
again,
> unless you lose weight or a lighter pilot solos in your plane.
>
> John
>
>
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