REFLECTOR:WEIGHT & BALANCE

Donald Royer reflector@tvbf.org
Sun, 25 Jan 2004 14:24:23 -0700


I wanted to check my construction manual before I entered this discussion.
When Tom started this thread, I read the information in my POH and it
struck me that there was a potential problem with the instructions given
there. (Incidentally the same information is given in the Final Assembly
and Finishing chapter of the construction manual.)  I feel that an
uncritical use of the instructions in the POH could lead to placing the CG
box about one inch aft of it's correct position. When we are talking about
the CG box one inch is significant.

The problem is the placement of the Reference Datum. According to my
reading of the construction manual, the Datum should not be the physical
nose of the aircraft, but rather the famous bolt hole in the fuselage
flange. On the first page of Chapter 5 Bulkheads, there is a boldfaced note:

NOTE: THERE IS AN INDEX HOLE IN THE FUSELAGE FLANGE 1" FORWARD OF THE
AIRPLANE. ALL MEASUREMENTS ON THE PLANE INCLUDE THIS 1".

Since this note is given in conjunction with the placement of the bulkheads
which determines the placement of the wings, I assumed that it would carry
over to the weight and balance measurements. At least that is the way that
I did the weight and balance on my plane. Before I cut off that last bit of
flange, I carefully measured the  front face of the canard bulkhead and it
was the required 38-1/2" from the reference hole so that I had a known
secondary reference. Note that when the POH calls for datum, it places
(nose) in parentheses.

If my interpretation is wrong, my CG box is one inch too far forward, but I
think that is unlikely. Because, while I have not done the aft CG flight
check, we had to get the CG about a half inch forward of the aft limit to
get enough nose down attitude to do the control flutter test at 210 knots.
(My elevator travel is slightly better than the book values in both
directions.)

Tom, I know that you are putting a 540 in a standard fuselage. Do you know
whether there were any changes made during the construction of the fuselage
to accommodate this engine? If there way any changes made in the location
of the main wing or the canard then all bets are off and you are on your
own! Incidentally, you are probably going to require a substantial amount
of nose ballast to keep the nose wheel on the ground when the plane is
empty. In my case, with a standard fuselage LW Elite with a Franklin engine
and an MT propeller, my empty plane CG (no fuel ,no pilot) was only 3-1/2"
forward of the main gear axles. This put about 30lbs on the nose wheel. I
have placed about 35lbs. of lead in the nose to make it safe to leave it
unattended on the ramp.

:

> [Original Message]
> From: Scott <scott@tnstaafl.net>
> To: <reflector@tvbf.org>
> Date: 1/25/04 7:47:08 AM
> Subject: Re: REFLECTOR:WEIGHT & BALANCE
>
> Its in the POH.
>
> You'll need to weigh the plane per the instructions to set up your 
Utility 
> or first flight CG box.
>
> Scott
>
> At 05:54 PM 1/24/2004, you wrote:
> >I bought a kit in progress, along with manuals, etc.
> >
> >With the help of professionals and consultation of factory reps, I am 
> >nearing completion (minus pain and interior).
> >
> >I have looked through my paperwork and cannot find weight and balance 
> >information.
> >
> >I simply want a CG envelope and the reference "datum" used by the
factory, 
> >along with maximum gross weight.
> >
> >With these pieces of information, I plan on simply doing an empty
weight, 
> >calculating the empty CG and proceeding with various loading scenarios.
> >
> >Does anyone have the W&B info I am seeking?
> >
> >
> >
> >
>
>
> "Those who sacrifice freedom to get security, deserve neither."
> - Benjamin Franklin
>
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