have done everything possible to keep my Patrol as light as possible
and today is the day I find out if I accomplished it. Most
Patrols have been coming in 1,120 and 1,200 lbs. My goal is to
have one closer to Bob's prototype Patrol which came in at 1,027 lbs.
Since his had a fixed pitch prop and mine has a constant speed
prop, mine will likely be a bit heavier, maybe somewhere around 1,050
lbs. so that is my goal - 1,050 lbs. Let's see how I did.
My EAA chapter has a simple set of scales that involve a
4:1 ratio device that allows you to weigh it on regular bathroom
scales. My first goal was to assure the scales were as accurate as can
be. To assure accuracy, I used a digital scale to calibrate the
other three scales. The digital scale is really accurate.
calibrate all the scales, I weighed my friend Mickey on the digital
scale and then weighed him on the other three scales, calibrating each
scale to read the same with him on each one.
with all the scales reading Mickey's weight of 179 lbs. exactly the same as the digital
scale, it was time to place a calibrated scale under each wheel and set the
airplane in the flight level condition.
You can't just jack up
each main wheel because the jack is in the way of the 4:1 scale device.
In order to pick up each wheel, we used the old fulcrum and lever trick
that we all learned in elementary school
with a 4:1 scale device under each main wheel, the tailwheel was
set on a single scale. Since the tailwheel is within the weight
limits of the scale, no 4:1 device is needed for it.
had to put a block of wood under the tire to make the fuselage
perfectly level. The scale is adjusted to read zero with just the
block of wood on it.
we checked that the fuselage was perfectly level at the bottom longeron
just behind the main gear mounts. Here is Burl checking it with a level:
Here is a picture of the 4:1 device with the scale under it. This looks pretty crude but is fairly accurate:
Note the plumb-bob hanging down from the leading edge of the wing.
Here is an overview of the whole set-up for weighing the airplane.:
Next we took measurements from the Plumb-bob line to all the critical locations:
Center of main axles (minus 2")
Center of tailwheel axle (203")
Center of Pilot's seat (10")
Center of Fuel Tank (22")
Center of Rear Seat (46")
Center of Baggage compartment (75")
with all of the weights and all of the measurements from the datum (the
leading edge of the wings) its time to do some calculations. A lot of head scratching and noodling going on here:
Here is what we came up with. The Patrol came in at 1,061 lbs.
A little shy of my goal of 1050 but still a very respectable
weight. Here is our report:
Bearhawk Patrol N316BP Weight and Balance
Max Gross Wt = 2000 lbs.
= Leading edge of wing
Forward CG Limit =
10.5" - 16%
Aft CG Limit =
21.5" - 32.5%
Main Gear R
Main Gear L
Here is a PDF showing the empty weight figures and some sample loadings both forward Cg and max aft CG with Max Gross weight. Click here for the PDF