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(Earl Stahl's Vultee XP-54... pg.2)
I was lucky to have Mike Midkiff with me during
initial flight tests of the plane. It also helped
to have my fearless chief test pilot, Hy G. Bender
at the controls. We started out by estimating
the location of the C.G. I added a big clay glob
to the nose to balance where we thought might
be a good start. Glide tests showed that the incidence
angle of the stab (as per plan) was creating too
much of a nose-up attitude, so we added a substantial
trim tab on the elevator to tone things down.
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After a few glides we wound in about 300 turns into
the motor. I started out with two loops of 1/8 and
one loop of 1/16 about 24 inches long. The first
flight was surprisingly smooth with a distinct hard
turn to the left caused by torque from that big
fan. We added some clay to the right wing tip to
compensate but ended up adding a small trim tab
as well.
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We then added a little nose weight to adjust the
glide. As we continued to adjust and add more turns,
we decided to remove the 1/16 strand and discovered
that two loops of 1/8 are enough to power this ship
with a resulting drop in torque. We were then able
to adjust the wing tab and remove almost all of
the clay on the wing tip for some nice flights of
30 seconds or better on 800 turns.
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Torque was still fairly high because she would climb
left until the motor reached cruise power and then
she would transition smoothly to a right hand circle.
We decided to give up for the day after about a
dozen flights feeling that we were ahead. I decided
that the prop area was a little too large and I
was not happy that the blades were made from cut
down plastic Peck prop blades. So I decided to make
a smaller area prop out of balsa to conserve on
weight.
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We were flying in an area with six foot
tall Johnson grass around us, and we almost
lost this ship twice in these weeds. The
picture to the right shows why. I never
claimed to be the brightest bulb on the
family tree... flying grass colored model
in these weeds.
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I trimmed 1/8" off the back of the props and
just cleaned them up for starters. The reduction
in area had positive effect on power but torque
seemed to still be there. The thrust adjustment,
1/16 shim at top of plug is definitely needed. Afterwards,
the first few flights were nice lazy climbs to the
left with a transition to a right hand turn about
midway through the motor run. But when power ran
out the glide was terrible. I played with the nose
weight and stab trim, and got only mediocre results.
Seemed like it was nose heavy on the glide. So I
pulled some weight off, and it then stalled in the
climb. I adjusted some nose down in the tab, which
helped, and I decided to leave while I was ahead.
So I returned home and, using acetone, I adjusted
the stab angle leading edge up about 2 degrees which
puts it 1 degree negative relative to the unadjusted
thrust line.
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