Page 21 - Index

mass with flap=7 degrees, the tailplane efficiency factor
variation of pitching from 1.0 decreases.
(100%) to 0.5 (50%), the effects
of icing on the aircraft tailplane
were simulated (see Figure Dynamic Stability
7). The results show that the For model validation purpos-
pitching moment versus angle es, the longitudinal dynamics
of attack gradient decreases as were analyzed by excitation of
the horizontal tailplane efficien- the short-period and long-pe-
cy decreases therefore aircraft riod modes using the eigen-
static stability also decreases as vectors (specific to modes) of
horizontal tailplane efficiency Matrix A to specify initial con-
decreases. ditions. The variables simulat-
The results also show that ed were relative changes (var-
the angle of attack for trimmed iations with respect to a trim
flight conditions increases as condition). The results show
tailplane efficiency decreases. that for a horizontal tailplane
Analysis of horizontal tailplane efficiency of 100% the aircraft
efficiency versus stick-fixed is statically and dynamically Figure 7. Pitch stability—pitching moment versus angle of attack.
static margin suggests that static stable with heavy and moder-
margin decreases as the horizon- ate damping for the short-pe-
tal tailplane efficiency decreases riod oscillation (SPO) and
and that the aircraft is neutrally long-period oscillation (LPO),
(statically) stable when the hori-
zontal tailplane efficiency is ap- respectively. In addition, the
proximately 0.68 for the generic model was independently ver-
business jet model in given flight ified by comparing results to
conditions (see Figure 8). a reduced order mode. When
Further analysis of elevator the efficiency is reduced to
deflection versus horizontal 80%, the response for the LPO
tailplane efficiency (see Figure is also stable, although with
9) suggests that increasing up less damping of oscillations
elevator (-VE deflection) is than the 100% efficiency case
required to maintain trimmed (see Figure 10, page 22). The
flight as the horizontal tailplane results of the dynamic stability
efficiency decreases. The range are in agreement with those of Figure 8. Elevator deflection versus tailplane efficiency.
of elevator deflection for the the static stability analysis.
generic business jet model was
20 degrees up and 15 degrees Effects of Flap Retraction
down. The results suggest that The results of a flap retrac-
as horizontal tailplane efficiency
decreases below approximately tion following a simulated
0.2 (20%), there is insufficient up tailplane stall (see Figure 11,
elevator to maintain trimmed page 22) were analyzed with
flight. the tailplane efficiency of
In summary, using estab- 100% and the flap deflection
lished theory and aircraft design of 7 degrees. At t=4 seconds, a
application software for a given tailplane stall was modeled by
generic business jet model, it a step reduction of 50% to the
was shown that horizontal tailplane efficiency,
• static stability decreases as which destabilizes the system
tailplane efficiency factor response. The aircraft pitches
decreases.
down (-30 degrees) within
• static margin decreases as 2 seconds. At t=6 seconds,
tailplane efficiency factor the retraction of flaps from 7
decreases. degrees to 0 degrees initially Figure 9. Tailplane efficiency factor versus static margin.
• neutral static stability is at helps, but not sufficiently to
approximately 68% tailplane stabilize the response with efficiency a large 20-degree elevator down during 1 second is
efficiency factor. 50% tailplane efficiency. The needed to initiate a large magnitude but stable phugoid response,
• negative static stability is effect of tailplane efficiency which is shown during the first 20 seconds for comparison pur-
poses.
at 20% airplane efficiency on the initial response to a 1 At 50% efficiency, a 1 second 2-degree elevator down input
factor. second elevator impulse (see destabilizes the system with oscillations, and at 20% efficiency,
• increasing up elevator (-VE) Figure 13, page 23) shows that 1-degree elevator down is sufficient to produce very fast diver-
is required to compensate as at 100% horizontal tailplane gence without oscillations. Load factor changes with 1 second el-
October-December 2021 ISASI Forum • 21