Aerospace and Electronic Systems Magazine October 2017 - 20

Measurement of Wing Deflections in Flexible Aircraft

BIXLER 2 MODEL AIRCRAFT
The Bixler 2 is a radio controlled, electrically-powered model aircraft. The body, wings, and tail are made entirely of foam, and
the onboard motors are driven by Lithium Polymer batteries. Its
specifications are listed in Table 1 below.

Table 1.

Specifications of Bixler 2 Aircraft.
Property

Value

Material

Expanded Polyolefin
Foam

Wingspan

59.05″

Length

37.91″

Weight

1.675 lbs

Motor

2,620-1,300 kv Brushless
Outrunner

Propeller

7×5

As described earlier, each wing of the model was paired with
one SansEC sensor. The left wing had its sensor mounted on the
upper surface, and the right wing had its sensor mounted on the
lower surface. Both sensors were located approximately equidistant from the centerline of the model, and were mounted to the
wing using a thin layer of epoxy. Grooves were also cut into the
wing to form a channel for the installation of the antenna. The
grooves allowed the antenna wiring to sit flush with the wing, so
as not to disrupt the flow of air around the wing during the wind
tunnel test. The antenna was then embedded into the wing using
silicone adhesive sealant. The silicone prevented the wiring from
dislodging itself from the channel during the test, while still allowing the wing to remain flexible. Figure 11a depicts the SansEC sensor mounted on the top of the left wing, while Figure 11b provides
a close-up view that shows the floating electrode attached to the
SansEC sensor. In Figure 11a, note the antenna wiring surrounding
the sensor. The wiring for the antenna was then run into the cockpit
of the model, where the network analyzer was mounted during the
wind tunnel test. A Universal Serial Bus cable was routed from the
network analyzer, through the wind tunnel wiring conduit, and out
of the wind tunnel, where it was then connected to the laptop used
to record the sensor's frequency response during testing.

EXPERIMENTAL PROCEDURES

Figure 11.

(a) SansEC mounted on wing of model aircraft with antenna surrounding sensor. (b) Close-up view of the underside of the wing showing the
floating electrode attached to the SansEC.

The experiments were divided into two phases. The first phase
sought to characterize the shift in SansEC's frequency response
through static bench testing using a whiffletree. The second phase
repeated the same with the aircraft mounted in a wind tunnel.
Static Bench Testing: The static bench test involved attaching a whiffletree loading structure to the wings of the model, and
then incrementally loading the tree with weights, so as to bring
about progressively increasing amounts of tip deflection. It is
noted that the whiffletree is used to obtain an elliptical load distribution on the wings, which is typical of what they experience
in flight. Two foam supports were constructed to support the nose
and the tail of the model. The model, with the whiffletree attached, was then secured to the supports. The setup is illustrated
in Figure 12.
With the network analyzer connected to the left sensor,
weights were progressively added, up to approximately 5.5 kg.
At each weight interval, once the wing had stabilized and any
transient oscillations had dampened out, the network analyzer
was used to interrogate the sensor and frequency response data
was captured. Once completed, the entire loading process was
repeated with the network analyzer connected to the sensor on
the right wing.
Wind Tunnel Testing: The wind tunnel test was conducted at
the Walter H. Beech Wind Tunnel, at Wichita State University. The
wind tunnel is a subsonic, return type, closed-throat facility, with a
test section of height 7 ft, width 10 ft, and length 12 ft. This facility is regularly utilized by the private industry, government agencies, and educational institutions for the purpose of aerodynamic
research and testing. Figure 13 pictures the model mounted inside
the wind tunnel prior to the start of testing. The test plan included the model being mounted at several angles of attack while the

IEEE A&E SYSTEMS MAGAZINE

OCTOBER 2017

Table of Contents for the Digital Edition of Aerospace and Electronic Systems Magazine October 2017