Night Alarm (22h-9h)

Table 12 lists the key design parameters for the Condor aircraft alongside the initial designs of Harmon and Hiserote for a clutch start, charge sustaining aircraft configuration as discussed in Chapter II Section 2.4 [11,10]. The Condor has a slightly smaller wing both in span and total area and a higher aircraft weight, leading to a larger overall wing loading at takeoff. Initially, the Condor was designed with a 4.57 m (15 ft) wingspan to match the aircraft envisioned by Hiserote [12]. Due to concerns about the strength of the wing material, the main wing of the

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Condor was reduced to a 3.66 m (12 ft) span with the option of adding an additional 0.91 m (3 ft) of wing using outboard wing extensions.

During the November 2011 flight test of AFIT-1 using the Honda GX35 engine with the aircraft ballasted to 15.9 kg (35 lbs), a wind gust hit the aircraft in flight with the 4.57 m (15 ft) wing span configuration. The increased lift and resulting wing deflection cracked the fiberglass wing coating approximately 0.6 m (2 ft) from the wing root. Aside from the structural concerns, the 4.57 m (15 ft) configuration was difficult to handle in the air and was prone to sudden

upwards pitching. The stability analysis in [18] also indicated lateral instabilities with the 4.57 m (15 ft) wing span. The larger wing was difficult to handle on the ground and the wing tips were prone to touching the ground during the taxi and takeoff rolls. Based on the experience with AFIT-1, the Condor team decided to pursue the 3.66 m (12 ft) wingspan for testing the HE propulsion system.

Table 12: Comparison of Condor aircraft to initial design estimates Physical Dimensions Harmon Hiserote Condor

Aspect Ratio 14.6 14.42 12

Wing Loading 90 N/m2 _{90 N/m}2 _{140 N/m}2

Wing Area ( ) 1.48 m2 _{1.48 m}2 _{1.115 m}2

Wing Span ( ) 4.65 m 4.62 m 3.6576 m

Wing Chord ( ) 0.32 m 0.321 m 0.3048 m

Aircraft Mass (Takeoff) 13.6 kg 13.6 kg 15.9 kg

Mission Parameters Harmon Hiserote Condor

Takeoff Altitude 1525 m (ASL) 1500 m (ASL) 300 m (ASL)

Mission Altitude 1525 m (ASL) 300 m (AGL) 300 m (AGL)

Endurance time 1 hr 3 hr 1 hr*

Aerodynamic Parameters Harmon Hiserote Condor

CL,max 1.25 1.25 1.507**

CD,o 0.036 0.036 0.040**

Oswald Efficiency Factor ( ) 0.85 0.85 0.85 (estimated)

* Reduced from 3 hours due to poor specific energy of COTS batteries within project budget constraints.

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The Eppler 210 airfoil has a greater CL,max than the NACA 4412 airfoil used in the initial

design simulations. While the aircraft itself uses an Eppler 210 airfoil, data on the Eppler 210 is difficult to find. In its place, both the author and Giacomo used the NACA 4412 data. The NACA 4412 airfoil is similar to the Eppler 210; the main difference is that near the trailing edge the Eppler 210 has slightly more under camber than the NACA 4412. This minor difference gives the NACA 4412 slightly lower induced drag as well as a slightly lower lift coefficient. It is the author's experience that once manufactured, the two airfoils are interchangeable in operation. Manufacturing inaccuracies wash out the theoretical difference between the foils, justifying the substitution of NACA 4412 data in the absence of Eppler 210 data.

Table 12 lists a larger takeoff weight than the ideal aircraft. At the time of the AFIT-1 flight test, the weight of the hybrid system was not finalized. However, based on the selected components, the 15.9 kg (35 lbs) was identified as an upper limit driven primarily by the extra structure, batteries, and avionics of the HE propulsion system. To verify the airframe could handle the increased weight, AFIT-1 was ballasted to 15.9 kg (35 lbs) using simulated payload. For the purpose of simulation, the hybrid system payload capacity is assumed to equal to the difference between the takeoff weight and the 15.9 kg (35 lbs) limit, even though the aircraft was not ballasted for the initial hybrid-electric ground and flight testing.

In his design, Hiserote assumed a battery specific energy of 200 Whr/kg, a high end value for COTS Li-Po batteries. Despite the optimistic battery estimates, Hiserote's optimized aircraft still struggled to perform a simulated 3 hr continuous loiter in some configurations [12]. Meanwhile, the batteries for the Condor are closer to 132 Whr/kg. The Condor batteries were constrained significantly by budget, leading to performance 30% to 40% lower than the

technological cutting edge for Li-Po batteries. Furthermore, other chemistries such as Li-S offer specific energies upwards of 300-600 Whr/kg as discussed in Chapter II, Section 3.4 [57].

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The endurance time of the aircraft is directly proportional to the specific energy of the batteries. From initial estimates, Hiserote's 3 hr loiter [11] was too aggressive for the Li-Po batteries within the ~$2000 battery budget for the project. Therefore, the objective value was decreased to Harmon's 1 hr loiter [10]. Thus, while the Condor falls short of the 3 hr loiter time, additional funding for top-end batteries on the current market as well the future advancements in battery technology could increase the energy capacity of the Condor allowing it to perform loiter missions approaching the 3 hr time frame suggested by Hiserote. The reported loiter time estimates for the Condor should be interpreted as the performance of an airframe constrained by budget and current COTS technology and not as a limit on the possible performance of the airframe under different budget or technological conditions.

Lastly, the designated mission for the actual aircraft has changed slightly from the missions envisioned by Hiserote [12]. The mission altitudes have been decreased to reflect the flight test location at Camp Atterbury, IN. Despite all of the changes from the initial optimized design, the Condor airframe is relatively true to the optimized design, recognizing discrepancies in wingspan and weight primarily due to optimistic design constraints and battery performance predictions.