Euclid sUAV Handling Qualities Evaluation Through Flight Simulation, Using Cooper-Harper Handing Qualities Rating Scale

Wingspan $$\bm{b}\mathbf{ }\left(\bm{m}\right)$$

Maximum Take Off Mass (MTOM) (kg)

Main wing area (S) (m²)

Stall (V_s)

Cruise (V_c)

Max (V_max)

2

2

0.35

9

15

30

Short Period

Damping ratio ζ_s = 0.702

1

Phugoid

Damping ratio ζ_p = 0.01

2

Roll subsidence

Roll mode time constant T_r = 0.36

1

Dutch Roll

Damping ratio ζ_d = 0.176

1

Spiral

Spiral mode time constant Τ_s = 12.93

2

Test description

Operator deflects from $${+\bm{\delta }}_{\bm{m}\bm{a}\bm{x}}$$ to $${-\bm{\delta }}_{\bm{m}\bm{a}\bm{x}}$$, all aircraft’s control surfaces (flaps, ailerons, rudder, elevator), twice, on ground. The purpose of this test is to make sure all control surfaces are moving freely and in the correct direction. It is a necessary preflight test, and it does not participate in the final score.

Result remarks

All control surfaces are moving freely and in the correct direction.

Cooper-Harper score

First evaluator N/A, Second evaluator N/A, Third evaluator N/A

Test description

It is a necessary test for hand launched UAV’s, such as Euclid. A reason Crrcsim flight simulator was chosen is because its ability to simulate hand launched procedures. Three main variables must be defined for the procedure:

1. Launch height, in 1 ft increments. This height is defined at 6 ft (~1.8 m), as a typical height a human’s hand can reach at an upwards semi-stretched position.

2. Initial θ pitch angle in rads. 3 different θ angles were simulated (0 rad, 0.262 rad & 0.524 rad), which correspond to 0°, 15° and 30° respectively.

3. Escape velocity $${\bm{V}}_{2}$$, calculated at 36.8 ft/s (11.2 m/s), using the UAV hand launch formula [2].



To record the θ angle at which the operator feels safer to launch the vehicle



To record the minimum throttle (%), the aircraft can be hand launched with the optimum θ angle.

Result remarks



Vehicle is able to be hand launched.



Among the three θ angles, θ = 15° is considered to be the safest.



At θ = 15°, the operator will find it hard to launch the vehicle using throttle <60%.



At θ = 15°, the operator will not face any difficulty at all, launching the vehicle at full throttle.



A general remark is that the operator must avoid violent elevator deflection during the procedure.

Cooper-Harper score

First evaluator 1, Second evaluator 1, Third evaluator 1.

Test description

A simultaneous simulation regarding aircraft’s longitudinal static stability and its short period response, is performed. During Straight and Level Flight (SLF), the operator temporarily cuts off the engine power, so the generated force from it, not to affect the progress of the phenomena. Afterwards, the operator deflects shortly and quickly the aileron at $$-{\bm{\delta }}_{{\bm{e}}_{\bm{m}\bm{a}\bm{x}}}$$ in order to for positive pitching moment (+Μ) to be produced, for the perturbation to appear. The object of research here is to evaluate the aircraft’s reinstatement to SLF.

Result remarks

Aircraft is longitudinally dynamically (therefore and statically), stable. The phenomenon is evolving absolutely satisfactory.

Cooper-Harper score

First evaluator 1, Second evaluator 1, Third evaluator 1.

Test description

A simultaneous simulation regarding aircraft’s directional & lateral static stability is performed. The flight behavior of both is dynamically reflected through the Dutch Roll output. During Straight and Level Flight (SLF), the operator deflects shortly and quickly the rudder at $$-{\bm{\delta }}_{{\bm{r}}_{\bm{m}\bm{a}\bm{x}}}$$, in order to for negative yawing moment $$\left(-\bm{N}\right)\bm{ }$$to be produced, for the perturbation to appear. For achieving the best results, it is important that the rudder stick returns to its neutral position as fast as possible. The optimum way to achieve this is to simply release the rudder stick and let it return using only the tension of the spring supporting it. The object of research here is to evaluate how well the Dutch Roll movement is damped.

Result remarks

Dutch Roll outputs a healthy damping ratio.

Cooper-Harper score

First evaluator 1, Second evaluator 2, Third evaluator 1.

Test description

Aircraft launches and after it gains safe altitude, it implements two sequential ascends and descents, deflecting the elevator only. In a well-trimmed aircraft only pithing angle θ should alter and none of φ & y angles, indicating that the aircraft’s Center of Gravity (CG) is in symmetry with $$\left(\bm{O}{\bm{x}}_{\bm{s}}{\bm{z}}_{\bm{s}}\right)$$ plane of stability axes. The object here is to evaluate if only θ angle is altered and the handling quality of the movement.

Result remarks

Only θ angle is altered, and the pitch handling is absolutely satisfactory.

Cooper-Harper score

First evaluator 1, Second evaluator 1, Third evaluator 1.

Test description

The aircraft launches, and after it gains safe altitude, it implements three indicative small bank turns using only the ailerons. The expected behavior and subject of evaluation should be mainly a variation in the roll angle (φ) and secondarily a smaller variation in pitch angle (ψ), because the UAV is designed with $${\mathbf{ }\mathbf{C}}_{{\bm{n}}_{{\bm{\delta }}_{\bm{a}}}\mathbf{ }}$$ > 0.

Result remarks

When deflecting ailerons, the aircraft is behaving exactly as expected.

Cooper-Harper score

First evaluator 1, Second evaluator 1, Third evaluator 1.

Test description

Aircraft launches and after it gains a safe altitude, only the rudder is deflected. The expected behavior and subject of evaluation should be mainly a variation in pitch angle (ψ) and secondarily a smaller variation in roll angle (φ), because the UAV is designed with $${\mathbf{C}}_{{\bm{l}}_{{\bm{\delta }}_{\bm{r}}}}$$ > 0.

Result remarks

When deflecting the rudder, the aircraft is behaving exactly as expected.

Cooper-Harper score

First evaluator 1, Second evaluator 1, Third evaluator 1.

Test description

While in SLF, the circular trajectory loop maneuver is executed with max thrust during ascent. The objective here is to investigate if the produced thrust is capable of executing the maneuver, and the pilot’s comfort while executing the maneuver, for the given type of aircraft.

Result remarks:

The aircraft is capable of executing the loop maneuver with adequate pilot comfort.

Cooper-Harper score

First evaluator 2, Second evaluator 1, Third evaluator 1.

Test description

While in SLF, a full 360° rotation is performed around the x axis, deflecting only the ailerons. Objective here is for the UAV to return to its initial position, with acceptable altitude loss.

Result remarks

Aircraft is capable of executing the roll maneuver with adequate pilot comfort and acceptable altitude loss.

Cooper-Harper score

First evaluator 2, Second evaluator 1, Third evaluator 2.

Test description

While in SLF, a 180° rotation is performed around the x-axis, and the UAV remains in this inverted position for 10 s. The objective here is to investigate if the aircraft is capable of sustaining inverted flight according to the CL_min variable’s value calculated and imported to the flight simulator FDM. If the aircraft can execute inverted flight, the minimum throttle (%) should be recorded for sustaining this flight condition.

Result remarks

The aircraft is capable of flying inverted with a minimum throttle of 75%.

Cooper-Harper score

First evaluator 1, Second evaluator 1, Third evaluator 1.

Test description

While in SLF, the aircraft performs the Immelmann maneuver with full throttle during ascent. If the aircraft can execute the loop maneuver, it should be able to execute the Immelmann maneuver as well. The object here is to evaluate the pilot’s comfort while executing the maneuver.

Result remarks

The aircraft is capable of executing the Immelmann maneuver with adequate pilot comfort.

Cooper-Harper score

First evaluator 2, Second evaluator 2, Third evaluator 2.

Test description

Split-S is a reverse trajectory maneuver of Immelmann’s. The main difference between the two is that Split-S does not require great thrust forces by the engine, because it takes advantage of the potential energy the aircraft has gained due to altitude. The object here is to evaluate the pilot’s comfort while executing the maneuver.

Result remarks

The aircraft is capable of executing the Split-S maneuver with adequate pilot comfort.

Cooper-Harper score

First evaluator 1, Second evaluator 1, Third evaluator 1.

Test description

While flying at a safe altitude, the engine power is cut off and the aircraft is let to glide for a short distance in order to reduce airspeed. Afterwards, the operator implements an elevator up command, for the remaining lift force to be destroyed completely and to put the aircraft in a stall condition. Operator’s opinion is recorded regarding the easiness of exiting form this condition.

Result remarks

Stall recovery can be executed with varying ease among the evaluators, but is fairly easy for the aircraft’s type and given mass. To exit the stall with this aircraft, all operators aggraded that first a nose down and then a throttle increase should be implemented.

Cooper-Harper score

First evaluator 2, Second evaluator 3, Third evaluator 1.

Test description

Flying at a high AoA, or high alpha, is a dynamically complex and volatile aerodynamic condition, where an aircraft flies at a high angle of attack, for an adequate time, in the borderline between the stall region and the normal controlled flight, without losing altitude [26].

For replicating this flight condition in the flight simulator, the operator must follow the same steps as the previous test 11 until the elevator up command, which should be maintained throughout the whole duration of the maneuver. At the same time, the operator must regulate the aircraft’s thrust accordingly, in order to maintain the evolution of the maneuver, even when φ & ψ angles are changing. High AoA is a test of great importance, because it can evince whether the lift distribution upon the wing is in truth elliptical as designed, and the wingtips will not suffer a stall before the wing root, resulting in aileron ineffectiveness and lost of control.When executed in the flight simulator, high AoA is better performed near the ground so the evaluator has a better perspective on possible altitude loss.

Result remarks

High AoA flight conditions can be performed safely. Aircraft is fully controllable, even when φ & ψ angles are changing.

Cooper-Harper score

First evaluator 1, Second evaluator 1, Third evaluator 1.

Test description

According to Sadraey [3], spin is a dangerous and continuous rotation of an aircraft around its z axis, which may occur after a stall. Aircraft suffers altitude loss with Rate of Descent (ROD) equal to 20–100 m/s and a Rate of Spin (Ω) equal to 20–40 rpm. Along with its axial rotation, it writes off a helicoid trajectory in space, with a radius equal to its semispan (R = b/2). Every aircraft type demonstrates a different behavior regarding spin. Usually, prone to spin are fighters and aerobatic aircrafts. The very opposite behavior have a lot of transport aircrafts, which are designed to exit the spin easily using big rudders (spin proof), or even being immune to spin (unspinnable).

A beneficial contribution to avoid, or to easily exit a spin, has the proper mass distribution within the aircraft itself, which affects the aircraft’s moments of inertia.

Official Federal Aviation Administration (FAA-H-8083-3C) textbook [27] describes exactly the procedures that must be followed by a pilot to willfully enter into a spin and to exit from it as well. In brief, to enter a spin after a stall, the pilot must deflect the rudder by $${\bm{\delta }}_{\bm{m}\bm{a}\bm{x}}$$ and to exit from the spin a $${\bm{\delta }}_{\bm{m}\bm{a}\bm{x}}$$ rudder of opposite direction must be applied.

For the current simulated spin test, the UAV operator is encouraged to follow the aforementioned procedure to record whether the UAV can enter a spin and, if so, to evaluate the ease of the exit attempt from it.

Result remarks

After multiple attempts to put the UAV into a spin, no one among the three evaluators succeeded to spin the aircraft.

Cooper-Harper score

First evaluator 1, Second evaluator 1, Third evaluator 1.

Test description

It concerns of a simple glide test, which aims to visually demonstrate in the computer screen, the C_L/C_D glide ratio of the UAV, which was found to be equal to 22.3 during Euclid’s aerodynamic simulations.

The current test is performed from a high altitude, with a disabled engine. Projected to earth travel distance, ability of controlling the UAV, and easiness of landing are evaluated.

Result remarks

The UAV is able to glide with ease, covering a safe distance upon its landing. During the glide test, evaluators agreed that the aircraft is well controlled as long as small and smooth inputs are given to it from the controller.

Cooper-Harper score

First evaluator 2, Second evaluator 1, Third evaluator 2.

Test description

This test assesses the flaps effectiveness during descent and landing. Flaps usage is evaluated regarding its ability to lead to a safer and of a short distance and speed, approach, and landing.

Result remarks

Using flaps, the aircraft can land more safely. Approach and landing distances and speeds are shortened.

Cooper-Harper score

First evaluator 1, Second evaluator 1, Third evaluator 1.