Testing Concept Aircraft Within X-Plane 10

Once the computational fluid dynamics software had provided a prediction at which airspeeds the aircraft would stall with respect to the angle of attack, the model of concept aircraft 1 was then flight-tested within X-Plane 10.

The flight simulation software was opened and the respective aircraft was uploaded with a minimal payload, which keeps the results constant with those of the CFD testing (whereby only the wing was acted upon by gravity). The aircraft was then taken up to an altitude of around 3000 feet, providing sufficient clearance for the recovery from the stall. At an airspeed of around 150 knots, the throttle was closed and the trim function was used to hold the aircraft at a selected angle of attack. Once the stall warner activated, the attitude was held for a few seconds to continue the deepening of the stall and then the aircraft was recovered by pitching the nose down.

	Minimal Load (5.5 Tonne)		Double Load (11 Tonne)
θ	Indicated Airspeed	Relative Airspeed	Indicated Airspeed	Relative Airspeed
10o	69 kts	67.95 kts	98 kts	96.51 kts
15o	66 kts	63.75 kts	96 kts	92.73 kts
20o	64 kts	60.14 kts	91 kts	85.51 kts
25o	63 kts	57.10 kts	90 kts	81.57 kts
30o	61 kts	52.83 kts	80 kts	69.28 kts

Testing Concept Aircraft Within CHAM Phoenics (CFD Software)

Firstly, the wing was configured at 10^o of pitch and the inlet velocity of 75 knots was chosen. At this speed, the airflow remained attached and the flow lines were constant over the length of the wing.

The inlet velocity was then changed to a lower speed- 65 knots. It was discovered that at this airspeed, the flow of air over the wing began to stall. The velocity plot shown by image 6.2a illustrates that at a distance of 3 metres from the wing root, the airflow started to separate from the upper surface of the wing, and the towards the trailing edge of the wing, the air begun to circulate at a lower speed. Any further reduction in the airflow over the wing would reduce the amount of lift produced by the wing and also further the stall.

Image 6.2a

The angle of attack of the wing was increased to 20^o above the horizon and an inlet velocity of 70 knots was selected. The resultant plot of image 6.2b shows the wing section (7 metres from the root, to the wing tip) established within a stall. The airspeed was then reduced to 60 knots, which caused the whole wing to enter into the stall as shown in image 6.2c. This shows that the critical airspeed for the stall to occur is between 60 and 70 knots.

Image 6.2b

Image 6.2c

Next, the pitch of the wing section was increased up to 30^o angle of attack and a starting inlet velocity of 60 knots was chosen. The fluid flow simulation was then run again and the resultant velocity flow plot was produced, as illustrated by image 6.2d.

Image 6.2d

The velocity plot shown in image 6.2d is position at a distance of 6 metres from the root of the wing, and from this point towards the wing tip the airflow had begun to stall over the upper surface. The inlet velocity was then lowered to 50 knots, in order to ascertain at what speed the whole wing would stall. From the simulation, the velocity plot as shown by image 6.2e was produced. This shows that at this lower speed the area closest to the wing root had stalled. The critical airspeed at which the stalling of the wing occurs is therefore between 50 and 60 knots.

Image 6.2e

Concept Aircraft Sketches

The first of the concept aircraft designs is the most conventionally configured aircraft and was based upon the Embraer ERJ145. It incorporates a mid-wing construction with two fuselage-mounted gas turbine engines. However, that is where the conventional characteristics finish. The tail of the aircraft is of the non-conventional V-tail design, whereby the horizontal and vertical stabilisers are replaced by a V-shaped stabiliser that is able to simultaneously control the pitch and yaw of the aircraft. Image 5.1.1 shows the design sketch for concept design 1:

The second concept aircraft was chosen to be of a completely unconventional configuration for a commercial aircraft. The design includes a forward-swept high-level wing and a canard-style elevator surface. It was also decided that two turboprop engines, similar to those of the Bombardier Dash 8-Q400, would be used to power the aircraft. The design sketch of concept aircraft 2 is illustrated by image 5.1.2:

The third concept aircraft design was the most ‘futuristic’ of the three designs. There are two sets of wings – one set is conventional aft swept wings, and the others are fore swept – and these join at the wingtips to form a blended winglet, preventing the spilling of high pressure air to the region of low pressure above both sets of wings. The aircraft is powered by two gas turbine engines, matching those of concept aircraft 1, and are mounted under the aft section of the wing. Image 5.1.3 shows the design sketch for this concept:

From the sketch, it can be seen that the empennage is of a non-conventional configuration. The vertical stabiliser and rudder control surface are of a normal design, however, the horizontal stabiliser and elevators are not present. Due to the dual wing layout, the aft section of the wing will act as a vertical stabiliser, acting about the centre of gravity, which will lie upon the aircrafts longitudinal axis perpendicular the wing tips. The elevator control surface is also located on the aft section of the wing, where the pitching moment would be at its greatest.

Validation of Results between Plane Maker and X-Plane 10

Due to the discovery during the research period that the importation of CAD models into X-Plane 10 has no effect on the flight simulation calculations, it was necessary for the whole of the modelling to be carried out within the Plane Maker application. However, before any investigations were performed regarding the correlation of the flight simulation and CFD software data, it was necessary to validate that any modifications made within the Plane Maker tool would translate into X-Plane 10, by means of a change in the handling performance.

It was decided that a Cessna 172 would be used to perform the validation, due to the popularity of the aircraft: it is used extensively world-wide for the provision of flight training, and is also provided as standard with a range of flight simulation software packages. The C172 is still in service, and there is an abundance of information available regarding the aircraft’s performance.

The flight simulation software was loaded with the standard Cessna 172 positioned on the threshold of runway 05 left at Manchester International Airport. The throttle was advanced and brakes released. Upon reaching 55 knots IAS, the aircraft lifted off and its attitude was set to give an airspeed of 70 knots IAS. The simulation was video recorded, detailing the length of the take off roll and also the distance for the aircraft to clear a 50-foot object.

Following this, another simulation was carried out to test the climb rate of the standard C172 model. The aircraft was of a clean configuration (flaps retracted) and the autopilot was used to maintain the aircraft’s heading. Using the trim wheel, the C172 was pitched nose high to hold an airspeed of 70 knots IAS. Whilst at this attitude and airspeed, the rate of climb was recorded.

A copy of X-Plane 10’s standard Cessna 172 was then made for the purpose of applying modifications to the aircraft model. Within the Plane Maker application, the aerofoil cross section of the wing was changed from the original NACA 2412 profile to the NACA LS(1)-0417 profile, which is known to have higher lift characteristic. The model was then loaded into the flight simulation software, and evaluated using the same two testing criteria specified above.

The results of the evaluation are as follows:

	Standard Model	Modified Model
Take off distance (ground roll)	840 ft	805 ft
Take off distance (to clear 50 ft obstacle)	1’673 ft	1’552 ft
Maximum climb rate	745 ft/min	987 ft/min