Aircraft flight analysis report

1. Introduction

1.1 Brief summary

For aerospace engineering, flight testing is a part which focus on data collecting through the flight on aircrafts. To analyze the data, there are a few parameters and background knowledge needs to be determined This report would involve the comparison of Cessna 172 and F-111, the background knowledge of longitudinal static stability and manoeuvre stability, and the data analysis of Jetstream 31

1.1

Cessna 172 Skyhawk is an American 4-seat aircraft which build with a single-piston engine and high fixed wings Since 1956, the first Cessna airplane have been produced. Until 2015, there were over 44,000 have been built by Cessna and its partner company. The model of Cessna 172M built in 1973-76 had a drooped wing that led the edge to make better performance on low-speed handling, which is known as ‘camber-lift’ wing in the market [1].

Cessna 172 follows the mechanical flight control system. The elevator on the tail controls the pitch on horizontal axis by pushing and pulling the control column, the ailerons on the wing control the planes longitudinal axis by turning left or right with the control column, and the rudder on the tail controls its normal axis by the rudder pedal [2]. Cessna 172 has a reversible control system, which allows the pilot to control the plane by moving the stick and the feedback transmitting of the control surface. Also, the Instrument Landing System (ILS) could provide the pilot visual instructions to let him flow down the plane in the pathway by extended the centre line of runway toward decision altitude. Moreover, it enables the plane to land automatically.

Cessna 172

Figure 1. Three view of Cessna 172 [2]

1.2 F-111 Aardvark

1.2.1 F-111A

The F-111A airplane is a two-seat, long-range fighter bomber. Its had featured a pair of variable-geometry wings, which allows a sweeping angle between 6 degrees and 72.5 degrees. The wings include leadingedge slats and double-slotted fowler flaps over its full length Its empennage is built by a set vertical stabilizer with a rudder for direction control, and a rolling tail for pitch and roll control. [3]

The F-111A flight control system is build up with pilot-assist modes, fixed-gain yaw damper, and a command augmentation which can rate the command and adapt the gain scheduling in pitch and roll movements. The terrain-following radar (TFR) could contribute into an automatic flight control system that allows "hands-off" flying at high speeds and low levels. [3]

1.2.2 F-111D

The F-111D is an upgrade of F-111A which equipped more powerful engines and an updated Mark II avionics. For the plane body, the intake geometry and the early glass cockpit has improved With the new Triple Plow II intake, the engine would not easily ingest by the sluggish boundary layer air. [3]

Figure 2 Sketch of F-111 airplane indicating airframe modifications

Table

Comparison of Cessna 172, F-111A and F-111D

2. Longitudinal static stability

2.1 Background knowledge

In mechanical flight control systems, the longitudinal static stability concerns the symmetry of lateral pitch-axis (y-axis) under the steady flight condition. This analysis is important as the pilot could determine whether they should control the pitch of aircraft without excessive attention [4] [5] Assume that the attack angle has been changed, the moment response ΔM should then be concerned by the distribution of angle ΔA. To stay longitudinal static stability, two of the following conditions need to be satisfied:

1.

2.����,��=0 >0 Where α is the angle of attack.

2.2 Stick Fixed and Stick Free Stability

There are two cases for the longitudinal static stability – stick-fixed and stick-free stability. For stick-fixed stability, the pilot could set the stick fixed to make the elevator remained in a fixed position for trimming without power boost However, to control the stick in a fixed position, the pilot needs to pay extra attention to exertmaul force [6]. Onthe other hand, forstick-freestability, the elevator should be free to float with relatively wind as the control stick is left essentially free. The trim-tab would enable to adjust the moment on the elevator to trim the aircraft to an equilibrium position [4].

Figure 3 Longitudinal static stability for lateral pitch-axis

Figure 4. Trim-Tab position for stick-fixed stability

Figure 5. Trim-Tab position for stick-free stability

2.3 Importance of Longitudinal static stability

This analysis of longitudinal static stability is necessary for pilot as they can pay less attention on controlling the pitch of aircraft. However, if the longitudinal static is instable, that may cause a lot of troubles. On 29 April 2013, a Boeing 747-400 crashed at the moments after taking off from Bagram, which took away 7 people’s life on board. The final investigation concludes that because of the improper regulate of cargo, the cargos then rolled to the back side of cargo hold and disabled the rear flight control system. This made the aircraft unable to control, and the aircraft could not be recovered from the

2.4 Data analysis of Jetstream 31

To analyse the longitudinal static stability of Jetstream 31 with real data, there are some parameters needed to be given in the first place:

Table

Given parameters for Jetstream 31 data analysis

Firstly, the total moment of Jetstream 31 needs to be calculated in each group of datasets.

unbalanced weight shifting [7].

2.

Table 3. Moment calculation of Group A

Figure 6. Boeing 747-400 crashed [7]

Table 4. Moment calculation of Group B

Table 5. Moment calculation of Group C

Table 6. Moment calculation of Group D

According to the result in Table 3,4,5,6, the centre gravity (CG) position can be calculated by the following equation:

On the other hand, with the mass calculation in Table 3,4,5,6, the lift coefficient (����) at each point can then be calculated with the following equation:

Where m is the total aircraft mass, ��0 is the acceleration due to gravity, ��0 is the air density at sea level, ���� is the wing area, ���� is the equivalent air speed.

By removing the lift coefficient data which has normal acceleration far away 1, the data set of each group can then be determined.

Table 7. Lift coefficient dataset of each group

2.4.1 Determination of Neutral Point (stick fixed case)

The elevator deflection η vs lift coefficient and in static stability can be compared according to Table 7.

By determined the gradient of and Figure 7, the comparison of ����/������ and vs centre gravity can be plotted, and the Neutral Point can be determined.

According to the result from cg position and Figure 7, it could be determined that while the cg position increased, thegradientincreased. Also, accordingto Figure8, all thedatasets arereaching longitudinal static stability as they located between forward and after limit, and the neutral point can be determined by the x-interception, which is ����.����������������%��.

Figure 7. Static Stability (Stick-Fixed Case)

Figure 8. Determining the Aircraft Neutral Point (Stick-Fixed Case)

2.4.2 Determination of Neutral Point (stick free case)

The trim tab deflection β vs lift coefficient and in static stability can be compared according to Table 7.

By determined the gradient of and Figure 9, the comparison of ����/������ and vs centre gravity can be plotted, and the Neutral Point can be determined.

According to the result from cg position and Figure 9, it could be determined that while the cg position increased, the gradient decreased. Also, according to Figure 10, all the datasets are reaching longitudinal static stability as they located between forward and after limit, and the neutral point can be determined by the x-interception, which is ����.����������������%��.

Figure 9. Static Stability (Stick-Free Case)

Figure 10. Determining the Aircraft Neutral Point (Stick-Free Case)

3. Demonstrate understanding of manoeuvre stability

Manoeuvring flight is the change form one flight state to another. While an aircraft is accelerating, whether it is pulling up, pushing over, or turning, the pitch rate would be generated. Manoeuvre stability would be the determination of the force that needs to be applied on the stick to change the level of constant force applied to the aircraft, which is also known as g-force [8][9]

Assume that the aircraft is flying sprightly and keep in same level height at the initial position, which the lifting force L is equal to weight W. If the pilot pitches the aircraft to a higher attack angle (L>W), the arch of the aircraft would turn up, and the flight path would turn in to a curve in the vertical plane, with a turn radius R and pitch rate �� = ����/����, where �� is the pitch angle. This operation has been known as pull-up manoeuvre [1].

Figure 11 Manoeuvring flight

Figure 12. Pull up manoeuvre – circular motion in the vertical plane.

When the aircraft is in longitudinal manoeuvre stable, it needs to satisfy the following condition [8]:

While

=0, manoeuvre is remained steady

Where �� is the elevator angle, �� is the pitching moment

Just like static longitudinal stability, the stick-fixed manoeuvre stability and stick-free manoeuvre can be determined. However, in longitudinal manoeuvre stability, the pitch rate needs to be considered as an additional factor.

With stick-fixed condition, the manoeuvre margin could be determined as the distance between the centre gravity and the manoeuvre point. It would also know as the measurement of manoeuvrability [9].

While doing conceptual designing, the stick-free neutral point would be closer to the central gravity compared with the stick-fixed neutral point It can make the centre gravity smaller for the aircraft [8]

Figure 13. Manoeuvre margin

Figure 14. Neutral point location

4. Conclusions

4.1 The importance of flight testing

Flight testing is part of aerospace engineering which focus on the data collection during the flight of aircraft. By analyzing the data, the information of flight characteristic can be evaluated and use for designing or safety aspects. There are two major tasks for the accomplishment of flight test –fixing, finding the issues, and double-checking the capability of vehicles that are acceptable for customer acceptance [10].

4.2 Summary

To summarize, the report has detailly describe the difference of Cessna 172 and F-111, the knowledge of longitudinal static stability and manoeuvre stability Moreover, by various of calculation and data analysis of Jetstream 31, the neural point of longitudinal static stability can be determined, and it could be further understanding how the data would affect the vehicle and assist to flight testing.

Reference

[1]Handbookon: “AER324FlightDynamics&Control”,YorkshireAeroClubandthe University of Sheffield”, Sheffield, United Kingdom, 2022.

[2] Prezi - Basic Flight Instruments and Controls of a Cessna 172, Robert Filmer, Apr 11, 2015.

https://prezi.com/haroyowtfkcf/basic-flight-instruments-and-controls-of-a-cessna-172/

[3]FlightComparisonof theTransonicAgilityoftheF-111AAirplaneand theF-111Supercritical Wing Airplane, Edward L. Friend and Glenn M. Sakamoto, DECEMBER 1978 NASA Technical Paper. https://ntrs.nasa.gov/api/citations/19790004885/downloads/19790004885.pdf

[4] Lecture slides: “Aircraft Static Longitudinal Stability - Part I”, Sheffield, United Kingdom, 2022

[5] Sforza, P. M. (2016). Spacecraft Flight Mechanics. Manned Spacecraft Design Principles, 303

390. https://doi.org/10.1016/B978-0-12-804425-4.00008-8

[6] Flightlab Ground School - 5 Longitudinal Static Stability Flight Emergency & Advanced Maneuvers Training, Inc. dba Flightlab, 2009.

http://www.flightlab.net/Flightlab.net/Download_Course_Notes_files/5_LongitudinalStatic%23 2BA158.pdf

[7] Katzman Lampert & Stoll Wins Top 3 Jury Award, Feb 15, 2019, Air Crash Litigation. https://katzmanlampert.com/katzman-lampert-stoll-wins-top-3-jury-award/

[9] Flightlab Ground School- 6. Longitudinal Maneuvering Stability. Flight Emergency & Advanced Maneuvers Training, Inc. dba Flightlab, 2009.

https://flightlab.net/Flightlab.net/Download_Course_Notes_files/6_%20LongitudinalManeu%23 2BA152.pdf

[10] Introduction to Flight Test Engineering, NORTH ATLANTIC TREATY ORGANISATION, July 2005. https://apps.dtic.mil/sti/pdfs/ADA444990.pdf