Aerospace Design, Test, Certification: A Literature Review

This report provides a detailed overview of aerospace design, testing, and certification, with a specific focus on the role of wind tunnels in aircraft development. It classifies wind tunnels based on speed regimes, including subsonic, supersonic, transonic, and hypersonic types, and explains their operational characteristics. The report also examines the relationship between the angle of attack, lift, and drag coefficients, highlighting how minimizing the angle of attack can reduce induced drag and improve aerodynamic efficiency. Furthermore, the report discusses aircraft test and certification practices, differentiating between civil and military aircraft procedures, including the roles of government agencies and manufacturers. The report concludes by emphasizing the importance of these factors in ensuring aircraft safety and performance.

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AEROSPACE DESIGN, TEST AND CERTIFICATION
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Abstract
The design of aerospace considers a several factors including the wind tunnels. This
assignment seeks to explore the various wind tunnels as well as the aspects involved in
certification and testing of aircraft. By extension, an investigation into the relationship between
the angle of attack of an aircraft, lift and drag coefficients is also investigated. The findings
reveal that wind tunnels are classified with regards to the speed of sound hence we have
subsonic, supersonic, transonic, and hypersonic wind tunnels. Also, minimizing the angle of
attack reduces the induced drag as a result of the presence of turbulence; hence, a significant
aerodynamic efficiency will be attained. Finally, aircraft test and certification is essential for
obvious reasons of human safety among others.

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Introduction
Wind tunnels are utilized by aerodynamicists to perform tests on models of particular proposed
aircraft. The engineer has the ability to carefully controlling the flow conditions within the
tunnel, which influences the forces acting on the aircraft (Gjelstrup et al., 2012). Accordingly,
we will consider some of the available wind tunnel types in regards to various design features in
the section below
Types of Wind Tunnel
Speed Regime
The speed of the wind tunnel in relation to the speed of sound helps is used in the design or
rather classification of the wind tunnel types. A Mach number is obtained from the relationship,
for instance, the Mach number = speed of air/ speed of sound. Hence, the various types of wind
tunnels in this category include subsonic, supersonic, transonic, and hypersonic.
1. Subsonic wind tunnel
These are wind tunnels utilized in operations which have a minimal Mach number and speed in
the test section close to 480 kilometers per hour. These tunnels can either be Eiffel type/open
type or closed return flow. The air is propelled into them via a propulsion system that is
comprised of substantial axial fans, which enhances the dynamic pressure so as to manage the
viscous loses.
1a: Open wind tunnel
The open wind subsonic tunnel operates on the Bernoulli’s principle which states that

Aerospace Design, Test And Certification 4
The contraction ratio of a wind tunnel thus is
The diagram below illustrates the open wind tunnel
This kind of tunnel has both of its end open and withdraw into the test section from the room.
1b: closed wind tunnel
For this return flow wind, the tunnel duct is made such that it minimizes the losses and ensures
that there is smooth flow for the test section. This subsonic wind tunnel follows the isentropic
flow below (Hansen, 2015).

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The diagram below illustrates the closed wind tunnel
Both of its ends are closed, thus recirculating the air within the test section.
2. Transonic tunnel
These are wind tunnels which have a Mach number that lies between 0.75 and 1.2. For these
wind tunnels, the highest speed is attained in the test section. Limitations are experienced with
this type of wind tunnel as a result of walls of the test section that reflects the shock waves.
Hence, it is recommended to utilize slotted or perforated walls in order to limit the shock
reflection emanating from the walls. The diagram below illustrates the transonic model

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3. Supersonic wind tunnel
This is a kind of wind tunnel which generates supersonic speeds with a Mach number that lies
between 1.2 and 5. The geometry of the nozzle determines both the flow and the Mach number
in this case (Barlow et al., 2015). Varying the density level achieves the variation in the
Reynolds number hence necessitating for a high-pressure ratio. When the temperatures become
scold in this scenario, gas liquefaction or condensation of the moisture is likely to take place.
4. Hypersonic wind tunnel
This kind of wind tunnel has been designed for purposes of generating a hypersonic flow field in
the operation area. The Mach number of the speed of the hypersonic wind tunnels varies between
5 and 15. In addition, the cross section is directly proportional to the power requirements. Thus,
it is less expensive to install a closed circuit wind tunnel in a continuous mode, unlike the
transonic tunnel which needs an intermittent installation (Aggarwal, 2010)

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Graph of lift and drag against the angle of attack
Considering the graph below

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In the y-axis, we have the coefficient of drag and lift, whereas in the axis we have the angle of
attack. When one moves through the air with the same speed/constant speed, there will be an
increase in the angle of attack. At the same time, the lift and the drag as well will increase up to
the point that a critical angle will be arrived at. This is the point when the lift will suddenly fall
away, and hence the aerofoil will start to stall. Critically looking into this case, the critical angle
is twenty degrees (Hartl et al., 2015).
There is a direct proportional relationship between the lift, the angle of attack and aircraft speed
squared. This implies that we can as well generate a similar lift when the speed of the aircraft is
high, and initiating with a lower angle of attack. When this angle of attack is minimized, the drag
which is induced will reduce as a result of the presence of turbulence; hence, a significant
aerodynamic efficiency will be attained (Hyde, 2013).

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Aircraft test and certification practices
The aircraft certification is the permission issued by civil aviation authority on how to operate
aircraft in each country and stipulates that the owner of the certificate has attained some
experience and knowledge associated with specific requirements and standards. It encompasses
taking of a flying test after which one becomes a pilot. (Orifici et al., 2010).
Certification structure
The certification of the pilots is done at various privilege levels with each level being rated.
Some of these levels include
 Student- is prohibited from carrying passengers and cannot fly alone, unless with a
certified flight instructor.
 Sport-can only flies during the day and carry not more than one passenger. Besides, it is
only allowed to fly light-sport aircraft.
 Recreational- can only fly during the day for pleasure only, at an aircraft horsepower up
to 180 HP or 130-kilowatt hour and restricted four seats.
 Private- these are no-hired authorizations for flying for personal business or pleasure.
 Commercial- these are required to have high training experience as they fly for
commercial purposes.
 Flight instructor- these are trained personals who have advanced knowledge, skills, and
teaching techniques in regards to safely flying people.
 Airline transport pilot- these just as the name suggest are authorized to fly US significant
airliners.
Flight testing

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It is a branch of aeronautical engineering which deals with generating and gathering, and
examination of data when an aircraft is on board for the validation of the design. It is aimed at
accomplishing two primary duties; determining and correcting any design issue, and verification
of the vehicle capabilities. (Pinier et al., 2012).
The difference between test and certification in the civil and military aircraft
Civil aircraft- civil testing is done by a government certified agency to a certain that all the
performance and safety retirements are met. The government certifying agency is not concerned
with the commercial success of the aircraft since the development is mainly funded by private
investors or the sole manufacturer. They are only limited to safety and performance.
Certification agency comes in for flight testing is when a developmental issue is found and fixed
or when it’s seeking certification (McLaren et al., 2012).
Military aircraft- in this case, a government issues a contract with the manufacturer for the
design and generation of aircraft with certain mission requirements. The government is directly
involved in the testing as well as the certification of the aircraft since it's the leading funder. Part
of the manufacturer’s flight test team is the military test pilots and engineers right from the
beginning. The final tests are done by solely government test team known as an operational test
which certifies the suitability of the aircraft. Further, flight testing is done in military facilities.
Conclusion
This research has investigated the various types of wind tunnels in aerodynamics. From the
above findings, the tunnels are classified basically in regards to their speed hence supersonic,
hypersonic, transonic and subsonic tunnels. Further, we also realized that the angle of attack is
directly proportional to both the drag and lift until a separation point when increase in turbulence
winds up causing instant deterioration of the lift force, and consequently a rapid rise in the drag,

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hence resulting in a stall. Finally, on aircraft test and certification, there exist a difference in the
on the civil and military aircraft on the aspect of government involvement on the later, while the
former it’s funded by either the manufacturer or the investors.

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References
Aggarwal, P.K., 2010. Dynamic (Vibration) Testing: Design Certification of Aerospace System.
Encyclopedia of Aerospace Engineering.
Barlow, J.B., Rae Jr, W.H. and Pope, A., 2015. Low speed wind tunnel testing. INCAS Bulletin,
7(1), p.133.
Gjelstrup, H., Georgakis, C.T. and Larsen, A., 2012. An evaluation of iced bridge hanger
vibrations through wind tunnel testing and quasi-steady theory. Wind and Structures, 15(5),
p.385.
Hansen, M.O., 2015. Aerodynamics of wind turbines. Routledge.
Hartl, D.J., Mabe, J.H., Benafan, O., Coda, A., Conduit, B., Padan, R. and Van Doren, B., 2015.
Standardization of shape memory alloy test methods toward certification of aerospace
applications. Smart Materials and Structures, 24(8), p.082001.
Hyde, R.A., 2013. H∞ aerospace control design: a VSTOL flight application. Springer Science
& Business Media.
McLaren, K., Tullis, S. and Ziada, S., 2012. Computational fluid dynamics simulation of the
aerodynamics of a high solidity, small‐scale vertical axis wind turbine. Wind Energy, 15(3),
pp.349-361.
Orifici, A.C., Thomson, R.S., Degenhardt, R., Bisagni, C. and Bayandor, J., 2010. An analysis
tool for design and certification of postbuckling composite aerospace structures. International
Journal of Structural Stability and Dynamics, 10(04), pp.669-681.
Pinier, J., Hanke, J.L. and Tomek, W.G., 2012. Ares i aerodynamic testing at the boeing
polysonic wind tunnel. Journal of Spacecraft and Rockets, 49(5), pp.853-863.