PRELIMINARY DESIGN OF A LSA AIRCRAFT USING [601788]

PRELIMINARY DESIGN OF A LSA AIRCRAFT USING
WIND TUNNEL TESTS

Norbert ANGI *1, Angel HUMINIC1

1 Aerodynamics Laboratory , Transilvania University of Brasov,
29 Bulevardul Eroilor , Brasov 500036, Romania
[anonimizat] , [anonimizat]

Abstract: This paper presents preliminary results concerning the design and aerodynamic
calculations of a light sport aircraft (LSA). These were performed for a new lightweight, low cost, low
fuel consumption and long -range aircraft. The design process was based on specific software tools as
Advan ced Aircraft Analysis (AAA), XFlr 5 aerodynamic and dynamic stability analysis , and Catia
design, according to CS -LSA requirements. The calculations were accomplished by a series of tests in
wind tunnel i n order to assess experimentally the aerodynamic characteristics of the airplane.
Key Words: aircraft design, Computer Aided Design , aerodynamics, wind tunnel 
1. INTRODUCTION 
The aircraft development process consists in the following main steps: market analysis
and customer requirements, mis sion specifications, conceptual and preliminary design,
detailed design, prototype manufacturing, flight test, and finally the aircraft production.
In the first stage, the aircraft structure is defined as concept, without precise calculations.
Thus, the prelim inary design phase tends to employ the outcomes of a calculation procedure.
As the name implies, the initial parameters, which are established in this step, will be
optimised during next stages of the design. Hence, the initial parameters have a significan t
influence on the detail design phase. These parameters are also used as input data to the 3D
modelling of the aircraft, the base shape being one of the main results of the preliminary
design. In a modern design process, the 3D model of the aircraft play s a crucial role.

Fig.1 – 3D view of the studied airplane

The base design of the studied aircraft, see Figures 1 , 2 and 3 was also made by studying
several airplanes in the same class of regulations CS -LSA [1], e.g. Flight Design CTLSi ,
Czech Sport Aircraft, Evektor Harmony . These were analysed according to the general
configuration, specific fuel consumption, flight range and main aerodynamic performance s.
The preliminary design of the airplane was made with the aid of Advanced Aircraf t
Analysis (AAA), DARcorporation [ 2], a state of the art software in the field of aircraft
design and analysis, and XFLr 5 [3] software.

Fig.2 – 3D view of the airplane – Details

The airplane , named Sky Dreamer [4], has the general characteristics shown in Table 1.

Table 1 – General characteristics of the airplane

Parameter Value
Crew Two
Empty weight
Max. Takeoff 315 kg
600 kg
Fuel capacity 100 L
Engine Rotax 912iS
Maximum speed
Cruising speed 290 km
205 km/h
Operational Range 1650 km
Service ceiling 5500 m
Lenght 6.45 m
Wing Area 11.5 m2
Wingspan 10.2 m
Fig.3 – Top, Front and Lateral views of the airplane Wing Airfoil Eppler 562 [5]

In the first stage, t he aerodynamic characteristics of the airplane were assessed for
the following conditions: cruise flight with gear up at 3000 m in the following atmospheric
condition s: temperature , pressure , density
and dynamic viscosity . The characteristic Reynolds
number compu ted with the mean aerodynamic chord was .
The theoretically estimated aerodynamic performances based on XFLr 5 and AAA
are shown in Figure s 4 and 5 .

Fig 4 – Preliminary results according to XFLr 5 [3]

Fig 5 – Preliminary results according to AAA [ 2]

According to [ 2], the relationship between drag and lift is expr essed by the following
equation .

. (1)
2. WIND TUNNEL TESTS

In order to assess also experimentally the aerodynamic characteristics of the
airplane, a 1:10 scale model was tested. The experiments were performed using the
infrastructure of the Aerodynamics laboratory of Transilvania University of Brasov. The
used win d tunnel, see Figure 6, has a closed test section of 1.2m x 0.6m x 1.2m, maximum

velocity of 40 m/s and the turbulence lower than 0.5%. It meets the requirements of the SAE
(Society of the Automotive Engineers) [ 6]. It has a four component strain -gauge balance
with a PC -based system of data acquisition, and a moving belt device for ground effect
simulation [7].

Fig. 6 – Axonometric view of wind tunnel
test section and (2) aerodynamic (strain -gauge) balance

The aer odynamic strain -gauge balance used for measurements consist of a sting
(used to support the model), the arm of balance and two elastic elements (thin walls tubes),
which is fixed on a frame. Details are shown in Figure 7.

Fig. 7 – The model with in the wind tunnel test section

The aerodynamic forces ( ) which are acting on the studied model are transmitted to
the elastic elements and their deformations are taking over by the strain gages, which are
glued on the elastic tubes. Finally , they are transmitt ed to the recording system which
convert them into electrical signals, the values of the latter ones being displayed by the
system of data acquisition.
Figure 8 show the results concerning the calibration of this tensometric device. They
describes the dependencies between the magnitude of the aerodynamics forces acting on the
model , and the values of the signals , lift ( ) and drag ( ), displayed by the data acquisition
system

(2)

Fig. 8 – Calibration curves of the aerodynamic balance

In order to achieve variations of aerodynamic coefficients lower than 1e -03, thereby
satisfying SAE requirements as stated in [5] ( ), the sensitivity of the balance
was set for the following values of calibration factors: and .
3. RESULTS

After the calibration process of the balance, the model was tested for various values
of the angle of attack ( ). The parameters of the airstream in the test chamber of the wind
tunnel were the following: temperature , pressure , density
and dynamic viscosity . The characteristic
Reynolds number computed with the mean aerodynamic chord was
( 34 m/s) .
The results are shown Figure 9 after the following wind tunnel boundary corrections
according to [8].
a) Solid blockage correction : there were applied corrections for wing and body,
as following:

(3)

(4)

(5)
b) Wake blockage correction: the complete wake blockage results for a three –
dimensional model are presented below:

(6)

(7)

(8)

where

(9)

where, A1 and A2 are constants

(10)

Aleso the measurements in the wind tunnel must met the following condition:

(11)

where A k is the model front area and C the test section area . According to the wind tunnel
analysis the value of varie s within range of 4.3027 to 6.8971, which respect the
prescri bed condition :
c) Correction on the angle of attack and drag coefficient

(12)

(13)

d) Dynamic pressure correction
(14)

where qa is obtained from tunnel calibration.

Fig. 9 – Theoretical and experimental results
4. CONCLUSIONS
According to the preliminary results, the studied airplane has higher
aerodynamic performances comparatively to the top light sport aircrafts, in the same class of
regulations CS -LSA.
Due to the higher aerodynamic performance it results lower f uel consumption and
10% hi gher flight range.
The errors between the preli minary cal culation using software tools and wind tunnel
analysis were . In order to check the current results, there will be analyzed another
model with a different fastening system, which has lower int erference for the tested model.
REFERENCES
[1] EASA, Certification Specification and Acceptable Means of Compliance for Light
Sport Aeroplanes, CS -LSA, European Aviation Safety Agency, 2013
[2] Roskam J., Airplane Design, Part I. Preliminary Sizing of Airplanes , University of
Kansas, 1985
[3] XFlr5, http://www.xflr5 .com/xflr5.htm
[4] Angi N., Udroiu R., Design of a LSA aircraft using advanced software , International
Conference of Scientific Papers – AFASES 2015
[5] Eppler R., Airfoil Design and Data , Springer Verlag, Berlin, 1990
[6] SAE, Aerodynamic Testing of Road Vehicle – Testing Methods and Procedures , SAE
Information Report SAE J2084 JAN93, 1993.
[7] Huminic A., Huminic G., CFD Study Concerning the Influence of the Underbody
Components on Total Drag for a SUV , SAE Technical Paper 2009 -01-1157, 2009,
[8] Barlow J., Rae W., Pope A., Low-speed wind tunnel testing , Third Edition, USA,
1999.