# senior-design

Code and analysis in support of aerodynamics on senior design project. Most recent last modified date was April 17, 2010 at 7:53 PM

##  2009-2010 AIAA Undergraduate Team Aircraft Design Competition Concept

April 12, 2010

![](./media/image1.png)
![](./media/image2.png)

## EXECUTIVE SUMMARY

The θBMaero Lamiar is an airliner designed with the environment in mind.
An environmentally friendly airfcraft is more fuel efficient, emits less
pollutants, and makes less noise. The Lamiar meets and exceeds these
challenges. Utilizing the blending wing concept and a multidisciplinary
design process, the Lamiar has been designed to satisify these goals
without sacrificing capacity or range. The geared turbo fan engine has
been engineered to run up to 10% quieter, burn 20% less fuel and run on
renewable organic fuels as well as traditional fuel. Improved
aerodynamics give the Lamiar a boost of 25% in lift-to-drag ratio in
comparison to the Boeing 737. All this has been done while keeping the
airplane stable, structurally sound, and the passenger and luggage
capacity of current airliners. Requirements of the American Institute
for Aeronautics and Astronautic’s request for proposal as well as
requirements based on the National Aeronautics Research and Development
Challenges have been met. The Lamiar represents the future of civil
transport.

## AERODYNAMICS (ASC)

### Introduction

The Lamiar was designed with environmentally friendliness in mind. In conjuction with the explicit *L/D* ratio requirement from the RFP more efficient aerodynamics were needed. After research on the topic, it was agreed that the best way to meet this requirement would be to design a BWB. Research shows that the BWB offers favorable aerodynamic benefits. (Qin, 2004) The initial sizing and constraint analysis provided by performance gave a starting point to the aerodynamic design, and as design progressed, the values become more refined. Table 4.1 shows the performance values that governed the aerodynamic design and the values attained at current design.

Table: Constraint Analysis Initial Figures

|                                  | Preliminary Design | Final Design |
|----------------------------------|--------------------|--------------|
| Wing Loading (lb/ft<sup>2</sup>) | 36.4               | 33.4         |
| Weight (lb)                      | 160000             | 173000       |
| Wing Area (ft<sup>2</sup>)       | 4400               | 5190         |

### Planform Design

Although the Silent Aircraft was used as inspiration, the Silent Aircraft made design choices that were not specific for this RFP. For instance, the wing sweep on the silent aircraft is about 38 deg. This is because it is optimized for most lift; however *L/D* is maximized at 42 deg. Since our design is keyed on *L/D* ratio, it makes more sense to sweep to 42 deg (Siouris, 2007).

The planform was designed based on a trade study of various BWB configurations. XFLR5 was used extensively during aerodynamic analysis as it proved an easy tool for rapid modeling using airfoil data. A MATLAB code was written to evaluate geometric values and using aerodynamic parameters calculated from XFLR5, the configurations were assessed. The preliminary design had problems in stability, so consideration was made to move the wing farther forward as to bring the neutral point farther forward while keeping the wing sweep around 42 deg. In total, approximately 10 iterations were made in this phase of the design study. Fig. 4.1 shows the L/D of several different candidate planforms. It was decided that the best iteration was FDR005 and was used as the basis for the next step in the planform design.

Figure: Planform design comparison of L/D.

After figuring out a wing placement and general shape, another trade
study concerning fitting the passenger compartment was conducted.
Another MATLAB code was written to give lines of constant heights of
13.25 ft and 10.5 ft (denoted by a solid and dotted red line in Fig. 4.2
respectively) to accommodate passengers (denoted by a blue line in Fig.
4.2). The diameters of each cylindrical component of the pressurized
cabin were 13.25 ft and 10.5 ft respectively. Fitting was achieved by
varying the airfoil selection, and tweaking dimensions. During this
secondary design study, approximately 10 more iterations were performed
until the suitable candidate FDR020 was reached. Fig. 4.3 shows a more
detailed plot with an isometric view to show the amount of height
available inside the aircraft.

![](./media/image29.tiff.png.png)

![](./media/image32.jpeg)

![](./media/image33.jpeg)

| Wingspan (ft)               | 160  |
|-----------------------------|------|
| Wing Area (ft<sup>2</sup>)  | 5200 |
| Wing Sweep (deg)            | 42   |
| Length (ft)                 | 98   |
| Centerbody Width (ft)       | 58   |
| Mean Aerodynamic Chord (ft) | 60   |

### Airfoil Selection

In order to find an airfoil that
satisfies a low drag condition at cruise, research was devoted to
finding transonic, or more specifically, supercritical airfoils. Several
supercritical airfoils were tested. The next airfoil needed was for the
centerbody. The centerbody airfoil poses a unique problem; an adequate
thickness is needed to fit the passenger cabin. A NASA supercritical
symmetrical airfoil was modified the airfoil to accompany passengers.
The modified airfoils, listed in Fig. 4 were customized to allow
necessary thicknesses were the cabin is located. This meant an 18.5%,
17.5%, and 16.5% thickness airfoil along the span respectively with
varying chordwise thickness locations. The outboard wing was chosen as
the supercritical airfoil NASA SC (2)-0714. Toward the tip, the
symmetric airfoil NACA-012 was used to prevent tip stall and provide a
more ideal *C<sub>L</sub>* distribution which is discuss further in
Section 4.5. As shown in the Table 4.3, the efficiency is high. This is
due to the BWB’s inherent better wing aerodynamics and the winglets.

| *C<sub>Lα</sub>*  | .037 (1/deg) |
|-------------------|--------------|
| *α<sub>L=0</sub>* | -2.3 deg     |
| *C<sub>m0</sub>*  | -.0369       |
| *e*               | .98          |

![](./media/image35.tiff.png)![](./media/image36.tiff.png)![](./media/image37.tiff.png)![](./media/image38.tiff.png)![](./media/image39.tiff.png)![](./media/image40.png)

### Drag analysis

The next analysis was the drag. For the BWB, most zero-lift drag comes
from skin friction drag. There is little interference drag on account of
the blended fuselage with the wing. Since the Lamiar travels at
transonic speeds, it was important to take into account transition
effects. A flat plate estimate was used for the discretized wing span.
It was estimated that the flow would be laminar for about 20% laminar
over the length of the fuselage and wing and allowing for the 20%
addition in laminar flow specified the RFP, it was estimated that over
the wing the flow would be approximately laminar for 45% of the chord.
Research engineers at the LaRC estimate that even as high as 50% is
reasonable (Braslow, 1999). Laminar flow control can be attained from
leading edge suction through microperforation (Braslow, 1999). The power
required for suction was added by the propulsion specialist. Fig. 4.6
shows the calculated boundary layer thickness and that the largest
thickness occurs somewhat expectedly along the centerline (McCormick,
1995). The center engine will ingest. Ingesting the boundary layer where
it is the thickest is ideal for aerodynamics. Due to boundary layer
ingestion caused by the engine placement, it was estimated during
performance analysis that a drag reduction of 5.7% can be achieved;
however, ingesting the boundary layer is generally bad for the engine
and this will be addressed further in Section 6.2.

![](./media/image41.jpeg)

| *C<sub>D</sub>* <sub>fuselage</sub>     | .0051  |
|-----------------------------------------|--------|
| *C<sub>D</sub>* <sub>wing</sub>         | .0014  |
| *C<sub>D</sub>* <sub>engine</sub>       | .00050 |
| *C<sub>D</sub>* <sub>landing gear</sub> | .0026  |
| *C<sub>D0</sub>* <sub>takeoff</sub>     | .0096  |

The drag polar can be calculated from the C<sub>D0</sub> and the induced
drag. Fig. 4.7 shows the drag polar evaluated at takeoff.



Figure: Drag polar at cruise.

The *C<sub>L</sub> v*alues are known at each segment from flight
conditions and wing area. Using *C<sub>Lα</sub>* data, it was determined
that the appropriate angle of attack for cruise would 1.74 deg, and to
ensure a level cabin during cruise, 1.75 deg is set as the incidence
angle. The *C<sub>L</sub>* at take-off is constrained by take-off
distance requirements provided by performance. After taking into account
ground effects, the angle of attack required at takeoff was calculated
to be 4.5 deg. To achieve this angle of attack it is necessary for the
landing gear to be designed in a way to add 2.75 deg to the incidence
angle. The values for various mission segments are listed in Table 4.5.

|                 | Takeoff | Cruise | Loiter | Landing |
|-----------------|---------|--------|--------|---------|
| *C<sub>L</sub>* | .48     | .149   | .281   | .48     |
| *C<sub>D</sub>* | .027    | .00681 | .0108  | .020    |
| *α* (deg)       | 4.50    | 1.75   | 5.30   | 4.20    |
| *L/D*           | 16.7    | 21.9   | 25.9   | 20.1    |

### Load Distribution

Although not valid for lift and drag calculation, XFLR5 was useful for
finding lift distribution. Fig. 4.8 shows the *C<sub>L</sub>*
distribution at cruise which was given to the structures specialist to
analyze. According to a study done at the University of Sheffield in the
UK, the best lift distribution is a medium between elliptical and
triangular. This is because an elliptical distribution gives the lowest
induced drag while a triangular distribution gives a lower wave drag. At
cruise speeds, wave drag should be considered. The lift distribution to
be targeted will is represented by the dotted line in Fig. 4.8 (Qin,
2005). An effort was made to match the lift distribution of the Lamiar
to this distribution by varying wing twist and adding a symmetric
airfoil at the tip. A twist of 5 degrees near the tip and 2.5 degrees at
the tip was found to help bring the Lamiar’s distribution close to the
ideal. To prevent tip stall the maximum *C<sub>L</sub>* along the span
was made to be at about 35% span, ensuring that the wing will stall
inward first rather than at the tips.



### Conclusion

It can be seen that the *L/D* requirement was met. Aerodynamically, the
Lamiar will be more efficient thanks to the utilization of novel
configuration optimization and laminar flow technology as specified by
the RFP and the National Aeronautics Research and Development
Challenges. An *L/D* of about 22 can be achieved during cruise; this is
an improvement over the current generation Boeing 737 which has an
approximate lift-to-drag of 17 at cruise. The *L/D* improvement was
achieved thanks to the BWB concept, boundary layer ingestion, and
laminar flow control. These achievements help to make the Lamiar an
environmentally friendly plane by lowering drag and in turn the thrust
required.