I would like to thank everyone who visited Hanley Innovations' booth (321) at last week's 51st AIAA Aerospace Sciences Meeting in Grapevine, Texas.
We had a great time seeing old friends and meeting new ones as we discussed the latest innovations in aerospace engineering.
I would like to remind you that Stallion 3D is now a component of the Aerodynamics ClassPack. The ClassPack is an excellent tool for aerospace engineering education for students studying basic aerodynamics as well as students working on senior year capstone design projects. More information about the Aerodynaics ClassPack can be found at: http://www.hanleyinnovations.com/classpack.html
The following video shows how Stallion 3D can be used with NASA vehicle Sketch Pad software.
Do not hesitate to contact us at (352) 240-3658 if you have any questions about our software products.
One intriguing aspect a futuristic flying car is the promise of fast personal transportation. You will hover off your driveway and arrive at your destination hundreds of miles away within a few minutes. Lunch in New York and dinner in Los Angeles.
To capitalize on this promise, the car must fly at a supersonic speeds. Supersonic flight involves shock waves (also called sonic booms) and this might not work so well for your neighbors. The following video shows a simulation of shock waves (generated using MultiElement Airfoils 5.0).
Shock waves/Sonic Boom Simulation
One way of reducing the effect of the sonic boom is to use the Busemann bi-plane concept. Of course, this arrangement of wings does not produce lift. However, they might be useful if integrated into the propulsion system or a cleverly designed shock wave deflectors for lifting surface.
The figures below show MultiElement Airfoils calculations of the Busemann airfoil operating at on- and off-design conditions.
On-Design Analysis of Busemann bi-plane without external shock waves
computed using MultiElement Airfoils.
Off-Design Analysis of Busemann bi-plane with external shock waves.
It is not too early to start your design of the next wave in personal transportation. Please visit http://www.hanleyinnovations.com/mefoil.html to find out more about our software for analyzing multi-element airfoils in subsonic, transonic and supersonic flows.
Why your next airplane design will be the best? Aircraft design is an iterative process. This is why Boeing, Airbus and even NASA need lots of scientists, engineers and mechanics to carry out the engineering process. Here's an exercise, fold a sheet of paper into a paper airplane and get it to fly to your satisfaction the very first time (how many times did it take?)
Because aircraft design is an iterative process, it becomes critical that every iteration or design step is efficient. In addition, each iteration in the design should advance the project in the right direction (this is called convergence ). In the modern aerodynamics design, tools such as analytic methods, computational fluid dynamics, wind tunnels, scaled models and flight testing are necessary to ensure a fast rate of convergence.
Why your next design will be the best?
1. There are a number of airfoil analysis software currently available to help you to quickly and accurately analyze cross sectional shapes for wings, struts, rudders, landing gears, flaps and other components. You can use these tools to select shapes that provide good lift at the expense of low drag. Another consideration (especially for wings) is the use of airfoils that produce high lift without huge destabilizing pitching moments (this reduces the tail drag). Some airfoil tools are free (see Xfoil). Other are efficient and accurate and help you to finish this crucial first iteration ahead of the pack (see, http://www.hanleyinnovations.com/vf50.html).
VisualFoil 5 can compare the performance of many airfoils on a single graph.
2. Once you have cross sectional shapes, the next step is the skeleton airplane. The skeleton airplane is essentially just wings, winglets, canards, flaps, tail and rudder. The skeleton airplane should be a good enough approximation to the actual aircraft to help you to compute lift, drag, longitudinal and lateral stability, angle of trim, 3 DOF trajectories, component loading (for stress calculations) and drag reduction (winglets).
Getting the most out of the skeleton aircraft is key to the next step in the design process. Free tools such as AVL (Athena Vortex Lattice Method) allows you to analyze the skeleton aircraft using a horse-shoe vortex lattice approach. If entering each component using a text file leaves you behind schedule, MultiSurface Aerodynamics (MSA) provides a modern user interface that expedites the design process (based on vortex rings method). MSA is the ideal tool to compute and identify form and induced drag from different wing components and design/position winglets, canards and the tail-plane (see http://www.hanleyinnovations.com/multisurface and http://pdf.aiaa.org/jaPreview/JA/2010/PVJA44453.pdf).
3. As a design engineer your imagination and experience are your biggest assets. By this time in the process, you have formulated your ideas and analysis findings into a 3D solid model that resides in a CAD program (Rhino, Solid Works, Autodesk Inventor, NASA's Open Vehicle Sketch Pad openvsp.org). This is the stage where efficiency is most critical because you must test the design as a unit.
A good way to proceed is to use computational fluid dynamics or CFD methods. Traditional CFD methods requires that you construct a mesh for each design iteration that you wish to test. This is often difficult and time consuming especially for 3D models (see http://www.symscape.com/blog/why-is-cfd-difficult).
The more parameters you can test, the better the design. If your next design is to be your best, you will benefit from Stallion 3D, a novel and accurate tool that eliminate the mesh generation process. This allows you to efficiently analyze and optimize your CAD models for this final step in the aerodynamics conceptual design process. The following video shows all the steps required to enter and analyze your aircraft design in Stallion 3D.
Stallion 3D can go from solid model to results in as little as 1.5 hours on a laptop computer.
NASA Open Vehicle Sketch Pad now has a hangar area with many 3-D models that you can use for inspiration and guides for your own original designs. The url is: http://hangar.openvsp.org/. The hangar currently lists 74 models for download.
I used Stallion 3D to analyze some of the models in the hangar. Simply export the model from Open Vehicle Sketch Pad in the .stl format and Stallion 3D can read in and analyze the geometry. The software can model subsonic, transonic and supersonic external flow fields. More information can be found at http://www.hanleyinnovations.com/stallion3d.html.
The following are some pictures from Stallion 3D.
Surface pressure on the surface of the F5 model at a speed of 290 m/s.
Velocity near the surface of the Q2-Model at V=100 mph.
Pseudo-Top-Gun Scene using the F15 for the F14 and the F5 standing in as the MIG. The airplanes were analyzed at a speed of 290 m/s.
Hypersonic waverider model at mach number of 6 (surface Mach number)
Slide an old or unwanted CD across a desk, table or smooth floor. With the shiny side down (read/write side) the CD will slide a long distance in ground effect. With the shiny side up, the CD will tend to stick to the surface.
Why?
The first thing to notice is that the label side of the CD is completely (well almost) smooth and flat. While the read/write side has a notch (ring) near the center hole of the CD (where the plastic is transparent) on an otherwise smooth surface.
I performed a 2-D analysis of the CD airfoil (at the center-line) using Hanley Innovations' MultiElement Airfoils software package. The notch was set to a height of 0.0125 inches and the CD was placed 0.025 and 0.0375 inches off the ground. The speed was set to 10 feet/sec and the Euler code was used to model the flow.
Grid generated automatically using MultiElement Airfoils.
The following is the results for the CD with the read/write side up (Cl = -0.105). The bottom line represents the ground plane:
With the read/write side up. The computed lift coefficient was -0.104 with h=0.025 in
Velocity distribution of flow near the notch (bottom line is the ground plane).
The negative lift coefficient or down-force caused the CD to stick to the surface. It will make a great race-car in this mode.
Next, the flow, with the CD read/write side facing down, was computed in MultiElement Airfoils. This time, the lift coefficient was +0.105
With the read/write side down, the lift coefficient was +0.105 with h=0.0375 inches.
Velocity distribution of the flow near the notch.
The positive lift coefficient caused the CD to lift free from the friction on the floor and provided a longer journey. This disc models a WIG (wing in ground effect) or Ekranoplan in this mode.
These results suggest that the notch-ring near the center of the CD is the reason for the wing-in-ground effect behavior.
Do your know of other simple ground effect experiment?
Are you in the process of designing a new aircraft, sailboat, or automobile. 3D analysis can play an important part in the design process. Please consider 5 reasons (not necessarily definitive) to use 3-D aerodynamics early in your design process.
5. Your design should not look like your analysis & design tool. If you are too comfortable with 2-D analysis eventually your real-world designs will all resemble airfoil shapes. A good 3-D design and analysis tool should render and analyze the exciting concepts that resides within your creative mind. Feel free to throw caution to the wind and reap the rewards of your imagination.
4. An airplane is a 3-D object and is usually designed to be stable in flight. Good stability in flight requires accurate computations of the location of the aircraft neutral point, the size of the vertical tail (for lateral stability) and effects of the wing's dihedral angles.
Stallion 3D calculations of the pitching moment with respect to
Angle of Attack (see previous blog post).
3. Like humans, air prefers to use the "extra" third dimension to get out of the path of a speeding car. If you wish to determine the down-force on a car wing in ground effect, two-dimensional analysis can provide much insight into the airfoil shape and angle of attack. However, in 3D the air has a tendency to flow around wings of low aspect ratio that are too close to the ground.
The figure below shows the same airfoil shape used on a wing of aspect ratio two. The downforce on this wing will be smaller than its 2-D counterpart. Use 3D aerodynamics to develop new and exciting methods to force the air through wings shapes that will capture the maximum downforce.
Stallion 3D analysis of Aspect Ratio 2 Wing in Ground Effect
2. 3D aerodynamics can be used to model the structure and planforms of wings that decrease drag (such as wing with winglets), increase downforce (end plates) or enhance the integrity of the structure (joined wings).
1. Several year ago, 3D analysis was costly and difficult. Now, 3D aerodynamics is easy and cost effective. My laptop computer is fast enough to analyze the 3-D Euler/Navier-Stokes equations (and so is yours). Take advantage of modern CFD codes such as OpenFoam, Caedium, grid generation software such as Pointwise or Stallion 3D for a complete aerodynamics conceptual analysis to enhance your creative process.
There are many reasons to make changes to the airframe of an airplane. These include improvements to the airfoil to reduce the profile drag and increase lift; wing tip modifications (winglets) to reduce induced drag; addition of stores and external components such as landing gear covers; increasing load carrying capacity or adding surveillance equipment.
Making changes to an airplane configuration can be expensive and sometimes dangerous. One method to reduce the expense is to test the proposed configurations in all possible modes of operations. Testing can be time consuming and has a natural enemy called "the deadline". Aerodynamics analysis methods based on computational fluid dynamics (CFD) methods can reduce testing time by rapidly screening models and pre-selecting only the promising ones for further testing (wind tunnels, scale models & flight testing).
Stallion 3D Automatic Gridding Dramatically Increases the Number of Models
That can be Tested Before the Deadline
If the goal of the design is to increase the load carrying capacity of the airplane, then each design iteration should be tested over a range of angles of attack to determine lift and the angle of attack for maximum lift.
Good Understanding of the Results can be Gained by Studying
Increasingly Complex Aerodynamic Models.
A good way to gain confidence (even in conceptual studies) is to study increasingly complex analytical and geometric models. The above graph starts with an airfoil analysis (using VisualFoil 5.0) and escalates using MultiSurface Aerodynamics (vortex lattice model for wing-tail) and Stallion 3D (Euler model for analyzing the full complex geometry).
for Quick 3-D Analysis of Complex Systems of Lifting Surfaces.
If your goal is to add equipment or payload capacity to the aircraft, then you must find the neutral point (or aerodynamic center) for each proposed model. The neutral point of the aircraft is defined as the position where Cm, the pitching moment coefficient, does not vary with a change in angle of attack (or dCm/d(AoA) = 0). To get a good understanding of this, one can plot Cm taken about a number of locations and plot each location as a function of angle of attack. To gain confidence in your analysis tool, you should use experience and a variety of methods to arrive at comparable results.
Cm vs AoA Taken About Various Positions from the Aircraft's Nose. The Stallion 3D Model
Compares Well with the MultiSurface Aerodynamics (MSA) Model.
The above graph shows that the neutral point is located about 3 meters from the nose of the aircraft. Here the slope of the Cm vs. Angle of Attack curve is zero. Ahead of the neutral point (0 < x < 3) m, the slope of the moment is negative. This means that if the center of gravity (CG) is located in this region, an increase in angle of attack (due to a gust for example) will be righted by an opposing moment about the CG. However, if the CG is located aft of the neutral point (3 < x < 8) m, then an increase in the angle of attack will be exacerbated by an enhancing moment action about the CG (this is not stable).
Another item to note is that as the CG is placed increasingly ahead of the neutral point, the restoring moment becomes larger. The distance between the CG and neutral point is known as the static margin. Increasing the static margin increases stability, however, the righting moment reduces the ability to control the aircraft. The design goal is to provide good stability with smaller control surfaces.
Studying the moment coefficients shows that in its current configuration, our aircraft will fly at an angle close to the zero-lift angle of attack. This is because the horizontal tail in the model (taken from NASA's Vehicle Sketch Pad program) is at zero angle of attack.
The Horizontal Tail Uses a Symmetric Airfoil at Zero Angle of Attack
To change the trim angle of the aircraft, we can control the angle of the horizontal tail surface. We assume that the CG is located 2 meters from the nose of the aircraft. The figure below shows that the aircraft will fly at angles of attack of -3 degrees, 0.7 degrees, 4.4 degrees for tail angle setting of 0.0, -5.0 and -10.0 degrees respectively.
MSA Analysis to Determine the Trim Angle of Attack of the Wing-Tail Model.
The fuselage shape and external components (stores and landing gears) can increase the drag of the airplane. The figure below compares the pressure drag computed by Stallion 3D against the profile and induced drag of the wing-tail configuration computed using MSA.
Drag Comparison of Two Models
The pressure drag of the fuselage, wing and struts adds to the total drag of the wing and tail. The goal of the design is to move the blue curve towards the green one. The green curve is the best that can be due given the wing planform shape and airfoil selection.
The results were complied after executing 6 cases in Stallion 3D with each run containing upwards of 700,000 cells. The the computations required about 8 to 10 hours per case on an HP laptop (2.4 gigahertz processor). The Stallion 3D floating licenses allow users to run the program on all available computers and processors. The time to set each case in Stallion 3D took less than one minute. The grid generation was automatic.
Stallion 3D was run at 6-different Angles of Attack for this Study
The cases ran in MultiSurface Aerodynamics were executed in less than one minute.
The above exercise involved longitudinal static considerations. We can repeat the exercise for lateral stability considerations. The above procedure can be carried out for design iterations and we could gain a good understanding of the behavior of the design before it advances to further testing.
