Flying car challenge

As part of a Grabcad challenge, I decided to be invlolved in a design of a flying car. The project or tender was promoved by Terrafugia, which wanted to see new designs in order to make the image of the new terrafugia TX-1 better.

My design was made using Catia V5, and the renders using KeyShot.

The characteristics of the design were the following:

Lift Body TF-X Car

This design is based in the idea of being able to fly. A flying car is a complex vehicle, because it is difficult to make a secure model that is able to go in a highway an at the same time can fly.

The other restrictions like the vertical takeoff and landing make it even much difficult.

For that reason, the basic design of this car is the body of the car can generate the enough lift force, so the wing does not have to be too long.

In a conventional plane, the wings are the heart of the plane, because are the only part that generate the lift force. However, the wings are almost always fixed, except in the ship based planes. Even in these cases, the wings that can be folded are design for being park in less space.

With a lift body, the wing can be reduced to the minimum, and can be easier foldable. The idea is based in some projects that improved the idea of the lift body planes like the X-24

Body

The body is made using two different airfoils, the Goettingen 561, and the 518. Both were chosen due to their flat lower side, that better to adapt in a car, and was more similar to the original drawing imagined.

These airfoils also were selected because have a really god lift features, a characteristic that this flying car will need. Being a slow plane, the lift coefficient of the airfoil is very important.

The body is designed for 4 people, two in the front seats, and to in the back seats. However, both pair of seats is more separated than in normal cars. The reason, is because between them is the place for the wings, and since the wings have to resist a good part of the weight if the car, need thickness area for the structure.

The doors are completely transparent so the passengers can enjoy the flight. The doors are opened and closed in a similar way to the Mercedes 300SL.

The body has two areas grooved so the wings can fit in the car configuration. This transition (the grooved area) has to be designed very carefully, so will not increase too much the parasite drag of the car.

The body has a lot of space to install the batteries (probably in the bottom of the body) and for the motors.

The wing

The wing is straight and rectangular. The reason for being straight is obviously the only configuration for a plane that won’t go in transonic or close to supersonic speeds.

The reason for the rectangular configuration is because it is the easiest and cheapest configuration. An elliptical or trapezoidal wing would cause more problems manufacturing.

Although the rectangular wing has more induced drag than the other two, it has more surface than the other both options, what give more lift coefficient, especially for a plane with such a less aspect ratio.  At the same time is the safest wing, because it can be controlled easier even if the plane has stall problems.

The elliptical configuration is much less safe, so I reject it, even if has the best aerodynamic features.

 The airfoil used was a NACA 4415, although in a more advanced analysis other airfoil can replaced it; especially a common body/wing airfoil.

The wings can be folded turning 90º in a horizontal axis, in a similar way to the carrier ship fighters like the F-18 Hornet.

Stabilizers

Two stabilizers inclined are installed in the rear of the car before the Duct fan. Even in high angle of attack conditions, the duct fan will sure that the air will pass through the stabilizers. The localization is provisional, so it could change after some aerodynamic analysis.

Propellers

The propellers used are a simple example, and can be changed. The simple model has 3 blades, although the number of blades cannot be chosen until some calculations are done.

The propellers can rotate 90º or even more so the car can takeoff/land in vertical.

Duct Fan

The Duct fan is going to propel the car through the air, it is installed in the back of the car, with no many interaction so the air can go through it with less problem.

One idea that cannot be said now (until some calculations) is that the position of the duct fan could help the air to be laminar for more time when it goes through the body of the car. This would increase the aerodynamic features; but it depends on many factors, and should be analyses with determination using a CFD software and a wind-tunnel.

The rear lights of the car are installed in the duct fan cage, so the other cars can have an idea of it height at night.

Other improvements and options

The first improvement is to install a solar panel on the roof of the car, that will increase the energy of the batteries, and then the range of the model.

The other improve is the configuration of the propels. The option is to use a propeller to propels the model, and two or four duct fan to lift it. The propeller has more efficiency propels a plane in different envelope of a flight.

On the other side, the duct fan is better for smaller speeds abut high rpm, with higher efficiency for vertical taking off and landing

Also I made a little and not so good looking video jajaja. The software used was Catia, which is not the best making renders and video renders. I am still improving in Keyshot to learn how to make video renders.

As a conclusion, I want to say that this design is based in the lift body idea, so the entire design has its limitations. 

Underrun truck challenge

This little project started as a challenge of the website GrabCad https://grabcad.com/challenges in which a company wanted to design a underrun truck protection.
Unfortunately, I was busy at that moment, so I couldn't participate in it. However, now with much more free time, I decided to do it by my own (without any compesation) to show how a small structure design can be done, and to show new engineer students. If I can, I will prepare a video on youtube to show step by step with all the details how I did it.

As the most important point, the company of the challenge made public the requirements of the underrun protector. All the features and requeriments are inside the next pdf file: https://mega.co.nz/#!ONggkC4K!DEhosz1uiOcregHUNwPCTLYPXKk6_LTQAem-wdBcJxQ

The most important points of the requirements are the dimensions, the load cases, the material, and the options that we can do.

The dimensions of the main protection (the beam) are a length of 2500 mm and 100 mm of width. The minimum thickness is 10 mm, but could be more.

The load values are defined by the client in three static load cases of pressure, that are distributed as it can see in the pdf or in the next image.

The first case of load is of 1,25e6 Pa, the second is 2,5e6 Pa and the third 1,25e6 Pa. 

The material selected y the customer is a normal Steel with a young modulus of 205GPa, a poisson value of 0,28 and a density of 7870 Kg/m3.

According to the customer, the maximum deformation allow is 40 mm, and the maximum stress value of 355 Mpa. The steel used has a elastic limit point of 200-250Mpa, so the value proposed by the client has sense since it is a protection devide that has to be taking out in case of an impact.

The steel a stress break point around 400 Mpa, so it represents a 1,127 of extra stress, that in my case I cannot be sure since the trucks industry is not my specialty. Taking that the extra value of stress is correct, if not it can be changed, I proceed wit the study/project.

The client also ask that the entire model must be designed in one piece, not as an assembly. The stress study could be done using one online CAE software that in my opinion is not the most accurate; so for this study I will use the CAD software Catia to design the protection, the Abaqus CAE in the Standard mode for the tress/deformation analysis and the software excel fot the mathematical operations.

Other designers during the challenge spent all their resouces in design a "cool" underrun protection. Most of then were designers not engineers, so a "cool" design is more their role. In my case, as an engineer, I prefer center the design in a protection that can resit all the client load cases, with the less material possible, and if it can be the less weight too using just one material, less volume means less weight).

For that reason, my objective is to find the minimum thickness of the beam (according with the shape of the section) that can resist the pressures.

Because start doing designs in catia and analysing with Abaqus until have the correctone would take months, the best way is to use the excel and the material mechanic to make the three load cases and determine the minimum thickness, and then check it using the computer softwares.

The next file is the excel, in which the three load cases are calculated. I compared a normal flat section with a square (empty inside) and this last one, was too strong, so the material wasted would have bee too much.

https://mega.co.nz/#!OA4HXbwS!VfPF-3lwYy9cDr2rGpuMoYUuzNqWt9WspD2WlFzcMNk

After determine the minimum thickness of 45 milimiters, I check the values using a catia model and run it using Abaqus CAE.

As it can be seen easily, if a comparation is done between the excel results and the Abaqus ones, the values are very close, showing that the protection can resit the impacts.