How can a vehicle fly?

 

How does a flying vehicle achieve flight?

Basically, there are four main ways to do this. It's all explained in the video below. Do take a look.

A summary of the contents of the video are given below.

Method one: Lighter than air

To achieve this, a vehicle must be lighter than air. Think of, say, a helium balloon, or a hot air balloon, or an airship. This type of flight uses the Archimedes principle to be airborne. Basically, the upthrust on anything in a fluid is equal to the weight of the fluid it displaces. If a vehicles displaces more air (in terms of weight) than itself, it will float.

It’s pretty easy to accomplish, if you can find a gas that is lighter than your ambient air. Helium can be pretty expensive. Hydrogen is an option, but it’s very flammable when mixed with air. Hot air is a pretty good compromise (the gas itself is not flammable), but you need a fuel source to, well, heat the hot air.

In this type of flight, you can change altitude by changing the overall density of your vehicle. This may be by reducing the amount of your lightweight gas (to loose altitude) or dropping something heavy like basalt (to gain altitude).

Method two: The reaction from a downwards force

Here, you can direct air downwards to create an upwards force that keeps your vehicle airborne. Think helicopters and jet packs. The advantage here is you can take off from pretty much anywhere and the vehicle isn’t massive like in the previous case.

The disadvantage is fuel requirement. A helicopter is more efficient than a jet pack, but you still need to produce enough lift to counteract the vehicle’s weight.

Method three: Fixed wing

Here, you use the shape of a lifting surface (wings or the whole vehicle) to create an upwards force based on speed. This is generally more efficient than straight up producing the thrust to lift it up. Think airliners and general aviation and fighter jets. These are, unsurprisingly, fast.

You can also have the unpowered version in gliders, where you can use air currents to generate the lift you need.

The problem is landing and takeoff. You need a long, clear area to take off and land. Because of the high speeds and the proximity to the ground, landings and takeoffs can be relatively dangerous. Modern airliners and airports are designed to be very safe. However, if you’re dealing with, say, the early days of aviation or a society that is just discovering this type of flight, it could be a point you can consider.

Method four: Flapping wing

This is what’s seen in most birds (the larger ones who glide a lot mix it up with fixed with flight quite a bit, and smaller ones may be going into a completely different type of flight). 

There have been man-sized ornithopters (as they are called) as well.

It’s pretty efficient, but the problem mechanical complexity if you want to make a machine that uses this type of flight. You can take off from most places (heavier birds still need a runup), and you can change to the more efficient and faster fixed wing flight once you’ve taken off or if you want to glide.

In short...

These are not the only ways you can achieve flight, but these are the most practical methods for vehicle sized things.

Expect more flight related videos and articles in the future.

Please let me know what you think in the comments, and please ask if you have any questions.

See you next time!

On giant mecha - how practical are they?

You know exactly what I am talking about. You've probably run into them at some point, be it through films or some form of animation. This article will be about their practicality, with current technology.

So, first things first, can it stand?

Let's look at some figures.
The tire pressure of an aircraft is the pressure it exerts on the ground (the surface area of the tire in contact with the ground changes depending on the weight of the aircraft, keeping the pressure constant). For most commercial aircraft, it's about 200 psi - or 1 379 000 pascals (Newtons per square meter, approximately 137 900 kg per square meter of tire surface). This is designed for the hard surface of runways and taxiways in an airport - such an aircraft can't land on soft ground and not sink into the ground at least and little.
The ground pressure (as it is called), for more everyday things - like humans - is a lot lower. A human exerts about 55 000 pascals when standing, though this can more than twice that when walking / running (source: wikipedia). A passenger can exerts about 205 000 pascals. A mountain bicycle exerts about 245 000 pascals, while a road racing bike exerts about 620 000 pascals. A stiletto heel can exert as much as 3 250 000 pascals - more than an aircraft (which is why they damage floors and many other surfaces).

Let's see what this translates to. If the ground pressure is to be the same as that of a normal vehicle, a 100 tonne mecha would have to have a surface area of (100 x 1000 x 10)/(205 000) = 4.878 m² in contact with the ground. To stand on 1 foot (and walk), this would require a foot that is about 2 m wide and 2.43 m long. For one that's half that weight, the required area of the foot would be half of that (about 1.5 m x 1.62 m).This is assuming that pressure is distributed fairly evenly by the foot, which is highly unlikely unless it has a rubber sole (which would immediately make kicks about one third as cool). Chances are, if the mecha are made like humans, more weight would be concentrated on the back of the foot.

Still, according to these calculations, a mecha would probably be able to stand on most surfaces.

Part II - can it not collapse under its own weight?

A major issue we face here is the square-cube law: doubling an object's dimensions, which multiplies its surface area by a factor of four, also increases its mass by a factor of eight. This is a problem, because properties like tensile and compressive strength depend on an object's cross-sectional area. So, when you increase it's strength by a factor of 4, you increase its mass by a factor of 8, which means you need more strength to support the increased weight.

Let's compare some comparable structures.

Falcon 1 rocket: Height: 21.2 m, Diameter: 1.7 m, Mass: 27.67 tonnes (source)
Boeing 747-8: Length: 76.25 m, Wingspan: 68.4 m, Mass (Operating empty weight): 220.128 tonnes (source)
Rockwell B-1 Lancer: Length: 44.5 m, Wingspan: 24 m - 42 m (swing wing), Mass: 87.1 tonnes (source)
Falcon 9 rocket: Height: 70 m, Diameter: 3.7 m, Mass: 549.054 tonnes (source)

I chose the Rockwell B-1 Lancer as an example because it includes a rather large moving part - the wing sweep can be changed in flight.

As you can see, chances are, an average mecha will not crumble under its own weight - if it was standing still. So, you can build a statue of it without a problem. However, that is not what we want, we want it to be able to move, to run, to shoot lasers, and to kick other mecha in the face.

So, it needs to move...

Therein lies the problem. To accelerate a part as heavy as a mecha's legs, you are going to need some very powerful motors. For a 20 m, 50 tonne robot, we can assume that its legs are about 10 m tall - approximately half its height. If one third of its weight is in its legs, and the centre of gravity of the leg is one third of the way down the leg from the hip (both are probably conservative estimates), to swing the robot's leg, you will need a torque of (10/3)*((50 000*10)/3) = 555.56 kNm. A 100 kNm motor looks like this (look at the images this page).

In addition to that, to accommodate all that movement, the legs will have to be strong. As in, it should be able to handle being swung at something at high speed, with something heavy attached to the end of it (the foot, the lower leg, and the knee joint, and all associated actuators/sensors) without bending in the middle.

But I got ahead of myself. In order to kick something in the face, the mecha has to reach said target, and if it is, indeed, terrestrial, it has to walk or run there. Walking can be rather complex. One foot has to be taken off the ground, while the weight balances on the other momentarily, and when that foot reaches the ground, the weight must be transferred to it in order to move the other leg. Running can be more taxing still - the mecha has to generate enough force for both feet to leave the ground temporarily. Besides, running exerts a lot of force on the ground (Newton's third law).

All this means a lot of bending moment on the legs, as it balances the body over the heel like an inverted pendulum. To counter this, you need very strong materials for the legs. If you want it to stand on the ground without turning a paved road into quicksand, and if you want reasonable sized motors / actuators, you will need a light-weight material. There are few materials that meet both these requirements.

Provided we found the right material, we still have to move the individual joints. We will need fairly large motors if we are going to use motors. These motors would probably need a lot of current, which introduces a host of other problems (motor control becomes more difficult, and the wires get thicker and heavier, among other things) Another viable option is hydraulics, which will also be very large and very heavy. You will also need a full hydraulics system if you select this option, which also translates to more weight,complexity, and issues with materials. In either case, the actuator we use must be fast,responsive, and very controllable. Finding or manufacturing such actuators will not be easy.

Power?

In order to do all of this, we need a source of power. Given the space constraints and the energy requirement, nuclear might be the only really viable option, but the reactor size will probably have to decrease a little. Power isn't my area of expertise, so I can't say for sure, but I don't think the technology is there quite yet.

Controllability

And now, my favourite part the discussion - how do you make the robot work?

First, you will need to know the robot's starting configuration - how the limbs are positioned, the robot's posture, whether it's stationary or moving, etc. For this, you will need sensors, and a lot of them. You will need to know the position of each motor. You will need to know the tension on the leg beams. You will need accelerometers and gyroscopes, probably in each limb, to measure current linear and rotational acceleration. All this is available, so there is no problem there.

The next problem is judging where the robot is going to step. You can use a radar to map the contours on the ground, and you could also use images from one or more cameras to help you. A laser scanner could also help, but it could be overkill in this case. Again, we have the technology - it's expensive, and difficult to implement, but we definitely have the technology. If there is any problem here, it's creating a transparent window through the foot to get the images necessary.

This information has to be processed. That shouldn't be too hard, but a possible issue is time delays. Chances are, all control will be by a central processor, which will command lower level processors in the limbs, etc, at a high level (at least, that is the design that makes the most sense to me). In order to get it to walk, the arms, legs, torso, and head movements must be coordinated. Delays in transmitting main control commands could potentially throw the whole system out of sync if the problem is bad enough. If the feedback from the limbs, etc. are delayed, or if the data from those sensors are gibberish, that could cause a problem as well. Also, there is the problem of sensors producing readings at different rates, which can be dealt with, but it can cause problems. The long distances can make data transmission errors more likely, but that can be dealt with.

The next problem is the actuators themselves. If my experience teaches me anything, it is that this part is going to be ridiculously difficult. As I mentioned before, finding motors or other actuators that are powerful enough and quick enough would be difficult. I can't be certain about hydraulics, but with motors, controlling it is going to be difficult because finding a motor control circuit that is small enough, and won't heat too much (or burn out) with intermittent operation would be nearly impossible. The other problem is managing space when installing them (though hopefully that wouldn't be too much of a problem with hydraulics.

To summarize,

Sensing and data processing can be done - it won't be easy, but it can be done.
If you can build it, it will be able to walk without sinking a couple of metres into the ground with each step.
Finding material that can be used to build it will be a problem.
Finding a power source is likely impossible right now.
Finding suitable actuators would be very difficult.

The verdict: It's not possible right now, but maybe it will become a reality in the near future. It might not have any practical use, but it'll be an interesting experiment for nerds like us.

You can follow me on Facebook here for news and updates.

Until next time!

The silent GPS

As a part of my work, I recently had to work on a GPS unit. This is about my misadventures trying to get it to work.
The trouble began with it being a rather old unit, and as such it wasn't exactly as simple as more modern units would have been. Still, I did figure out how it was supposed to work - so far, so good. I got the components, set everything up, and expected to get a reading.
Except I got no such thing.
My immediate first guess was a communication problem - I wasn't too familiar with it after all and the power light was on. So I looked it up, and checked the cable. Nope. It's working perfectly. I checked the settings against the manual. My settings were correct.
Then I went through the manual again to see whether any of my commands or settings were wrong. Nope.
The only other option was power. On closer inspection, the unit wasn't drawing any current. So, I had identified the problem.
The unit had a fuse. That was my first suspect. Tested it - no, it wasn't blown.
Then I checked the power circuit. It said 12 V, but the GPS itself was rated to handle a range of voltages, so to be on the safe side I had gone with 11.5 V. On closer inspection I saw a 7810 regulator. The rated input is 12.5 V, but even with a lower voltage it should have given a steady DC output, though probably at less than 10 V. The GPS should have worked under those circumstances. still, nothing had worked and I was a little short of resorting to an exorcism, so I thought I might as well increase the voltage to 12.5 V. Still, no response. It simply wasn't drawing any current.
At this point, I was reaching the concluded that something was possibly fried.
The next task was identifying what was fried. It was either the power supply or the GPS. Fortunately the designers of the unit had allowed for measuring the current output. That allowed me to determine that the output power from the supply was zero.
Having determined that, I checked the supply again. Possibly there was something I had missed, something that would allow me to identify the real problem. Perhaps a small switch on the board...
There was no such thing. Finally, I closed the box, and lo and behold, on the outside of it, was a rather large power switch. It was in the off position.
I turned it on, and well, it worked.
At least, thanks to this fiasco, I had read the manual thoroughly and all the connections were right when I finally switched it on. On the flip side, I wasted quite a few hours of my life.
So, the point I want to make is, always check the obvious, and do not blindly trust power buttons.


yours truly,
Falcon-15-X-C

Evolution of technology - a perspective

Those of us who have tried world-building, be it for a story or for some other purpose, have run into this problem at some point or the other. How would the environment affect the evolution of technology?

For this discussion, I will focus on aircraft, mostly because it is one of my favourite areas. Also, what makes it ideal for discussing this topic is that aviation as we know it developed a little over a century ago, and most of its progress is recorded.
What is discussed here is the hypothetical scenario where someone or a group is approaching the development of aircraft. How will they approach it, realistically?

Where do you begin?

Imagine a civilization is developing aircraft for the first time. Where would they start? One of the first things most people would look to is birds - provided birds exist in this hypothetical scenario, of course. They're everywhere, and they're obviously flying, and they make it look easy. This is why we have stories of this sort - Deadalus and Icarus, as well as various fairy tales.
Assuming this doesn't work, what would you look to? The most obvious answer would be gliding - like eagles, for example. Remember, it is entirely possible to glide for hours if you can launch yourself off from a height.
Lighter than air craft is another possible option. These are hot air balloons, blimps, and airships. This requires some understanding that air is a fluid, and that things can float in it. This is probably not exactly obvious to someone who hasn't encountered this before, but at least you can expect scientists to be aware of this.
Lastly, there are fixed wing aircraft. This is the type we use most commonly - with fixed wings providing lift, with thrust provided by engines. The speed of the air moving over the wings creates a pressure differential, which creates the lift necessary, in the simplest terms. The concept is easy enough to discover - try moving a plate of some sort through the air at a slight upwards angle through the air. However, identifying the accurate relationship between speed and lift, and the drag generated in the process, may take time and a lot of experimentation.

What limits it?

Material

A major problem that most early attempts at flight encountered was the lack of suitable material. In general, you want the material in question to be light and strong. Modern aircraft are mostly made of alloys (mostly aluminium based, or titanium based) and composites which meet this requirement. Most models are made of Styrofoam, or balsa wood and spruce wood, and plywood and carbon fibre may be used for specific components. Birds have 'hollow bones' - actually, it doesn't have any marrow inside, but is supported by bone struts to help it take the stresses of flight. Unless you can find material that will do the job, flight would be impossible.
In general, you will need high strength for the wings and wing attachments, engine attachments (if there are any), control surfaces, and joints in ornithopters (bird-like aircraft). You'll also need high strength for internal components of engines (depends on the type of engine).

Power

Another main limiter is power. Early attempts at powered flight were made with steam engines. These tended to be on the heavy side, which was a problem, since the engine had to produce enough power to lift its own weight and the weight of the air-frame off the ground. Lifting a higher weight needs more power, which needs a heavier engine - you get the idea. So, you're going to need a power source with a reasonable power to weight ratio.
There are more ways to produce the power necessary than just engines. You can use some form of jets (again, depends on material and someone actual getting the idea), rockets (Me 163 Komet, for example), or even an electromagnetic catapult to launch it into the air. Of course there is nothing stopping you doing the same with a catapult or a crossbow, but I am not sure the pilot will appreciate it.
In a fantasy setting, you can always manipulate the airflow around the aircraft in question directly, which will likely reduce the power requirement drastically (airbending, in Avatar the last airbender, and Legend of Korra, for example).

Controllability

Figuring out how to control a plane with no prior knowledge about it can be tough. The Wright flyer used wing warping - that is, using cables to warp the wings and control surfaces to make it turn or otherwise respond to commands. Most modern aircraft use a variation of the same - instead of warping the entire wing, they move dedicated control surfaces, like the rudder, elevator, or ailerons. An ornithopter can differential flapping and moving the tail to control itself.

Other Challenges

Size scaling

A bee does not fly the same way an eagle does. Directly scaling up things does not always work when trying to develop an aircraft. For one, if you scale length up by two in all three dimensions, the area quadruples while the volume is multiplied by eight. This is a problem because lift depends on area, while weight depends on volume. You can be in major trouble if you don't realise this (running off the end of the runway without lifting off, for example). This can happen if you're developing the entire field as you go along - people have made incredible obvious-in-hindsight mistakes in similar situations. Another is that the characteristics of airflow change completely based on the size of the object flying - but the exact mechanics are enough material for an entire article on its own.

The risk

If an automobile loses control, especially at low test speeds, you can expect the driver to walk away with relatively minor injuries. Not so with aviation. It's one thing if it doesn't take off, but if the beginning of your flight involves a jump off a tower or a cliff, things can get nasty if the aircraft doesn't actually fly. The same situation can happen if the fragile test aircraft breaks up in midair for some reason. In this case, unless the person inside can fly independently of the aircraft, or is damage resistant, he's likely to suffer some form of grievous injury if not death on contact with the ground. How the characters handle this risk - whether they test it themselves, investigate the possibility of unmanned tests, or delegate the task to others can give some insight into their character.

In conclusion, the development of a new technology is a long and involved process. The presence or absence of an element can drive things in a completely different path. If they had strong, light materials and powerful engines in the renaissance, who knows, we may have started aviation with ornithopters. If it was just the material, gliding may have become quite popular a long time ago. This availability, on the other hand, could have caused other problems that we could never have anticipated. Who knows?

I haven't even begun to cover this immense topic here. If you would like to read it, I can do a much more in-depth, technical article on the basics of flight, with a better explanations of the many things I have mentioned in this article.

I hope that helps!
Not actually an avian,
Falcon-15-X-C