Aerial Lift

Posts Tagged ‘Aircraft’

Aerial photography is as challenging as it gets for the professional photographer. Many decisions need to be made to get spectacular results, everything from type of aircraft to subject matter and time of day. Teamwork is also required as the photographer and pilot have to communicate well in order for the photographer to get the desired images. This article covers aerial photography platforms with a small amount of photography technical information. Part 2 will cover the technical and artistic side of aerial work.

While aerial photography has been accomplished with everything from hot air balloons to space shuttles for most of us we are a little limited in the resources we have available. I have used helicopters, fixed wing aircraft and ultralights for my work and I’ll cover these in a little more detail in my personal order of preference.

Helicopters:

Aerial photography from helicopters is likely the easiest platform to work from under most circumstances. When used specifically for photography most pilots will allow the removal of a door leaving a large workable shooting area available. This can be very advantages as you can literally pan the camera to keep the subject within the frame while still travelling in a straight forward direction. Helicopters also have very impressive turning characteristics so you will find that there is far less lost time as you circle back to shoot from a different altitude or angle.

There are a few downsides to shooting from helicopters however. Firstly is the big expense, easily $500 per hour or so for a Robinson R22 to $1,500 or more for a large jet. It’s very impressive how much you can shoot in a few hours but the credit card can take a big hit after you land. Do you need a jet helicopter for most uses? I have used both the smaller Robinson’s and large jet helicopters and have had very good results with both. Some will argue that the bigger helicopters are a little safer but I’ll leave that up to the experts. Jet helicopters are significantly faster so if you are travelling large distances they can have an advantage. Secondly, vibrations can be an issue depending on a number of factors. My experience has been that a good pilot can often hit a “sweet spot” where the helicopter settles into a somewhat smooth forward motion. This generally is not while you hover, forward movement plays a part.

Helicopter photography from a technical standpoint can be both a challenge and an exhilarating experience. If you can’t remove the doors wear dark clothing and make sure to have a lens shade installed. Most of the windows are Plexiglas and tend to have scratches so you will probably want to shoot fairly wide open to limit the depth of field. Window tint might also be a problem although this can generally be cleaned up in Photoshop or some other editor. I recommend shooting RAW for this reason. Whatever you do, do not place any part of your body or camera against the sides of the helicopter as the vibration will transfer over to the camera and cause unsharp images. Life is easier without doors but be aware of the turbulence if you lean out a little too far. The buffeting can be quite strong. All gear and other equipment needs to be securely fastened to your body or a harness, you don’t want to think about what might happen if you drop a lens or camera out the door! I go as far as taping the lens hood to the lens as a safety precaution as I’m sure the tail rotors  would make quick work of a lost lens shade, possibly with bad consequences. If at all possible use a few different cameras so you can keep changing lenses and memory cards down to a minimum.

I try to keep my shutter speeds around 1/1000 or faster if at all possible but have had reasonable success around 1/500. If this means increasing the ISO as the light fades I do this in preference to having somewhat blurred images. This should allow for an aperture of about f5.6 in most circumstances although as the light fades you might be looking at f2.8 or so, a good reason to have fast lenses.

Ultralight:

I first did aerial photography from an ultralight in Costa Rica a few years back. I must admit I really didn’t know what to expect as all my previous aerial photography had been done from helicopters up to that point. I expected a large amount of vibration and bad wind buffeting but was in for a shock. Ultralights are actually an amazing aerial photography platform under the right conditions which is when you tend to fly them anyway. They do get tossed around a little bit but generally the vibrations are not as bad as helicopters. While they aren’t as maneuverable as helicopters they are better than fixed wing aircraft. Possibly the only downsides are, they are somewhat slow and you have to feel comfortable in them as they are very bare bones and seat of the pants!

Fixed wing aircraft:

Likely the bulk of aerial photography is done with fixed wing aircraft. While not as maneuverable as helicopters they are still very competent shooting platforms under the right conditions. Try to get an airplane with a high wing like the Cessna 172 Skyhawk to get the best view. The low winged aircraft really limit the view below! Even with high wings the wing strut will probably be in the way, it’s just not generally located in a good position for photography. I’m sure some people fly with the doors off but in general you will be flying either shooting through a small opening window or through the glass. Either way, positioning of the aircraft is very critical to line up the image so a good pilot preferably with experience working with photographers is a must. What’s the biggest advantage of a fixed wing platform? Cost! Likely 1/4 or less of what the helicopter will cost.

Getting organized:

Flying in circles looking for photographs could be very exciting and entertaining until you land and find out how much money you spent without really accomplishing anything. Do your research beforehand and get a good idea about what you want to photograph and how you will accomplish it. What side of the aircraft will you be shooting from? What altitude or different altitudes are required? When will the light be the best? Often you will find that one flight will not produce all of the required images due to some of these decisions and a second or third flight might be required.

Once you have done your homework it’s time to find your aircraft. What’s your budget is likely the biggest decision here as well as what type of aircraft are available? Hire a good pilot, preferably one that has experience working with photographers! Pilots do vary and some are better at others when it comes to understanding the requirements of aerial photography. Go over a flight plan and stick with it. The most important part of the shoot is the pilot calls the shots and has the final say in what will be done. They know the regulations, safety issues and the bottom line; they are responsible for you, the aircraft and the people on the ground!

Happy shooting!

1. Introduction 

                Aerodynamics is the science of air in motion and explains how and why an aircraft flies.  It can be compared to, and contrasted with, aerostatics. 

2. Aerostatics               

                Contrasted with aerodynamics, aerostatics is the science which explains how and why a hot air balloon, or similar craft, attains lift.  These aerial vehicles do so by means of the buoyancy principle.

                Air is compressible—that is, its own weight compresses it.  The lower its location in the atmosphere, the more air—and therefore weight—is above it, rendering it densest at or near the ground.  Conversely, as it rises, it becomes thinner.

                Hot air balloons utilize these varying conditions to attain lift.  Heated air, or lighter-than-air gas, within a balloon’s envelope causes the balloon itself to rise, because its internal air is less dense than the surrounding air.  When it reaches the altitude where the density of its internal air equals that of the surrounding air, it ceases to rise and attains a state of internal and external equilibrium—that is, 

Internal gas density = external gas density 

                At this point, the downward pressure exerted on the balloon equals the upward pressure on the balloon.

                Balloons are designated “aerostats” because their lift is attained in a static air mass—that is, an air mass which does not move.  An aerostat, such as a balloon, moves vertically, but relies on existing wind direction and speed for its horizontal motion.  As a result, it cannot be relied on for specific-direction transportation.

                Aerostats with controlled movement employ one or more propellers for velocity and direction, and are designated “airships,” but these propellers do not provide or augment lift.

There are two types of airships:

Non-rigid airships, such as the Goodyear blimp. Rigid airships, such as the Hindenberg, which had contained an internal framework. 

3. Aerodynamics 

                Unlike an aerostat, an aircraft is heavier than the air it displaces and hence cannot be “buoyed up” in a static air mass.  Its lift can only be achieved by the science of aerodynamics.

                Aircraft are subjected to four forces in flight: thrust, drag, lift, and weight.

                Thrust opposes drag, while lift opposes weight.  It is these latter two, however, which play the greatest role in aerodynamics.

In order to overcome weight, itself the result of gravity, an aircraft must create a force at least equal to it to produce straight-and-level flight.  That force, of course, is lift, but how is it created?

                Part of the answer lies with a Swiss mathematician, Daniel Bernoulli, who had sought to determine pressure differentials of water streams flowing at varying speeds.  Because he had died in 1783, or one year before the Montgolifier Brothers of France had successfully made the world’s first aerial balloon ascent, his experiments had no connection, or intended connection, with aviation, although they ultimately did.

                Many of these experiments had been conducted with the aid of a venturi tube, which, because of its varying diameters, had been able to restrict the flow of liquid through it at certain points.  It had been at these smaller diameters that flow speeds of liquid had increased, but, surprisingly, their associated pressures had decreased, resulting in an inverse correlation and the law of physics which states: 

As speed increases, pressure decreases. 

                This law partially aids us in determining how lift can be generated when its principle is transferred to a wing.  Before we discuss how this occurs, we first need to review a few wing-related parameters.

                The wing itself, of course, is that surface which creates lift on heavier-than-air craft and can provide the platform to which the engines are attached.  Its leading edge is its forward, geometric edge, while its trailing edge diametrically opposes it.  An airfoil is a cross-section of a wing and its camber is the characteristic bulge or hump on its upper surface.  That camber is tantamount to its ability to produce lift.

                When a free stream of air, which has a uniform velocity, intercepts a wing’s leading edge, it does so at what is known as the “stagnation point,” whereafter it divides and either flows over the wing or under it.  This, however, is where its uniform velocity ends, because the distance it must travel over the wing, as a result of that bulge-like camber, is greater than the distance it must travel below it, yet both flows reach the trailing edge at the precise second.  The only way the upper surface flow can achieve this is to increase its speed.  Imagine a student leaving his house and walking one mile to school.  His brother, who lives in the same house, leaves at exactly the same time, but takes a route which covers two miles.  Yet he arrives at the school at the exact same time as his brother.  The only way he had been able to achieve this had been to travel twice as fast. 

                With this increase in speed, the Bernoulli Principle comes into play.  As you recall, as speed increases, pressure decreases.  And this is exactly what occurs on the wing’s upper surface.

                With pressure now diminished, the wing is free to rise, producing lift.  This lift can also be partially explained by another physics principle, which states that “an object always takes the path of least resistance.”  If you had been locked in a room with two doors and one of them could not be budged open with all your strength, yet the other opened with minimal effort, which path would you take?

                As pressure decreases above a wing’s upper surface, the path of least resistance is up!  An imbalance of pressure forces, as had occurred with the aerostat before it had been disconnected from its tether on the ground, now exists between the upper and lower wing surfaces. Unlike the aerostat, however, the wing’s lift is only produced by the motion of the air over and under it.  As a result, the “air” is said to be “dynamic,” and the contraction of these two words results in the term “aerodynamics.”

                Whether air movement over an airfoil is produced by the wing itself traveling through it, or the air blown over a stationary wing, mounted in a wind tunnel, the same result is obtained.  Since few people have wind tunnels in their homes in which to test these principles, it cannot be demonstrated to any scientific degree to the amateur.  Nevertheless, two informal methods exist with which to do so.

                The first, intrinsically attempted by most children, occurs when they extend their arms out of a car traveling at significant speed.  Seeming to ride a cushion of invisible air below, and no longer obstructed by equally invisible, but greatly reduced pressure above, they react by rising up and it usually requires concerted effort to keep them from doing so.

                The second method entails blowing air over a slender, wing-representative strip of paper.  Logic may tell you that, as you blow over the top of the paper, that it will be forced downward, but instead, verifying the Bernoulli Principle and the forces of aerodynamics, it rises.  Lift has therefore been created it.  Try it!

                A very small amount of lift is also created when an aircraft is close to the ground, such as shortly after take off or shortly before touchdown.  The force of the aircraft is exerted downward, while the ground itself reacts and sends a counterforce upward, to the aircraft, echoing Sir Isaac Newton’s Third Law of Motion.  “Every action has an equal, and opposite, reaction.”

                Because the amount of camber is integral to the creation of lift, wings can artificially increase this parameter by two methods:

An aircraft can increase its angle-of-attack, pitching upward so that the upper wing surface offers a greater curve to the air’s path. Wing leading and trailing edge slats and/or flaps increase the wing area and curved path the air must follow, particularly during slower, post-take off and pre-landing flight realms.

                The next time you fly, you will know a little more why.

The Scorpion Aircraft Tug is very resourceful and valuable in the aircraft industry today. It saves space, money time, and gas or diesel fuel costs.

This recently designed battery operated maintenance vehicle not only saves a private and or community airport a remarkable amount of money in several ways but it also saves FBO aircraft mechanics a significant amount of time when servicing airplanes.

Several pieces of equipment are usually required when servicing an airplane, equipment such as a utility vehicle, a tow truck, a crane, a tug tractor, and an auxiliary power unit.

This aircraft maintenance vehicle has the ability to tow aircraft up to 15,000 pounds gross weight, Lift its arm capacity 1,000 pounds (lift up to 2 feet high), it quickly converts from a tug to a crane, the drive throttle controls offer ultra-smooth acceleration control for speeds as slow as 1 fpm up to 4 mph, the drive system features “dead man” controls, automatic braking, and the drive handle pivots 90° for zero turning radius, it includes a folding rider plate for use as a walkie or stand-up rider, it includes headlights for improved visibility, a built in auxiliary power unit, a fire extinguisher, and amber operation light and it is clean-air battery powered for a quiet, smooth operation.

This well-built aircraft tug also allows airports to save on gas and diesel expenses. Since it is battery operated all it needs is a little overnight charge.

Read more about this newly designed and successful Aircraft Tug at Air Technical Industries.