Morgan Sabala
November 20, 2012
Dr. Harlynn Ramsey
Writing 340
Radar Proof Your Pick-Up Truck: The Engineering Behind Stealth Technology
Biography
I am currently in my final semester at USC where I am studying civil engineering. I
transferred to USC from Whittier College two years ago as a part of their 3-2 engineering
program. After graduation I plan on continuing my education at USC as I pursue my master
in construction engineering and management. I am also a member of CMAA (Construction
Management Association of America) and will be competing on the graduate team for the
2013 Sparks Competition.
Abstract
With the rapid increase of technology, military tactics are continually being updated
and created. Stealth technology, which was introduced decades ago, began with simple
camouflaging to avoid visual observance from the ground. With the development of new
technology, radar in particular, stealth technology takes on a bigger challenge than just
visibility. Although radar detection has also been extremely beneficial in many ways for the
military, with its development and other detection tactics it will always create challenges
for stealth technology. With cost being a primary issue of stealth development, the real
solution relies on today’s scientists and engineers breaking down the basics behind stealth
tactics and finding the most inexpensive and efficient methods.
Keywords: Military, Stealth, radar, visibility, infrared, acoustic, Doppler effect,
Multimedia Suggestions:
http://www.radartutorial.eu/11.coherent/co06.en.html
Radar Proof Your Pick-Up Truck: The Engineering Behind Stealth Technology
Introduction
One day my grandma began telling me about this show she had been watching
called Rocket City Rednecks. The show stars Travis Taylor, an aerospace engineer who has
worked for the United States Department of Defense and NASA for the past 16 years.
Taylor’s best friend and three relatives join him and together they use their advanced
knowledge of science in solving more “real world” challenges such as tornado proofing
your outhouse or creating a rocket that uses moonshine as its fuel. In one particular
episode, Taylor and the guys set out to radar proof their pick-up truck using stealth
technology. The goal was to create radar proof panels that would avoid radar detection
long enough so that the driver could spot the police officer and slow down. Every episode
of the show focuses on taking some of the most advance engineering technology and
breaking it down to cheaper, simpler and understandable concepts. When one thinks of
stealth technology, highly sophisticated and intense engineering techniques come to mind.
Although stealth technology is a highly advanced topic, understanding the basic
engineering concepts behind it, will help its development and efficiency for the future.
History
Stealth technology, also known as “low-observable” technology, is a set of
techniques that are used to make military vehicles, aircraft and ships unobservable. In
particular, stealth technology focuses on suppressing radar, which is the primary
technology used for aircraft detection. Additionally, it also incorporates visual, infrared and
acoustical tactics.
Stealth technology began developing before World War I in 1914 [1]. At this time
radar had not been invented; therefore the focus of stealth technology was visibility. In
1912, German designers began creating what they called transparent aircraft. Transparent
material made from cellulose was used to cover the aircraft’s body and wings while other
parts were painted with light colors. This technique made the aircraft invisible from the
ground when flown around 900 feet or higher [1].
When radar was invented in the 1940’s, it was extremely effective at detecting
aircrafts. This posed a new challenge for stealth designers and changed their focus from
visibility to radar. Radar detection can be avoided in two ways: by radar absorption or
radar reflection. In 1945, the United States developed a radar-absorbent paint containing
iron that made aircrafts less radar reflective [2]. Unfortunately, the paint was heavy;
putting several coats on an aircraft made it difficult or even impossible to fly. Although the
United States found more effective engineering methods to avoid aircraft detection
throughout the 1960s and 1970s, the cost of engineering them were and still are extremely
expensive [1]. The first US aircraft initially designed around stealth technology, as seen in
Figure 1, was the Lockheed F-117 Nighthawk costing approximately $100 million [2]. As
stealth technology continues to develop, breaking it down into simpler concepts, like Travis
Taylor does, may help create the most effective, affordable solutions.
Figure 1: F-117 Nighthawk
Source: Gale Encyclopedia of Science
The Lockheed F-117 Nighthawk was the first
US aircraft that was specifically designed
around stealth technology. Its first flight took
place in 1981 and it was acknowledged in
1988.
To be “Stealthy”
As aircraft detection technology advances, stealth technology will also advance.
Right now, there are four main characteristics of stealth technology: visual, infrared,
acoustic and radar. For an aircraft to be considered “stealthy”, it must be visually
unobservable, have limited infrared radiation, be inaudible, and be able to avoid detection
by radar.
Visual
The first characteristic of stealth technology is low visibility. Stealth designers use
certain colors for aircraft material to help them blend in with the environment. For
example, daytime fighter aircrafts are painted a shade of blue to blend in with the day sky.
Stealth aircrafts mostly fly at night and therefore are painted black or dark grey to blend in
with the night sky [1]. This is more commonly known as camouflaging. For the stealth truck
in the show, Taylor and the guys decided to make the stealth panels camouflage by spraypainting them black, brown and green. By doing this, the truck can blend in with the
environment and hopefully cause a delayed reaction by the police officer to use the radar
gun. Although visibility is an easy concept to understand and incorporate, it will always be
an important characteristic of stealth technology.
Infrared
The second characteristic of stealth technology is decreasing the infrared radiation
produced by the heat of the engine or wing surfaces. This is important because missiles can
be designed to seek heat and will pick up the infrared radiation produced by the aircraft
engine. More infrared radiation is emitted from hot materials than cool materials, therefore
to create infrared stealth requires keeping the engine and other parts of the aircraft as cool
as possible. To do this, engines can be embodied within the aircraft and covered by extra
shielding, or the hot exhaust can be mixing with cool air before it is emitted [1]. The F-117
Nighthawk designed by the United States lacked efficient methods of reducing infrared
radiation. As infrared detection advances, stealth designers will need to put more focus on
this characteristic for stealth technology.
Acoustic
The third characteristic of stealth technology is acoustical stealth. Although this
characteristic may not be focused on as much as the others, it is still important to make
stealth aircrafts as inaudible as possible. Acoustical stealth is accomplished by using small
internal combustion engines quieted by silencer suppressor mufflers [1]. It can also be
accomplished by using sound-absorbent linings inside the engine intake and exhaust
cowlings. The F-117 had turbofan engines where low-pass velocity flowed through
reducing the sound of the engine [1]. Once again, because radar signals cannot pick up
sound, the guys did not have to incorporate this characteristic into their design.
Figure 2: Doppler Shift
Source: http://www.redorbit.com
As an ambulance drives towards you, each wavelength reaches your ears faster than the previous
wavelength. This causes the wavelengths to bunch together and create a higher frequency and
making the ambulance sound louder as it comes towards you than when it goes away from you.
Radar
The most important and biggest challenge of stealth design is suppressing radar
detection. Radars operate by emitting electromagnetic waves or energy in the direction of
an object and then use an antenna to detect the echo that is reflected back by the object [3].
The echo reflected back has an increase in wavelength or a shift in frequency that can be
explained by a physics concept known as the Doppler Shift. As an object moves towards the
radar, each wavelength reflected back takes less time to reach the antenna than the
previous wavelength [4]. This causes the wavelengths to bunch together creating a higher
frequency as seen in Figure 2. Doppler shift is also the reason
why a siren on an ambulance or police car will sound higher in pitch as it is coming
towards you than when it is going away from you.
Knowing the frequency and the wavelength of the echo, the velocity can be
calculated using the equation 𝑣 = 𝜆𝑓, where 𝜆 is the wavelength and 𝑓 is the frequency.
Knowing the velocity of the object and the time it takes for the echo to be reflected back to
the radar, the distance between the radar and the object can be calculated by the most
commonly used and basic physics equation 𝑑 = 𝑣𝑡. This is how police officers use radar
guns to detect the velocity of vehicles and why the biggest challenge in designing the
stealth truck was avoiding radar detection. Stealth technology focuses on two ways to
suppress radar: absorption and deflection.
One of the main strategies of suppressing radar is by using a material that will
absorb radar signals instead of reflecting it. Many airplanes today are made out of
aluminum or other metallic material that easily reflects radar, which is useful for
commercial airplanes because it is important to know their location at all times. A stealth
aircraft needs to either be made out of or coated with a radar absorbing material. More
often stealth designers try to make the aircraft out of absorbent material because coatings
add unnecessary weight.
Radar absorbent plastics, carbon-based materials, ceramics or a combination of
these three are most commonly used for stealth design. The F-117 Nighthawk material
consisted of carbon and glass fibers embedded in plastic and the B-2 Spirit that first took
flight in 1989 was made of a carbon-graphite composite material. Both of these aircrafts
reflected as much radar as a hummingbird [1].
To incorporate this concept on the stealth truck in the episode, Travis and the guys
used charcoal as the radar absorbent material because it is a cheap carbon composite
based material. The charcoal was smashed into powder and suspended into urethane foam,
which was then poured into the stealth panels.
The second strategy for suppressing radar is by deflection. Most often, radars will
not only emit the electromagnetic waves, but also act as the antenna and detect them.
Therefore, stealth aircraft needs to be designed in such a way that the electromagnetic
waves reflect in any direction except towards the radar. To accomplish this, stealth aircraft
is shaped with many angles and no flat surfaces that would be observable from the ground.
The geometry of the aircraft can also be designed so that it not only reflects
electromagnetic waves, but also absorbs them. For example, the wings of the aircraft are
shaped as small cones or pyramids that are filled with absorbent material. When the
electromagnetic waves hit the aircraft, there is a higher chance of absorption because of the
increased signal path length created by the cones [1].
For the stealth truck, the Travis and the guys drilled a series of cones into the
panels. The cones were then filled with the charcoal foam that acts as the radar absorbent
material. Once the panels were complete they were put on the truck as seen in Figure 3. As
Taylor mentioned, “In any science experiment, you need a control.” For this experiment,
Taylor drove the truck without the stealth panels towards the radar gun and its speed was
picked up about a quarter of a mile away. Once the stealth panels were put on the truck, the
radar gun did not pick up the speed of the truck until it was an about an eighth of a mile
away. Therefore, the radar proof pick-up truck was a successful experiment.
Figure 3: Stealth Pick-Up Truck
Source:http://channel.nationalgeographic.com/channel/rocket-city-rednecks/
The image shows the stealth truck that Travis Taylor and his team made. The truck is
covered by the “stealth panels” which are coned shaped to deflect radar, and filled
with radar absorbing material.
Conclusion
By taking advanced engineering topics, and breaking them down into basic
understandable concepts, solutions can be developed for all kinds of challenges, including
radar proofing your pick-up truck. The experiment proves that stealth technology can be
used not only for aircraft, but military vehicles as well. If radar guided ammunition was
fired at a stealth convoy, it would have to be approximately 50% closer to the convoy to
detect it. As Taylor concluded, “We really could make stealth vehicles, with pretty simple
technology.”
As mentioned before, cost is a major challenge for the future of stealth technology.
Building stealth aircrafts are extremely expensive and the cost will only continue to grow
as technology grows. To overcome this challenge, we must either find cheaper abundant
resources that can be used, or other methods to make aircraft low observable.
Citation:
[1] Ed. K. Lee Lerner and Brenda Wilmoth Lerner. Vol. 5. 4th ed. Detroit: Gale, 2008. p41304134
http://go.galegroup.com.libproxy.usc.edu/ps/i.do?action=interpret&id=GALE%7CCX2830
102205&v=2.1&u=usocal_main&it=r&p=GVRL&sw=w&authCount=1
[2] (2006, October 17). Stealth Technology [Online] Available:
http://www.engineering.com/Library/ArticlesPage/tabid/85/ArticleID/96/StealthTechnology.aspx
[3] M. Skolnik, "Description of Radar," in Introduction to Radar Systems, McGraw-Hill, 2002,
ch. 1, pp.1.1 - 1.20
[4] Doppler shift. (2004). In An Illustrated Dictionary of Aviation. Retrieved from
http://www.credoreference.com.libproxy.usc.edu/entry/ida/doppler_shift