Basics of Aerodynamics

Tuesday, August 3, 2010


Well , i read many articles and tried to search in lots of books for easy understanding of various terms in aerodynamics and their origins... but have found only few.

Thus here i am trying to simplify the concepts and basics of aerodynamics for people who likes to start from the scratch in field of aerodynamics and aeronautics.

Aerodynamics :

Aerodynamics is a branch of dynamics (in Physics) that actually concerns with the study of motion of air , specially when a object moves in air.

Derived from Fluid Dynamics and Gas has made way not only to the frequently used mode of transportation i.e aircraft but also has made possible to fly at speed higher than sound (greater than sonic speeds) with huge advancements in defense aircrafts and even in high speed trains and formula one (F1) racing car designs.

Origins of Aerodynamics :

It was very difficult to understand how aerodynamics came to existence. then i came across a book which actually discussed few historical examples ... given here are those examples as there is no better way i found than these to explain the origins.

" On 8th August, 1588 , the waters of English Channel churned with gyrations of hundreds of warships. The great Spanish Armada had arrived to carry out an invasion of Elizabethan England and was met head-on by the English fleet under the command of Sir Francis Drake. The Spanish warships were large, heavy, packed with soldiers and carried formidable weapons. In contrast, English ships were smaller, lighter, had no soldiers on-board and armed with lighter and short-range cannons.
The balance of power in europe hinged on the outcome of this naval combat. On that crucial day of 1588, when the English floated six fire-ships into the Spanish formation and drove headlong into the ensuing confusion, the history of Europe was in balance.

The heavier, sluggish, Spanish ships were no match for the faster , more maneuverable, English ships and by that evening Spanish armada lay in disarray, no longer a threat to England. This naval battle is of particular importance as it was first battle to be fought by ships on both sides powered completely by sail (wind).

It taught the importance of Naval power to politicians, in turn naval power became dependent greatly on speed and maneuverability of the ships. To increase the speed of ships, it is important to reduce the resistance created by the water flow around the ship's hull. Suddenly, the resistance or drag on the ship's hull became an interesting engineering problem, thus, encouraging people to the study of FLUID MECHANICS / DYNAMICS. "

Images showing Bow and Hull of the ships.

Aircraft Wing Design Developments :

I will here omit information on developments and equations given by Sir Isaac Newton,which made him first aerodynamicists, or by Jean Le Rond d'Alembert or by Leonhard Euler and Bernoulli , as these relates with the flow of fluid around the body which comes in advance aerodynamics and fluid flow which definitely is not for the beginners and purpose of my writing this article is to simplify the study...

In summer of 1901, Oliver and Wilber Wright , were struggling to make a successful glider design, at Kill Devil Hills , 4 miles south of Kitty Hawk ( North Carolina)

The aerofoil & wing design of glider were based on aerodynamic data published in 1890, by great German aviation pioneer Otto Lilienthal and by Samuel Pierpont Langley.

Due to constant failures, Wilbur wrote "Having set out with absolute faith in the existing scientific data, we are driven to doubt on thing after another, untill finally after 2 years of experiment , we cast it all aside & decide to rely entirely upon our own investigations."

In fall of 1901, they designed & built a 6 ft. long, 16 inch sq. wind tunnel powered by a two bladed fan connected to a gasoline engine. ( which became the first wind tunnel ). They tested various airofoils / wing designs. the data collected are taken logically and carefully. In spring 1902, they design a new glider with the improved and new information collected. Rest is all astounding history.

Thus , this was how humans learned to fly, with the deliberate and constant hard-work and study of the enthusiasts in aircraft designs.

Parts of Aircraft: Its becomes important to newbies , to understand various parts of aircraft and their uses , before jumping on various concepts and theories that actually formed the aircrafts.

Displayed below, are the most important parts or basic parts , which are required to create a stable flight of an airplane in today's time..

CAD image of a civilian aircraft.

CAD image of a military aircraft.

Parts / Terms Description:

1. Fin - Used to improve the balance or stability of the aircraft.

2. Rudder - Direction control of aircraft , in horizontal plane.

3. Tailplane - Small wing at back of the aircraft. It is fixed & thus mostly absent in military aircraft.

4. Elevon / Elevator - Part of tail-plane in aircraft, for vertical (altitude) climb and descent.

5. Fuselage - The main part of the aircraft. A cigar shape body to which wings, tailplane & fin are attached.

6. Aileron - A part of the wings, which are used for turning the aircraft in left or right direction i.e. control its roll movement. These are also moved up and down to control aircraft balance.

7. Flaps - Part of wings, which are moved up & down to control the altitude movement in sustained and gradual way unlike elevators which does in improper variations.

8. Leading Edges / Slats - The front or forward edge of the aircraft wings. These are generally slotted for generating proper air flow around the wing during take-off and landing.

9. Nose Cone - Front part of the fuselage, where RADAR and other navigation , control and avionics equipments are stored.

10. Cockpit / Flight Deck - Area at the front os a large plane where pilot, copilot sits to control the aircraft.

11. Canopy - The glass window or covering in fighter aircrafts. These are unbreakable, flexible , movable and sometimes have explosives embedded in them for emergency ejection time.

12. Engines - Main and heart of the aircraft. Classified usually as - Turbo Prop, Turbo Jet, Propeller and Pulse Jet. Gives power to aircraft's avionics as well as generates lift to fly the aircraft.

13. Engine Cowling - Metal covering for an engine.

14. Starboard Wing - Right side wing of the aircraft.

15. Port Wing - Left side wing of the aircraft.

16. Spoilers - It is a part of the wing and sometimes fuselage. As its name is, so is its work, it spoils the sustained flight by increasing the drag of the aircraft and reducing the altitude of the aircraft. It is also used as air-brakes and used in combination with flaps during landings.

17. Lift - Upward force generated by the flow of air around the airfoil/wing.

18. Drag - Resistive force experienced by the aircraft body by air due to its forward motion.

19. Thrust - Its the force experienced by the aircraft which helps it to move forward and fly.

The value of thrust and lift components should be higher than weight and drag components for an aircraft to fly.

All the aircraft designs are basically modifying these four components as per the desired requirements and situations. These components are varied, to make a flight either more stable, or Maneuverable or during take-off or landing of an aircraft.

20. Shockwaves / Bow-Shock - It is not a part of aircraft, plays an vital and crucial role in flight of an aircraft. To understand them lets move back to the concept of Fluid Dynamics as discussed above.

As boats moves in water , making a way by removing water from its way , a trail is created. Similarly, when a object moves in air it makes its way by removing air particles from its way.

The speed of the particles being very less in comparison to the speed of the object, thus the air particles are not able to move away from the aircraft's body faster, thus , a wave (trail as with boats) is created known as shock-waves or bow-shock. These are not visible , unlike trail in water, but can be seen using UV spectrum or when a aircraft breaks sonic barrier at a low altitude it can be seen due to condensation around the aircraft's body.

Stealth Aircrafts

Thursday, May 27, 2010

" No aircraft detected .. Radar is clear ... airspace is secure .. !! ????"

STEALTH meaning to hide, work secretly, hidden ...

Lots of Hollywood movies with the help of special effects would show aircraft disappearing from visual ... and trying to show how stealth works buts that's not how actually it works.


The earliest of Stealth Aircraft of the world is seen to be the Horten Ho 229 fighter-bomber, developed in Germany during the last years of WWII.

Designed by Reimar and Walter Horten and built by Gothaer Waggonfabrik. It was the first pure flying wing powered by a turbojet and was the first aircraft designed to incorporate what became known as stealth technology.

The Ho 229 was of mixed construction, with the center pod made from welded steel tubing and wing spars built from wood. The wings were made from two thin, carbon-impregnated plywood panels glued together with a charcoal and sawdust mixture. The wing had a single main spar, penetrated by the jet engine inlets, and a secondary spar used for attaching the elevons. It was designed with a 7g load factor and a 1.8x safety rating; therefore, the aircraft had a 12.6g ultimate load rating. The wing's chord/thickness ratio ranged from 15% at the root to 8% at the wingtips.

Control was achieved with elevons and spoilers. The control system included both long span (inboard) and short span (outboard) spoilers, with the smaller outboard spoilers activated first.

The aircraft utilized retractable tricycle landing gear, with the nosegear on the first two prototypes sourced from a He 177's tailwheel system. A brake parachute slowed the aircraft upon landing. The pilot sat on a primitive ejection seat.


In the end days of the world war II , the US allied forces and the USSR red army, both were in the race to capture the German R&D facilities and developed prototypes of war. With the US launched Operation Paperclip - large portions of German prototypes were captured mainly V1, V2, V3 (Ho-229).. .and numbers of scientist involved in these projects were given US citizenship on request. USSR too had its share taking V1 and V2 and
Heinkel He - 178 and He - 280 prototypes.

Meanwhile, during the war US based Aircraft development company - Northrop - also was working on a similar project as of Ho-229 flying wing body aircraft known as YB - 49 series which later got scrapped due to funds problem as well as constant failures in YB - 49's flight stability.

The secured prototypes from Germany were sent to Northrop and Lockheed for analysis which laid the foundation for the advance stealth fighters in the coming years.


After the war Reimar Horten said he used a mixture of charcoal dust with wood glue to absorb electromagnetic waves of radars. Though no documents exist to confirm that Germany was working on any stealth technology development, this information made grounds for further research. Later the theories of Mr. Horten on stealth were proved correct by Northrop- Grumman and Lockheed-Martin.

With the end of WWII and start of the cold war, the two most powerful states of the world were in a race to make each other feel inferior and to balance the power in the world. This lead to rapid development in various kind of technologies specially in the field of military and intelligence. USA and USSR fought numbers of wars , none face to face, but all with the weapons and intelligence gatherings. Thus it became important to both that they secure their countries, USSR started to develop a range of long-range RADARS and made it difficult for US to infiltrate its aerospace.

This initiated the requirement of a high altitude, Low Observable, High speed reconnaissance aircraft by USA. Lockheed-Martin's SKUNK WORKS under Clarence Kelly Johnson presented what is known as U-2 Spy plane codenamed "Dragon Lady".

Although not completely stealth , but designed to operate at very high altitudes U- 2 was suppose to be hidden from the radar detection of USSR air defense network. But on May 1, 1960 , a U-2 spy plane , flown by Francis Gary Powers, was shot down while taking photographs of USSR nuclear plants and vital SAM sites. This made clear that as previously expected , USSR 's long-range radar coverage was better than it was told.

With the aging of U-2 , USAF required a new and better spy plane. Once again Lockheed-Martin secured a contract. The previous research laid
the way for a very high speed , high altitude low observable aircraft now known as the SR - 71 BLACKBIRD. Designed to have low Radar cross sections and drag at high speeds .. Blackbird used RAM or Radar Absorbing Material (came from U-2) , Operating at an altitude of 70,000 to 80,000 feet and at a speed of Mach 3.2 to avoid radar contact, Blackbird served in many wars collecting vital data, pictures and information on enemy.

Image of SR-71 Balckbird Cutaway.

SR-71 remained a spy/reconnaissance plane forever. The success of the SR-71 project encouraged USAF to launch a project "
HAVE BLUE" for the development of a stealth fighter/bomber to invade enemy airspace and have first kill capability.

Image of a HAVE BLUE/ Hopeless Diamond prototype.

In 1964, Russian mathematician P.Y.Ufimtsev published a seminar on " Method of Edge Wave in Physical Theory of Diffraction"and showed that the returning RADAR waves after hitting aircraft body is more related to the edges present in the aircraft than its size and one can calculate the RCS or Radar Cross-Section Area across the wings and edges of the aircraft. Thus no matter how big a aircraft is in size, it RCS (representing a DOT on the RADAR screen) can be reduced by producing multiple edges at certain angles. However such a design will make the aircraft system aerodynamically unstable to fly.

After suffering heavy causalities on bombers against sophisticated SAMs of Soviet origins in Vietnam war,in 1980, USAF decided to get a bomber that can penetrate enemy air defense silently. Thus DARPA (Defense Advanced Research Projects Agency) announced the project "HARVEY". The contenders being Northrop and Lockheed.

The Lockheed advance projects team now called as SKUNK WORKS started to work on a top secret project codenamed "HOPELESS DIAMOND" as the initial prototypes for such a aircraft/bomber. The designs this time came from Ben Rich , a team member of Kelly Johnson 's, and a engineer in SR-71 team. Using the research of Ufimstev and computer aided control systems they presented two prototypes of hopeless diamond.

As first thought , just like its name , Hopeless Diamond was not quite satisfactory to the design team , still the RCS of the HOPELESS DIAMOND came out to be 1/10th of the RCS of Northrop-Grumman team.The radar operators used to check the presence of the prototypes as they became completely invisible on the screen during RCS tests by DARPA. Success of the HOPELESS DIAMOND initiated a dark project, completely top-secret and unknown to the world and even to the pilots and the R&D team known as project "HAVE BLUE".

The Have Blue prototypes being test vehicles missed many advancements and sophistication. After the contract was awarded to Lockheed the modifications started and the HAVE BLUE was was upgraded to "SENIOR TREND" which finally was renamed, after rigorous tests, as F-117A "Nighthawk" Stealth Bomber.

It was not until April 1990, that F-117 made their debut in a war. In 1990, US launched an offensive on Panama in Operation JUST CAUSE , and for the first time it checked the effectiveness and long waited war operational capability of the bomber.

But the actual test and experience came during Operation DESERT STORM, which witnessed large numbers of F-117As in combat. Only F-117A was allowed as the first wave of attack as well as to enter the fortified Baghdad. Although only 42 Nighthawks were used, they inflicted a 80% hit rate using GBU / Guided Bomb Unit (LGB and JDAM) munitions, hitting more than 30 % of the high profile targets in first 24 hours of the Operation Desert Storm, thus rupturing the backbone of enemy by destroying the targets as well as the air defense network achieving the objective it was designed for.


F-117 design success came with certain problems regarding its limitations with range and payload (as a compromise for stealth). Thus , in 1979, "BLACK PROJECT" , which involved the R&D of top secret stealth programs, started to look for new bomber , much better, versatile , advanced and have a larger payload (also nuclear) and increased range capability, was termed as the Advanced Technological Bomber (ATB).

This time, as per the requirements, the Northrop-Grumman Designs were selected in competition with Lockheed/Rockwell designs.

Based on the old , and scrapped designs of Mr. Northrop, design team started working upon the YB -49's blueprints. With latest and advanced CAD (Computer Aided Design) and presence of the composite material made the "FLYING WING" design possible and the previously encountered flight instability was counter-measured using advance on-board computers. In 1989, Northrop introduced B-2 "Spirit" heavy bomber with advance LO (Low Observable) features or stealth.But no one expected that it would take a decade to get this advance technology war tested.

In 1999, following massive uprising and hostile environment in Yugoslavia, USA sent its B-2 stealth bombers to invade and fragile the air defense network. B-2 was responsible for the 33% hits of the Serbian targets in the first eight weeks of US involvement in Kosovo War.


With F-117 and B-2 becoming successful and popular world over their technology also became obsolete for USA who always like to have a edge in technology in war. The developments of anti-stealth defense systems as well as the maintainance cost and various trade-offs (compromises) on conventional functions of aircraft like range, speed, aerodynamics, countermeasure systems, payload, limited role in war and cost of production ... led to initiate the development of more mordern and advance projects in USAF both being awarded to Lockheed/Rockwell .. YF -22 now know as F-22 "RAPTOR" advance, air-superiority, multi-role stealth aircraft and X-35 , known as the latest F- 35 "JOINT STRIKE FIGHTER".

F-22 incorporates various new features of stealth , without setting any trade off with speed and conventional aircraft features, although payload still being a factor of concern. It uses advance radar and avionics systems to locate the target, and attain the "FIRST LOOK - FIRST SHOT - FIRST KILL" capability. Both F-22 and F-35 have the capability to obtain the information from various ground systems as well as even from the enemy locations. Incorporating AESA radar and surface fused sensors technology.

Unlike F-117 and B-2, F-22 and F-35 have the afterburners for dogfights and high speed scenarios. F-22 also exhibits THRUST VECTORING whereas F-35 for the first time after BAE - SEA HARRIER aircraft incorporates a VTOL (Vertical Take-Off and Landing) System.

On the other hand , now Russia, with its always new designs have introduced SU-47 "BERKUT" or "GOLDEN EAGLE" with the ideal stealth designs with the help of carbon-composites - Forward Swept Wings - and state of art avionics.

More advance researches are still going on now with various nations to get the hold of stealth technology, which have now chaged the face of the war limiting it to few days time giving hard precise hits on enemy without getting a scratch.


Russian/India - PAK FA - FGFA and lot many more. We still will be seeing lots of advancements, limited, but still to come in the chapter of stealth systems.

(Stealth Technology, Working and Terms will be included in the upcoming articles)


Air to Air Missiles : An Introduction

Tuesday, February 16, 2010

At the time of outbreak of World War II, electronics was gaining momentum. Its role in war ended as radio equipment for communication and detection of enemy in a particular topography.The use of electronics in combat technologies increased only after World War II. Today, the military has electronic surveillance equipments like UAV’s, radars, jamming devices, GPS navigation systems, and precision weapons like guided missiles and smart bombs that are far more accurate than any other weapon. This article elucidates the technology behind air-launched anti-aircraft guided missiles with advanced guidance technologies and their basic design concepts.


The use of electronics has increased after World War II. Today, military has electronic surveillance devices, jamming devices, GPS (Global positioning System) and precision weapons like guided missiles and smart bombs or GBUs (Guided Bomb Unit) which are more accurate in attacking their target then any other weapon.

Guided missiles are self-propelled air borne projectiles carrying explosive charge and guided in flight towards the target.


Missiles are broadly classified on the basis of:-

· Launch Environment Used

· Guidance Used

Launched Environment Used:

1) Air-launched Missiles

a)Air-to-Air Missile

b)Air-to-Ground Missile

2) Surface-launched Missiles

a) Surface-to-Air Missiles

b) Surface-to-Surface Missiles

Guidance Used:

1 Radar Command Guidance

2 Radio Command Guidance

3 Wire Guidance

4 Inertial Guidance

5 Astro Guidance

6 Terrain Comparison Guidance (TERCOM)

Air-Launched Anti-aircraft Missile:

The air-launched anti-aircraft missile is launched from an airborne aircraft to wipe out its target.

Various parts of this missile are:-


Rocket Motor - Provides thrust to the missile by burning solid propellant material.

Target-Seeker - Searches for the target.

Electronic Guidance Control (EGC) - Guides the missile.

Control Actuation - Adjust the fins on the instruction received from EGC.

Warhead - Explosive device which destroy the target.

Battery - Provides power to the missile onboard electronics.

Umbilical Cable - Connects the missile onboard electronics with the computer of the aircraft called as ‘avionics’.


Before the launch, the pilot designates a target. The data goes to the missile guidance control. As soon as the missile is launched the target seeker is activated and it searches for the target. The rocket motor burns the solid propellant material which provides thrust to the missile. The wing of the missile provides the necessary lift and the electronic guidance control guides the missile towards the target.

Three types of guidance system are used in general:

Semi-active Radar Homing Guidance

Target has to be illuminated by a radar transmitter from parent radar. The reflected waves are received by the receiver in the nose of the aircraft.

Active Radar Homing Guidance

The missile carries it own target seeking radar. The inbuilt radar hunts for the target. This system is costlier and bulkier and is used in long range missiles also called as ‘beyond visual-range missile’ or BVR missile.

Infrared Homing Guidance

The infrared homing guidance system is mainly designed to destroy the target using infrared homing. It seeks infrared radiations available and are also called as ‘heat seeking’ missiles.

Infrared Tracking:-

The target image appears as bright and dark shining spots which indicate the hotter and colder regions of the target. This image is called as the ‘infrared signature’ of the target. The infrared sensor array is coupled with a mechanical scanning system which scans a larger section of the sky. It continuously moves reflectors and lens to feed light to the sensors.

The guidance control system figures out position of the target based on the fluctuations in the detected infrared light.

Guidance System:-

· The Target Seeker.

The infrared sensor that will respond to the wavelength of IR radiation from aircraft are placed in a circular matrix arrangement and grouped into four arrays. An array is one sector of circle.

· Positional Information

If the infrared image falls exactly on the centre of the nose of missile, all the arrays will get IR radiations with equal intensity. When signal from any one array is stronger than other it indicates target has changed the position.

· Speed Information

If target is moving from right to left, right array will receive the image which will generate a pulse. Then the left array will receive the image and will generate a pulse. Measuring the time interval between the two pulses and calculating it with pre-calibrated values speed of target can be known.

· Distance Information

The strength of the signal diminishes as the distance between the missile and target increases. So, measuring the signal strength and comparing it with pre-calibrated values distance of target is obtained.

After calculating speed, position, distance, EGC designates control to fin actuator. Fin actuators are used to actuate the fins to steer the missile.


· Ready to fire missile

· Highly Precise

· Cost Effective

· Could be shoulder launched


· Low Range

· Get deflected by Flares

By - Vishal Bhatnagar