Exploring the Fantastic Utility of Vertical Take-Off & Landing (VTOL) Aircrafts

By July 13, 2016 Article, Technology No Comments
2 Yak-38 with Folded Wings

^ Yak-38 with Folded Wings Onboard a Soviet Aircraft Carrier  

Image Courtesy of the United States Navy at http://www.dodmedia.osd.mil/Assets/1986/Navy/DN-SN-86-00833.JPEG   

Retrieved From https://en.wikipedia.org/wiki/File:Yak-38_Forger_wings_folded.jpg 

How Important is Resource Management?

In his 1989 bestseller The Negotiator, Frederick Forsyth makes a billion dollar observation through a fictional character named Marshal Koslov of the Soviet Red Army. It goes like this:

Like all experienced combat men, Koslov knew better than most that battles are not won by courage or sacrifice or even clever generals; they are won by having the right gear in the right place at the right time and plenty of it.

By transporting great many and diverse kinds of aircrafts to within striking distance of the battle zone, aircraft carriers ensure just that – plenty of right gear in the right place at the right time.

Harrier Jump Jet is among the Most Successful & Famous of V/STOL Aircrafts Image Courtesy of the United States Navy at http://newshome.news.navy.mil/view_single.asp?id=22150 Retrieved From https://en.wikipedia.org/wiki/File:AV-8B_Harrier_II-.jpg

Harrier Jump Jet is among the Most Successful & Famous of V/STOL Aircrafts
Image Courtesy of the United States Navy at http://newshome.news.navy.mil/view_single.asp?id=22150
Retrieved From https://en.wikipedia.org/wiki/ File:AV-8B_Harrier_II-.jpg

What is more, these gigantic carriers can have a virtually unlimited stock of food, ammunition, and equipment. A navy with an aircraft carrier can tilt the scales of wars and battles in its favor even before the war begins.

It does not matter that that the conflict zone might be thousands of miles from the mother country. These giant floating bases enable a nation to project its military arm in distant lands without the necessity of building extravagant and fixed air bases.

Staying put in the sea at some distance from the coast and loaded with sophisticated radars and other sensors, aircraft carriers can quickly detect and neutralize approaching threats.

Among warships of comparable size, aircraft carriers of today are least vulnerable to attacks. Fixed air bases can become sitting ducks. Isn’t that how the Viet Minh devastated the isolated airbase at Dien Bien Phu in 1954 and sealed the fate of the French in the First Indochina War?

Fixed wing aircrafts that we know as airplanes have their own set of merits and demerits vis-à-vis rotary wing type i.e. helicopters. One distinct disadvantage of conventional airplanes is they need a long runway to take-off and land.

Employing fixed wing aircrafts on aircraft carriers can therefore add to the size, complexity, and expense of the carrier. But as compared to rotary wing aircrafts, they are faster and can cover longer distances while carrying greater payload of men and materials.

Military operations never go completely according to plan. Flexibility is paramount. By eliminating the need for long runways, vertical take-off and landing (VTOL) aircrafts provide such flexibility and further extend the principle of right gear at right time in right place.

While in the hovering mode, these can drop personnel, equipment and supplies at spots located on difficult terrain – rugged mountains, deep valleys, deserts, and water bodies – spots where it is impossible to land conventional, runway-friendly aircrafts.

And within limits, VTOL aircrafts and their numerous variants can also operate without an aircraft carrier because they can take-off and land anywhere. Or almost anywhere.

Technology of VTOL Aircrafts

VTOL aircrafts can also operate as:

  • short take-off and landing (STOL) aircrafts that require short runways for take-off as well as landing
  • short take-off and vertical landing (STOVL) aircrafts that need short runways for take-off but land vertically
  • conventional take-off and landing (CTOL) aircrafts that demand a normal runway for take-off and landing
    A Sketch of the Soviet Yakovlev Yak-38 VTOL Aircraft showing the Directed Exhaust Image Courtesy of Tosaka Retrieved From https://en.wikipedia.org/wiki/File:Yak-38_Lift_Engines_NT.PNG

    A Sketch of the Soviet Yakovlev Yak-38 VTOL Aircraft showing the Directed Exhaust
    Image Courtesy of Tosaka
    Retrieved From https://en.wikipedia.org/wiki/File:Yak-38_Lift_Engines_NT.PNG

Powerful jet thrusters direct the fast moving mass of exhaust gases downwards. According to Newton’s Third Law of Motion, every action produces an equal and opposite reaction. The downward moving exhaust gases therefore produce an upward thrust i.e. lift.

Changing the direction of the thrusters produces a thrust in the opposite direction while in air or when on ground. The pilot can thus move the jet forwards, sideways, and backwards.

But a VTOL aircraft can take-off only if it produces lift greater than the weight of the aircraft and the loads that it is carrying. This imposes an inherent limitation on the amount of load a VTOL can carry.

And the sizable amount of fuel it has to burn when taking off ensures that its range remains limited. This creates the need for STOL aircrafts that use the lift generated by the forward movement of the aircraft. VTOLs and STOLs also use a short ski-ramp to get this additional lift.

To understand how forward motion of an airplane generates lift, we need to understand the take-off process of a CTOL. Aircrafts can be:

  • Fixed Wing Aircrafts: with immovable wings. Commonly called airplanes, it is the movement of the aircraft and the shape of the cross section of the wing that generates lift
  • Rotary Wing Aircrafts have rotating wings. These are generally called helicopters and it is the movement of the wings – not the aircraft – that generates lift
Sketch: How Airfoil Section Produces Lift

Sketch: How Airfoil Section Produces Lift

Stationary of rotating, aircraft wings have the cross section of an airfoil. Air flows over their lower surface at speeds slower than those over the upper surface.

Therefore, the static pressure on the lower side becomes greater than that on the upper side. It is this pressure differential that generates thrust from the lower side of the wing to the upper side i.e. upward thrust or lift.

Such pressure-velocity variation is in accordance with the Bernoulli Principle viz. any increase in the velocity of a fluid flowing along a streamline is accompanied by a proportional drop in static fluid pressure and vice versa provided the flow is at constant elevation.

VTOLs sometimes use forward motion along the ski-ramp to get such lift in addition to the upward thrust that the jet nozzles generate. This boosts the aircraft’s range and payload capacity. VTOLs and STOLs are usually bunched as V/STOL i.e. vertical and/or short take-off and landing.

After umpteen partially successful and failed experiments starting from the 1950s, VTOL technology finally came good in the late 1960s and the 1970s. Trials on numerous designs and concepts are in progress.

F-35B Taking Off from an Aircraft Carrier   Image Courtesy of the United States Navy at http://www.navy.mil/view_image.asp?id=108357   Retrieved From https://en.wikipedia.org/wiki/File:US_Navy_111005-N-ZZ999-055_The_F-35B_Lightning_11_takes_off_from_the_amphibious_assault_ship_USS_Wasp_(LHD_1).jpg

F-35B Taking Off from an Aircraft Carrier
Image Courtesy of the United States Navy at http://www.navy.mil/view_image.asp?id=108357
Retrieved From https://en.wikipedia.org/wiki/ File:US_Navy_111005-N-ZZ999-055_The_F-35B_Lightning_11_takes_off_from_the _amphibious_assault_ship_USS_Wasp_(LHD_1).jpg

V/STOL aircrafts made in substantial numbers include:

  • Harrier: Hawker Siddeley developed these in the 1960s. Informally called Harrier Jump Jets, these were the only successful V/STOL design for a long time. There are four Harrier variants made between 1967 and 2003
  • V-22 Osprey: is a transport aircraft that can operate as VTOL and STOL. It combines the merits of a helicopter with that of a propeller- driven aircraft

After its first successful trial in 1989, production started in 1998 and they are still making this Bell Helicopter designed aircraft. It has served well in Iraq, Afghanistan, and other areas

  • Yakovlev 38 Forger: Soviet Union built these specifically for its Kiev Class aircraft carriers. Produced between 1971 and 1981, these were retired in 1991
  • F-35B: is a V/STOL variant of Lockheed Martin’s F-35 Lightning II all-weather, stealth-mode fighters. This currently under-development aircraft is expected to be the (near) future of the V/STOL technology

Of these, the V-22 Osprey uses the tiltrotor technology while the F-35B and the Harrier uses directed jet thrusters. We have already seen how directed jet exhausts work in accordance with Newton’s Third Law.

V-22 Osprey by Bell Boeing is a Tiltrotor VTOL   Image Courtesy of the United States Navy at http://www.navy.mil/view_image.asp?id=41624 Retrieved From https://en.wikipedia.org/wiki/File:US_Navy_061206-N-0458E-076_A_U.S._Marine_Corps_V-22_Osprey_helicopter_practices_touch_and_go_landings_on_the_flight_deck_of_the_multipurpose_amphibious_assault_ship_USS_Wasp_(LHD_1).jpg

V-22 Osprey by Bell Boeing is a Tiltrotor VTOL
Image Courtesy of the United States Navy at http://www.navy.mil/view_image.asp?id=41624
Retrieved From https://en.wikipedia.org/wiki/File:US_Navy_061206-N-0458E-076_A_U.S._Marine_Corps_V-22_Osprey_ helicopter_practices_touch_and_go_landings_on_the_ flight_deck_of_the_multipurpose_amphibious _assault_ship_USS_Wasp_(LHD_1).jpg

Tiltrotor aircrafts combine the merits of fixed wing and rotary wing aircrafts. The rotors rotate in the horizontal plane and provide lift for take-off. When the aircraft gains speed, the rotors shift gradually to rotate in the vertical plane to provide forward and / or sideward thrust.

Finally

While we do not know for sure if Darwin did say something about species boosting their chances of survival by adapting to their environs in precariously and perilously changing times, the truth in the statement in undeniable.

Apparently, the same law of adaptability or flexibility applies to machines. The VTOL species offers the necessary flexibility to military operations. Unquestionably, it is here to stay and evolve.

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