Introduction
Vertical flight is the ability of a plane or a helicopter to fly or land without the need to utilize a runway, these characteristics are vital as they enable air transportation in urban areas without producing much noise. A helicopter is able of taking off and landing vertically, this enables it to take advantage of limited space and also hover around. Vertical flight capabilities allow “pesticide application, access remote areas for environmental work, deliver supplies to workers on remote maritime oil rigs, take photographs, film movies, rescue operations, transport accident victims, and put out fires and military applications”(Hought and Brock 2003, p.6). This paper seeks to understand vertical flight: history, development and the various engines that make it possible.
History and developments in vertical take-off and landing (VTOL)
In the 1480’s Leonardo da Vinci conceptualized how the first helicopter would be in his drawings. In the 20th Paul Cournu was the first man to from the ground use a helicopter though only for a few seconds. The Frenchman Cournu and Russian Igor Sikorsky designs faced one single problem “no one had yet devised an engine that could generate enough vertical thrust to lift both the helicopter and any significant load (including passengers) off the ground” (Hought and Brock 2003, p.6).
This problem was evaded to some extent by a Hungarian engineer Theodore von Karman whose design could only hover when tethered. Juan de la Cierva made the autogiro which was designed to solve the problem of planes losing engine power and crushing when about to land, he did this by separating the lift and thrust capabilities. Since the plane was driven by ordinary engines landing difficulties were avoided by “the engine being disconnected and the autogiro brought gently to rest by the rotor, which would gradually cease spinning as the machine reached the ground” (Hought and Brock 2003, p.6). This design was advanced by Sikorsky who was able to hover for about 120 minutes.
Dr. A.A Griffith in 1941 suggested the how he could use “small lift engines for lift only and not for normal flight” (Kermode 2007, p.7). This was to make an aircraft more effective in its operations. This was the birth of VTOL advanced by “the five important criteria of high thrustweight ratio, low efflux velocity, low fuel consumption and low machinery noise were successfully dealt with” (Kermode 2007, p.7).
The Rolls Royce Company built the flying bed stead’ was a double engine plane which “Air bled from the engine compressor was fed to four downward-pointing nozzles which, were used to control in pitch roll and yaw” (Kermode 2007, p.7). The ATAR Volant developed in France was better in design in that “It had an advanced system of auto stabilization and a very neat form of pneumatic deflection of the jet efflux to give control above the horizontal axis” (Kermode 2007, p.7).
COLEOPTRE was the first VTOL plane to fly. The Ryan × 13 with its delta engine was the first plane to “make a successful transition from jet born hovering to wing born flight and back to hovering and landing”. The next design was the Bell × 14 which had “a horizontal fuselage attitude and employing a jet pope deflection on its two horizontal engines” (Kermode 2007, p.7). The Pegasus engine was utilized in “the hawker p1127” which was succeeded by the now popular harrier.
Thrust
This is derived from Newton’s second law were given a mass that is constant “force, F, is equal to mass, m, multiplied by acceleration a” (Kermode 2007, p.9).
F = m × a
Assuming that drag is absent when accelerating horizontally thrust, F, is the predominant force, therefore;
W = m × g
On deriving mass from the above equation,
m = W / g
the above equation is substituted to force,
F = W × a / g
F / W = a / g
F/W is referred to as thrust to weight ratio. This ratio is “directly proportional to the acceleration of the aircraft” (Kermode 2007, p.10) meaning that the higher the thrust to weight ratio the higher the acceleration and also results in a higher rate of climb. For a higher than one thrust-to-weight ratio drag is negligible and can result in “the aircraft can accelerate straight up like a rocket” (Kermode 2007, p.10) thus all engine designs that could achieve vertical flight had to have this characteristic.
Types of VTOL
Vertical altitude take-off and landing
Here the aircraft takes off vertically; it resumes horizontal flight on gaining enough altitude. This model had the benefit of not needing moving wings or propellers, though it required advanced takeoff machines and high thrust meaning that safe landing could not be guaranteed if the engine failed at the beginning.
Tilted engine or propeller
Though this design solved some of the problems in the previous model, engine site was a major drawback, it had to be placed in such a way that the propellers slipstream or jet efflux would clear the aircraft for all positions of the engines” (Wilson 2010, par.7).
Deflected slipstream or Jet efflux
In this model thrust is given off by “forcing the air backward and the stream of air which flows over the fuselage, tail unit and other parts of the aircraft” (Wilson 2010, par.2). Jet efflux is used in jet-powered aircraft. Vertical lift is attained by deflecting slipstream or jet efflux downwards rather horizontally as is the case in ordinary planes. This design is utilized by the harrier aircraft allows its nozzles to deflect the jet efflux being produced.
Two different engines
In this model apart from the engines that allow ordinary flight, the plane has another engine specifically for the purpose of lift. This system has the limitation of being heavy since the horizontal are not in use during vertical flight and otherwise. This is utilized in the Balzac type of aircraft.
Types of vertical takeoff engines
Lift jets
These engines are simple and light; a good example is the RB 132 which can work when placed vertically or horizontally and is able to slide at different angles. It produces “a thrust of 6000 pounds at a thrust to weight ratio of 16:1” (Wilson 2010, par.4).Different airframe configurations can be used in this design since lift jets have high versatility. A nozzle with many lobes helps lower ground erosion.
Lift Turbofans
Unlike jet lifts these have lift turbofans have the added benefit of being of producing less efflux velocity and noise. The two fans in front and behind are powered by the lift jet while the reduction gear is only used when required. Compressed air is produced by a propulsion engine and directed to the fans hence lift is given off. A turbine phase can be added to a normal engine to propel fans at the front thus producing a variety of lift turbofans.
Turbofan engine
This is the advanced version of the gas turbine engine, the main engine is covered by two fans; one at the front and the turbine fan behind. Both are made of a variety of blades and are joined to another shaft though not all move at the same time. The turbofan operates by holding air via engine inlet; some of the air passes the fan to the core compressor finally to a burner where it burns. In an ordinary turbojet the now hot air is released through the nozzle via the core and fan turbine. Some of the air enters the fan but misses the engine, free streaming allows this air to move at a higher speed. Thus the turbofan engine thrust is produced by both the core and the fan.
Lift propulsion engine
This combines both lift and propulsion engines, with the ability to shift from one to another. It works on the law of vectored thrust where its nozzles and cascade vanes allow exhaust stream to be deflected at a right angle to the center of gravity of the plane. Thrust deflection is achieved “by a deflector system consisting of four swiveling nozzles” (Wilson 2010, par.7).
Lift fans and lift jets
Lift jets achieve throttle maneuver more easily than lift fans which have higher inertia and take more time to increase velocity they are also “more unlikely to the jet, it gets no immediate response to the change in temperature before the rotational speed has time to change” (Wilson 2010, par.7). Lift fans use less fuel and also produce less noise.
Reference list
Hought G.J., and Brock V.B. 2003. Aerodynamics for Engineering Students. New York: Stamford publishers, p.7-10.
Kermode, A.C. 2007. Mechanics of Flight. Cambridge: Cambridge university press, p.2-15.
Wilson, T. O. 2010. Vertical Take off and Landing. Web.