17 Jun 2011, 05:35
The NAVY Jul-Sept 2008 Vol.70 No.3 - The Magazine of the Navy League of Australia —
How to Fly a Sea Harrier Part 3 – The Landing by Mark Boast [ex-A4G Pilot]
“...The aim of the Rolling Vertical Landing was to achieve a minimum distance ground run consistent with avoiding the possibility of foreign objext damage to the engine and aircraft inherent in the pure Vertical Landing. The desired fifty knot groundspeed (add the headwind component to get actual airspeed) was achieved by moving the nozzles slightly aft of the Hover Stop position. The remaining small amount of wing lift only added five hundred pounds to the “bring back” or fuel/stores weight of the Sea Harrier and therefore had limited usefulness. The much larger wing and flap on the later Harrier II (AV-8B)/GR-7/9 exploited this area and quite significant “bring back” advantages could be gained. The STOVL JSF programme is also looking at utilizing this same technique for landing on large carrier decks in order to exploit the “bring back” increase to cater for expensive weapons and fuel loads that may be required when working with larger air groups.
The Creeping Vertical Landing was a very slow forward speed landing used in locations where a vertical landing was required, but FOD damage likely. By moving forward the aircraft would be clear of the majority of ground debris which would be blown behind the engine intakes. This technique was not required on FOD free flight decks and therefore was not employed on the small UK carriers where space usually precluded landing with any forward speed.
The pure Vertical Landing was set up by entering a stabilised hover over the touchdown point on land, or abeam the carrier landing spot (there were a number to choose from) at sea. The nozzles were left in the Hover Stop position for manoeuvring in the hover and the aircraft was either tilted in the pitch and roll by the control stick, or rotated in yaw by use of the rudder pedals. To assist the pilot there were low authority autostabilisers for pitch and roll and a yaw stabiliser that primarily sought to avoid dangerous sideslip. A rudder pedal shaker also warned the pilot of high sideslip rates. A very useful device in the Sea Harrier that was not incorporated in the other Harriers was the “nozzle nudge” facility that used the speed brake switch on top of the throttle to select the nozzles either ten degrees forward or aft. This useful tool enabled the pilot to move forwards or backwards without having to tilt the aircraft in the hover excessively and therefore complicate the situational awareness challenge. It also helped when matching the ship’s speed when hovering alongside.
A rate of descent was established by a slight reduction of thrust and a constant descent rate was maintained through to touchdown. At touchdown (and not before!) idle power was rapidly selected to avoid “bouncing” on the efflux that rapidly built up between the aircraft and the ground or deck surface, and the nozzles selected aft to avoid heating up the surface and [with?] engine exhaust. Whilst this technique sounds simple on paper, in practice it was moderately difficult due to the piloting tasks and situational awareness challenge of flying a pure vertical descent. Unlike a helicopter which is very responsive to control inputs in the hover, the Harrier has a sluggish response due to its relatively high mass. The pilot also has very little downward vision and therefore has to rely on both fore/aft and lateral references that can be some distance from the landing point. For this reason it was often said by some that it was easier to land on the ship due to the easily seen visual references. On a calm day with no ship movement and no one else on the deck — maybe! But the very close proximity of superstructure, other aircraft, and above all, people, never induced an air of languor in my experience.
So why have I made so much about situational awareness? As in all naval aviation, success comes down to the ability to conduct embarked flying operations not only in good conditions, but also in poor weather and/or at night. The transition from instruments to a visual hover alongside a ship is very different from the transition for a conventional landing ashore. Whilst the ship itself provides potentially excellent visual cues of direction (ship centreline) and height (masts and superstructure), the sea conditions often cause the ship to heave, roll, and sometimes weave. As the Harrier’s hovering characteristic was determined by its mass, it was very unwise to “chase” the ships motion. As the thrust requirements were already very high, any unnecessary bleeding of compressor air to feed the reaction control system for control inputs, or extra demands by the throttle to climb and descend around a moving hover point, would use up the remaining thrust available. This could mean only one thing!
The answer was straightforward and largely relied on the Sea Harrier’s very effective Head Up Display and reliable inertial attitude system. Pilots were taught to establish a stable hover at approximately 90ft (forty to fifty feet above deck height) above the water alongside the landing spot, transition laterally whilst maintaining altitude, stabilise in the hover about forty feet above the landing spot, and then descend vertically. No external commands were involved with the pilot making all decisions. Some coaching or advice was usually available from a duty pilot in the Flying Control position but usually reserved for initial deck qualifications and emergencies. An abbreviated and informal flow of “patter” was used by an experienced pilot in Flying Control to assist those making night approaches as the ships visual cues for establishing a visual hover didn’t appear until quite late in the approach. Affirmation of a good final approach through closure rate (“fast, slow, looking good”), height above the water (“high, low, looking good”), and deck issues such as movement and landing spot availability were the most frequented topics.
The Sea Harrier always flew a common visual and instrument straight in approach at night despite various attempts to devise a safe night visual circuit. The critical piloting task was to judge the point at which to commence the final deceleration to the hover. Too early and the aircraft could be left too far behind the ship with insufficient visual cues to maintain a safe hover. Too late and the aircraft would be ahead of the ship with no visual reference whatsoever! This latter error was jocularly termed an “anchor inspect-ion”. In real life it was hardly jocular and if sever required a nerve wracking transition back to wing-borne flight for a very abbreviat-ed second approach with minimum fuel. The final Hover Stop selection point was hard to reliably achieve from the curving/des-cending final approach of a visual circuit, so the best technique was to come straight in and take advantage of the relatively stable aircraft parameters to exploit information from the aircraft’s own radar and range calls from the ships approach radar controller.
To provide a solution to night and poor weather approaches, a unique approach system was installed on aircraft and carriers. Microwave Assisted Digital Guidance Equipment, or MADGE as it was called by its friendly acronym, was a digital range and azimuth finding system based on a ship based active antenna for aircraft interrogation and a passive angle measuring antenna. Aircraft were equipped with complementary avionics including backup indicators on the conventional secondary flight instruments. Developed originally as a system for helicopter approaches in poor weather and night to tactical landing sites in the land environ-ment, this system provided very accurate ILS like information including a very accurate range for deceleration cues. Additional benefits were the exchange of aircraft information such as Call-Sign, fuel weight, angle of attack and altitude to the Flying Control position. As far as most of us pilots were concerned, the other big benefit was that only the aircraft carrier had this system....”
The 'Fixed Nozzle Slow Landing' and the 'Fixed Throttle Slow Landing' for the SHAR are described in the attached PDF also. I'll look to see what else is in the USMC NATOPS about these landings.
- Attachments
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HowHarrierLandsBOASTedPLUS.pdf- (1.09 MiB) Downloaded 276 times
A4G Skyhawk: www.faaaa.asn.au/spazsinbad-a4g/ & www.youtube.com/channel/UCwqC_s6gcCVvG7NOge3qfAQ/videos?view_as=subscriber
