巴基斯坦空军当年试飞J-7MG的过程~~~~~~~~~英文好的请进 ...

想说的是：从屠基达那辈开始，中国的外贸军机制造商就懂得如何利用手里现成的技术去讨好用户。F-7PG获得巴基斯坦空军的高度评价也因为它超强的性价比！

F-7MG Flight Trials by Pakistan Air Force

Gp Capt Kaiser Tufail and Wg Cdr Jamshed Khan (both now Air Cdres) were detailed to test fly the F-7MG (later known as F-7PG in PAF service) in July 1997.  A total of 12 sorties were planned in which the complete flight regime was to be explored, with particular focus on the improvements in performance of the already in-service F-7P.  A similar number of sorties were to be flown after a few months, when the GEC-Marconi Super Skyranger was ready.

Soon after arrival in Chengdu, the wet tropical weather of Southern China made it quite obvious that the flight trials would take longer than expected.  Two other unusual challenges were the language barrier and the issue of finding enough airspace over non-populated areas.  Chengdu is one of China’s largest metropolitan centres and is located in Sichuan Province, which happens to have the country’s densest population per acre.  In such environments, supersonic flights as well as low-level max-Q trials left no room for area violation in the narrow sliver that had been allocated for flight trials.  The pilots had also been told that their departure back home could be delayed in case the adjacent Chengdu International Airport were ever to lodge an air violation.  The hint was well registered!

PAF’s evaluation was the first by a prospective foreign customer, although the aircraft had accumulated almost 10,000 hours in the PLAAF since its induction in late 1995.

Major Improvements
The F-7MG airframe has essentially the same F-7P fuselage, inner wing portion, tail plane and fin.  The outer wing section incorporates the major change, with a reduced 42° sweep and automatic manoeuvring flaps.  The F-7MG is powered with an improved and more powerful WP-13 engine, which is also operational on the      F-7III (Chinese version of the MiG-21MF).  Additionally, cockpit layout, avionics and several ancillary systems have been changed, in line with modern trends.  The important systems that remain unchanged (compared to the F-7P) are the fuel system, weapons payload capacity and internal guns.

Double Delta Wings

Like the Su-15, the Draken J-35, as well as the more modern X-31 post-stall manoeuvring demonstrator, the F-7MG has a double-delta wing planform, which offers an excellent solution to a slender delta’s inherent low aspect ratio problem.  The aspect ratio of conventional deltas is, at best, of the order of about 2.4, with the low end notched up, surprisingly, by India’s LCA; at 1.75 it stands behind the bat-winged double-delta Saab Draken, whose very low aspect ratio of 1.8 was considered to be a convenient remedy to the transonic CP shift, albeit at the expense of overall aerodynamic efficiency.

ASPECT RATIO & AERODYNAMIC EFFICIENCY

Creating lift in an aircraft incurs an unavoidable penalty in the form of induced drag.  Aerodynamic efficiency is achieved by designing a wing that produces maximum lift for the least drag.  This is done by having a high ‘aspect ratio,’ which is the ratio of the square of the wingspan to the wing area.  Since induced drag is inversely proportional to the aspect ratio, greater the wingspan, lower the induced drag.  A high aspect ratio is thus an important factor in combat, as it helps in sustaining turn rates.  High aspect ratio also improves endurance and ceiling and, shortens take-off/landing distances.

As fighters become faster, their aspect ratios have to be reduced to minimise supersonic wave drag.  This is done by presenting a smaller frontal area to the supersonic airflow with the help of a smaller wingspan, besides other profile streamlining techniques.  It can thus be seen that the conflicting requirements of high-speed flight and subsonic manoeuvring flight have a bearing on the aspect ratio and, compromises invariably result.  

Wingtip stalling has never been an issue on the F-7P, but the double delta wing brings with it an added bonus in this respect.  The strong vortex of the inner wing re-energises the boundary layer of the outer wing, preventing span-wise flow towards the tips.  This allows even more-carefree manoeuvring at ultra-low speeds.

Testing the Wings

On the first take-off, it was evident that the aircraft was impatient to get off the ground and had to be held down to prevent it getting airborne prematurely.  Compared to the F-7P’s take-off speed of 310 kph, the MG lifted off at 280 kph with ease and the advertised 35% improvement in take-off distance was on the mark.  The sight of the auto-manoeuvring flaps at work reminded the pilots of the F-16’s computer-controlled leading edge devices.  Packaging the servo motors and actuators within the thin leading edge without the tell-tale bulges has certainly been a marvel of engineering at Chengdu Aircraft Corporation (CAC).

The feel of the aircraft was smooth in all domains, none more so than in transonic flight.  As expected, CP shift was minimal and both the test pilots were unanimous about the decrease in stick forces.  Transonic being an important combat flight regime, this is a welcome improvement.

A good measure of a wing’s lifting efficiency is at high alpha, a regime that the PAF pilots have learnt to perform in almost as an art form.  What better than to pace the MG through a slow speed loop?  Normally, a safe entry speed for a loop would be between 800-900 kph (at 15,000 AMSL) on the F-7P.  In the absence of any guidelines on a slower version of the manoeuvre, it was decided to try 700 kph at first.  The MG went through smoothly without any hint of judder or slip at the top.  With full faith in the leading edge flaps, the next loop was performed at 600 kph.  Again, the same results were achieved and the aircraft went through a perfect loop without any jitter or judder.  At lower altitudes it might do even slower and better, but airspace limitations at Chengdu did not permit low level aerobatics.



Air Cdr Kaiser Tufail gives a thumbs-up before an evaluation sortie (top left) and talks with CATIC engineers (bottom left) after a sortie.

Pictures Courtesy: Air Cdr Kaiser Tufail





Several flights followed the first check of the aircraft’s aerodynamic efficiency.  It was a most pleasant surprise to note that the turn rates were nearer to the F-16 at medium to high altitudes and, were exactly as advertised.  A 33% improvement over the F-7P at 5,000’ AMSL, 50% at 10,000’ and 66% at 20,000 would certainly call for an end to the “supersonic sports plane” sobriquet that dogged its forerunners.

The results of the flight trials were so encouraging that the test pilots were tempted to simulate a flamed-out engine landing pattern, a not very ‘done’ thing on delta-winged fighters.  While the Chinese manuals suggested a rectangular pattern that can put one’s judgement and nerves to test, the standard overhead spiral pattern was tried out initially from a high-key height of 15,000’ AGL.  With engine idling and speed brakes out to simulate a dead engine, the aircraft glided much like the F-16, so after a few approaches, the high key height was lowered to12,000’ AGL.  The sink rate was well under control and, in fact was so well manageable that all later sorties were terminated through practice dead-engine approaches.  At 1:8.5, the glide ratio compares favourably with some of the modern Western fighters.

Landings on the F-7MG could be made at 270 kph, compared to about 290 kph on the  F-7P.  The test pilots felt that the speed could be lowered further, were it not for the length of the gear struts, which are not long enough to allow a higher nose attitude.  Hydraulic brakes, though still hand-held (like those on a bicycle handle-bar), were very effective and, the unlimited braking facility was a welcome improvement over the  bled-off pneumatics of the F-7P.

New Engine

The WP-13 engine of the F-7MG produces 1,200 lbs of more thrust than the F-7P’s WP-7, giving it a thrust-to-weight ratio of about .9 compared to .8 of the latter in clean take-off configuration.  A 50% improvement in spool-up time is a welcome feature, particularly on final approach and landing where a sudden gust of wind has resulted in many a tail scrape on the F-7P.  Go-arounds are also prompt and a bad landing is actually a thing of the past on the MG. Use of titanium alloys in compressor blades and an increased TBO are indicators of improvements in Chinese jet-engine technology.

The thrust increase was evidenced by a 25% improvement in acceleration time from 500 kph to 1100 kph and an equally impressive time-to-climb to 36,000’ AMSL.  All improvements were verified and were found to be as advertised or even better.  Even more remarkable was the fact that these trials took place in hot and humid weather, well outside the 15°C, 1013 hP environments in which the specifications are usually engineered.

Miscellaneous Systems

The F-7MG has several modern avionics upgrades.  These include a Stores Management System, which is essentially a useful cockpit-pilot interface to help establish the status of stores including configuration, fusing and weapon codes etc.  A voice warning system, colour video recorder, elaborate cockpit lighting and a more precise and jitter–free AOA probe are nice-to-have improvements.  The colour EFIS includes two displays, one for the attitude and the other for the heading and navigation sub-systems like ADF, VOR, TACAN, ILS etc.

The PAF pilots used to advanced cockpits like the F-16 were quick to point out several ergonomic improvements and had detailed discussions with CAC design bureau.  Switchology changes and relocation of several instruments led to a much improved cockpit; it has been suggested in a lighter vein that a nomenclature change to F-7PG2 might just be in order.  (‘G’ incidentally stands for ‘gai’, meaning ‘improved’ in Chinese.)

Radar

The F-7MG was originally designed to have the GEC-Marconi Super Skyranger.  At the time of initial PAF trials the radar was not ready.  Trials were held again several months later after the prototype radar was installed.  In the event the radar did not come up to PAF specifications and GEC-Marconi was not able to surmount the problems associated with the small nose cone, including antenna size and equipment air-conditioning which was insufficient.

The PAF eventually retrofitted their F-7Ps and F-7PGs with the FIAR Grifo-7.  To say that miniaturisation technology is at its best in this marvellous Italian radar would be an understatement.  An excellent pulse Doppler radar with respectable ranges and a medium order azimuth and elevation scan, the system is married to the all-aspect AIM-9L Sidewinder, making it a lethal combination.

FT-7PG

CAC did not design a double-delta version of the F-7MG.  On PAF’s request, the existing FT-7P cockpit was redesigned on lines of the PG to ensure standardisation and the resultant dual seater was re-designated FT-7PG.

Analysis

The F-7MG has considerably improved subsonic and transonic flight performance.  Coupled with excellent turning capability and acceleration, the combat potential is enhanced tremendously.  The Grifo-7/AIM-9L combination on board PAF’s F-7PG brings the aircraft much closer to the F-16 in close combat capabilities and the PAF must be credited with extracting the maximum from an innovatively redesigned low-cost fighter.

原文地址:
http://www.pakdef.info/pakmilitary/airforce/ac/f7pg.htm

想说的是：从屠基达那辈开始，中国的外贸军机制造商就懂得如何利用手里现成的技术去讨好用户。F-7PG获得巴基斯坦空军的高度评价也因为它超强的性价比！

F-7MG Flight Trials by Pakistan Air Force

Gp Capt Kaiser Tufail and Wg Cdr Jamshed Khan (both now Air Cdres) were detailed to test fly the F-7MG (later known as F-7PG in PAF service) in July 1997.  A total of 12 sorties were planned in which the complete flight regime was to be explored, with particular focus on the improvements in performance of the already in-service F-7P.  A similar number of sorties were to be flown after a few months, when the GEC-Marconi Super Skyranger was ready.

Soon after arrival in Chengdu, the wet tropical weather of Southern China made it quite obvious that the flight trials would take longer than expected.  Two other unusual challenges were the language barrier and the issue of finding enough airspace over non-populated areas.  Chengdu is one of China’s largest metropolitan centres and is located in Sichuan Province, which happens to have the country’s densest population per acre.  In such environments, supersonic flights as well as low-level max-Q trials left no room for area violation in the narrow sliver that had been allocated for flight trials.  The pilots had also been told that their departure back home could be delayed in case the adjacent Chengdu International Airport were ever to lodge an air violation.  The hint was well registered!

PAF’s evaluation was the first by a prospective foreign customer, although the aircraft had accumulated almost 10,000 hours in the PLAAF since its induction in late 1995.

Major Improvements
The F-7MG airframe has essentially the same F-7P fuselage, inner wing portion, tail plane and fin.  The outer wing section incorporates the major change, with a reduced 42° sweep and automatic manoeuvring flaps.  The F-7MG is powered with an improved and more powerful WP-13 engine, which is also operational on the      F-7III (Chinese version of the MiG-21MF).  Additionally, cockpit layout, avionics and several ancillary systems have been changed, in line with modern trends.  The important systems that remain unchanged (compared to the F-7P) are the fuel system, weapons payload capacity and internal guns.

Double Delta Wings

Like the Su-15, the Draken J-35, as well as the more modern X-31 post-stall manoeuvring demonstrator, the F-7MG has a double-delta wing planform, which offers an excellent solution to a slender delta’s inherent low aspect ratio problem.  The aspect ratio of conventional deltas is, at best, of the order of about 2.4, with the low end notched up, surprisingly, by India’s LCA; at 1.75 it stands behind the bat-winged double-delta Saab Draken, whose very low aspect ratio of 1.8 was considered to be a convenient remedy to the transonic CP shift, albeit at the expense of overall aerodynamic efficiency.

ASPECT RATIO & AERODYNAMIC EFFICIENCY

Creating lift in an aircraft incurs an unavoidable penalty in the form of induced drag.  Aerodynamic efficiency is achieved by designing a wing that produces maximum lift for the least drag.  This is done by having a high ‘aspect ratio,’ which is the ratio of the square of the wingspan to the wing area.  Since induced drag is inversely proportional to the aspect ratio, greater the wingspan, lower the induced drag.  A high aspect ratio is thus an important factor in combat, as it helps in sustaining turn rates.  High aspect ratio also improves endurance and ceiling and, shortens take-off/landing distances.

As fighters become faster, their aspect ratios have to be reduced to minimise supersonic wave drag.  This is done by presenting a smaller frontal area to the supersonic airflow with the help of a smaller wingspan, besides other profile streamlining techniques.  It can thus be seen that the conflicting requirements of high-speed flight and subsonic manoeuvring flight have a bearing on the aspect ratio and, compromises invariably result.  

Wingtip stalling has never been an issue on the F-7P, but the double delta wing brings with it an added bonus in this respect.  The strong vortex of the inner wing re-energises the boundary layer of the outer wing, preventing span-wise flow towards the tips.  This allows even more-carefree manoeuvring at ultra-low speeds.

Testing the Wings

On the first take-off, it was evident that the aircraft was impatient to get off the ground and had to be held down to prevent it getting airborne prematurely.  Compared to the F-7P’s take-off speed of 310 kph, the MG lifted off at 280 kph with ease and the advertised 35% improvement in take-off distance was on the mark.  The sight of the auto-manoeuvring flaps at work reminded the pilots of the F-16’s computer-controlled leading edge devices.  Packaging the servo motors and actuators within the thin leading edge without the tell-tale bulges has certainly been a marvel of engineering at Chengdu Aircraft Corporation (CAC).

The feel of the aircraft was smooth in all domains, none more so than in transonic flight.  As expected, CP shift was minimal and both the test pilots were unanimous about the decrease in stick forces.  Transonic being an important combat flight regime, this is a welcome improvement.

A good measure of a wing’s lifting efficiency is at high alpha, a regime that the PAF pilots have learnt to perform in almost as an art form.  What better than to pace the MG through a slow speed loop?  Normally, a safe entry speed for a loop would be between 800-900 kph (at 15,000 AMSL) on the F-7P.  In the absence of any guidelines on a slower version of the manoeuvre, it was decided to try 700 kph at first.  The MG went through smoothly without any hint of judder or slip at the top.  With full faith in the leading edge flaps, the next loop was performed at 600 kph.  Again, the same results were achieved and the aircraft went through a perfect loop without any jitter or judder.  At lower altitudes it might do even slower and better, but airspace limitations at Chengdu did not permit low level aerobatics.



Air Cdr Kaiser Tufail gives a thumbs-up before an evaluation sortie (top left) and talks with CATIC engineers (bottom left) after a sortie.

Pictures Courtesy: Air Cdr Kaiser Tufail





Several flights followed the first check of the aircraft’s aerodynamic efficiency.  It was a most pleasant surprise to note that the turn rates were nearer to the F-16 at medium to high altitudes and, were exactly as advertised.  A 33% improvement over the F-7P at 5,000’ AMSL, 50% at 10,000’ and 66% at 20,000 would certainly call for an end to the “supersonic sports plane” sobriquet that dogged its forerunners.

The results of the flight trials were so encouraging that the test pilots were tempted to simulate a flamed-out engine landing pattern, a not very ‘done’ thing on delta-winged fighters.  While the Chinese manuals suggested a rectangular pattern that can put one’s judgement and nerves to test, the standard overhead spiral pattern was tried out initially from a high-key height of 15,000’ AGL.  With engine idling and speed brakes out to simulate a dead engine, the aircraft glided much like the F-16, so after a few approaches, the high key height was lowered to12,000’ AGL.  The sink rate was well under control and, in fact was so well manageable that all later sorties were terminated through practice dead-engine approaches.  At 1:8.5, the glide ratio compares favourably with some of the modern Western fighters.

Landings on the F-7MG could be made at 270 kph, compared to about 290 kph on the  F-7P.  The test pilots felt that the speed could be lowered further, were it not for the length of the gear struts, which are not long enough to allow a higher nose attitude.  Hydraulic brakes, though still hand-held (like those on a bicycle handle-bar), were very effective and, the unlimited braking facility was a welcome improvement over the  bled-off pneumatics of the F-7P.

New Engine

The WP-13 engine of the F-7MG produces 1,200 lbs of more thrust than the F-7P’s WP-7, giving it a thrust-to-weight ratio of about .9 compared to .8 of the latter in clean take-off configuration.  A 50% improvement in spool-up time is a welcome feature, particularly on final approach and landing where a sudden gust of wind has resulted in many a tail scrape on the F-7P.  Go-arounds are also prompt and a bad landing is actually a thing of the past on the MG. Use of titanium alloys in compressor blades and an increased TBO are indicators of improvements in Chinese jet-engine technology.

The thrust increase was evidenced by a 25% improvement in acceleration time from 500 kph to 1100 kph and an equally impressive time-to-climb to 36,000’ AMSL.  All improvements were verified and were found to be as advertised or even better.  Even more remarkable was the fact that these trials took place in hot and humid weather, well outside the 15°C, 1013 hP environments in which the specifications are usually engineered.

Miscellaneous Systems

The F-7MG has several modern avionics upgrades.  These include a Stores Management System, which is essentially a useful cockpit-pilot interface to help establish the status of stores including configuration, fusing and weapon codes etc.  A voice warning system, colour video recorder, elaborate cockpit lighting and a more precise and jitter–free AOA probe are nice-to-have improvements.  The colour EFIS includes two displays, one for the attitude and the other for the heading and navigation sub-systems like ADF, VOR, TACAN, ILS etc.

The PAF pilots used to advanced cockpits like the F-16 were quick to point out several ergonomic improvements and had detailed discussions with CAC design bureau.  Switchology changes and relocation of several instruments led to a much improved cockpit; it has been suggested in a lighter vein that a nomenclature change to F-7PG2 might just be in order.  (‘G’ incidentally stands for ‘gai’, meaning ‘improved’ in Chinese.)

Radar

The F-7MG was originally designed to have the GEC-Marconi Super Skyranger.  At the time of initial PAF trials the radar was not ready.  Trials were held again several months later after the prototype radar was installed.  In the event the radar did not come up to PAF specifications and GEC-Marconi was not able to surmount the problems associated with the small nose cone, including antenna size and equipment air-conditioning which was insufficient.

The PAF eventually retrofitted their F-7Ps and F-7PGs with the FIAR Grifo-7.  To say that miniaturisation technology is at its best in this marvellous Italian radar would be an understatement.  An excellent pulse Doppler radar with respectable ranges and a medium order azimuth and elevation scan, the system is married to the all-aspect AIM-9L Sidewinder, making it a lethal combination.

FT-7PG

CAC did not design a double-delta version of the F-7MG.  On PAF’s request, the existing FT-7P cockpit was redesigned on lines of the PG to ensure standardisation and the resultant dual seater was re-designated FT-7PG.

Analysis

The F-7MG has considerably improved subsonic and transonic flight performance.  Coupled with excellent turning capability and acceleration, the combat potential is enhanced tremendously.  The Grifo-7/AIM-9L combination on board PAF’s F-7PG brings the aircraft much closer to the F-16 in close combat capabilities and the PAF must be credited with extracting the maximum from an innovatively redesigned low-cost fighter.

原文地址:
http://www.pakdef.info/pakmilitary/airforce/ac/f7pg.htm