The Design Of The Das D-9 Hawk Moth

An alternate study to meet the LCA Mk.1A/Mk2 requirement. One of the great lacunae in planning  of our weapons programmes is the lack of alternative studies. Even in tightly state controlled economies competitive proposals are mandatory. It is economical in every sense to have competition. 
The LCA Mk1a /Mk2 are engineering effort wise new proposals. The prototypes are expected circa 2025. We have no back ups for this class of aircraft. The Bisons will have gone. 

It seems that the fuselage of the MiG 27 combined with a new fixed wing - a 45 degree based on the existing wing  or one based on the LCA's wing plus a tail could be copied much faster.and could meet all the problems- lack of real estate, gun firing,etc reported in the CAG report.

At least a preliminary study is mandatory! It should cost no more than a crore and six months.

A proposal to study

the MiG23/27 air frame with the GE F414 engine

As a backup for

the LCA Mk1A and the Mk 2 programmes.

Prodyut Kumar Das

Designer/ Engineer

 Professor IITK etc. (retd.)                                                   Kolkata, 27 February 2019

TABLE OF CONTENTS                                                                            pp.

1.      SYNOPSIS                                                                                        3

2.      THE NEED FOR THE STUDY                                                     4

3.      THE ADVANTAGES OF USING A BASE A/C                           4

4.      THE MIG 23/27 AS A BASE                                                          4

5.      BACKGROUND TECH.NOTES  MIG 23/27                              5

6.      THE DEVELOPMENT STRATEGY                                           6

7.      THE ENGINEERING CHANGES                                               6

8.      THE LIMITS OF THE STUDY                                                     8

9.      OTHER PROJECT STUDIES                                                       9

10.  ESTIMATED MANPOWER                                                          9

11.  CONCLUSIONS                                                                              10

12.  A TABLE OF COMPARISONS                                                    10

13.  SIDE VIEWS                                                                                   11

SYNOPSIS

The IAF is today in a critical situation in relation to the LCA category of aircraft. This has happened because of past lacunae in organization and management of the LCA programme. We have to consider what would have been our situation today had we in 1989 when the review had shown that the proposed LCA was not going to meet specifications, we had   alternative projects studies to fall back on. What the impact of such precautions may have had on the situation today needs no elaboration

 The LCA Mk1 does not meet specifications. The PAC 2153/ CAG report 114 indicate that the airframe is deficient in performance and expandability. The extent of re-engineering on the airframe is around 40% for the airframe alone. The configuration is difficult to develop. The amount of work to transform the Mk1 to the Mk.1A is at least as much as was required to transform the Mirage III into the Mirage 2000. The seasoned, well organized French took four years to get the Mirage 2000 into IOC.

The Mk2 is almost a new aircraft with attendant risks. India must have viable alternatives rather than rely on “Hope” when 2023 comes. There is a strong need as of  the present for a “what if –in case” study of meeting the LCA Mk2 specifications based on the proven MiG23/27 along with several similar such studies. Such back up studies are standard practice in most aircraft programmes and should have been done ab initio at the launch of the LCA programme.

This proposed project is to study if a structural surgery of the MiG 23/27 series aircraft.

Structural surgery is the next evolutionary step to the upgrade programmes carried out on the Jaguar, MiG 21 and the MiG 23 aircraft and about which the IAF has commendable experience. In the upgrades programme the systems have to be upgraded within the constraints of “not touching the airframe”.

In structural surgery (see Indian Defence Review paper II/1990 pp.110-119 by the present author) the airframe is also modified to evolve a new and more suitable aircraft. The MiG 27 itself is an example of structural surgery on the basic MiG 23 aircraft with changes to the nose, cockpit, intakes, wheels and afterburner to make the aircraft suitable for close support duties. The Israeli Kfir is another example.

Since modern engines and avionics are more compact, lighter and superior in performance to those of the MiG 23 vintage the advances in performances seen in Upgrades are further enhanced and optimized by the structural modification of a basic airframe. It is possible to evolve a design that will not only meet the Tejas Mk2 requirements it will be a more certain to achieve its time targets thanks to a more certain “base” i.e. the MiG 23/27 aircraft. The comparative figures are on page 10.

A provisional funding of Rs. 5 crores for the project study and a time scale of 6 to 8 months should be sufficient. If it cannot be done in that time it will never be done. Te sum of money is affordable but potential in terms of time saving and “pacing” the LCA project, and the knowledge gained is incalculable.

THE NEED FOR THE STUDY

The Tejas programme continues to be uncertain. This is reflected in the recent CAG report. In summary:

i)                    The airframe is significantly overweight. It so happens that the configuration is particularly weight sensitive.

ii)                  It will not achieve its range payload specifications.

iii)                The design still needs considerable refinement and cleaning up. It will not meet its energy related performance specifications.

iv)                The airframe is too small to house all the equipment now desired.

The configuration of the aircraft- tailless delta with FBW results in any change leads to a cascade of changes. Whilst technically there are no big challenges in doing all of the above these changes have not happened 18 years after first flight.

To base the successor design LCA MK2 on a somewhat “kuchha” base of the LCA Mk.1 as it exists at present  without having a back up may lead to a repetition of what has happened previously. The strongest reason is the poor delivery on promises by the concerned organizations which now has to be planned for.

THE ADVANTAGES OF USING A BASIS AIRCRAFT

1)      CFD and wind tunnel studies are useful for comparison but less accurate and reliable in absolute terms. This is eliminated as the basis aircraft acts as a full scale wind tunnel model and also can be instrumented to generate needed data.

2)      Less experienced design teams may find it difficult to design a service friendly aircraft. The use of an existing design gives a readymade list of features to be retained or need to be improved.

3)      Advances in technology over the design era- sixty years in the case of the MiG 23/27 means significant and guaranteed improvements in utility can be achieved –even in a “ditto” or “Chinese” copy. The CPAFAF‘s TU-16/H5 is a case to the point.

4)      Very large efforts required to perfect handling, cockpit ergonomics, safety and Weapons delivery and gun firing which may require an additional thousand sorties are reduced to a fraction.

5)      There are psychological resistances during the certification process. The availability of proven structures and systems speeds up the process and these are considerable.

The intelligent designer can slash the work load by 50 to 70%.

THE MiG23/27 AS A BASIS FOR THE LCA MK.2 SPECIFICATIONS.

i)                    The MiG 23 was the original BVR fighter. Its airframe performance equals or exceeds those required LCA Mk.2 specifications.

ii)                  The aircraft was in prolonged IAF service and used in combat. Its advantages and shortcomings are well known to the customer. The exact areas of improvements are in sharp focus.

iii)                Much of the documentation and airframes are available as is the human knowledge of the operators. This information will cut down the need for repetitive trials in many significant areas- air brake location on the fuselage or gun firing trials for example. Detail design problems are under emphasized in India and are more time consuming than aerodynamic problems and make the difference between a disliked aircraft and a well loved one.

iv)                “De-tuning” the design from a Mach 2.3 to Mach 1.6 will easier than refining the LCA in terms of the speed.

v)                  The basic MiG 23/27 airframe is amenable to development. Being a conventional layout there will be less “cascade” or “linked” changes. For example if the FBW is not cleared for flight to match the flight programme the configuration can be be re-arranged as a conventionally stable aircraft until the problem is sorted out. This is not possible in the LCA. The proposed canards for the LCA Mk2 will also require considerable refining lest the traps in the canard layout-fore plane/main wing interference for example or the higher induced drag of the low AR fore plane is not fallen into.

vi)                The reduction of the Mach 2.3 speed to Mach 1.6 means that the 72 ^o wing sweep and indeed the VG requirement can be totally eliminated. There were Russian proposal to such effect but at that time the Mach 2.3 top speed was considered sacrosanct so a VG was essential.

THE MiG 23/27: Some background technical notes.

Why the MiG 23 needed VG.

The MiG 23/27 was designed in the 1960s and the VVS’s requirements were:

i)                    A top speed of Mach 2.3 at 12,000 mts

ii)                  Comprehensive BVR and IRST capability along with CCM capability.

iii)                Ability to operate from Soviet Warpac rough fields. The last was not an IAF requirement.

The Russians experimented with lift engines and variable geometry (VG) before choosing the then fashionable VG configuration with outboard hinge and three positions manually selected swept wing. The heavy weight and the size of the Russian Saphir 23 radar and the Mach 2.3 top speed needed a heavy and powerful engine and its consequent load of fuel. This enforced the use of the VG to keep the landing speed within reasonable limits despite its obvious penalties including around 400kgs extra weight i.e. 4% of the empty weight.

The reduction in top speed to Mach 1.6 means less required power and hence the size and weight of the engines. The modern ELTA radar preferred by the customer is both lighter and requires less base power. 1960s Soviet technology accessories- hydraulics, electrical and avionics were both heavy and bulky and can be replaced by lighter modern systems. The same applies for materials including brake materials. All these result in an inward weight spiral so that the specifications can be met by a “cut down and squeezed” MiG 23/27 which no longer requires a VG wing to have an acceptable field performance. The downward weight spiral estimate is given in the Engineering Changes.

THE DEVELOPMENT STRATEGY

As detailed below the direct weight savings due to replacement of the wing sweep mechanism, the engine and radar will amount to a weight savings of 1500 kilogrammes. The consequent “cascade” changes will result in a total weight saving of 2000 kilos.

Since the top speed of Mach 2.3 is no longer required the max.wing sweep of 72 degrees and the extra engine power will be eliminated and the Mach 1.6 speed of the specification can be met by a simple fixed wing based on the existing design but with greater emphasis on leading edge flaps to retain the airfield performance. No composites will be used in the prototypes as this militates against the rapid modifications that are needed

THE ENGINEERING CHANGES

The engineering changes vis a vis the Mig 23 will be as listed below.

1.      Radome

The radome contours will be based on the MiG 23 suitably modified for the ELTA 1M 2032. The radome is expected to be somewhat smaller than the SAPHIR 23 base radome saving weight and drag.

2.      Cockpit

The armoured cockpit of the MiG 27 will be retained. The Glass cockpit technology already developed for the upgrades will be used. Rear view can be improved via sensor fusion and MFDs. The ejection seat will be replaced by a modern seat.

3.      Intake

Given the lower power of the GEW 414 or similar engine vis a vis the R 29B the variable intake of the MiG 23 BN will be retained as opposed to the fixed intake of the Tejas or the MiG 27 at least in the demonstrator aircraft.

4.      Mid Fuselage

 the customer will have two options:

i)                    Keeping the existing MiG 27 fuselage cross section and use the space for equipment and extra fuel

ii)                  “Squeezing” the fuselage to closely wrap around the F414 which is 103 mm smaller in diameter. This will reduce the transonic cross section and help improve drag, transonic acceleration and energy related performance as also further weight reductions but reduce the radius of action compared to i) above.

5.      Deletion of VG and lowering of wing datum

i) As already indicated the VG feature is no longer strictly necessary and the wing will be replaced by a wing of similar area and aerofoil section but with the sweep fixed at approximately 45 degrees. The LE flaps will be improved and made full span the technology developed for the LCA. A study will also be made to compare the performance with the wing using the Sukhoi Su 7 aerofoil section which was noted for its excellent handling in combat speeds.

ii) If roll coupling problems have been reported it may be possible to improve this by lowering the wing datum by the 53 mm vis a vis the centre line of the fuselage. Coupled with the lighter engine the handling of the aircraft in rolling will improve.

The elimination of the extreme sweep of 72 degrees will give a bonus in that the Aerodynamic centre (AC) will shift back much less. Consequent to the reduction in the AC movement the “tail volume” will be reduced Hence the rear fuselage aft of the Cg will be reduced in length by about 1 metre saving weight and drag.

6.      Elimination of folding underfin

It is expected that the fin and the tail plane will be reduced in size and it is quite possible that the folding under fin can be replaced by a smaller fixed under fin/eliminated with saving in weight and drag.

7.      Relocation of pylons for better optimization

To avoid the usage of variable sweep pylons as in the American F 111A the Russians elected to put all the pylons in the wing glove. This was sub optimal as the forward cg meant a larger than necessary tail empennage as well as a heavier nose under carriage. With a fixed sweep wing it will be possible to relocate some of the pylons out on the wing thus relieving wing bending moments as well as allowing the missile sensors a greater field of view. The weight of the nose undercarriage can be reduced.

8.      Smaller engine inlets

The smaller mass flow of the GE engine 86 kg/sec vs 105 kg/sec means that the intakes will be smaller. This will result in weight and transonic drag reduction whilst the greater L/D ratio of the intake duct means that better “surge resistance” can be expected during gun firing.

Alternately if the fuselage cross section is kept same as the present (p.6 pt.4) an additional 550 lits of fuel can be stored.

9.       Deletion of JATO Pylons

The MiG 23/27 was equipped with JATO pylons to meet rough field operations. If these are not a part of the doctrine these pylons will be eliminated saving weight and drag.

10.  Artificial Intelligence

AI will be introduced into the aircraft to improve serviceability as well as give a pilot reminder and warning aural messages. Depending on the advantages of each incremental surgery the changes have to be menu-ed against time and organized into a minimum list and subsequent changes can be introduced as per production block. The LCA Mk1 software already developed can be incorporated.

Weight Savings

The MiG 23 aircraft was designed using the technology of 60 years go. Improvements in technology since then has resulted a possibility of considerable savings which could radicalize the concept of the aircraft.

Direct savings.

Feature changed                                            Weight                        Weight saved

Elimination of the VG mechanism                                                                 400 kgs.

(Estimated from Soviet sources)

Replacement of engine R29B by F 414

Weight of Tumanskii R29B                            1830kgs

Weight of GE 414                                          1130 kgs                                  700kgs

Replacement of Radar

Weight of  Saphir 23                                       385 kgs

Weight of Elta 1M2032                                  100kgs                                     285 kgs

Total direct weight saved                                                                                                                                                                                                                  1380 kgs

The direct savings will lead to further indirect savings due to aerodynamic and structural reasons. These are:

1.      Reduction in fuselage lengths approx 1mts  as AC movement is reduced                                                                                                                             100kgs

2.      Deletion of folding  ventral fin                                                                 85 kilos

3.      Reduction due to ducting cabling wiring pipeline etc                              100 kilos

due to 1 above

4.      Reduction in tailplane area due to lower a.c. shift                                   50 kilos.

5.      Due to replacement of Soviet era connectors                                           60 kilos

6.      Due to lighter wheel and brakes of modern technology                           75 kilos.

7.      Due to better location of pylons and deletion of RATO pylons              40 kilos

8.      Weight improvement to the undercarriage                                               40 kilos

There will be a significant saving in changing from Soviet era connectors and 28v electrical systems to modern Western equipment and 115 v. constant frequency systems as no doubt the Air Force is well experienced in.

Generally a two ton (2000kgs) weight saving can be expected at this stage of estimation.

The prototype aircraft can expect to be around 7500 kilos basic empty weight without using composites which can be introduced only after the design is proven. Using composites on the wing skins alone can save around 350 kilos above the given figures and they should be introduced in the later blocks.

The Limits of the study

To serve its purpose such a study should be severely limited and focussed scope to be achieved in a strictly defined time. The study is a “what if we do this – what will we get “ confirmation of the above idea and should not take more than 2 to 4 crores per study though no doubt people can find means to overshoot the budget.

The study should explore:

i)                    Does the MiG 23/27/F414 hybrid meet the MK2 specifications without any concessions?

ii)                  The extent of “stretch ability” of the design over the next two decades to accommodate future growth. The layout will score heavily in this.

iii)                What and where the information resources are available should the project go up to the next stage.

iv)                The cost estimates and timescales for an FSED and for the next step i.e. detail design and mock up.

Scope of the work

i)                    Preparation of three project studies using the F414/ Eurojet/M88 and Russian engines and along with matching accessories. This is to avoid commercial pressures which will be inevitable if the project is attractive.

ii)                  Performance studies based on comparative CFD and wind tunnels studies. The availability of the MiG 23/27 will be particularly valuable in underwriting the data.

iii)                Identification of resources required to build mock ups and or prototypes and their availability in India.

Other Project studies

There should be the following other project studies either jointly with the original licensor or independently. These should cover:

i)                    Jaguar “big wing” with the Maritime fuselage which was an original BAe programme in the 1980s.

ii)                  The HF 24 powered by the Honeywell F 125. The airframe’s potential is unarguable and its known quirks can be tamed by modern technology.

iii)                The MiG 21 UPG/LCA systems packaged in to a modified air frame based on the Gnat much as the Orpheus powered Gnat was evolved from the Viper powered Midge of one third the power of the Orpheus. The peculiarities of Military marketing are such that people will listen to a “Combat Hawk” proposal but not consider a superior solution in the Gnat re- surgery.

It appears that the HF 24 drawings and documents have been destroyed. This requires an investigation but the absence of drawings does not stop the HF 24 from being considered as a base for initial project studies. Modern e-engineering techniques such as laser scanning and spectrography can regenerate all the data on the platform and the rest of the study is no more than an upgrades programme. What will be needed will be a one or two airframes in a reasonable state of preservation. The technical history of the programme can be recreated given our great oral traditions as exemplified by the Canberra reintroduction.

Intellectual property Rights issues may rise but since structural surgery with new equipment and systems the resulting aircraft is essentially new and so IPR problems can be tackled. In any case the vendors would be tackled by the prospects having lucrative markets for the supply of the accessories and can be handled at the Government to Government levels.

Estimated Manpower

A total of 10,000 to 15,000 man hours need to be budgeted for. Tentaitively the need is for 6 engineers preferably with about ten years MiG 27 experience and about 6 CAD/CAE engineers capable of working under guidance on modern CAE software. Another two documentation staff would be indicated ,i.e. 15 engineers working for six months.

Work location

Modern communications makes the workplace location less important. Closeness to the customer to understand his needs is the first requirement. The ideal at this (preliminary) stage would be Air HQ as a project cell or IIT New Delhi. Admittedly IIT New Delhi does not have an Aeronautical Department but it is overruled by the fact that the project cell can be in almost daily interaction with the Customer and the industrial back ground of NDLI can allow for small mock ups etc to be quickly fabricated.

The other location could be BRD 11 Nashik which would have the base aircraft at hand. In the case of the Delhi location one CAT C sample of the airframe and as much documentation as available will have to be located at the campus.

Conclusions

It is common sense and standard practice that when unproven technological advances are incorporated into a design to have not one but several plan Bs. These plan Bs are carefully calibrated in terms of risks against an abscissa of time. Such efforts are continued until the main project is reliably out of the woods. Failure to do so has created the crisis.

Contrary to the views broadcast bt the import lobbies the keeping of multiple projects is not expensive. It would have cost us only 50 or 60 crores i.e. 10% of the LCA budget of that time over perhaps six years to have funded any of the HF 24 based derivatives in 1983. The annual additional expenditure would have been in the region of perhaps ten crores. The impact of having a HF 73/HF25 prototype around 1989 does not need elaboration.

We cannot correct the past. The present has to be seized. The LCA Mk2 as much as the LCA mk.1A and the.AMCA must have at least shadow competitors at this nascent stage.

Prodyut Kumar Das

Engineer .Professor (retd)

Kolkata

Contact details: prodyut.das7@gmail.com/ ph.9007434226

 April 20 -2019

Sl.no.	Parameter	MiG 23/27	Redux
1.	Length	16.84	15.04
2	Span	13.995/7.779	10
3.	Height	5.145	5.145
4.	Wing Area	37.27/34.16	34
3.	Empty Weight	9595 kgs.	7500-7000 kgs.
4.	Clean TO with 2 CCMs.	14,625 kgs.	12,625 kgs.
5.	MTO	18,570 kgs.	16,975.kgs.
6.	Internal Fuel	4670kgs.	4670kgs.
7.	Fuel Fraction	0.5586	0.80/0.5586
8.	Engine Thrust	83.6/127 kN	57.8/98 kN
9.	Wing Loading ( clean Combat)	430 kg/sq.mts.	371 kg./sq.mts.
10.	Power Loading ( clean combat)	0.886	0.89
11.	Fixed Weapon	6x30 GSh.	6x30GSh.

The three view drawing sshowing the MiG 27 fuselage with the LCA wing panels and one with a MiG 27 based wing at fixed sweep will be published in due course.