A Polymorph for the Future?    a review of inherent upgradability and the pontoon  “chassis”    Prof.Prodyut Das.  Poly morph –literally “many forms” here is taken to mean an airframe that is inherently suitable for “infinite” modifications and up gradations.

Should design for upgradability be a conscious part of the design requirements for combat aircraft?  Given the factors that are shaping the conceptual design of combat aircraft and India’s own dependence on foreign vendors, the answer is definitely a “yes”. This crippling dependence on vendors is an unacceptable situation that must be compensated by technological innovation as represented by the “Ponton” (pontoon). We must be able to design aircraft where it should be able to replace entire “sources” on an airframe in case of difficulties with supplies. This means that entire imported packages are relegated source wise and misbehavior by any one vendor will result in the entire package being disqualified. This will mean the other vendors in the package  will also bring pressure on the misbehaving vendor.

The question of inherent upgradability to alternative engines and systems arose after Prof. KK Sarma of Guwahati University ( to whom thanks) wrote to me about considering the possibility of using the AL 41 F with thrust vectoring for the LCA which, like all pretty young things, has with time, transformed from a maidenly LCA to now a more matronly MWF.  

As a knee jerk reaction we both agreed that the engine was “impossible” but further prodding by Prof. Sarma triggered thought. What has emerged is an idea of “inherent upgradability” and some conjectures as to meeting the MWF and AMCA requirements with a Ponton/AL41F based solution.

A short resume of upgradability

The story is told in the backrooms of Aeronautical bars about the chap who designed the perfect aeroplane. He had to be sacked because he had violated a basic rule of aircraft design- his aeroplane could not be improved! Perhaps there is wisdom in old wives tales and bar room ditties which we tend to ignore as infra dig ; the commercially successful warplanes were always “developable” or “upgradable”.

Until the 1930s upgradability was not to be considered. Wood and fabric aircraft structures would decay in normal service within a few years and in any case the pace of aeronautical development was so furious that the airframes’ aerodynamics was obsolete within months. The Albatros D III was formidable when it entered service with Herr Rittmeister Manfred von Richthofen’s Jasta 11 in 1917 but by June 1918 the Fokker D VII’s amazing-   what is now called high AoA ability- enabled the Fokker, even at high altitude,  to hang on to its prop and pour fire into its opponent from behind ( Note 1). The Fokker was such a sensation that it was required in the terms of the Armistice for Germany to surrender “alle apparte DVII”. The Albatross was obsolete within a year.

The advent of all metal monoplanes of the mid 1930s was the first time that upgradability tip toed onto the scene. Final versions of the fighters like the ME 109 had three times the power and perhaps 12 times the firepower of the first prototypes and pointed the way to the future.

One cannot design useful aircraft by focusing just on the engineering. Indeed the Chief Designer’s main contribution is the distilled wisdom of his  “situational awareness”. The early German Jet aircraft designers were conscious of the need to make the aircraft upgradable. The early German jets- the Arado Ar 232 Blitz, the ME 262 Schwalbe, the Heinkel He 280. The Junkers JU 287 and even the projected Messerschmitt Me P1101 all had under slung or podded  jets which, given the state of flux the German jet engines development was at that time, was a very sensible engineer like decision despite the drag penalty; it made re-engineering for another type of engine less disturbing.

It was with the coming of the transonic and supersonic fighters that upgradability should have been considered as a design requirement.  Transonic flight required enormously strong airframes. At Mach 1.2 low level- which as fast as anyone would wish to go at low level ,the fuel consumption being roughly 20 litres per kilometer- puts on dynamic pressures in the region of 3.5  atmospheres. Designing for such dynamic air loads meant that the strength of the airframes was probably greater than required for having a life where the  the airframe would be written off due to accident, wear and tear and in- service degradations. (Note2) This  bonus could not be reaped because at that time, the SAM was not yet perfected for the all weather point defence tasks the airframe performance demands were still creeping up for the Mach 2 regime so the aerodynamic design of the airframe was “unstable- going upward”. This “uncertainty” prevented emphasis on the “inherently upgradable airframe.

The service life of an aircraft is not entirely decided by airframe fatigue. The “other” factors determining the retirement of aircraft are:

i)                    Difficulty in obtaining “running” spares- tyres, brake pads rubber seals etc.

ii)                  Difficulties in replacing major aggregates such as engines and such type specific items as the Hobson unit etc which are particularly difficult to get in the open market.

iii)                 Operational attrition which reduces fleet size which makes maintaining the fleet difficult or uneconomical.

The succeeding generation of engines, avionics and accessories were smaller and lighter yet upgrading often faced problems. The item not only had to match the performance but also the “shape” for a successful fit without too much re-manufacturing. For example upgrading the engine of the Hunter/ Lightning with the suitable versions of the RB 199 was possible in theory and would give a significant improvement but unfortunately the aircraft had semi monocoque  structures s which made fitment difficult. It was economically impossible to “rebore” the fuselage to take the new engine and its ducting.  

Engineers beat this constraint by designing the replacement as a ”drop fit” or “specific to type” item. A handy example would be the MiG 21. Given the enormous production run of about a thousand for the plain vanilla Mig 21 F for example, the Russians developed the rather natty GSh 23 mm  for the MIg 21 M which gave the aircraft the roughly the same weight of fire as the Vulcan six barreled but of course at the cost of thermal stability. For the engine they had the R 13 and the R25 to replace the R11. Drop Fit put constraints on the extent of upgradability.  One early  example of an “inherently upgradable” design of the era  was the Douglas A4 Skyhawk where of course the one piece low wing acted as a” Ponton” (pontoon) foundation.

The Ponton.

The Ponton (“pontoon”) is a concept known well enough in Automobile design and indeed the Mercedes Benz 220 was nicknamed “Der Ponton” though for my money the little Citroen 2CV was a more brilliant example of the true “pontoon”. I had the opportunity to tape and micrometer an old 2CV for a light low cost car project (what one had to do to make a living as an engineer! ah, me!) and came away impressed. The stiff chassis, a closed torsion box, used rolled sections and did not require heavy presses to make, was brilliant. It permitted the little Citroen’s coach work to be made from steel tube and corrugated sheet- again without needing heavy presswork. Though of ancient design, as an example of frugal engineering, its study was a almost religious communion and a humbling experience.

If the idea of the Ponton were to be translated into aeronautical engineering terms what we will have is the use of the wing and stabilizer and a connecting structure to form a ponton which will carry the cockpit, fuel tanks, equipment on the top and the engine (s) underneath all faired by unstressed composite panels. This would allow infinite upgradability because much of the fuselage volume would be accessible..

A current example of the “Ponton” approach is the Russians. A look at the photos of MiG 29 under production shows how easy it is to upgrade the aircraft because the centre section acts a “ponton”. Perhaps the Russians, who examined several conventional semi monocoque layouts, realized that in the state of flux, it made sense to have future upgradability in mind ab initio even with some penalty. In the MiG 29 for example the changes to the systems or to the engines or a more “stealthy” configuration at a future date will be easy to engineer when compared to equivalent western types. The FGFA/T 50 is but built on a Su 30 Ponton.

The “Ponton” has its draw backs. Greater cross sectional area and wetted area –because of the under slung engine will lower performance and  its supersonic acceleration (note 3) but current engines say the RD 33 in comparison to the Avon have about two and a half times more power per unit cross section. This additional power of current engines enabled Northrop for example to do away with area ruling in the F20; the “conformal” packs on the F 16 Bl 60 are another example of how advanced engine capabilities allow “abuse” of aerodynamics. The structure will be heavier but, as the Russians have shown, this is within manageable limits.

India and the “Ponton”

For India the Ponton concept is an imperative for our future combat aircraft and I am including the AMCA and the MWF as “future “fighter projects. The caution that these two projects are “Future” is because:

i)                    the dates of the first flight are being given by people who will have retired before those dates.

ii)                   The present concepts may require major redesign amounting to “new” design by the time the prototype flies.

iii)                The aircraft is very likely to fail to meet the basic performance parameters- I am just going by the way the development cards are being played. Too many new technologies – stealth, sensor fusion, super cruise are being tested on a new unknown test vehicle – the AMCA. Even the US did not go for the moon ( F 117) without an intermediate test vehicle- the “Have Blue”.

iv)                 The major vendors may wish to make a “killing” at an inconvenient situation midstream.

We have been up these streets before. We must have inherently upgradable fighter designs for several compelling reasons.

1.      Resistance to sanctions and arm twisting- we have had experience of a vendor upping the price of a product forcing us to choose an alternative at the last moment. In the case of the HJT 36 for example the Larzac had to be replaced by the NPO Saturn AI 55 fairly late in the day for reasons which included commercial unviability. Earlier with the HJT 16 the Viper had to be replaced by the de-rated Orpheus. Who will guarantee that it may not happen a third time?

2.      Whilst vendors are offering airframes with 6000 hrs life this feature is meaningless without inherent upgradability. Statistics show that about two thirds of the fleet will be written off- depending on the role – between 2300 hours and 3000 hrs which is about 15-20 years. The remaining aircraft –typically about 60-70 aircraft,- if upgradable- represents a cost effective solution to air power problems only if they can be fully upgraded. ( note 4)

The MBT and the AMCA

3.      Combat aircraft concepts and design is at a point that Tank design was in the early 1940s. Four unrelated changes- radio telephony, track metallurgy, the high speed Diesel engine and dual purpose main armament converted the “infantry” tank to the MBT. In  aircraft design we are also at such a point. Today’s concept of the fighter will have changed by 2025 to that of a ”carrier” relying more on GW, AI and missile systems to do the job-that is if that job is not already been taken over by UAVs and SAMS.

The potential for a significant change in the concept and specifications of the fighter has been long overdue but this has been always stymied by a lobby which wants to push the most complex and expensive specifications that the market will bear. The impact of the following uncertainties and new technologies has to be noted.

i)                    Is “stealth” i.e. the F 117 style total stealth achievable for frontline fighters? Or it will be a specialist “hush hush” weapon operating from special bases and requiring may be only two percent of all combat sorties flown ? The rest 98% can be flown by vanilla warplanes. This question has to be settled because “stealth –is design wise, dreadful. It makes the aeroplane inefficient, high cost and technologically challenging. Stealth itself may also become obsolete/ obsolescent by 2025. Old stagers have always said that that many of “must have “features are just  “marketing”.

ii)      To what extent will thrust vectoring and HMDS and the R 73 style “cueable” CCMs render traditional “aerodynamics based maneuverability” obsolete?

iii)                People are tiptoeing around the “Vartamaan “combat. Was the result of that combat an “outlier” or was it the proverbial “you can tell from a single grain if the pot of rice is done”. Let me put it more bluntly. The 64 billion dollar question is-Could an aircraft even simpler, smaller, cheaper and lighter than the MiG 21- i.e. inherently less detectable by eyeball, radar or IR with only ,say Mach 1.3 aerodynamics but capable of cueing the R 73 CCM and replicating reasonably the aerodynamics performance of the MIG Bison to the extent as actually used on that day- have done the job? The answer is obviously “Yes” and a (relatively) low performance but smart platform with lower signatures is actually be a better solution given the fearsome proven reliability of the CCM.

iv)                 I concede there can be no perfect decision in procurement and this is a particularly damning question. There will always be more expensive and “safer” ways of fighting a war. We can play “safe” and order the same as everyone else until we skid to the borderline of dangerously low fleet sizes which without a doubt will be unsustainable in war. You will lose. New thinking, starting from fundamentals, is needed.

v)      What is the impact of sensor fusion and artificial Intelligence on Combat aircraft design? For example designers have always returned to the all round vision canopy after going on for “flush” canopies e.g. Mc Donnell F 4 Phantom to Mc Donnell Douglas F 15 but today but can rearward facing cameras and “facial recognition” techniques with promptings from ADGES do the job? The possibilities of AI in terms of maintainability. Flight safety and situational awareness is limitless and impactful.

vi)                Finally there is the undeniable truth that Mach 2 plus capability was an old Western requirement to supplement the failings of the early SAMs and plays havoc with “sensible” airfame design. Today the point defence tasks for VPs and VA should mainly be shouldered by the SAMs . We should trade supersonic aerodynamics for “fuselage volumes” which augurs well both for range – always a most useful feature for warplanes- and upgradability. As an example, the useful fuselage volume of the MiG 21 , that is the fuselage volume theoretically available after deducting the engine and duct volumes is for example only is 49 percent. The pontoon is around 63 percent and can be expanded. Even if the figure is approximate the fact that the “Ponton” is both practicable and “infinitely” modifiable is undeniable.

vii)              The above questions cannot be ignored anymore by India which has limited design  management resources and budgets. Again let me repeat – there can be no perfect decision. The Japanese sacrificed “recklessly” by Western standards-battle damage resistance to get range. It was to the IJN an arguably  sensible decision and if Japan lost it was not because of its design philosophy but because its industrial potential was limited. To cut myself short- if we do not examine the possibilities of the polymorph-  what will happen is that, even if the AMCA and MWF programmes are on time, we will have produced aircraft that are not modifiable or upgradeable to the extent required. Nor can they stand up to commercial or political arm twisting. The Designer cannot estimate the likelihood of such an event but he can provide in his design features to reduce the impact of such moves.

The danse Macbre

Aircraft design is not just a three legged race of the junior schooldays but probably a multi legged race where the lengths of the legs- i.e. the development cycles of all the various systema are all very different. In the case of this category of combat aircraft the “legs” comprise of:

i)                    Airframe aerodynamics

ii)                  Propulsion Technology. People are working now on variable cycle engines ( we should not even think of such things!)

iii)                Airframe materials

iv)                 RAM coatings ( applicability, maintainability and disposal)

v)                  Radar reflecting geometry i.e. robust stealth.

vi)                Control technology- FBW, FBL, “Puff Pipe” e.g Harrier,

vii)              Artificial Intelligence

viii)            Radar and avionics

ix)                Power and power control systems- hydraulics, FBW, FBL, electrics for working the various sytems.

Only the first- aerodynamics- is now relatively “stable”. Indeed it is regressive- top speeds are coming down, manouvreability is being substituted by “pointability” and high AOA is less in demand than two decades ago but ii) to ix) have changes which will have significant impact on future configurations.

Aircraft Engineering is Technology but Aircraft Design is Humanities and is strongly linked to the technological environment .Indian designers must keep vulnerability of supply lines very much more in their minds than in designers in other countries. The LWF is coming in a big way once the last F 35 has been “flogged” and suppose then there was a genuine shortage of the F 404/ F 414 engines in the market. Where will we be then with the AMCA?

A different way of doing things

We must fly our prototypes earliest. First flights cannot be BVR! The idea that if we tinker around long enough we will somehow come out with a trouble free aircraft does not work. (Note5). The universal successful method is to cobble together something reasonably promising and get it flying within 3 or 4 years of “go ahead” and then patiently squash all the inevitable worms that crawl out of the woodwork. 

A “ponton” for the AMCA/MWF?

With all that as a part of what is going on in my mind I will propose the designs.

We begin by accepting that:

i)                     we do not have the time to do ab initio design

ii)                   the aircraft must be cobbled together using known and proven sub assemblies and come to a firm base which is flexible enough to develop further.

 Our “menu” is as below:

Wings: 

i)                    MiG 21 wing and stabilizer

ii)                  .LCA wings and since I dislike tailless deltas we pick up the stabilizer of the MiG 27MIG 29 wing and empennage.

iii)                  The Su 30 wing and empennage to be scaled down to around 35 ^M2 wing area.

iv)                The AMCA wings and empennage presuming that the documents are prototype ready.

It will be noticed that only aerodynamics that are “available” to us is being considered

In the engine we have a choice of six contenders.

i)                     The RD 33

ii)                   The AL 41 F / AI31F with thrust vectoring

iii)                III)  The Eurojet 2000

iv)                SNECMA M 88

v)                  F 404/414

In avionics the electronic suites to be considered are those of the Mig Bison, the MiG 29 the Sukhoi 30 and the LCA.

Thus we have about 5-600 options. Many of these options will be rapidly discarded after cursory examination and tabulation e.g. the MiG 21 wing with RD 33 and the Su 30 systems. This option will require a “new” centre section to be developed and a 23 M ²wing area is a shade too small. The potential for further development will be marginal. Nevertheless these have to be rejected only after due diligence. Record of the discards and the reason thereof is important. We will end up with about 12 or so feasible solutions. It will not be possible to discuss all the twelve or so possibilities. Two of the possibilities stand out by “gut feel” and in no way dismissing the others will discuss these two in some more detail.

The MWF ponton

The first possibility is to use the wing panels of the LCA as available at the moment along with its systems and avionics as is and creating a “pontoon” to pick up the two panels and the stabilizers. I dislike tailless layouts for their “finnickyness” The stabilizer of the MiG 27 is in terms of area more or less “right” and probably has sufficiently low aspect ratio not to stall before the wing! These will be attached to a pontoon which will carry the SU 30 nacelle for the AI 31/41 F underneath and the LCA MK1A cockpit and systems are attached to the pontoon.       (Fig1) I expect that the disadvantages of the 1.76 AR wing and its consequent high induced drag in a turn will be compensated in combat by thrust vectoring and HMDS/R 73 systems. so we have a possible solution.

The MiG 29 Ponton

Another probable solution is based on the MiG 29’s with a single AL 41 F TV. (Figs 2, 3.) The basis of the aircraft will be the MiG 29 ponton which consists of the wing outer panels the tailplanes and the centre section which also carries the cockpit. There will be temptation to redesign the MIg 29s wing by replacing the R 177 aerofoil with something “more suitable” for the Mach 1.3 range- the promise of having 20 percent fuel volume in the wings is alluring but this goes against the philosophy of “make do and mend” type of design and will hamper the target of getting something into the air as fast as possible.

The centre section pontoon is based on the existing MiG 29’s centre section (CS) with such “irrelevant- for the flight test aircraft- features as the louvered intakes etc deleted. The two tunnels that are used by the RD 33s is replaced with a single larger central tunnel for the AL41F. The ponton on the prototype will also carry hard mounts so that the engines position relative to the CG can be shifted longitudinally for the flight trials in case the FBW is delayed. The entire engine nacelle of the SU 30 is the basis of the propulsion “egg” and is slung under the CS as mentioned. ALL systems and aggregates are identical except the change in loom length as dictated by the change. The MiG 29’s undercarriage will not reach down sufficiently to cater for the 200 mm bigger diameter of the AL31/41 engines and so the solution will be re-examine the MiG 27’s undercarriage and “appliqué” them, to use a term in dressmaking, on to the sides of the nacelle or shift the datum of the tunnel upwards for the AL41 by the same amount.. The nose wheel and the brakes of the MiG 27 will be used and the nacelle will have to be modified accordingly or – at least for the prototypes -a 4 wheel undercarriage where the nose wheel is also appliquéd onto the front of the nacelle can be considered. The existing twin fins , though probably slightly excess in area , can be retained for the prototypes.

Each of the solutions has their problems. The MIG 29 based solution is good because the development and detail design work will be the least but the problem is that the Russians may  need to be placated with a license fee. The LCA based solution is free from such hazards but will mean more engineering work. It is always thus- no prefect solutions. The test aircraft will not be built to any operational requirements or comply to any standards being in the “X”-experimental- category. The aim is to clear the aircraft for about 500 hours of testing to see if the idea has promise.

Creating useful Technology Demostrators

 India has used the prototype as a technology demonstrator.  This is both false economy and only guarantees delay. The AMCA does not have a TD repeating the mistake of the LCA. The TD for the AMCA for stealth alone should be the simplest aircraft that will:

i)                    Confirm that the theoretical calculations are confirmed.

ii)                  Confirm that the technology of acquiring, cueing and launching of weapons on the target are working

iii)                The stealth characteristics of the aircraft are reasonably maintainable in the field.

In all other respects the TD can be as different from the AMCA as chalk and cheese. (Note 6)

The F117s are showing increased and renewed activity at Tonopah. This is probably an indication that more work is needed on the F 35 and that only the “Hopeless Diamond” works for real and at all times. Incidentally the story going around is that disposing of the F 117 is a nightmare. One removes the canopy- which is gold plated- and then buries- yes buries- the thing in the remotest desert. Unless this is the kind of story one tells to frighten the little girls it is an indication of the need to “get real” with stealth as far as India is concerned. We should have had a Stealth TD for the AMCA NOW not wait till the cocnut is broken in 2025 to learn of the horrors. The Ponton is particularly suitable for developing Stealth Technology Demonstrators. The Ponton allows for quick development of the shape changes that testing may show up. The ability to move the engine up along he vertical centre plane will mean quite pronounced vertical “s” to shield the engine face can be done- and increased without performance penalties

The DASA/Rockwell X31

So far India has not built a Technology Demonstrator aircraft as described above- like a patch work quilt.  “Patchwork quilting” method is standard. Fighter designers always minimize risks ( because of the pressing need to be commercially successful) by using proven ,yawningly familiar, systems and aggregates to build a trial quick build “canter horse” e.g. YF 17, EFA, T 50 etc usually without a very formal “specs”.

As an example this is what Rockwell DASA did for the X (note “X”-experimental) 31.

i)                    An existing cranked Delta wing and long moment canard by MBB who had developed it for the EFA- note again that no one shoots for the moon in one go - the precursor for the Eurofighter. The wing was approximately “good enough” for Rockwell.

ii)                  Thrust Vectoring system –with paddles that had been developed for the F 14 Tomcat’s spin testing. To be noted was that it was “good enough” TV – certainly not as good what could have been done later- but it worked!

iii)                Landing gear adopted from the F 16 with wheels from the Cessna Citation and Vought A 7 tyres. Note the extent of “scrounging around” for ready- made task reducing parts!

iv)                Ejection seat, instrument panel ,stick and throttle taken directly from the FA 18

v)                  GE 404 GE 400 engine taken from the F 18

The entire aircraft as made with aluminum except for the Wing skins but as already noted the entire wing was a “bought off the shelf” item from MBB.

The aircraft had no specifications but explored what was possible in terms of super manouvreability  -AOA of 70⁰ and low speed handling at 28kts and a turn radius of 100mts. The technology developed has been salted away and will reappear as the new “wonder formula” for marketing at a future date. The flight test programme was limited to 500 sorties- pl. also note. It was destroyed in the last flight under circumstances which to me at least sounds so careless as to be fishy. Except for the last flight we can faithfully follow the American approach for our programmes.

Summary

1.      Aircraft design is different from aircraft engineering and the Chief Designer’s “situational awareness” makes all the difference between an effective warplane and a lemon.

2.      The fight scenario is uncertain and so are weapons specifications. The only certainty in following Western Concepts totally is that it will be expensive. They have had little success in predicting their own requirements ( note 7). Who are we following? Quo quo sclesti , Ruitis?

3.       The Americans have always survived by their unfettered “thinking –on the- feet” ability and we must do so too. We must learn to use the wisdom ingrained in our Panchatantra!

4.      Aircraft Marketing doctrines are to be viewed sceptically. Take the case of airframe fatigue life where 6000 hours is being now flouted and talks are going on for 10,000 hours- anything you can do I can do better is the game! My studies show that 50% of a fleet will have been written off by about 1500 hours to 2300 hours depending on the operational profile flown. Fatigue life without inherent upgradability is paying for a feature one will not be able to use!

5.      The pontoon chassis concept allows for easy upgradability of engines and systems over the years. For India, with a weak base in terms of engines and upgradability the study of the pontoon concept deserves particular emphasis. The pontoon also is relevant because as discussed above it can be an “experimental” aircraft to serve as basis for our AMCA and MWF aircraft.

6.      We must re-examine what we mean by a Technology Demonstrator. Calling a prototype a TD serves no engineering purpose. The true TD –like Arjun- must aim for a single technology. For the LCA a Ajeet airframe or even a HJT 16 but built using progressive amounts of composites would have been the true technology demonstrator- for composite- und so weiter – for the other technologies such as FBW etc. We lost about 15 years that could have been easily paralleled and ready by mid 90s.

7.      The AMCA’s lack of technology demonstrator as above is going to be a cause of delay because the unknown problems of stealth are remaining unknown.

Fund and develop the AMCA demonstrator!

Table 1

Sl.no	Parameter	LCAmk2	MiG  29	MiG 29 Polymorph	AMCA	MWF	LCA Polymorph	Boeing X32-JSF
1	Length	14.2	17.61	17.61	17.6	14.55	14.8	13.72
2	Span	8.2	11.41	11.41	11.13	8.2	8.2	9.14/10.97
3	Ht.	4.4	4.357	4.357	4.8	4.4	4.357	4.02
4	Wing area	38.4	38	38	55	40.4	38.4	54.8
5	Empty weight	7700	10,800	10,200	12,000	7700	8100	10,000
6	Clean TOW	11,400	15,800	13,780	12,000	11,000	11,400	18,144
7	MTOW	16,500	18,500	23,900	20000/,25000*	17,500	20,600	22,680
8	T/W	0.86	1.05	0.97	1.02/0.81	0.89	0.93
9	SFF	0.366	0.255	0.218	0.255	0.336	0.269
10	Engine thrust	1xGE 414 – 98kN	2x RD 33 2x83kn	1xAL41F(TV)142.2/ 86kN	2x98kN	1x98kN	122.4/76.2AL31F	P&W F119 -156kN
11	Aspect Ratio	1.75	3.4	3.4	2.25	1.8	1.9
12	Internal Fuel	3300	3630	3630	5000	3300	3300	8618
13	Payload	5500	3600	10,000	1500/5000	6500

Note 1

The Fokker D VII sturdiness and tractability and sturdiness came from Goettingen 298 aerofoil of 14.5  percent  thickness not only give immense structural strength – spar bending strengths go up as the cube of the depth and torsional rigidity is proportional to the enclosed area of the torsion box - but also the thick rounded aerofoil with its large nose radius worked better at the Reynolds Numbers involved than the earlier thin “clutching hand”  aerofoils- based on birds wings of the earlier aircraft. There is some dispute about the nomenclature of the aerofoil. Some say the nomenclature is Go 298 and others say that the aerofoil upper surface is Go387 and the lower surface is Go 418 with 14.5 % at the root tapering to 9% at the tips. The confusion is because the aerofoil actually came “out of the head” of Rheinhold Platz and was later formalized by Goettingen. Rheinhold Platz, Fokker’s talented Chief Designer, was a welder by trade, had like his contemporary Sydney Camm of Hawker’s , a flair for aerodynamics. Platz went on to design many of Fokker’s thick wing monoplane airliners after the war. It so happens that Einstein (yes! HIM!) also designed an aerofoil “ Die Katzenbuchenflache ” ( Cat’s back) which was so weird that it is perhaps better that he went back to Relativity!

One interesting side show to this is why the German’s were so considerably in advance to the British in terms of theoretical aerodynamics even though it was Stokes who formulated and first proposed the circulation theory (the Navier’s Stokes equation). I would cautiously ( 400 pages 280 odd differential equations-though easy ones)  suggest that if you get a chance to read Prof. David Bloor’s “The Enigma of the Aerofoil”( University of Chicago Press, 2011)  don’t miss it. The politics and personality clashes that affect scientific development will be familiar to us. It seems Lord Rayleigh’s formidable clout stifled a freer exploration of alternatives,putting Britain at a considerable disadvantage during the Great War and brings to mind the old adage that Science and technology progresses by Deaths!

Note 2

Out of a sample batch 38 Lightning F6s 17 i.e. about 45% were struck off charge due to all causes. Of these 17 about 7 were lost to engine fires- a problem to which the type was probne thanks possibly due to the engine disposition. The average fleet life of the Lightnings was – if my sums are right- about 2100 hours though individual Lightnings went up to 4000 hours. The Lightning was a well loved “pilot’s “aircraft and shows the potential if upgrades had been possible.  Given that our MiG 21s flew amore punishing role it would be interesting to do the same for our MiG 21s.

Note 3

When the Lightning was a gleam in Petter’s eyes he was looking for an aircraft that would be a supplement to the Bloodhound SAM i.e. a point defence interceptor. The Lightning was of the manned missile genre of its contemporaries eg F 104, F 106 etc.  After examining several dozen possible configurations, Petter chose the vertically and longitudinally staggered engine layout. The two Avons and their afterburners were thus behind the Pilot’s “shadow” and thus the cross section – critical in supersonic flight -was at a minimum. On the flip side it was a headache to maintain and any leakage of fluids from the upper engine or hydraulics would result in an inflight fires – a great plague in Lightnings.

Note 4

As an example of the cost effectiveness of upgradability one cannot probably beat the American B 52! They developed theB!,B1A and the B2 but it is a fair bet that the B 52 will see the younger aircraft off- especially if the Americans can think of refurbishing theB52s in India! .

Note 5

One is reminded of an old cartoon strip where a scientist is seen busily scribbling data – humidity, density, hardness and many complex equations on the side of a large block of marble in his laboratory. He then after much further scribbling marks a point “x” on the side of the marble with a plumb line and with a chisel gives a tap. A rubble of marble falls away and there is revealed a magnificent horse, rampant, on a pedestal that Cellini would have been proud to have produced . However the Scientist is distraught and is seen wailing “No!No! there was supposed to have been a rider on the Horse!”. In aircraft design also –as our programmes have shown- there is a limit to what can be done by theoretical studies. Getting the first prototype up in the air at the earliest is the first step to success.

Note 6

For testing the aerodynamics of the slender delta Mach 2 Concorde, BAC built two  TDs. The FD BAC 221 for the high speed end and the ogival configuration and for the low speed handling they built the Handley Page HP 115. Engineering wise the HP was interesting. All metal in construction, it had a plywood leading edge so that changes as dictated by the flight trials could be made almost on the flight line. The fuselage was a light alloy girder suitably faired over and the engine was a little B.S. Viper. It is amusing to note that the test bed for a Mach 2 airliner had affixed undercarriage!

It is true this was in the late ‘sixties and CAE/CFD has made enormous strides since then but unfortunately CFD/CAR will only answer the questions you ask! Building “way out” (by our current thinking!) TDs is imperative or else we will repeat the LCA saga!

Note 7

Predicting the future is an admittedly difficult task. The West has employed – particularly America- thousands of talented people over the years to predict what kind of wars will be fought and therefore the kind of equipment that should be procured. By a process that is not clearly understood the Americans ,in particular, has always chosen solutions that involved manufacturing the most expensive ( as opposed to useless) equipment which could at a pinch do the job. I am not being uncharitable. The Americans, in the ‘fifties developed the F 105 for nuclear strikes against the CCCP whereas they should have developed low cost equipment to knock out NV truck parks, power stations and bridges ,preferably at Night and in bad weather which in Vietnam was really bad. That they have not lost the proclivity is seen by the fact that they are extremely cautious about where and how they use the F 22 and the F 35 for reasons that do not make common sense to the Taxpayer. Why they do such things is a topic in itself but I will caution that in following American procedures beyond a certain point means that we are going for a very expensive way to meet our defence needs. Will the honorable FM Mrs Sitharaman be amused?