The Plan B AMCA- The Horten wing-based stealth Intruder                

Prof. Prodyut Das

19 July 2025

This is a discussion on using the Horten Wing technology to develop a 5th generation “Malacca Straits” intruder using existing aggregates and resources.

The Horten History

The Horten wing is best described by its German appellation Nurflugel i.e. “only wing” aircraft. The Horten “Nurflugel” is an aircraft with only the wing and a vestigial fuselage and is different from the Lippisch “Nurflugel” which has a fuselage, a fin but no stabilizer. Two brothers, Reimar and Walther Horten, over the period 1930-37 designed and built at home a series of 7 (Horten I to VII) tailless gliders. The first one was so disappointing the brothers took it home and burnt it. Because there was no fuselage and tailplane the weight and drag were considerably reduced giving the powered versions of the Hortens tremendous range. This inherent characteristic resulted in the twin Jet Horten Ho 9 winning the Luftwaffe’s Drei Tausende (3- thousands) programme for an aircraft with a 1000 km combat radius at 1000 kmph. with a 1000 kg. war-load. An early engine related crash- at that time German engines were using one tenth of the high temperature alloys required – prevented the full testing to be done before the cessation of the hostilities- but the aircraft appears to have been set fair to meet all design targets. Considering that the power came from 2 x 9 kN ( sic)  engines weighing 900  kgs each and with a s.f.c of 1.1 kg/kg of thrust the performance is impressive even today.

Understanding the Nurfluggel.

There are various mis-apprehensions about the tailless Nurfluggel -stability, safety and general acceptance by the user. These are from a lack of information.  Indeed, the very first tailless aircraft- the British Dunne Tailless- was designed 1910 to increase flight safety by increasing stability!

Tailless aircraft have a bad reputation because of problems which had nothing to do with the Tailless concept e,g. the DH 108s was because it was a wooden aircraft trying to break the sound barrier, the AW 52 possibly due to poor lay out, end plate fins on high AR wings. the Chance Vought F7U Cutlass which entered US Navy service in some numbers the reputation came from it having too low a power for a Shipboard fighter - when coming in to land on a heaving deck there simply not enough power left to correct any mistakes in the approach funnel.

 The real problem of the “Nur fluggel” was its lack of a fuselage; it was a “niche” configuration, useless in general situations but if you were looking for low RCS aircraft and long range with a limited/specialized war load then it is almost unbeatable, which is why, even after 90 years, we see it’s influence in the design of the American B2 and now, the Chinese Hong 35. Those people know what they are doing.

With this as a short introduction to the configuration, the question is raised that given the present situation with the AMCA, about which I believe ADA is leading us up the garden path, and given that though the B 52 is neither “stealth” nor “ super-cruising” and yet is a valued US war asset, then there is definitely  room for a subsonic Indian 5^th generation a B 52 but with stealth-  fulfilling a role like a PI- 8 but optimized for the anti- shipping rather than the anti submarine role  with the ability to reach the Straits of Malacca.

 The aircraft will have the internal war-load of a B 52 but with a smaller range- more in the region of a 2000km radius of action @ M=0.85. We should not fall into the US trap of excessive specifications and then make the second mistake of trying to achieve all that in one bold leap like the AMCA. That is doomed to fail. However, the Plan B by being very circumspect about the specifications, and using the factor of the high-quality missiles developed by the DRDO to achieve mission objectives, done via a set of common-sense steps we will be there very surely, on time and to costs.   

AMCA Situation summary

The Government of India is going ahead with what is a super cruising 5^th generation AMCA. Having allotted Rupees 25,000 crores in 2025 values, it proposes to invest another Rs.66,000 crores for the 120 kN engine in collaboration with Safran where I believe we get to do the outer spool and the accessories. 

After 70 years of Government led development if we still need “collaboration” under “2^nd fiddle” conditions isn’t it time to think that we pull the Government completely out of weapons development? It is not doing the country any good. Let the Government be an investor.

Given the present closer supervision- there was none in the earlier dispensation- the AMCA may roll out on time but there is good chance some unknown -unknown will hold up the project. What then? We don’t have a plan B and it will be the Tejas all over again. The Tejas has survived- in earlier eras it would be declared obsolete- because the growth of weapons capabilities compensated for its shortfalls in the platform. 

It is also time to insist on at least two contenders. Imagine if in 1989, when the ADA proposal failed to pass the IAF muster the HF 25 was there running as a parallel project. ADA cannot at one time sup with the Devil of the Import Lobby to ensure that there were no competitors to its design efforts   and blame the same import lobby for its supposed ills.

The official answer given against having multiple projects at start is financial constraints prevents running parallel projects. This is willful ‘ostrich” disinformation .

 90% of the project’s cost come after the fly off in testing and selection of the fly off winner.-17, 000 hours of testing for the F 35 all variants, and certificating the aeroplane. That is why multiple proposals are run by the US. We spend 10%-20% more in the beginning but end up with alternatives and much useful data and avoiding imports and corruption.

 How much should the additional competitor cost? The Government has enough data. An actual corrected PDV figure i.e. Rs.@ 2025 would be around Rs. 1200 Crores per different type up to complete fly off tests. So at least two proposals, for flyoffs has been the successful US pattern. Our Punditry scream for US levels of funds but shrink in horror from competitive fly offs.

Change the process of development to History based evolution.

The design of an aircraft begins with an intense search of History. In the West they are so steeped in History that they do not do it consciously. The Chief Designers have lived through it. In our case we have to do it in a structured manner which if you go about, it methodically might be an advantage by being bias free:

1.      Collect all likely layouts including some of the concept studies which show promise.

2.      Pass collected layouts through the following filters

i)                  When, by who, what for?

ii)                Were they prototyped? Flown? Results?

iii)              Selected for production? If not why not? Rejection is often not for technical lacunae and in any case our constraints may be different.

iv)              Cost of project? Service records if any.

v)                Proportion of “robust stealth” i.e. shape dependent, in the layout?

vi)              How relevant to an Indian scenario

Going through these filters about a dozen aircraft layouts seemed promising. Apart from the usual suspects -F 117, F 35, F 22, F 32, XF 40, Horten /Gotha 229, there were some unusual candidates- the MiG 21, The Folland Gnat and the Avro Vulcan, the Swiss EW 20 series (for it’s nice bulged ‘universal” weapons bay-can that be “stealth-ed”) and the SAAB Draken! Note that the last few in the clutch includes conventional and Lippisch types.

Each candidate has to be screened for its pros and cons but below is the case summary for the Horten IX.

1.      It was flown and would have met the performance demanded.

2.      Enough information exists to create a NMG Horten 9 on the computer. It would be possible to use the existing data to act as a firm base for proceeding with the modifications necessary over 70 years with great confidence.

3.       The Horten 9’s dimensions of 16.7 mts wing span , 7.8  mts length, 2.7 ht is a very right size. It is small and simple enough to be built quickly and yet not too small so that we get into Reynolds number problems when we scale it up to study the Malacca Intruder. Empty weight 4590 kgs. Normal loaded 7484 kgs, MTOW weight 8981 is just right for a TD to establish the technology and then be scaled up to the desired.

4.      Just by area reduction alone the aircraft will have a radar return varying from 0.2 (frontal) to 0,3 (side elevation) to 0.15 rear that of a Canberra at any given range. This is any exclusion of further reductions due to shaping, surface coatings, angle effects and surface finish.

5.      The prototypes were built for 5 lakh Reichsmarks= $ 200,000 in USD 1944 by a Locomotive and wagon factory, GothanaerWaggonFabrik, which indicates we will not need exotic machinery demands e,g,  50K ton press for  PM turbine disc currently doing the rounds. The nerve to ask!

6.      It has an interesting structure- a steel tube space frame centre fuselage, wooden wings with bonded wooden skins. It can be described as a transition between steel tube and fabric structure to a stressed skin design. Sometimes less advanced is better as in this case, very appropriate for a TD. The space frame allows equipment to be fitted very quickly, the wooden skins can be replaced by composites skins with modified contours as indicated during stealth measurements in actual situ.

7.      The engines are located such that a fairly large range of engines and inlets can be tried easily to optimize the stealthiness.

8.      FBW is not necessary at first flight.

The AMCA Plan B TD.1100

The Ho 9 is so perfectly sized for the task in hand that it is best to start with the Horten design and only make what changes is deemed essential or obviously advantageous. The replacement of Jumo engines and fuel system by the TFE 334 high bypass turbofans of 18.6kN as used in bijjets will see a weight reduction 1100 kilos. The Ho 9 was built using “scrounged” parts- the undercarriage came from a bomber so some weight savings would be possible using better modern equipment. The differences are put in the table. The disposable weight is considerable and much equipment can be added or removed,

The Horten and the TD

Sl.No	Item	Horten 9	TD	Remarks
1	Span	16.76	16.76
2	Length	7,5	9.5
3	Height	2,7	2.7
4	Wing Area	52.49
5	Empty wt.	4590	4200
6	Weapons Load	2x500 kgs, 4x30 mm	See. notes	A 4 mts x1.6 mts Universal Bay for trial . UseASMs eg, Harpoon,  etc. Pockets for AAMs, 1 x 23 mm.
7	Normal Loaded	7484	7484
8	Max Loaded	8981	11,000 kgs
9	Power	2x Jumo 9.81 kN	2x TFE 731-5 @ 20.6 kN
10	Fuel Load	2620	2620
11	Max W/L	171	209
12	T/W at Max wt	457kg/kN	266kg/kN
13	Max. span loading
14	Max. Speed	962 kmph	1070 kmph approx..M 0.92
15	Max Range	1896 km.	1960

 

T is common sense that if an aircraft could be developed 80 years ago in war time Germany for a then value of $ 200,000 and built by a Locomotive and Wagon company and even today the basic idea is held to be valid then we can generally agree that a Horten type flying wing can be built with basic facilities and low cost within a short time.

I was alarmed to find that the specific fuel availability (kg. of fuel available per kN of cold thrust ) of the proposed AMCA is actually 20% less than that of the Tejas. Again common sense says if there is less fuel to burn per unit installed thrust then the range will be less i.e. the AMCA will have shorter range and endurance than the Tejas. Here we are trying to enter into expensive collaborations to ensure getting a super cruising, an ability that is already compromised by a basic proposal which itself is short legged so what is this about super cruising? If point is valid then super cruising for how long and to what utility? If this is the quality of proposal scrutiny it is heading for the docks. Who passed it? Why did ADA overlook such a simple obvious  point?

In the 5^th, generation super cruise is the deliberate technology trojan Horse designed to keep the competitors out. We seem to have fallen for it once again or is their a deliberate plan. If so by whom?

The Government must investigate why certain projects get so needlessly mired with problems that should have been nipped in the bud.

Given the above situation a TD based on the Horten Nurfluggel would be a firm step in securing 5^th. Generation technology. It would give us the data to confidently design, using supply chain security firmly in the foreground, two 5^th Generation type.

1.      A stealth intruder of the class of a Canberra i.e. 5000 kg weapons load but with perhaps 60% more range. Tis would use a rectified Kaveri or any suitable secure turbofan engine of the 50kN class.

2.      A Heavy Intruder of similar configuration with a 10 ton war load and a combat radius of 2000 kms.       

3.      The Project costs asked by the State enterprises and Laboratories are ridiculous. It is time the Government got out this business. It will find that project costs will come down by a factor of five to ten times.