[V.Narayan]

4th September 1964, HJT-16 flew for the first time

HAL Kiran HJT-16, Basic Jet Trainer


The HAL HJT-16 Kiran has thus far been the most successful Indian designed fixed wing aircraft with 190 built. Only in the last few years have orders for the Dhruv+Rudra exceeded this number. Kirans were produced by HAL from 1968 to 1990. And it has served with the IAF from ~1968 to date. They are now being replaced by the Pilatus PC-7 Mk II. It was designed by Dr VM Ghatge who in the 1950s and 60s was to Indian aeronautics what President Dr APJ Kalam was to missiles in the 1980s and 90s.

Dr. Ghatge’s approach was to go step by step from the HT-2 primary trainer to the Kiran jet trainer to an advanced trainer and then attempt a light attack aircraft. Nehru preferred to aim for a supersonic jet fighter in one go and brought in Dr. Kurt Tank who developed the HF-24 Marut in the 1960s. While the Marut flew it was a tad too much to digest by a nation that had not even learnt how to design a scooter let alone a jet fighter. HAL struggled to iron out the kinks and the IAF played its role as the stand-off customer. This laid the ground for [in my view] an erroneous philosophy of aiming for the stars and landing on the barn roof. Dr Ghatge was right after all. The HT-2, also designed by Dr Ghatge, was India’s first ever indigenously designed aircraft and the second most successful after the Kiran! And mind you he was achieving this when we were learning how to assemble coal fired steam engines and sewing machines.

In the 1950s and 60s when we were among the poorest of countries we could successfully design and build trainers like the HT-2 and Kiran HJT-16 and today 50 to 60 years later as the 5th or 6th largest economy we can’t design a replacement.
The aircraft was built in three versions – Mk 1 was the basic trainer powered by a 1135 kgf Rolls Royce Viper turbojet license assembled in India; Mk 1A had two hard points for practice bombs to provided elementary armament training; Mk II was powered by a de-rated 1700 kgf Rolls Royce Orpheus turbojet which was being produced locally for Gnat, Ajeet, Marut. Number of hardpoints were increased to 4 and total external load to 2000 lbs. All 4 hardpoints were wet points. The Mk 2 was a competent, vice free basic trainer.

The aircraft served for several years as the platform for the IAF Surya Kiran and IN Sagar Pawan aerobatic teams.

Crew: 2; pupil and instructor
Length: 35’
Wingspan: 35’
Max. takeoff weight: ~4,250 kg
Powerplant: Rolls-Royce Orpheus turbojet flat rated to ~1700kgf
Maximum speed: ~700 km/h at sea level
Training Endurance: 1 hour 45 min
Weapons: 2 7.62mm machine guns for training; 2 x 68mm SNEB rocket pods + 2 x 500 lbs bombs


Group Captain Suranjan Das with dignitaries on the day of the maiden flight -- 04.09.1964
Suranjan Das was a man of exceptional calibre and character. You can read more on him here in post #71 https://www.team-bhp.com/forum/comme...age-6-a-5.html (Indian Aviation - HAL Ajeet, the Folland Gnat Mk II. EDIT: 1965 war IAF documentary on page 6)

Kiran on its maiden flight


Dr VM Ghatge, the Chief Designer on right


Kiran Mk 2 of the Surya Kiran aerobatic team


The classroom


Weapons, typically used for basic armament training.


Typical training sortie over Air Force Training School, Bidar


Scale model 1:36

[FrozeninTime]

Originally Posted by V.Narayan

4th September 1964, HJT-16 flew for the first time

HAL Kiran HJT-16, Basic Jet Trainer

They are now being replaced by the Pilatus PC-7 Mk II. It was designed by Dr VM Ghatge who in the 1950s and 60s was to Indian aeronautics what President Dr APJ Kalam was to missiles in the 1980s and 90s.

Sir could you explain why a propeller Pilatus PC-7 Mk II was chosen to replace a jet trainer?
Also could you shed some light on Iskra trainer.
Very little is mentioned about Iskra other than it was Polish jet trainer chosen by Soviet over their designs to support industries in Comecon countries

[skanchan95]

Originally Posted by FrozeninTime

Sir could you explain why a propeller Pilatus PC-7 Mk II was chosen to replace a jet trainer?

I could be wrong but wasn't the PC-7 was chosen to replace the HPT-32 in the Basic Trainer Aircraft role? If I remember correctly, at the time when the PC-7 contract was signed, the HTT-40( HPT-32's replacement) existed only on paper. It is only later after the arrival of the PC-7 Mk.IIs that the HTT-40 project gathered steam.

The IJT-36 Sitara was supposed to replace the Kiran Mk.II in the Intermediate Jet Trainer role.

[V.Narayan]

Originally Posted by FrozeninTime

...could you explain why a propeller Pilatus PC-7 Mk II was chosen to replace a jet trainer?

This is a really good question and the answer will take us into the elements of training. Traditional military pilot training is broken into 3 phases - (1) Ab initio ie from scratch; (2) Basic or Intermediate; (3) Advanced. Earlier till say early years of this decade the three were conducted by the HPT-32, Kiran and BAe Hawk. How much of flying skill you can learn & master is a function of the trainer aircraft's speed in level flight. The HPT-32, typical of ab initio trainers has a maximum sustained speed of ~140 knots. The syllabus on it is of 40 hours plus some more for practice. After that the pilot must graduate to a machine that can fly faster, climb faster, turn faster etc. Typical intermediate trainers used to be jets that flew at 275 to 375 knots sustained - Kiran, BAC Jet Provost, Canadair Tutor, etc. This speed was high enough for a pupil to start getting some feel for the faster more powerful jets he/she will eventually fly while still being unswept, thick wings that were slow and safe enough for a trainee. This syllabus needs a further 90 to 120 hours to master.

Now with thinner faster unswept wings and more advanced props it is possible to design a turboprop that can (almost) mimic a jet's flight characteristics in the 100 to 350 knot range at literally a fraction of the fuel cost. Further clever modern software enables the same aircraft to fly as a benign primary (ab initio) trainer in one sortie and then as a basic (or intermediate) trainer in another sortie. This was not possible even as recently as 15 years ago. The Pilatus PC-7 Mk II is a superb machine just benign enough for the ab initio training and yet with a top speed of 275 knots and strong aerobatic capabilities just good enough for intermediate training too. So for now in the IAF syllabus, I believe (and am open to correction) it has replaced the HPT-32 and is replacing the Kiran HJT-16. The pupils start on the Pilatus do their ab inito + intermediate on it and then transition to the the Hawk straight from the PC-7 Mk II. Hope this helps.

Also could you shed some light on Iskra trainer.
Very little is mentioned about Iskra other than it was Polish jet trainer chosen by Soviet over their designs to support industries in Comecon countries

In 1968 we had the Kiran Mk I entering service replacing the Vampires that were beyond their last legs. HAL could not get produce the Kiran fast enough. Hence the IAF was forced to seek an alternative as a stop gap. The USSR & rest of the Warsaw Pact was using the Czech Delfin and all the production was locked up for their demand. The only other Warsaw Pact trainer available was the Polish Iskara which was ready for fulfilling our large order with its rapid production need*. Hence in came the Iskara. Interestingly the Iskara was the better of the two - Delfin & Iskara but lost out due to internal Warsaw Pact politics. It was powered by the British Rolls Royce Viper a reliable engine we were very familiar with. Later in the 1970s Kiran production rates stepped up obviating the need for more imports. The Iskara had a very good track record with the IAF.

* In those days our precarious forex reserves ruled out Western imports. In the 1960s despite our low forex reserves we used to tax exporters at higher rates!!!!- Oh the joys of the license raj, Mahalanobis and wolly thinking.

PZL TS-11 Iskara in IAF colours. Source: airliners.net

[Sutripta]

Originally Posted by V.Narayan

Further clever modern software enables the same aircraft to fly as a benign primary (ab initio) trainer in one sortie and then as a basic (or intermediate) trainer in another sortie.

The Pilatus is fly by wire?
The propeller - who is the manufacturer?
How does the Pilatus compare costwise with what it is replacing,

Sutripta

[V.Narayan]

Originally Posted by Sutripta

The Pilatus is fly by wire?

No , not fly by wire. Fly by wire is only needed for a unstable designed aircraft. Worth it only for fast combat jets that also need to be very manoeuverable. Think of it like we today we have Eco mode, Normal mode and Sports mode in cars. So the software can be geared for different syllabus..

The propeller - who is the manufacturer?

Hartzell, aluminium alloy, 4-blade

How does the Pilatus compare costwise with what it is replacing,

I do not know the real cost to the IAF or what the Kiran procurement costs were. But the single biggest cost for trainers is fuel given that both these machines would be doing about 400 to 500 hours a year. A Kiran at 75% thrust consumes very roughly 1200 to 1300 kgs per hour. A PC-7Mk II at 90% power consumes about 200 kgs an hour. My calculations. Directionally correct. Gives a sense. Hope this helps.

[Sutripta]

Originally Posted by V.Narayan

No , not fly by wire. Fly by wire is only needed for a unstable designed aircraft. Worth it only for fast combat jets that also need to be very manoeuverable. Think of it like we today we have Eco mode, Normal mode and Sports mode in cars. So the software can be geared for different syllabus..

Not my (possibly wrong) understanding of fly (or anything else) by wire.
Unstable aircraft to fly need constant (and I mean constant) trim corrections taking into account a whole lot of information. Needs processing power of a modern computer, and ultimately the computer flies the plane.
Does not mean computers cannot fly normal planes, regulations permitting. With change of software pilot feels he is flying aircraft with different characteristics.

Hartzell, aluminium alloy, 4-blade

Whatever happened to Hamilton?
What is great about this propeller? What are the relevant metrics for a propeller? Something similar to lift to drag?

Sutripta

[Jeroen]

Originally Posted by V.Narayan

Now with thinner faster unswept wings and more advanced props it is possible to design a turboprop that can (almost) mimic a jet's flight characteristics in the 100 to 350 knot range at literally a fraction of the fuel cost. Further clever modern software enables the same aircraft to fly as a benign primary (ab initio) trainer in one sortie and then as a basic (or intermediate) trainer in another sortie.

Thanks for all these interesting insights. Am I understanding you correctly the current version of the Pilatus has this ability to switch role through software. It is not a a fly by wire plane, so how does it do that? How do you get different flight characteristics through software in a non fly by wire plane? (slow down the hydraulics?). Maybe I am misunderstanding what you are saying?

One other argument I have heard about using the Pilatus as a “jet trainer” is that it also has a jet engine. Turbo prop admittedly, so there is prop torque to deal with, but the throttle response of a turbo prop is more akin to a jet engine. Regular (piston) prop engines need very different handling. Starting is a very different matter all together. And as (to my knowledge) there are no prop engines with FADEC, so handling of the throttles and engine response is always very different to a jet / turbo prop.

You can’t just shove the throttles into the firewall on a piston engine. On a jet engine the FADEC takes care of all of that and more too.

Jeroen

[PGA]

Originally Posted by Sutripta

Not my (possibly wrong) understanding of fly (or anything else) by wire.
Unstable aircraft to fly need constant (and I mean constant) trim corrections taking into account a whole lot of information. Needs processing power of a modern computer, and ultimately the computer flies the plane.
Does not mean computers cannot fly normal planes, regulations permitting. With change of software pilot feels he is flying aircraft with different characteristics.

Aircraft are designed for stability which can be categorised as statically stable, dynamically stable or inherently unstable. Stability may also vary across the flight envelop. To obtain high maneuverability with thrust vectoring nozzles modern fighter aircraft tend to be inherently unstable therefore FBW is essential for control and to come out of tight situations. If I recollect in our context the first digital FBW after Mirage 2000 was new A320 procured by IA, which is not an inherently unstable aircraft. There was also lot of talk of FBW causing the Bangalore crash in 1990.

Software enabling an aircraft to fly with changing control laws has been around for about two decades now, in the unclassified domain. Calspan at Niagara Falls specialises in it, perhaps the only one in the world at least till some years ago. It has a couple of aircraft, Lear Jet and Gulfstream and F-16 VISTA as airborne platforms to test the airborne control systems and train Test Pilots and Engineers. Our LCA also validated its control and stability laws on its platforms.

https://en.wikipedia.org/wiki/Genera...ics_F-16_VISTA

History of the company is deeply coupled with the progress of aviation technology in the world and in automotive safety. Its a phenomenal story of professional excellence over so many years now.

https://www.calspan.com/company/history/

[Sutripta]

Originally Posted by PGA

A320 procured by IA, which is not an inherently unstable aircraft.

In the Indian context the best known example.
The A380 is apparently even more so.

I think I have discussed partly the 'by wire' concept elsewhere on this forum, but wrt automobiles, not aircraft. Principles remain the same.

Sutripta

[Jeroen]

I think there is a difference between changing control laws in commercial aircraft such as the Airbus/Boeing, and changing flight characteristics to the point where pilots feel they are flying a different aircraft.

To my understanding the various different control laws on Airbus/Boeing have to do with restrictions on the flight envelop. For instance the computer prevents the pilot from stalling, or hitting the tail on take off (or landing). Going into different control laws remove the various levels of protection. But it still handles as an Airbus respective Boeing.

The basic flight characteristics remain the same.

Having a computer control the plane in such a different way it feels like an entirely different plane is a very different matter all together. The Gulfstream NASA modified for Space Shuttle simulation landings is probably a good example of a plane handling completely different compared to its original role/design.

https://www.nasa.gov/vision/space/pr...week5_sta.html

Jeroen

[V.Narayan]

Spicejet launches India's first scheduled seaplane service.

Spicejet launched India's first seaplane service from Ahmedabad's Sabarmati river to the Sardar Patel Statue of Unity on 31-10-2020, Sardar Patel's 145th birth anniversary. Spicejet is using Twin Otter 300 seaplanes for the route.

Encouraged by the good response to its Statue of Unity-Ahmedabad seaplane service, private carrier SpiceJet has said it plans a similar flight between Surat and the 182-meter tall statue located in Kevadiya in Gujarat’s Narmada district. The 18-seater plane covers the distance in about 40 minutes, while it takes around four hours to reach Kevadiya from Ahmedabad by road. SpiceJet is also exploring other routes and destinations for the seaplane service, including Port Blair to Havelock, Delhi to Haridwar, Delhi to Rishikesh and Naini Lake, Udaipur, Dal lake, Leh and backwaters in Kerala.

The Twin Otter seaplane weighs about 3.3 tonnes empty and 5.6 tonnes at maximum take-off weight. It seats 18 passengers in its 51 feet length. It is powered by two Pratt & Whitney PT-6A turboprops generating 620 shp each and cruises at 180 knots.

India has been woefully short sighted where using seaplanes as a means of bringing air links to remote places. A versatile seaplane like the Twin Otter needs calm waters and about 700 metres of running space to operate from and a simple jetty. It does not need expensive runways, large tracts of land, airstrip maintenance etc. Yet we are by instinct not a water or sea minded people. I hope this brings seaplane services to hundreds of other potential routes in India.

[Foxbat]

Originally Posted by V.Narayan

[b]

India has been woefully short sighted where using seaplanes as a means of bringing air links to remote places. A versatile seaplane like the Twin Otter needs calm waters and about 700 metres of running space to operate from and a simple jetty. It does not need expensive runways, large tracts of land, airstrip maintenance etc. Yet we are by instinct not a water or sea minded people. I hope this brings seaplane services to hundreds of other potential routes in India.

Completely agree with your assessment for the more usage of Sea Planes in India. But the safety aspect is something that concerns me with the type of unruly passengers we often see in India and terrorist threats. I flew on one of these(DHC-6 Twin Otter) during a memorable Island hopping flight in Seychelles. The ease of access to the cockpit for the passengers was astonishing, perhaps some doors can be installed.

[audioholic]

Originally Posted by V.Narayan

Spicejet launches India's first scheduled seaplane service.

Spicejet launched India's first seaplane service from Ahmedabad's Sabarmati river to the Sardar Patel Statue of Unity on 31-10-2020, Sardar Patel's 145th birth anniversary. Spicejet is using Twin Otter 300 seaplanes for the route.

I hope this brings seaplane services to hundreds of other potential routes in India.

Can you also shed light on the economics of a sea plane? I understand it doesnt need runway infrastructure everywhere. But does the operational costs work out? Since we are in a phase where smaller airports are being developed to at least support turboprop operations, and India being a landmass, I fear that such projects are more for tourism purposes rather than transport. Since you have very well been in the industry, do you really think there are potential routes within the country which can also be cost effective for sea planes to be used as a mode of transport?

[V.Narayan]

Originally Posted by audioholic

Can you also shed light on the economics of a sea plane? I understand it doesnt need runway infrastructure everywhere. But does the operational costs work out? Since we are in a phase where smaller airports are being developed to at least support turboprop operations, and India being a landmass, I fear that such projects are more for tourism purposes rather than transport. Since you have very well been in the industry, do you really think there are potential routes within the country which can also be cost effective for sea planes to be used as a mode of transport?

These are most appropriate set of questions.

First the economics of the flight itself. Today seaplanes tend to be small aircraft more suited to regional commuter routes - typically below 19 pax. Larger seaplanes called flying boats are now used only in limited numbers by the some Coast Guard forces for coast guard type of work. Till the 1940s they were also used for long passenger routes and epitomized the luxury of flying. Coming back to the small commuters we have today. For short distances below 200 nautical miles (~370 kms) they are as cost efficient as a land equivalent on a seat mile basis give or take 5% to 7% due to the drag of the floats. If they were used for longer distances the drag of the floats burns more fuel due to increased time in the air. Flight hour for flight hour they need more maintenance on their hulls due to the effects of water corrosion. This is so even with fresh water. In terms of infrastructure costs of the operating air station they are much much cheaper. There are limitations of landing in choppy waters. So a seaplane operating back to a river landing could be limited due to torrential fast flowing waters in monsoons. Those operating from a lake or backwaters would be much less affected by bad weather at least where choppiness of waters is concerned..

These seaplanes are actually amphibians i.e. they can take off and land on both water and an airstrip. This increases versatility of linking a small town next to a water body to a larger city wit ha regular airport. That is really where linkage comes in. So many of our Tier IV towns lack an air connection which could boost trade and commerce if they were connected. For a small town an air connection to two large cities is like a village getting its first paved road link - it changes the economy. I hope we take these forward.

This makes most sense for certain tourist destinations for sure, as you stated. It also makes sense to link up two Tier III and IV towns at least one of which is next to a water body and does not have an air strip. Example - Puri to so many locations; any number of smaller town in West Bengal & Assam to X, Y and Z; any number of towns near lake-dams or along major river systems in India to X, Y or Z; Nainital to X, Y, Z etc. You get the drift.

This was actually something the Ministry of Civil aviation was pushing for at least since 2017-2018..