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Kaveri & aero-engine discussion

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shiv
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Re: Kaveri & aero-engine discussion

Postby shiv » 31 Dec 2017 12:59

JayS wrote: Dont fix whats not broken.

Don't break what can't be fixed is an equally vital principle. One cannot compromise on factors that cannot be predicted. If different gun propellant powders and 23 mm shell varieties or newer missiles that might appear in future cannot be predicted, the design has to avoid gas ingestion and cannot be more lax with a newer model "more tolerant" engine and less lax with an older model engine. I cannot imagine a designer saying "It's OK if some gases are ingested. That is imprecise and a formula for disaster. "How much gas gets ingested and under what conditions" would be critical. Unless that is studied by testing there will be needless accidents. That is the reason why testing takes time, which is where the discussion started.

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Re: Kaveri & aero-engine discussion

Postby Indranil » 31 Dec 2017 13:22

And if you ask me, this is where the discussion should end. We have gone round the circle at least once.

ramana
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Re: Kaveri & aero-engine discussion

Postby ramana » 31 Dec 2017 13:42

Abhibhushan wrote:Re heat and dust of India and Aero engines.

An annecdotal piece of info

In 1947 - 48 we had purchased the Hawkwers Tempest II as our main ground attack aircraft. The aircraft was powerful and effective for its role. It was powered by a radial engine that used a conceptually ‘new’ rotating sleeve valve. These engines worked well in Europe. Unfortunately, the sleeve valve technology could not survive in the Indian environment. Fine dust in the air of northern India started to jam these valves often. We had to admit defeat and junk the fleet of Tempest II by 1953/54.


What do you make of this gun firing brouhaha for LCA?

Thakur_B
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Re: Kaveri & aero-engine discussion

Postby Thakur_B » 31 Dec 2017 15:27

prasannasimha wrote:They went to IIT's and NIT's for recruitment and guess what the number was zero. . They have asked for university integration guess what zero. Easy to say Hire and fire when you can't hire in the first place.


Is this a recent phenomenon? My classmates/batchmates were selected from campus selection and one of them made an important contribution to the river project as well.

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Re: Kaveri & aero-engine discussion

Postby prasannasimha » 31 Dec 2017 19:10

IIST was started as Madhavan Nair APJ Kalam got zero people coming for IIT's to ISRO and DTDO. The ones they wnated refused and the ones they got were not adequate in their knowledge and they then thought they should start an Institute to train people for their requirements.

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Re: Kaveri & aero-engine discussion

Postby chetak » 01 Jan 2018 15:35

shiv wrote:
chetak wrote:never ever heard of an engine that requires overhaul more frequently because of gun firing but I have heard of airframes that add extra time to the airframe hours whenever an armament related sortie is flown.

This is because gun gases are prevented from entering engines by rigorous testing. Air Marshal Rajkumar in his chapter in the MiG 21 history book says that K-13 missile firing was always done only after turning on the engine relight switch.


many airline companies and also many mil operators have SOPs that require that the ignitors are turned on during heavy rain too.

The position of the guns are usually dictated by the aircraft geometry and not many positions are available either to mount internal guns or gun packs. Testing and firing limitations have to be determined keeping these constraints in mind.

Almost always its a tradeoff.

chetak
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Re: Kaveri & aero-engine discussion

Postby chetak » 01 Jan 2018 16:38

shiv wrote:
chetak wrote:
How come other manufacturers haven't ever reported such unique conditions which would have resulted in a lot of engine testing in such "unique" Indian conditions??

They have - but this is about the air force. I have heard (literally) that wear and tear of IAF engines is higher because of smoke and dust. But I am unable to provide a source - will try and locate one.


let me give you the example of flying in goa. The IN flies predominantly from coastal bases and different contaminants affect IN engines. That's why IN aviation, (as well as non aviation) equipment is "marinised" The IN engines, the airframes and the LRUs are much more expensive because of such "marinisation" incorporated into the design, build as well as the extensive + expensive lengthy testing procedures required for the qualification of such equipment.

The goan air has a very high particulate matter content and the particulate matter is predominantly iron ore dust. This comes from the open cast mining practiced in goa.

Goa has a saline atmosphere like any coastal city/state due to the high saline content of the sea air.

So, you wind up with salt, water, and iron which when put together forms a perfect battery compromising anode, cathode, and electrolyte. Currents flow in these localized batteries and produce corrosion of the engine blades apart from the abrasive problems posed by such particulate matter

I still remember, after all these years, the utter surprise and deep shock on the face of a gora tech rep when we "washed" a running engine in front of him by pumping a mixture of distilled water and some chemicals directly into the intake of a running engine. The process took 25 minutes to complete and he was in a great panic throughout and he tried to stop us many times. For us, it was merely a mundane procedure that we carried out regularly and as a matter of routine.

Our procedures were not even known to the Designer/manufacturer of the engine nor was anyone else interested in following our procedures which served us very well in safeguarding our engines.

The dazed gora tech rep later asked if he could have a copy of our "washing" procedure and it was willingly given to him.

Much later, I heard that some others in India also started "washing" their engines when earlier they had loudly laughed at us.

Engines with a high magnesium content tend to have corrosion and other abrasion problems, especially in an atmosphere like goa. Many many countries have similar or even more diverse airborne particulate and chemical issues in their atmospheres. P&W seems to be flying OK there or is it simply too expensive to talk of "special conditions", especially when lawyers also attend tech meetings in those countries??

These days magnesium is mostly out and/or other alloys have taken their place which are treated and show vastly improved performance in the presence of contaminants both particulate as well as chemical.

So when some joker from P&W condescendingly yaps about the "special conditions" in India, its pure, unadulterated BS and someone there thinks that he has bamboozled us dumb SDREs.

In some form or the other, such conditions obtain all over the world. and their piss poor new gen 321 engines are supposed to perform, notwithstanding, and if they do not, it can usually be traced back to a design issue.

There is enough shooklaw type paid media to carry fake news in every part of the world, especially when hired gora guns are hunting SDREs just to silence them.
Last edited by chetak on 01 Jan 2018 16:49, edited 1 time in total.

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Re: Kaveri & aero-engine discussion

Postby Abhibhushan » 01 Jan 2018 16:45

Ramana wrote
Re heat and dust of India and Aero engines.
What do you make of this gun firing brouhaha for LCA?


Gun gas ingestion is an old challenge for a designer. We had our full measure of gas ingestion problem with the Gnat. Finally we accepted the aircraft with a compromise solution: the engine power was reduced automatically by a ‘Dip Switch’ if guns were fired above 20000 feet altitude. (Fortunately, the Gnat never faced an enemy at above 20K in its total operational life.

Problems faced by the Tejas will also be overcome, through technology or through operational techniques/compromises)

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Re: Kaveri & aero-engine discussion

Postby JayS » 01 Jan 2018 17:30

chetak wrote: when we "washed" a running engine in front of him by pumping a mixture of distilled water and some chemicals directly into the intake of a running engine.


Now that's what I call it "Badass". :wink: Very interesting info. Thanks for sharing.

Which engine was that.? If you don't mind sharing..

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Re: Kaveri & aero-engine discussion

Postby chola » 03 Jan 2018 15:02

Time to set up multiple engine development oganizations, including the private sector, that can compete with each other.

If not, even a successful SNECMA Kaveri won’t make much of a difference. We need an INDUSTRY not a singular project.

The PRC looks like it had broken through the engine barrier in 2017 with a flood of new prototypes and tests. Maybe dhoti-shivering can create some urgency.

Posted in AFM:
https://forum.keypublishing.com/showthread.php?140394-Chinese-air-power-thread-18&p=2424982#post2424982

2017 Engine Advances
1) WS-10 variant on J-20 bort number 2021

2) WS-10X with AVEN nozzles on a J-10B/C

3) WS-19 engine prototype assembled *

4) WS-20 engine nearing testing on Y-20

5) CJ-1000A prototype assembled **

6) WS-15 reported in March to be “ready soon” ***

7) WZ-10 turboshaft reported to be ready and powering Z-20 prototypes

8 ) 2nd FC-31 prototype reportedly flew with WS-13

* The WS-19 is to be the uprated engine to be paired with the FC-31 which is increasingly cited as the next Chinese carrier fighter.

** The CJ-1000A is a LEAP-level domestic engine from ACAE, a commercial engine builder, for the C-919

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Re: Kaveri & aero-engine discussion

Postby shiv » 03 Jan 2018 20:31

As the video below shows, jet engines are designed to tolerate water well. It is small solid particles that cause damage. Smoke by definition includes small particles - apart from hot gases that may result from gun/missile plumes. Engine blade tips that rotate reach near supersonic speeds - which means each particle of dust is a little bullet that chips off a little bit of blade. Not much - but over time it accelerates damage.
https://www.youtube.com/watch?v=faDWFwDy8-U

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Re: Kaveri & aero-engine discussion

Postby JayS » 03 Jan 2018 20:56

shiv wrote:As the video below shows, jet engines are designed to tolerate water well. It is small solid particles that cause damage. Smoke by definition includes small particles - apart from hot gases that may result from gun/missile plumes. Engine blade tips that rotate reach near supersonic speeds - which means each particle of dust is a little bullet that chips off a little bit of blade. Not much - but over time it accelerates damage.
https://www.youtube.com/watch?v=faDWFwDy8-U


Indeed. A very good video you might like to watch showing this damage and how to repair it. Actually 2 parts. (PS: This channel is very nice for a jet engine stuff). Composite fan blades have Ti leading edges to make them damage tolerant from all kind of damage including this.

https://www.youtube.com/watch?v=p5doVAKb4Ro

Also you may know already, civilian engines have mechanism to throw out foreign objects after booster/LPC from the core flowpath. Its based on inertia so bigger particles typically get removed here. Its the medium to fine particles which must be getting in mostly. Apart from mechanical damage to compressor, they can also block cooling holes on turbine blades. I would say, its the medium size of particles which would be most dangerous for the engine. Finer particles are relatively easy to be swept away by airflow. Mechanical properties such as hardness of the particle would also be an important factor.

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Re: Kaveri & aero-engine discussion

Postby JayS » 05 Jan 2018 01:03

Abhibhushan wrote:
Ramana wrote
Re heat and dust of India and Aero engines.
What do you make of this gun firing brouhaha for LCA?


Gun gas ingestion is an old challenge for a designer. We had our full measure of gas ingestion problem with the Gnat. Finally we accepted the aircraft with a compromise solution: the engine power was reduced automatically by a ‘Dip Switch’ if guns were fired above 20000 feet altitude. (Fortunately, the Gnat never faced an enemy at above 20K in its total operational life.

Problems faced by the Tejas will also be overcome, through technology or through operational techniques/compromises)


I suppose for trying to stop engine surging or help it recover post surge due to hot gas ingestion during missile/rocket firing, reducing engine power by reducing fuel flow and changing compressor IGC positions to increase surge margin are standard methods. FADEC takes care of these changes when rocket/missile is fired. The aircraft sends signal for firing to engine FADEC and then FADEC reduces engine power and adjusts IGV for a short while.

Here is a paper which talks about issue of engine surge due to rocket firing on AH-1 Cobra Helicopter.

http://www.dtic.mil/dtic/tr/fulltext/u2/a290130.pdf

The AH-1 Cobra helicopter has the capability to launch 2. 75 inch folding fin aerial rockets (FFARs)
equipped with Mark 66 (MK66) rocket motors to engage battlefield taigets. Following a class A
accident in which an AH-1 suffered. a tail rotor drive shaft milure while launching MK66 FFARs,
a joint engineering investigation of the AH-1F helicopter was conducted by the Airworthiness
Qualification Test Directorate (RQTD) of the U.S. Army Aviation Technical Test Center and the
U.S. Army Aviation Applied Technology Directorate (AA1D). The results of this investigation
which recommend an engine inlet shield to defiect rocket exhaust gases away from the engine
are
oontained in a U.S. Army Test and Evaluation Command (TECOM) Fmal Report, TECOM Project
No. 4-C0-2~16, dated June 1991.
Subsequent to this work, the U.S. Army Avi3tion Systems Command (AVSCOM) in conjunction
with the NASA Lewis Research Center directed Chandler Evans, the engine fuel control supplier
for the AH-1 helicopter, to investigate potential modifications to the fuel control to alleviate the
rocket fire surge problem. The work at Chandler Evans WclS based on a computer simulation of the
engine, fuel control, and AH-1 helicopter.
The objective of the investigation was not to preclude engine smge following hot gas ingestion but
to recover smoothly from surge and avoid overtorqueing the rotor drive system. This objective, if
achieved, would have application not only to rocket firings, but to helicopter operation in general
where inlet distortion effects and engine deterioration can also cause the engine to surge and
potentially cause damage to the rotor drive train
.


The fuel control system must be modified to actively prevent engine surge or to ~ to engine surge
in some fashion to attenuate rotor drive train torque spikes.
In an attempt to prevent surge, it was assumed that closure of the compressor inlet guide vanes
(IGVs), when synchronized with rocket firings, could go a long way to block the amount of hot
gases· entering the engine and thereby preclude surge. The IGV s must be modulated between the
open and closed position for each rocket fire because closing down the IGVs for a prolonged time
period would degrade engine power and cause loss of rotor speed and helicopter lift.


Note that as I said earlier, the main culprit is the hot gases which cases inlet distortion (and high temp of intel air to obviously) which causes surge in turn.

Next, I found a mention in one old reference for F404, that F404 also has this function in its FADEC. Which means there is a every possibility that LCA also be able to utilize this functionality for handling engine surge due to any kind of hot gas ingestion from gun/missile/rocket firing.

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Re: Kaveri & aero-engine discussion

Postby ramana » 05 Jan 2018 01:12

Wow, So it can be handled by software fix using the FADEC as the Dip Switch.

Maybe its already enabled for all we know if older references to F404 have this feature.

Can you post this for further reading?

So can lurk back till further news.

shiv
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Re: Kaveri & aero-engine discussion

Postby shiv » 05 Jan 2018 07:38

JayS wrote: Which means there is a every possibility that LCA also be able to utilize this functionality for handling engine surge due to any kind of hot gas ingestion from gun/missile/rocket firing.

There is every possibility that all this may be completely unnecessary if the gun positioning is good enough - but only comprehensive testing can prove that - without waiting for an American termed "Class A" accident. I think a class A accident is a write off. This is after all how this discussion started "Why don't they get on with gun integration?" The Cobra accident example shows how a well established airframe can show up unexpected problems from different munitions.

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Re: Kaveri & aero-engine discussion

Postby JayS » 05 Jan 2018 12:17

ramana wrote:Wow, So it can be handled by software fix using the FADEC as the Dip Switch.

Maybe its already enabled for all we know if older references to F404 have this feature.

Can you post this for further reading?

So can lurk back till further news.


http://www.dtic.mil/dtic/tr/fulltext/u2/a164562.pdf

Aussie paper from 80s. Has a mention of FADEC modes.

Another interesting fact mentioned in paper is the underestimation of Time at max temperature and time of AB usage during design of F404. Or rather overutilization of engines in real life depending on how you want to see it. Real life values of these two parameters were 60% higher. I had posted on BRF earlier how F404 has severe life issues during service until mid 90s. Now I know why. GE ironed out the issues eventually.

Another one, this paper says one key outcome of F404 project in realization of how much more Low Cycle fatigue is important for engine life. By merely keeping track of Equivalent Design Cycles actually utilized in real life one can increase engine utilization significantly and also manage MRO schedule much better. This is the genesis of Life Tracking System in GE Engines, I think. RM12 has seen significant hike in utilization of engines (I am not sure if the figure is in public domain already, so wont post) Similar approach for airframes can also increase utilization of airframes significantly. I was delighted to know during recent Aero India that Kaveri also has Life Tracking system. The snecma guy told me they had this system in all their engines right from starting (like 50s/60s). But I don't believe him. Can't take marketing guys at face value :mrgreen: .

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Re: Kaveri & aero-engine discussion

Postby JayS » 05 Jan 2018 12:21

shiv wrote:
JayS wrote: Which means there is a every possibility that LCA also be able to utilize this functionality for handling engine surge due to any kind of hot gas ingestion from gun/missile/rocket firing.

There is every possibility that all this may be completely unnecessary if the gun positioning is good enough - but only comprehensive testing can prove that - without waiting for an American termed "Class A" accident. I think a class A accident is a write off. This is after all how this discussion started "Why don't they get on with gun integration?" The Cobra accident example shows how a well established airframe can show up unexpected problems from different munitions.


Of course, first thought in designer's mind it to eliminate any anticipated/known issue. But if it cannot be eliminated, then it has to be dealt with somehow. This power adjustment is the second approach. But note that the mode is also useful in other scenarios, for example, at high AoA when airflow might be reduced somewhat, or under severe sideslip.


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