EvilWesteners
FULL MEMBER
- Joined
- Oct 17, 2020
- Messages
- 161
- Reaction score
- 0
- Country
- Location
Thanks for the good answer.
When you said Iran should build R-35 or Al-21 turbojets instead of turbofans, I was not convinced.
Only when I recently checked the data on these both engines I realized how close they are to comparable western turbofans in terms of thrust and fuel consumption.
So your point was a very good one.
For commercial high volume production Iran will go with the CFM56-5 in the future, probably with Mapna as producer.
But for limited numbers and non-commercial fighter applications, JT8D is the technology that has been mastered and is working.
The Spey on British F-4 was around 30% more fuel efficient then other F-4 with J79.
JT8D could do the same for Irans F-4 and make a better and somewhat more efficient engine for the F-14.
Getting R-35/Al-21 TBO levels high enough could be a challenge.
Grabbing some lunch at work, let's see if I can address some of your great points in your post.
Wished you were here, I could take you out (my treat) to a great fish restaurant in Seattle and we could brainstorm an engine for Iran, and talk about it for 10 hours.
I will try to address a few things, in no particular order. I will rush through it, and no doubt lots of grammar error as usual.
FUEL EFFICIENCY
------------------------
U.S. (and their gang of economic rapists) have used the idea of "turbofan" as the means to convince counties (like S Arabia) to buy expensive, hard to maintain (requiring high level of technical expertise) engines, so they can have personnel in these countries, essentially controlling what they sell, constantly making money from maintenance contracts, allowing the door to be open for CIA operatives, and keeping a tight control, etc. etc.
For oil producing countries that have refineries and can produce jet fuel, ... it is madness to have turbofans in most cases. Because it does not make logical/practical/financial sense.
Fuel efficiency depends on quite a few factors, depending on low-level, mid-level, or high-level flight, and also on the type of engine, and the payload, and the aerodynamics of the aircraft. Let me give some basic examples:
F5-E has got an incredible aerodynamic efficiency due to its pointy nose (people often forget the slim body and low wings of course). But it is very efficient in producing relatively very little drag.
F4-E is also the same (relatively) let's say compared to a mig-29. Even though F-4E is bigger, heavier, less thrust, and yet it has substantially higher maximum take off weight that mig-29 or mig-35. Mig29/35 never should have been a 2-engine aircraft. So much drag. What is the point of fuel efficiency in one area when there so much inefficiency in another area. Just simple engine comparison is illogical.
Most turbofans and turbojets use lower amounts of fuel at lower altitudes. With the exception of F4E which uses about 400kg-600kg of fuel during take off, depending on weapons load. This is due to its engine design having the priority for high altitude air flow specific design. In fact F4E is great for low level flight handling and high altitude flights, but bad at mid-level, especially fuel consumption. REALLY bad.
Al21F is good at low level (which is why it was preferred over R29 for Su-24), and it is good enough for mid-level flight. But not so good above 40,000 ft.
TF30 that Iran got for F-14A actually has one of the best fuel efficiencies around. You will not find this anywhere on the Internet. Iran's 20,900lb max afterburner thrust engine, produced almost 11,000 lb non afterburner around 0.67 lb/lbfh - and the upgraded U.S. TF30 was about 0.76 - of course depending on many factors, but just generally speaking. The reason for this is what we call MAXing OUT an engine, meaning that you add more stages to the engine to get maximum thrust at turbine stage considering the limits of the air flow for the engine. The U.S. MAXed OUT the TF30 to about 25,000 lb of thrust and hence about 15% less fuel efficient.
Most turbojet engines for fighter jets are low-level bypass and hence they are about 10%-30% increase for a turbojet compared to a turbofan, comparing apple for apple (e.g. low level, or mid level, size, weapons load, drag ratios, etc.).
The turbofans the Brits used for F4 and later decided to use it for testing design concepts for EuroFighter, was actually about I think 30% more efficient as you said compared to J79 (as long as we do not compare them at low level flight). But Al21 is actually much more fuel efficient than J79. In fact, these two engines weight almost identical, same length, same width, diameter, mostly same technology, about 10 years of technology apart, couple of air-flow differences (deliberately at design requirements required expectations), and J79 is a 17/11 engine and Al21 is a 24/17 engine (afterburner/non afterburner). And Al21 is 20%+ more fuel efficient depending on scenarios we can discuss.
Al31F is only about 10-17% more efficient than Al21f.
Again, as I mentioned above most of these engines fan/jet, have similar (ish) fuel consumption during take off. At very low level, there is higher air density, higher oxygen that can burn, and hence lower fuel consumption for power generation. And all these aircraft engines perform quite a bit similar if we look at apple for apple, aerodynamics, wing surface, drag ratio, weapons load, etc. etc. This is however only for low level flight.
One odd thing I would mention here that no one else seems to want to talk about. During take off, fighter jets use afterburner. In most cases, afterburner turbojet engines use slightly less fuel than turbofan engines ... like about 10% or around that.
As soon as you go to mid level, above say 10,000 ft to 35,000 ft, the above no longer holds true. That is where you can see major differences between fuel efficiencies.
F4E was designed for low level attack, and Su-24 was designed for lo-hi-lo, so depending on how you intend to use your platform, the engine may or may not be efficient for what you are trying to do.
One thing I see all the time: engines that are not sold to many countries, and hence the "truth" about its performance cannot be disputed ... then the manufacturer will BLATANTLY LIE publicly about the engine performance. Let me give you an example. The engine in F22 (F119-PW-100) is not a 35,000 lb thrust engine. It is a 41,000lb thrust. The U.S. lies to hide calculations regarding certain combat scenarios with its adversaries. However, both Russians and Chinese take this into account anyways.
Considering the above as a basis for choosing an engine for Iran, I suggested R35 or even AL21F for the following reasons:
- Iran can easily reverse engineer R35, as the Chinese did the R29 which is the same engine although R35 is (almost) MAXed OUT. Iran can take R35 to 30,000lb/20,000lb with today's technology and materials engineering while increasing turbine stages.
- I would rather have a 20,000lb non afterburner than a 17,000lb non afterburner even if the former has higher fuel consumption because that extra 3,000lb is huge amount of thrust at 35,000 ft when you are looking at T3 (time to target), without burning almost triple fuel consumption with afterburner, and higher heat signature.
- Russia built I think (my number is not exact) about 15,000+ or more R29s/R35s - older versions and upgraded versions for newer mig-23s. That engine has a huge history, detailed documentation (which Iran can get from China), and it is a proven engine with many known knowns. The engine was very reliable although the aircraft not very successful in combat. Iran does not need to take much risk and start adding and modifying parts and components and testing JT8D. If I thought Iran can do this fast, then I would want Iran to reverse engineer a D3 engine (Mig-31) which Iran has plenty of (Il-76) and knows it quite well (to a degree), just need to modify a few things with that heavy turbofan engine.
- Iran already has R35 engines and has been testing them for almost 20 years but not put a serious effort into it. Like everything else with Iran funding of the Air Force.
- Both Al21F and R35 offer high thrust engines which Iran can utilize for quite some time (may be the next 10 years) before having to seriously consider more advanced engines to keep up.
DEVELOPMENT TIME
------------------------------
Almost the first 10 years of my career I was in design, manufacturing, materials engineering, quality improvement, and quality assurance. The next 10 years of my career was project management (or actually a little bit more that that). Now I am a fat a$$, lazy, has-been, who gets paid for virtually doing something fun that I use to do at post grad projects, which is to play with technology for the next 10 years in the aviation industry, be it tools, components, process manufacturing, robotics, ergonomics, modern management systems, value-chain management software, partner integration systems, IT security systems, project management tools, AI automation, sourcing, and a lot of useless things to keep me busy. But I am not complaining since I am over paid, and I can take 3 hour lunches and no one cares.
My point is ... development time is extremely IMPORTANT.
Yes I very much believe Iran can build a turbofan out of JT8D given time, resources, effort, and full 100% political will. But is it the FASTEST in my opinion based on all my years of design and project management?
I would say ... I rather bet on Iran reverse engineering an AL21F or R35. Just a gut feeling hunch, based on so many projects and so many things I have seen that can happen from the start to the end.
If JT8D-based fighter jet low bypass engine development is being "concurrently" done while doing a AL21F .... then HECK YES. YES, yes, yes, yes please.
But Iran can only afford one platform at the time (well apparently NONE at this very time).
If all put on the table and I had to choose ... I would choose AL21F or R35. Just me though. I could very well be wrong.
TBO
------
I do not at all worry about this one. Iran has incredible capabilities with overhaul and maintenance. I doubt if people can imagine how HARD Tf30 is to maintain and overhaul and inspect and make sure the freakin thing works okay without radical temperament. AL21F is much better and easier and materials can be used for the temperatures at higher thrust and hot and high that would help enormously (relatively).
So, TBO for a country that has low cost of labor, does not concern me, and high level of expertise and it is its OWN built engine.
If the engine is simple (and turbojets are indeed much simpler, fewer parts/pieces, easier to manufacture, etc.) then it costs less, more can be built, then engines can be rotated in 30 minutes and the aircraft is air worthy now and allows for higher number of sorties, which the other engine is being inspected and repaired, damaged parts replaced, or overhauled if needed.
This is only the opinion of a lazy old man. hehe.
Now I better go back to work before they can my a$$ and I lose my retirement bonus. hehe.
Thank you PeeD for bringing to all of us your knowledge. I very much enjoy reading and learning from your posts, especially the missile stuff you know. WOW. I am trying to learn and keep up. Have an awesome day.