CVF, JSF & MRA4 Problems
Tourist, that has made my day, not ever watched the programme but that was funny, more so because, like you said, it does have the ring of probability about it given the current state of affairs.
JF
Operational flexibility is indeed important, and it's an area of military aviation that is not much exploited, and one way or another we have to deal with anti-access threats.
However, my concern with JSF (I wonder if it would have been shared by that other, much missed JF) is that the joint spec has compromised the flexibility. F-4-sized jets with lots of funny materials on their edges, doors &c are not (I fear) very compatible with soccer fields, industrial parks and random bits of road, or ships under 50000 tons.
That other JF, too, was not a big fan (geddit) of LPLC because of the challenges of STO, with no or limited ability to vector the lift engine thrust, and the consequent inlet momentum drag. JSF-B is in that sense an LPLC. I know that the cascades can vector the fan thrust about 50 degrees aft, but it seems at first sight that the effective area has to decrease in the process.
If JSF-B STOs from a ship at the same T/W as a Harrier, it does so at 50000 pounds or so - the same fuel fraction as a clean F-16, with 2 x 1000 lb bombs and two AMRAAMs.
When the LO requirement was added to STOVL, things got harder to a degree that was not appreciated.
For your respectful consideration,
LO
Operational flexibility is indeed important, and it's an area of military aviation that is not much exploited, and one way or another we have to deal with anti-access threats.
However, my concern with JSF (I wonder if it would have been shared by that other, much missed JF) is that the joint spec has compromised the flexibility. F-4-sized jets with lots of funny materials on their edges, doors &c are not (I fear) very compatible with soccer fields, industrial parks and random bits of road, or ships under 50000 tons.
That other JF, too, was not a big fan (geddit) of LPLC because of the challenges of STO, with no or limited ability to vector the lift engine thrust, and the consequent inlet momentum drag. JSF-B is in that sense an LPLC. I know that the cascades can vector the fan thrust about 50 degrees aft, but it seems at first sight that the effective area has to decrease in the process.
If JSF-B STOs from a ship at the same T/W as a Harrier, it does so at 50000 pounds or so - the same fuel fraction as a clean F-16, with 2 x 1000 lb bombs and two AMRAAMs.
When the LO requirement was added to STOVL, things got harder to a degree that was not appreciated.
For your respectful consideration,
LO
Do a Hover - it avoids G
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LO
Since you addressed your post to me it would be impolite for me not to reply (a notion probably appreciated only by you and I and a handful of other corresondents on this forum)
If you are using operational flexibility as synonym for operating site flexibility then all well and good but I think that the two phrases have very diferent meanings to many people
I don't know what anti-access threats are.
I don't see how the operating site gives a toss about the material of the leading edges or door shapes etc. I think the operating site only knows (and reacts to) exhaust gas velocity and temperature.
As for low observable features compromising a design - well of course that is true but surely that fact applies accross the board to all aircraft and not just STOVL designs?
Your next para "That other JF, too, was not a big fan (geddit) of LPLC because of the challenges of STO, with no or limited ability to vector the lift engine thrust, and the consequent inlet momentum drag" made my brain hurt a tad (easily done these days) as I tried to divine just what you meant.
The lift plus lift cruise types that I know of are not greatly bothered by doing an STO (unless we are considering engine failure) and some were very good at it. I agree that the lift plus cruise ones (very different animals) most certainly did have STO problems but these were related to the need to use moderate alphas in mid transition (to make the wing work) which pointed the lift engines forward and slowed you down again if they were not fitted with enough rearwards tilt capability. Nothing to do with intake momentum drag though.
I don't see the JSF-B as a LPLC aircraft at all. LPLC were a subset of those designs that used a combined power plant for hover. The JSF-B uses an augmented powerplant for hover and is one of three augmented categories
For those that find words even harder than me I will try and post a picture at this point.
Don't know what you are suggesting in your penultimate para. Not arguing the numbers just wonder why you pulled the F-16 out of the hat? It can't play without a suitable runway can it? So we are back to the beginning about the need for operating site flexibility.
As to your last sentence you may be right - I just don't know. What are the elements that were not appreciated?
JF
Since you addressed your post to me it would be impolite for me not to reply (a notion probably appreciated only by you and I and a handful of other corresondents on this forum)
If you are using operational flexibility as synonym for operating site flexibility then all well and good but I think that the two phrases have very diferent meanings to many people
I don't know what anti-access threats are.
I don't see how the operating site gives a toss about the material of the leading edges or door shapes etc. I think the operating site only knows (and reacts to) exhaust gas velocity and temperature.
As for low observable features compromising a design - well of course that is true but surely that fact applies accross the board to all aircraft and not just STOVL designs?
Your next para "That other JF, too, was not a big fan (geddit) of LPLC because of the challenges of STO, with no or limited ability to vector the lift engine thrust, and the consequent inlet momentum drag" made my brain hurt a tad (easily done these days) as I tried to divine just what you meant.
The lift plus lift cruise types that I know of are not greatly bothered by doing an STO (unless we are considering engine failure) and some were very good at it. I agree that the lift plus cruise ones (very different animals) most certainly did have STO problems but these were related to the need to use moderate alphas in mid transition (to make the wing work) which pointed the lift engines forward and slowed you down again if they were not fitted with enough rearwards tilt capability. Nothing to do with intake momentum drag though.
I don't see the JSF-B as a LPLC aircraft at all. LPLC were a subset of those designs that used a combined power plant for hover. The JSF-B uses an augmented powerplant for hover and is one of three augmented categories
For those that find words even harder than me I will try and post a picture at this point.
Don't know what you are suggesting in your penultimate para. Not arguing the numbers just wonder why you pulled the F-16 out of the hat? It can't play without a suitable runway can it? So we are back to the beginning about the need for operating site flexibility.
As to your last sentence you may be right - I just don't know. What are the elements that were not appreciated?
JF
Foz was not a believer in LPLC, because drag increased very rapidly with acceleration, until the lift-jets could be shut down. The result was that LPLCs (in his view) were not as efficient in STO as a Harrier.
In this respect JSF is basically similar to an LPLC, in that the lift fan is similar to a jet. However, it may be possible to play games with transferring thrust from the fan to the main engine, and as I noted there is some vectoring capability on the fan.
As for stealth technology: I'm more concerned about the durability and maintainability of stealth features in a non-pristine environment.
What I can't get an answer on is the STO TOW of Dave-B. If the thrust/weight ratio required for STO is the same as the Harrier, the warload and radius of Dave B will be disappointing to users who are expecting to go much farther and carry more than the Harrier does.
In this respect JSF is basically similar to an LPLC, in that the lift fan is similar to a jet. However, it may be possible to play games with transferring thrust from the fan to the main engine, and as I noted there is some vectoring capability on the fan.
As for stealth technology: I'm more concerned about the durability and maintainability of stealth features in a non-pristine environment.
What I can't get an answer on is the STO TOW of Dave-B. If the thrust/weight ratio required for STO is the same as the Harrier, the warload and radius of Dave B will be disappointing to users who are expecting to go much farther and carry more than the Harrier does.
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LO
As you say Foz was not a fan of LPLC but with all respect to his memory that was a quarter of a century ago and a lot of things have changed since those days. He was extremly critical of the Forger (for example) because it "could not do an STO" Well of course we now know that it could and did. It was extremly vulnerable to an engine failure as it needed all three to work - but that is a different issue and not much to do with STO efficiency.
I really do take issue with you over classing the JSF-B as an LPLC though. Not just from the pedantic point of view because it is a single engined aircraft but from the way the control system operates. Varying the thrust between the fan and the rear nozzle is fundemental to the control of the B and with modern FBW capabilities is not at all open to the same doubt as the Forger. Indeed I don't know whether you know but the three engines of the Forger were controlled by a HYDRO-MECHAINICAL computer! A bit like the challenge of doing a hydraulically controlled TV set for the lounge. When their CTP offered me a ride in the Forger way back in '92 I said thanks but no thanks for just that reason - I saw no point in taking the risk (however small) as one would learn nothing of relevance to the future because nobody would ever control an aeroplane again that way today.
Now if the offer had been for the 141 my answer would have been very different but that was not on the table!
I don't know how the STO perf of the B would compare with the Harrier (and if I did this is not really the place for such facts) but it does offer stealth and speed not possible with the Harrier. Given the proclivity of modern weaopons to produce direct hits every time perhaps old fashioned notions of numbers of stores are just that.
I suspect I must know you but there you go.....
JF
As you say Foz was not a fan of LPLC but with all respect to his memory that was a quarter of a century ago and a lot of things have changed since those days. He was extremly critical of the Forger (for example) because it "could not do an STO" Well of course we now know that it could and did. It was extremly vulnerable to an engine failure as it needed all three to work - but that is a different issue and not much to do with STO efficiency.
I really do take issue with you over classing the JSF-B as an LPLC though. Not just from the pedantic point of view because it is a single engined aircraft but from the way the control system operates. Varying the thrust between the fan and the rear nozzle is fundemental to the control of the B and with modern FBW capabilities is not at all open to the same doubt as the Forger. Indeed I don't know whether you know but the three engines of the Forger were controlled by a HYDRO-MECHAINICAL computer! A bit like the challenge of doing a hydraulically controlled TV set for the lounge. When their CTP offered me a ride in the Forger way back in '92 I said thanks but no thanks for just that reason - I saw no point in taking the risk (however small) as one would learn nothing of relevance to the future because nobody would ever control an aeroplane again that way today.
Now if the offer had been for the 141 my answer would have been very different but that was not on the table!
I don't know how the STO perf of the B would compare with the Harrier (and if I did this is not really the place for such facts) but it does offer stealth and speed not possible with the Harrier. Given the proclivity of modern weaopons to produce direct hits every time perhaps old fashioned notions of numbers of stores are just that.
I suspect I must know you but there you go.....
JF
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John,
What a pleasure to have you on this thread - good manners AND exceptional knowledge - what a pleasant combination!
Hope I can measure up...
Good to see the AHS 'Wheel of Misfortune' again - I've always thought it was an really clever piece of work, and the very small number of operationally successful designs makes clear just how hard powered lift really is. Makes the Harrier all the more remarkable.
I agree that the F-35B is not an LPLC design - I knew Paul Bevilaqua, who came up with the concept, and he was quite clear that he was aiming at exploiting the thermodynamic and installation advantages of an augmented power plant. Puts the 'up and away' engine at the rear, helps with HGI, and maximises powered efficiency.
LO is right that it's not quite as fexible as a pure vectored thrust design, but it does have a very good STO performance, especially with a ski jump. I can't go into figures here, but it's well above anything a Harrier could do. Think Buccaneer/F-4 cat launch weights and you may be in the right area.
Ski jump STO performance isn't solely dependent on thrust/weight ratio - ramp angle and entry speeds are key determinant, and entry speed depends on deck run as well as T/W.
LO maintenance - very classified, but bear in mind that F-35 is the US's fifth generation LO aircraft - they've learned a lot of lessons about taking care of it along the way.
Best Regards
Engines
What a pleasure to have you on this thread - good manners AND exceptional knowledge - what a pleasant combination!
Hope I can measure up...Good to see the AHS 'Wheel of Misfortune' again - I've always thought it was an really clever piece of work, and the very small number of operationally successful designs makes clear just how hard powered lift really is. Makes the Harrier all the more remarkable.
I agree that the F-35B is not an LPLC design - I knew Paul Bevilaqua, who came up with the concept, and he was quite clear that he was aiming at exploiting the thermodynamic and installation advantages of an augmented power plant. Puts the 'up and away' engine at the rear, helps with HGI, and maximises powered efficiency.
LO is right that it's not quite as fexible as a pure vectored thrust design, but it does have a very good STO performance, especially with a ski jump. I can't go into figures here, but it's well above anything a Harrier could do. Think Buccaneer/F-4 cat launch weights and you may be in the right area.
Ski jump STO performance isn't solely dependent on thrust/weight ratio - ramp angle and entry speeds are key determinant, and entry speed depends on deck run as well as T/W.
LO maintenance - very classified, but bear in mind that F-35 is the US's fifth generation LO aircraft - they've learned a lot of lessons about taking care of it along the way.
Best Regards
Engines
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Engines
Thank you for your kind words
Good to hear about the STO stuff.
In my view the simplicity of the straight vectored thrust notion was in 1960 THE way to go because basic mechanical reliability let alone electrics for autostabs etc was nowhere near where things are today. But today we can feel happy with complex systems and reap the performance benefits resulting from the hovering thrust you can get out of a fan (propellor) compared to a pure jet. To say nothing of the HGI issues.
Yours
John
Thank you for your kind words
Good to hear about the STO stuff.
In my view the simplicity of the straight vectored thrust notion was in 1960 THE way to go because basic mechanical reliability let alone electrics for autostabs etc was nowhere near where things are today. But today we can feel happy with complex systems and reap the performance benefits resulting from the hovering thrust you can get out of a fan (propellor) compared to a pure jet. To say nothing of the HGI issues.
Yours
John
JF and Engines,
Thanks for these inputs. I'll have to look at more recent Yak material. The use of a hydromechanical computer (sort of a monster version of a complex pre-DEEC engine control, I imagine) sounds altogether too much fun.
I agree that the nifty bit of the F-35B system is the elimination of non-lifting reaction controls and the use of nozzle area to shift the thrust balance fore and aft. Credit to Paul Bevilaqua for the idea, and credit to many for making it work in practice. Some day we may find out about the classified Lockheed-NASA SSF precursor program and exactly what was found out there.
Weights: nod's as good as a wink to a blind horse, guv.
However, I still predict an entertaining year on JSF, and that the UK will, even if all goes well, be very happy to have set a timetable that allows them to use the F136. Phrases we never hear in STOVL: "It turned out that we didn't need the extra thrust after all."
LO
Thanks for these inputs. I'll have to look at more recent Yak material. The use of a hydromechanical computer (sort of a monster version of a complex pre-DEEC engine control, I imagine) sounds altogether too much fun.
I agree that the nifty bit of the F-35B system is the elimination of non-lifting reaction controls and the use of nozzle area to shift the thrust balance fore and aft. Credit to Paul Bevilaqua for the idea, and credit to many for making it work in practice. Some day we may find out about the classified Lockheed-NASA SSF precursor program and exactly what was found out there.
Weights: nod's as good as a wink to a blind horse, guv.
However, I still predict an entertaining year on JSF, and that the UK will, even if all goes well, be very happy to have set a timetable that allows them to use the F136. Phrases we never hear in STOVL: "It turned out that we didn't need the extra thrust after all."
LO
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LO,
You are absolutely right - powered lift aircraft performance depends on two basic attributes:
THRUST and WEIGHT
I believe that the F136 will be key to getting F-35B operational, and I also predict that weight control will be the order of the day for years to come. Just following the maths...
Incidentally, the Sea Harrier flew around quite contentedly with a hydromechanical FCU, developed (I'm told) from the Avon's unit. The Pegasus is still the free world's fastest accelerating and declerating engine, essentially surge free and operating from zero to just over Mach 1 with an open fixed intake and a simple IGV setup plus a couple of blow off valves. And it's British. Makes yer proud, don't it? And that's why Brits are doing a lot of key propulsion related work on the F-35B.
Happy days
Engines
You are absolutely right - powered lift aircraft performance depends on two basic attributes:
THRUST and WEIGHT
I believe that the F136 will be key to getting F-35B operational, and I also predict that weight control will be the order of the day for years to come. Just following the maths...
Incidentally, the Sea Harrier flew around quite contentedly with a hydromechanical FCU, developed (I'm told) from the Avon's unit. The Pegasus is still the free world's fastest accelerating and declerating engine, essentially surge free and operating from zero to just over Mach 1 with an open fixed intake and a simple IGV setup plus a couple of blow off valves. And it's British. Makes yer proud, don't it? And that's why Brits are doing a lot of key propulsion related work on the F-35B.
Happy days
Engines
I was once told that the core of the Pegasus was actually based on the Orpheus.
Is that true?
The fastest accelerating jet engine I've ever heard is whatever powers the Lockheed U-2.....
Back to V/STOL, I've walked past the static VAK191B at the Bremen Airbus site many times. One thing I've always wondered - with 3 engines, where on earth did they also find the space for the 2100 kg of fuel it was supposed to carry.
The 220 nm range must have been thought-provoking!
It must have been fun conducting rapid rolls at high speed with such a challenging B/A ratio.....
Is that true?
The fastest accelerating jet engine I've ever heard is whatever powers the Lockheed U-2.....
Back to V/STOL, I've walked past the static VAK191B at the Bremen Airbus site many times. One thing I've always wondered - with 3 engines, where on earth did they also find the space for the 2100 kg of fuel it was supposed to carry.
The 220 nm range must have been thought-provoking!
It must have been fun conducting rapid rolls at high speed with such a challenging B/A ratio.....
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Engines
I am not sure about the Pegasus FCU being based on the Avon unit. That would have been strange as the Pegasus was a Bristol engine (as BEags mentions with the Orpheus connection). The BS 53 (two vectoring nozzles and one fixed) was based on the Orpheus. When Ralph Hooper suggested to Mr BS 53 (Gordon Lewis) that he should bifurcate the jet pipe and put two more nozzles on Gordon designed a new engine to this spec from scratch.
As to the Harrier flying around on a hydro mech fuel system well yes it did for many years but it was the weakest part of the whole powerplant reliability thing and cost us several aircraft before the manual fuel control system mod was added. The MFCS which is a simple pipe from the tank to the burners with a direct tap operated by the throttle handle. There was no control of fuel flow other than that provided by the pilot. No accel control, no altitude control, no IAS control, no JPT control and NO max RPM governor. So if the Pegasus had not been such a forgiving donk it would have been an impossible task.
The Forger hydro mech computer was something else again. It controlled all three engines with the pilot having a single throttle lever and a single thrust direction selector just like the Harrier. It sat under the cockpit floor and was several feet long.
JF
I am not sure about the Pegasus FCU being based on the Avon unit. That would have been strange as the Pegasus was a Bristol engine (as BEags mentions with the Orpheus connection). The BS 53 (two vectoring nozzles and one fixed) was based on the Orpheus. When Ralph Hooper suggested to Mr BS 53 (Gordon Lewis) that he should bifurcate the jet pipe and put two more nozzles on Gordon designed a new engine to this spec from scratch.
As to the Harrier flying around on a hydro mech fuel system well yes it did for many years but it was the weakest part of the whole powerplant reliability thing and cost us several aircraft before the manual fuel control system mod was added. The MFCS which is a simple pipe from the tank to the burners with a direct tap operated by the throttle handle. There was no control of fuel flow other than that provided by the pilot. No accel control, no altitude control, no IAS control, no JPT control and NO max RPM governor. So if the Pegasus had not been such a forgiving donk it would have been an impossible task.
The Forger hydro mech computer was something else again. It controlled all three engines with the pilot having a single throttle lever and a single thrust direction selector just like the Harrier. It sat under the cockpit floor and was several feet long.
JF
<<I believe that the F136 will be key to getting F-35B operational, and I also predict that weight control will be the order of the day for years to come.>>
No company bias here of course...
I agree. The key issue is that the F136 design was frozen after LockMart found that the gremlins had welded several thousand pounds of extra metal into the B when the engineers were on teabreak.
So why does the USAF keep trying to kill the F136?
No company bias here of course...
I agree. The key issue is that the F136 design was frozen after LockMart found that the gremlins had welded several thousand pounds of extra metal into the B when the engineers were on teabreak.
So why does the USAF keep trying to kill the F136?
Ecce Homo! Loquitur...
Thread Starter
So why does the USAF keep trying to kill the F136?
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John,
You are probably right - the Avon ancestry of the Peggie FCU was only ever a rumour. Even so, the ability of the engine to operate across a wide range of speeds, heights and inlet conditions without recourse to electrics was always amazing to me.
In my experience, the FCU was pretty reliable, if correctly set up (help from the friendly local RR rep was useful).
LO, Ref the F136:
The key issue is that the F136 design was frozen after LockMart found that the gremlins had welded several thousand pounds of extra metal into the B when the engineers were on teabreak.
Not really - the 136 is still under development, although at an advanced stage. The story about B weight issues is a good one, but can't be repeated on this thread, sadly. Whatever, it wasn't down to gremlins...
Attepmts to kill the 136 are a pure budget drill. There are plenty of people in the US (including USAF specialists) who will, at all costs, wish to avoid having a single souyrce for combat aircraft engines. Politically, GE have great clout and the engine is pretty damn good too. I think it'll survive, and it will be good for all variants if it does.
You are probably right - the Avon ancestry of the Peggie FCU was only ever a rumour. Even so, the ability of the engine to operate across a wide range of speeds, heights and inlet conditions without recourse to electrics was always amazing to me.
In my experience, the FCU was pretty reliable, if correctly set up (help from the friendly local RR rep was useful).
LO, Ref the F136:
The key issue is that the F136 design was frozen after LockMart found that the gremlins had welded several thousand pounds of extra metal into the B when the engineers were on teabreak.
Not really - the 136 is still under development, although at an advanced stage. The story about B weight issues is a good one, but can't be repeated on this thread, sadly. Whatever, it wasn't down to gremlins...
Attepmts to kill the 136 are a pure budget drill. There are plenty of people in the US (including USAF specialists) who will, at all costs, wish to avoid having a single souyrce for combat aircraft engines. Politically, GE have great clout and the engine is pretty damn good too. I think it'll survive, and it will be good for all variants if it does.
Oops They Did It Again
http://www.flightglobal.com/articles...35-engine.html
I think we all know that this is an accounting gimmick. It allows the DoD to remove money from the projected numbers for JSF procurement and development, in an effort to avoid a Nunn-McCurdy breakout and consequent annual reporting and recertification. (N-McN requires reporting if the projected average unit procurement cost including R&D runs more than a certain percentage above the original projection.)
They know that Congress will put the money back in. They hope. But what happens when GE says "enough of this
, the entire JSF business is a tiny percentage of what we make on civil engines, we're taking our ball and going home" and calls off its lobbyists?
Kind of silly, though.
I think we all know that this is an accounting gimmick. It allows the DoD to remove money from the projected numbers for JSF procurement and development, in an effort to avoid a Nunn-McCurdy breakout and consequent annual reporting and recertification. (N-McN requires reporting if the projected average unit procurement cost including R&D runs more than a certain percentage above the original projection.)
They know that Congress will put the money back in. They hope. But what happens when GE says "enough of this
, the entire JSF business is a tiny percentage of what we make on civil engines, we're taking our ball and going home" and calls off its lobbyists? Kind of silly, though.
And someone from RR will be on the 'phone to Des Browne, who will in turn call David Millibrand and Gordon, and they, in turn will 'phone someone to protest and issue a veiled hint that without RR input into the engine, we'll seriously consider dropping the JSF, and if the level 1 partner bails out, what will that do for sales, and then....
Getting to be something of an annual ritual now, isn't it?
Getting to be something of an annual ritual now, isn't it?
