Northrop / McDonnell Douglas ATF - YF-23 and EMD F-23

lantinian said:
Many thaks to Flaterick to pointing out my patent research thing. I would not have said it myself.

Still elmayerle had a very good in Reply #21 . YF-23 design allowed not only aft and fore movement of the Bays but also increase in depth. There are no engines or airducs on top of the bay, only fuel and minor systems..

Looking at the F-23A as an aircraft designer I would say: yes its longer but since when lengthening the airplane is more risky than making it shorter, because the F-22A is indeed shorter and thinner in its middle section where you have weapons, fuel, air intakes, gun magazine. Packing the same stuff in less space is more riskier to me. Also lets not forget that F-22A had completely redesigned main weapons bay doors.

Now if we recall some of the problems the F-22 design went trough.

1. Overheating rear fuselage in Supercruise. Compare the rear of YF-22 and F-22A.How thinner it is on the production model. The F-23 with widely spaced engine blocks would not have had the problem of overheating.

2. Shockwaves in the Engine inlets requiring a strengthen forward fuselage after Raptor 01. No wonder, the air intakes on the A model are obviously shorted than the prototype. The F-23A has inlets way more optimized to handle supersonic airflow and the adoption of the concept by the F-35 only proves it.

3. F-22 was always criticized by not being able to carry big bombs. The latest FB-22 proposal features bulged up main weapon doors so it can house the 2000lb JDAM, yet the fuselage is the same is used with no lengthening to reduce cost. The YF-23 had a deeper bay and would have no problem fitting the 2000lb JDAM.

4. The 1994 redesign due to signature problem, costing probably a year delay in the F-22 program. Looking at the F-22A and you ca see it borrowed a lot of the Black Widow features: he shape of the nose, the way the aircraft brakes, the probes measuring AoA on the side of the radome, the minimum number of edges every panel, the topside of the engines, the clipping of the all moving tails. Yet the F-23A design features stealth/performance blending from the next level, like the inlet cone design.

5. Weight. The inability for the F-22 design to meet it weigh target is attributed to the failure of its designers to meat their goal of 50% Composites in the Airframe(2 as well). From the news article flaterick send me it is clear that the F-22A proposal in material is similar to the YF-23 design (one step behind). Also the F-23A featues not only 50% composits but BMI termosets account for a higher percentage out of that than the same BMI termoset do out of the total composits used on the F-22A, which are only 24%.(Flight International March 1997)

To me the F-23A would have had easier time meeting its weight target. As far as risk goes the change between Lockheeds 1985 winning design and the YF-22 tells me all I need to know about confidence in concept and the ability of USAF to choose their aeroplane based on their flying qualities. Same with the Rockwell F-X submition looking so much like SU-27. I hope the PAKFA does not turn out the be looking like the YF-23. I am going to be massively upset with defense secretary Rice, who chose the F-22

Regards, to all

P.S. I hope you are all enjoyng this discusion as much as I am ;)
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Reading through this thread again, I think some of the early takes require some corrections in light of more recent information.

Concerns about overheating of the aft fuselage were common to both the YF-22 and YF-23, but this was a solvable issue and it's no longer an operational concern for the F-22 after flight test validation. Similarly, the EMD F-23 would have had its engines toed in to be slightly closer but the volume between the nacelles would have had a fuel tank that would help act as a heat sink.

Regarding weapons bays, this has been discussed recently and while the F-23 has at least as much volume in this regard than the F-22, the geometry meant that weapons had to be stacked vertically, which current U.S. ordnance is generally not designed for. That said, I do think that this issue could have been resolved through EMD, perhaps by using an adapter similar to Sidekick that's currently planned for the F-35A/C which would bring the F-23's internal AMRAAM carriage to parity with the F-22. Overall, the added volume of the F-23 over the YF-23 in the weapon bays and fuel tanks may not help with drag but it would have enabled better operational characteristics (range specifically). On the note of volume, I'm not sure if the F-23 would have been lighter than the F-22, especially since the F-23 is more voluminous with some 20% greater internal fuel tank capacity. BMI proved to be a tricky material to work with for both Lockheed and Northrop, and perhaps contributed to the F-22 having such a high percentage of titanium by weight (more than any fighter, I believe).

It's very unlikely that the F-22 borrowed any features from the F-23. The F-22 design certainly evolved as it went through PDR and CDR after the EMD down-select, but the outer mold line remained largely unchanged from what Lockheed submitted for EMD in December 1990, with the differences mainly in the panel lines. As such it's unlikely that the shaping of the F-22 took much influence from the YF-23; rather, this was likely because of the major design by the Lockheed team starting in summer 1987 resulting in the YF-22 being quite immature by the time it was frozen in May 1988, so the F-22 had more room to evolve from the YF-22 than the F-23 from the YF-23, which had evolved from the same Northrop configuration since early 1986. EDIT: In fact, the Northrop HSF configuration was very recognizably YF-23-like as far back as 1985, based on a wind tunnel model in Paul Metz's book.

Performance-wise, the YF-22's late redesign and changes before the design freeze meant that its aerodynamics weren't quite as refined as the YF-23, whose design saw a gradual progression from Northrop's Dem/Val submission and still greatly resembled it. The YF-23 did have superior performance in supercruise with speeds in the Mach 1.7 range, notably better than the YF-22's Mach 1.58 but not quite as much as what has been exaggerated over the years; I think many got carried away by the novel aesthetics. The much more refined F-22 can match the YF-23's speed but that said, any objective comparison is difficult to make because neither aircraft flew the same test points. Again, statements from the SPO indicate that both aircraft met requirements and while each had its advantages, neither were decisively better in performance.

Ultimately, I think the biggest benefit of the F-23 would have been the greater internal fuel capacity, and better all-aspect stealth. However, I don't think the advantages would have been great enough for what USAF is currently seeking from NGAD.
 
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I suspect the more conventional, tightly-packed airframe layout of the F-22 was also the structurally less risky choice. We may never know what challenges (and associated cost increases) would've cropped up with a post-EMD F-23. It entered that development stage with a higher degree of maturity, as you say, but I'm not sure there weren't still unknown pitfalls waiting to rear their ugly heads.
 
One of the issues regarding the F-23's weapon bay were missile packaging. The F-22 has a nice flat bay for the AARAAMs but can only load a smaller JDAM weapon. Yes, we did have a nice deep main weapons bay on the YF/F-23 but did have risk in an appropriate launcher configuration. The F-23 did have a smaller forward bay for AIM-9s. A rotary missile launcher was one of the configurations evaluated as were others, missile weapons carriage was a significant risk area.

Supercruise was high and even though I was on the program, the USAF has kept the lid on pretty tight regarding actual maximum supercruise speed attained on PAV-2. It was better than 1.7+. NG has definitely capitalized regarding all that was developed and learned on the YF-23 program, especially when they bid for the USN F/A-XX. Even though NG is not bidding the USAF NGAD, NG has garnered excellent naval experience with the X-47B project and probably other classified efforts as well.
 
The YF-23 did exceed Mach 1.7, but that was with PAV-1 with the YF119, which tested flutter out to Mach 1.8 in afterburner; PAV-2’s highest speed attained was Mach 1.72, and maximum speed in afterburner would have been higher, north of Mach 2 although reaching this performance limit isn’t one of the test points. That said, the Northrop guys I listened to were proud of their ability to meet predicted performance.
 
Interesting information about the YF-23 that I did not know about previously icyplanettnhc(Steve), I am surprised that NG never went for the Mach 2 top speed flight during the testing.
 
icyplanetnhc (Steve) said:
Reading through this thread again, I think some of the early takes require some corrections in light of more recent information.

Concerns about overheating of the aft fuselage were common to both the YF-22 and YF-23, but this was a solvable issue and it's no longer an operational concern for the F-22 after flight test validation. Similarly, the EMD F-23 would have had its engines toed in to be slightly closer but the volume between the nacelles would have had a fuel tank that would help act as a heat sink.

Regarding weapons bays, this has been discussed recently and while the F-23 has at least as much volume in this regard than the F-22, the geometry meant that weapons had to be stacked vertically, which current U.S. ordnance is generally not designed for. That said, I do think that this issue could have been resolved through EMD, perhaps by using an adapter similar to Sidekick that's currently planned for the F-35A/C which would bring the F-23's internal AMRAAM carriage to parity with the F-22. Overall, the added volume of the F-23 over the YF-23 in the weapon bays and fuel tanks may not help with drag but it would have enabled better operational characteristics. On the note of volume, I'm not sure if the F-23 would have been lighter than the F-22, especially since the F-23 is more voluminous with some 20% greater internal fuel tank capacity. BMI proved to be a tricky material to work with for both Lockheed and Northrop, and perhaps contributed to the F-22 having such a high percentage of titanium by weight (more than any fighter, I believe).

It's very unlikely that the F-22 borrowed any features from the F-23. The F-22 design certainly evolved as it went through PDR and CDR after the EMD down-select, but the outer mold line remained largely unchanged from what Lockheed submitted for EMD in December 1990, with the differences mainly in the panel lines. As such it's unlikely that the shaping of the F-22 took much influence from the YF-23; rather, this was likely because of the major design by the Lockheed team starting in summer 1987 resulting in the YF-22 being quite immature by the time it was frozen, so the F-22 had more room to evolve from the YF-22 than the F-23 from the YF-23.

Performance-wise, the YF-22's late redesign and changes before the design freeze meant that its aerodynamics weren't quite as refined as the YF-23, whose design saw a gradual progression from Northrop's Dem/Val submission and still greatly resembled it. The YF-23 did have superior performance in supercruise with speeds in the Mach 1.7 range, notably better than the YF-22's Mach 1.58 but not quite as much as what has been exaggerated over the years; I think many got carried away by the novel aesthetics. The much more refined F-22 can match the YF-23's speed but that said, any objective comparison is difficult to make because neither aircraft flew the same test points. Again, statements from the SPO indicate that both aircraft met requirements and while each had its advantages, neither were decisively better in performance.

Ultimately, I think the biggest benefit of the F-23 would have been the greater internal fuel capacity, and better all-aspect stealth. However, I don't think the advantages would have been great enough for what USAF is currently seeking from NGAD.
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As we now know, seeing the EMD F-23 configurations, the weapons issue was solved with two separate weapons bays. Also, the only feature I can think of that the YF-23 had that the YF-22 didn't and ended up in the production version, was using the flight controls for deceleration as a opposed to a dedicated air brake. But, to me, that's just a refinement of the FCS.

What's interesting to me, is that when asked what the best aircraft he ever flew was, Paul Metz replied the YF-23. He was the Chief Test pilot on the YF-23 and The F-22A. I would be interested to know why he thought that. Of course, that would probably entail references to classified capabilities, so I doubt we'll never know why he thought that.
 
Indeed, even though Paul Metz spoke very highly of the F-22, he still thinks that the YF-23 edges it out, which speaks for how well Northrop did with the flight controls.

View: https://youtu.be/HSeApmqE_z4?si=eOInxZa_xqKC4Gkm&t=2046

FighterJock, while the YF-23 could have exceeded Mach 2, the maximum speed tested was Mach 1.80 for PAV-1 (P&W) and Mach 1.72 for PAV-2 (GE). Supercruise was Mach 1.43 for PAV-1 (P&W), and while it was never explicitly stated what the speed was for PAV-2 (GE), it was likely Mach 1.72 as PAV-2 wasn't the flutter test vehicle (I believe PAV-1 was the workhorse for envelope expansion). The Dem/Val flight test program is such that contractors are free to choose their own test points and how they want to execute it.
 
I could have sworn I had a copy of the comparison report between the YF-22 and YF-23 that I got from this forum, if not this specific thread.

Can't find it.

Does anyone have a copy?
 
ScrutorAudax said:
In the event of a failure of this air data system, the vehicle would revert to fixed control gains.
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I’d be curious how this would work if the aircraft is statically unstable, which requires constant adjustments from the flight control computers. Perhaps some pre-determined deflection of control surfaces would be enough to shift the aerodynamic center further aft?
 
icyplanetnhc (Steve) said:
I’d be curious how this would work if the aircraft is statically unstable, which requires constant adjustments from the flight control computers. Perhaps some pre-determined deflection of control surfaces would be enough to shift the aerodynamic center further aft?
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Other aircraft also have this feature; it's usually limited to specific aircraft configurations and specific parts of the flight envelope to be able to recover to a very limited attitude envelope. Really more just like giving you more time for straight and level flight to eject, definitely nothing like full performance.
 
Sorry to interrupt your conversation, but I found this image while watching the documentary about the YF-23 uploaded by the Western Museum of Flight. You can find it at 15:14 in the video. I am not sure if this is a rendition of an F-23 or F-22 concept, but it seems to show an HMD targeting system. Is there any information that the F-23/F-22 were supposed to have an HMD?
 

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iwantmoresources said:
Sorry to interrupt your conversation, but I found this image while watching the documentary about the YF-23 uploaded by the Western Museum of Flight. You can find it at 15:14 in the video. I am not sure if this is a rendition of an F-23 or F-22 concept, but it seems to show an HMD targeting system. Is there any information that the F-23/F-22 were supposed to have an HMD?
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The HMD and IRST were dropped to reduce risk IIRC.
 
I've seen a photo of engineers working on what looked like a stealthy housing for the AIRST but on both the F-22 and F-23 where was it intended to be placed? Nose? Wing root?

Speaking of other cut features, the F-22 originally had space in the nose reserved for side AESA arrays which were intended to expand radar coverage. Ultimately these were never used, but did the final F-23 design going to allow for similar arrangement?
 
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flateric said:
Searching for 'IRST' in this same thread will bring you answers with pics. Fact that Lockheed wanted side-looking AESA doesn't obligatory mean that Northrop team wanted the same.
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I see the picture you are referencing. The section of fuselage it was attached to just seemed quite different from the shape on the F-22 so I wasn't sure. That and the logo being the right-way up even though the whole assembly is flipped upside-down.

I had thought the side AESA arrays were because of a stated ATF requirement for greater radar coverage, in which case the F-23 would have to have some answer (presumably similar or some sort of array in the leading edge of the wing). But maybe it was never a requirement at all.
 
I don't see any internal volume provisions or apertures for side looking AESA arrays here. I see pair of MLD apertures at top and bottom though.
 

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Having self-censored several smartass replies, all I can say is that it was left undefined in the drawing. Best guess would be detection of missile emissions in the EM band.
 
Yup, that seems most likely. Previously, launch detection was indeed effected via the radar warning receiver by listening for threat radar mode changes that indicate a missile being guided. This is difficult with track-while-scan radars giving mid-course updates to active-radar homing missiles however, as the switch to STT for target illumination does not occur. It was always impossible with IR missiles, but those were mostly SRAAMs where relying on detection of the launch with the naked eye was a practicable approach.

With ARH missiles, the big tip-off in the RF spectrum only occurs long after launch, once the missile goes active during the terminal phase of flight - hardly what you'd call missile *launch* detection. Certainly the ATF would have had to anticipate the opposition deploying ARH missiles relatively early into the aircraft's expected career, so a different approach was required.

This leaves passive optical detection and active RF sensors, both of which have been implemented. The Eurofighter Typhoon has active MMW radar sensors watching for missiles, and one advantage is that range and speed of the missile can be measured easily and reliably. That enables evasive maneuvering advisories for the pilot to be generated, it's further capable of tracking missiles after motor burn-out (which is most of the flight for most missiles...) no problem at all.

For a platform strongly concerned with stealth like ATF having active RF sources emitting in all directions is hardly very clever, though. Optical detection is better in that regard, but early sensors could only track boosting missiles because they were not sensitive enough to detect airframe heating. There's also a false alarm problem, which is why UV sensors were sometimes used in addition or in place of IR - not many things beside a rocket motor plume are hot enough to generate significant UV radiation.

Inferring from the missile launch detection term, we might guess that the F-23 was going to use early IR or UV sensors that relied on the missile plume. More sophisticated systems that can also track coasting missiles are typically called missile approach warners.
 
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I've compiled information from Tony Chong's Flying Wings and Radical Things, Paul Metz's Northrop YF-23 ATF, and the classic Advanced Tactical Fighter to the F-22 Raptor by Aronstein, Hirschberg, and Piccirillo and wrote a summary of the YF-23 design history on Wikipedia. I was just tired of seeing poorly made articles and videos pop up about the YF-23 and the ATF, most of whom probably got their information from Wikipedia, so I was compelled to change that since this is probably the most easily accessible information about the airplane that most people have. Feel free to review and give me corrections if you see them. I did the same thing for the YF-22 article.

en.wikipedia.org

Northrop YF-23 - Wikipedia

en.wikipedia.org en.wikipedia.org
en.wikipedia.org

Lockheed YF-22 - Wikipedia

en.wikipedia.org en.wikipedia.org
 
I was intrigued by the provision for an IRST as shown in this drawing. Since it just uses IRST as a generic term, i assume that either: Northrop wanted to develop an IRST during EMD
use an existing one (AN/AAS-42?, Falcon Eye?)
or it is just meant to be there in case one is developed in the future.

Is there really no available info on what type this IRST was supposed to be?
YF-23-1.jpg
 
iwantmoresources said:
I was intrigued by the provision for an IRST as shown in this drawing. Since it just uses IRST as a generic term, i assume that either: Northrop wanted to develop an IRST during EMD
use an existing one (AN/AAS-42?, Falcon Eye?)
or it is just meant to be there in case one is developed in the future.

Is there really no available info on what type this IRST was supposed to be?
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During evaluation of the avionics in the simulator the pilots tested what kind of tactical or strategic difference the implementation of IRST would make to the combat outcomes. They found that having an IRST did not make a big enough difference in outcomes to justify the cost.

The EMD proposal was preliminary so I would guess they didn't go for a specific unit at that point, because the simulator testing showed that it was not needed and therefore dropped. By that time the EMD propsal was probably already made.

Just my guesses, based on what Paul Metz and the other test pilots said in various documentaries and what I read in Metz's Book about the YF-23.
 
sferrin said:
I would sure like to hear "the straight dope" from Paul Metz some day.
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In or about October 1992, the F-22 EMD 'chief engineer' (actually VP and Air Vehicle IPT Leader) Don Herring, RIP, asked me to sit in his conference room with Paul Metz, roll out the F-22A arrangement drawings, and 'walk around' the airplane. Apparently it was Metz's first day on the job in Marietta GA. He and I got right down to business -- no intros, no small talk, which left me a bit uncomfortable.

Metz seemed to be already aware of the basic external differences between F-22A and the YF-22. So I went through the inboard profile drawing, pointing out subsystems, equipment and other internal features, but he was mostly quiet. I was hoping for some reaction either way to specific design details, to get a sense of how the proposed F-23A approached things (for my own understanding).

He asked only two questions during our half-hour session, so I remember placing significance on them and why they remain etched in my memory 32 years later.
1. Do the flush UHF antenna apertures meet the requirements? (I answered yes and gave him the relevant performance)
2. What's the supercruise speed? (I answered that our current status is Mach 1.76)

Answering Question 2 is the only time his facial expression changed from that World Poker Tournament look.

Thought I'd share this experience with the forum.
 
joewee said:
Answering Question 2 is the only time his facial expression changed from that World Poker Tournament look.
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Interesting, although I'm not sure what is being inferred here since it could be any number of things.

As far as supercruise speed goes, the limitation may not just be driven by airframe shape but also engine temperature limits. Beyond a certain Mach number, inlet heating from adiabatic compression means that the engine won't be able to maintain rotor RPM for mil thrust, whether that be your compressor discharge or your TIT/FTIT. The F120 being a lower OPR engine than the F119 is perhaps less restricted in this regard, although it's also reportedly a thirstier engine.

I'd also be interesting in know how the inlet on the F-23 compares to the F-22. The former has a bumped compression surface with serrated cowling, while the latter has a caret compression surface. The YF-23's trapezoidal inlet did have some distortion issues, if I recall.
 
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icyplanetnhc (Steve) said:
Interesting, although I'm not sure what is being inferred here since it could be any number of things.

As far as supercruise speed goes, the limitation may not just be driven by airframe shape but also engine temperature limits. Beyond a certain Mach number, inlet heating from adiabatic compression means that the engine won't be able to maintain rotor RPM for mil thrust, whether that be your compressor discharge or your TIT/FTIT. The F120 being a lower OPR engine than the F119 is perhaps less restricted in this regard, although it's also reportedly a thirstier engine.

I'd also be interesting in know how the inlet on the F-23 compares to the F-22. The former has a bumped compression surface with serrated cowling, while the latter has a caret compression surface. The YF-23's trapezoidal inlet did have some distortion issues, if I recall.
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The contractual performance spec and the Air Force's System Operational Requirements Document (SORD) defined supercruise simply as sustained speed in level 1g flight where Total Drag = Net Thrust in military power, equivalent to Ps = 0. Other operational limitations may be real constraints, but my guess is you'll run out of gas first.

The F-22 caret inlet is quite impressive, with high recovery and very low distortion, but I don't remember any more than that. The brains behind its design are/were true Skunks ( Miller and Santman, see https://www.secretprojects.co.uk/threads/who-is-the-designer-of-f-22-raptor.44044/#post-701026 ) and Mike Schoop, RIP, who carried on to refine the design. Because of classification, I don't think you'll find any AF or NASA reports comparing the F-22 and F-23 inlets.
 
joewee said:
The contractual performance spec and the Air Force's System Operational Requirements Document (SORD) defined supercruise simply as sustained speed in level 1g flight where Total Drag = Net Thrust in military power, equivalent to Ps = 0. Other operational limitations may be real constraints, but my guess is you'll run out of gas first.
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True, I was brainstorming more from a technical perspective on what may drive those limits for the airframe-engine combination.

I believe Tony Chong's 2016 book Flying Wings & Radical Things stated that based on the YF-22 with YF120 reaching Mach 1.58 supercruise, General Electric engineers estimated that the YF-23 with their engines could be pushed to around Mach 1.8 or so in supercruise, although I don't believe PAV-2 was actually tested to this speed as PAV-1 with the P&W engines was the flutter test vehicle for envelope expansion.

Based on his reaction from your 1992 meeting with him, did Metz give any inklings on what the PSC F-23 was supposed to achieve?
 
icyplanetnhc (Steve) said:
True, I was brainstorming more from a technical perspective on what may drive those limits for the airframe-engine combination.

I believe Tony Chong's 2016 book Flying Wings & Radical Things stated that based on the YF-22 with YF120 reaching Mach 1.58 supercruise, General Electric engineers estimated that the YF-23 with their engines could be pushed to around Mach 1.8 or so in supercruise, although I don't believe PAV-2 was actually tested to this speed as PAV-1 with the P&W engines was the flutter test vehicle for envelope expansion.

Based on his reaction from your 1992 meeting with him, did Metz give any inklings on what the PSC F-23 was supposed to achieve?
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Zilch, nada. He couldn't have had a flatter affect. Then again, it was my first and only time interacting with someone possessing the Right Stuff -- but even the mighty Chuck Yeager would yuck it up.
 

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