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

F119Doctor said:
The other possibility is that Northrup knew that their YF-23 inlet design did not function well above M1.8, possibly resulting in excessive inlet distortion and engine stall. I don't know if this is true, but there may have been a reason that they did not demonstrate a Mn higher than the YF-22, and there was a significant inlet redesign for the EMD F-23.
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Very good point.

Don't know why I keep forgetting the total inlet redesign for the EMD version. *facepalm*
 
Given how amazing job they've done on the YF-23 model, I wrote to Top Mach Studio to consider crowdfunding the development of a model of the production F-23A version.

They agreed that it makes sense to consider this and they may do a poll to their users.

Lets do one here and I will send fwd them the results in few weeks.

The poll was added in this topic.

https://www.secretprojects.co.uk/th...os-for-microsoft-flight-simulator-2020.49210/

TeamWork.jpg
 
F119Doctor said:
The other possibility is that Northrup knew that their YF-23 inlet design did not function well above M1.8, possibly resulting in excessive inlet distortion and engine stall. I don't know if this is true, but there may have been a reason that they did not demonstrate a Mn higher than the YF-22, and there was a significant inlet redesign for the EMD F-23.
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I wonder if the suction panels on the YF-23 had a limit on how much boundary layer can be absorbed, before the increasing BL at higher Mach numbers make distortion unacceptable. While not a DSI, the conical compression bump (half shock cones) on the EMD F-23 design may have redirected the boundary layer flow path to make it easier to absorb with the BLC.

Northrop Grumman retained the same kind of inlet design for their later FB-23 RTA proposals, which leads me to believe that they were able to solve that problem.
 
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icyplanetnhc (Steve) said:
I wonder if the suction panels on the YF-23 had a limit on how much boundary layer can be absorbed, before the increasing BL at higher Mach numbers make distortion unacceptable. While not a DSI, the conical compression bump (half shock cones) on the EMD F-23 design may have redirected the boundary layer flow path to make it easier to absorb with the BLC.

Northrop Grumman retained the same kind of inlet design for their later FB-23 RTA proposals, which leads me to believe that they were able to solve that problem.
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That would be exactly my hypothesis. With the inlet aperture so close to the wing LE, BL growth is going to be almost exclusively shock induced, so that with increasing Mach it might at some point outpace the capacity of the bleed system seems highly plausible. Whereas with the EMD conical compression bump, the BL diversion effect due to the shock might have a favourable Mach dependence of its own.

I tend to think the bleed system on the EMD design would've been more about flow matching (avoiding spillage drag) than BL control. Actually, all else equal the bleed requirement for flow matching would likewise tend to increase with Mach number, possibly exacerbating the BL control situation more quickly in the YF-23 where unlike EMD the bleed was the only means of doing so.

EDIT: Be interesting to see how well this post ages... technical judgement while mildly concussed from a bike crash - what could possibly go wrong?
 
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The conical compression bump may have some effect on diverting the boundary layer but I don't think that's the main design consideration. On a true diverterless supersonic inlet (DSI) designed specifically to minimize BL entering the duct, the cowl is forward-swept and the aft-most point closes against forebody as mass flow ratio decreases to prevent much of the diverted BL from entering, and I don't really see that kind of geometry in the EMD F-23 inlet cowl. That said the the shock cone/bump may have a bit of BL diversion effect, or perhaps direct the flow path so that it can be bled more efficiently, although these DWGs don't really have the granularity to say what the exact mechanism would be.

The boundary layer control vents as seen on the YF-23 are still present in the EMD F-23 design, although the outer panel geometry is simplified. The general arrangement F-23A DWGs don't really show the internal BLC mechanisms or flow paths, although as general arrangement drawings these details are probably purposely omitted. I do agree that the BLC likely serves as a flow matching function for spillage drag and inlet stability (i.e. buzz) as well, unless there is a bleed system further downstream not depicted, which Paul Metz makes no mention of this in his book and the drawings don't have apparent indicators of additional vents further downstream.

I think it's also worth considering that on the contemporary NATF-23 design, inlet design is a serrated cowl with a compression bump shaped as a quarter cone similar to the F-111 albeit fixed in this case, and offset from the fuselage by a gap to bypass the BL. So the bump does not seem to have BL diversion as a main design consideration, certainly not to the extent of a true DSI.
 
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Do we know what Federal Standard color was used during the restoration process for PAV-1 on display at the National Museum of the USAF? From what I can gather the official color was never made public by Northrop (proprietary/classified?) and FS colors are assigned to production aircraft and not to prototypes. I've seen FS 36118 being suggested for model kit builds, but curious what the restoration team used. Overall, I'm intrigued on the color selection process and who determines the color (contractor or government)?
 
You can try to write to NG and USAFM restoration team.
 
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Ogami musashi said:
This comment from someone who was from a defense contractor back then, argue the f-22 had better thrust to weight ratio, longer range and higher gs limit. What do you think about that?
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The obvious question would be why he had that data on the other team's aircraft. No one on the YF-22 team should have known the specifics on the YF-23. Maybe some of their senior management would get that at the post-selection debrief, but how much would flow down to the rest of the team?

As mentioned by @lantinian, there's also the difference between the demval prototypes and the production aircraft to consider. How would Lockheed/Boeing/GD know what Northrop/McDonnell were offering?
 
whatismoo said:
Maybe from after boeing bought McDonnell?
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YF-22 selection, 1991
Boeing purchase of McD: 1997

At that point, why would anyone care?

And beyond that, why would an individual software engineer know that. You don't have time to deal with anything but the programme you're working on right now, and you don't have the need to know anything outside your immediate remit.
 
DWG said:
And beyond that, why would an individual software engineer know that. You don't have time to deal with anything but the programme you're working on right now, and you don't have the need to know anything outside your immediate remit.
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Spoken as true management? ;)
 
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Regarding the radone sizes, I always thought YF-23 had a smaller radome than the production F-22. We're both planes built to fly the same sized radar? and would a production version of the YF23 have had an enlarged radome?
 
The F-23A technical drawings have been public for years, so yes: the F-23A would have had a larger radome. YF-23 radome shape was dictated by the planned IRST window (a requirement that was dropped by the USAF after the Northrop demonstrator design was frozen) above the radar. The F-23A had the option to have an IRST fitted under the nose, freeing a useful volume in front of the cockpit.
 

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According to Aronstein, Hirschberg, & Piccirillo 1998, the YF-23's empty weight is listed as higher than the YF-22's, 37,000 lbs versus 31,000 lbs. That said, it's not clear if these empty weight figures are "apples to apples", i.e. is it the OEW, or airframe empty weight, etc. The contractor teams also had discretion on what they wanted to test and what equipment/instrumentation they wanted to install. Also, F-23 apparently has a slightly lower gross weight than the F-22, which is a bit eyebrow raising, but I think that should be caveated with the fact that we don't know what kind of weight growth the F-23 would have experienced if it had been selected. That said, I do agree that the F-22 having greater range seems unlikely, since the EMD F-23 DWGs indicate greater internal fuel volume, and while the F-22 was a significant aerodynamic improvement over the immature YF-22, I don't think it would have overcome the F-23's likely higher fuel fraction. But again we don't know what development challenges may have occurred if it had been selected.

I think one area we can say the F-22 had the advantage over the F-23 with some degree of confidence is that it probably had better sustained turn rate, since its wing aspect ratio is a tad higher. I'd wager the roll rate onset is also better since closely spaced engines likely had smaller moment of inertia.
 
excerpts from

ATF Contract Competitors Abandon Thermoplastic Resins as Major Material
MICHAEL A. DORNHEIM/LOS ANGELES

AWST Apriil 15, 1991

give some idea of weight penalties of YF-23A and weight savings prospectives looked for EMD F-23

Northrop’s materials emphasis is on composites, while Lockheed uses an equal amount of titanium. The Northrop Boeing Military Airplanes fabricated the wings for the Lockheed/Boeing/General Dynamics YF-22 in Seattle. Boeing also builds the composite outer wing panels for the Northrop B-2 bomber. F-23 proposal calls for approximately 50% composites, 20% titanium, 20% aluminum and 10% steel, according to Thomas R. Rooney, Northrop ATF program manager. Other materials, such as ceramics for possible use in the exhaust troughs, are not in this rough count. Lockheed’s F-22 is made of about 35% composites (20% thermoset and 15% thermoplastic), 33% titanium (22% 62222 alloy and 11% 6-4 alloy), 11% aluminum, 5% steel and 16% other materials. Northrop used about 35% titanium in the YF-23 prototype because it was quicker to make than some composite parts, and to cater for possible high engine bay temperatures that did not materialize.
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Northrop plans to use high-temperature aluminum alloys in place of some titanium and composites in parts of the engine bay, while Lockheed does not plan to use this alloy. Instead, the team will use thermoplastics in some engine bay applications.
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One of the most severe environments in Northrop’s design is the engine exhaust trough. Temperatures there reach 2,500F when the engine is in afterburner, and 1,500F at military power (maximum without afterburner). The troughs on the Air Force/Northrop B-2 bomber only reach 800F. The trough is loaded structurally, and sound levels are estimated at up to 180 dB., posing the threat of sonic fatigue. The company’s goal is to have the trough last the life of the aircraft, or 4,000 hr. Carbon-carbon material originally was proposed for the trough, but it appeared the substance would oxidize in just one flight, Rooney said. The prototype instead uses the actively cooled Lamilloy material developed by Allison. Lamilloy is made of layers of titanium sheet diffusion-bonded, with photo-etched cooling passages in each sheet. Rooney said drawbacks of the Lamilloy are that it is expensive and heavy. Engine bleed air is blown through the porous Lamilloy for cooling, which extracts a thrust penalty. Three passively-cooled alternate trough materials have proved promising in ground tests. “We’ve had some breakthroughs,” Rooney said. “We'll pick the lightest and cheapest for full-scale development.” One material is flexible blankets. They have been tested at full afterburner and are expected to last 1,000 hrs. Another alternate is ceramic tiles, and a third is ceramic matrix materials. Rooney believes ceramic matrix has the best prospects for light weight.
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Substitutes for steel are being considered in areas where there is a large potential weight savings. The Northrop ATF has two massive all-moving tail surfaces, rotating on steel spindles in the YF-23 prototype. The company has been testing spindles made of continuous fiber silicon carbide in a titanium matrix that promise up to 40% weight savings, which is important in the tail for proper balance.
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F-23 proposal calls for approximately 50% composites, 20% titanium, 20% aluminum and 10% steel, according to Thomas R. Rooney, Northrop ATF program manager. Other materials, such as ceramics for possible use in the exhaust troughs, are not in this rough count. Lockheed’s F-22 is made of about 35% composites (20% thermoset and 15% thermoplastic), 33% titanium (22% 62222 alloy and 11% 6-4 alloy), 11% aluminum, 5% steel and 16% other materials. Northrop used about 35% titanium in the YF-23 prototype because it was quicker to make than some composite parts, and to cater for possible high engine bay temperatures that did not materialize.
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I have to wonder if the F-23’s high percentage of composites is an area considered risky by the Air Force. I thought I recall reading somewhere that the YF-23 did have some thermal issues with the engine bay during flight tests (I don’t have Paul Metz’s book handy). The exhaust liners were another very risky area and I think the Lamilloy exhaust liners became a lawsuit between Northrop and Allison that was only settled in 2004.

And the EMD/production F-22 ended up being about 40% titanium and 24% composites (vast majority of which are thermosets). Some of that was because of the abandonment of thermoplastics, and some due to ballistic testing, whereafter every 5th wing spar was replaced by titanium. A tail fin buffet problem also caused the rear vertical tail spar to be changed to titanium. Lockheed Dem/Val program manager Sherm Mullin did say that the reduced application of composites was the main thing that he was disappointed with during the F-22’s development.

Overall I get the impression that there is perhaps more uncertainty and risk with what the weight of the F-23 is going to be, given the ambitious goals with the application of composites and also the uncertainty with exhaust liner material. Given the budget reductions and multiple re-baselines that the F-22 experienced in the 1990s during EMD, I’m not sure if the F-23’s technically riskier areas and potentially its weight growth would have fared better in that kind of financial environment if it were selected.
 
icyplanetnhc (Steve) said:
I thought I recall reading somewhere that the YF-23 did have some thermal issues with the engine bay during flight tests (I don’t have Paul Metz’s book handy).
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Right above:

"Northrop used about 35% titanium in the YF-23 prototype because it was quicker to make than some composite parts, and to cater for possible high engine bay temperatures that did not materialize."
 
The cooling airflow for the exhaust trough Lamilloy liners was fan bypass air bleed that was switched on during AB operation. This didn’t affect Mil power supercruise performance, but would reduce AB thrust by wasting the pressure energy of that bleed mass flow and reducing the amount of air available for AB combustion. The YF-22 / F-22 nozzle design didn’t have the AB thrust penalty.
 
F119Doctor said:
The cooling airflow for the exhaust trough Lamilloy liners was fan bypass air bleed that was switched on during AB operation. This didn’t affect Mil power supercruise performance, but would reduce AB thrust by wasting the pressure energy of that bleed mass flow and reducing the amount of air available for AB combustion. The YF-22 / F-22 nozzle design didn’t have the AB thrust penalty.
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Wouldn't it have been possible to increase the fuel flow, since ~3/4 of the airflow through a jet engine is unburned in the combustors, and therefore available for burning in the afterburner?
 
Scott Kenny said:
Wouldn't it have been possible to increase the fuel flow, since ~3/4 of the airflow through a jet engine is unburned in the combustors, and therefore available for burning in the afterburner?
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The bypass bleed air for the exhaust trough is reentering the gas pass flow at a low energy state in the boundary layer of the exhaust trough well aft of the augmentor combustion zone.

As the Turbine Inlet Temperatures continue to increase beyond 3000F with advances in turbine technology, we are probably getting toward the point where 1/2-3/4 of the air flowing thru the core is being burned. But the AB is intended to burn the remaining oxygen that passes thru the core plus any bypass air, minus the bypass air necessary to cool the augmentor liner and nozzle. Effectively, probably 90% of the air coming thru the engine inlet is being burned by the end of the AB (when functioning). Additional bypass air bled off for the trough is not available for combustion.
 
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F119Doctor said:
The bypass bleed air for the exhaust trough is reentering the gas pass flow at a low energy state in the boundary layer of the exhaust trough well aft of the augmentor combustion zone.
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Right. That's not the air I was talking about.



F119Doctor said:
As the Turbine Inlet Temperatures continue to increase beyond 3000F with advances in turbine technology, we are probably getting toward the point where 1/2-3/4 of the air flowing thru the core is being burned.
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Isn't more air required for cooling at those temperatures? Ergo, not available for combustion to make normal thrust?



F119Doctor said:
But the AB is intended to burn the remaining oxygen that passes thru the core plus any bypass air, minus the bypass air necessary to cool the augmentor liner and nozzle. Effectively, probably 90% of the air coming thru the engine inlet is being burned by the end of the AB (when functioning). Additional bypass air bled off for the trough is not available for combustion.
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Right. Once all the cooling air that flows through the engine it's available to burn in the AB. Add fuel in the AB until you've used all the oxygen (which yes means running super hot AB temps)

So you've got awesome AB thrust, but maybe reduced MIL thrust.
 
The Lamaloy tiles actively cooled the YF-23 aft deck with boundary layer air. The production F-23 was going to use advanced ceramic tiles/cooling solution to simplify things. From what I understand, Northrop had already developed the tiles so if they won, the tiles would have been ready for EMD and production, addressing a critical feature ahead of time.
 
Scott Kenny said:
Isn't more air required for cooling at those temperatures? Ergo, not available for combustion to make normal thrust?
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Typically, as TIT rises, more cooling air is directed to the turbine vanes and blades, as well as using it more effectively.

However, a larger portion of the core airflow is used for dilution in the combustor, lowering the combustor exit temperature from the local stoichiometric burning temperatures of 4000F+ down to the desired TIT levels and radial profile. This is the “unburned” air that is available aft of the turbine for AB combustion. As TIT levels go up, there is less combustor dilution air being used and less unburned air left over.
 
F119Doctor said:
Typically, as TIT rises, more cooling air is directed to the turbine vanes and blades, as well as using it more effectively.

However, a larger portion of the core airflow is used for dilution in the combustor, lowering the combustor exit temperature from the local stoichiometric burning temperatures of 4000F+ down to the desired TIT levels and radial profile. This is the “unburned” air that is available aft of the turbine for AB combustion. As TIT levels go up, there is less combustor dilution air being used and less unburned air left over.
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Thank you.

This is what I get for being ~25 years behind on engines.
 
Just spotted this Agile Manoeuvrable Fighter concept by Northrop from 1984 while watching


I tried to look for that specific drawing anywhere online and I believe it has not been posted here before.

The only other place I found it is on Facebook.

The top fuselage opening sidewinder bays are a definite highlight.

Also notable is how much the front view is similar to the YF-23, proving Northrop design was much more mature at the time of DEM/VAL contract award.
 

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Tony Chong summarized it pretty well both in his book and in this presentation with the WMOF, as did Paul Metz in his YF-23 book. Basically, AMF is basically a further evolution of N-360, with the main changes being wing position moving from high to mid-wing, and having two canted vertical tails rather than a single one, and retaining the two-dimensional thrust vectoring nozzle. AMF was the best performing in terms of aerodynamics between it, HSF, and USF ("Christmas Tree"), and when HSF became the preferred concept, Northrop spent a lot of work to reduce the aero performance gap between HSF and AMF.

Interestingly, as noted in Chong's presentation, AMF, HSF, and USF (being "black world" designs) were all quite different from the ATF RFI concepts that Northrop had submitted, which were all very small and light by comparison. If I were to hypothesize, I think HSF and USF emerged entirely from Bob Sandusky's fighter team within its "black world" B-2 division, while AMF was the aerodynamic performance yardstick and derived from more "white world" N-360, since I think "black world" can pull from "white world" but not vice versa. All the initial ATF RFI concepts were likely "white world" as well, especially since VLO was not yet a consideration.

By the way, the image of the flat plate models of AMF, HSF, and USF on the YF-23 Wikipedia article is literally a screenshot from that presentation by Tony Chong.
 
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Interesting to see that design by Daryl Harsha; it was made during the time that I was a Manager of Configuration design under Jerry Huben. The Northrop white world Advanced Design group evolved from the team that designed the F-18L, the land-based version of the F/A-18A. Security requirements at the time required that only US-born citizens could work on "black" programs so we were staffed with some excellent foreign-born engineers. The rest were off-site under Bob Sandusky developing the YF-23 and there was no cross- pollination between the teams. In fact at one point TW came over and confiscated all drawings of any designs that we had that utilized diamond wings! I think our primary purpose was to train new configuration designers fresh out of college while they waited for their clearances. Daryl was one of those and as soon as he got his clearance he left for the ATF Configuration group.
 
BillRo said:
Interesting to see that design by Daryl Harsha; it was made during the time that I was a Manager of Configuration design under Jerry Huben. The Northrop white world Advanced Design group evolved from the team that designed the F-18L, the land-based version of the F/A-18A. Security requirements at the time required that only US-born citizens could work on "black" programs so we were staffed with some excellent foreign-born engineers. The rest were off-site under Bob Sandusky developing the YF-23 and there was no cross- pollination between the teams. In fact at one point TW came over and confiscated all drawings of any designs that we had that utilized diamond wings! I think our primary purpose was to train new configuration designers fresh out of college while they waited for their clearances. Daryl was one of those and as soon as he got his clearance he left for the ATF Configuration group.
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As I recall you were at the presentation that Metz and Sandberg put on at the WMOF. Didn't Yu Ping Liu also have a part in that presentation?
 

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