Engine inlet bleed doors removed?

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disconnectedradical

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Unread post04 Nov 2022, 14:29

So on the F-22, the first two dozen aircraft had these inlet bleed doors a few feet behind the inlet, but they were deleted afterwards. What were these bleed doors for and why weren't they needed anymore? There's already the serrated overpressure or spill doors located further back near the engines.
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f119doctor

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Unread post05 Nov 2022, 06:28

The inlet bleed doors opened under high AOA conditions to increase the boundary layer bleed flow to reduce inlet distortion to the engines and also provided additional nose down pitch authority. They were deleted after EMD flight testing determined that they were not needed for either of these. Reduced cost, weight, complexity, maintainability, and probably improved the signature.
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Unread post05 Nov 2022, 17:15

Are the grids behind those doors meant for inlet boundary layer bleed?

One thing about F-22 is it doesn’t have the scoop inlets for cooling and ventilation like on the F-35. How does it handle the cooling? Does F119 bleed air provide that? I saw a RAND table showing airflow of F119 as 266 lb/s, but also only 30,000 lbs of thrust, so maybe that’s the YF119? That’s about how much airflow is in F110, and I would think F119 has more.
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wrightwing

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Unread post05 Nov 2022, 18:09

disconnectedradical wrote:Are the grids behind those doors meant for inlet boundary layer bleed?

One thing about F-22 is it doesn’t have the scoop inlets for cooling and ventilation like on the F-35. How does it handle the cooling? Does F119 bleed air provide that? I saw a RAND table showing airflow of F119 as 266 lb/s, but also only 30,000 lbs of thrust, so maybe that’s the YF119? That’s about how much airflow is in F110, and I would think F119 has more.

35,000lbs is a conservative rating for the F-119. Years ago, I'd see ratings between 37,000-39,000lbs listed.
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disconnectedradical

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Unread post05 Nov 2022, 19:57

wrightwing wrote:
disconnectedradical wrote:Are the grids behind those doors meant for inlet boundary layer bleed?

One thing about F-22 is it doesn’t have the scoop inlets for cooling and ventilation like on the F-35. How does it handle the cooling? Does F119 bleed air provide that? I saw a RAND table showing airflow of F119 as 266 lb/s, but also only 30,000 lbs of thrust, so maybe that’s the YF119? That’s about how much airflow is in F110, and I would think F119 has more.

35,000lbs is a conservative rating for the F-119. Years ago, I'd see ratings between 37,000-39,000lbs listed.

YF119 had a smaller fan and was designed for original requirement of 30,000 lbs.
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Unread post05 Nov 2022, 23:51

disconnectedradical wrote:Are the grids behind those doors meant for inlet boundary layer bleed?

One thing about F-22 is it doesn’t have the scoop inlets for cooling and ventilation like on the F-35. How does it handle the cooling? Does F119 bleed air provide that? I saw a RAND table showing airflow of F119 as 266 lb/s, but also only 30,000 lbs of thrust, so maybe that’s the YF119? That’s about how much airflow is in F110, and I would think F119 has more.


That is correct, the grids behind the doors is the fixed boundary layer bleed from the perforated inner and upper inlet ramp areas, and the doors would augment this bleed under certain challenging conditions.

The F-22 utilizes the inlet splitter flow for cooling in place of any external scoops. This flow exits from the grills behind the cockpit. The moveable gills on the back of the aircraft are to increase total inlet flow to maintain inlet performance and stability when the engine is not flowing enough air to keep the inlet happy. The F-15 & F-16 keep the engine at a minimum of Mil power when above 1.4 Mn to prevent inlet buzz. Hard to slow down in the F-22 when Mil gives you supercruise at 1.5+ Mn. There is compressor bleed flow to an air cycle machine for cockpit pressurization and system cooling.

Don’t believe the speculation on F119 thrust of 37k+. The Rand numbers are not accurate either. Remember that even if the F119 airflow was in the same ballpark as the F110, its fan pressure ratio and nozzle pressure ratio are significantly higher, giving higher Mil ratio thrust at both static and especially supersonic conditions. Because it is a lower bypass ratio, there is a lower percentage increase in static thrust from Mil to AB than in the F110, even though the AB thrust is higher. The F119 thrust ratings have not changed since initial production, except for the recent engine OFP update that does increase thrust in parts of the flight envelope where hot section life is not significantly impacted. There have been no thrust increasing hardware updates.
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disconnectedradical

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Unread post06 Nov 2022, 00:16

The speculation of higher thrust might be from conditions other than static numbers. Like how the F110-GE-400 on F-14B is rated for 28,000 lbs, but reaches 30,200 lbs at Mach 0.9 at sea level.

I thought the serrated doors on the back of the F-22 is meant for dumping excess air, but it can also increase airflow when necessary?

I think a core update on the F119 can provide some decent improvements to fuel burn and possibly thrust now, with more than 20 years of newer technology available.
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Unread post06 Nov 2022, 15:13

disconnectedradical wrote:The speculation of higher thrust might be from conditions other than static numbers. Like how the F110-GE-400 on F-14B is rated for 28,000 lbs, but reaches 30,200 lbs at Mach 0.9 at sea level.

I thought the serrated doors on the back of the F-22 is meant for dumping excess air, but it can also increase airflow when necessary?

I think a core update on the F119 can provide some decent improvements to fuel burn and possibly thrust now, with more than 20 years of newer technology available.


Yes, the thrust of the engine will vary throughout the flight envelope, depending on inlet conditions. Higher in the lower right corner with high ram pressures, very much lower in the upper left corner with low inlet pressure. If accurate, 30k thrust for the F110-100/400 at 0.9mn sea level is pretty pathetic since the ram inlet pressures are nearly 2x static pressures- should be 40-50k with double the fuel flow in those conditions. There must be a significant cutback on these engines under hot ram to protect some feature of the engine. I have read that the -129 is significantly better in the lower right corner than the earlier versions of the F110.

The bypass door dump extra air overboard that cannot be processed by the engine. They open when engine airflow is less than the inlets need to flow for stable operation, such as when the throttles are pulled back to slow down from supercruise conditions. There may be other flight conditions where increasing inlet airflow improves supersonic ram recovery performance enough to add more system thrust that offsets the drag caused by the overboard bleed of the air. These bypass door opening is controlled to dump a controlled amount of air that varies by flight condition and engine airflow. The doors do not increase engine airflow, only inlet airflow as necessary.

The F135 core is advanced over the F119 core even though they are very similar, and rolling the F135 tech into the F119 during depot overhaul has been studied. I’m pretty sure that the F135 EEP core technology could also be incorporated if the USAF wants to invest in F-22 improvements. The EEP tech would likely reduce fuel consumption and might enable some thrust increases in parts of the flight envelope, although these would probably be limited if the fan airflow and pressure ratio remains the same
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Unread post06 Nov 2022, 20:51

Application of F135 EEP or even the XA101 core should allow better pressure ratio, and I think more airflow can be better too because that can allow more bleed air for cooling. That said, does the F-22 inlet even have the capacity for additional airflow across the envelope? Since F119 hot section overhaul is shorter than the cold section, would upgrades be inserted during depot overhauls?

EEP core might be relatively easy to integrate but the XA101 core might be more difficult, but according to a USAF ADVENT/AETP slide, a scaled A101 core can improve range by 18%, which is pretty big.

One other thing, you’ve mentioned that integrating the F119 into older airframes may be difficult because it’s bigger in diameter but also shorter. But even the YF119 is longer than F100 at 203 inches versus 191 inches, and the YF119 is smaller than the F119. Is this because the F119 has a stealthy afterburner and special flat nozzle (which wouldn’t go on older airframes), while the actual turbomachinery from the fan, compressor, and turbines are shorter?
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Unread post08 Nov 2022, 00:34

disconnectedradical wrote:Application of F135 EEP or even the XA101 core should allow better pressure ratio, and I think more airflow can be better too because that can allow more bleed air for cooling. That said, does the F-22 inlet even have the capacity for additional airflow across the envelope? Since F119 hot section overhaul is shorter than the cold section, would upgrades be inserted during depot overhauls?

EEP core might be relatively easy to integrate but the XA101 core might be more difficult, but according to a USAF ADVENT/AETP slide, a scaled A101 core can improve range by 18%, which is pretty big.

One other thing, you’ve mentioned that integrating the F119 into older airframes may be difficult because it’s bigger in diameter but also shorter. But even the YF119 is longer than F100 at 203 inches versus 191 inches, and the YF119 is smaller than the F119. Is this because the F119 has a stealthy afterburner and special flat nozzle (which wouldn’t go on older airframes), while the actual turbomachinery from the fan, compressor, and turbines are shorter?


On a military mixed flow turbofan, thrust is primarily a function of fan airflow and pressure ratio. The core determines where in the envelope that the fan can achieve its design airflow and pressure ratio. As the intake temp goes lower, the core does not have to provide as much of its design capacity to drive the fan to its capacity. As the inlet temp goes up (roughly 100F at 1.5M at altitude), the core is pushed to its limits to keep the fan at full capability. At some point, the fan / LPT reaches it max mechanical rotor speed and airflow will drop off with increasing inlet temp regardless of the core capability to drive the low rotor.

The F135 current core primarily has a more advanced hot section than the F119, along with some cost and complexity reductions. As I hear it, the EEP core is an improved high compressor with increased adiabatic efficiency, which takes less power to drive and lowers compressor discharge temps, both of which reduce turbine inlet temps, all things remaining constant. Higher turbine temp capability along with lower turbine temps gives longer life, more ability for customer bleed air off take, and the ability to drive the fan to full flow / pressure ratio over a larger portion of the envelope, or utilize any overflow capacity that is available. Most fans can flow more air than their design point by turning faster within their mechanical speed limit, but there is a penalty in fan efficiency and stall margin in this overflow condition.

The F119 has the shortest augmentor of any modern turbofan. The 2D nozzle may be a little longer with the long divergent
flaps. Even though the compressor has fewer stages than earlier engine, the fan and compressor all have wide chord airfoils that add axial length to those portions of the engines
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disconnectedradical

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Unread post09 Nov 2022, 13:51

So the ADVENT/AETP chart shows a scaled core would improve range on F-22 by 18% but on F-15 and F-16, it increases range and thrust. Is that because the core of older engines like F100 and F110 doesn’t allow the fan to be driven at full capability, while on the F-22 the fan is the limiting factor?

Image

Would the F119 be shorter than F100 and F110 if it weren’t for the nozzle then? It has fewer compressor and turbine stages and a short afterburner but overall length is quite a bit higher, which I thought is because of the nozzle.
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Unread post09 Nov 2022, 14:30

F119 is a generational leap from F100 and F110. The fan, compressor, turbine, combustion chamber are all different. The performance of mil turbofan is limited by a number of factors. From inlet to nozzle, every component has its limits. Plus the atmospheric conditions.

The nozzle is an integral part of the engine. Does it matter if it is longer or shorter without the nozzle?
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Unread post09 Nov 2022, 19:21

disconnectedradical wrote:So the ADVENT/AETP chart shows a scaled core would improve range on F-22 by 18% but on F-15 and F-16, it increases range and thrust. Is that because the core of older engines like F100 and F110 doesn’t allow the fan to be driven at full capability, while on the F-22 the fan is the limiting factor?

https://pbs.twimg.com/media/E2hAh-uWQAM ... =4096x4096

Would the F119 be shorter than F100 and F110 if it weren’t for the nozzle then? It has fewer compressor and turbine stages and a short afterburner but overall length is quite a bit higher, which I thought is because of the nozzle.


I think you are misinterpreting the AETP slide. When it says a scaled AETP core could be applicable to F-15/F-16/F-22, I believe they are saying that a new adaptive engine with scaled AETP core could be developed for those application, not that a scaled AETP core could be inserted into the existing engines. The small print "or Component applications" would be the insertion of AETP developed advance hardware technologies into the existing engines.

As I noted before, the wide chord airfoils used in the F119 Fan and High Compressor make each individual stage longer, even though there are fewer of them. The F119 fan with 3 stages is definitely longer than a F100 fan module. The LPT with one stage is shorter than the F100 2 stage LPT, but the multifunction Turbine Exhaust Case is significantly longer than the F100 TEC. If you designed a round nozzle for the F119, it would be lighter and probably shorter, although you would lose the long divergent section with highly variable exit area that optimizes the supersonic expansion needed for supercruise performance.

Remember that the nozzle itself is usually mounted aft of the airframe structure (i.e. length is not a limitation). In addition, closely spaced round nozzles are hard to integrate cleanly with the airframe, resulting in high levels of turbulence around the nozzle, which is the reason the external nozzle flaps were removed from the F-15 and B-1B (they kept breaking). Widely spaced engines (F-14, Su-57) are cleaner to integrate, but they increase supersonic base drag and bring asymmetric thrust issues to the table (ref: Modern Combat Aircraft Design - Klaus Huenecke).
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Unread post09 Nov 2022, 20:14

zhangmdev wrote:F119 is a generational leap from F100 and F110. The fan, compressor, turbine, combustion chamber are all different. The performance of mil turbofan is limited by a number of factors. From inlet to nozzle, every component has its limits. Plus the atmospheric conditions.

The nozzle is an integral part of the engine. Does it matter if it is longer or shorter without the nozzle?


The length question is more of a theoretical exercise of fitting F119 on older airframes. The bigger diameter means that only something like the F-14 or F-111 would fit, but apparently the length can also be an interfacing problem.

f119doctor wrote:As I noted before, the wide chord airfoils used in the F119 Fan and High Compressor make each individual stage longer, even though there are fewer of them. The F119 fan with 3 stages is definitely longer than a F100 fan module. The LPT with one stage is shorter than the F100 2 stage LPT, but the multifunction Turbine Exhaust Case is significantly longer than the F100 TEC. If you designed a round nozzle for the F119, it would be lighter and probably shorter, although you would lose the long divergent section with highly variable exit area that optimizes the supersonic expansion needed for supercruise performance.


I’m surprised the turbine module is longer, since F119 not only has fewer HPT and LPT stages, but being counterrotating means there’s no turbine stator too. I’m assuming there turbine has other functions that makes it longer?

About the nozzle, I remember in the mid-2000s where there was talk about future F-22 variants having a round F135-like LOAN nozzle for additional thrust and less weight, but maybe the additional drag offsets that? This was mentioned for the FB-22.
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Unread post09 Nov 2022, 23:39

disconnectedradical wrote:
I’m surprised the turbine module is longer, since F119 not only has fewer HPT and LPT stages, but being counterrotating means there’s no turbine stator too. I’m assuming there turbine has other functions that makes it longer?


Having fewer parts doesn't equate being smaller or shorter.

F119 doesn't have turbine stator is a much repeated misconception. The PW PR drawing of the F119 shows there is stator before the low pressure turbine.
f119.jpg
F119 PR
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