Isn’t that the F-15SG?
The korean one?
With USAF number? No. OFC no.
Also no.
As u can see… There is USAF roundel.
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so basically F-15E trying to be F-15EX ?
Uh… Well, this aircraft is tech demonstrator/prototype of all Advanced Eagle series. Also this aircraft is Silent Eagle in ~2010
ok thx
I made mistake. This photo is after silent eagle program.
and this before. Maybe ~2003
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@quartas121 I don’t know how well the F-15E with PW-229 engines can supercruise, if it can at all. I’d hazard that it can’t very well for the following reasons; Note I am not an expert. I understand most of this from reading information on the internet. There may be inaccuracies or bad info and I am open to any corrections.
What permits supercruise and how the F-22 does it better;
Spoiler
To supercruise requires a much higher exhaust velocity than the free stream air around you. The force leaving the back of the plane simply has to overcome sufficient force from the front caused by the drag at supersonic speeds. Generally speaking, 1.6 mach has 3x the drag penalty as 0.8.
The F-22 can supercruise at “mach 1.7+” - indicating that the “+” expands well beyond mach 1.7.
The reason for this is simple, they want the engine to be able to supercruise at a lower speed and then pull back the throttle a little bit. Designing the engine around supersonic operation and at thrust levels that can push it beyond the efficient cruising speed are a part of ensuring you have “overhead”. The engine is stressed out pushing the aircraft to 1.7 mach, but the temperatures and pressures at 1.5 mach are far more tolerable. The fuel efficiency in that range is optimized. Lifespan is improved. It can sit at that speed for a considerable amount of time.
To achieve a high exhaust velocity in a turbofan, you have to first understand the basic concept of a turbofan.
Spoiler
Again, generally speaking, the turbojet requires a jacket surrounding the engines hot sections to protect the airframe from the heat. The turbofan eliminates the need for so much dead weight by cooling the outer shell of the engine. Inlet air is compressed and sent through the core, but also around the core through the “bypass”. Beyond this, the cooling air improves efficiency of the engine and adds fresh oxygenated air to the exhaust that can be utilized to improve the performance of the afterburner - vastly increasing the exhaust velocity. It also allows a higher pressure ratio at the throat of the nozzle without overheating it by providing a boundary layer of cooler air.
Now, what factors affect supercruise?
Spoiler
-
Bypass ratio
– the amount of air going around the core is slowed to often times below 0.5 mach for turbofans in fighter jets. The more you can compress the air before it ever even enters the engine - the better. Less wear on the engine and less additional stages needed.
– The flop side of that is that the bypass air is also slow. When it enters the exhaust stream the core flow also needs to work harder to mix with the cold and slow air. This means more work is put towards the turbine and not towards the exhaust. This results in less thrust and if not designed properly - can result in worse performance. -
Pressure ratio
– The pressure ratio is generally calculated from all of the points of the engine to find the overall average pressure ratio. The important thing to note is that a higher internal pressure means a higher exhaust velocity in most cases. The pressure ratio is kept as high as possible at most times in the engine with the limiting factor being temperature. As the air comes in the front it is heated up by friction. Once the compressor air reaches a temperature limit (T3), the engine must dial back the pressure or risk damaging itself. There are a multitude of ways to reduce the temperature, but for supercruise this is the important part. -
Temperature limits
– The temperature limits for the cold side and the hot side are most important here. The larger the difference between the compressor (cold) temps and the turbine inlet (hot temps), the higher the thrust will be for a given engine.
– The F-15E’s PW-229 has a very low turbine inlet temperature limit, and thus is limited heavily on the amount of dry supersonic thrust it can make. By comparison the EJ200 was thought to be able to push a conventional tailed aircraft (not optimized for supersonic drag) to only ~1.13 mach in a study by the British Defense Research Agency in 1995 with a slightly larger bypass, slightly lower pressure ratios, and much improved temperature limit.
How does the F-15 compare to other gen4 ‘supercruisers’?
Spoiler
The F-15E is powered by the PW229, I will compare it to the EJ200.
(F-15 / EFT)
Bypass ratio: 0.36 / 0.4
Pressure ratio: 32 / 26
Temp limit: 1620K / 1800K
These are some of the important factors at a glance to understand. What you must also consider is that the Typhoon is CONSIDERABLY better optimized in regards to the airframe for supersonic flight. It requires far less thrust than the F-15E to achieve the same given airspeed.
Now, the bypass ratio is lower which is good because the amount of energy in dry thrust needed to spin the turbine and accelerate the bypass flow is less. The pressure ratio is higher, which is also good. The issue stems mostly from the very low temperature in the hot section of 1620K. The British Defense Research Agency presented a paper in a 1995 symposium on advanced engines. They detailed the EJ200 explicitly as a datapoint to compare “future engines” to. In there, they discovered that with a lower pressure ratio they were already reaching a temperature limit at the turbine that prevented their mock-up fighter (tailed, similar to F-15 layout) from reaching more than 1.13 mach maximum in supercruise. Even the improved variant modified primarily for the intercept job maxed out at 1.43 mach. These were with lower pressure ratios and a higher turbine inlet temperature limitation.
Note that with a higher pressure ratio, you will reach temperature limits earlier in the flight envelope than an engine that has lower pressure. Naturally the temperature of the inlet air increases with airspeed, it takes more effort to compress the air and slow it down to subsonic speeds before it enters the engine. The Eurofighter has an alleged limit of 1.5 mach in supercruise. This means the efficient range will be far lower. The expected efficient supercruise range imo will be somewhere around 1.3 or less. The F-15E by comparison, with a draggier airframe and similar specifications will run into the temperature limit sooner.
To enhance supercruise performance;
A variable bypass can be used, to allow more or less air to bypass the core. The temperature limits for the cold and hot sections must be increased to allow lifespan overhead for such use. Ideally there will be an optimized gap between compressor and turbine temperatures to allow efficient operation in dry supersonic cruise conditions. All of these variables must be optimized on a per-case basis and matched with the airframe in mind to create the best conditions and supersonic cruise MUST be a requirement in the basic design parameters.
This is of course, not everything. There is more to go over but I do not have the time or information to confirm the data for these two engines as the info is still somewhat under wraps.
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With normal real config - cft with pylons. It certainly cant. The drag on that plane is insane.
Right, so my post is pretty accurate. The PW-229 is slightly worse for supercruise than the EJ200 and the airframe is far draggier. Interesting that it can in theory “supercruise”.
Yep, it’s not even statically unstable so there is also the concern of trim drag and other things that the Typhoon would benefit from - aside the fact that the Typhoon’s airframe configuration (Canard Delta) has CONSIDERABLY better wave drag.
So, Variable Bypass Ratio F100 is needed.
F100-PW-232 would probably be better suited for supercruise as it incorporates some F119 technologies, likely enhancing temperature limits. It was not pursued. It’s said that it can produce the same thrust as the PW-229 but inspection intervals increase by 40% when doing so, I suspect this indicates a lower bypass ratio and higher temp limits to create more of the thrust from the core but that’s just a uninformed guess.
With the Rafale getting its AESA radar, should we expect the MSIP-II to get the 63V2/V3? Or would it not make a difference with how the developers are handling AESA implementations.
Definitely not now
hopefully first update of 2025
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It is more realistic
I feel like there is some very specific conditions where it can accelerate to mach without afterburner, because there is a warning about passing mach without afterburner at altitude during level flight in the flight manual
F15Cs and F15Es missing HPRF TWS
F15Cs and F15Es missing target aspect in HUD
F15 missing missile’s time to impact for sparrows
F15 HUDS showing incorrect closure rate.
F-15 HUDs are missing target range, Rmax2 and incorrect range scale
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It can, up to M1.15 actually. It’s M1.15 at 40klb clean.
From what I have read, a supercruise capability is not truly efficient unless the engine has been designed with it in mind AND the aircraft can ‘cruise’ at an airspeed above mach where wave drag is no longer affecting it as much. This usually occurs above 1.3-1.4 mach. Thus, it is generally considered “supercruise” only when an aircraft can cruise on dry thrust at speeds of 1.5 mach or higher.
That being said, the definition is not specified by any governing body very well so if it is simply surpassing the sound barrier on dry thrust… then yeah a lot of aircraft can do that.