F-16.net

Hey all,

I've been wondering why the F-22 wasn't designed with Diverterless Supersonic Inlets (DSI) similarly to the F-35, rather than a traditional BL diverter?

My two theories are:

1) The tech just wasn't available during the initial design phases.

2) There is some limit on speed that the DSI imposes that would render it impractical for the F-22.

Any input? My apologies if this has been brought up before...

Thanks!

Rhoads

The F-22 and F-35 are optimized for different speed ranges.

wrightwing wrote:The F-22 and F-35 are optimized for different speed ranges.

Yes, I just wonder if the DSI tech was mature back then or not. Is DSI less favorable for supercruise well above M1?

Rhoads

The DSI development was a direct result of the experience with the F-22 inlet. It was found that the F-22 inlet configuration was complex and difficult to manufacture with boundary-layer diverter and various bleed air holes, ducts and doors. With the advent of Computational Fluid Dynamics (CFD), engineers could instead design a bump that actually divert the boundary layer flow away from the inlet opening without being ingested into the inlet duct and by the engine. The use of DSI resulted in a much simpler and lighter inlet design that also provide some signature benefit. The basic concept was thoroughly flight tested in a modified F-16 Viper during the early to mid 1990's to provide risk reduction for later F-35 application.

I am go for 1). DSI design requires huge amount of CFD simulation. Basically put the inlet and bump into virtual space, build a mesh around them, with millions and millions of nodes connected to each other. Then solve the pressure on each node with some mathematical magic. Repeat different inlet/bump configurations under different condition (mach numbers, ect). Until find the best one.

Generally the finer the mesh is, more accurate the result is supposed to be. But finer mesh will have a lot more nodes, way more memory and computing hours. Pre-mid-1990s computers (ancient technology comparing what is available now) were not capable enough for this kind of work.

One can view two photos of the Viper test aircraft with the DSI modification in the Hall of Fame Gallery within this site;

http://www.f-16.net/aircraft-database/F ... file/1450/


11 Dec 1996 [act] 83120 USAF USAF 416 FTS F-16C Block 25



F-35 Inlet Installed
Modified inlet as an X-35 test bed with General Electric F110-GE-129 engine. This inlet resembles the airflows that are created when flying with the X-35. The flight test program consisted of twelve flights flown in nine days in December 1996.

Here is the CodeOne Magazine article about the F-16 testbed for DSI.

http://www.codeonemagazine.com/article.html?item_id=58

Can someone teach me how to insert a photo into a post? I have no luck at all. Copy & paste does not work. What is the Img button for?

If the image is on the web (like imgur.com), then put the url of the image between the [img] brackets.

Code: Select all

[img]http://www.google.com/intl/en_ALL/images/logo.gif[/img]

If the image is coming from your computer, then use the "upload attachment" process located below the text window.

When you are entering text in a post, you will notice a "BBCode" url on the right, click it and there are instructions.

faq.php?mode=bbcode

As others have mentioned, it's due to the fact that the F-22 is an older plane that was designed back when the industry was making the transition from primarily relying on classical analytical theory (ie pencil and paper calculations) to primarily using computer-based numerical methods such as Finite Volume or Finite Difference solution schemes for assessing the aerothermodynamic properties of intake designs. The ubiquity of CFD numerical methods that could be run on personal computers from the 1990s onwards basically made it possible to cheaply design and analyze a specifically contoured bump that could generate surface pressure distributions that could passively force boundary layer air away from the inlet without the use of a diverter or splitter plate.

CFD was in use during the F-22 design era but was mainly relegated to rudimentary verification of a few aerodynamic aspects here and there. For the F-35 CFD was crucial to the design of the DSI as the precise shape of the bump was something that needed to be perfected at minimal cost in order to work to an acceptable degree of effectiveness.

rhoads56 wrote:

wrightwing wrote:The F-22 and F-35 are optimized for different speed ranges.

Yes, I just wonder if the DSI tech was mature back then or not. Is DSI less favorable for supercruise well above M1?

Rhoads

In other words, the inlet designs used in the F-22 and F-35 differ, due to the speed range that they're optimized for, not due to available technology. The F-22's super cruise speeds are near the max limits of DSI, and its top speed exceeds those limits.

It is generally acknowledged that Lockheed Martin F-35 is the first aircraft to apply the DSI technology after a thorough developmental effort that culminated in the F-16 flight test in the mid 1990's. Nonetheless, Chinese Chengdu fighters J-10B, J-17, and J-20 all have been observed to have adopted also the DSI in recent years. The J-17 DSI was shown in a photo below. It has been a puzzle to me why the J-17's DSI is full of bleed air holes. Was the DSI design deficient such that corrective measure was needed? Of course, the Chinese are more sensitive about the J-20, and no close-in photo of the DSI has been seen in public to my knowledge. Maybe someone in this Forum can shed some light on this matter.

I guess that I just do not know how to post a photo in this forum!

If interested, someone can Goggle "Diverterless Supersonic Inlet" and look at the thousands of photos of DSI. Most of them are of the Chengdu fighters.

scat wrote:It is generally acknowledged that Lockheed Martin F-35 is the first aircraft to apply the DSI technology after a thorough developmental effort that culminated in the F-16 flight test in the mid 1990's. Nonetheless, Chinese Chengdu fighters J-10B, J-17, and J-20 all have been observed to have adopted also the DSI in recent years. The J-17 DSI was shown in a photo below. It has been a puzzle to me why the J-17's DSI is full of bleed air holes. Was the DSI design deficient such that corrective measure was needed? Of course, the Chinese are more sensitive about the J-20, and no close-in photo of the DSI has been seen in public to my knowledge. Maybe someone in this Forum can shed some light on this matter.

This is a decent image of the J-20's inlet. The bump itself doesn't seem to have holes, but there are porous plates right behind the intake.

That's either a photoshop of the best picture of the J-20 I've seen, referring solely to the quality of the image.