F-16 Inlet Variants

flateric

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From AIAA-81-1394
F-16 Variable-Geometry Inlet Design and Performance
L.G. Hunter and J.E. Hawkins
General Dynamics/Fort Worth,TX

"Advanced versions of the F-16 are being considered
to upgrade its present mission capabilities
as well as to expand its capabilities to embrace new
more demanding missions. The addition of a variable
geometry inlet (VGI) to the F-16, made possible by
the modular construction of the aircraft, has been a
designed-in capability since the start of the F-16
program. Fig. 1 illustrates the variable-geometry
inlet option being considered for advanced versions
of the F-16 currently in the prototype development
stage at General Dynamics' Fort Worth Division. Both
the variable-geometry and normal-shock inlet options
are available with the final choice dependent on the
future mission requirements of a production aircraft.
Fig. 2 illustrates the performance benefits of a
relatively simple, conformally shaped, variable-ramp
inlet design that has been developed for F-16 application.
Increased acceleration and higher speeds
to reduce intercept times, higher sustained load
factors and turn rates to outmaneuver advesary aircraft,
and greater persistence to enhance multiple
target and reattack capability at high supersonic
speeds, are chief benefits.
 

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Hmmm I think Elmayerle already talked about this intake, at least on the whatif modelers forum...
 
It would make a lot of sense for the F-16XL in its SCAMP iteration, with the emphasis on supersonic cruise, to have such an intake to improve performance at high Mach numbers.
 
Archibald said:
Hmmm I think Elmayerle already talked about this intake, at least on the whatif modelers forum...

I'm rather rare visitor there, so didn't see it - moreover, I always think that it's better see it once than hear of it thousand times)))
 
The F-16 inlet is a mixed-compression (at least two-shocks in the duct) inlet right?

KJ_Lesnick
 
I don't remember from my aero classes...but I did fly the F16...and always understood it to be a "simple" inlet...all subsonic flow inside the inlet. Isn't the plate above the inlet to create the shock so that all flow is subsonic?
MMO is 2.05, 800KCAS at low altitudes.
Also - there are two inlets...SI (small inlet) and BI (big inlet). The latter added 6 inches to each side of the "smile" and was for the increased mass flow needed for the GE engines (F110-100/129/134). I flew GEs with both SI and BI - and it was amazing the thrust increase just from the extra air.
 
Kind of odd that they managed to make a pitot-inlet work effectively at high-speed. From what I was told the F-16 had great acceleration at high-supersonic speeds,

KJ
 
KJ_Lesnick said:
Kind of odd that they managed to make a pitot-inlet work effectively at high-speed. From what I was told the F-16 had great acceleration at high-supersonic speeds,

KJ

Transonic and low supersonic, yes. Mach 2, not so much.
 
You know, looking at that duct, it looks like it has a notable convergent divergent shape to it. Could be wrong here but that generally looks like it wouldn't be subsonic from the entry to the exit.

DSCN0778.jpg


Could be wrong though


KJ Lesnick
Let's hope I don't get a heart-attack :p
 
This was the picture I wanted to post
 

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F-16 inlet (both 'old' "small mouth" Normal Shock Inlet (NSI) and 'new' "big mouth" Modular Common Inlet Duct (MCID)) are Normal Shock Inlets. http://www.habu2.net/vipers/viperblocks/
It's convergent divergent diffuser inlet actually.
I'm attaching some pics that can make situation more clear.
 

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flateric said:
F-16 inlet (both 'old' "small mouth" Normal Shock Inlet (NSI) and 'new' "big mouth" Modular Common Inlet Duct (MCID)) are Normal Shock Inlets. http://www.habu2.net/vipers/viperblocks/
It's convergent divergent diffuser inlet actually.
I'm attaching some pics that can make situation more clear.

I'm actually more confused!

The second picture appears to show multiple shock-waves, and the 4th picture shows clearly "Oblique Shock" which is a shockwave that slows flow from a supersonic to a lower, but still supersonic speed... not a normal shock which slows you down from a supersonic to a subsonic speed...

While I'm at it, I might as well ask some other questions
-What's that thin rod-like thing in the inlet duct (standing vertical in the middle of the duct)?
-What's the ECS-inlet?
-In the third image on the underside of the fuselage ahead of the intake are several markers (HRF3/F14, HRF2/F1, HRF1/F13)


KJ_Lesnick
 
KJ_Lesnick said:
The second picture appears to show multiple shock-waves, and the 4th picture shows clearly "Oblique Shock" which is a shockwave that slows flow from a supersonic to a lower, but still supersonic speed... not a normal shock which slows you down from a supersonic to a subsonic speed...

True. Those pictures you mention probably apply only to the J-79 powered F-16-79 as indicated by the file name. That inlet seems to be slightly different to the standard Falcon intake, looks like it used an oblique shock followed by a curved isentropic compression ramp to slow the air to subsonic speeds before entering the divergent duct section of the standard F-16 inlet. I'm not sure whether the latter has a convergent section at all.

KJ_Lesnick said:
-What's the ECS-inlet?

Environmental Control System?
 
ı don't have anything to say but I do remember that the J-79 engined aircraft "had the shocks" , can't truly translate it from the idea in my mind in Turkish , but the rest of the F-16s had simple inlets .
 
The F-16's inlet is a pitot inlet and the bar in the middle, based on what I've been told, is a heater for anti-icing.
 
"...a thin, centerline, airfoil-shaped tension strut member
inside the cowl, which minimizes cowl deflections under load and allows a lighter
and less costly structural design. Flow quality is not affected by the strut."

YF-16 INLET DESIGN AND PERFORMANCE
J. E. Hawkins
Senior Propulsion Engineer
General D'ynamics' Fort Worth Division
Fort Worth, Texas

AIAA 74-1062
 
And now for something completely different...
 

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Mach 2 in an F-16? That's impressive; I thought it topped out around M1.6. That inlet design looks dead sexah, too.
 
"...a thin, centerline, airfoil-shaped tension strut member
inside the cowl, which minimizes cowl deflections under load and allows a lighter
and less costly structural design. Flow quality is not affected by the strut."

Thanks, I had wondered about that, but didn't have any evidence for it.
 
If the F-16's inlet was highly limited in speed, where did all that stuff I heard awhile back online about the F-16 accelerating particularly well at supersonic speed (something a typical pitot-type inlet wouldn't be able to do very well) come from? ???


Kendra Lesnick
 
M2.2 inlet design for F-16. May be similar to what was installed on the F16/79.
 

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KJ_Lesnick said:
If the F-16's inlet was highly limited in speed, where did all that stuff I heard awhile back online about the F-16 accelerating particularly well at supersonic speed (something a typical pitot-type inlet wouldn't be able to do very well) come from? ???


Kendra Lesnick

It wasn't a pitot inlet, really. There is a compression ramp (which also serves as a boundary layer splitter), but it was fixed at one setting (probably optimized for M1-1.2 or so, I'd guess). Getting good higher supersonic performance means you'll want a variable inlet ramp.
 
KJ_Lesnick said:
Getting good higher supersonic performance means you'll want a variable inlet ramp.

Neither the XF8U-3 nor F-22 have a variable inlet ramp and have no problem with Mach 2+ speeds. There is more than one way to skin a cat.
 
Last edited:
F-16 VARIABLE RAMP-INLET Conformal IIIA
 

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You have all the ambiant air, more or less in stagnation, activated by the pressure difference caused by the engine, rushing toward the inlet from all the volume of air surrounding the airplane. Hence, a lot of that air flow impinge the inlet cowl at a high angle of attack. Hence the vortex cores all around its lip.
 
F-2 inlet with a block 50 inlet. The F-2 nose drops and it had to be redesigned, supposedly optimized for the F110-IHI-129.
 

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F-16 inlet (both 'old' "small mouth" Normal Shock Inlet (NSI) and 'new' "big mouth" Modular Common Inlet Duct (MCID)) are Normal Shock Inlets. http://www.habu2.net/vipers/viperblocks/
It's convergent divergent diffuser inlet actually.
I'm attaching some pics that can make situation more clear.
I think F-16/79 has slightly longer splitter plate so maybe it is mixed compression inlet? but normal F-16 is internal compression?
 
They're all going to be external compression only, to avoid unstarts (hard enough for the SR-71 in cruise, let alone a maneuvering fighter).

As flatric says, the NSI and MCID are normal shock ("pitot") inlets. All the supersonic compression is done by a single, strong normal shock at the intake aperture. On the other hand, in the F-16/79 the splitter plate was designed to act as a fixed compression ramp (6° initial wedge angle, followed by an isentropic compression surface turning the flow to 12.7°). There does not actually seem to be a convergent duct section (supersonic internal compression) at all. The terminal normal shock (much weaker due to the previous compression/deceleration) is not swallowed into the intake but remains at the opening.
 
They're all going to be external compression only, to avoid unstarts (hard enough for the SR-71 in cruise, let alone a maneuvering fighter).
What is unstart?
On a mixed compression inlet like the SR-71, there is one external oblique shock from the tip of the center cone, followed by several internal oblique shocks reflecting back an forth between the outer cowl and the inner cone before terminating in a normal shock at the narrowest portion of the air path. The multiple oblique shocks gently slow and compress the air, giving the best possible supersonic ram pressure recovery.

These internal shocks have to be positioned very carefully to remain stable as the air flows from low pressure to high pressure inside the intake. If this positioning is disturbed, the flow breaks down and the high pressure inside the inlet pushes the shocks forward outside the inlet, resulting in what is essentially a pitot inlet with its poor high Mach pressure recovery and greatly reduced engine thrust. This is an “unstart”. To recover, the center cone is moved forward to establish the external oblique shock, then moved aft until that shock reaches the outer duct lip and the internal shocks are reestablished, restarting the inlet.

Inlet upstarts are not an issue with external compression inlets, either pitot normal shock or oblique ramp designs within their Mach number design limits.
 
As reported, the F-16 small mouth and large mouth intakes are both pitot normal shock designs. These have good pressure recovery efficiency up to around 1.5M, then start falling off relative to multi-shock designs. However, they still behave well beyond that point and the thrust available in the engines from the F100-200 thru the F110-129 can all push the aircraft to 2.0M.

The inlet strut on the F-16 is a structural brace that keeps the intake from sucking in at low speeds and from bulging under high ram pressure. It is not rigidly connected, allowing for a small amount of inlet deflection before it hits the stops. There was one event where the pilot was complaining about a loud trump when he advanced or retarded the throttle. It was eventually found that the inlet strut mounts were binding and when the throttle was advanced the strut initially resisted the inlet deflection, then broke loose and slammed into the stop, which was immediately below the pilots seat, resulting in the big thump felt by the pilot.
 
As reported, the F-16 small mouth and large mouth intakes are both pitot normal shock designs.
So basically F-16, F-35, Rafale, Eurofighter , Gripen inlet are all external compression inlet to prevent the unstart phenemenon right?. How about F-100 or Mig-19 inlet? Are those two internal compression inlet?. Which one are mixed compression? F-15?
 
As reported, the F-16 small mouth and large mouth intakes are both pitot normal shock designs.
So basically F-16, F-35, Rafale, Eurofighter , Gripen inlet are all external compression inlet to prevent the unstart phenemenon right?. How about F-100 or Mig-19 inlet? Are those two internal compression inlet?. Which one are mixed compression? F-15?
As far as I know, the only mixed compression inlets have been the A-12/SR-71 family and the XB-70. The MiG-25/31 fly fast enough that a mixed compression inlet could be advantageous, but they appear to be variable multi-ramp external compression designs.
 
As reported, the F-16 small mouth and large mouth intakes are both pitot normal shock designs.
So basically F-16, F-35, Rafale, Eurofighter , Gripen inlet are all external compression inlet to prevent the unstart phenemenon right?. How about F-100 or Mig-19 inlet? Are those two internal compression inlet?. Which one are mixed compression? F-15?
As far as I know, the only mixed compression inlets have been the A-12/SR-71 family and the XB-70. The MiG-25/31 fly fast enough that a mixed compression inlet could be advantageous, but they appear to be variable multi-ramp external compression designs.
That interesting, I have always thought that maybe the shock cone of F-16/rafale/gripen inlet are close enough to the internal that they are essentially mixed compression.
I can only think of Mig-19 and f-100 for internal compression though
 

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