Forum: F-16 Design & Construction

Hey there guys! My mind was wandering off on its own again today and I got to thinking about the F-16's HUD (and HUDs in general) and how it works. I have the basic concept down, but there are still a few things I don't quite understand.

The first question I have is why the multiple panes of glass (the "combiner" glass) ? Back when I was selling Chevys, I used to love using the HUD in the new Corvettes Smile

. The 'Vette didn't use multiple pieces of glass, instead it merely projected the information onto the windshield. Don't get me wrong, I can understand not using the Viper's canopy for the HUD display "surface", instead I just can't see why you'd need more than one piece of glass Shrug

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The other question that comes to mind is what type of projector is used in the F-16's HUD? I mean is it similar to the projector that would be used to project an image of a computer screen in an office meeting? Does it use an LCD or a CRT or what Confused

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Thanks in advance - you guys are great Thumb

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Salute!

I don't have an answer for the double combiner glasses. might have to do with cutting down the glare when the sun comes straight down on the CRT.

Yep, it's a CRT. You can stand on the ladder and look down at the thing. Image is upside down, gets 'erected' (don't get all excited TC!!!) by the combiner .

Another consideration for the Viper HUD is the canopy. Two things:

1) The sucker must be able to withstand many knots of wind! Imagine ejecting and the sucker comes loose and decapitates you before the seat moves an inch.

2) There are 'canopy coefficients' in your software that correct for the distortion the thick canopy has. They are printed on each canopy rail.

During one bomb-comp, I worked with the 466th USAFR outfit, and we experimented changing the coefficients to take out vertical dispersion of actual bomb impacts. I had to leave Hill before the competition, but that outfit had the Top Gun and might have won overall. Hmmmmmmmmm

out,

While I cannot answer your question directly, it does remind me of something I've been curious of.
Every time I see a picture of the F-16C HUD in use, or even while I'm flying Falcon4, the HUD always seems a little crowded in some circumstanses. Why couldn't they have changed to a HUD like the one used on the F-15E? It has a lot wider angle. Also, it seems to be a single pane of glass, which your original question addressed. From looking at the F-16 canopy, it looks like there should be enuf room. What are anybodys thoughts on this. Thanx.

It's really a tight fit when the canopy is closed. Not alot of room to expand. The block 40's did have a wide angle HUD and not really sure why the 50's didn't.

Purplehaze

Thanks for all the great info guys Very Happy

! Please keep it comin'! Gums, that seems like a perfectly good reason for the combiner glass, but then again the Raptor (yeah, I know it's a whole new bird) has a nice, big, one piece HUD. I'll keep doing my research and maybe we'll figure this one out Smile

. Have fun guys!

All Viper HUDs I'm aware of are single pane, but really thick with chunky mounting rails. Gums touched on it: The Viper HUD glass has to be as thick as it it 'cause it has to withstand the windblast in an ejection. In the case of the Eagle and Hornet, they both have 2-piece canopies and their HUDs are tucked in under the front portion which constitutes a windscreen, so for ejection purposes they don't need to be quite as beefy as what you see in the Viper, and to the same extent in the Raptor. Essentially, a jet with a single-piece canopy needs a sturdier HUD for, if nothing else, pilot safety reasons.

Purplehaze wrote:

The block 40's did have a wide angle HUD and not really sure why the 50's didn't.

The wide-angle raster HUD (WAR HUD) in the Block 40 was needed when employing LANTIRN. While flying low-level heads up using the NAV pod, the HUD needed to display the raster video generated by the NAV pod (the same video format your PC generates so the CRT can display it) along with the stroke video which drew the flight symbology (FPM, airspeed, etc.). Since the Block US Block 50 wasn't originally designed to carry LANTIRN, it didn't need to have the WAR HUD. Now, the Korean Block 52s do have the WAR HUD 'cause they employ a LANTIRN-type device on that version. But you don't NEED to have a LANTIRN capability to have the WAR HUD. If you want it just 'cause you think it'd be cool to have, that's an option you can select at the time you place your order.

Thanks for the info link Smile

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The WAR HUD is a diffractive HUD, it has a 15.0 degree radius FOV, and the combiner assembly is made up of 3 pieces of glass, the image is projected from the CRT onto the smaller piece of glass at the top which reflects the image back onto the viewing glass.

The WAC HUD is a refractive HUD, and has a 12.5 degree radius FOV, and the combiner is made up of a single piece of glass, which the image is projected straight onto (or should I say projected curved onto).

The Raptor HUD is a Holographic HUD. The combiner actually has two pieces of glass stuck together, this is how the hologram is formed.

All the HUDs are design to withhold some amount of birdstrike before breaking! They are then designed to break in a nice safe manner, collapsing in a way that the glass does not shatter and spray the pilot with thousands of small shards of glass.

At present all of these HUDs use CRT's for display source, though the next generation (if there is a next generation, with HMD's wanting to take over!) will use LCD or Laser. The problem with LCD's is getting the brightness required from a HUD at the same time making it last long enough without burning out. The problem with Laser's is keeping them at the right temperature, on a hot sandy runway it needs to be kept cool, but at 30,000 feet it needs to be kept warm!

Both HUD's are capable of displaying curisve symbology overlaid on raster video image, but the wider field of view gives you more video to see.

Thanks for the great detail Very Happy

! I think I get the idea now.

Gums wrote:

Image is upside down, gets 'erected' (don't get all excited TC!!!) by the combiner.

ROLFMAO!!! Well, hey, as long as the image can "get up", it works right? Wink

Always curious as to why they didn't retrofit older Vipers with the HUD used in some of the later blocks. I realize not everybody employs LANTIRN, but wouldn't it have helped with standardization, and commonality purposes?

Or was it not that big a deal, so they decided not to do a universal retrofit?

Beers and MiGs were made to be pounded!

TC, I think cost was probably a big factor in the decision not to retrofit. That and they probably didn't think that too many of the jets that needed the bigger HUDs will be lost before they're retired Wink

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Or was it not that big a deal, so they decided not to do a universal retrofit?

The HUD comes in 2 parts the Display Unit, and the Electronics Unit. The electronics unit is really the important part as it controls what symbology is displayed, etc. And the software in the electronics unit works really no differently whichever type of HUD DU is attached, apart from positioning a few symbols further away from the centre.

I believe that the software in the electronics units has been upgraded by the USAF guys up at Hill so it should be common across the USAF planes.

On the Block-60 aircarft the job of Electronics Unit is now performed by the MMC.

Being a engine run guy... I hardly ever turn the hud on...But It's fun to shine a multuple led flishlight directly into it at night. And see yourself as the the green grench, reflecting in the glass

Am I right thinking that the pilot is only able to adjust the brightness of the displayed lettering / symbology, not the colour (in other words, intensity, not hue) and that the option of cycling through the HUD's colours has only been made up for the needs of flight sims?

Yep...brightness and maybe even some contrast, not sure, it's been a few years. AFAIK the color has always been green because it stands out so well against the real-world backdrop. The Viper sims I worked on used actual flight hardware (the DU and EU that ln mentioned) and none of them let you select HUD colors. Is that a PC-based sim you're talkin' about?

I could be wrong but the use of green may also be a function of where it falls in the spectrum (remember ROY G. BIV?). Since green sits right in the middle, the eye processes it easier than a color on either side of it. But there I go a'speculatin' again.

Forum: F-16 Design & Construction

Heads Up Display (HUD) design and construction