Forum: F-16 Design & Construction

Thanks for the answer. Wink

I knew there was something back there, didn't know what it was called.

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sry for bringin the thread up again bt i got a question..
when viewed from design eye thru a USAF viper's WAC HUD, is there an obvious flat "cut" on the top edge of the projection circle as in the below picture?
http://www.rv-8a.net/images/F-16C%20Cockpit.jpg
cheers all!

Not to my knowledge. But then again, you're not supposed to see the circle at all unless the intensity is turned way up, like in the photo. If you're not piping a raster video to the HUD (like from a nav pod), the only thing that should be visible is the symbology. See http://www.f-16.net/gallery_item46375.html

fatcap wrote:

sry for bringin the thread up again bt i got a question..
when viewed from design eye thru a USAF viper's WAC HUD, is there an obvious flat "cut" on the top edge of the projection circle as in the below picture?
http://www.rv-8a.net/images/F-16C%20Cockpit.jpg
cheers all!

Yes, there's a flat cut on the top of the circle. If you look at LinkF16SimDude's picture in the previous post, you can actually see it as well. If you look at the reflections, you can see that the circle that projects the image is covered by the rear end of the UFC, making the flat cut appear...

The "flat cut" tieu is referring to looks to be a HUD framing structure, true, but it's not what is depicted in fatcap's pic. The photog was prolly resting his camera on the headrest to get all the cockpit in frame and was therefore not in the design eye. The HUD display is simply clipped because of where the camera was.

And you would never fly around on a regular basis with the intensity turned up so high that you'd see the raster disc anyhow.

thanks for the replies!
so regarding "The HUD display is simply clipped because of where the camera was", LinkF16SimDude could you tell me what is actually clipping the HUD display in that pic? Obviously the clipping edge is below the top of the HUD glass..
and for the raster disc, i also assume that under normal daylight lit background it's hardly visible, but what if you point the nose onto somewhere darker say, the sea or a shaded valley, would you be able to see the circle?
cheers!

Nothing is physically clipping the display. You just don't see a portion of it because of the camera's position and angle to the glass. If the camera were just a bit lower (at the design eye) and the intensity was turned up like that, you'd see a nearly complete circle (the raster disc). The HUD display reflected off the glass is highly directional (aka "collimated"). Any head movement outside the collimation area and you may not see some stuff. It's just the nature of the optics.

I've never known anyone that flew around with the intensity up that high. Sure, in bright sun conditions you can turn up the brightness but you won't come anywhere near the level in your pic. It would just wash out everything. With the HUD in Auto Bright it takes care of brightness levels for you. It doesn't compensate for light/dark backgrounds but will adjust for ambient light levels.

You have the same clipping effect even though when you are sitting correctly and at design eye. The effect is most prominent at night,, especially flying with NVG's when you have to increase the strength of the HUD intensity in order to see the symbology in the goggles. If you don't turn down the intensity and either goggling up or take off your NVG's, you can clearly see that the top part of the circle is clipped off. I'm not sure if the raster disk is not a complete circle, or if its the UFC that's blocking the top part of the circle, but you are not able to see a complete circe in the HUD no matter how you position your head/eyes...

so now we have two opinions regarding the shape of the raster disc.. Link16 says it's nearly a complete circle and Tieu says it's clipped on the top.
could it be the result from different projectors installed on different blocks?
Link16 said nothing is physically clipping the display, and from what I understand if the viewing angle is off-axis then the display will be visually clipped by the edge of the raster disc itself. From the pic i posted earlier the raster disc must be flat on the top then?
im modifying the raster disc shape/color in FalconBMS sim, here's some screenshots and i hope i can get all details right. Thanks for the inputs guys!
cheers!
Laughing

I have a question regarding the HUD symbology.
Is there anywhere an option for A0A digital marker being dispalyed on the HUD? For instance the F/A-18 has featured AOA on a HUD, why not F-16?
I didn't seen such in routine sorities.

@fatcap: With all due respect to the quest for exacting detail, this clipping thing you're concerned with isn't a big issue in the real world. Really. As long as you can see what ya need to see for any given HUD mode, it's all good. Take it from someone who spent many an hour staring at real HUD displays, the one in your cockpit shots looks pretty spot on just as it is. Even in the off-angle shots. (although the radar altimeter value in one is incorrect and the steering cue is different than what I remember, which is off-topic)

Patriot wrote:

Is there anywhere an option for A0A digital marker being dispalyed on the HUD? For instance the F/A-18 has featured AOA on a HUD, why not F-16?

Perhaps, with a little research and an update to the HUD Symbol Generator (SGU), the alpha value could be shown. I'm sure LockMart can figure it out. I don't know the reasoning behind not showing it on the Viper vs. showing it on the Hornet (USAF vs. Navy specs I suppose). I was in high school and didn't get the memo. Wink

Patriot wrote:

I have a question regarding the HUD symbology.
Is there anywhere an option for A0A digital marker being dispalyed on the HUD? For instance the F/A-18 has featured AOA on a HUD, why not F-16?
I didn't seen such in routine sorities.

Possibly because the F-16 has an AoA limiter and the pilot does not need to monitor it. The indexer works fine to landing AoA.

First of all I must express that saying I'm not an authority on HUD design is a huge understatement at the very least Smile

.

My understanding is that the F-16 LANTIRN HUD is described as being of the multi-bounce quasi-axial configuration as opposed to the single element off-axis design seen in the F-15E, Eurofighter Typhoon etc. I believe the reason GEC chose the less elegant solution for the F-16 HUD was because it was alot simpler. The single element off-axis design is apparently extremely complex, and there is the question mark as to whether the technology was a available (taking design, cost, reliability etc into account) to GEC when designing the WAR HUD back in the early eighties. The WAR HUD is in fact one of the earliest designs of a holographic HUD and perhaps the first placed in an aircraft.

The F-15E has a curved HUD glass, I believe this to be necessary for collimating the image. I think it may have been developed with this curve as that may have been the simplest way of increasing the iFoV at the time, however I'm not 100% sure.
The Typhoon has what initially appears to be flat pane, but in essence is to pieces of glass that are flat on their outsides, but are curved where they are sandwiched together, one side on one piece is convex while the other is concave. It is the inner curved surface that is used to collimate the image. This is very similar to the middle glass in the F-16 WAR HUD (The WAR consists of 4 pieces of glass, one with two pieces stuck together as in the Typhoon, the middle glass).
I could be wrong but I believe the differences between the basic design principles of the F-15E HUD and Typhoon HUD, are down to advances in technology. When the F-15E's Honeywell HUD was designed, curving the entire pane was perhaps the most efficient way to manufacture it, however things have moved on since then.

As for the Corvette HUD, does it provide a collimated image or does the driver have to refocus when switching from the outside world?

I hope this helps

Thanks for your comment LinkF16!

In the sim when i call up the AMRAAM, the top bit of the bore circle is clipped by the flat top, which i guess shouldn't happen in RL. BTW, the wrong radar altimeter readout might be due to incorrect main altimeter pressure setting.

Forum: F-16 Design & Construction

Heads Up Display (HUD) design and construction