HUD pitch ladder

[Cobra747]

I was lucky enough to have a go at the demo of the F-14 at the Oz Flight Sim Expo and there was a weird behaviour with the pitch ladder on the HUD.

 

When pitching up and down the pitch ladder (i assume that what the horizontal bars are on the HUD!!??) moved with the pitch of the aircraft. Not perfectly but they didn't stay as a reference to say the horizon.

 

I noticed this happened on the video they did the other day. If you jump to around 38:20 he drops his nose a bit and you can see what appears to be the 0 degree pitch ladder drop below the horizon. Any ideas why or what there are?

 

Thanks, cant wait for this to be released!

 

[Cobra847]

;3702255']I was lucky enough to have a go at the demo of the F-14 at the Oz Flight Sim Expo and there was a weird behaviour with the pitch ladder on the HUD.

 

When pitching up and down the pitch ladder (i assume that what the horizontal bars are on the HUD!!??) moved with the pitch of the aircraft. Not perfectly but they didn't stay as a reference to say the horizon.

 

I noticed this happened on the video they did the other day. If you jump to around 38:20 he drops his nose a bit and you can see what appears to be the 0 degree pitch ladder drop below the horizon. Any ideas why or what there are?

 

Thanks, cant wait for this to be released!

 

 

The pitch ladder only refreshes it's position once a certain delta has been reached (basically delta pitch). So it'll move "with" the aircraft until it jumps to a new position.

[Cobra747]

The pitch ladder only refreshes it's position once a certain delta has been reached (basically delta pitch). So it'll move "with" the aircraft until it jumps to a new position.

 

Thanks for the reply Nicholas. I thought it would be something like that.

 

:thumbup:

[Moafuleum]

Hi

 

 

i hijack this thread bc the initial question was answered but still i have a question about the pitch ladder, especially about the refresh rate.

 

 

 

In the first video of first answer of this thread

 

 

https://forums.eagle.ru/showthread.php?t=225585

 

 

at about 3.17 min. you see a hud projection. In this video, the pitch ladder seems to go very smooth, being continuously updated. Is this maybe another branch of the F-14? Does someone know more?

 

 

thanks

[Eldur]

IIRC refresh rate is higher in combat modes than in nav mode.

[BlackLion213]

IIRC refresh rate is higher in combat modes than in nav mode.

 

The refresh rate for all modes is 60 hz iirc, so plenty fast. The problem isn't "refresh rate" it is resolution of pitch changes. The combat and cruise modes use a 4:1 compression for the pitch ladder, so the apparent resolution is 4x finer. This makes the pitch ladder look quite smooth and it only really looks coarse in landing or A/G mode.

 

However.....thats not the ergonomically difficult aspect of the HUD - its the layout. In the F-14 HUD, the airplane symbol and pitch ladder are depressed 5 degrees from the aircraft datum line. That is why the horizon line did not match up with the horizon as the OP asked.

 

Here is a real world example and represents the pilot's view in terms of the relationship between the HUD and horizon(in landing mode for the video):

 

 

 

We aren't quite sure why this decision was made by the F-14 engineers, but suspect it has to do with the lack of a combiner glass (which was part of the original F-14 mock-up, but later removed). Because the HUD projects onto the windscreen, there was only so much space for the symbology of the projection. The aircraft's axis of flight is high in the windscreen, so it seems that between the heading tape, aircraft symbol, TVV, and pitch ladder - the upper HUD would be really crowded. So they decided to depress the aircraft symbol and associated pitch ladder 5 degrees to space everything out. This means that the "horizon line" will lie below the horizon most of the time, but if you roll to 90 deg AOB it lines up and if you roll inverted it will be 5 deg above the horizon.

 

In cruise mode and cruise AOA, the horizon line (in 4:1 compression mode) is generally close to or slightly above the horizon in level flight. But to "level" the aircraft, you need to line up the aircraft symbol with the horizon pitch line and not the horizon itself - since they are different.

 

This reinforces what our SMEs say about the F-14A/B HUD - it is not a primary flight instrument, but meant as a tool for weapons employment. It takes a moment to get used to, but adds to the F-14 charm imho - you use the HUD differently in the F-14 than other fighters.

 

-Nick

Edited November 29, 2018 by BlackLion213

[Cobra747]

Thanks BlackLion, very interesting info and I agree, its the nuances of an aircraft that really seem to give them their charm.

[Cobra847]

Also, with regards to the video referenced above, note that rotational precision is much much higher than pitch movements.

 

So to say: The pitch ladder appears smooth in rotation, but it will "jump" to a new position in pitch.

[Moafuleum]

Thanks BlackLion and Cobra for the insight!

 

However, i think because of this peculiarity, many people will open bug report threads about this :D

 

Cheers

[Deano87]

Thanks BlackLion and Cobra for the insight!

 

However, i think because of this peculiarity, many people will open bug report threads about this :D

 

Cheers

 

I agree. It’s certainly going to be alien for a lot of people who are used to modern jets. Can probably be mitigated though by HB doing a in depth video explaining everything about the HUD that people can watch and get their head around.

[bies]

I love how you model imperfections of the HUD and other systems.

[Gunslinger22]

I love how you model imperfections of the HUD and other systems.

It may be considered a imperfection now, but in 1970 it was quite the achievement.

[MRSHADO]

The refresh rate for all modes is 60 hz iirc, so plenty fast. The problem isn't "refresh rate" it is resolution of pitch changes. The combat and cruise modes use a 4:1 compression for the pitch ladder, so the apparent resolution is 4x finer. This makes the pitch ladder look quite smooth and it only really looks coarse in landing or A/G mode.

 

However.....thats not the ergonomically difficult aspect of the HUD - its the layout. In the F-14 HUD, the airplane symbol and pitch ladder are depressed 5 degrees from the aircraft datum line. That is why the horizon line did not match up with the horizon as the OP asked.

 

Here is a real world example and represents the pilot's view in terms of the relationship between the HUD and horizon(in landing mode for the video):

 

 

 

We aren't quite sure why this decision was made by the F-14 engineers, but suspect it has to do with the lack of a combiner glass (which was part of the original F-14 mock-up, but later removed). Because the HUD projects onto the windscreen, there was only so much space for the symbology of the projection. The aircraft's axis of flight is high in the windscreen, so it seems that between the heading tape, aircraft symbol, TVV, and pitch ladder - the upper HUD would be really crowded. So they decided to depress the aircraft symbol and associated pitch ladder 5 degrees to space everything out. This means that the "horizon line" will lie below the horizon most of the time, but if you roll to 90 deg AOB it lines up and if you roll inverted it will be 5 deg above the horizon.

 

In cruise mode and cruise AOA, the horizon line (in 4:1 compression mode) is generally close to or slightly above the horizon in level flight. But to "level" the aircraft, you need to line up the aircraft symbol with the horizon pitch line and not the horizon itself - since they are different.

 

This reinforces what our SMEs say about the F-14A/B HUD - it is not a primary flight instrument, but meant as a tool for weapons employment. It takes a moment to get used to, but adds to the F-14 charm imho - you use the HUD differently in the F-14 than other fighters.

 

-Nick

 

That my friend, was an extremely thorough and interesting explanation. Gems like this is why I love this community. Thanks BlackLion213

[Victory205]

I agree. It’s certainly going to be alien for a lot of people who are used to modern jets. Can probably be mitigated though by HB doing a in depth video explaining everything about the HUD that people can watch and get their head around.

 

The team developing this module is impressive- very dedicated and talented. They remind me of CSI investigators.

 

No one told the real pilots about the vagaries of the HUD. We learned the symbology, where the same symbols meant different things depending upon what mode was selected and what the sensor state was. It was up to the crews as to how to employ the features.

 

You can’t fly off of the F14A/B HUD like you can in current aircraft- airspeed and altitude were not displayed for one thing, nor was the rate of descent display usable for precise control. I gave up on the E bracket the first time I tried using it for FCLP's. It just didn't work like you see in the Hornet.

 

The HUD was fine for weapons employment, but almost everyone I know either turned it all the way down for landing on the ship, or completely off. Pretty much useless other than needle position, which was less relevant once you picked up the ball.

 

The F14D finally got a combining glass and a decent HUD system.

Edited November 29, 2018 by Victory205

[Flamin_Squirrel]

Great info, thanks.

[Manuel_108]

I wouldn't have guessed that some pilots simply turned it off completely. I guess it makes sense for landing, as you watch the ball anyway. AOA is also right in front of you. Man this is going to be something else.

[Ben Sones]

Okay, this is a bit of a thread resurrection, and maybe this has been discussed elsewhere already, but I've been trying to learn the F-14 module (and get back into sims in general after a ~10 year hiatus), and have been running into a bit of a brick wall when it comes to this particular topic, and there's a lot of conflicting information on this forum, reddit, etc., and also no real information in the game manual (which I know is a work in progress) and Chuck's guide. Both references tell you that these HUD elements exist, but do not describe how they work. And I'd really like to understand how stuff on my HUD works. "Just turn it off, LOL" is not a very satisfying solution. 

 

So, how do the pitch ladder, horizon line, and various HUD symbology (aircraft reticle, ADL cross) actually work? Do they work? Why does the pitch ladder's horizon almost never line up with the actual horizon? Which symbol actually indicates the direction the aircraft is pointing--the reticle, or the ADL cross? I jumped into a free flight mission to do some experimentation, and it turns out that the answer to that question is: they both do. I'll explain.

 

I put the aircraft into level flight, let it cruise along for ten seconds or so to let all the gauges settle down, and then I tried putting the reticle right on the horizon. Not the pitch ladder horizon--the actual horizon. Then I paused the game and snapped two screenshots: one of the HUD, and one exterior shot from the side, to see how the aircraft is pitched relative to the horizon. With the reticle on the actual horizon, the aircraft is pretty clearly pitched up. Or rather, part of it is. Because the F-14 is not actually straight when viewed from the side--the nose and cockpit are "bent down" relative to the rest of the aircraft. So while the wings are clearly pitched back with the reticle on the horizon, the nose lines up with the horizon perfectly. Just look at the AoA sensor on the tip of the nose. It is perfectly parallel to the horizon. So, the reticle depicts where the nose of the aircraft is pointing. 

 

 

Next, I tried putting the ADL cross on the (real) horizon. And yes, that does indeed put the wings parallel to the horizon. Which makes sense, since the weapons are mounted parallel to the wings, and the ADL cross depicts the direction in which their sensor heads are pointing. And you'll notice one more interesting thing in the first shot, below: putting the ADL cross on the real horizon aligns the reticle perfectly with the pitch ladder horizon. So that's why the pitch ladder horizon line is always below the real horizon in level flight: because it's calibrated to the nose of the aircraft, and the nose points down. Putting the aircraft reticle on the pitch ladder horizon means that the longitudinal axis of your wings is aligned with the actual horizon. And it makes a certain amount of sense to do it that way, because the ADL cross is not depicted in all HUD modes, but the reticle is. But wow, it's super confusing to anyone that has ever used, I dunno, any other HUD. It's easy to parse once you understand what you are looking at, but I can't imagine that anyone would figure this out intuitively. 

 

 

"But wait," you are saying, "Sometimes the horizon line of the HUD lines up with the real horizon. Sometimes it's even above the horizon. What's up with that?" 

 

This had me confused for a while, too, but the answer is that the F-14's HUD is unlike other HUDs you might have used in yet another way: it has different pitch ladder scales based on the mode you are in. I'm sure you've noticed that in cruise mode or air-to-air mode, you only see pitch lines in 30-degree increments. But what you might not have noticed is that it's not just hiding the pitch lines in between those values--it's effectively "zooming out" to let you see more of the pitch ladder. 

 

This is going to require some illustrations. In the following two shots, I have used Active Pause to allow me to switch HUD modes while everything else stays the same. In the first shot, the HUD is in takeoff mode, and the pitch ladder displays 5-degree increments. We are trimmed for level flight, and the reticle is just about on the pitch ladder's horizon line. We can see the 5-degree line toward the top of the HUD, but the 10-degree line is not visible--it's off the top of the HUD. 

 

In the second shot, we are in cruise mode. This shows us the 30-degree lines, but what's noteworthy is that we can see them. Like, we can see both the 30-degree line and the minus 30-degree line, right at the very top and bottom of the HUD. The position of the top 30-degree line corresponds roughly to the ~7.5-degree position in the first screenshot. 

 

So, what the what?!

 

 

Here's the explanation: the HUD modes that show you 5-degree increments on the pitch ladder work exactly the same as most other HUDs you've probably used. The "focal length" of the HUD display is intended to match the focal length of the human eye, and the measurements literally describe what you see. If you measured 5 degrees off the horizon in real life, it would line up exactly with the 5-degree mark on the HUD. The horizon line is always fixed in the same position, no matter how you move your head or turn the aircraft. In most aircraft, it would always remain fixed on the horizon (approximately), but in the F-14 it always remains fixed a bit below the horizon for reasons explained above. The important thing is, it doesn't move. 

 

But in cruise mode and the various combat modes, the HUD displays the pitch ladder at a different focal length, allowing you to see more of the scale--think of it like viewing the pitch ladder through a fisheye lens. This introduces some weirdness, though, because in these modes the pitch ladder is only accurate at its center point. That 30-degree line is not actually 30 degrees up from the horizon line--that point in the sky is actually about 7.5 degrees up from the point in the ocean that the horizon line is over. Note that the horizon line hasn't changed positions; that's because we are pointing the reticle directly at it, and the center point of this fisheye pitch ladder display does indeed show the accurate inclination relative to the world. 

 

Let's see what happens if we pitch up in cruise mode, though:

 

 

The 30-degree line has come down somewhat--we're moving toward it. But the horizon line has followed us up, and is now above the actual horizon. That's because in this HUD mode, the horizon line will only be in the right place relative your "sight picture" when the reticle is pointing directly at it. If you aren't pointing the reticle at the horizon line, then the only information the HUD is giving you is that the horizon line is in that direction. You are not seeing its actual location. If we pitch down to put the reticle back onto the horizon line, the horizon line will move away from the reticle, and we won't "catch up" to it until we reach the position where it should actually be. 

 

So that's all kind of confusing, and not at all how pitch ladders work on most aircraft (the 5-degree increment ladders in takeoff and landing modes do work the same way that pitch ladders work in other aircraft). But once you can wrap your head around how it works, you can at least understand what the HUD is showing you, which hopefully lets you use it more effectively. It's not broken or wrong (and it's not an artifact of slow polling/updating of the sensors--though that does exist, and is why the pitch ladder doesn't move smoothly, but instead sort of hitches along like it's running at a really low framerate). It's just kind of... unconventional. 

 

 

Edited July 11, 2021 by Ben Sones

[Naquaii]

The reason for you having trouble with understanding how the pitch ladder on the HUD references to the outside world is simple to be frank, it doesn't. The times it does is coincidental, it was never constructed to be.

 

In the F-14 the HUD is not a primary flight instrument unlike later HUDs and the pitchladder needs to be viewed as simply being an ADI moved up onto the HUD, like having the pitchladder from the VDI on the HUD, which in fact, is exactly what it is. The pitchladder only references the aircraft wings displayed on the HUD, nothing else. You can trim it to be somewhat correct but it will only be correct for that specific situation.

 

You are right in that the HUD displays the pitchladder differently while in landing and take-off modes while compressing it in others, that was done to declutter the HUD and as they don't reference the outside world it doesn't matter much.

 

As for the HUD being difficult to read it's likely because you're used to modern HUDs. The F-14 on the other hand had a very advanced HUD for its time but lacking in other regards. This is one of the reasons for the HUD later being upgraded.

 

[Ben Sones]

It actually does reference the outside world in takeoff and landing modes, though. Try setting it to one of those modes, and fly around. The horizon line and the pitch lines are absolutely fixed, and do not move in relation to the world, just as you would see in the HUD in an F-16 (for example). They are offset about 3-4 degrees down from the real world, but that's because the pitch ladder is calibrated to the reticle/nose, and the nose points down in level flight. But you absolutely can use the HUD's pitch ladder and horizon as a flight aid, as much as you can in any other aircraft. In takeoff and landing mode, it functions no differently than the HUD in an F-16, aside from the offset. So long as you are focusing on the reticle's location relative to the pitch ladder, and not its location relative to the real horizon, it's exactly as useful as the HUD in any other aircraft.

 

Even in cruise or combat mode, it accurately depicts whatever the reticle is pointing at. That's less useful as a navigation aid, obviously, but it's not like it has no relationship to the outside world. 

 

Again--you can verify all of this in-game. For example, try putting the reticle on the horizon line of the pitch ladder, then pause and go to an external view and take a screenshot. Leave the external camera where it is (it won't move again unless you move it) and go back to the cockpit. Unpause, and pitch up 15 degrees. Pause again, return the the external view, and take another screenshot. 

 

 

If the pitch ladder is, indeed, an accurate reference to the real world, the aircraft will have pitched up fifteen degrees. This is easy to measure in Photoshop. 

 

 

That's a change in pitch of 14.91 degrees, which I'm going to call "within the margin of error." Seems like an accurate real world reference to me!

Edited July 12, 2021 by Ben Sones

[Ben Sones]

I should note that I have no idea if this is accurate to the real F-14B. It may not be. But in Heatblur's simulation of the F-14B, the HUD pitch ladder and reticle seem to be as much an accurate reference as they are in any other aircraft (in takeoff and landing modes).

Edited July 12, 2021 by Ben Sones

[Naquaii]

40 minutes ago, Ben Sones said:

It actually does reference the outside world in takeoff and landing modes, though. Try setting it to one of those modes, and fly around. The horizon line and the pitch lines are absolutely fixed, and do not move in relation to the world, just as you would see in the HUD in an F-16 (for example). They are offset about 3-4 degrees down from the real world, but that's because the pitch ladder is calibrated to the reticle/nose, and the nose points down in level flight. But you absolutely can use the HUD's pitch ladder and horizon as a flight aid, as much as you can in any other aircraft. In takeoff and landing mode, it functions no differently than the HUD in an F-16, aside from the offset. So long as you are focusing on the reticle's location relative to the pitch ladder, and not its location relative to the real horizon, it's exactly as useful as the HUD in any other aircraft.

 

Even in cruise or combat mode, it accurately depicts whatever the reticle is pointing at. That's less useful as a navigation aid, obviously, but it's not like it has no relationship to the outside world. 

 

 

It does not reference the outside world though and like I said it’s not supposed to. The fact that it’s offset proves this as you need to trim the display for this to happen. And the pitch ladder is not calibrated to anything and wasn’t in the real aircraft either, it simply wasn’t intended to. That said it still correlates to the outside world, an ADI that didn’t do that would be useless. Imagine holding up an imaginary ADI in front of the HUD, the ground and sky would be in the right places but you would need to reference the wings on that instrument for exact information, not the real horizon. This is the same as the pitchladder on the F-14 HUD and why it wasn’t considered a primary flight instrument. In addition the granularity and update rate simply wasn’t there either and no effort was made to have it correlated to the outside world like the weapons symbology was. IRL there might even have been a slight positional error as well in the display that’s hard to model in DCS adding to this problem.

 

If you like to use it and find it useful that’s great but you’re trying to find explanations that need none except that it wasn’t constructed to do what you assume. All this is detailed in the real F-14 manuals and is what we used as sources when we modelled them.

[G.J.S]

Don't rely too much on the horizon line when airborne, the HUD isn't a primary device. 

The only thing i do with regards the horizon line is when on the pan before lift off, i use the HUD Trim dial to bring the horizon line up to match visible horizon and set it there whilst aircraft at rest.

I'm guessing the OP is digital-gen slave, used to the see all and display all HUD's.

 

Proper aircraft require pilots - laptops require displays.

[Ben Sones]

3 hours ago, Naquaii said:

It does not reference the outside world though and like I said it’s not supposed to. The fact that it’s offset proves this as you need to trim the display for this to happen. And the pitch ladder is not calibrated to anything and wasn’t in the real aircraft either, it simply wasn’t intended to. That said it still correlates to the outside world, an ADI that didn’t do that would be useless. Imagine holding up an imaginary ADI in front of the HUD, the ground and sky would be in the right places but you would need to reference the wings on that instrument for exact information, not the real horizon. This is the same as the pitchladder on the F-14 HUD and why it wasn’t considered a primary flight instrument. In addition the granularity and update rate simply wasn’t there either and no effort was made to have it correlated to the outside world like the weapons symbology was. IRL there might even have been a slight positional error as well in the display that’s hard to model in DCS adding to this problem.

 

If you like to use it and find it useful that’s great but you’re trying to find explanations that need none except that it wasn’t constructed to do what you assume. All this is detailed in the real F-14 manuals and is what we used as sources when we modelled them.

 

 

I've never touched the HUD trim dial--it's just at whatever default value it's always been at. It seems like a weird coincidence that the default pitch ladder exactly corresponds to the aircraft reticle, though, such that placing the reticle on the pitch ladder's horizon line places the longitudinal line of the aircraft exactly parallel to the horizon. Are you saying that it isn't set up like that on purpose? Like I said, that seems like an unlikely coincidence. I get that it's not referencing the world in the sense that it's auto-calibrating itself to the outside world and can be hand calibrated to not match anything. But it sure seems like it's been hand-calibrated out of the box to accurately correlate with the real world. I sure didn't set it up that way. 

 

The online manual has no info about any of this, at least not that I can find. It only mentions the HUD pitch ladder to say that there's a knob to adjust it, and it doesn't mention the reticle at all. I don't have a real F-14 manual handy to reference. 

 

[Callsign JoNay]

I actually have started to use the dial to trim the ladder to the outside world during recovery. It's pointless to do when cruising around, or in A2A, because it's aligned to the wings symbol, but landing mode gives you a FPM, so there is some logic to using the trim dial to align to the outside horizon when landing. I still pay more attention to the VSI though. It's more accurate than the pitch ladder.

[Naquaii]

4 hours ago, Ben Sones said:

 

 

I've never touched the HUD trim dial--it's just at whatever default value it's always been at. It seems like a weird coincidence that the default pitch ladder exactly corresponds to the aircraft reticle, though, such that placing the reticle on the pitch ladder's horizon line places the longitudinal line of the aircraft exactly parallel to the horizon. Are you saying that it isn't set up like that on purpose? Like I said, that seems like an unlikely coincidence. I get that it's not referencing the world in the sense that it's auto-calibrating itself to the outside world and can be hand calibrated to not match anything. But it sure seems like it's been hand-calibrated out of the box to accurately correlate with the real world. I sure didn't set it up that way. 

 

The online manual has no info about any of this, at least not that I can find. It only mentions the HUD pitch ladder to say that there's a knob to adjust it, and it doesn't mention the reticle at all. I don't have a real F-14 manual handy to reference. 

 

 

I think we're talking about different things here. If you place horizon line on the HUD on the wings the aircraft will be in level flight. That's exactly it's purpose and also how an ADI works.

 

Saying that it's referencing the real world like a modern HUD isn't though. If it did the horizon line on the HUD would always exactly mark the real horizon in the outside world, that the F-14 HUD can't do. You can trim it to be at the horizon in the real world but a change of altitude or even a roll will change this and make it not so. This fact is what makes it not reference the real world in the HUD sense. The ADI function will always work and show aircraft aspect though, as long as you only check the pitch ladder against the other HUD symbology, not the outside world. In a modern HUD you would always be able to use all these symbols against the real world outside as well and the lack of this in the F-14 is what disqualifies it as a primary flight instrument.

 

This coupled with the lack of granularity/resolution and speed of update is what made the real pilots turn it off and not use it as many preferred to just use the VDI instead as it was less confusing and also how many were used to if they transferred from older aircraft.

 

The lack of an in detail description of the HUD in the manual is on my todo list and will be added.