Let’s just assume for a moment that ED corrected a prior error and the current behavior is correct. That’s my assertion.
The reason is probably technological. The HMS has positional sensing but not gyro sensing. The sight knows where you are looking but not the attitude of your head.
The pilot gets used to this first by knowing it is just the way things are. But actually in some ways, it is a feature rather than a bug. For the FLIR background to match the visual horizon, the pilot’s head must be level to the Earth. Any difference is immediately recognizable as either aircraft- or head-bank. And while that maybe confusing if the pilot is looking at the horizon, it is still an accurate image of where the rounds will hit; which is what ultimately matters.
As for attitude and flight control, the system also works once you get used to it. Let’s say that we have the cruise attitude ladder cued. Let’s further say that we are in forward flight and banked hard left while looking right with a small amount of right head roll and considerable head pitch down (looking right and down). The PNVS is giving the best possible information in this confusing scenario. It is looking where we are looking. But the attitude (right IMAGE (not helicopter) bank) doesn’t match the attitude of the helicopter. Yes, this is confusing on first brush but once we adjust our expectation, it tells us exactly what we need to know—that the image is banked left relative to the ladder. Now, even though I am looking right with my head rolled right, them image in one eye is letting me know clearly that I am in a left turn.
If I really loathe the fact that the PNVS image doesn’t match the actual horizon, I can roll my head to make it match or simply accept the roll for the moment with the knowledge that the point that I am targeting is correct.
Another way to look at this: Close your free eye and forget about where your head is looking. Doesn’t matter. You are in thick fog at night. Total blackout. The only image you have is the display. Forget the IR image if there is one. Just look at the ladder. Everything it is telling you is true. That is why you won’t smack into the ground. And I think that is the reason that they made the system this way.
How are you interpreting the ladder? I’ve never been able to figure out a way to make use of it to tell aircraft orientation since it follows my head axis as if the lines are extending from my ears. I can use it to understand my own head orientation relative to “horizon” but only if I’m able to see that horizon (daytime). In pitch black I have nothing visible to reference it against. And since it’s not stabilized to the “horizon” like a traditional HUD or ADI, I honestly don’t know how to read it.
The image isn’t banked relative to the ladder for me, they’re both banked. I need something parallel to the horizon to be displayed in the IHADSS for me to make sense of anything when flying night/low visibility.
I’ll keep typing but I should say the obvious before I continue. I have no idea how the Apache works. I assume that ED is doing it roughly in line with reality but there is a 50/50 chance that it is a close to the real thing as a Mario Kart to a Mercedes F1 car. I also know nothing about putting “warheads of foreheads” as Casmo likes to say. I only know that weather has come as close to killing me as anything else in aviation so that is where my head always resides when I approach flying new machines, even virtual ones.
Let’s anthropomorph the sight. As an instrument I want to give you the pilot all the information you’ve asked for. But I feel an obligation to do so consistently. I ask again for you to close your left eye and either fly in night IMC or pretend that you are doing so. Put the cruise ladder up and try to think about how I, your sight, can tell you about the world around you consistently. When you bow your head, notice that the pitch on the ladder hasn’t changed. That’s because (hopefully) the helicopter is still in forward level flight. While being careful not to roll your head, look side to side. Notice that the heading doesn’t change. That’s because (again hopfully) the helicopter’s heading hasn’t changed. Now for roll the same rules apply. I guess the best way for me, the instrument, and you, the pilot, to relate is that in moments of possible confusion, minimize head roll. I can even help you do that in VMC. When the PNVS horizon matches the actual horizon, your head is level. When the two disagree, regardless of bank, your head is rolled.
The horizon reference line (and pitch ladder in cruise) as well as PNVS image are not stabilized to horizon. They’re stabilized to the gun cross x-axis. In my VR image the gun cross should be shaped more like an x relative to the horizon reference line, telling me that my head is tilted.
Screenshot 1. Helicopter level in pitch and banked slightly left. Pilot looking down and left.
Photo 1. Helicopter pitch level with slight right bank. Pilot looking ahead.
Photo 2. Helicopter very slightly nose up and banked right. Pilot looking slightly right.
Photo 3. Helicopter level in pitch but banked left. Pilot is looking well down and left. (quite similar to screenshot 1)
Screenshots 2 and 3. Helicopter is landed. No pitch. No bank. Pilot is looking slightly left with severe head-lean also to the left. All five shots are consistent. In fact, notice how in photo 3 the pilot seems to be looking 10-20deg below the horizon but the guncross is right on the horizon (even though it’s not). That’s consistent. The IHAADS is telling him that he is level in pitch, going fast and descending to the left at 1500 fpm. It’s great because he knows two things: 1) where the gun is pointed and 2) where the helicopter is pointed. It’s pretty darn brilliant to me. What we don’t know from the photos is if the pilots had any head-lean. That’s the only information that would differentiate their photos from the two screenshots.
Sure there is. In your screenshot you’ve introduced a head-lean to the left. In the photos we do not have that information, only where the pilot is looking (but not the attitude of the head).
The attitude of the head is indicated by the gun cross rotation relative the horizon reference lines. The real PNVS images are all when the aircraft is flying level with the pilot looking left or right.
Ah looks like there is some turn going on in some of those
@Clutch I don’t believe you are correct. Sorry. But the guncross is consistent. It shows attitude of the helicopter, not the head. Look at all the shots, both screen and photo. Guncross “north” is the rotormast. Guncross “south” is between the wheels. “East” and “West” are the pylons.
Now you are going to point out that the last screen shows a guncross at an angle. But that is only because your head is at an angle. The cross itself, relative to the horizon is still consistent N, S, E, W. AND N, S, E, W always matches those same cardinal positions on your eyepiece.
Was your head tilted some 30 degrees? If so then that’s correct.
Let’s take your marked up image:
You are correct that the PNVS picture isn’t matching the real world horizon. But it is 100% correct in relation to the aircraft as @smokinhole was discussing. The line on the canopy rail in pink is parallel with the tree line you marked in pink. The tree in the PNVS FLIR image marked in yellow is parallel with the horizon line of the ladder marked in yellow.
The PNVS is showing you that the sensor ball, which tilts/rotates along the roll axis of the helo only if the helo itself rolls, is not rolled/banked. This is correct.
The Transition Horizon Line is stabilized to the PNVS FLIR image horizon, which is absolutely correct. That’s exactly what the sample image you provided showed. We can estimate where the pilot is looking at via the field of regard box, and we can estimate how their head might be leaning based on bio-mechanics but that doesn’t change that the TADS assembly can’t roll to match any lean the pilot might have.
I’m assuming you’re familiar with the modern day HUD from say the F-15C. Let’s say we export the HUD to an eye piece very similar to the IHADS setup. There’s no sensors on your helment, since it’s just a HUD repeater, not a HMD. On your eye piece is just the HUD info of the F-15C, no FLIR picture, just pitch ladder, roll/bank indicator, etc. The jet is flying along perfectly level. You could sit upside down and backwards in the cockpit and the HUD displayed in your eyepiece would indicate straight and level moving forward because that’s what the jet is doing.
Explained that way it makes sense. If I zoom in on one of the shots so the FPM’s stubby wings are visible, they match the gun cross.
Now the remaining question is how do I keep the PNVS image level when I don’t know if or how much my head is tilted on its roll axis? If I close my eyes and move my head around, stopping at various points, I have no idea where my head is looking until I open my eyes. Exception being to points nearer the extreme of my neck mobility.
Frankly, if you’re flying instrument conditions, it doesn’t matter. Fly the instrument data showing up in your IHADS. Level up the acceleration cue with the horizon line, and have 0 on the VVI and you’re flying level, this is true regardless of where you’re looking, and how your heads titled.
That’s a great question. The answer I believe is that it becomes 2nd nature quickly. If you have the PNVS displayed on the sight, you can use your head to keep the PNVS image “roll-slewed” with the image you are seeing. If it is night and you can’t see much besides the world displayed to your sight, you can try to match the PNVS image with the horizon line. Eventually, you will get used to it.
For pure IFR yeah, but for combat when trying to target things and find cover or concealment the PNVS tilt gets annoying. The other day I tried to put my guncross over an object of interest and it (rather my head) was going the wrong way because the image was tilted and I didn’t know it.
This weekend I’ll play with it and see if I can use the horizon reference line to unfrak my head tilt like Smokinhole mentioned.
I gotcha. This is honestly probably where having some “game” elements would make for a fairer “simulation”. In VR you won’t have your butt and gravity telling you which was is down and the outside of the turn. Your vestibular system does a really good job real world of knowing what direction is up and how from level you are. Real world it’s probably pretty intuitive to figure out.
I would say the best way to picture this is PNVS is a camera on the helo nose that can pan and swivel but not tilt, it will always display the helo’s bank attitude to the horizon.
The IHDASS FLIR image is a like a TV set on your face, not like your cellphone with a roll sensor.
So if you tilt the TV set, the picture tilts with it, regardless of what the camera is doing. If the camera tilts, the image in the TV tilts…but since as we established unlike a TGP the Apache PNVS doesn’t roll independently, whatever bank the Apache has the image has as well.
I agree that this system works best for a level helo and a level pilot. Banking is for tight maneuvering and not fighting!
