Question about collimated display systems.

[wledzian]

767 Airplane Characteristics for Airport Planning
See section 4, page 109. In my early model, I used this information to derive an eyepoint. I found a to-scale model of a 767 in the Sketchup library and took a section cut through a vertical plane offset 21 inches from centerline per the Boeing document. From this section cut, I extended the upper and lower eyelines through the window edge intersection with the section cut and took their intersection as the eyepoint.

The mirror axis for a cross-cockpit display should be set at 90° to the floor at some point along the aircraft centerline. In a full-scale cockpit with the mirror axis directly between the pilots, the minimum offset would thus be 21 inches. If the axis is located behind the pilots, the offset would be larger.

So far, my optical calculations have been based on a symmetrical field of view, centered around the mirror axis. My cockpit will be single-seat, and the only horizontal offset I'm allowing is to account for my eyes being forward of my neck. In that case, the optics are consistent throughout the horizontal field of view. In a two-seat cockpit, these optics calculations only hold true along a plane defined by the eyepoint and the mirror axis, and in your case would correspond to looking 90° left. I haven't fully worked out the raytrace algorithm for off-plane viewing to see if the focal surface still lines up. The math is not undoable, I just haven't taken the time to do it yet.

As things are going, I think we may not be too far from having a functional prototype mirror, which should at the very least give us a good idea of the feasability of this project. If you can wait a few more weeks before cutting parts, I think we'll have a lot more to report.

Oh, and your wife must be very understanding to go along with having your simulator take up so much of the bedroom.

[mikesblack]

Thanks for pointing out this document. I understand the meaning of offset. I did re measure this point and rather than 18 inches as I had written, I think I am closer to the 21 inches as per the real aircraft.

If you could explain, I am not totally sure I understand this?

"My cockpit will be single-seat, and the only horizontal offset I'm allowing is to account for my eyes being forward of my neck. In that case, the optics are consistent throughout the horizontal field of view. In a two-seat cockpit, these optics calculations only hold true along a plane defined by the eyepoint and the mirror axis, and in your case would correspond to looking 90° left."

[wledzian]

I am not totally sure I understand this?

Me neither.

The raytracings I've done to determine the screen shape are for rays in-plane with the mirror axis. A ray in this plane stays in this plane from the screen to the eyepoint, so my calculations are relatively simple. I cast a ray to the mirror, determine its intersection point and angle, and calculate the reflected ray. Doing this with several parallel rays produces an intersection point which defines a point on the screen. It doesn't matter that the eyepoint is offset from the axis, as the rays are still in-plane. Since I'm not worried about a second crewmember, this works well for me. A small offset to allow for my eyes being forward of my neck (the rotational axis of my head, assumed to be coincident with the center of the mirror) has no effect on the raytrace calculations.

For more significant offset, it cannot be assumed that the cast rays will be in plane with the mirror axis. I now have to cast the rays in a plane defined by the mirror center (not the axis) and the ray itself. This requires transforming the coordinate system to the new plane, casting the rays, determining the intersect, re-transforming the screen point to the original coordinate system, and finding a clean way to visualize the new screen points in relation to the in-plane surface.

Visualize if you will, the mirror around your cockpit. If the center of the mirror is directly between captain and copilot and you look directly to your left (as captain), you'd expect to be looking at a reflection of some point on the screen directly above your line of sight. On the other hand, if you look directly forward, you'd expect to see what is directly in front of the aircraft. This image, if properly located on the screen, will be directly over the cockpit centerline. Your line of sight is directly forward to the mirror, but the reflected ray is up and to the right, to intersect with the centerline of the screen.

The problem is that the collimation is not perfect. The directly-forward eyelines for the captain meet the screen slightly to the left of forward, and for the copilot, slightly to the right of forward. The offset is significantly less than if you were looking at a real image on a surface a few feet away, but it is real. The effect is lessened by the use of larger mirrors.

I haven't done the math yet, so beyond the concept I don't have an idea about the magnitude of the distortion or whether it will be acceptable or absolutely horrible. Once we have a working prototype, we'll be able to tell you more.

[mikesblack]

Thanks. Have to say that I'm very impressed by your level of understanding and detailed knowledge of this subject.

There is definitely quite a bit to it, and for me, without the good fortune of this site and more specifically folks like you who have been most generous with sharing knowledge, I would be lost and without hope of even being close to getting this done.

I am looking forward to the process, and even if not successful, I still think learning this has been worth the effort.

Cheers!

[castle]

Your wife has to be one fine lady!

175_7528.jpg

Bit fortunate here, have an extra stall in the garage, but it is a bit tight. Starting to build the shell and already seeing that it is not going to work if and when the mirror system is installed.

175_7529.jpg

I jokingly suggested pehaps the wife would like to park her car outside and along with an icy stare she suggested maybe I wouldn't mind sleeping in my truck.

All kidding aside, gotta love them, amazing how they tolerate the kid in us and all our crazy hobbies

[mikesblack]

She says she loves me for that quality, of course that's until I start really start acting like a kid or perhaps I should say childish. Then she gets annoyed.

[castle]

While I've gotten some prelim numbers that suggest you might be able to fabricate three acrylic forms for around $2K (does not include first surface mirroring) and wanted to use those on a vacuum system instead you would have to drill a gazillion tiny holes to suck up and stretch the mylar. So here is a crazy idea..

Going back to the idea of building a more conventional frame; use a multilayer approach for the concave surface. Base layer is strips of conventional peg board, cover that with a coarse cloth, apply a top layer of felt. Use two sided carpeting type in horizontal and vertical strips to hold the sandwich together and bonded to the board surface.

JW

[crashdog]

Don't know if this vid has been shown before it's one year old. But I just stumbled upon it. You can see the mounting of the collimated visual from day 9 to day 11. Enjoy


Gery

[mikesblack]

crashdog,

That was great. Thanks for bringing this up. I have been looking for something like this.

Fantastic,
Mike

[Matt Olieman]

Gery, FRIGGEN FANTASTIC!!!!!!

I haven't seen this one, good find and THANKS!!!!!

Matt Olieman