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Forward visibility in IVA

Jesus-Ninja - 25/11/08 at 01:25 PM

Section 32:

Check that when seated in the driving position, the driver has a full unobscured
view of the road to the front and forward of the near side and
offside of the vehicle (180° forward). The lower edge of the forward field of
view must not be above the “windscreen horizontal plane” as defined in
Annex 1 of this section.

OK so I understand, from Annex 1, how the windscreen horizontal plane is defined. Although the angles listed are a bit odd.

ANGLE
150 – 190
200 – 240
250 – 290
300 – 340
250 – 390
400 +

I assume this is meant to read:

ANGLE
15 – 19
20 – 24
25 – 29
30 – 34
35 – 39
40 +

, given that the figures in the picture, and for a reclining seat, match up with the 25 deg figures in the text:

quote:

In the case of a seat with an adjustable back rest, the measurements
should be made with the seat back rest adjusted to an angle of 25°, line ‘A’
being parallel to the centre line of the seat back rest.

What I'm not clear on is what is defined as "the forward field of view" in the first paragraph above. I think I'm right in saying that this is "the road the driver can see", and this area must all be above the windscreen horizontal plane - ie no bonnet bulges or dash etc must obscure it. But who defines what the forward field of view is. There seems to be much in the way of detail about defining the windscreen horizontal plane, but is the field of view simply what the testers can see when he or she is sitting in the car. Surely the results are different if the tester is a midget or a giant?

Or am I missing a trick somewhere?

[Edited on 25/11/08 by Jesus-Ninja]

[Edited on 25/11/08 by Jesus-Ninja]

matt_claydon - 25/11/08 at 01:35 PM

You are correct about the angles, they should read 15.0 - 19.0 etc. They are essentially corrections made to the theortical eye point for seats whose back angle is not 25 degrees (i.e. if you have a very laid back seat your eyes will be lower).

The forward field of view is the full 180 degrees from looking sideways to your left round to looking sideways to your right.

spdpug98 - 25/11/08 at 03:55 PM

quote:

The forward field of view is the full 180 degrees from looking sideways to your left round to looking sideways to your right.

How does this work with a full rollcage in place, I have ordered my kit with a fulll cage and this has me a bit worried

matt_claydon - 25/11/08 at 04:26 PM
A-pillars are allowed in the forward vision area. An A-pillar is definied as the structure that supports the roof. It would be up to the interpretation of the examiner but I would say the front uprights of the cage could be considered as A-pillars.

Jesus-Ninja - 25/11/08 at 05:10 PM
quote:
Originally posted by matt_claydon
You are correct about the angles, they should read 15.0 - 19.0 etc. They are essentially corrections made to the theortical eye point for seats whose back angle is not 25 degrees (i.e. if you have a very laid back seat your eyes will be lower).

The forward field of view is the full 180 degrees from looking sideways to your left round to looking sideways to your right.

Hmmm, I'm still lost with this.

See attached pic.

The short bloke cannot see any road (unless it's a very steep hill in front of him!)

Big bloke can see plenty of road

Average chap can probably see the road, but only in the distance.

See what I mean?
Rescued attachment visibility.JPG

matt_claydon - 25/11/08 at 05:21 PM
The manual specifies height A, so the test is always done for the 'average chap' as you put it (although the eye point isn't quite where you've drawn it, it's where line C, the 187.2mm line and the dashed line all meet. The only thing that changes the height of the eye point is the seat-back angle.

[Edited on 25/11/08 by matt_claydon]

spdpug98 - 25/11/08 at 05:27 PM
quote:
Originally posted by matt_claydon
A-pillars are allowed in the forward vision area. An A-pillar is definied as the structure that supports the roof. It would be up to the interpretation of the examiner but I would say the front uprights of the cage could be considered as A-pillars.

Thanks, that's put my mind to rest

Jesus-Ninja - 25/11/08 at 09:35 PM
quote:
Originally posted by matt_claydon
The manual specifies height A, so the test is always done for the 'average chap' as you put it (although the eye point isn't quite where you've drawn it, it's where line C, the 187.2mm line and the dashed line all meet. The only thing that changes the height of the eye point is the seat-back angle.

[Edited on 25/11/08 by matt_claydon]

Ah! Gotchya! So the line C is the lowest line of vision. So if line C can extend to the road ahead with no obstruction, then all's well?

spdpug98 - 25/11/08 at 10:05 PM
Jesus-Ninja - sorry for the thread hi-jack

Jesus-Ninja - 25/11/08 at 10:34 PM
quote:
Originally posted by spdpug98
Jesus-Ninja - sorry for the thread hi-jack

No worries

Jesus-Ninja - 26/11/08 at 06:04 PM
OK, last check on this I'm about to make some fairly committed decisions abot my body shell....

Looking at the attached pic, am I right in saying that this shows visiblity "on the limit"

Jesus-Ninja - 26/11/08 at 07:17 PM
Hmm, I'm still not happy with this... Who ever wrote the IVA has no idea what a plane is..

quote:

The windscreen “horizontal plane” is at the point where the projection of line ‘C’ intersects the windscreen / windshield, or if above the windscreen /windshield, the vertically projected plane of the windscreen / windshield (line ‘D’).

How can a plane be at a point? A plane is defined by 3 points. I could almost accept the notion that the plane is defined the line "C", sweeping to each side to descibe the side of a cone across 180 degrees, but then why wouldn't they say that it's the line C? And if it is, then what has the intersection with D got to do with anything?

Very confused (and worried about passing visibility tests!)

Jesus-Ninja - 1/12/08 at 11:07 AM
For those who are interested, VOSA have replied:

quote:
Hi,

Section 32 in the light vehicle manual has changed slightly in respect that the annex was incorrect, in regards to the intersection of 'D' this is only to determine whether or not there is a windscreen or windshield fitted, the projected line through the windscreen to the floor must be unobscured like the second diagram below shows. The height of 'C' is determined by the angles in Annex 1, also the lower edge of the forward field of view must not be above the “windscreen horizontal plane” 'C' as defined by Annex 1

Angle ‘A’ ‘B’
15° - 19° 582.5mm 178.8mm
20° - 24° 572.0mm 182.6mm
25° - 29° 562.5mm 187.2mm
30° - 34° 553.4mm 191.3mm
35° - 39° 543.5mm 194.9mm
40° + 534.1mm 198.8mm

So, if I read that correctly, I was right in my assumption. Unfortunately this only relates to the forward line of sight, and doesn't tell us whether or not the lower field of vision extends in a flat plane to either side, so I replied:

quote:
Many thanks for your response, Darren. So I was correct in my assumption that the line C is the lowest line of sight that must be unobscured.

I have one other question then. The line C projects forward, angled down 4 degrees from the horizontal. Clearly this is true for straight ahead, as shown in the diagram, but what of in other directions, ie to the left and right of the line C (if the car were viewed from above). Are other lines in the same plane as line C, or do all lines radiating from the theoretical view point angle down 4 degrees fro the horizontal plane. In other words, is the lowest edge of the field of view a flat plane, or a cone shape?

[Edited on 1/12/08 by Jesus-Ninja]