Reading nomogram (needed to adjust my truck roof air deflector)

[Trilis]

I have this nomogram. Need to find H meaning

I can measure A and B.

Example:
Distance "A" = 1,700 mm
Distance "B" = 1,475 mm
This gives adjustment dimension "H" = 1,145 mm.

So if my Distance "A" is 1,750mm, how can I get H meaning?

 

[Dr.Peterson]

View attachment 10263
I have this nomogram. Need to find H meaning

I can measure A and B.

Example:
Distance "A" = 1,700 mm
Distance "B" = 1,475 mm
This gives adjustment dimension "H" = 1,145 mm.

So if my Distance "A" is 1,750mm, how can I get H meaning?

What do you mean by "meaning"? Are you asking for what physical quantity it represents, or what formula would give H in terms of A and B, or just the value of H for a value of A not shown?

It may help if you show what was said about this "nomogram". (I would just call it a graph; what I think of as a nomogram is typically more elaborate than this, usually involving drawing a line two cross two or more given lines.) What is its source?

Also, what is your context? Are you just in a profession where you need to use this, or in a class where you are learning about equations? Is this a real problem, or an assignment to find the equation?

 

[Trilis]

What do you mean by "meaning"? Are you asking for what physical quantity it represents, or what formula would give H in terms of A and B, or just the value of H for a value of A not shown?

It may help if you show what was said about this "nomogram". (I would just call it a graph; what I think of as a nomogram is typically more elaborate than this, usually involving drawing a line two cross two or more given lines.) What is its source?

Also, what is your context? Are you just in a profession where you need to use this, or in a class where you are learning about equations? Is this a real problem, or an assignment to find the equation?

Typically would be great to get a formula. I need this to adjust my truck roof air deflector, as on the instructions there is given only this graph. Adding the full instruction and source picture. Tryed to think all the way, but seems I am missing something, can not understand this. Maybe I am thinking wrong direction.

The article:



1. Measure distance "A" from the rear edge of the door to the front edge of the bodywork.

2. Measure distance "B" from the weld flange/leading edge on the rear wall to the top edge of the bodywork.

3. Read value "H" in the nomogram.

4. Undo the screws at both the front and rear of the roof air deflector attachments.

5. Adjust the roof air deflector.

 

[Dr.Peterson]

Typically would be great to get a formula. I need this to adjust my truck roof air deflector, as on the instructions there is given only this graph. Adding the full instruction and source picture. Tryed to think all the way, but seems I am missing something, can not understand this. Maybe I am thinking wrong direction.

The article:

View attachment 10267

1. Measure distance "A" from the rear edge of the door to the front edge of the bodywork.

2. Measure distance "B" from the weld flange/leading edge on the rear wall to the top edge of the bodywork.

3. Read value "H" in the nomogram.

4. Undo the screws at both the front and rear of the roof air deflector attachments.

5. Adjust the roof air deflector.

I can write an equation to give H for a given B, for one of the values of A shown, since the equation is just a straight line. Unfortunately, it is clear that the slope of that line does not depend linearly on the value of A, and just three known values are not enough to be at all sure how it does depend on A (especially since I know nothing from the physics or aerodynamics to tell me what form the relationship should have). Really, you need to go back to the source of the graph and ask them either what formula they used, or what the graph will look like for your A=1750.

I played with the numbers on a spreadsheet, and can at least make a guess at something that may not be far off. What I find is

H = 1085 + m(B - 1330)
​

where, possibly,

m = 0.000000343(1850 - B)^2 + 0.0865
​

If so, then for A=1750 and B=1475,

m = 0.000000343(1850 - 1475)^2 + 0.0865 = 0.13473

H = 1085 + 0.13473(1475 - 1330) = 1104.5
​

What the m does is to tilt the line for A=1700 down a little bit, and the result looks about right on the graph. Really, you could just draw a new line slightly below the broken line (about 1/3 of the way down to the next line), but still going through the point where all the lines meet, and you'll probably be accurate enough.

 

[Trilis]

Is it really 1850-B or you just made a mistake?