… solution by reading from a scale

[WebPilot]

 More practice.

Question #2: What is the estimated exhaust diameter for a 100 lbf pulse-jet? Determine the exhaust area.

[Kool]

More practice.

Question #2: What is the estimated exhaust diameter for a 100 lbf pulse-jet? Determine the exhaust area.

I've enlarged the picture with Paint, so it's not very accurate

I drew the line from the origin to the 100 lbs value. The inside ring gives exhaust diameter, and readed from my enlarged drawing, gives that an exhaust diameter of 5.7 inch. Checked this with square the 5.7 value I become the D² value: 32.49. From that side I've looked to the the inner scale of the outer ring, and that gives also the 100 lbs thrust value.

In the pulsejet calculator I get 5.64 inch, and I think with an better picture of the scale 'device' that it more matches.

exhaust area: π x r²
I'm not very common with inches, so I have also added a metric value. In inches this is. (0.5 x 5.7)² x π= 25.5 inch²(??)
5.7 inch = 144.78mm. (0.5 x 144.78)² x π= 16462.926mm² = 16.5 cm²

[WebPilot]

 Paint?

 Very good, Poech. As a check, I submit the following.

 This is a partial pic of my chart's Rev B and the inner ring now has an additional scale: the inner is now De and the outer scale is Ae or the exhaust area.



 Having drawn a red line from the center to 100 lbf, one can read on the inner ring: De = 5.69 in and Ae = 25.4 in². 

 Using a calculator (no need to with Rev B), Ae = π/4 × (5.69 in)² = 25.43 in²

 Thus, I can read quite easily and accurately from this circular chart and agree with what you posted.

[WebPilot]

 Point taken, Poech, concerning mm to/from inch conversions. I can use the program, units, on my machine to often times do the conversion for me.

Code: Select all

$ units
2445 units, 71 prefixes, 33 nonlinear units

You have: 5.7 in
You want: mm
	* 144.78
	/ 0.0069070314
You have: 25.5 in in
You want: cm cm
	* 164.5158
	/ 0.0060784435
You have: 

 I am working on another chart to do just this conversion of units. Maybe someday I'll add a ring to the thrust/diameter chart to incorporate both systems of units.

[WebPilot]

 Yesterday, I was able to do this chart. It converts from in to mm und vice versa.

   (c.t.)

[WebPilot]

 I like this scale. I don't use the MKS system too much, and it's nice to have a feel immediately of what size or scale the problem at hand is. With this scale you can quickly do that without a calculator and not get all caught up in pressing the keys in the wrong order or even worse the wrong key and having to start over again.

Well, you might ask yourself, "what good is a conversion scale if it only goes to 10 mm?" It's plenty enough and here's why.

 Let's convert 0.1 mm to inches

• at the bottom right of the scale, locate 0 and 0.5 and the remaining 4 somewhat large tic marks each respectively denoting 0.1, 0.2, 0.3, 0.4 . Put your mouse cursor on 0.1 and read the inch scale as 0.004. Why? The midway point to 0.01 is 0.005 and each division is 0.001.

[WebPilot]

 

• Now move up the scale just a 'tad' and find 1 on the mm scale. Looking to the left, read 0.0395 . If you divide both by 10 (or move decimal to the left by one position), we have another, even more accurate estimate for 0.1. Namely, 0.00395 !
  
  That's 0.00005 less than the above reading.

[WebPilot]

• Now continue moving up the scale and locate 10 on the mm scale. On the left scale, read 0.393 plus ¾ of a division, which is .75 × .001 = .00075 . Combining these together, all done in your head, one obtains 0.39375 in for 10 mm.
  
  If you divide both by 100 (or move the decimal point to the left by two positions), we have another, even more accurate estimate for 0.1 mm. Namely, 0.0039375 in !
  
  If one multiplies both by 100 (or move the decimal point to the right by two positions), we have the estimate 39.375 in = 1000 mm = 100 cm = 1 m.
  
  All done with a conversion scale from only 0 to 10.0 mm .

[WebPilot]

•  
• With practice, the rest of the scale can easily be read to 3 digit accuracy, which is plenty for most engineering computations.

[WebPilot]

(c.t.)
  Rev-B

[WebPilot]

... more to come.

[WebPilot]

 Feb 05? Seems like I'm overdue for a new 'rule.