Blowing machine

[Terry McGee]

On a quick look, Tunborough's measurements appear to match mine, though I should probably measure mine independently and report those if we get to doing anything where that matters. But the tip of the beak doesn't perfectly match either of those beak images. We should probably go more on measurements of the head. Here's what I had measured:

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Feadog Mk1?		
Length	Height	Width
0	2.08	8.48
2.15	1.82	
14	1.7	
16.32	1.61	
21.9	1.53	
24.81	1.5	8.23
Average	1.71	8.355
CSA (ave)	14.2592	
		
Window	5.3	8.23

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Feadog (MkIII?)		
Length	Height	Width
0	1.87	8.64
12.93	1.55	
14.57	1.47	
17.61	1.36	
20.84	1.24	
24.03	1.14	
25.2	1.14	7.9
		
Window	6.49	7.9

[Terry McGee]

Those look remarkably consistent with the first two. We're ready to try whistles, and I'd be most interested in the old Generation and the Feadog. For the whistles, if it's not too much trouble, I'd like to see more data points, say every 3 or 4 L/min rather than 5. Thanks for all the numbers.

No worries. I'll pick numbers that are easier to read, like 24, rather than 25, which requires estimating 12.5 on two flow gauges!

[Terry McGee]

Hmmm, reading between the lines from the Feadog website, it seems to suggest:
Mk1 1978-1991?
MkII 1991? - late 2001
MkIII Late 2001 to date.

Seem credible? Works for me.

[Terry McGee]

OK, here's a run on the Feadog Mk1

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Feadog Mk 1				
Flow	MM(H20)	√A/P	Res.	First run
0	0	0.0	0	0
4	4	2.0	0.50	5
8	11	3.3	0.41	11.5
12	25.5	5.0	0.42	26
16	45.5	6.7	0.42	45.5
20	70	8.4	0.42	74.5
24	88	9.4	0.39	94
28	130.5	11.4	0.41	134.5
32	162	12.7	0.40	170.5

Note:
The "resistance" at 4L/Min is much higher than the others. Suggests measurement error at low levels?
The first run figures in right column. I took those down, then rejected them as subsequent checks suggested lower pressures. Wondering if it's because I'd just turned the compressor on? I'd imagine the air from a compressor that has just filled its tank is considerably warmer than air from a compressor that's been idling and just has to top itself up. Or was it when the cool air in the tubes was replaced by warmer air?

I could run a test at one setting and see how it varies with time.

I could probably also measure the air temp coming through with a thermocouple temperature meter poked up the slot. Just tried that and it reads 20C. Room temp is 21C, my finger tips 30C. Poking the thermocouple up the windway slot increases the measured air pressure, so that's not a long term solution! I could always add another T-joiner in the tube leading to the Whistle Connector if we did feel we needed to monitor incoming air temp.

Apart from air temp, I cant imagine what else could be affecting results. I'll keep the antennas up....

Those figures are for fingering ooo ooo. I tried it on xxx xxx and couldn't see any changes in pressure or flow.

[Tunborough]

Those numbers are fitting in very nicely with the results from the calibrators, according to my current model. The 4 L/min reading is definitely an outlier, but if the true flow was actually 5 L/min, or even 4.7 L/min, it falls right into line. It does call into question the accuracy of the flow meter at low levels, but it isn't a big deal in the grand scheme of things.

I was assuming an air density for 21 C, but it's interesting that the model lines up even better when I use 20 C. We'll want to keep an eye on the temperature.

I can't explain the higher pressures of the first run. They would be more consistent with cooler, denser (much denser) air in the whistle, rather than warmer, lighter air.

[waltsweet]

...It sounds like you need a Mass Air Flow (MAF) sensor. I ran into these when I owned a VW Golf. As the name indicates, it tells the mass of air flowing into the engine.
...I understand this to be the principle: The intake air is directed thru a duct of known cross-sectional area. In the path of the air is a calibrated heater wire. We know that a cooled conductor will have a lower resistance. We apply a controlled voltage but with more airflow, the wire cools, and this effects a change in the electrical resistance and current. A sensitive monitoring circuit translates these changes into the mass of the air flowing thru the system. From there, the car's computer tells the other components how much fuel to add to the mix.
...Every flowmeter I've seen has been calibrated for a specific temperature and gas mix. Certainly the humidity factor will compromise the values.
...Sometime around 2018, Trevor Wye made a blowing apparatus (The Automatic Trevor) to test the Cooper Scale on flutes. I don't know the workings of it.
...It seems to me that the setting will have a great influence on the pressure value used: legato phrases, tonguing, and the interval of notes in proximity. And the name of this message board is Chiff and Fipple after all, so the starting characteristics (flow & pressure) will differ from the value of a sustained note. Players pay great attention to ease of speaking and speed of response, and these often dominate the overall opinion of the instrument. Benade discussed the details of transition between initiation and the sustained status.

[Terry McGee]

Hmmm, I tried to catch the compressor out by leaving it off for an hour or two, making sure it was empty, turning it on and monitoring flow, pressure and air temp at the whistle window for a few minutes as it filled up. Nothing much to report.

I got a bit more of a change by holding the whistle and the whistle connector in my hands for a minute or so (as if installing the whistle), and repeating the above. I did see the pressure and the temperature drop a little, but again it wasn't much. I think I'll just have to be vigilant when I carry out these tests to make sure I'm getting repeatable results.

[trill]

. . .

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Test new Pressure-Take-off arrangement		
Flow	Old	Res
20	74	0.430
40	306	0.437

What does that say to us?

Terry, my good sir, I have a request.

Could you run 3 data points ?

What I have in mind is:
1) hook the digi-manometer up to *both* the T and the spigot
2) read the pressure in "differential" mode
3) run 3 cases: 36, 38, and 40 lpm
4) Old Gen or Killarney on the end.

Yes, I'm trying to run down whether your flowmeters are calibrated for oxygen or air.

Kindly humor me . . .

[edited to add item 4 above]

[Terry McGee]

Now, I've actually taken the T-junction out of service, but could swap it back if needed. But let me check first. With the T-joiner and spigot hooked up to the differential inputs of the manometer, is it a problem or complication that the T-junction has a 9.5mm bore, but the spigot opens up on a bore about 13mm? Or can you calculate around that?

[waltsweet]

When I started making whistles back in 2003, I used a tapered bore ("Pro" model and later "WD Sweet" and "Black Pearl" model pennywhistle). Rather soon, the field evaluations seemed to break into two camps, one comparing to Generation and the other to Copeland. Generation is straightbore while Copeland is tapered. I came to understand that there were two blowing styles, and that affected the tuning: the tuning that players could perceive, and the tuning that I could quantify with a Strobotuner. The harmonics have a great influence the perception of the fundamental (I still hate most piccolos on their low D). In short, all my engineering, evaluation and redirection had their limits in terms of meeting the expectations of the market.

[david_h]

I was assuming an air density for 21 C, but it's interesting that the model lines up even better when I use 20 C. We'll want to keep an eye on the temperature.

If that sort of temperature difference is relevant the density of the air in the flow meter might be.

Equations here:https://en.wikipedia.org/wiki/Density_of_air having laboured to put that into a spreadsheet I looked for some numbers to check against and found this: https://www.omnicalculator.com/physics/air-density which would have saved lot of trouble. It gives the same numbers - so either Wikipedia is right or the people who did the calculator used that as well. (I think some related Wikipedia pages may have typos)

Over the range of my wall barometer (950 to 1050 mb) air density varies +/- 5% from that at a standard pressure of 1000 mb (one atmosphere is a bit more). As with car speedometers I guess the real world and Terry's workshop rarely go to full scale.

360mm of water is 35mb, which is a 3.5% change in density as the flow goes up with that pressure.
Going up from 20 degrees C to 25 is a 1.7% drop in density

Those calculations are for dry air. At 20 centigrade the difference between 0% and 100% humidity is about 1%

In the context of flow meters trill earlier gave an equation that had drag varying with directly with density [edit to corrected - wrongly put pressure originally]and with the square of gas velocity. As flow is proportional to velocity (at one point in the meter) I suspect that the flow meter reading varies with the square root of density. I think a floating bead type meter is a 'variable area flow meter'. There is a calibration equation on this page: https://www.brooksinstrument.com/en/blo ... gas-with-a though it is not clear if it's for the same sort of meter.

Not a big problem for us whistlers but maybe Tunborough needs Terry's workshop T, P and humidity.

[trill]

. . . but could swap it back if needed. But let me check first. . .

The diameter change will yield a pressure change. That pressure change might be enough to discriminate between 40 and 42 lpm flow.

My best guess is that, if the flowmeters are calibrated for oxygen, the true flow will be about 42 rather than the indicated 40 lpm.

I asked for a differential reading so as to have only 1measurement instead of 2.

[trill]

. . . an equation that had drag varying with directly with pressure and with the square of gas velocity. . .

Pressure: ??

Square of velocity: yes

[david_h]

. . . an equation that had drag varying with directly with pressure and with the square of gas velocity. . .

Pressure: ??

Square of velocity: yes

Sorry, I meant density and that later (and have corrected it). But in this context it would be much the same as density varies directly with pressure.

Having looked at the products from the company that gives the calibration equation i think it is what we need.



The ratios inside the square root side boil down to density change. We still don't know what gas and conditions Terry's flow meters are calibrated for but it allows a 'sensitivity analysis'. Those flow meters look a bit posher than Terry's and quote accuracy as 1-2% FS

[trill]

. . . https://www.omnicalculator.com/physics/air-density . . . There is a calibration equation on this page: https://www.brooksinstrument.com/en/blo ... gas-with-a though

I ran across the omnicalculator page too. Very nice.

Thank you for the brooksinstrument link and the formula. Very handy.

. . . We still don't know what gas . . .

That's why I bought a flowmeter and ran a test.

At 6lmp, I saw 0.3lpm difference between air+oxygen. I posted a link to a video showing it.

Scaling up to 40lpm would give about 2 lpm difference between indicated and actual flow.

That's why I asked Terry for the cases at 36, 38, and 40 lpm.