TOV Sail Testing Report 2019.pdf

TOWER OF VOICES SAIL TESTING REPORT

MORTON ILLINOIS 10-27-2019 TO 11-4-2019

Nord Embroden

Sail testing week included a wide variety of wind and weather conditions which allowed a review of performance in optimum and less than optimum conditions.

TESTING WEEK SYNOPSIS

Sunday

Sunny, calm and moderate temperatures. Almost California weather.

Sunday evening I met with Brett and received a tour of his facility and discussed the schedule for the coming days.

Monday

Weather was nice but the winds were light and variable.

Worked to prepare the tracks with additional holes and appropriate fasteners. Installed identical stop screws at the end of the tracks. Marked track positions on all end plates for bidirectional car positions.

Assembled fan test and observed wind speed and effective area Determined fan HP combined (.72 HP) was inadequate . Effective area was only a 20” W X 18” H rectangle. This would require 2 HP minimum from two larger fans. Airflow was fairly even but wind speed was 4 mph base with momentary gusts to 7 mph from the sweeping fan at 4- 5 feet from the fan bank.

Sail B was completed.

Wrapped the tower column with plastic to reduce turbulence.

Removed the top of the scaffolding.

Chime tubes were completed and installed on the tower and the Sail A and Sail C were hung and observed.

Tuesday

Freezing rain with light to moderate wind from the North Tested all sails on the tower cycling from North to South.

Observed turbulence around tower and back winds near the tower on the South side causing frequent sail spinning.

Wednesday

Blowing snow increasing through mid-day. Winds moderate with stronger gusts to 19 mph peak primarily from the North.

Sails, chimes and tethers had iced overnight with ¼” of flow ice completely down the North chime assembly.

Observed a deadening of the chime when iced.

Removed sails by defrosting the hardware with hot water and allowed them to warm inside. Waxed the entire sails and endplates to moisture to sheet off and reduce ice buildup.

Stiff frozen tethers continued to function properly during testing without noticeable degradation of movement.

Thursday

Cold and overcast with wind chills to 9 degrees. Light to moderate winds. Rapidly variable wind speeds. Winds primarily from the West.

Continued cycling sails through the North and South assemblies. This was an excellent day for comparisons as the wind was primarily perpendicular to the tower cross arms.

Made comparison observations as well as zeroing in on optimum track positions in a variety of base wind speeds.

Friday

Cloudy and warmer with lighter winds from the South and South West. Continued comparison testing and observed different performances from each sail from previous days as a result of wind changes.

Saturday

Moderate variable winds. Continued to observe optimum track positions for the varied winds. Sail comparisons were altered by different wind conditions. Removal of all the scaffolds.

Sunday

Sunny and warmer with light to moderate winds from the South, South West and West. Great day of testing in a variety of winds as the tower was much clearer of obstructions to the West without the scaffolds.

Solid work on fine tuning optimum track positions for a variety of winds.

Debriefing with Brett, Chris and myself.

Monday

Measured track positions and center of gravity for each sail. Reweighed each sail with tracks on. Debriefing session with the team prior to my departure mid-day.

SAIL SELECTION CRITERIA

1. Performance

2. Strength

3. Fatigue Strength

4. Ease of Construction

5. Aesthetics

6. Cost

SAIL PERFORMANCE

1. Starting Power

2. Functional Wind Range

3. Strike Power Db

4. Strike Frequency

5. Tone and Sustain

6. Weight

7. Ability for high wind throttling

SAIL DESIGN A

Most stable of all three designs in all wind conditions.

Requires a longer adequate wind period to accelerate and produce strikes than C. Slower to get started producing strikes but once moving continues through a variety of light wind conditions from 4 mph to 7 mph.

Able to produce clear strikes with good sustain in winds as light as 5 mph through winds 15 mph with gusts to 19 mph as experienced during test week.

Reliable producer of clear light, moderate and heavy strikes with good sustain.

At times the frequency of strikes were less than Sail C but sufficient in number.

Does not tend to stall in light winds.

Does not get caught backwards as the airfoil shape is symmetrical.

Sound occasionally heard from the sail chamber. Sail cavity could be foamed with urethane to eliminate sound.

More difficult to construct with lots of labor in threading and screw installations.

SAIL DESIGN B

This was the last sail to begin testing.

In many ways Sail B has a motion similar to Sail C but does not respond as quickly as A or C to increasing wind speeds.

Able to produce clear strikes with good sustain in winds as light as 7mph through winds to 15 mph with gusts to 19 mph.

Asymmetrical sail allows the sail to get caught backwards in light winds on occasions to 9 mph for some conditions of stable wind. Turbulence assists in returning the sail to a driving position.

More prone to being caught backwards than Sail C and remains in this condition for a longer period of time.

Moving tracks to outside far weather position improved this issue considerably almost preventing this backwards stall from occurring.

Slowest of sails to pick up and get started. Once moving continues to make good clean strikes.

Frequency of strikes is good once in motion.

Sound occasionally heard from the sail chamber. Sail cavity could be foamed with urethane to eliminate sound.

Most difficult to construct with tabs and screws.

SAIL DESIGN C

Able to produce the most starting power in light wind of all the sails.

Will initiate motion and strikes in winds as low as 4 mph to 7 mph.

Excellent light wind acceleration. Best of all the sails.

More radical motion, less stable with harder jarring strikes than Sail A in the higher wind speeds.

Easiest and quickest to construct and assemble.

Able to produce clear strikes with good sustain in winds as light as 5 mph through winds to 15 mph with gusts to 19 mph as experienced during test week.

This sail consistently showed excellent performance with frequent clear strikes.

GENERAL OBSERVATIONS

Turbulence from the wide flange tower beam had a considerable effect on the downwind test side which often times made it very difficult to compare performances.

The scaffolds created considerable turbulence at the sail level and dropped the wind speed by 2 to 3 mph with winds from the West. Removal of the top helped. Eventually we removed all the scaffolds on Saturday to clean up the airflow.

Winds were always variable in direction and widely variable in wind speeds with short durations for gusts. These conditions existed every day of testing regardless of the weather, wind direction or speed. The site had considerable wind obstructions to the West, South and East that created wind shadowing and turbulence. These conditions slowed our progress and made it difficult to hone in on the exact optimum track position for any given wind speed.

Turbulence and the time period of useable starting wind have a huge influence on the starting motion of the sails and the time required to initiate useable strikes. Once the sails are in motion the striking will continue down to wind speeds of 4 mph as the strikes becomes more subtle.

CONCLUSIONS

Over this week of testing I observed firsthand the effects of wind shadow, turbulence, wind speed variations, gust duration and strength on how each of the sail designs reacted. Each sail design had times that their performance was superior to the others.

Sail A provided a slower response to starting in light winds and required a longer duration of 6 mph to 7 mph of steady wind to get started generating strikes than Sail C. Once moving Sail A was a reliable generator of clear strikes down to 4 mph and up to our maximum gust of 19 mph. Sail A was the most stable and reliable sail in the higher winds producing well space clear strong strikes.

Sail B was a good producer of clear strikes with a similar motion to Sail C. Sail B was the most difficult to get started generating strikes in light wind and developed a radical motion in higher winds like Sail C. Sail B is relatively stable in a stalled backward position in winds from 4 mph to 7 mph and can remain stalled for several minutes in light steady wind. Setting the attachment tracks to the far outside and turbulence reduces the chance of stalling.

The overall trend throughout the week was superior starting performance from Sail C in light winds 4-7 mph. I also observed better power generation and strikes from Sail C in severely turbulent conditions around the lee side of the tower. Only the opening slot between the two sails needed to be exposed to some clean air to get the sail generating and producing strikes. In winds of 15 mph and above Sail C develops a more radical and jarring motion with strong and rapid strikes.

During the week of testing we were able to evaluate the sail attachment points and narrow them down to a usable range of about 3” top and bottom. Movement of the top position effects the optimum position on the bottom track. The starting point of this range is from the center of gravity of the sail forward. The bottom tether position needs to be slightly ahead of the top suspension position for the sail to function properly. The optimum point is dependent on the wind speed and level of turbulence the sail is experiencing. Further analysis of our data from this test week will allow us to select the optimum positon for the widest range of expected wind conditions.

From this test data we will be able to locate our fixed points on the production sails.

RECOMMENDATIONS

I observed the sails and chime assemblies in action. The assembly and sails are both subject to strong, frequent and repetitive vibrations. The overall reductions in screwed and bolted connection will increase the reliability of our system. Care and cleanliness must occur during fabrication and assembly with the use of single use Nylox nuts, maximum thread engagement and Loctite for blind assemblies. We need to improve the sail finish and quality of construction using roll bending rather than step bending. Sails should be constructed to reduce labor and the possibility of failure from screws and fasteners coming loose as a result of vibration. Additional care should be taken in the accuracy, production, assembly and finish of the sails to provide a reliable and optimized power source for the chimes.

I feel that it is very important to analyze the sail performance in the actual tower in Pennsylvania. The test should be performed by taking measurements and observations of the sail at three levels in the tower (lower, middle and top) and also in obstructed and clear ported locations. I believe these tests will identify the optimum sail or sails for the actual conditions at the site. I believe these tests are critical to avoid a miss step created by not testing in the actual working conditions at the tower. This could be as short as a one or two day test and would verify that we have an operable and optimized system prior to production.

Absent of performing an actual sail and chime assembly test, wind measurements and turbulence should be observed. At a minimum the wind speed and characteristics should be established by taking measurements and observations of turbulence at three levels in the tower (lower, middle and top) and also in obstructed and clear ported locations. This data can be compared to the data we collected at the Fugate Morton test tower and will assist in optimizing the connection positions and verify that we have selected the appropriate sail design.

In the absence of any actual site testing and data, my recommendation would be to move forward with Sail Design C at this time understanding its limitations and radical movement at higher wind speeds. Throttling method may need to be designed, tested and incorporated prior to final production.