A couple of weeks back I posted about our experiment conducted on an airport taxiway where we hauled gourds through the air at various speeds, measuring the wind speed and the lateral force exerted by the gourd on the pole at those wind speeds.
Here's a representation of our data. We are very pleased with the way the data came out, force tending to increase exponentially with wind speed as aerodynamic principle predicts.
Let us suppose 16 gourds on a single pole, subjected to a 70 mph wind gust in a violent thunderstorm. Our data estimates that...
16 Supergourds would exert a total sideways pull of 88 pounds (5.5 lbsx16) on the pole.
16 Naturelines would exert a total sideways pull of 80 pounds (5.0 lbsx16) on the pole.
16 Big Bos would exert a total sideways pull of 56 pounds (3.5 lbsx16) on the pole.
Mike Scully
Forces Generated by Winds on Gourds
-
Rich Jewell In
- Posts: 129
- Joined: Sat Aug 28, 2004 5:56 pm
- Location: Indiana Crown Point
Mike
What kind of a pole would you have to have to withstand these pulls?
Rich
What kind of a pole would you have to have to withstand these pulls?
Rich
-
Guest
Scully, the data makes a nice curve in all 3 cases. Did you use Excel to derive a best-fit curve for the data? With this data it's not that difficult to calculate the bending moment on the pole and the deflection of a given size pole when from this force.
You have sure come up with some nice ideas for your student's projects. I'll bet they are greatful to have you as a teacher.
On a side note, I have 2 daughters that attend an elementry school about 1/4 mile from my house (as the crow flys). They have kindergarten - 5th grade at the school and my daughters are in 5th and Kindergarten. I have considered putting up martin houseing at their school similar to what you have done but on a smaller scale (maybe 1 pole the first year). What do you think about a martin project with this age group (5th grade is oldest)? Also, do you think it would work very well with a parent initiating this instead of a teacher?
You have sure come up with some nice ideas for your student's projects. I'll bet they are greatful to have you as a teacher.
On a side note, I have 2 daughters that attend an elementry school about 1/4 mile from my house (as the crow flys). They have kindergarten - 5th grade at the school and my daughters are in 5th and Kindergarten. I have considered putting up martin houseing at their school similar to what you have done but on a smaller scale (maybe 1 pole the first year). What do you think about a martin project with this age group (5th grade is oldest)? Also, do you think it would work very well with a parent initiating this instead of a teacher?
Rich... at this point we haven't tested any poles. Actually we were surprised that the force of the wind acting on the gourds was a small as it was. We weren't sure going into it that our force sensor would have a high enough range to record the data. Based upon that experience I sure would hate to speculate about pole strength.
We use the old slender Carrol telescoping poles supporting up to eight gourds and have twice over the years had poles bend but not break in storms. it is a sobering thought though to imagine pulling sideways on the top of one of our poles with even forty pounds of force.
Mike Scully
We use the old slender Carrol telescoping poles supporting up to eight gourds and have twice over the years had poles bend but not break in storms. it is a sobering thought though to imagine pulling sideways on the top of one of our poles with even forty pounds of force.
Mike Scully
HW... The data DOES look good doesn't it 
I should reiterate though how we collected the data. Briefly; two runs per gourd type at 70 mph, 50 mph, 30 mph and 10 mph (as indicated on the car speedometer, the actual wind speed varied).
The software collecting the force data did not record the data in a chronological time-specific manner like the wind speed software did, but instead just recorded time as seconds after the start of the run.
It was not possible to start both programs at exactly the same time hence we did not know exactly what force reading went with each specific wind speed reading within each data run. However, when plotted on a graph, the shape of the force data rising and falling as we began and ended a run closely resembled the shape of the wind speed data rising and falling for that same run. Unable to match data exactly, we picked the top ten recorded values for force and wind speed for each run and paired them as ten lines of data, high to low.
The four separate clusters of data for the different speed trials on each graph fit the curve pretty well. Note the Natureline data is the most scattered, we feel this reflects the thrashing around that occurred when this gourd was driven through the air at speed (probably due to the flat bottom, see photo below)
We had Excel plot the curve, "exponential" fit best, even better than "2nd order regression". At this point I'm gonna have to consult the Excel manual and a stat book
before we can start dabbling in regression.
With regards to the poles, we'll start looking at that next. Somewhere on my hard drive I have a URL to Chuck Abare's article on calculating pole strength.
Its late and I'm fried, allow me to respond at length to your school query tomorrow.
Mike Scully
I'd thought I'd just edit in a comment here. We have used Natureline gourds very successfully (alongside Big Bos and Supergourds) at our school colony for a number of years, the fact that they were the most unstable in the wind under our test conditions is not meant to imply any design fault.
Along those lines, we plan to go out to the airstrip again, this time with the test gourd attached to a rod and free to swing on only one plane as they would be in actual use. We will drive them down the airstrip and videotape them at different speeds.
This out of intellectual curiousity more than anything else.
I should reiterate though how we collected the data. Briefly; two runs per gourd type at 70 mph, 50 mph, 30 mph and 10 mph (as indicated on the car speedometer, the actual wind speed varied).
The software collecting the force data did not record the data in a chronological time-specific manner like the wind speed software did, but instead just recorded time as seconds after the start of the run.
It was not possible to start both programs at exactly the same time hence we did not know exactly what force reading went with each specific wind speed reading within each data run. However, when plotted on a graph, the shape of the force data rising and falling as we began and ended a run closely resembled the shape of the wind speed data rising and falling for that same run. Unable to match data exactly, we picked the top ten recorded values for force and wind speed for each run and paired them as ten lines of data, high to low.
The four separate clusters of data for the different speed trials on each graph fit the curve pretty well. Note the Natureline data is the most scattered, we feel this reflects the thrashing around that occurred when this gourd was driven through the air at speed (probably due to the flat bottom, see photo below)
We had Excel plot the curve, "exponential" fit best, even better than "2nd order regression". At this point I'm gonna have to consult the Excel manual and a stat book
before we can start dabbling in regression.With regards to the poles, we'll start looking at that next. Somewhere on my hard drive I have a URL to Chuck Abare's article on calculating pole strength.
Its late and I'm fried, allow me to respond at length to your school query tomorrow.
Mike Scully
I'd thought I'd just edit in a comment here. We have used Natureline gourds very successfully (alongside Big Bos and Supergourds) at our school colony for a number of years, the fact that they were the most unstable in the wind under our test conditions is not meant to imply any design fault.
Along those lines, we plan to go out to the airstrip again, this time with the test gourd attached to a rod and free to swing on only one plane as they would be in actual use. We will drive them down the airstrip and videotape them at different speeds.
This out of intellectual curiousity more than anything else.
HW... I would encourage you to initiate a colony at your daughter's school as long as you can accept the worst-case scenario. That being you end up doing all the upkeep yourself and that when your children no longer attend that school, the colony may have to be taken down or else end up being neglected.
First off, make SURE the district is OK with the concept. (Again, worst case scenario; they ask you to take it down mid-season). Try hard to get other parents (from the PTA?) involved. Also, a committed and enthusiastic teacher on campus would be an invaluable help.
I can help you draw up suggested lessons that teachers could use to present to their classes. This would be an effective draw to teachers, who as a group are always looking for new lessons to present.
In my experience few parents, teacher or students will object to the presence of martins, and feeding in live nest cam feed to classrooms is relatively easily done if you wanted to go that route.
Two school-specific stumbling blocks are going to be possible vandalism and what to do about starlings and sparrows. I would imagine lethal control (at least openly practiced lethal control) will not be an option. Otherwise, despite your best explanations the kids and faculty at large will tend to focus on the issue of "killing birds" rather than propagating martins.
I would recommend gourds; somewhat less susceptible to S&S, plus individual kids and/or classes could get a sense of ownership by adopting a gourd or even making gourds from natural gourds (school garden opportunities here too).
Our colony would not be possible without the effective SREH's available today, and we still lose an occasional nest and/or martin to intruding starlings. For both starlings and house sparrows we trap, clip tail feathers and relocate. A practice which works for us but which as generated recurring controversy on these boards (I would kill them if I could, but I can't in our setting).
For deterring vandalism, thus far we have found that splitting the appropriate diameter PVC pipe and then hose-clamping both halves around the bottom of the pole works wonders, (especially if the pipe is coated with vaseline
). In our experience, most acts of vandalism are done on impulse, and are easily deterred by making such that the would-be vandal has to exert some effort.
So... give it a try, just be prepared for the worst case scenarios above, and feel free to ask me for help/advice.
Mike Scully
First off, make SURE the district is OK with the concept. (Again, worst case scenario; they ask you to take it down mid-season). Try hard to get other parents (from the PTA?) involved. Also, a committed and enthusiastic teacher on campus would be an invaluable help.
I can help you draw up suggested lessons that teachers could use to present to their classes. This would be an effective draw to teachers, who as a group are always looking for new lessons to present.
In my experience few parents, teacher or students will object to the presence of martins, and feeding in live nest cam feed to classrooms is relatively easily done if you wanted to go that route.
Two school-specific stumbling blocks are going to be possible vandalism and what to do about starlings and sparrows. I would imagine lethal control (at least openly practiced lethal control) will not be an option. Otherwise, despite your best explanations the kids and faculty at large will tend to focus on the issue of "killing birds" rather than propagating martins.
I would recommend gourds; somewhat less susceptible to S&S, plus individual kids and/or classes could get a sense of ownership by adopting a gourd or even making gourds from natural gourds (school garden opportunities here too).
Our colony would not be possible without the effective SREH's available today, and we still lose an occasional nest and/or martin to intruding starlings. For both starlings and house sparrows we trap, clip tail feathers and relocate. A practice which works for us but which as generated recurring controversy on these boards (I would kill them if I could, but I can't in our setting).
For deterring vandalism, thus far we have found that splitting the appropriate diameter PVC pipe and then hose-clamping both halves around the bottom of the pole works wonders, (especially if the pipe is coated with vaseline
). In our experience, most acts of vandalism are done on impulse, and are easily deterred by making such that the would-be vandal has to exert some effort. So... give it a try, just be prepared for the worst case scenarios above, and feel free to ask me for help/advice.
Mike Scully
-
Guest
Scully,
A couple of questions:
Do you think this project should be directed toward 5th graders? What about the younger students? (I'm sure all the kids would love watching the nestcam and that would be the direction I would like to go) What age are your lesson plans directed toward?
Location of housing: Do you try to keep the poles away from playgrounds where kids may swing around the pole or balls bang against the pole? To consider all possibilities, what if the housing falls?......it seems away from the playground would work better.
I have an extra gourd rack like Dave pictures above (I think mine has the shorter rods and the longer rods make nest checks easier so I may need new hanger rods). I would need the gourds, pole, nestcam, and whatever it takes to hook the nestcam to the school television circuit.
A couple of questions:
Do you think this project should be directed toward 5th graders? What about the younger students? (I'm sure all the kids would love watching the nestcam and that would be the direction I would like to go) What age are your lesson plans directed toward?
Location of housing: Do you try to keep the poles away from playgrounds where kids may swing around the pole or balls bang against the pole? To consider all possibilities, what if the housing falls?......it seems away from the playground would work better.
I have an extra gourd rack like Dave pictures above (I think mine has the shorter rods and the longer rods make nest checks easier so I may need new hanger rods). I would need the gourds, pole, nestcam, and whatever it takes to hook the nestcam to the school television circuit.
Dave... To answer your question... I dunno exactly
The force exerted on a gourd by the wind would, of course, increase with the cross-section area of the gourd as presented to the wind. The Big Bo gourd may actually be larger around looking from the top down than it is when viewed from the side. Which indicates that forces acting upon those gourds hanging perpendicular to the direction of the wind and unable to pivot away from it may actually be somewhat less than those which can pivot end-on to the wind.
Another factor inducing force would be the shape of the gourd and the degree to which it disrupts the air flow, causing drag-inducing turbulence. When the Big Bo is presented end-on to the wind, as in our experiments, the long tapered neck may act as streamlining. On the other hand the bottom of the gourd is relatively flat, and may induce turbulence.
Interestingly, the gourd which appeared to move around least in the wind (perhaps indicating the least turbulence) was the Supergourd, which is also the most uniformly shaped
Our data is probably best considered as a ballpark estimate of what happens in the wind. And at 70 mph, in the absence of better data, I would expect the gourds on the rack pictured to each exert a force somewhere around the 3.5 lb to 5.5 lb range indicated by our data.
Not very specific I know....
Hey HW... gotta get back to teaching, I'll reply shortly...
Mike Scully
The force exerted on a gourd by the wind would, of course, increase with the cross-section area of the gourd as presented to the wind. The Big Bo gourd may actually be larger around looking from the top down than it is when viewed from the side. Which indicates that forces acting upon those gourds hanging perpendicular to the direction of the wind and unable to pivot away from it may actually be somewhat less than those which can pivot end-on to the wind.
Another factor inducing force would be the shape of the gourd and the degree to which it disrupts the air flow, causing drag-inducing turbulence. When the Big Bo is presented end-on to the wind, as in our experiments, the long tapered neck may act as streamlining. On the other hand the bottom of the gourd is relatively flat, and may induce turbulence.
Interestingly, the gourd which appeared to move around least in the wind (perhaps indicating the least turbulence) was the Supergourd, which is also the most uniformly shaped
Our data is probably best considered as a ballpark estimate of what happens in the wind. And at 70 mph, in the absence of better data, I would expect the gourds on the rack pictured to each exert a force somewhere around the 3.5 lb to 5.5 lb range indicated by our data.
Not very specific I know....
Hey HW... gotta get back to teaching, I'll reply shortly...
Mike Scully
-
Guest
Scully, I apologize for semi-hijacking your thread.
Were your tests ran with porches on or off?
Were your tests ran with porches on or off?
-
John & Linda - KY
- Posts: 599
- Joined: Wed Nov 12, 2003 10:19 pm
- Location: Kentucky/Hawesville
Do you thnk the weight of the gourd makes a significant impact on the forces you measured? If so, the weight of the nest in the gourd would have to be considered, although this is probably out of the scope of a school project. -- John
Sorry to be gone so long...
Hogwild... our tests were run with porches off because they would probably have gotten broken and to level the playing field between gourds. I dunno how much force they would add.
John and Linda... Since we were measuring lateral forces, within the weight range of gourd/nest combinations weight shouldn't matter much to our tests. At higher wind speeds, ALL the gourds were blowing back horizontally, but one supposes that a heavier gourd would resist lateral displacement at lower wind speeds, possibly presenting a different profile to the wind.
I have some dried nests from last year we can weigh, I'll get back to you on that. As for the weight of eggs. At 4 grams each six eggs would come in at 24 grams, the young hatch and get heavier. If a pretty heavy nestling weighs 60 grams at peak those same six nestlings would collectively weigh 360 grams, plus two heavy (60 grams) adults equals 480 grams. More or less a ballpark figure of 1 pound.
I'm going to ballpark at this point a nest weight of another pound for the nesting materials.
A Supergourd weighs about 2 lbs, a Natureline about 1 1/2 pounds. A quick browse didn't reveal the weight of a Big Bo but I'm guessing about one pound. Thus for peak expected weights of gourds (gourd plus nest and martins) we get between 3 and 4 pounds. Double or more the weight of an empty gourd given a large nest and brood.
You have a good point, given that our lateral forces on empty gourds were only in the order of 3 to 8 pounds, an extra two pounds of force from nest and young pulling down could have changed the way the gourd rode in the wind. How the lateral force (pulling sideways on the pole) would be affected would depend upon the shape of the gourd.
Sigh!.... prob'ly we should weigh 'em down and re-test
Mike Scully
Hogwild... our tests were run with porches off because they would probably have gotten broken and to level the playing field between gourds. I dunno how much force they would add.
John and Linda... Since we were measuring lateral forces, within the weight range of gourd/nest combinations weight shouldn't matter much to our tests. At higher wind speeds, ALL the gourds were blowing back horizontally, but one supposes that a heavier gourd would resist lateral displacement at lower wind speeds, possibly presenting a different profile to the wind.
I have some dried nests from last year we can weigh, I'll get back to you on that. As for the weight of eggs. At 4 grams each six eggs would come in at 24 grams, the young hatch and get heavier. If a pretty heavy nestling weighs 60 grams at peak those same six nestlings would collectively weigh 360 grams, plus two heavy (60 grams) adults equals 480 grams. More or less a ballpark figure of 1 pound.
I'm going to ballpark at this point a nest weight of another pound for the nesting materials.
A Supergourd weighs about 2 lbs, a Natureline about 1 1/2 pounds. A quick browse didn't reveal the weight of a Big Bo but I'm guessing about one pound. Thus for peak expected weights of gourds (gourd plus nest and martins) we get between 3 and 4 pounds. Double or more the weight of an empty gourd given a large nest and brood.
You have a good point, given that our lateral forces on empty gourds were only in the order of 3 to 8 pounds, an extra two pounds of force from nest and young pulling down could have changed the way the gourd rode in the wind. How the lateral force (pulling sideways on the pole) would be affected would depend upon the shape of the gourd.
Sigh!.... prob'ly we should weigh 'em down and re-test
Mike Scully