40 Footer Fact Sheet
How big is the Reel EFX tornado
Our tornado is 40 feet tall, and the funnel ranges in size from about a foot to 20 feet across. It is driven with hundreds of horsepower worth of fans. The highest wind speed that we have measured in our tornado is 60-80 miles per hour. This makes it a big F0 or a small F1 tornado on the Fujita Scale from F0 through F6. Of course, we can "turn down the volume" on ours to change the size, shape and speed. This makes our tornado a much better camera subject. And, of course, we can run ours for a long time, any time we want, compared to trying to find one naturally.
Why build your own tornado? Why not just go film a real one?
It is very hard to get close to a tornado to make accurate measurements or get high quality film footage. Most tornadoes only last 5-10 minutes, and move a couple of miles in that amount of time. Certainly, there are a lot of tornadoes in some parts of the country (Tornado Alley), but even there, you have to be in the right place at the right time. If you were only 25 miles away from a reported tornado and drove at 60 mph to get there it would probably be gone when you got there. Dr. T.T. Fujita, a noted tornado researcher at the University of Chicago, chased tornadoes for 20 years before actually seeing one.
The popularity of camcorders in the last few years has meant that a lot more people happen to be in the right place at the right time with equipment to get pictures. As a result, there are literally hundreds of amateur tornado videos available now, although none are of broadcast or theatrical quality. This unpredictability (and uncontrollability, too), is why we created an artificial tornado.
How are tornadoes rated?
Tornadoes in the U.S. are rated on the Fujita scale from F0 to F6 based on the estimated wind speed (see the attached chart) and overall size. About 45% of all tornadoes are rated F1, and only 2% are F3 or bigger. An F4 or F5 tornado is a really big one, doing millions of dollars in damage in a 1 or 2 mile wide swath dozens of miles long. There have been very few accurate measurements made of the wind speed inside a tornado for a lot of reasons. First off, it is hard to actually catch a tornado to put instruments into it: Scientists have chased them with planes and helicopters firing rocket probes, doppler radar, and teams of observers hoping to be in the right place at the right time. Normally, scientists usually estimate the speeds, after the fact, by the amount of damage they do. For instance, the roof comes off a typical midwestern house at around 100 mph.
Do we have tornadoes in Southern California?
Although it isn't widely known, we typically get several tornadoes a year in Southern California. We don't get the big F5 monsters that you might see in Oklahoma, but we do get our share of F0, F1 and F2's. Sometimes, tornadoes in our area are referred to by euphemisms like "intense vorticular clouds", "freak wind storms", and so forth. However, if you go look at the damage patterns, and see circular scour marks, you can be pretty sure it was a tornado, and not just a extremely strong Santa Ana.
What causes a tornado?
A tornado is caused by a sufficiently strong updraft, combined with a general swirling motion of the air. As the air is sucked up and in towards the center, it picks up speed, just like an ice skater pulling in her arms in a spin. Of course, since tornadoes are hard to see into and make measurements on, there is a lot of speculation in the scientific community about the details, such as exactly how a tornado gets started, and what is inside a really big one.
The updraft almost always comes from a thunderstorm. In the late spring in the midwest, the conditions are right to form what are called "supercell thunderstorms", from which tornadoes can form. There are also cases of tornadoes being spawned from the updraft from a big fire. In the only known tornado death in California, an oil storage tank farm caught fire, creating a 900 acre lake of flaming oil. The updraft from the flames caused tornadoes to form, which subsequently wandered several miles. One of them crossed over a watchman's shack, picking him up and killing him. An earthquake in Tokyo in the 1920's started a huge fire covering many square miles of Japanese houses (made of wood and rice paper). The updraft from the fire spawned a very large tornado, which subsequently killed tens of thousands of people who had sought refuge in a park in the middle of the city.
In our tornado, we make the updraft with a modified helicopter rotor, essentially a giant fan. We get the swirling motion of the air by using large fans set at a distance and aimed at carefully determined angles to produce the desired effect.
Has any one made a tornado this size before?
Not even close. Our tornado is about 10-40 times the size of normal laboratory scale tornado simulators, which create funnels about a foot high and a few inches across. It is at least 5-10 times the size of the largest simulator we have found in the literature. Furthermore, all the tornado simulators that others have built require large walls surrounding them to remove external influences, and complicated vanes or curved walls to get the tangential flow. Ours is the only one we have heard of which is entirely open, and which uses arrays of fans to get the swirl, a feature which is patent pending, by the way.
Why did you do this?
We made the tornado for use as a special effect in a television commercial, and also to experiment with the technology towards building an even bigger tornado simulator (100-300 feet high). Nobody has built artificial tornadoes on this scale before, so there is very little reliable information available. We are doing experiments with our 40 footer to figure out what the scaling laws are, and what the requirements are for a much larger simulator.
How did you know how to make a tornado like this?
We started by researching the scientific literature and talking to people who had built other tornado simulators, as well as building a classic "Science Fair tornado demonstrator" using a fan and two curved walls. We found that virtually all other tornado simulators have walls around them to direct the air flow and remove external influences, which wouldn't work for filming, since the camera needs a clear view through and around. We hired SARA Inc., a company who normally does work for the Department of Defense and Department of Energy to analyze the fluid mechanics of scaling up the classic "science fair" tornado demonstrator, and found that it probably wouldn't work.
Looking at the results of our analysis, and looking at how tornadoes form in nature, we decided to use an approach which established the circular air flow at a substantial distance (and out of the camera's view) from the eventual tornado. We then built a 1/7th scale model (about 8 feet high) in our shop, with which we then did extensive experiments to determine air flows and fan configurations. From the results of those experiments we designed our full scale simulator.
Is it dangerous?
Not really. Unlike a real tornado, ours can be controlled, and, it sits in one place, so neighboring trailer parks need have no fear. Furthermore, we can turn it off. However, the wind speeds are high enough to pick up small gravel and debris and fling them around. At full power, the wind would knock you down, and the intense swirling and turbulence would make it very hard to get back up. Much of our analysis during the design and testing dealt with safety issues, since we have to work in and around the tornado while it is running. For instance, we have to carefully clear the area where the tornado is running of all loose debris that might be sucked up into the fan, or otherwise blown around.
Fortunately, we don't have to worry about the tornado getting out of the simulator, since it depends on the updraft to work. If it starts to wander out from under the big updraft fan, it would die from lack of energy.
Where would I find out more about this tornado?
Send us email at tornado@reelefx.com, or call Reel Efx, Inc. at 818/762-1710
An interview article with two guys from BBDO London about the commercial
