Stormscope or Strike Finder? Placing that question before the Saturday morning breakfast bunch is like asking which is better, a Skyhawk or a Cherokee. Theres no shortage of opinion about which is the best.
Of course, that opinion might not be supported by anything remotely resembling a fact, but thats where we come in.
Like the Skyhawk and the Cherokee, the Stormscope and Strike Finder perform the same function, dont look all that different and from an operations point of view, you use them the same way.
But they have some significantly different characteristics that might play on which one you decide to purchase if you have none at all or you want to upgrade an older instrument.
Weve used the WX-10, WX-900 and WX-950 Stormscopes over a period of years. But most of our experience has been with the WX-950 and weve have studied and photographed its weather mapping traits over a four-year period.
Recently, Aviation Consumer borrowed a new Strike Finder from Insight Avionics and installed it side-by-side in the same aircraft, with a number of flights conducted during the peak thunderstorm season. The test was not a scientific one but we collected enough data to inform the buying decision for any owner. Heres our report.
Hardware
The Stormscope has been through many model iterations since inventor and pilot Paul Ryan developed it during the 1970s. Goodrich Avionics Systems, the current manufacturer, sells four models-the WX-500, WX-900, WX-950 and WX-1000. Well describe our test article, the WX-950.
Its a two-component system-a panel mounted processor/display unit and external antenna- with no remote boxes; except for the antenna, the thing is contained in the panel unit itself. For airplanes so equipped, the WX-950 display can be heading slaved by connecting it to a heading output from an HSI or other source.
A CRT display is used to plot what the WX-950 detects. The display can be switched between a 360-degree view and 120-degree forward view display thats similar to the view of a weather radar. Brightness of the display is manually controlled through a dual-function knob that also serves as the on-off switch. Four buttons along the bottom of the display control range, access menu options and clear the display.
The controls-few as they are-are easy to operate and logical. We doubt if anyone would have any problem understanding this instrument after a few minutes with the manual.
The Strike Finder has been manufactured by Insight since its development in the early 1990s by John Youngquist. Although it has been improved over the years, theres only one principle model in the product line.
After Insight introduced the Strike Finder, it enjoyed a considerable price advantage over competing Stormscopes and it sold like hotcakes. Goodrich, then known as B.F. Goodrich, took notice and went after Insight for patent infringement. Goodrich was able to convince a judge that Insight infringed on several of its patents and blocked the sale of the Strike Finder in the United States for several years. Sales continued outside the U.S. and resumed here after the patents expired.
The Strike Finder is also a two-piece system consisting of processor/display and antenna. It can be heading slaved to an HSI but the Strike Finder has a unique option that allows heading stabilization without external heading source.
Realizing that many aircraft lack a slaved compass system, Insight created a stabilization module that rotates the display relative to aircraft heading changes. It can be ordered integral to the processor/display or it can be added to the rear of the instrument later as a snap-on module. Older Strike Finders can be retrofitted with the heading module, a $1500 option.
Two display options are offered for the Strike Finder, gas plasma or ultra bright LED; both operate in a 360-degree view only. Brightness is controlled automatically with no manual control. Four buttons at the bottom of the display control range, clear the display and activate the time travel feature, more about which later.
Install, Skin Map
Installation of the WX-950 and Strike Finder in some aircraft can be tricky because you cant always just stick them in any available hole. Theres got to be enough space behind the panel to accommodate the nearly foot-long processor/display.
The 3-inch ATI faceplate configuration of the WX-950 requires a special square-shaped mounting hole but most good avionics shops are equipped with an expensive punch that can modify an existing round hole without major panel surgery. The Strike Finder processor/display will fit a standard 3 1/8-inch mounting hole and if ordered without the stabilization module, it enjoys a slight length advantage over the Stormscope, which is to say its shorter. In some airplanes, an inch matters and in these cases, the Strike Finder may be the only option.
The WX-1000 is a three-unit instrument, with the processor housed in a remote box in the avionics bay, a more complex installation problem. Another option is the WX-900, which is shorter than the WX-950.
Both devices are sensitive to antenna placement and may not work correctly if the antenna is placed near electrical noise sources in the airplane, such as strobe power supplies, flap motors and the like. Installations therefore usually include skin mapping to find a quiet spot for the antenna.
The Strike Finder has a self-contained mapping feature while shops installing Stormscopes usually have special equipment to locate the antenna.
Good Listener
Both the Stormscope and Strike Finder are passive, receive-only devices that listen for the electromagnetic energy created by thunderstorms. They listen for this energy through antennas that operate much like the combined loop and sense antenna of a modern ADF.
Not surprisingly, azimuth to the storm is determined in a way similar to how the ADF finds a non-directional beacon. Distance to the storm is calculated by comparing the energy received from the storm to the signature of a generic thunderstorm stored in memory.
If the signature of the detected electrical activity is close to that of the memory-stored thunderstorm, then the distance should be reasonably accurate. Stronger or weaker energy will skew the depicted distance closer or farther.
You dont have to be an electrical engineer to see the limitations of sferics devices. Both Goodrich and Insight make advertising claims such as advanced ranging algorithm and digital signal processing to tout the accuracy of their instruments.
In the real world, neither is perfect. Theyre superior to the first generation Stormscopes, of course, but it still takes a healthy measure of experience to use one of these devices effectively, due to inexact ranging. Determining range can be more art than science and may require ground radar reports from FSS or ATC to help.
The Stormscope is unique in its ability to display thunderstorm discharges via two modes- the cell mode or the strike mode. The strike mode plots more or less the raw, unfiltered data as its received with an x display graphic and it tends to lead to less compact and more spread out groups of discharges.
Lack of filtering was a weakness of early Stormscopes and, indeed, in strike mode and in active conditions, the WX-950 shows classic radial spread, the pie-shaped wedge of discharges common to early model Stormscopes. The Stormscope cell mode, on the other hand, performs some sophisticated filtering to reduce radial spread. Cell mode tries to associate discharges it receives with others detected in the selected display range and view. If a detected discharge cant be associated with a group in the selected range and view, the Stormscope doesnt display it unless its within a 25-mile radius of the aircraft. This tends to create tightly packed groups of discharges on the display using a + symbol more or less, painting a crude picture of the cell.
The Strike Finder plots strikes through tiny dots on the display. At 100 and 200-mile ranges, single dots represent a 100-square mile area (10 miles by 10 miles). Multiple strikes within the same area may only plot as a single dot.
When zoomed to 25- and 50-mile ranges, single dots are transformed into at least four dots that enhance the perceived size of the weather area. If a single dot on the 100- and 200-mile range represents more than one strike, it will transform into more than four dots when zoomed to the 25- and 50-miles.
In action, the detected weather presentation of the Stormscope in the strike mode and the Strike Finder are nearly identical. It appeared to us that when there was a difference, the Strike Finder had a definite edge in accuracy vs. the strike mode of the Stormscope.
We tested accuracy by comparing the aircraft airborne position at a certain time with a ground-based radar plot of the weather retrieved after landing. Where the two instruments diverge is when youre using the Stormscope in the cell mode. The Stormscope displays what it detects in a much more defined way when using the cell mode and the ranging appears to be more accurate than the Strike Finders, again compared to the ground-based radar plot.
Display Differences
One of the most visible and significant hardware differences between the two devices is the display. The most oft-heard criticism of the Strike Finder concerns its gas plasma screen. Some complain that its sometimes difficult to see in bright lighting conditions.
Insight has definitely fixed this with the new ultrabright LED display. Even with bright sun shining on the display, it was plainly readable. The automatic brightness level feature worked well and we never longed for a manual adjustment.
The CRT of the Stormscope, however, gets our vote for the best display. It can produce a finer, more detailed picture than the Strike Finder, especially on the shorter ranges. This came into play during our flight tests. While flying parallel to a weather area and trying to locate a gap ahead large enough to safely fly through, we were able to identify a hole with the Stormscope through a combination of the cell mode view and the finer resolution of the CRT display.
The Strike Finder view was too coarse to pick out the gap. After reviewing videotape of the flight, we could see how perhaps the Strike Finder did depict the gap, but in the dynamics of flight, we couldnt discern it.
Using the Stormscope cell mode is not without its problems, however. A weather area has to have a fairly high level of electrical activity before the Stormscope will depict it. Thats most likely one of the reasons behind the development of the dual strike/cell mode Stormscope. Goodrich realized that the cell-mode only Stormscopes werent depicting activity areas that might not tear your wings off but would certainly get your attention.
We experienced this once when flying with the cell-mode-only WX-900. Users of cell-mode only Stormscopes-WX-1000 and WX-900- should keep this in mind.Airborne, we use the Stormscope strike mode as the rest posture. When activity is detected, we switch between modes to try to pin down range with a strong bias toward the cell mode, which cleans up and defines the display.
Bells and Whistles
The Strike Finder has a feature dubbed time travel. This utility replays the last 4000 strikes or one hour of storm activity. Insight says it paints a dynamic picture of thunderstorm life-cycle and movement and amplifies weather indications that may be slow, vague and unrecognized in real time.
We tried using it a few times but, frankly, we couldnt make effective use of it. Owners weve talked to have mixed views about this feature. Some think its a gimmick, others say its useful.
The Stormscope has a utility that we found quite useful- the discharge rate indicator, sometimes called strike rate counter. This is a numerical tally of the average number of strikes received per minute. We found this to be a valid indication of storm severity.
Unlike the counter on the WX-900, the WX-950 rate counter is adjusted for the strikes detected in the selected range and view.
The Stormscopes 120-degree forward view is another feature that we use often. It presents a more detailed view of the weather and it eliminates from view the WX-950s somewhat misleading view to the side. (See sidebar.)
Our Strike Finder test article came with the heading stabilization module and we found it to be handy but not absolutely necessary.
To employ the Strike Finder effectively, the clear button must be used frequently to assess the rate of strike population, giving some clue to storm severity, whether the display is heading stabilized or not.
Both the Stormscope and Strike Finder will accept inputs from various heading devices.
Insight developed their ingenious stabilization module for airplanes without slaved heading systems, but its not the only way to achieve relatively inexpensive heading stabilization. Sigma Tek makes a directional gyro that will output heading to other appliances. List price is from $1550 for an unlighted unit without autopilot interface to $2700 for a lighted one thats autopilot capable.
Last, the instructions shipped with each unit: Insights Strike Finder Pilots Guide beats the Goodrich offering hands down, in our estimation. It provides a well-written narrative of how to effectively use the instrument. Issues such as how to deal with heading versus track when flying in crosswind conditions are discussed and useful rules of thumb are offered. The Stormscope manual is adequate but nothing special. You can actually download it from Goodrichs Web site.
Conclusion
In this side-by-side test, we found the Stormscope cell-mode ranging solution to be the best, in terms of accurately painting the distance to the weather. But the Strike Finder, in our view, has a better antenna system that provides the best 360-degree view.
We like and use the Stormscopes discharge rate counter but the Strike Finder rejects discharges received via atmospheric skip more effectively than the Stormscope does. In other words, in some conditions, the Stormscope will show weather thats not there but is, in fact, many miles over the horizon.
In the end, both the Stormscope and the Strike Finder will keep you out of thunderstorms if you use them correctly. Theyre not instruments to find a tiny hole in an intense line of thunderstorms but are best used strategically in conjunction with eyeballs to make gross deviations around thunderstorms. The price advantage of the Strike Finder is attractive and bought purely on price, we think the Strike Finder is the better value. But if price isnt the driving consideration, the WX-950 does offer compelling features that make it worth the extra money. But the two are so close in performance and value that installation considerations or dealer preference may tip the scales in favor of either.
Also With This Article
Click here to view “Checklist.”
Click here to view “Strike Finder, Stormscope, Radar and Eyeball.”
Click here to view “The Stormscopes Blind Sides.”
Click here to view “Stormscope/Strike Finder Compared.”
Click here to view “Addresses.”
-by Bill Kight
Bill Kight is a captain for a major U.S. airline and owns a Mooney 201.
