Thunderstorms are one of the most terrifying causes of accidents for general aviation aircraft. Short of a CB-proof vest for your airplane, a weather avoidance system can make the difference between life and death, or at the very least, the difference between a smooth flight and a terrifying ride.
The problem is all weather avoidance systems are so darn expensive. Theres radar, theres Stormscope and theres Strike Finder. Soon there will be data-linked weather information to boot. Judging by what weve seen thus far, it wont be particularly cheap either, although it will have added capabilities.
No matter which way you go, youll spend significant coin to remain clear of convective activity. But wait a minute, theres always a cheaper way with this stuff, right? Some way to avoid that coronary-inducing avionics invoice.
So the Aviation Consumer went bargain hunting. The theory is simple: With new technology systems from Insight and BF Goodrich entering the market, surely there must be some outstanding examples of the last generation available on the used market. Are they worth hunting down and installing in your airplane?
History of the Line
Stormscopes are essentially AM radios. Like an ADF, or maybe that Philco radio in the 49 Ford Victoria you listened to on those summer nights parked in Lovers Lane. Remember that crackle that told you there was lightning somewhere? Instead of trying to filter it out, the Stormscope listens for it, analyzes it and decodes natures static shock, providing a relative bearing and distance to the event.
Its the accuracy of that process that defines the Stormscope generations. When Paul Ryan invented the Stormscope, we had little experience and data available to define the characteristics of lightnings signature. As a result, early Stormscopes, such as the WX-7, merely hinted that there was significant discharge activity over there.
By comparison, the latest generation WX-950 can tell you, with fair accuracy, that there are strikes at 37 degrees and 75 miles and it can tell you how many there were in the past 15 minutes. Still, both systems are saying the same thing, dont go there.
The Stormscope product line began with Paul Ryans pioneering WX-7 in the late 1970s and later the 7A. It was a four-box system, with a 360-degree CRT display, a separate receiver box with range buttons, a processor and an antenna. The CRT painted dots where lightning strikes were believed to be. For its day, it was a hot item, since radar was the only other choice. It was expensive and heavy.
There are lots of WX-7s still out there but we dont think theyre worth installing used. Besides the size and weight, electronically, theyre very susceptible to radial spread, which confuses the range picture. Further, they lack the self-diagnostics that give us lots of confidence in modern Stormscopes.
Next came the WX-8 and WX-9 models, which had smaller remotes and better displays. The WX-8-made in the days when 3M had the line-squeezes the display and processor into a single panel-mounted box/display while the WX-9 went back to a separate and rather large remote processor box.
Both the WX-8 and WX-9 had forward-looking only displays; the -8 through 135 degrees in 15-degree increments, the -9 through 180 degrees. Neither of these models had adjustable range. On the -8, range was determined by colored segments and on the -9, the pilot merely guesstimated based on a pair of range lines at 50 and 100 miles. Both were limited to 100-mile range, although with the radial spread problem still extant, ranging was not as accurate as current models are.
We havent seen many WX-9s show up on the used market, but WX-8s are fairly common. Although an improvement over the WX-7, the WX-8 falls far short of our first choice. In energetic storm conditions, the colored range segments flash like a Las Vegas slot machine and alternate between confusing and alarming, in our view. (Flashing segments indicate severe activity.) Better than nothing, perhaps, but not up to WX-10 and later standards. Furthermore, the WX-8 will probably require skin mapping to get a clean install.
Many in the avionics business consider the WX-10 through WX-11 to be the first of the modern Stormscopes. These models re-introduced the 360-degree view the WX-7 had and also had variable ranging out to 200 miles, with discharges displayed on a CRT rather than the LCD used in the WX-8. Thanks to improved processing, the range and display was better than in earlier models, although radial spread was still a problem. The WX-11, introduced in 1984, added gyro stabilization from an external gyro.
Although you probably havent seen one, 3M also had a WX-12 Stormscope, which was designed to generate storm discharge data for display on airborne weather radar.
Towards the end of 3Ms stewardship of the line, the so-called Series II scopes debuted. The WX-1000 featured an impressive CRT and fancy algorithms that helped reduce if not entirely eliminate the radial spread problem. The display itself could be toggled between a 360-degree view and a 120-degree forward-only view and additional features such as checklists and systems monitoring were added.
The WX-900 was a low-cost variant, which was limited to 100-mile range and used an LCD display in place of the WX-1000s pricey CRT. Both have greatly improved self-diagnostics to alert against false negatives. The WX-900 suffers a little for its drab display but it works more than well enough to get the job done. Like the WX-1000, it includes some system monitoring features, such as bus voltage.
The latest product is the WX-950, which has all of the Series II features, plus a cell versus strike mode and a strike counter feature that helps assess the intensity of distant convection. The WX-500 is a remote version of the -950 designed to feed into other displays, such as the Avidyne or ARNAV MFD.
Which of these are best? Obviously, we would pick any of the Series II units first and/or a Strike Finder, which has comparable capabilities and is available in only one model. Since few Series II units are likely to turn up used-ditto Strike Finders-we think any model from the WX-10 on is worth considering, depending on price.
Whats Out There?
Did we uncover a treasure-trove of good used Stormscopes just waiting for installation? Unfortunately, no. Typically, if the last generation Stormscope is working, it stays in the airplane. Many new Stormscopes and Strike Finders are going into airplanes without old units to replace. The used market is fickle and the supply, while not nonexistent, is limited with demand high. So although bargains are rare, they do crop up from time to time.
A recent Trade-A-Plane issue had a passel of WX-8s selling in the $2000 range, WX-10s and 10As for $2500 to $3500 and a few WX-1000s here and there selling for between $5500 and $8000, depending on features. The best bargain in this lot? A WX-900 for $2950. In our view, its easily worth $1000 more than an old WX-8 and will provide modern storm avoidance capability for a reasonable price.
Installation
Early generation Stormscopes are usually three-box systems. Theres an antenna, a CRT display that requires a 3-inch instrument hole and yards of space behind the panel and a remote-mounted processor unit. This stuff has to be mounted and cables routed.
Because the Stormscope is tuned to look for static discharge, installation is critical. Even trivial electrical activity in the airframe can show up as a significant storm in the Stormscope. After all, the signal created by motor brush noise four feet from the antenna would look like a killer storm if the scope assumed the noise had traveled 100 miles.
For this reason, a good installation includes a skin map. No, this isnt a survey of nude beaches in California, but an evaluation of electrical activity in the airplane. The right way is to place an antenna on the skin and feed the signal into a spectrum analyzer.
Running the engines and all accessory equipment, you look for stray signals that might look like a thunderstorm. The Stormscope antenna is then installed in an area with minimum signal in the frequency band of interest.
The second way to skin map is with the Stormscope system itself. Duct tape the antenna where you think it ought to work and power the system up. Again, run all of the systems and see if any storms develop on the display.
This works but we cant duplicate all of the conditions that might be encountered in flight while the airplane sits on the ramp. Weve seen airplanes that would put up dots at 225 degrees bearing whenever the autotrim would run, which may only occur as the CG shifts with the nav lights on…
Newer generation Stormscopes, such as the WX-900, take the skin mapping a bit further and are more clever. The unit incorporates a spectrum analyzer designed for the installation process. You can find the best location without an expensive spectrum analyzer or the BFGoodrich skin mapping kit.
In addition, the system can be calibrated. You can teach the Stormscope. You program the system to ignore the defrost blower or flap motor. Effectively, you instruct the system to reject the signals aboard and flag the new signals that represent real threats.
Expensive Wires
The next installation caveat is the expense of the wiring. Stormscopes dont use ordinary wire, but special cable designed to keep out, you guessed it, electrical noise. Stormscope processor cable can cost as much as $8.50 a foot, with other antenna cable at $4.50 per foot.
Besides the cost, running a stiff bundle the diameter of a supermodels calf through the airframe is challenging. In avionics installation lingo, challenging means time-consuming, which means expensive. Install this golden wire bundle wrong and the Stormscope is as useless as that AM radio in the Ford Vic.
Another installation consideration is heading transfer or slaving. By tying the Stormscope into a source of aircraft heading, you can make the dots track your every move. When you turn away from the storm, you can see it pass safely off your wingtip. Without slaving, the dots remain until you either clear them all or they fade with age. The result is an inaccurate picture of the storms.
Typically, the slaving source is an HSI. Many (but not all) have something called a bootstrap synchro. Mechanically connected to the azimuth card is an electric position transmitter that keeps the display aligned electronically. The cost to retrofit a bootstrap synchro in an HSI can exceed $1000.
A few DGs have bootstraps, but theyre rare. Besides the synchro in the HSI, you also have to provide an AC reference source, which, depending on the HSI or DG system, may have to be an external power supply. More money, more installation cost.
The Insight Strike Finder has another approach to slaving. If youre fortunate enough to own a Bendix/King KCS55A, you can connect the azimuth stepper signals directly to the Strike Finder. The DG in a KCS55A doesnt drive the compass card directly. Instead, after its aligned with magnetic north, the gyro steps the card left or right, in 1/4-degree increments as the airplane turns. The Strike Finder simply does the same thing, tracking directional changes.
We spoke with Greg Bernickis of JA Air Center near Chicago, a leading purveyor of used Stormscopes. Bernickis told us that while they do see many pilots trading in older units on new technology, he isnt eager to put these into other airplanes.
If you look at the difference between a new Strike Finder, which is at $5000 or a used WX-10, which might be $3500, plus installation, for an older technology unit, most people would prefer to have a new unit, with new technology.
Repairs and Support
Stormscopes are very specialized radios. Proper maintenance would be impossible without specialized test equipment. Performance is also a closely protected secret, the subject of a notable lawsuit.
What does this have to do with used equipment? When it breaks, it has to go back to the factory for service. One problem with factory service, besides time and shipping, is duplicating and remedying problems. Do old ones break more often? Maybe, maybe not. But the older a unit is, the more problematic the repairs.
If BFGoodrich cant find an intermittent fault, the unit will make several trips. An unreliable processor could find itself homeless. It could find itself waiting for somebody to come along in search of a bargain. That someone could be you.
For the time being, BFGoodrich pledges full support on all Stormscopes, including the very first WX-7. However, this is subject to parts availability, which is bound to become increasingly difficult with time, especially for purpose-made parts such as antennas.
Conclusion
At the moment, the market isnt flooded with good used Stormscopes. Used Strike Finders are even rarer. Nonetheless, they do spring up here and there. But ask yourself some questions before taking the plunge on someones pre-owned spark detector. First, why would someone yank a perfectly good unit? Could be because theyre upgrading to a new Series II scope or they just got tired of the old one. Or it could be the old one doesnt work very well.
Second, put a sharp pencil on the bottom line. A brand new out-of-the-box WX-900-a basic but adequate model-sells for about $4000 installed. Stepping up a grade, the WX-1000 could be slipped in for about $8500, depending upon features and accessories. The latest model WX-950 can be installed for around $6000 or so. In this field, new Strike Finder are mid-priced, at about $4500 installed.
So what can you get the used one for? If its a $2000 WX-8, allowing for installation, youll have $3000 invested in a minimally performing system compared to $4000 for a new WX-900. Not a good value, in our view. The WX-8 wasnt the best performing scope to begin with and its future serviceability is debatable, in our opinion. Other than the CRT, the WX-900 has everything you need for safe storm avoidance, including impressive self-diagnostics.
On the other hand, if you can snag a WX-10 or WX-11 for the same price and you can confirm that its not harboring any nasty faults or tricky intermittents, it might be worth considering.
Otherwise, if budget is a limitation, a new WX-900 or Strike Finder represents the better value. The price delta over a used one is not that great, installation may go easier and youll be assured of product support for the foreseeable future.
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by Gary Picou
Gary Picou is Aviation Consumers avionics editor. Hes also VP of marketing for PS Engineering, an intercom maker.
