Next time youre droning along on a cross country on a hot day, feel around the edges of the bezels on your avionics faceplates. In most airplanes, even ones with avionics cooling fans, theyll be hot-not warm-to the touch.
But trust us, theyre probably a lot cooler in operation than they are merely baking in the hot sun on a summer day when the airplane is on the ramp with no cockpit cover or sun screens.
We were recently astonished to learn that interior cockpit temperatures approach 200 degrees on a bright Florida day and that cant be good for the avionics, not to mention the upholstery and all the sundry stuff stored in the average airplane.
Yet as cheap as covers and sun screens are, we would say fewer than 10 percent of owners have and use them, judging by a golf-cart survey down a flight line or two.
Frankly, we think thats dumb. Heat hurts the radios and ultra-violet fades and weakens upholstery, eroding the resale value of your airplane.
So, given that covers or sun screens are a must, which is better? We like exterior covers in general-more on that later-but sun screens are cheaper and perhaps a little more convenient, so lets survey whats on the market.
Prior to the mid-1980s, about the only type of interior shades commercially available were the thin curtain type made of space blanket reflective material held in place by self-sticking Velcro dots attached to the door and window molding.
Several companies marketed this stuff, including Thermacron Sun Shields by Morgan Stanford Aviation Inc. Try as we might, we couldnt find a current source for this type of product, which may be just as well. Other than being foldable and light, this material isnt durable and the Velcro dots tend to wear out. Worse, the dots wear out over time and when exposed to heat, they inevitably turn into sticky blobs of hard-to-remove, dirt-catching adhesive.
No surprise then that around 1985, Kennon introduced the thicker, semi-rigid insulated shades made of a bubble-wrap type material coated with a reflective metallic foil that are the standard sun screen today. Even though these are more bulky and problematic to store inside the aircraft when not in use, most practical shades today are of this design.
Nearly all of this bubble-wrap type material is manufactured in bulk rolls primarily by two U.S. plants. The laminated raw material is about 1/4-inch inch thick and is actually two layers of 2 to 6 mil material laminated together. These two layers are then covered on both sides by thin aluminum foil.
Aluminum has excellent reflective properties and can actually reflect some 93 percent of the ultra-violet rays rather than absorbing them and heating up the shield and the cockpit, at least according to claims by the manufacturers.
The Sun Foil products have a gold-colored Mylar foil as an option. Whether its as effective as the aluminum is a moot point, since both radically reduce interior temperatures.
The main use of this basic sandwich material is for pipe and household HVAC duct insulation. For aviation use, its bound along the edges with Sunbrela type material (or equivalent) and fabricated to fit each airplane type.
Worth noting is that for aviation use, the material is coated on both sides with a thin layer of clear polyester plastic which keeps the raw aluminum from flaking and, more important, from scratching the relatively soft surface of the Plexiglas windows.
At any well-stocked home or hardware store, you can find sources of bulk roll do-it-yourself material and Sportys sells the same uncoated material for $10 per yard, plus $4.95 for enough Velcro coins to do one airplane. Four yards will do the typical airplane, allowing for waste.
Wisely, the Sportys product plainly warns to keep the material away from the glass or risk scratching. The catalog copy also has a prominent note warning of potential scratching. The theory is that the owner will use the Velcro so as to not directly attach or come in contact with the Plexiglas itself. Good luck.
We cant determine how much the uncoated material really scratches windows in everyday airplane use. Could be, the damage is insignificant. Then again, maybe it could ruin your new windshield in one flying season. We can tell you that rubbing the uncoated material against a piece of clear Plexiglas will cause visible scratches. Our view is that pre-made shields of coated material are cheaper than replacing even one window or a windshield. Plus you dont have to bother with making screens that actually fit and youll avoid Velcro entirely, which we think is a good idea.
Kennon Aircraft Shields is the oldest major player in the insulated sun screen field. Kennon makes a wide range of exterior covers and sun screens, using only coated material.
In the early days, Kennon got caught in the coated versus uncoated controversy. According to Kennons Ron Kensey, because of worries about scratching, the company issued what amounted to a massive recall of some 4000 screen sets made from uncoated material, a decision that draw accolades from many owners.
While Kennon makes both interior and exterior covers, Sun Foil Sun Screens concentrates solely on interior screens and claims to have the majority of the market. Sun Foils main claim to fame is an up-scale line of optional gold-colored Mylar-coated screens which the company says makes the shades stiffer and more shrink resistant than the aluminum variety.
Arlington, Washington-based Cunningham Aircraft Covers Inc. makes both interior and exterior covers and its principal, Lynn Cunningham, is a former partner of Ron Kensey in the Kennon operation. Cunningham doesnt use the gold Mylar for his inside sun screens, however, and agrees with Kennon that the high-tech reflective surface doesnt improve performance. However, Sun Foils Julie Shaedel argues that the Mylar shades last significantly longer in severe sun, thus justifying the premium price. We have no evidence to prove or disprove that claim.
Products from all three companies are well made, in our view. In fact, we found them to be among the best designed aviation products weve seen.
The Kennon covers-like the other two products-are custom cut for each aircraft and fit snugly for a force fit in the window opening. Theres a single shade for each window, although the windshield may have one or two covers. Installing them requires some awkward crawling around the cabin, but thats true of all three systems.
We found that the shields are indeed a perfect fit and slip into the window frame with little or no fuss. Mere seconds per window and youre done. Perfect fit or not, we think the screens inevitably shrink with age or otherwise become loose enough to fall out. To guard against that, Kennon screens for some aircraft models have plastic tabs that slide into the space between the interior Royalite and the window glass.
As do the other manufacturers, Kennon provides a cloth storage case and recommends that the screens be rolled rather than folded or placed flat and then loaded last, on top of the baggage. This supposedly preserves the fit but it also consumes space in the baggage compartment so we suspect most owners just cram them into the bag flat or folded.
Kennon screens cost $169 for most single and light twins. Business Class cabin-class twins are $225 and commercial, military and helicopter sets are also available.
The Sun Foil screens come in two varieties; with standard high-grade aluminum foil or with the option of Mylar film for an extra $40. Single and multi-engine cockpit sets, which cover only the windshield and front windows, cost $155 for aluminum and $195 for Mylar. For a full set for all windows, the cost is $185 and $265 respectively. Prices are higher for turboprops and helicopters.
The Mylar looks snazzier, in our view, but were not sure that justifies the additional cost. Also worth noting is that Kennon claims the Mylar coating blocks the reflective properties of the aluminum and absorbs the heat. Our trials confirm that but we believe the heat gain is trivial.
Again, the Sun Foils are well-made screens, with carefully constructed edge trimming, a labeling system on the inside of each screen and elastic straps to aid in removal.
Rather than the plastic tabs Kennon uses, the Sun Foils have suction cups on the glass side of the shield, which provide a fierce grip, even if the shield is exposed to a stiff breeze when you open the door. The cups may leave the typical round tattoo behind, but this is easily removed with routine cleaning. The cups also assure that regardless of shrinkage, these screens will stay put.
Cunninghams screens are more or less the equal of Kennons products but theyre less expensive. For most GA aircraft, Cunningham charges $130. For a cockpit set for a light twin-windshield and front windows only-the price is the same. For $160, Cunningham will ship screens for all windows in a twin.
To find out how effectively the screens shade the cabin, we did some temperature tests with a RayTeck ST2C digital thermometer. This unit measures surface temperatures digitally and remotely from a short distance away by merely pointing the radar-gun like instrument at the surface.
For our trials, we examined various internal components of six Mooneys, including seats, avionics bezels, windows, glareshields and control wheels.
We did our tests on bright Florida days, with OATs in the lower 90s and temperatures sampled at mid-day. Amazingly, with no protection at all, internal cabin temperatures were 85 to 90 degrees higher than OAT, varying from 167 degrees to nearly 200 degrees on black glareshields.
We found that avionics face plates and control wheels warmed up to 167 to 188 degrees, depending on whether the item was in direct sunlight or shaded. No wonder the seats and controls are hot to the touch on a summer day.
We installed all four sun screen products-including the Sportys do-it-yourself material-and measured the temperatures after a day of baking in the sun.
In our estimation, all the products performed virtually identically, reducing the internal cabin temperatures to 106 to 111 degrees on control wheels, avionics panels glareshields and seats. That means the average temperature rise over ambient was only 16 to 21 degrees. Quite impressive, in our view.
We found that the gold Mylar coated Sun Foils yielded internal temperatures about 4 to 6 degrees hotter but we dont think this is significant as far as heat protection is concerned and, in any case, it was well within the error margin of our informal testing. Interestingly, the temperature of the glass itself was consistently between 107 and 113 degrees, with no protection at all, internal or external. When the covers were installed-either internal or external-the glass temperatures were nearly the same.
In our view, theres no appreciable difference in performance between these products. They all ward off the suns heat equally well. Even though the Mylar wasnt quite as effective, the difference is probably insignificant in the real world.
As noted in the sidebar, we think that external covers are a better way to go since they protect the glass from the outside and provide some protection against water leaks. Further, heat-induced outgassing from vinyl and other interior plastics are suspected of causing cloudiness in Plexiglas. Whether thats true or not, reduced cabin temperatures cant hurt, in our view.
But if you dont want the hassle of an exterior cover, sun screens are a must. These products strike us as a cheap way to protect interior components against UV and heat damage.
Also, given the reasonable prices of the ready-made products, we dont recommend the uncoated material just to save a few bucks at the risk of scratching the glass. Furthermore, the ready-made products are nicely edged and fit like a glove. Your home-made version probably wont.
We found all of the sun screens to be worthy, well-made products. For the conventional aluminum foil type, its a toss-up between the Kennon and Cunningham products. Theyre too similar to differentiate, in our view. But the Cunninghams are the undeniable value leader, since theyre cheaper.
If you like the sharper looking gold Mylar screens, go with the Sun Foils. True, theyre not quite as effective as plain aluminum but we doubt if a few degrees matters much over the long haul.
The main point here is that if your airplane is on a hot, sunny ramp, it needs some kind of protection against UV damage. Charts, sheets or a towel thrown over the panel wont do the trick.
by Coy Jacob
Coy Jacob owns and operates the Mooney Mart/Mod Squad Complex in Venice, Florida.