Aeronautical engineers spend countless hours trying to reduce airframe drag. (Only to have the manufacturing division tell them that flush glass and perfectly formed skins are out of the question.) As those engineers learned in school, airframe drag comes from two major sources. One is induced drag, or the drag that stems inevitably from lift production. The other, parasite drag, comes from myriad other sources like profile or form drag (air having to move around airframe components), cooling-air drag, and drag produced by skin friction.
In one form or another, each airframe manufacturer tries to minimize various elements of parasite drag. Smaller cooling inlets and better internal baffling in newer airplanes like the Mooney Ovation help reduce overall drag, as do the fairing in of protruding surfaces like flap hinges and control-surface connections. Over the years, a few airframes have enjoyed substantial speed increases due to incremental improvements in streamlining and the resulting reduction in parasite drag.
Few manufacturers, however, attack head-on the skin friction part of the drag picture. That's where KSBP Speed Cote comes in. According to the product's distributor, Darren Friberg, formerly a flight-test engineer for McDonnell Douglas on the MD-11 program, surface friction can make up as much as 40 percent of overall parasite drag. Speed Cote is produced by Kent Integrated Scientific Systems, maker of Kiss-Cote, a surface treatment for marine applications. For aviation duty, Speed Cote (whose KSBP prefix stands for Kiss-Cote Self-Bonding Polymers) is touted as an easy-to-apply treatment that can reduce surface friction as well as protect paint and make the surfaces easier to clean.
Friberg is quick to point out that Speed Cote is not Teflon-based. It is supposed to be easier to apply than Teflon coatings and remain bonded to the paint better than other silicone-based products. Supposedly, a mono-nuclear layer (about 0.012 microns thick, according to Friberg) is all that's needed for the application. Based on wind-tunnel tests, the Speed Cote provided a 2-percent overall drag reduction at Mach 0.88, while a low-speed test (56 mph) disclosed a reduction of 0.4 to 0.8 percent. A Cessna 172 treated with Speed Cote posted a 2-knot cruise-speed increase, according to the company.
We tried the Speed Cote product on a Mooney 231; specifically a 1983 model with original paint that is in better-than-average condition for its age. Before applying Speed Cote, Gerdes Aviation in Fullerton, California, cleaned and polished the airplane. That's not a necessary step, says Friberg, but doing so optimizes any drag reduction. The application of Speed Cote had two of us working for two hours.
The idea is to apply the product quite thinly, leaving the polymers and just a trace of the petroleum distillate carrier, which flashes off quickly. Actual treatment is quite easy, since you need not work the product into the paint like a wax or polish. When you're done, the airplane takes on a glossier appearance. According to the company, the treatment will last one to two years under normal conditions.
Yes, but does it make for a quicker steed? We performed numerous tests with the Mooney and noted a slight increase. Compared to the nominal cruise figures — compiled over more than 300 hours of extensive data logging — the Speed Cote added 2 knots at 12,000 feet density altitude. Measured with a two-way GPS-verified speed run, the Mooney turned in 170 knots true on 70 percent power. Historically, this airplane remained quite close to the book figure of 168 knots true at the same altitude and power. Similarly, at FL180 and 70 percent power, the 231 posted a 179-knot cruise, a gain of 3 knots over the normal 176-knot performance.
Those numbers arrived with a clean, newly treated airplane. After a month of flying and sitting in the hangar, the Mooney had accumulated the usual grime; at this point speeds returned to the nominal, book figures. Which may help prove that the Speed Cote does what it says, but also indicates that the effect remains only as long as the airplane is kept quite clean. For the shine fanatics this won't be a real concern, but for those whose airplanes reside out of doors, keeping the benefits may well be more effort than they are worth.
Speed Cote also claims to make the airplane easier to clean, and more willing to shed water and ice. We didn't have any icing encounters with the Mooney during the test period, but we did note that it was somewhat easier to remove dust and light grime after the treatment. And while the product is supposed to help repel water from the windows, we didn't notice any appreciable improvements over the usual glass treatments.
Weighed against the cost — $150 for a 4-ounce bottle that was more than sufficient to treat the Mooney — you have to answer the racer's question of "How fast do you want to go?" with "How much am I willing to spend?"
For more information, contact Speed Cote, 3301 South Bear Street, #51D, Santa Ana, California 92704; telephone 714/751-0411.
Sirius Products Cap-A-Tank
Occasionally the most effective solution to a vexing problem is also the simplest. For aircraft equipped with flush fuel caps, water ingestion is a major ill. Even with fresh O-rings these flush caps tend to collect water, waiting patiently to spill their load into the fuel tank. Many fixes have been tried, from beefed-up caps to umbrella caps; the umbrella cap has, rather than a flat upper surface, one curved to force moisture around the tank opening.
As an alternative to the umbrella cap, there's the Cap-A-Tank from Sirius Products. A 7-inch-diameter plastic cover with weatherstripping around the flange, the Cap-A-Tank is intended to stay on the airplane only while parked. The 1.6-pound disk requires no permanent installation; it stays in place thanks to the surface friction of the gasket and its wing- hugging weight.
Sirius says the Cap-A-Tank will stay in place in winds of up to 50 mph and prevent moisture intrusion even in heavy downpours. Though we didn't try drenching any fuel tanks, we did put the Cap-A-Tank to the wind test. Mounted to a Mooney wing — and needing a bit of twisting and flexing to match the curvature of the wing — the Cap-A-Tank managed to stay attached to an outboard section up to an indicated airspeed of 40 knots. One advantage we see is that if you forget to remove the Cap-A-Tank there will be little likelihood of aerodynamic degradation; the cap will have been flung to the runway well before rotation speed. One disadvantage to the setup concerns security. If some local miscreant wants your Cap-A-Tank for a high-tech Frisbee, it's his; there is currently no provision for locking the device to the airplane.
Sirius says the Cap-A-Tank will fit flush filler caps and raised caps (as on the Cherokees) equally well. Normally, the Cap-A-Tank sells for $60 a pair, but the company is running a special promotion through the end of 1994 for $29.99 a pair plus $5 shipping. For more information, contact Sirius Products, Post Office Box 31271, Palm Beach Gardens, Florida; telephone 800/675-8477.
Mombasa Aviation Clipper kneeboard
Kneeboards are a dime a dozen, right? Pinchpenny pilots may opt for the discount-store brown clipboard, while the high-tech types can be seen with something that may have been Space Shuttle surplus. In the range of product there's seemingly something for everyone.
Well, here's another twist on the kneeboard theme, from Mombasa Aviation. The company sells three versions of the Clipper, which are basically sheets of folded clear acrylic. In the line there's the Clipper I (at 9 x 12 inches and $21.95), the Clipper II (9 x 16 inches; $23.95), and the Clipper III (12 x 16 inches; $25.95). All feature a pair of clips, one large enough to hold the now-defunct bound NOS Instrument Approach Plates and the other of sufficient girth to grip a small note pad. Each also has a fabric leg strap secured with hook-and-loop fasteners.
We tried the Clipper I in several airplanes and found it to be a fine compromise between the demitasse thigh boards and the typical lap- squishing all-in-one board. The folded acrylic allows you to place charts or notes underneath for quick reference, while the pair of clips helps tame the usual explosion of sectionals. We also printed up a handful of checklists and memory-joggers and slipped them into the board; thanks to a tight fit between the folded sheets, slips of paper aren't likely to slip out. What's more, you can use an erasable marker to take notes during the flight and the acrylic will wipe clean easily.
Mombasa achieved high build quality with the Clippers we saw, preferring conventional fasteners to a passel of rivets, which helps in the event repairs are needed.
For more information, contact Mombasa Aviation, 478 Cahaba Landings, Birmingham, Alabama 35210; telephone 800/956-6638 or 205/951- 0711.
Briefly Noted
Aviation artist Sam Lyon's new, limited-edition print Cub Daze is now available through the Wright Bros. Collection. The 17.5- x 22-inch unframed print is available for $110 or a 27- x 35-inch framed version is available for $240. Call Wright Bros. Collection at 800/SPORTYS or 513/732-2411. — Peter A. Bedell
Unless otherwise stated, products listed herein have not been evaluated by AOPA Pilot editors. AOPA assumes no responsibility for products or services listed or for claims or actions by manufacturers or vendors. However, members unable to get satisfaction regarding products listed should advise AOPA. To submit products for evaluation, contact: New Products Editor, AOPA Pilot, 421 Aviation Way, Frederick, Maryland 21701; telephone 301/695-2350.
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