The AR-5: The hottest airplane money can't buy.

No, you can't buy a kit or plans for Mike Arnold's 213 mph rocket, but the videos will definitely make you drool, and teach you a thing or two in the process.

By Robert Goyer, Sport Pilot Magazine, May 1994

For years aircraft designers have been trying to get the most performance out of the least engine, and there have been some pretty amazing success stories. Back in the 1960s, composite innovator Ken Rand came out with a pair of lightning quick fiberglass wonders he called the KR1 and KR2. With 80 hp VW engines, these little speedsters flirted with the 200 mph level on a regular basis. Formula One racers have pushed the envelope even harder. With stock 100 hp Continental engines, these aerial hot rods have done major damage to the 250 mph mark. As regular readers of "Sport Pilot" know, the Formula One racer "Nemesis", piloted by John Sharp, set a new world's speed record at Oshkosh last summer when it clocked a run of better than 277 mph.

But of all the speed records I've run across, few have inspired in me the kind of awe I felt when I first heard about Mike Arnold's mark in a Rotax 582-powered aircraft. 213 mph. Read on!

The AR-5 is not a revolutionary aircraft in any one way. It's made of standard wet-layup fiberglass/foam construction. It makes use of a conventional low-wing taildragger configuration. And its powerplant is an off-the-shelf Rotax 582, producing about 65 hp. What makes Mike Arnold's incredible little aircraft so amazing is its ingenious combination of design, materials, and approach. In a phrase, the AR-5 is an airplane which gets maximum results out of minimal weight without, and this is the key, being a minimal aircraft.

Mike has been building aircraft out of fiberglass since the late 1970s when he moved to the town of Mojave in the High Desert of Southern California, then the Mecca of composite aircraft construction and started working on fiberglass planes.

In 1981 Mike started drawings for the AR-5 with the thought of possibly selling plans or kits of it when the product liability mess finally got straightened out. Well, you know that story, but Mike went ahead and built the airplane anyway. At the time when he began work on the structure, 1982, there weren't really any engines available which were light enough and could produce the kind of power Mike figured he'd need for the plane. Mike admits that it took him a while to warm up to two-stoke engines, but as their design and reliability improved, they started looking better and better to him. Not only were they powerful enough for their light weight, but by 1987 Rotax's new water-cooled 532 was putting out a lot more power (65 hp) than he had even dreamed of. He actually had to beef up the engine mount to carry the extra weight. It was a problem Mike was more than happy to have.

Mike first flew his AR=5 in 1991 with the 532 and was getting about 175 mph top speed with a prop which gave him a 1500 fpm rate of climb. After a few experiments, Mike switched to a Craig Catto race prop and things really started happening. After bolting on the Rotax 582 and straightening out the installation and cooling problems, Mike realized he was really on to something. Especially when he clocked a run at 207 mph. Though he admits he didn't know much about records, a friend told him that 207 was probably a record for an aircraft in its category. So Mike called the FAI (the international organization which officiates on record attempts) and went through the involved process of going for the mark.

As they say, the rest is history. On August 30, 1993, Mike in his AR-5, made four runs over a closed course, all which would have broken the old record of 201 mph. For his efforts, the FAI awarded Mike the coveted Louie Bleriot medal. Each year the organization bestows only three (or fewer) of these awards, so the honor is a very real one. It's just another of the ironies behind the saga of the AR-5. Mike never intended to use the plane to set records; that just sort of happened. Quality, as they say is its own reward.

The record took the world of flying by surprise. Like many others, when I first heard news of the new mark, I suspected it might be a joke. After I realized the record was for real, I just had to know how the feat was accomplished.

According to Arnold, there's no one secret behind the success of the design. Instead it's a combination of factors which allows the AR-5 to achieve the remarkable figure 3.28 mph per horsepower.

Mike believes that one of the major factors contributing to the efficiency of the design is the remarkably low interference drag of the airframe. Interference drag is that which is produced when the clean airflow from two structures meet and violently disturb each other. On light aircraft this is most pronounced at the junction of the wing and the fuselage. After extensively researching the subject, Mike went to work modifying his basic design to minimize this interference drag. His work in this area has evidently paid off handsomely.

Another major factor is the plane's remarkably small drag area, a flat plate area of less than one square foot (.88, to be exact). Interestingly, it wasn't until after Mike set the record that he set out to calculate the plan's aerodynamic profile. When he came up with this figure, aerodynamicists were stunned. Some refused to believe it. It turns out the AR-5 was the first man-carrying airplane in history to break the one-square foot flat plate area limit. If it sounds esoteric to you, believe me, in the world of aerodynamics, it's a big deal.

Despite the fact that the AR-5 is the fasted thing in the sky in its category, Mike says he never intended it as a racer. Instead, he sees it as a sport plane, one which will provide plenty of performance while still exhibiting excellent slow speed manners and outstanding stability. When you look at the long wing and large tail surfaces, it becomes clear that Arnold could have made the plane faster by going with a shorter, thinner wing and smaller tail section. But it would have been at the expense of low speed stability and structural integrity, areas in which Mike was not willing to compromise.

Due to a freak accident, Mike got an unwished-for chance to find out first-hand just how strong the structure really was. Last summer on a return trip from a friend's airport, the AR-5's engine quit (the result of a throttle cable ferule coming off and getting into the works). After a hard off-airport landing, Mike walked away unhurt. Though the engine and prop were destroyed and the plane's landing gear, cowl, and a couple of fairings were damaged, the major structure came through the incident without any real damage. Ironically, this incident has given Mike the chance to make a few changes to the plane. As of this writing he's already completed a new landing gear and set of wheelpants, and he's installed an in-flight mixture control to help keep the 582 cooler during descents. The mixture control should also help the 582 reduce more power at altitude.

Mike hopes to have the AR-5 up and flying again by this summer {it flew again in April, 1994, it's better than ever!...M.A.}, at which time he hopes to get back into the air and get flying again. He really misses his little rocketship.

Those of you who want to learn more about the project are in luck. Mike's firm, The Arnold Company, offers two excellent video tapes which tell you all you could every hope to find out about the AR-5 (except, perhaps, where to send for plans!).

The first tape, entitled "Why It Goes So Fast", is an in-depth look at the record setting performance. But more interestingly, it also goes into great detail on how Mike came up with such an incredibly clean structure. There's commentary from aerodynamicist Bruce Carmichael, who, like the rest of us, seems positively in awe of Mike's achievement. For those of you who like practical aerodynamics, this is a fascinating tape. Especially interesting to me were the discussions involving the interference drag phenomenon.

The second tape, "How It's Made", is a two-hour discussion of how the AR-5 came together. Mike and his colleagues take us through the process of creating fiberglass and foam structures, actually making a few of them as we watch and listen to Mike's commentary on the ins and outs of the construction techniques. If you've ever wanted to build your own fiberglass aircraft, this tape is an absolute must, as it takes dry theory and puts it into the goopy, real world of wet lay-up construction. Fascinating!

If you love this kind of stuff as much as I do, you should get these tapes. "Why it goes So Fast" retails for $29.95; "How It's Made", for $39.95, or you can get both of them for $59.95. That's $20.00 off the original price. To order either or both of these fascinating tapes, send a check or money order to The Arnold Company, 5960 S. Land Park Dr. , Sacramento, CA 95822. If you want to get plans for the AR-5, you'd better write to Washington and get them going on liability reform. If that works out, who knows, maybe you'll get your chance.

Robert Goyer, Sport Pilot Magazine, May 1994

{Note: We now sell four tapes. Please see below. M.A.}

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