Arnold AR-5 Homebuilt

Why It Goes So Fast

The Arnold AR-5

In August 1992, an ex film-maker from Northern California set the normally studious world of aerodynamics ablaze.

AR-5 under construction
90% finished, 90% to go… The AR-5 in Mike Arnold’s Pinole, CA, workshop. (© The Arnold Company. Used with permission.)

It wasn’t just that Mike Arnold had designed and built his own plane in a cramped former restaurant, or that he’d set an official world speed record for aircraft under 300kg (FAI Sub-class C-1a/0) of 343.08 km/h over a 3km straight course.

It wasn’t even that he’d clocked 213.18 mph with fixed landing gear and a Rotax 582 two-stroke engine rated at only 65HP. (Think about that for a minute…)

What really had the NASA scientists and aviation media beating a path to Pinole, CA was that Mike had broken the fabled one square foot drag barrier, and he’d done it without any formal training or qualifications.

It was a unique sequence of triumphs for homebuilding.

Mike Arnold and AR-5
A man and his art… Mike Arnold runs up the Rotax of his near-perfect speed machine. (© The Arnold Company. Used with permission.)

That square foot barrier

In aerodynamic circles, building a man (or woman)-carrying airplane with less than one square foot of drag area had been the equivalent of the 4-minute mile to 1930s athletes and the sound barrier to 1940s test pilots.

The AR-5 had smashed that ‘impossible’ mark with a flat plate drag area equivalent to just 0.88 square feet.

Arnold AR-5 cockpit
The AR-5’s comfortable, compact cockpit – everything the pilot needs, and nothing he don’t! (© The Arnold Company. Used with permission.)

Up until that point the benchmark for slipperiness, certainly among propeller driven aircraft, had been the P-51 Mustang.

Drawing on a wealth of brilliant engineering, aerodynamic expertise and exhaustive wind tunnel analysis, the P-51 team achieved a drag coefficient of 0.004 with the Meredith Effect doghouse negating cooling drag and the landing gear neatly retracted.

By comparison, the home-made AR-5 had a drag co-efficient of just 0.0038 – legs to the wind.

But when the experts turned up at Mike Arnold’s workshop there were no wind tunnels or sophisticated computer analyses in sight (or even in the same county, for that matter).

And when they pored over the AR-5 with their slide rules and crazy-long equations, all they found was good design and the meticulous craftsmanship of an artist.

A work of art

When he was ready, Arnold shared his ‘mystery ship’ with a number of pilots from leading aviation magazines. They all agreed that the little speedster was also a sweet-handling machine, with beautifully harmonised controls and plenty of room for the pilot.

It sounded like an impossible combination – but there it was.

The disarmingly simple lines of the AR-5 – but every curve and junction has been carefully considered. (© The Arnold Company. Used with permission.)
The disarmingly simple lines of the AR-5 – but every curve and junction has been carefully considered. (© The Arnold Company. Used with permission.)

Dave Martin, Editor of Kitplanes magazine (in 1999) went so far as to say it had the most nicely harmonised controls of any aircraft he’d flown; placing it on a par with the Stelio Frati-designed Sequoia Falco. Another homebuilt, you’ll notice.

Watch and learn

I won’t kid you – this is a film, not a clip, and it will take over an hour of your time. But if you have an interest in aircraft design generally, or aerodynamics in particular, you’ll be richly rewarded.

AR-5 construction detail
The AR-5 under construction. The foam was shaped, sanded, glassed, then sanded and sanded and sanded… (© The Arnold Company. Used with permission.)

It’s not heavy-going either. Thanks to his film-making experience, Mike Arnold is a gifted story-teller and his World Speed Record gives Why it goes so fast a genuinely entertaining plot and structure. Plus, Arnold’s gravelled voice and homely style makes it all feel like an aerodynamics adventure starring Jimmy Stewart.

Once you’ve watched this film you’ll have an enriched understanding of airflows, aerodynamics and drag reduction. You’ll be able to look at any aircraft and know why the designers did what they did – and where they made compromises.

Aviation film festival

Arnold had originally planned to sell plans for the AR-5 but, while he was satisfied with the design, he decided to wait and see how the gathering storm of product liability suits would play out. Well, we all know how that went – and our loss is some law firm’s gain.

Instead, Arnold fell back on his first craft, producing a series of movies about his beloved plane and selling video copies to homebuilders and aviation enthusiasts. The full set of films is:

Why It Goes So Fast

How It’s Made

Moldless, Low-Drag Wheel Pants

The AR-5 In Action

Making Fibreglass Molds

Making A Molded Fuselage – Shaping The AR-6

There is no CGI or even a pretty diagram in any of them. There is a load of heart though, and each documentary offers an engaging story as well as plenty of information.

Arnold AR-6 'Endeavour' surfaces
Photo finish – the glass-smooth perfection of Arnold’s work shows in this striking shot of the AR-6. Even reg. numbers aren’t allowed to disturb the airflow. (© The Arnold Company. Used with permission.)

Thank you for your genius

The AR-6 ‘Endeavour’ of that last film is the curvaceous crimson Formula One racer, designed and built by Mike for owner/pilot Dave Hoover. It would go on to win the Reno Gold Championship Races in 2007 and 2008.

Arnold AR-6 Reno Racer
The AR-6, dubbed ‘Endeavour’, at Reno. As per Formula One rules, it flies with a wing area under 66 sq.ft. and an O-200 up front – but tops 250 mph! (© The Arnold Company. Used with permission.)

It is now owned by Steve Senegal and is still racing at Reno, although Lady Luck is yet to smile on the partnership.

Meanwhile, the AR-5 was donated to the Hiller Aviation Museum in San Carlos, CA, where it is currently on display.

Mike Arnold died just over a year ago – October 6th, 2015. He considered his aviation films his legacy and, after his passing, the Arnold family generously shared all six on YouTube.

It’s hard to think of a more appropriate way to remember this quiet genius of homebuilding, composite construction and amateur (in the truest sense of the word) aerodynamics.

You can read more at The Arnold Company website. (The ‘Tapes’ link will take you to all six movies on YouTube.)

Arnold AR-6, Dave Hoover
The curvaceous AR-6 fulfils its design function, with a note from race pilot Dave Hoover that says it all… (© The Arnold Company. Used with permission.)

18 thoughts on “Why It Goes So Fast

  1. You mentioned the P-51 as being the peak of ‘slipperiness’ in terms of performance. I do NOT have the drag figures to hand, but in propeller-driven fighter terms (production machines, that is) Jeffrey Quill, the British test pilot, took a Supermarine Spiteful up to 494 mph!

    1. Hi Ross, I don’t have the numbers either – although they must be out there somewhere… Anybody??

      Anyway, given the the Spiteful was basically a developed Spitfire fuselage with a new laminar flow wing, I imagine it would have been very slippery indeed.

      On the other hand, Spitfires were quite a bit more draggy than Mustangs, even though their elliptical wing was the pinnacle of efficiency and had a very high critical number. The telling factor always seems to be cooling drag – and the Spiteful had the same underwing radiators as its Spitfire ancestors. These kept growing (multiplying, even) throughout the latter’s development.

      The Mustang’s great advantage was its use of Meredith effect to negate or even reverse this cooling drag.

      Given Meredith was a British engineer working at the RAE, Farnborough, it seems strange that his discovery wasn’t taken up by British manufacturers. He published in 1936, obviously too late for early Spitfires or the Hurricane, but why couldn’t the technology have been incorporated by the Spiteful?

      NAA can hardly have felt they ‘owned’ the solution, and anyway, surely HM Government might have traded it for, oh I don’t know, radar or the jet engine or something…

  2. Homemade is the best, right? After all the Kitty Hawk was homemade too. Thanks for sharing this story and the YouTube links. I’ll definitely be watching them because I really need to know more about aerodynamics.

    1. You’re so right. Unimaginative aircraft manufacturers really squandered the private flying booms of the 1950s through 70s – and did GA a huge disservice into the bargain. And ever since, the EAA and homebuilders worldwide have shown what light aircraft could/should be.

      I imagine this film would be a great prep for learning about aerodynamics because it’s such a practical, applied demonstration of the fundamentals in action. Enjoy.

    1. Thanks for reading and for your comment Matt. I think self-building is strong and getting stronger. The EAA’s annual gathering is by far the biggest aviation event in the world, after all.
      On the other hand, the art of self design and building, like Mike Arnold did, is probably slipping back in favour of kits and proven designs. It would be nice to see a resurgence in that specific area too.

  3. I had the good fortune to have met Mike Arnold, and to have visited his design/fabrication studio “under the bridge.” He had just completed a composites fabrication job for Aero Union Corporation (Chico, CA). Having heard that he was “building his own airplane in his living room,” we dropped in to visit, whereupon he treated us to a one-hour tour. This would have been 1981 or ‘82… thereabouts, and the fuselage looked pretty much structurally complete, though the whole thing had quite a ways to go before flying.

    My stark impression: “Mr. Arnold is a true craftsman.” His passion for his art, combined with his down-to-earth, friendly manner and approachability were truly a unique combination.

    You don’t run into a character like that very often.

    1. Thanks for sharing your encounter, Eric. I have to say, your impressions of Mike Arnold’s character all come through loud and strong in his films – and I dare say that’s a large part of what makes them so enjoyable.

      I’d add that Mike’s widow, Sandra Arnold, was amazingly gracious when I asked her permission to use her photos for this post.

      They were clearly good people, through and through. I wish I’d had the chance to visit with him too.

  4. The minimum wing area for Formula 1 is 66 square feet. Not under as stated in the caption. Also, Mike did not build the AR-6, though it is his design, and he did create the fuselage plug.

    1. You’re absolutely right on both counts, Juan. I have an idea the AR-6 wing area was a shade less than the regulation 66 sq.ft. but I can’t recall the details. Thanks.

  5. Too bad the writer does not know anything about product liability law and apparently has a political axe to grind. There is no product liability for amateur-built design or plans. Zero. If someone who bought build plans found that they were too complex to follow, they could ask for their money back, but that’s it. You build your own airplane and it’s your product.

    1. @Thaddeus Stacy “Too bad the writer does not know anything about product liability law and apparently has a political axe to grind” — did you miss the part of the article where the author states that it was *Mike Arnold’s* opinion that liability is a problem? Arnold himself wrote about this on numerous occasions; see “Getting the most out of 65 horsepower” for an example, where he said: “Liability is more a problem now than ever. I’ve been listening to the horror stories for ten years, and I’m scared to sell plans.”

      Plus, you’re just plain factually wrong. There are MANY examples of liability problems with homebuilt aircraft. Legal basis or not, a surviving family member can sue, thanks to the litigious nature of the USA. A good example is the fact that plans for the French Luciole MC-30 are never sold to American citizens due to the threat of liability. See also the Airbike saga, where a disgruntled builder kept suing the designer repeatedly. But okay Mr Law Guy, “they could ask for their money back, but that’s it” – whatever, reality and historical precedent show the exact opposite of your ignorant comment. #swoti for the win

      Also, this was an excellently written article and a fun read. Thanks airscapemag!

      1. Bob-

        A little knowledge of the law does not help. I am a products liability lawyer. While it is true that anyone can initiate a lawsuit against anyone for anything, that is only the beginning of the process. Like someone who does not know how to play poker putting down money to sit at the table. It’s possible, but not smart.

        A products liability lawsuit over amateur-built aircraft plans would quickly be tossed out of court for the following reasons: A “product” means a “thing” that is manufactured and then put into the stream of commerce by a manufacturer. Amateur Airplane plans are not products. They are similar to books or magazines. Plans are not manufactured things put into the stream of commerce. Which is why I wrote that if someone was unhappy about the plans they can ask for their money back but there is no liability for a product since no product is involved. Those who say otherwise do not know what they are talking or writing about.

        The fundamental problem with suing a plans writer for a “defective product”, an amateur built aircraft built by an amateur who bought or stole the plans, is that the amateur built it. The plans writer did not build the product, did not make the product, and did not put the product into the stream of commerce. So, the builder would have to sue him or herself for whatever it was that they built. Not a promising lawsuit, don’t you think? I can guarantee no products lawyer would file such a suit. Any lawyer who did try to bring such a suit would be laughed out of court by the other lawyers. Anyone can look at the documentation written and published b the FAA regarding amateur built aircraft. The liability is on the builder and then on the pilot to verify that what they built or are going to fly is airworthy- that is the law. The amateur builder controls the build – good, bad, or ugly. Anyone who sells plans for anything is well-advised to put a little reminder in there similar to the one that the FAA requires every builder to prominently display on every amateur-built aircraft. Basically, the notice gives this alert: “Look out- this is not a product manufactured in accord with any government aircraft certification program- fly in it at your own risk”. That’s the get out of jail free card. Buyer beware.

        Now, the chamber of commerce has done a good job of scaring the bejeezus out of many people, but that is just chamber propaganda trying to establish a political base for its agenda. Good honest people need to recognize propaganda when they smell it. It always smells the same. The Chamber, a very well funded industry lobbying propaganda machine, has a very real agenda to insulate its members from lawsuits that may be very justified due to their member negligence- say something like the 737 Max crashes. The Chamber even lobbied the Chinese Communist Party for liability protection for products Chamber members have made in China. See, there is a method to their madness. But it applies to products, not amateur plans for building amateur-built airplanes or wheelbarrows for the matter.

        So, again, plans are not products. There is no product liability for amateur build aircraft plans.

  6. I would love to buy a kit for the AR-5, or plans. I would be pretty excited to just have a scan of the aircraft and be able to build a scale model.

    1. Hi Jiro, as you may have gathered Bob Arnold did not release any of his plans into the public arena. The best you could hope for would be an dimensioned 3-view and some educated guesswork. Unfortunately, I’m not sure where you’d even find those. Good luck though.

  7. Any phone with a lidar, or a higher end laser unit could now be used by anyone to scan the aircraft for dimensions and 3D modeling in the hiller museum. You would need a lift of some kind, have them lower it, or use a drone, but it’s now quite possible.

    1. just google it! pictures amd wiki is free🤷‍♀️as for most aircrafts ever built! it has a wingload of about the ususal 35 kilos/m2 for cruisers that is normal….i need to watch his videos, but in the early 80 ies his surely new idea was to use foam cores for the construction and kepp it light🤷‍♀️and slick! most people underestimate drag from all the stuff protruding from surfaces….his wgaer between retractable and cowöed landing gear is nothing spectacular either…he simpky knew what he was doing! 🤷‍♀️most designers have no idea, not even bale to calculate stress loads….his design seemingly had a mind behind this who knew! well done…sadly 30 yrs later aviation is outlawed more and more in terms of safety and certification only making things expensive, not better,,,,🤷‍♀️cool birds, like them…thanks for showing!

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