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.)
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4 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.

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