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12/12/2017

Member Projects n' Planes
Bob Rogers' Mustang II - Return to Project n' Planes

UPDATE:

EAA honored my Mustang II by making it the airplane for March in its 2015 calendar.

UPDATE:

At the 2014 AirVenture event, EAA selected a picture of my Mustang II in flight to mount as a full-sized poster for display in the EAA Welcome Center/Young Eagles tent. Check it out in the pictures above.

UPDATE:

I am very pleased to announce that the Experimental Aircraft Association (“EAA”) has published an excellent article on my Mustang II in the March 2014 issue of their on-line Experimenter magazine. You can read it at http://experimenter.epubxp.com/i/271000/10 . I felt honored that EAA wanted to do an article on my plane.

UPDATE:

In July 2013, the Mustang II carried me to Oshkosh for the first time, where EAA management decided to do a writeup on my plane and a photo-shoot for the EAA Experimenter magazine. What a thrill!

UPDATE:

On June 10, 2010, my Mustang II rolled out of the paint shop with beautiful new colors. It is a joy to behold and a dream come true.

UPDATE:

On Wednesday, March 18, 2009, at approximately 10:00 a.m., my Mustang II took to the air for the first time. After almost 18 years of building (when time permitted), the first flight was exhilarating and deeply satisfying. The turbocharged Mazda rotary 13B engine ran well and all temperatures stayed in the green. It produced more power than I needed. The airplane is a joy to fly and made all the effort to build it worthwhile. I look forward to many adventures in the air after the initial 40 hour test period is flown off. See you in the skies!

UPDATE:

N62BT received its Special Airworthiness Certificate on December 20, 2008. For years, it was only a slowly growing collection of aluminum parts and pieces, but now, my Mustang II is a real airplane, ready to fly!

THE BACKGROUND:

At some point, I became aware of the homebuilt movement and the excellent things that the Experimental Aircraft Association ("EAA") was doing to encourage development of alternatives to factory-built aircraft. My first trip to the annual EAA air show at Oshkosh in 1990 was like going to heaven! I discovered that maybe there was a way to realize my dream and own an airplane. I would build it!

For those of us who are willing to spend the time and effort, and who have some mechanical aptitude, achieving the dream of owning and flying one's own airplane by building it has a lot of merit. There is now a homebuilt aircraft kit or design for almost every taste and pocketbook, and a lot of the kits offer much higher performance than what you can get from a similar factory-built airplane. In most cases, acquisition costs can be spread out over time and made bearable by purchasing kit segments and components as they are needed. For me, one of the most important aspects of building my own airplane was the recognition that I could avoid the prohibitive costs of paying someone else to do all the maintenance and repair necessary to keep my airplane running (after I finished building it). This brings to mind an important point. A large drawback to this approach is the time and dedication that it takes to build a kit plane. A project like this is not for everyone. Of course, we could talk about all the satisfaction that one gets in creating a flying machine with one's own hands, but that is another story.

Buoyed by the inspiration of all those beautiful homebuilts at Oshkosh, I set out to find a plane that was just right for me. Within a few months, I had settled on the Bushby Mustang II. It seemed fairly straightforward to build, came in a kit, was not real expensive, and was well tested, having been around for over 20 years. Also, I thought it was the best-looking kit plane among all the choices available to my pocketbook. I wanted an aluminum, two-place airplane that was moderately priced and relatively fast (180-200 mph). My choice finally narrowed to either the Bushby Mustang II or the RV-6. Ultimately, I chose the Mustang II, because (with apologies to all you RV owners out there) I did not like the fat wings and the swing-up canopy on the RV-6 (they have since eliminated one of my objections with the introduction of a sliding canopy).

In spite of its many attractive features, the Mustang II has not been as popular with the homebuilding crowd as the RV-6 or some other recent additions to the kit plane market. I think it is because Mr. Robert Bushby (the originator of the Mustang II) was principally a one-man show and never tried to mass-market the kit; however, there has been a change in emphasis. Declining health forced Mr. Bushby to sell the production rights for the Midget Mustang and Mustang II kits in 1992 to a company called Mustang Aeronautics, under the management of a very energetic Chris Tieman. He has made several enhancements in the kit, making it easier and faster to build. Also, periodic coverage of the Mustang II in EAA's Sport Aviation and the Kitplanes magazine generated new interest in and enthusiasm for a time-tested design.

After choosing the basic airframe, my last sticking point was the engine. Certificated aircraft engines seem overly expensive, both to acquire and to maintain, and that got me to thinking about alternatives. Automobile engines are generally inexpensive and readily available, but for the most part, they are too heavy for the power generated. Also, because almost all auto engines develop their maximum power at or above 4500 RPM, it is necessary to attach some sort of mechanical device to slow the propeller, called a propeller speed reduction unit ("PSRU"). A normal propeller should not turn more than about 3000 RPM, or the tips will exceed the speed of sound, at which time they lose most of their efficiency and are prone to disintegration. A shorter propeller might avoid the danger of high tip speeds, but short propellers are not very efficient at any speed.

Another major consideration, often overlooked by zealous auto engine converters, is the fact that most auto engines are designed to run at less than 50% of maximum power most of the time. Any attempt to run most unmodified auto engines at 75% (or more) of maximum horsepower for more than a few minutes would most likely result in rapid engine failure. Translated, this means that reliability should be a matter of prime concern for any auto engine converted to aircraft use. To make matters worse, many attempts to use auto engines in aircraft have been accompanied by extensive modification of the engine, usually in an effort to extract more horsepower than the engine was designed to produce. All this, coupled with the lack of an operating history for any particular engine conversion and its PSRU, make an auto engine conversion for use in an airplane an uncertain venture, at best.

All of that said, I am still undaunted by the problems which seem to accompany auto engine conversions. Aircraft engines also have their problems; just look at all the Airworthiness Directives, which the FAA has issued on them over the years. As everyone knows all too well, not even aircraft engines are immune from in-flight failures. In searching for an auto engine that might fill the bill as a suitable candidate to power my airplane, I needed one that could generate somewhere between 180 and 200 horsepower ("hp"), and which weighed about the same as an equivalent aircraft engine. The list gets narrow really fast when you limit the weight to no more than about 350 pounds with all accessories installed. One promising candidate is the Subaru SVX 3.3 liter, horizontally-opposed, six cylinder engine, which puts out over 200 hp and is almost light enough. However, with double overhead cams, 24 valves, and computer-controlled fuel injection, the engine is extremely complex, as well as being a bit too heavy for my purposes.

I have found what I think is the answer. The Mazda rotary engine is a marvel of simplicity and compactness. Properly prepared, it has a power to weight ratio which is much higher than other automobile piston engines and which approaches that of a turbine engine. Real World Solutions, Inc. of Bell, Florida ("RWS") has developed a compact, lightweight, planetary-geared PSRU to fit several auto engine conversions, including the Mazda rotary engine. By all accounts, this PSRU is virtually bullet-proof. Even with a radiator for cooling, the Mazda rotary engine, PSRU, and all accessories weigh about the same as a Lycoming 180 hp aircraft engine installation.

I was surprised to learn that the Mazda rotary engine is one of the few automobile engines that is designed to run at high power output continuously. The non-turbocharged version of the Mazda rotary engine (designated 13B), in its most recent stock form (1989 through 1992 Mazda RX-7, Second Generation Rotary), generates 160 hp at 7500 rpm. The stock turbocharged Second Generation Rotary generates 200 hp at 6500 RPM. Rotary engines have seen numerous racing applications, and are capable of generating substantially more than stock horsepower when appropriately modified. On the stock 1993 Mazda RX-7 (Third Generation Rotary), the use of twin sequential turbochargers (on what is otherwise essentially the same basic engine as earlier models) results in 255 hp at 6500 rpm. Racing applications for the rotary engine are known to generate peak horsepower of more than 400 HP and 10,000 rpm; however, reliability then becomes a factor. It may be of interest to note that, because of the gearing in the eccentric shaft (the equivalent of a crankshaft), the rotors actually only turn at one-third (1/3) of the shaft output rpm. Therefore, in a rotary engine that makes maximum power at 7000 shaft rpm, most of the moving mass of the engine is turning around at a leisurely rate of 2333 rpm, slower than most aircraft engines.

The answer is not as simple as taking an engine out of a used Mazda RX-7, bolting on a PSRU, and stuffing it under the cowling of your nearest airplane. Most solutions to complex problems are never simple; however, this one seems to be within the realm of possibility. The Mazda rotary engine is unusual, to say the least. It has no pistons, no valve train, no camshaft, and is different in many other respects from traditional auto engines. Rather than pistons and a valve train, the engine has two triangular (wedge-shaped) rotors that continuously turn around a geared, eccentric shaft to produce the four cycles of intake, compression, power, and exhaust. Intake and exhaust flow through strategically placed openings (ports) in the rotor and end housings. The reduced number of moving parts and the turbine-like operation of the rotor give the Mazda engine unparalleled smoothness and durability. Early engines produced by Mazda in the 1970's suffered problems with their rotor apex seals, and from high fuel consumption. The fuel shortage caused by the OPEC oil embargo in 1973 created additional problems for Mazda, because although their new rotary engine produced significant power, it was at the expense of relatively high fuel consumption. Over the past three decades, however, problems with the engine's reliability and high fuel consumption have been completely solved.

Because of its design, the rotary engine has a noisy (and hot) exhaust, when not properly muffled. To solve the noise problem, the stock Mazda rotary uses a heavy-duty exhaust manifold that collects and co-mingles gasses from both combustion chambers right at the exhaust ports. While this is great for reducing noise, the back-pressure and restriction of exhaust flow is terrible for power output. Readily available lightweight aftermarket exhaust systems will allow a virtually unrestricted flow of exhaust for the rotary (boosting its power by 20% to 30%) and still keep the noise at a level comparable to that of a certificated aircraft engine. The noise level is acceptable for aircraft, but not for street legal automobiles. However, because exhaust gas temperatures of a rotary engine can reach 1700 degrees Fahrenheit at full throttle, the muffler must be durable (and only a few meet the test). An alternative that provides substantial muffling without much more weight, but with a lot more power, is a turbocharger. Properly installed and monitored, the turbocharger can reduce the exhaust noise to acceptable levels and provide enough boost to maintain 100 percent power up to 17,000 feet (which is the altitude at which a normally aspirated engine generates one-half of its sea-level power). Although turbochargers add considerable complexity, for this particular application, the benefits outweigh the added installation problems, which caused me to modify my initial impression and decide to use a turbocharger.

There are a number of aftermarket companies that cater to the strong appetite for racing and hot-rod applications of the Mazda rotary engine. Among other things, these companies offer rotary engines for less than $4,000, which have been rebuilt to racing standards and which offer proven professional modifications to enhance the performance and reliability of an engine that will be run at sustained high power levels. Most rebuilt engines, however, are only what some people refer to as the "short block." When you add all the other components needed to make the engine run in an aircraft, such as oil pump, water pump, ignition components, customized headers and exhaust system components, along with a special aftermarket fuel injection system, aluminum radiator, and a PSRU, the total cost approaches $10,000. This price is not much different from that of a used aircraft engine with several hundred hours left on it, and we have an engine with little or no operating history in airplanes.

So what is the advantage of such an auto engine conversion? Other than the personal satisfaction of doing what others have not yet achieved, the advantage appears to lie in greatly reduced maintenance costs. Also, the replacement cost for almost any component in the system is substantially less than the cost of equivalent certificated aircraft engine components (often less than one-half the cost). If you have your aircraft engine rebuilt, or buy one which has been fully re-conditioned to new specifications, the price, even without accessories such as starter, alternator, manifolds, exhaust, oil cooler, belts or other miscellaneous attachments, is going to be $15,000 - $20,000. When you compare this to the price of a Mazda 13B rotary short block rebuilt to better than factory specs at $3,800, the savings become readily apparent. It is also possible to find new, or almost new, rotary engines from overseas suppliers, but they still have to be converted to aircraft use.

My Mazda rotary auto-engine conversion does not use a magneto system for ignition. However, it does have a highly reliable stock electronic crank angle sensor, with four high-performance coils, powered by the alternator and backed-up with a standby alternator and the battery. Each rotor is served by dual spark plugs; only one plug per chamber is required to keep the engine running, but firing of both plugs is desirable for optimum burning of fuel in the combustion chamber (just like a certificated aircraft engine). The fuel and ignition controller (manufactured especially for this aircraft conversion application by Real World Solutions, Inc. of Bell, Florida) has two separate units, either one of which will fully operate and control the fuel and ignition system. Although I do not have the statistics to prove it, I would be willing to bet that this Mazda rotary ignition system is more reliable and less prone to failure than the standard magneto systems installed in most certificated aircraft engines.

The alternator provides the primary source of electricity to the engine's ignition system and electric fuel pumps (there is a primary and a backup fuel pump). If the primary alternator fails, a warning light comes on in the cockpit (as well as a warning sound in the headphones), and the malfunction shows up on the ammeter and voltmeter gages on the instrument panel. A switch activates the standby alternator, which is a 35-amp permanent magnet alternator. Interestingly, the permanent magnet alternator does not need a battery hooked up to it in order to generate electricity. Either alternator can be manually taken off-line by a switch in the cockpit without disturbing the electrical power to the engine from the battery. Without either alternator, the time that the engine will continue running is determined by the amount of electrical charge in the battery. Using a system such as this requires that special attention be paid to the status of the electrical system when flying, and during routine maintenance.

All-in-all, the use of a Mazda rotary engine to power my Mustang II has a certain elegance and simplicity that appeals to me. Symbolically, it is like thumbing my nose at the establishment that for so long denied me the pleasure of owning and flying my own airplane, just because acquisition and maintenance of a certificated aircraft was so outrageously expensive. Now, when I press the start button on my Mazda-powered airplane and it easily starts (first time, every time) and runs smoothly and powerfully with no fuss, a little smirk of self-satisfaction starts to creep in around my lips. It feels good!

EAA Chapter 1246 - Webmaster