Midget Mustang (oz10819)

About this Plan

Midget Mustang. AMA Formula I pylon racer. Wingspan 48 in, wing area 455 sq in. For K&B 40 R/R or F/R.

Direct submission to Outerzone.

Update 7/11/2022: Added article, thanks to theshadow.

Quote: "The 'Midget Mustang' presented here is a very time-proven design that should be interesting to the sport flyer who may want to give Formula I a try. Most of the older Form I flyers have found one design that is their favorite and have developed it through a series of 'updates.' So it has been with my Mustang.

OriginaIly, I found the design to have some distinct assets which are very favorable to model use. Formula I models fly very easily, in spite of their speed, actually much better than other types, especially in wind. Their one drawback would be take-offs and landings. This is where the 'Mustang' excels, with its well-located and wide-track landing gear, it is far superior in this respect than any other racer.

Every time I have bounced one of my other designs about a bit, the urge has always been to go back to the Mustang. More than just think many times I have, and each one has incorporated the improvements and added niceties that experience brings.

This latest Mark V version features all the latest advances which offer the greatest speed and utility.

First, let's take a look at the full scale machine. Dave Long, of Piper Aircraft Corp., designed and constructed one of the very first full scale Goodyear racers (now known as Formula I). Dave called it the 'Pea Shooter'; it proved to be very successful and created a considerable amount of interest. Encouraged by the interest, he continued development of the basic design, through several modifications finalizing with the version renamed the 'Midget Mustang.' This version was so successful that it was put into production in kit form by the Bushby Aircraft Corp. While all this was years ago, its success is exemplified by the appearance of several newly constructed Midget Mustangs at recent full scale air races.

The model presented here is much more of a 'scale' design than are most of our model Formula I designs in use today. The reason for this is the hope to get a few more of the cherished handicap points, plus the fact that the basic design was so well done that it leaves little room for improvement, even for model use. As a result you will find few changes except in minor details. You will also find that it fits the intent of our Formula I racing rules very closely. Lastly, of course, is that it is a very competitive design which has won more races for me than any other (Formula I) I have had.

The fuselage of the model is constructed a bit differently from the average Form I design. The object being to have a longer lasting model (several have made their way through 3 years of hard competition), have more utility, allow quicker inspections and repairs between heats and to gain more efficiency from the engine.

The ruggedness of the design comes from constructing the forward portion of the fuselage (where most wear and tear shows up) from plywood. The basic fuselage is simple, two sides separated by bulkheads with fairing on top and bottom. The difference is that the sides are plywood from the trailing edge of the wing forward, with balsa spliced on for the tail section. Using plywood bulkheads between the plywood sides creates a very strong and wear resistant 'box' that is far superior to balsa or plastic.

The use of an inverted engine provides some advantages which are hard to come by with any other configuration. The only disadvantage could be in starting; however no problem has been encountered as the use of the pressure fuel system alleviates flooding.

By inverting the engine, two features are possible which time has proven very desirable. First, it is the most practical way to use a so-called 'power pod.' By using a power pod, the power department, in its entirety, becomes instantly accessible. This can be a valuable asset for inspections and repairs between heats, when time is so valuable. As an example: a fuel tank check, which could take over an hour without the pod, can be done in minutes. A not so obvious advantage is the ability to use various types of engines in the same model, in fact they can be interchanged. With other designs this can be practically impossible. With this Mark, V version, both the front rotor and the rear rotor K&B engines can and have been used and interchanged. If a more drastic change in engines was desired, simply constructing a second power pod would be all that was necessary. The two K&B , engines are completely interchangeable, if you do not mind a larger spinner gap with the front rotor engine. For mine, I simply made a modified spinner back plate which filled in this gap without any modifications.

One of the ways to go faster, of course, is to gain more efficiency from the engine. The better the engine is cooled the more efficiency it has. Anything which can be incorporated to improve cooling is a plus factor. The Mustang uses what is known as a 'pressure cowl.' With this type of cowl the air is rammed into the cavity and, by means of baffling, it is held momentarily in the cooling fins, thus heated and exited at a higher velocity than the entering speed. The differential in airflow speed.creates a faster than normal flow, thus more air passes the engine with greater cooling results. With the Mustang, such a system is easily created by the internal shaping of the cowl blocks. Over the years that it has been used, it has proven to be a valuable asset.

What is also obvious is that with the power pod a variety of fuel tanks can be easily used. Not only are they easy to inspect exactly as they are being used, but in turn, different types can be experimented with without resorting to different flying sessions. Versatility is always an asset with any model.

The Mustang wing is exceptionally light, efficient, stable and above all strong. The airfoil used is the NACA 65009 section, which has an excellent lift/drag ratio. This means that the greatest lift is available from the minimum wing area while keeping drag at its lowest possible point. In addition, this series of airfoils are among the most stable available; which means excellent control at all times, including low speed landing approaches.

The structural design is stressed skin, which, while providing simplicity of assembly, is also very light and strong. With suvch a design the strenth comes from the outer skins (required no matter what construction is used) rather than from spars, etc..."

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