Cobra helicopters page 3
| MUSTANG 532 HELICOPTER | |
|---|---|
| Engine type | Rotax 532 (64-hp) |
| Maximum speed | 75 mph |
| Rate of climb | 1000 fpm |
| Endurance | 1.0 hr |
| Range | 75 miles |
| Hover in ground effect | 8000 ft |
| Service ceiling | 10,500 ft |
| Empty weight | 385 lb |
| Design gross weight | 766 lb |
| Useful load | 383 lb |
| Length overall | 22 ft |
| Height | 6.3 ft |
| Skid width | 4.0 ft |
| Disc loading | 2.44 p/sf |
| Power loading | 12 lbs/hp |
| Main rotor diameter | 20 ft |
| Chord | 8 in |
| Tail rotor diameter | 42.0 in |
| Chord | 4.0 in |
| Seating | 1 place |
| Fuel capacity | 5 gal |
What do we do when we reach the bottom of the glide? We flare - bring the nose of the ship back up - to convert speed into lift, and, as the wing starts to slow down, the lift decays and we settle gently to the ground. In the helicopter? Exactly the same - as we near the ground, we bring the collective back up, and the momentum of the blades keeps them turning (slowing down, though) while they provide enough lift for a gentle touchdown.
There is one additional finesse to setting down a chopper with no power, though a different kind of flare which not only kills off forward speed, but provides extra blade energy to cushion the touchdown. Any wing, whether fixed or rotary - will glide at a given angle, but will do so at a higher speed if wing loading is increased. Thus, if we were able to increase the wing loading somehow, the rotor would speed up. We are able to do this by flaring hard - around 50 feet off the ground. This not only arrests our forward speed, typically about 60 mph for a minimum rate of descent, but momintarily pulls some "Gs" making the helicopter seem to weigh more, so rotor speed increases; thus, more kinetic energy is stored as rotor momentum, giving the pilot an additional couple of seconds in which to feel for the ground.
Needless to say, practice autorotations are a major item of any helicopter syllabus. Initially, they’re practiced only to a power recovery well before touchdown.
Gary tells us that in order to keep their Cobra helicopters as safe as possible, many components, including the main rotor blades, are assembled at the factory. He explains: We start with a solid 7075 T-6 extruded aluminium leading edge spar which is 30 percent of the chord. The ribs are cast from aluminium alloy and are machined to an exact size.
They are then placed every 12 inches along the spar, and total 13 per blade when all installed. The trailing edge is also extruded aluminium alloy in a V shape. The ribs and trailing edge are all covered with 2024 T-3 Alcad skin which is .032 – inch thick. Now, the parts are chemically treated to help in the bonding process. A special bonding compound is used, along with rivets for strength, durability and safety. The whole blade is placed in a jig which electrically heats and bonds the bldes together and insures that the blade is perfectly straight and true. This bonding process takes eight hours per blade.
The rotor blades are made in sets and are set up for a particular hub and grip assembly, which is well marked before shipment to the customer. The blades have never failed in any way and are considered to have an infinite life.
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| MUSTANG 532 single seater |
The tail rotor blades are made of stainless steel, shaped to form the blade. An aluminium alloy spar is used where the blade grip holds the blade. The blade is then placed in a jig and precisely drilled and riveted together.
All gearboxes on the helicopter are made of a special aluminium alloy. This is a very strong, light and reliable alloy. These gearboxes are cast and heat treated, then machined by a highly qualified machinist to top quality tolerances. The gears are made for us by a gear manufacturer and are stressed at well over requirements. At our factory, we assemble the gearboxes complete with gears, input – output shafts, bearings, and seals. They are then sent to our customers as completed, ready – to – install units.
Gary Helton, realises that not everyone wants or needs a beautifully streamlined, Lycoming – powered helicopter. Many homebuilders would be very satisfied with an ultralight – style true helicopter, so he utilised the components from the Commuter I I , removed all unnecessary weight, and after substituting the reliable Rotax 503 or 532 engine, called his new helicopter the “Mustang”.
The new single – place helicopter, small and ruggedly constructed, may be stored in an average size garage without folding the main rotor blades. It also has an overall height less than most standard garage door heights, thus the owner may store the helicopter in his or her garage, thus saving thousands of dollars a year, which might have been spent for commercial hanger rents.
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MUSTANG 532 single seater |
The small and rugged construction of the Mustang also has a number of other benefits, one of which is being able to get in and out of many tight locations unreachable in larger helicopters. This enables the pilot to land in small parking lots, yards, or secluded hunting or fishing sites.
Another is that the Mustang’s rugged construction allows it to land off – airport or non – paved areas to get into these secluded spots. The Mustang’s welded tube construction makes the airframe very strong and lightweight. To this airframe are attached two skids which serve as the main landing gear, a type of gear which makes landing in unimproved sites easier and safer, as the skids will span small holes in the ground which a wheel – type landing gear may not. The airframe and landing gear are made of 4130 chromoly steel tubing, the same type used in most small aircraft, helicopters and fixed – wing aircraft, because it’s very strong and able to withstand the flight loads and stresses put on it in this application.
Although, with an empty weight of 366 pounds, the Mustang does not qualify as a true ultralight aircraft in the FAA category or classification, it still weighs less than half of any helicopter available. Considerable engineering and design work was done to reduce the weight to this amount, while still maintaining the requirements of a good rugged and reliable helicopter.
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| MUSTANG 532 single seater helicopter |
If you have seriously studied the possibility of designing and building your own helicopter, you are aware of the many complex problems to be solved in such an undertaking. Many people have tried this only to find that they have expended many hours of work and several thousand dollars on a machine which might not even get off the ground; or worse yet, may prove to be dangerous to operate.
Designing a helicopter without being aware of the aerodynamics, centrifugal forces and mechanical loads to be encountered can be very costly and very dangerous. Vibrations, gyroscopic forces and unbalanced conditions can destroy a poorly designed helicopter in seconds.
For all these reasons, the Mustang was designed using proven technology in an ultralight airframe with an ultralight engine. The proven technology is the fact that we use the transmission, tail rotor gear box, tail rotor blades and rotor control systems used in the Commuter helicopter. (See full description of Commuter at beginning of this article.)
What makes the Mustang different from the Commuter? The difference lies in using the lighter weight Rotax engine as its powerplant. Although the Rotax was not available when the Commuter was designed, because of the acceleration of ultralight aircraft development during the last several years, the Rotax engine has since proven itself by providing homebuilders with thousands of hours of reliable service. We have coupled the Rotax engine to a new design, a lighter – weight airframe, and the result is the new Mustang.
Before you pilot the Mustang, you’ll need to get instruction from a qualified helicopter instructor. In most moderately large cities, you can find a helicopter operator qualified to give you flight training in his or her machine. If you already have a pilot’s licence, you can step up to a helicopter rating with a small amount of flight instruction, sufficient practise, and a checkride. Under no circumstances should the builder teach himself to fly his own helicopter without previous training.
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NOTE: Cobra Helicopters are no longer in existence and their Cobra, Mustang and Predator helicopters are longer in production. Article date 1990 courtesy Norm Goyer.
