The 70's

Google Translation from French of "Mechanix Illustrated" from April 1973

https://www.delta-club-82.com/bible/639-hang-glider-vj-23.htm

(English copy pending)

Article written by Wayne Thoms

Foot-launched gliders really took off with early aviation pioneers flying down the sand dunes to improve the technology for powered flight.

One of the first recognized PUL gliding flights took place on August 28, 1883. It was carried out by J. Montgoméry near San Diego. A few years later, in 1891, Otto Lilienthal tested his gliders.

Recently, we have seen a revival of this flying philosophy. For example, two years ago, a spontaneous gathering of 15 PULs took place on the west coast (NDA: we are in the United States). Most of the participants didn't realize there were so many of them stealing in the area.

Now the movement is launched. Every sunny Sunday, there is a large collection of PULs along the sand dunes located three kilometers south of Los Angeles International Airport. Currently, the sport is spreading rapidly across the country _ wherever man has a fascination for flying.

It is a low-cost outdoor sport. While the form of PULs evolves from giant kites to biplane flying wings, we are in the presence of one of the most evolved. It (NDA: the VJ 23) is designed in a very professional manner, fully flight tested and accessible to amateur builders.

Designed by Volmer Jensen and Irv Culver, its creation cost Jensen approximately $400 in supplies. Total construction time is estimated at three months of free time construction. Furthermore, Jensen is a professional builder who flies a seaplane designed and built by himself. He built his first 40 years ago (NDA: see VJ 11) and has built many others since. Culver is an aerodynamicist who designed the profile of the VJ 23 SwingWing and carried out the fatigue study (NDA: verification rare enough in this aero domain to be underlined...).

Most PULs slide down the slope in a few seconds or hold along the terrain when the wind is strong enough. What sets the SwingWing apart from other PULs is its unusual ability to stay aloft. With a modest wind of around thirty km/h, the pilot took off on his own in less than two or three steps, and then flew as long as he could maintain himself in the ascending part.

During a SwingWing demonstration, Jensen remained in the air for more than 40 minutes, flying along and past a 35 ft (10 m) elevation dune 300 yards long. The 23° slope seemed to have excellent performance ideal for dynamic flight.

The cruising speed is between 25 and 40 km/h, but to land, you just have to land facing the wind (NDA: no comment on the flight technique of the time...!). Landing is done in one or two steps. Usually the landing occurs due to the weakening of the wind.

For short flights, the pilot is suspended by leggings, but a seated harness with a seat can be used for longer flights. The total weight of the SwingWing is 100 lbs (NDA: 45kg), which seems a bit heavy to take off and put down. Pilots, however, claim this is not the case. The SwingWing can be suitable for pilots weighing up to 200lbs (NDA: 91 kg), but the lighter the pilot, the better.

The VJ23 is piloted with just the right hand using a stick, which coordinates the ailerons, fin and elevator. This control system is the secret to the safety of the SwingWing. Many PULs are controlled by shifting the center of gravity. The problem, Jensen says, is that with a large enough wing capable of soaring, it's impossible to move far enough off the trapezoid to create lift once the wing has gained enough tilt. The consequence is then spiral instability and a dive until the wing hits the ground. Jensen thinks it's a bad idea to fly under an uncontrolled glider at a height higher than your legs can handle.

It is not necessary to hold any certificate to fly PUL. Although the VJ23 prototype has Federal Aviation Administration registration number N474VJ, registration and no patent are required. When Jensen began building the SwingWing, he contacted the FAA (NDA: equivalent of the DGAC in France) to find out if registration in the experimental category was necessary. After examining the SwingWing, a member of the FAA felt that this must be the case if the aircraft was capable of soaring over long distances and at high altitudes, which it is not. the case. Later, the FAA ruled that PULs, much like skydiving, did not significantly penetrate airspace and therefore did not require a license to fly them.

While an experienced pilot will find flying the SwingWing relatively easy, a builder with no flight hours will be able to learn on their own. He will of course have to start with short, easy flights, land with wind, and make shallow turns. Jensen notes that because the speed range is between 16 and 25 mph, most airplane pilots have a little difficulty at first because they are not used to flying at such low speeds. A simple speed indicator is attached near the handle.

The VJ23 has a wingspan of 9.88 meters and a length of 4.96 meters. The cantive wing has a relative thickness of 16%, thus eliminating reinforcement by cables or guying. The wings, tail, fin, fixed planes and elevator will be ????????, while the disassembled device is designed to be assembled in 30 minutes. The wheels, which were custom-made to be as light as possible, are not necessary in flight but make handling on the ground easier on the take-off area. If the pilot misses his landing and falls, the VJ23 can land on its wheels by sliding on its belly - the pilot's belly in fact. There is no structural element placed directly behind the pilot which could injure him.

The VJ23 is one of the most advanced PULs and is recognized as one of the safest of the new wave of PULs. To build it, you must acquire a set of plans and a serial number from Volmer Jensen, but also mastery of wooden construction and certain skills.

Supplies. You won't need to have large supplies. You will build your wing in two parts of 4.88 meters and assemble it with three bolts just before flight. The tail boom, an aluminum tube 10 cm in diameter and 4 m long.

The tools. The VJ 23 is made mostly of wood, just like a smaller model, but easier to build. In addition to the hand tools that you will find in all good DIY stores, you will need a scroll saw, a band saw and a circular saw. A drill press might be useful, but a hand drill will do the trick.

Wing and tail. The wings, which weigh 15 kilos each, are sized with a limiting load factor of 2G and an ultimate load factor of 3G-more than the loads that will be seen over the life of the aircraft. The leading edge of the wing is made from 1mm plywood, which looks particularly good unpainted. The leading edge ribs are made of 1cm thick marine plywood, while spruce (NDA: it is a type of wood commonly used in aeronautical construction due to its specific resistance) for the ribs of the empennage , and rods for the wing spar. Jensen does not use epoxy for the VJ23, preferring the white glue he has trusted for years. The wings and empennages are covered with an aeronautical dacron sold under the name Ceconite, a light fabric of 1.8oz/sqrd (NDA: for your information, the dacron used on current delta wings is of the 5.8oz/sqrd type). The wing is considered simple surface because the lower surface of the trailing edge is not covered, an aerodynamic consideration which also facilitates construction. No need for larding because ????? (NDA: I was unable to translate the English term). Apply the fabric without stretching it, then apply a coating to ensure waterproofing. The fabric can then be stretched using an iron but being careful not to go overboard. Jensen says you can indeed break the structure.

Structure and linkage. The vast majority of orders can be manufactured to plan by following the manufacturing instructions. Numerous tests were carried out in order to have a correct deflection, and the final result is a combination judged correct by Jensen between the rudder, the ailerons and the elevator. They are combined together in order to have a single flight command.

The Swingwing has a glide rating of 9, meaning that at its best glide angle speed (18 to 20 mph) it will fly up to 9 times its height. Performance is modest compared to traditional gliders, some of which have a glide ratio of 40. This explains why the VJ23 is docile and easy to fly.

With Jensen's 40 years of glider building experience, the Swingwing appears to be an ideal aircraft for the amateur builder interested in the various facets of aviation. With the VJ 2", you can fly anywhere there is a hill with a big enough landing field and a little breeze. It's the ideal way to learn the real basics of flying. As Volmer Jensen himself says , “it’s the most regenerating sport. As soon as your feet leave the ground, even a few meters, you feel like you're flying 300 meters above the ground.