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s, ultralights.USA, 1929. [1][2]]]

The triangle control frame (TCF or A-frame) is widely used in hang gliders, powered hang gliders, and ultralight aircraft. TCF is just one of many sorts of control solutions. TCF resolves a means of using weight-shifting attitude control in parasol aircraft. Also, a large use of the TCF in aircraft has been the holding of landing wheels and bracings for the wings.

Flying like a bird has become possible and practical partly because of the isosceles triangle. Beginning with Abbas Ibn Firnas and Leonardo da Vinci, the triangle played a role in the control of flying machine experiments.

The vast majority of modern hang gliders, and foot-launch powered hang gliders (FLPHG) use a triangle control frame (TCF) to help control the flight experience during gliding and soaring. Aircraft that are towed, onboard powered, or used in gliding-or-soaring-unpowered mode have structures and airframes that allow successful flight, controlled flying, and takeoff and landing mechanisms. A nearly ubiquitous elementary truss or triangle has found its way into airframes in a very strong way, when it comes to control, safety, flight performance, economical construction, handiness, and even aerobatic flying. TCF disadvantages and advantages both lead to a culture of TCF improvement. Beginning as the most simple truss, the TCF evolved its place in aviation through experiments, use, and commercial competition. The design and use of particular TCF affects points won in sport competitions. Pricing varies from pennies for three bamboo sticks to several hundred dollars for yacht-level design and quality.[3] [4]

The most elementary simple truss - the single triangle - stayed in aircraft airframes by cables or rigid struts has shown itself over at least three centuries in aircraft. When the triangle is collapsed to a single post (two down tubes joined as one), then a head-butting control part occurs. When the triangle loses the lower tube, then control is achieved only by using the two downtubes. When the triangle is stayed by struts, some advantages occur for some aircraft. When the triangle is cable stayed, then some benefits and disadvantages occur. The A-frame control sub-assembly has a colorful history spanning over at least three centuries; crafts from the following aircraft makers are included: Abbas Ibn Firnas, Leonardo da Vinci, Percy Pilcher, Augustus Herring, John J. Montgomery, Gottlob Espenlaub, George A. Spratt, Charles Richards, Barry Hill Palmer, Mike Burns of Aerostructures, and others in the manned ski-kite sport, and then many in the modern hang glider, trike, and ultralight world. Variously, the A-frame allowed both rigid and non-rigid pilot holds while the A-frame permitted various ways of controlling the aircraft from foot-rest all the way to the simple single-point pendulum swing-seat hold of the pilot exhibited by George A. Spratt in 1929 for hang gliders--after which any designer was free to use the same efficient arrangement. This article will study the history, physics, specifications, modifications, advantages, disadvantages, safety interfaces, and other aspects of the triangle control airframe part that is nearly ubiquitous in modern manned towed ski kites, hang gliders, trikes, and ultralights.


Physics of the A-frame or TCF

the TCF-staying cables to get lower drag.]]

Statics, stresses, buckling, defects, damages, resonance, etc. of the TCF are foci of engineers, manufacturers, and using pilots. When TCF is cable-stayed and being operated in normal flight-loaded position, the two side edges or legs of the TCF are in compression and the lower base edge is in tension. The integrity of the two side compression edges of the TCF is important to avoid buckling, as they are mostly used in compression. The base edge - when a tube - sometimes has an internal backup cable inside of the base tube; since normally that base edge is in tension during flight, if the main base edge's tube broke, then the cable would still hold much of the aircraft's flight integrity. A fully cable-stayed TCF often has three cables to each foot of each of the two legs (one to the spanwise spar, one to the front of the wing, and one to the rear of the wing or central keel). A fully strut-stayed TCF is trussed in various ways while having no position-staying cables to the TCF; struts in flight stresses may at times be tensional, neutral or compressional--depending on negative or positive or zero wing loadings. Struts are frequently carefully faired; but TCF staying cables and/or struts and legs are sometimes faired (but when faired, there is a reduction in profile drag [1]) as the subject aircraft tolerates the drag arriving from the unfaired cables. Specific windtunnel testing provides engineers with data to describe and improve TCFs. TCF is set at a certain angle relative to the wing's root chord; TCF at its apex is located along the wing's central root chord at specific places; these setting affect the stresses and flight handling characteristics of a particular TCF-using aircraft. Octave Chanute was an expert in both bridge and glider trussing familiar with queenposts and kingposts; the TCF can be traced back into work done by him. Octave Chanute Glider; Trusses Truss Types; Science and Technology; Octave Alexandre Chanute & Augustus Moore Herring

Positioning and Staying the Position of the A-frame or TCF

, 1921. Notice that he chose to rigid strut the TCF.]] In 1895 Augustus Herring's TCF was positioned so that the top parts of the two side edges of the triangle were able to doubly serve as a two-part kingposting that he used to hold considerable dihedral in the wings of his hang glider. In 1908 a gliding club used for a hang glider a cable-stayed TCF Schlesischer Flugsport Klub of Breslau 1908.from Stephan Nitsch Collection. Sometimes the TCF was stayed with rigid struts instead of cables Biography, Gottlob Espenlaub with 1929 photograph of strut-stayed TCF.

Barry Hill Palmer, aeronautical engineer in 1960-62 chose deliberately not to cable-stay his versions of the TCF as he wanted to avoid cable kinking; his first strut-staying of the TCF also allowed him to use two long frontal struts for exploring correct control positions of the pilot; his seventh or eighth version of a Rogallo-wing (Fleep inspired) hang glider was with strut-stayed TCF in front of him and finally with a swing seat; he went on to invent a motorized Rogallo-wing hang glider or trike. In 2008 there is yet a Rogallo-winged ultralight using the TCF in a lateral-strutted manner (the four fore and aft cables still help stay the TCF); the advantages involved are several: no cable-set replacements, no kingposts, less drag, easy ground handling, firm handling, and hangerable.[5][6] A long-leg TCF with image echo of the George A. Spratt longer-legged Template:Convert/Tcuft showed up mid-leg cable stayed in a first commercial hang glider in Britain in 1971 by McBroom and Partners; the airframe of the wing was the four-boom structure seen around the world from NASA's Paresev 1B variants: The First, British Hang Gliding Museum.

Cable-staying the TCF along the lines specially exhibited in 1929 by George A. Spratt for hang gliders included such designers as John Dickenson of Australia, Bill Moyes, Bill Bennett, Dave Kilbourne, Michael Riggs of Seagull Aircraft, Dick Eipper, and many others. Strut-staying or cable-staying the TCF involves advantages and disadvantages no matter the choice; streamlining for low drag is a challenge; portability choices affect the design decision on how to stay the TCF. In 1921 Gottlob Espenlaub decided to strut stay the TCF.

Some ultralights are having the TCF base or lower tube partially enclosed in a enclosed cockpit without abandoning the George A. Spratt contribution of cable-staying the TCF; [7]

Alternative Terms for the A-frame or TCF

Since the TCF or A-frame was used naturally as a simple truss in early aviation in the 1800s, specific names are difficult to find. It is the near ubiquitous use of the part in modern times that permitted a high focus on the part along with names. Contemporary manufacturers making TCF will abbreviate to "control frame" for the TCF. The two upgoing edges of the TCF receive various names including uprights (UK), downtubes (US) or uptubes (Self-Soar Association, USA; alternate spelling: "up tubes" or "up-tubes"; "up" was favored over "down") or legs. The horizontal lower edge of the TCF is sometimes called base tube, or control bar (CB) or variously spelled basetube or controlbar (CB) or basebar. Some high performance TCFs receive special names for the edges of the TCF; e.g., speed bar or speedbar or "speed-bar" or fast bar, or "fastbar", or fast-bar" for a well streamlined low-drag basetube (see comment on bellybar). Sometimes "control bar" refers to the entire TCF and sometimes to the basetube only.In the early 1970s manufacturer Bill Bennett's published plan for Model 210 Glider Kite named the basebar "handlebar."[8] The two legs of the TCF are sometimes called control bar legs while the basetube would be called control bar base. Also, "bottom bar" refers to the TCF's basebar[9].Occasionally the TCF is called the fuselage of the aircraft when the TCF is the predominant part below the wing; the fuselage would also include the parts that hang and hold the pilot and the TCF staying cables or staying struts. Other terms are in the literature: tandem control bar and carbon basebar. Also, aerofoil uprights, round base bar fast base bar, and carbon fiber speed bar.

In the 1970s tall-sitting hang glider pilots in standard hang gliders sometimes used a basebar with a forward double-jogged portion in its center that allowed pulling one's belly forward for pitching the hang glider for speed. Some mixed use of the term of bellybar to early speedbars occurred as many more pilots flew prone. The bellybar's double jog in the basebar allowed for an ergonomic gripping for prone and upright pilots that aided pilots in flying and speeding. Slightly different was the streamlining of not just the TCF's uprights (legs, downtubes, uptubes) but the basebar also for low drag for better performance, speed, and penetration of the glider. A speedbar that had the belly jogs (evolving to be more an ergonomically correct holding-angled portion of the basebar became a leading format for high performance basebars.


Distinctions of TCF from other flying controlbars

The following control bars are very different from the TCF of hang gliders, trikes, and ultralights:

  • Control bar specifically designed for kiteboarding, landboarding and snowkiting.[10]
  • In paragliding there is a very different part called "speedbar" or "speedbar."[11] This paraglider part should not be confused with the basebar of the TCF in framed hang gliders.

Streamlining the A-frame or TCF to Effect Low Drag

Various studiers have faced the challenge of streamlining the TCF for low drag. Some people have studied publicly the question of net drag over the alternative of staying the TCF with cables versus staying with rigid streamlined struts. Streamlining of the TCF up-going edges has been achieved by special low drag tear-drop cross-section aluminum extrusions and also by hand layup of carbon fiber composites.

The Paresev and Bensen gyrocopter control wing TCF essentially joined the two legs of TCF to have a down control stick; however, a contemporary experiment on a gyrocopting hang glider (unpowered and flight not achieved more than a hop) by Stephan Nitsch used an open-legged George A. Spratt-like TCF AUTOGIRO AS HANG GLIDER?.

Usage of the A-Frame

TCF as "Cockpit" and holder of accessories

Since the pilot is near and even in touch with the TCF, the TCF often holds accessories: variometers, GPS instruments, transponders, altimeters, flight planners, transceivers, airspeed indicators, Issues of crowding the TCF space with accessories where the pilot operates includes hazards and distractions.

TCF as a hazard in some formats

When a TCF inappropriately gouges into the ground or water during a landing, the momentum of the pilot's moving mass will put the pilot moving forward either to hit or miss the TCF; in hitting the TCF, both the TCF and the pilot's body may be injured; the TCF staying cables or staying struts may be broken or weakened--for safety sake, such a situation should be logged in a pilot's log book and be cause for initiating an inspection of parts. Pilots making good landing will avoid such TCF ground gouging of the TCF's basebar.

Wheels, skids, skis, floats, etc. and the A-frame or TCF

The TCF as a place to mount aircraft wheels has a strong presence. Many various wheel mounting methods have punctuated the history of aviations TCF. The lower feet of the two upper sides of the triangle's "A" in "A-frame" remain vertical or are sometimes structured horizontally as extensions of the lower "base" beam or bar or cross-beam of the "A" in the TCF; such lower feet or extension form one of the places that wheels have historically been places. Wheels have been used for several purposes (ground handling, takeoff rolls, landing rolls, water holdinging, assistive-fuel holding, etc. Instead of wheels, skids and skis and floats and even surfboards have been mounted on the TCF to meet specific utility.

Specific Uses

Hundreds of specific uses of the TCF have occurred in history. The TCF is part of the airframe of most hang gliders, trikes, and very many ultralights. Then the "C" part of the generic describer has to do with controlling the flight path of the aircraft. Variations of use of the TCF varied throughout the centuries from near rigid hold of the pilot in place to full pendulum swinging freedom of the pilot's body as George A. Spratt demonstrated. Between the extremes, the TCF had been used as a foot-rest, a pitch-only push-pull device where pilots would use control surfaces for yaw and roll. Besides airframe and control, other uses of the TCF have become fact in the history of hang gliders, trikes, and ultralights. Attaching instruments to the two up-going sides of the triangle or to the base edge or base tube of the triangle results in a handy place for such things. Some stunt pilots use the TCF for standing in the TCF even without safety tethering to the airframe; with rescue parachute at the ready, some stunters have done gymnastics on the TCF during flight. That the triangle goes to a narrowing point has allowed the saving of some accidental un-hooked pilot to climb up the two up-going sides of the triangle. Adding wheels, skids, and skis to the lower part of the TCF has various allowed rolling or sliding takeoffs and rolling or sliding landings. Using such devices at the lower section of the TCF also allows moving the aircraft on the ground. During fly-and-hike trips and bivouac excursions, the TCF allows the aircraft to provide shade and tenting for the camping or sitting grounded pilot. At airshows this use is evident. Waiting for the wind to be just right finds pilots and friends beneath wings held up by the TCF.

Control aspects of TCF

The TCF is sometimes fully released from any hold by a pilot of a hang glider, microlight, trike, or ultralight; however that situation is not the common status. In tandem flying, the immediate pilot in command (PIC) will hold the TCF for controlling the aircraft. The pilot will have occasion to hold the TCF at different locations on the legs or basebar, depending on what is needed for controlling the aircraft. There are many different circumstances and types of aircraft that will define just what would be appropriate handling of the TCF. Ground handling for parking, ground handling in the preamble to a takeoff, takeoff time, near after takeoff, special towing flight sectors, flying, gliding, turns, aerobatics, recovery from unexpected disturbances, landing approach, landing, testing trim, and field carrying. When the aircraft has controls beyond mass-shifting of the pilot's mass, then controlling the TCF will be altered.

Related use topics

The very important topics of how to operate the TCF for takeoff, flying maneuvering, landing, and aerobatics is answered in the literature surrounding each type of aircraft: hang gliding, triking, and ultralighting. Further, each specific model of an aircraft that utilizes a TCF will have specific directives of how to operate the TCF. How to inspect TCFs for damage occupies the attention of both users, dealers, and manufacturers. How to repair and replace TCFs is an extended topic. How to upgrade from a lower quality TCF to a higher quality TCF has its specific challenges. Selling new and improved TCFs is a significant part of the related industry. How is the TCF operated during tandem flight (discovery flights, tandem aerobatic flights, instructional flight)? When does one replace a TCF? How are hidden wearing and ageing questions answered by TCF owners? Manuals, articles in magazines, books, and discussions in forums blossom with advice about these matters. Making notes about one's TCF in one's flight logbook can help resolve questions. Gripping, grasping, and holding the TCF differs among specific aircraft. Launching a kite hang glider's TCF using the grapevine hold is frequently instructed; landing such a hang glider involves other grips and holds like a bottle grip; timing transitions from one grip and hold to another is part of learning to fly with the TCF. [1]

TCF in Flight Simulators

Clubs have set up fixtures letting the public hang in a harness or seat while manipulating a TCF while watching video of a flight. Pilots have set up TCF in their homes and garages to practice the postures used in actual flight.[2] The TCF is often set on the ground while a "hang check" is made just prior to flight; a short hanging-self simulation occurs. Manufacturers and homebuilders sometimes mount the TCF on a car or truck along with he hang glider or ultralight wing and run wind and loading tests on the wing. The TCF itself is sometimes mounted in windtunnels for studying the airflow around the cables, legs, basebar, corners, and connected parts. Compression stress tests all the way to destruction are sometimes done.

Injuries to Pilots Involving the A-frame or TCF

Injuries to pilots have occurred in relationship with the A-frame or TCF. Gouging the lower bar or feet of the TCF into sand, water, grass, dirt, etc. puts a rapid torque on the aircraft's airframe and often causes a rapid braking of the airframe; those two actions in the face of momemtum of the pilot's body has proven to be an important problem in TCF-equipped aircraft, especially hang gliders having the pilot in free-pendulum hold where the pilot might keep moving forward during a sudden stop and possibly hit his or her head on an airframe or wing part. Wheels, skis, skids, streamlined floats partially face the challenge. Mastery of landing skills play a large part in lowering the possibility of injury from gouging the TCF into the non-air matter.

TCF and Advanced Modern Materials

Carbon fiber is being used on advanced TCF to achieve certain advantages; Kevlar fibers are being composited with carbon fiber. Carbon nanotubes are being considered for making further advances for the TCF. Stainless steel backup cable is embedded in the basebar of some TCFs.

TCF Historical Timeline

800s :: Abbas Ibn Firnas constructs a hang glider featuring a control frame in order to fly and return to the place where he flew from, though the landing ended in failure.[3][4]
1500s :: Leonardo da Vinci flying machine designs included some TCF instances.
1800s :: Percy Pilcher, Augustus Herring, John J. Montgomery.
1900s :: The Breslau-located "Klub" of 1908 demonstrated the TCF most simply. Carl S. Bates (struted TCF in a biplane hang glider), George A. Spratt, Barry Hill Palmer, Richard Miller, Mike Burns, John Dickenson, Michael Riggs, Bill Moyes, Bill Bennett, Dick Eipper, Peter Brock, Bob Wills, Mike Markowski: These and other people tweaked the TCF as they produced proprietary hang gliders from 1960 forward.
2000s :: Manufacturers' TCF improvements continue.

The TCF history timeline notes verifiable noteworthy TCF changes: varied functions, auxiliary uses, style, size, position, staying methods, relative position with respect to aircraft's center of gravity, relative position with respect to aircraft's center of pressure, composition, strength, weight, finish, appliques, color, competitors (other control frames), secondary uses, tandem TCFs, interfaces with various towing methods, assistance interfaces, and extraordinary uses.

-1892 Otto Lilienthal sketched for a second hang glider; in his sketch he employed a TCF that double functioned as a kingpost; the basebar was complex and integrated with framing that helped to stay the monoplane wing. [5]
- 1895: Percy Pilcher, hang glider
- 1896: Octave Chanute Multiple-Wing Gliding Machine, German patent 1896. [2]
- 1898: Augustus Herring, hang glider and compressed-air powered hang glider.
- 1908: A college gliding club Schlesischer Flugsport Club in 1908 in Breslau. demonstrated a cable-stayed simple triangle control bar with pilot hung from wing behind the control bar. Breslau 1908. A photograph is researched and obtained by Stephan Nitsch.
- 1922: Gottlob Espenlaub, hang glider with strut-stayed TCF and pilot behind TCF.
- 1929: George A. Spratt, hang glider with pilot behind TCF in single point hang of cable-stayed TCF and tensionally held pilot for weight-shift control of the hang glider; this opened up a winning combination that would be by far the most popular in hang gliding in the following decades up to present time; competing control frames from this basic mechanical model have niche applications while the size of the TCF would be scaled to fit particular needs.
- 1960: Barry Hill Palmer, hang glider with pilot far in front of strut-stayed TCF.
- 1961: Charles Richards for NASA reduced the TCF to single control stick (two triangle side legs become one down leg, and thus no need for basebar) used still as Spratt did--to have the hung pilot push and pull the stick to control the attitude of the Parasev 1B wing.
- 1961 Tom H. Purcell had control of his aluminum hang glider kite towed over land; then in 1962 he was towed over water with pontoons in the Rogallo kite. He was inspired by the Fleep.[6]
- 1961: Barry Hill Palmer, hang glider with pilot in front of strut-stayed TCF.
- 1962: Barry Hill Palmer, hang glider with pilot behind strut-stayed TCF.
- 1962: Mike Burns assists Bill McLachlan toward materializing TCF on Ski Plane.
- 1963: John Dickenson built a manned towed ski kite with strutted-stayed open-top-legged TCF and then decided to cable-stay the TCF in models after his first exploratory half-size kite.
- 1965 Richard Miller fully struts a small TCF and chooses parallel bar pilot-hold rather than a tethered seat (early 1800s and 1900s hang glider sometimes had tethered seats).
- 1966: Barry Hill Palmer, trike with cable-stayed TCF and pilot behind TCF.
- 1967: Bill Moyes, manned towed ski kite and tow and release to hang gliding. TCF with surfboard and floats.1968 Bill and Molly Moyes tandem in George A.Spratt-like TCF
- 1969: Bill Bennett, (ornamental patent, not mechanical-process patent) [7] design patent approved showing a tow-part on the base tube of the TCF for a manned tow kite. U. S. Patent D224248 was filed Sep 24, 1969 showing the TCF with a special tow-point structure on the mid base bar or lower edge of the TCF; such tow point in functioning towed kites or towed hang gliders is discouraged in preference of a safer arrangement.[8] [9]
- 1970 Single-piece TCF design by Michael Riggs. The TCF used circular cross-section aluminum tubing and received a quality finish.
- 1971?: Mike Koman and Joe Faust designed a no-cross-spar bowsprit Rogallo-wing hang glider using the Spratt TCF mechanical process; the sail was outsourced to Dick Eipper's sailmaker; the hang glider was flown by Faust for a nationally-shown Dial Soap TV commercial. Mike Markowski of Man Flight Systems also made and flew a bowsprit hang glider with TCF and a tail.
- 197? Eddie Paul mounted two jet engines to TCF base corners.
- 197? Bill Bennett holds TCF while backpacking powered propeller.
- 1975 c. TCF holds liquid fuel container
-____ Japanese hang glider has an empty-based TCF where the TCF legs were firm posts and where the basebar was replaced by empty air to allow free movement of the vertically hanging pilot. This method of absent-basebar TCF was to be repeated by the Woopy-fly kite [10] hang glider and similar ski-slope speed hang gliders used specifically for fast downhill ski-based flying. In these versions, the legs are near parallel, so the apex of the implied triangle was virtually distant, yet the control principles were mechanically still following what George A. Spratt demonstrated well in 1929).
- ___ Instruments begin to be mounted on TCF.
- ____ TCF attaches to double-surface wing (DSW or DS) rather than just single-surface wings (SSW or SS)
- ___ TCF legs are streamlined commercially from high drag round cross-section to tear drop low-drag cross-section.
-___ TCF basebar are offered commercially in special shapes allowing comfort for long cross-country (XC) flying.
- ___ TCF is offered commercially in carbon fiber composites.
-___ Dr. Donnell Hewett, physics professor: Hewett's towing safety advice Criteria for Safe and Efficient Towing alters how hang gliders are towed and how the TCF is disinvolved in counter-use to the 1969 Bennett ornamental design for the TCF tow-part implication. [11]
- ___TCF position changes relative to pilot position as powered harnesses are made and flown; liquid fuel is hung on uppter part of TCF.
-____ TCF is used in Strutted Maverick 14.9 Wing integrated with land wheels and water floats for an amphibious ultralight. Amphibious ultralights featured that use TCF fully cable-stayed as well some with lateral struts.
-2004 TCF finds itself partially enclosed in cockpit cowling on powered hang gliders and ultralight aircraft while still providing the base for mass-shifting control. Example: Seagull Aerosports, designer: Michael Riggs (his TCF designing continues from 196? to the present time, over 38 years for hang gliders, trikes, and ultralights).
- 2009 Paramontante has a version that applies triangle control system.


See also


External links

Patents related to the A-frame or TCF


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