The Hirth Hi 27 Acrostar was designed by Arnold Wagner to win aerobatic competitions, in part by having handling independent of orientation, upright or inverted. A single engine, single seat low-wing monoplane, it was built in

West Germany West Germany was the common English name for the Federal Republic of Germany (FRG) from its formation on 23 May 1949 until German reunification, its reunification with East Germany on 3 October 1990. It is sometimes known as the Bonn Republi ...

Wolf Hirth Wolfram Kurt Erhard Hirth (28 February 1900 – 25 July 1959) was a German gliding pioneer and sailplane designer. He was a co-founder of Schempp-Hirth, still a renowned glider manufacturer.Segelflugbildkalendar 2011 Hirth was born in Stuttgar ...

GmbH in the early 1970s, and dominated Championships for a brief period.

Design and development

The Hirth Hi 27 Acrostar is a competition

aerobatic aircraft An aerobatic aircraft is an aerodyne (a heavier-than-air aircraft) used in aerobatics, both for flight exhibitions and aerobatic competitions. Most fall into one of two categories, aircraft used for training and by flight demonstration teams, whic ...

designed by the Swiss aerobatic champion, Arnold Wagner. Wagner and three others, two of them German ex-champions, sponsored the construction. The

team was led by Prof. Richard Eppler of the

Stuttgart Technische Hochschule The University of Stuttgart () is a research university located in Stuttgart, Germany. It was founded in 1829 and is organized into 10 faculties. It is one of the oldest technical universities in Germany with programs in civil, mechanical, indu ...

, starting work in the Summer of 1969. The first flight of what was known as the Acrostar Mk II was on 16 April 1970. The Acrostar is a conventionally arranged low wing single engine aircraft. The wing is straight tapered, the leading edge slightly swept and the trailing edge unswept. The aerofoil section, designed by Eppler, is quite thick with a

thickness-to-chord ratio In aeronautics, the thickness-to-chord ratio, sometimes simply chord ratio or thickness ratio, compares the maximum vertical thickness of a wing to its chord. It is a key measure of the performance of a wing planform when it is operating at t ...

of 20%. It is a symmetric section and mounted at zero incidence. There is also zero dihedral. Full span control surfaces are fitted, flaps inboard and proportionally moving

ailerons An aileron (French for "little wing" or "fin") is a hinged flight control surface usually forming part of the trailing edge of each wing of a fixed-wing aircraft. Ailerons are used in pairs to control the aircraft in roll (or movement around ...

outboard. The ailerons are balanced not by the usual horn or hinge line extensions but by small surfaces which project beyond the

wingtip A wing tip (or wingtip) is the part of the wing that is most distant from the fuselage of a fixed-wing aircraft. Because the wing tip shape influences the size and drag of the wingtip vortices, tip design has produced a diversity of sha ...

s. Unusually, both ailerons and flaps are coupled to the

elevator An elevator (American English) or lift (Commonwealth English) is a machine that vertically transports people or freight between levels. They are typically powered by electric motors that drive traction cables and counterweight systems suc ...

position; this camber changing control system, together with the highly symmetric wing, produces the same control characteristics for normal and inverted manoeuvres. The basic idea in this arrangement was to keep the centerline of the fuselage horizontal in both normal and inverted horizontal flight. The result, beside this, is good controllability in low speed ballistic flight, around zero G. Another unusual control feature, allowing for independent trimming in pitch and yaw, are the independent

trim tabs Trim tabs are small surfaces connected to the trailing edge of a larger control surface on a boat or aircraft, used to control the trim of the controls, i.e. to counteract hydro- or aerodynamic forces and stabilise the boat or aircraft in a pa ...

on the flaps. The plywood covered wing is built around a single glass fibre spar using foam reinforced ribs. Aft of the engine, the fuselage is a wooden semi-monocoque. The single seat cockpit is enclosed with a rearward sliding canopy. The fin and balanced rudder are straight tapered and square tipped, as is the rearward set horizontal tail. The prototype had elevator trim tabs but these were removed in favour of the flap trims noted above. Extra fin area is provided by a long

strake On a vessel's Hull (watercraft), hull, a strake is a longitudinal course of Plank (wood), planking or Plate (metal), plating which runs from the boat's stem (ship), stempost (at the Bow (ship), bows) to the stern, sternpost or transom (nautica ...

on the lower fuselage, extending aft to the tailwheel. The Acrostar is powered by a 220 hp (165 kW) Franklin 6A-350-C1 six cylinder horizontally opposed piston engine. This is mounted in a steel frame which is integral with the fixed

cantilever A cantilever is a rigid structural element that extends horizontally and is unsupported at one end. Typically it extends from a flat vertical surface such as a wall, to which it must be firmly attached. Like other structural elements, a cantilev ...

main undercarriage and its optionally streamlined, tapering legs and faired wheels. This arrangement places the main

landing gear Landing gear is the undercarriage of an aircraft or spacecraft that is used for taxiing, takeoff or landing. For aircraft, it is generally needed for all three of these. It was also formerly called ''alighting gear'' by some manufacturers, s ...

further forward than usual, providing a drag moment to oppose that of the fin in vertical flight. The tailwheel is steerable.

Operational history

The first prototype ''D-EMKB'' appeared in competition, three months after its first flight, at the 1970 6th World Aerobatics Competition at

Hullavington Hullavington is a village and civil parish in Wiltshire, England, just to the north of the M4 motorway. The village lies about southwest of Malmesbury and north of Chippenham. The Fosse Way, a Roman road, forms the western boundary of the par ...

, England where it was placed 4th on the individual men's list. Nonetheless, it made a strong impression and attracted orders from Germany, Switzerland and Spain for participation in the 1971 European and 1972 World Championships. Acrostars gained 1st and 3rd places at the former, the Trophée Biancotto held at

Carcassonne Carcassonne is a French defensive wall, fortified city in the Departments of France, department of Aude, Regions of France, region of Occitania (administrative region), Occitania. It is the prefectures in France, prefecture of the department. ...

, France. By January 1972 four had been built and another five were due for delivery ahead of the 7th World Championship, held in

Salon-de-Provence Salon-de-Provence (, ; or , ), commonly known as Salon, is a commune located about northwest of Marseille in the Bouches-du-Rhône department (Metropolis of Aix-Marseille Provence), region of Provence-Alpes-Côte d'Azur, Southern France. It ...

, France in July 1972. Four participated with Swiss pilots coming 4th and 8th, bringing their team in 3rd place behind the US and USSR. During 1973 Acrostars won first place in the Coupe Champion Amberieu in France, the Scandinavian Cup, the Swiss International Championships, the West German Championships and the Zadar Cup in Yugoslavia. In all 9 Acrostar Mk IIs were built. The sole Mk III weighs less and has performance and handling improvements. These include lightened control surfaces and refined

wing root The wing root is the part of the wing on a fixed-wing aircraft or winged-spaceship that is closest to the fuselage,Peppler, I.L.: ''From The Ground Up'', page 9. Aviation Publishers Co. Limited, Ottawa Ontario, Twenty Seventh Revised Edition, 1 ...

fairings. It also has engine cooling and lubrication changes to allow glider towing without overheating (Mk III remained a project). The Acrostar prototype ''D-EMKB'' remained active until at least June 2009. The third Acrostar, ''F-AZJF'', previously ''HB-MSA'' was undergoing restoration in early 2010 and ''EC-CBS'' has been on display in the Museo de Aeronautica Y Astronautica,

Cuatro Vientos Cuatro Vientos is an administrative neighborhood () of Madrid belonging to the district of Latina. Geography Cuatro Vientos is situated in the south-western area of central Madrid, close to the motorways A5 and M40 and to the homonymous airpor ...

Madrid Madrid ( ; ) is the capital and List of largest cities in Spain, most populous municipality of Spain. It has almost 3.5 million inhabitants and a Madrid metropolitan area, metropolitan area population of approximately 7 million. It i ...

. Serial number 4009, originally D-EOIG, now HB-MSK, is since 1980 in private ownership, based at

Donaueschingen Donaueschingen (; Low Alemannic German, Low Alemannic: ''Eschinge'') is a German town in the Black Forest in the southwest of the States of Germany, federal state of Baden-Württemberg in the Schwarzwald-Baar ''Districts of Germany, Kreis''. It ...

, Germany.

Specifications (Mk III)

References

{{reflist, refs= {{cite book , title= Jane's All the World's Aircraft 1972-73, last= Taylor , first= John W. R. , year=1972, publisher= Sampson Low, Marston & Co. Ltd, location= London, pages=90–1 {{cite book , title= Jane's All the World's Aircraft 1974-75, last= Taylor , first= John W. R. , year=1974, publisher= Jane's Yearbooks, location= London, isbn=0-354-00502-2, page=93 {{cite book , title= Airlife's World Aircraft, last= Simpson , first= Rod , year=2001, publisher= Airlife Publishing Ltd, location= Shrewsbury, isbn=1-84037-115-3, page=397 {{cite web , url=http://events.fai.org:81/aerobatics/chronology.asp?id=13 , title=FAI Aerobatic Championship records , accessdate=2010-09-19 , archive-url=https://web.archive.org/web/20060516201938/http://events.fai.org:81/aerobatics/chronology.asp?id=13 , archive-date=2006-05-16 , url-status=dead {{cite web , url=http://www.airliners.net/search/photo.search?aircraftsearch=Hirth+HI-27+Akrostar+MkII, title=Acrostar images, accessdate=2010-09-19 {{cite web , url=http://www.abpic.co.uk/search.php?page=0&q=Hirth%20Hi.27%20Acrostar%20II&u=type&sort=country_z_a&limit=5, title=''F-AZJF'' restoration, accessdate=2010-09-19 {{cite web , url=http://www.abpic.co.uk/search.php?q=Hirth%20Hi.27%20Akrostar%20II&u=type , title=''EC-CBS'' displayed, accessdate=2010-09-19 {{cite magazine , title= Aerobatic technology., magazine=

Flight Flight or flying is the motion (physics), motion of an Physical object, object through an atmosphere, or through the vacuum of Outer space, space, without contacting any planetary surface. This can be achieved by generating aerodynamic lift ass ...

, issue=23 July 1970 , page=117 , url= http://www.flightglobal.com/pdfarchive/view/1970/1970%20-%201361.html {{cite magazine , title=Private flight- Hirth Acrostar., magazine=

, issue=21 March 1974 , page=369 , url= http://www.flightglobal.com/pdfarchive/view/1974/1974%20-%200427.html {{cite magazine , title= European aerobatics, magazine=

, issue=22 July 1971 , page=119 , url= http://www.flightglobal.com/pdfarchive/view/1971/1971%20-%201279.html {{cite magazine , title= Aerobatic Salon., magazine=

, issue=17 August 1972 , page=237 , url= http://www.flightglobal.com/pdfarchive/view/1972/1972%20-%202104.html 1970s German sport aircraft Aerobatic aircraft Low-wing aircraft Single-engined tractor aircraft Aircraft first flown in 1970