Čáslav Open Day, 2017

May 20, 2017 saw me take a trip to Čáslav air base in the central part of the Czech Republic to partake in the biannual open day there. The weather was overcast all day, but thankfully the rain in the forecast stayed away.

I have to say that I came away with some mixed feelings about the 2017 edition of the event. The static display areas were much larger than in previous years, but I’m not sure the best use of the available space was made to best accomodate both those who were looking at the statics and those watching the dynamic show. Many of the static aircraft were placed between the crowd and the dynamic showline. As such, I had trouble getting close to some static aircraft because of people watching the dynamic show from in front of static display areas.

The increased size of the event also led to and increased size of crowd. The result of that was the special train running from the Čáslav rail station to the air base was inadequate for moving the volume of people going there and back in a timely manner.

Hopefully, these matters will be better handled at the next open day.

That said, here’s a small sampling of what was available to be seen on the day:

The 2017 open day included the public debut of an Aero L-159 ALCA in a special scheme reflecting a Supermarine Spitfire Vb flown by František Peřina (1911-2006) who flew in both the French air force and RAF during WWII and was a patron of 212 Squadron, the unit operating the L-159, later in his life.
The flying show started off with a Piper Cub which did very well for itself in the face of some strong winds early on in the show.
Another early performer on the day was this Tiger Moth.
A Čáslav based Saab Gripen after a spirited performance.
A look along a section of the static display that included fast jets from France, Germany, Poland and the Czech Republic.
Another look at the French Alpha Jet.
Soon to be gone from Czech skies, one of two Yakovlev Yak-40 transports the Czech air force keeps on charge was in attendance. A replacement for the two aircraft is in the works.
A Panavia Tornado ECR in from Germany.
A usual visitor to the Čáslav open day event is the Belgian air force F-16 solo display. As usual, they did not disapoint.
Ground crew tend to the Belgian F-16 following the display.
Another Belgian participant this year was the Agusta A-109 display.
The Patrouille Suisse team brough six jets, though opted for a four plane performance. I’ve seen them perform with more jets and can say their four jet show is no less impressive.

Book Review: “Ol’ Shakey”

Ol’ Shakey: Memories of a Flight Engineer
By: Byron Gene Fish
Outskirts Press (2013)

Through the 1950s and 1960s, the distinctive looking Douglas C-124 Globemaster II was the primary heavy lift aircraft of the U.S. Air Force. It was a bulky, hulking aircraft that was difficult to mistake for anything else on a flightline of the period.

It was also a very distinctive aircraft from a standpoint of operating it and had a habit of keeping crew members, particularly flight engineers, alert and busy with a myriad of mechanical idiosynchrasies.

This book gives one a very good overview of the training involved to become a flight engineer on “Ol’ Shakey” as the C-124 was nicknamed in service. It also examines how crews had to have complete trust in each other to operate the aircraft effectively and what could happen if that trust was compromised.

The book also details a range of scenarios that were typical  when working with the aircraft, such as crawling through a maintenance tunnel that ran through the wings in order to examine and service the engines in flight.

Beyond the aircraft itself, the book also gives the reader an idea of what the crews experienced at the various spots around the world they flew the aircraft into. It also gives one a feel for what the inter-service and inter-unit politics and rivalries of the time could be like.

Most of what is in this book are solid flying stories, though there are a few stories of off duty clowning about to add comic relief to the mix.

As it deals with the transport mission, it’s not the most exciting book you’ll find. Nonetheless, it is an accessible and informative read from a very qualified voice on the subject.

The author, Byron Gene Fish, spent the bulk of his professional life in aviation with many of those years spent at the flight engineer station of the C-124 aircraft.

This link will take you to the book’s profile on the publisher’s website:


Beneš-Mráz Be-50 Beta Minor – A Favourable First

Beneš-Mráz: Short Lived, but Successful 

Be-50 Beta Minor seen at Pardubice, Czech Republic in 2016.

The name Beneš-Mráz may not be well known outside the Czech lands, the company only existed from 1935 to 1939. However, in that short window of time, the company produced no fewer than 14 aircraft designs for the civil market.

The company was founded by accomplished aviation engineer Pavel Beneš and businessman Jaroslav Mráz. Previous to partnering with Mráz, Beneš had founded the famous Avia company in 1919 with fellow engineer Miroslav Hajn.  Beneš also spent time working in the aircraft division of the Praga company before partnering with Mráz in the mid 1930s and setting up a factory in Cocheň in the northern part of today’s Czech Republic. By 1939, Beneš had divested himself of his part of the company and it was renamed Mráz to reflect the change in ownership.

Through the German occupation of World War II, the rise and fall of Socialism and a number of name changes of the years; the legacy of Beneš-Mráz has carried on to today in the form of Orličan a.s., a sailplane manufacturer that continues to operate in their ancestral home of Cocheň.

The Be-50 Beta Minor: A Solid Start 

Beta Minor at Pardubice in 2016.

Summer of 1935 saw the first flight of the first aircraft type designed by the newly established Beneš-Mráz company, the Be-50 Beta Minor.

The Beta Minor was designed for touring, training and sport flying and proved an excellent start for the company. The aircraft was a very clean design with viceless handling qualities that made it popular with flying clubs of Czechoslovakia at the time.

With a large part of the airframe comprised of wood, the Beta Minor was, at 460 kilograms, a light yet sturdy aircraft. It was powered by a domestically designed and built Walter Minor four cylinder engine that could propel the aircraft to a very respectable top speed of 195 kilometers per hour. A combination of light weight and efficient design gave the Beta Minor a range of 750 kilometers without refueling. The aircraft gave a quite good account of itself at a number of distance based races in the late 1930s.

Outside of being very much a pilot’s plane, the Be-50 was also appreciated for mechanical reliability, ease of maintenance and very good short take off and landing performance. A total of 43 Be-50 aircraft were made in the original run by Beneš-Mráz and developed further via the Be-51 series in 1936.

The Be-51 was based on the Be-50, but featured a fully enclosed cockpit and a somewhat shortened wingspan; these modifications gave the Be-51 improved speed and aerobatic ability over the Be-50. The Be-50 shared the Beta Minor name with the Be-51.

In the Reich and the Resistance 

The clean lines of the Be-50 seen to good effect over Pardubice in 2016.

As with so many other domestically developed aircraft in Czechoslovakia, the existing Be-50 and Be-51 aircraft in the country were commandeered for Luftwaffe service with the 1939 arrival of German occupational forces.

The Luftwaffe made use of both Be-50 and Be-51 types for liason and training work.

Beta Minors also found their way into the service of the Independent State of Croatia and the Slovak State, two German friendly puppet states that existed during the Second World War. The aircraft were primarily used as trainers and couriers by both bodies.

A strong anti-Axis partisan resistance movement rose up in Yugoslavia through the Second World War and at least one Beta Minor aircraft was captured from Croatian hands by partisan forces late in the conflict.

Very few Beta Minors survived the war and those which did were destroyed soon after the end of hostilities.

The Be-50 Today and Further Reading 

The world’s sole Be-50 Beta Minor at Pardubice in 2016.

For many years, the world had no extant examples of the Beta Minor in any form.

Happily, the original plans of the Be-50 have survived to the present and through several years of careful work in the early 2000s, the Military Historic Institute of the Czech Republic (VHU) built a fully fresh Be-50 faithfully following the original plans. The aircraft was put on static display to the public in 2013 and flew for the first time in 2015. It’s currently active on the Czech civil register and makes appearances at shows around the country.

The aircraft has a few concessions made for modern aviation regualtions and was given construction number 44 to fit in with the original 43 made by Beneš-Mráz themselves so many years before. It is considered a true Be-50 rather than a replica in many quarters.

When it is not flying, it is usually kept on display at the Methodius Vlach Aviation Museum in Mladá Boleslav, north east of Prague in the Czech Republic.

The following links have all been through a translator function and their English is somewhat rough as a result. However, they do contain a good amount of information about the original Be-50 development as well as the new built example:




Beech Model 18 Revisited


Putting a New Shine to an Old Article

Those of you that have followed this blog for a while are likely aware that I’ve had an entry about the Beechcraft Model 18 for sometime. In fact, it may be one of my earliest entries.

Between last weekend and this one, I decided it was time to bring that article up to the standard of my more recent ones.

Revisions included editing and extension of text, refreshment of photographs and an extended section of links for further reading.

I’m much happier with the revised article and I hope you will be too.


Fiat G.91 – Gina go Lightly

Legendary Bloodlines 

Former Luftwaffe G.91 R/3 seen preserved at Berlin-Gatow in 2016.

Fiat Aviazione, the aircraft division of the legendary Fiat automobile company, was established in 1908 in Turin and was responsible for some of the Italian aircraft industry’s most famous aircraft from the early interwar period to the late 1960s when it left the airframe manufacturing busines to concentrate on aero engines.  Since 2013, though a series of mergers, acquisitions and rebrandings dating to the late 1960s, the legacy of Fiat Aviazione has lived on through in Avio S.p.A., a Turin based subsidiary of General Electric’s aviation arm.

The G.91 was part of a series of aircraft designed by the masterful Giuseppe Gabrielli (1903-1987) during his tenure with the company which lasted from 1931 to the end of their airframe design activities in the late 1960s. In the catalogue of Fiat aircraft, Gabrielli designed machines are easily recognised by the “G” prefix; this was in keeping with Fiat’s practice of using the designer’s initials as the prefix for the aircraft model number.

While the G.91 was designed to be a strightforward and simple aircraft, the story of it’s development and introduction to service is anything but. At that, Let’s spend some time with the Fiat G.91, or “Gina” as it was nicknamed by many who worked with it:

Defining the Light Fighter 

Former Luftwaffe G.91 T/3 trainer preserved at Berlin-Gatow in 2016.

Very early in the jet age, with the reality of nuclear conflict looming large in the background of rapidly increasing Cold War tensions, the nations of NATO were forced to reevaluate the shape and nature of how their air combat assets were deployed and maintained in continental Europe.

The Korean War had highlighted the need for greater air support of ground forces in modern combat and revealed some of the drawbacks of the increasingly complex nature of jet combat aircraft. One of the main drawbacks was that with increasing complexity came rising costs that sharply curtailed the number of aircraft that could be ordered to the point that they could not be purchased in high enough numbers to be deployed in battle effectively. Air bases were getting bigger to accomodate more complex aircraft support facilities, runways longer to support heavier aircraft and the distance between the air base and the front lines was increasing to the point where the aircraft would have very little time over their targets before having to return to base for fuel. Additionally, the larger size of fixed air bases made them very easy targets and impossible to conceal.

Consideration of those factors led NATO to issue a requirement in 1953 for a new light weight strike aircraft that could be deployed away from large bases and with minimal support facilities. The aircraft would also be able to be produced in large numbers cheaply and be seen as an expendable asset that could be used widely in NATO.

The specification for the new aircraft stipulated that it had to be operable from grass and straight stretches of road, take off in 1,100 metres, have a combat range of 280 kilometres that included 10 minutes time over a target, carry a fixed armament of four 12.7mm machine guns or two 20mm cannons in addition to 454 kg of unguided munitions under the wings, have a maximum speed of Mach 0.95 and a maximum empty weight of no more than 2,268 kg.

It was a high order for the time period and the state of jet combat aircraft technology of the time. However, thanks to work already done in Great Britain in the very early 1950s, it was not an impossible goal to attain. By 1952, work on what would become the Folland Gnat trainer was well underway and work on the Bristol Orpheus engine that would power it had begun in 1953. By late 1954, the Orpheus engine had been run for the first time.

The Orpheus would solve one of the biggest obstacles to the light fighter concept at the time, finding an engine which could deliver the required thrust and yet be light enough to keep the aircraft within the stipulated weight parameters. The Orpheus, like the aircraft it was designed to power, was of simple design and easy to service without specialised equipment.

Selection and Development

Another angle on the G.91 T/3 preserved at Berlin-Gatow in 2016.

By July of 1955, after nearly two years of selection, NATO announced their shortlist of the winning designs which would be approved for prototype development and final competition for the new light fighter. Fiat’s competition came in the form of the Dassault Étendard VI and Breguet Br.1001 Taon, both from France. Aside of the original specifications, NATO had also dictated that all three competing aircraft were to use the Orpheus engine as a power source.

The selection of the Orpheus was due in large part to America heavily funding the engine’s development through the US Mutual Weapons Development Programme. In fact, though British by design, relatively little British money funded the development of the engine.

The G.91 first flew in August of 1956, nearly a full calendar year before the first flight of either French design going against it. Despite this headstart, the initial G.91 prototype experienced some control and vibration problems and was lost in a crash in early 1957. After extensive investigation and reworking, a revised second prototype flew for the first time in July of 1957.

Third and fourth G.91 prototypes were sent to France, where the competition was being held in Autumn of 1957, and performed very well. NATO anounced the G.91 to be the winner of the competition in January of 1958.

While the G.91 had been successful in the competition for NATO’s new light fighter, political and financial factors as well as fading interest in the light fighter concept would conspire against it becoming a widely used aircraft. Initial users of the G.91 were to be France, Italy, Turkey and West Germany. America would provide partial funding for the French, German and Italian G.91 purchases and fully fund the Turkish order.

France, using the loss of the first G.91 prototype as an arguing point, disputed the outcome of the competition and opted to further develop the Dassault Étendard on their own rather than have anything to do with the Italian aircraft.

In 1961, evaluation samples of the G.91 were provided to Greece and Turkey as well as the U.S. Army and U.S. Air Force. In the end, none of them accepted the aircraft into service. After evaluation, Turkey cancelled their G.91 order and the aircraft that had already been built for them by that point were given to West Germany instead.

Interest in the G.91 was shown by Austria, Israel, Norway, South Africa and Switzerland. However orders from the European nations never materialized and the Italian government vetoed sales to Israel and South Africa for political reasons.

Ultimately, all Ginas built served only Italy, Portugal and West Germany.

The G.91 in Production and Service 

Former Luftwaffe G.91 R/3 preserved at Berlin-Gatow in 2016.

The G.91 enjoyed a 19 year production run and assembly lines existed for it in both Italy and West Germany. While production totals vary somewhat by source, most place the number of Ginas built between 750 and 770.

The G.91 had given NATO nearly 40 years of service when the last ones were retired from Italian service in 1995.

West Germany was the first G.91 user to retire their fleet of the aircraft, doing so in the early 1980s. Over the years, many former German Ginas and spare parts for them were purchased by Portugal. It was in Portuguese service that the G.91 would see combat; several of the aircraft were sent to Africa for close air support of ground troops in the Portuguese Colonial War which lasted from 1961 to 1974. Portugal continued to use the G.91 until 1993.

Five main operational variants of the G.91 were produced:

G.91 R/1
The R/1 was the first production version of the G.91 and differed outwardly from pre-production machines by having a redesigned nose capable of holding cameras for reconnaissance work. Changes to avionics and instruments created the R/1A subvariant while structural strengthening created the R/1B.

G.91 R/3
This was a variation for the Luftwaffe which was equiped with a pair of 30mm cannons as fixed armament.

G.91 R/4
Initially intended for Greece and Turkey, the R/4 fleet was transfered to the Luftwaffe and used for training until retirement in 1966. Several of this variant were sold to Portugal after their Luftwaffe days were over.

G.91 T/1
This was the two seat training variant used by the Italian air force.

G.91 T/3
The T/3 was the Luftwaffe training variant. Several found their way into Portuguese service.

G.91 PAN
While not a major operational version, the PAN is worthy of note being as how it was a long time mount of the Italian air force air demonstartion team, Frecce Tricolori.

I have not included the later two engine G.91Y in the above list as it is only a G.91 in the most nominal of senses. Beyond a passing resemblance and a designation that suggests it being a member of the G.91 family, the G.91Y was a completely different aircraft nose to tail that didn’t have a single component in common with the single seat G.91 line.

The Gina Today and Further Reading

Many examples of the G.91 survive in museums across Europe and further afield, so getting a close look at one today is not an overly difficult task depending on your geographic location.

At the time of writing, March of 2017, I could find no evidence that there ever has been a G.91 restored to airworthy status on any civil register. However, I was able to find some small bits of information regarding a long term project in Germany to restore a T/3 to flying status. While I could find no information on that project more recent than 2015, the information I could find included photos of the disassembled aircraft components in a  hangar and seemingly well cared for.

Time will tell if the world will see the G.91 fly again.

The following two links will give you some insight into the early development of the G.91:



These two links will give you similar insights into the Bristol Orpheus engine:



These links will give you some information on the Gina’s French competition:



This link will show you some pictures of a G.91 PAN preserved in America


František Truhlář – A story Worth Telling

A documentary about a very brave young man who fought for his country and was then rejected by the very same people he fought for. Video biography of F/Lt František Truhlář who was to suffer sever burns in two separate aircraft crashes during WW2. The first when he was an air-gunner with 311 Sqn when […]

via F/Lt František Truhlář suffered severe burns during WW2. — Aviation Trails

Bolkow Bo 105 – The Teutonic Twister

A Pioneer of Pedigree 

Red Bull’s Bo 105 performing at Pardubice, Czech Republic in 2016.

By the late 1960s, the helicopter had proven itself as a credible technology worthy of developing. The Korean War of the early 1950s and the Vietnam War that was raging at the time had proven beyond a doubt the helicopter’s value to military operations. In the same period of time, the civil sector was also warming up to the benefits of rotary flight.

The Bolkow Bo 105, which flew for the first time in 1967, was a major revolution in helicopter development that has had far reaching influence on helicopter design through the years. It is fitting that such a revolutionary machine should come from the company founded by the decorated and visionary Ludwig Bolkow.

Ludwig Bolkow (1912-2003) was born into aviation. His father was a forman in the Fokker aircraft company. Ludwig himself began his career in aviation working for the Heinkel aircraft company before studying aero-engineering in Berlin. Upon his graduation in 1939, he was hired by Messerschmitt and was heavily involved in development of the Bf-109 fighter and the Me-262 jet fighter.

He created his own company in 1948 and built it into one of the largest and most respected aviation companies in post WWII Germany. He is celebrated not only as a key architect in the reconstruction of the German aircraft industry, but also as a father figure to today’s Airbus Group; Bolkow’s company was one of the cornerstones that the Airbus Group was built upon.

Bolkow was not only visionary from an aviation point of view; he was a proponent of alternative fuels and spent much of his later life researching hydrogen and solar based energy sources. Additionally, he was also revolutionary as an employer through active mentoring of his employees, company pension schemes and flexible working hours. All of those things were quite radical ideas at the time he offered them to his workers.

Advancing the Blade 

Bo 105 of the German army at Ostrava, Czech Republic in 2015.

MBB, the company created by a merger of Bolkow with Messerschmitt in 1968 and a further merger with the aircraft division of Blohm + Voss in 1969, is credited with creating the Bo 105. However, the aircraft’s design was cemented and the first flight taken prior to the merger. The Bo 105 was concieved and born in the Bolkow stables.

The Bo 105 was the world’s first light helicopter to be powered by two turbine engines. This not only gave the aircraft impressive power and performance for the class, but also increased reliability and safety.

More significantly, through the Bo 105, Bolkow introduced the rigid rotor system to the aviation world. The rigid, or hingeless, rotor system was designed around a solid titanium main rotor head that was connected to rotor blades made of composite materials that were lighter, stronger and more flexible than metal ones of the day. The rigid rotor design did away with the hinges that connected the rotor blades to the rotor head in traditional fully articulated rotor systems and used the increased flexibility of the composite rotor blades to do the job the hinges normally would do.

Savings in weight, materials and maintenance were all benefits of the rigid rotor system. The greatest benefit of the new rotor system, however, was in giving the helicopter an unprecedented level of agility and maneuverability. It was through the higher flexibility and torsional strength of the composite rotors that the Bo 105 was given it’s legendary acrobatic abilities. The Bo 105 became famous for loops, rolls and other aerobatics that previously had not been in the abilities of helicopters.

As the Bo 105 was a fully new design, great care was taken in developing it. The fuselage, main rotor and twin engine arrangement were all tested separately before being brought together.

The first prototype, designed to test the fuselage, was fitted with American engines and a main rotor of a Westland Wasp helicopter from Great Britain. Meanwhile, the rigid rotor system was first tested on a French built Sud Aviation Alouette II.

A total of six prototype aircraft were built and the Bo 105 was put into production in 1970.

Building a Legend 

German army Bo 105 seen at Ostrava in 2014.

The Bo 105 saw three decades of production before the last one was built in 2001. Nearly 1500 of the type were built on assembly lines in Canada, Germany, Indonesia, the Philippines and Spain.

The Bo 105 was originally intended primarily for the civil sector. However, through it’s agility and high rate of climb, it did attract the attention of military buyers soon after it debuted. Covering a range of 25 different variants, the Bo 105 has found much popularity with civilian and military users alike in it’s life.

Perhaps the most recognisable role for the Bo 105 to the casual observer is that of air ambulance, a vocation it excelled at for many years worldwide until was succeded by newer designs.

In civilian circles, it also has found much use in police work, film and television as well as corporate transport to name a few.

In military use, the type has been employed successfully in both inland and off-shore applications that have included training, anti-tank work, infantry support, maritime reconnaissance and border patrol.

The biggest user of the Bo 105 was the German army, who retired the type in 2016. At the height of the Cold War, the former West Germany used a variant of the aircraft called the PAH-1 as an anti-tank platform. The machine’s speed and agility, particularly below treetop level, in addition to it’s small size made the Bo 105 well suited to that role.

Progeny of a Pioneer 

The Eurocopter EC-135 is one of the Bo 105’s direct descendants. This one was seen at Ostrava in 2013.

As one would expect of a successful design, the Bo 105 was developed and became the parent of a family of light utility helicopters that inherited the rigid rotor system and admirable handling qualities of their progenitor.

However, due to a number of mergers and rebrandings in the European aerospace industry over the years it is not always easy to identify by name which helicopters have the Bo 105 in their ancestry.

MBB existed as an independent company until it was purchased in 1989 by another Germany company, DASA. By 2000, after several name changes and reorganisations, DASA was merged with Aérospatiale-Matra of France and CASA of Spain to create EADS, European Aeronautics Defense and Space. EADS eventually restructured as the Eurocopter Group and became Airbus Helicopters in 2014.

While the Airbus Group currently claims the legacy of the Bo 105 and descendant designs, the family ties can be sorted with a bit of work. Here’s a general overview of the Bo 105’s progeny:

MBB/Kawasaki BK 117 / EurocopterEC 145 / UH-72 Lakota / Airbus H 145

The first major development of the Bo 105 was the BK 117, a joint project between MBB and Kawasaki of Japan. The two companies had been working independently on light utility helicopter designs before making a deal to create a single design together.

MBB took responsibility for the rotor, tail, flight controls and hydraulics while Kawasaki tended to the landing gear, fuselage and transmission among other things. The Prototype first flew in 1979 and production began in 1982. BK 117 production ceased in 2004.

During the time the BK 117 was in production, the European share of the project came under the jurisdiction of Eurocopter in 1992. This change did not affect partnership with Kawasaki. In 1999, after a number of  of upgrades to the BK 117 were made, the Eurocopter EC 145 was introduced. The EC 145 was the basis of the UH-72 Lakota, the winner of the US Army’s light utility helicopter contract in 2006 to replace outdated Bell UH-1 and OH-58 helicopters. Another military variant was known as the EC 645.

After rebranding as Airbus Helicopters in 2014, the EC 145  and  EC 645 were redesignated as the H 145 and H 145M respectively.

MBB Bo 108 / Eurocopter EC 135 / Airbus H 135 

EC 135s in ambulance configuration seen at Ostrava in 2013

MBB started working on a refined version of the Bo 105 called the Bo 108 during the 1970s, much of that work focussed on streamlining at aircraft’s fuselage and improving controls. Development of the Bo 108 was a protracted matter that saw Aérospatiale of France becoming involved. The first of two prototype Bo 108 aircraft flew for the first time in 1988.

Initially the Bo 108 was only intended as a technology demonstrator, but developments of the aircraft through the 1990s were encouraging enough that production certification was pursued. By that point, Eurocopter had been formed and the Bo 108 was redesignated as the EC 135. A military version was developed and designated the EC 635.

In 2014 Airbus renamed the EC 135 and EC 635 the H 135 and H 135M respectively.

The Bo 105 Today and Learning More 

This TV camera equiped Bo 105 was seen at Zeltweg, Austria in 2013.

The Bo 105 is far from retired and remains a very active flyer. As of 2014, approximately 700 of the type were known to still be flying in both military and civil forms.

With technical support networks for it still firmly in place and a demand for it’s qualities still present, the Bo 105 isn’t likely to be leaving the skies any time soon and your chances of seeing one are good depending on your location.

The following links will provide you with a good deal more information on the Bo 105, it’s history, development and those behind it’s success:

This article from 1967 will give you a good idea of how the aircraft was viewed while still a prototype:

This timeline on Airbus Helicopters’ website will show you where the Bo 105 fits in their history:

This article covers German army flight training with the Bo 105 in:

This article gives a good description of the difference between rigid and fully articulated rotor systems:

This obituary will tell you a good deal about Ludwig Bolkow: