Flight test: Ultralight Concept SV4-RS
PUBLISHED: 17:01 22 October 2018 | UPDATED: 17:01 22 October 2018
Proving very popular on the Continent, the ultralight Belgian-built SV4-RS imitates the original Stampe but is not (officially) aerobatic | Words Stefan Degraef - Photos Edwin Borremans
After WWII, the Belgian-designed but French-built sleek Stampe-Vertongen SV.4C open-cockpit biplane was used extensively by the French armed forces as a training aircraft.
Built under licence by SNCAN (Société Nationale de Constructions Aéronautiques du Nord) and the Algeria-based Atelier Industriel de l’Aéronautique d’Alger, some 940 aircraft saw operational service within the elementary flying schools of the French Armée de l’Air (Air Force), Aéronavale (Navy) and ALAT−Aviation Légère de l’Armée de Terre, based in North Africa. Similar to the pre-WWII A-variants, C-models were equipped with a 140hp Renault 4-P engine.
The Service de la Formation Aéronautique de la Direction Générale de l’Aviation Civile (Civil Aviation Directorate) also used SV.4s in their various training centres all over France (Centres Nationaux de Vol à Moteur) for initial aerobatics and instructor training.
The Stampe’s excellent flying and simple maintenance characteristics inspired the French Service de l’Aviation Légère et Sportive (Light and Sport Aviation Directorate) to offer the ubiquitous SV.4C to aeroclubs at bargain prices.
Its future as France’s dedicated civilian pilot training aircraft seemed settled well into the future... except for the unfortunate fact that the unstoppable quest for both technical and performance improvements, and the availability of more advanced and better-equipped general aviation and training aircraft, quickly made the old biplane obsolete for training purposes.
Luckily, a renewed interest in vintage aircraft and nostalgic compass-and-stopwatch flying in France and across Western Europe made the then low-priced SV.4 variants a sought-after and desirable collector’s item for a new generation of private and professional pilots.
Today, the SV.4 is well-known on the European vintage aircraft scene, with a large number of aircraft still flying. Dedicated Stampe events for owners in Belgium and France are well attended, and aircraft go to a multitude of local fly-ins, generating keen interest from fans and other owners alike.
The increasing popularity and cost of these old biplanes (similar to DH Tiger Moth and Bücker Jungmann aircraft) have put them out of reach financially of the ‘average’ pilot and for training, in terms of operating and maintenance expense. Today’s recreational pilots are increasingly looking for more cost effective alternatives in the form of modern and well-equipped micro- and ultralight aircraft, which are becoming more prevalent in Europe’s skies.
Since micro/ultralight aircraft came along in the eighties, dependent on and complying with the various national regulations, a plethora of companies have developed, offering a wide array of modern, well-equipped and ergonomic aircraft at budget-friendly and competitive prices (compared with standard aircraft).
In recent years the renewed desire for vintage-like but much cheaper ultralight aircraft has generated various start-up companies on a mission to develop ‘as close as possible’ replicas of the ‘old masters’. One of these niche market ultralight companies is Belgium-based Ultralight Concept, offering the eye-catching SV4-RS ultralight, based on the orginal SV.4C trainer.
Designed by a pilot
The Ultralight Concept aviation company and its SV4-RS ultralight biplane are the brainchild of Raoul Severin, a former Belgian Army Aviation and Air Force helicopter and fixed-wing pilot. At the end of his active army career he created his own metal distribution company, also specialising in aviation materials.
Raoul Severin’s first step into the world of ultralight aviation was the construction of a Platzer Kiebitz biplane, based on and using the plans bought from Michael Platzer. Distributing welded steel tubing, usable for Kiebitz and other amateur-build aircraft, he quickly became familiar with the needs and desires of a large number of (mostly German) ULM aficionados.
Once proficient at relatively easy self-build aircraft, some members of that self-builder community were moving on to more realistic replicas of existing vintage aircraft.
Sensing business opportunities, having good contacts within the German and French amateur building scene, and−above all−being willing to design and fly his own vintage-style ultralight, Raoul started to conceive his own ULM (french microlight) design. In order to achieve his business plan and objectives, he had to choose as a basis for this brainchild an easy-to-build, sleek and eye-catching aeroplane that would be popular in Germany and France. These neighbouring countries, within driving distance of his eastern-Belgium homebase, had witnessed an increase in homebuilding activity.
Meeting all prevailing microlight/ULM legislation and regulation would hugely boost the aircraft’s home-build appeal, making it more easily saleable and marketable in other (more remote) countries. The decision to use the Belgian-designed vintage SV.4C biplane trainer as the model of choice was straightforward since a large number of original SV-4 models were and are still flying all over Europe.
Original drawings used
The ambitious SV4-RS project started in 2007 with the purchase of CD-ROM-stored original manufacturing drawings of the SNCAN SV.4C variant from the Espace Air Passion museum. Based at Angers-Loire airport in western France, this museum houses one of France’s most important collections of aircraft manuals and technical archives of unequalled importance within France’s vintage aviation community.
Gradually deciphering and confirming in detail all dimensions (overall length, wingspan etc) of the original
SV.4, Raoul quickly concluded that the widely available pre-welded aluminium tubes in his possession, used for Kiebitz biplanes, were of limited use for this. Since all Kiebitz-like tubes have a standard length of five metres and the original SV.4C measures 5.15 metres, the only way to build and market a 100% ultralight-replica was to acquire new metal tubes and consign the undersized ones to the dustbin.
Convinced a 97% scale replica would deter future customers and home-builders from buying the kits, the decision was quickly taken to focus on a 100% replica and be the first to offer this type of ultralight in a growing leisure aviation segment.
Since Raoul was still working part-time as a military helicopter and HEMS pilot, assigned to the Centre de Secours Médicalisé de Bra-sur-Lienne HEMS-organisation based at Bra in Belgium’s eastern Ardennes-region, the development of the SV4-RS proceeded slowly.
In 2013 he constructed the fuselage, ailerons and tailplane for his prototype. Soon afterwards he was contacted by FH Aachen (Fachhofschule Aachen) to allow students following the University’s Luft-und Raumfahrttechnik - Vertiefungsrichtung Flugzeugbau (Aerospace) syllabus to use various technical aspects of the SV4-RS as a subject for their master-degree graduation paper.
The technical input of these young motivated engineering students boosted the development process. The various aircraft components were designed by these students, calculating in advance all technical and structural characteristics and limits in anticipation of future official validation.
Finally, in 2015, a bare, engine-less SV4-RS with wings, fuselage, ailerons and undercarriage was exhibited at AERO-Friedrichshafen (Germany) and Festival International de l’Aviation Ultra Légère in Blois (France). In the aftermath of these well-known ULM events, ten SV4-RS kits were sold at competitive launch prices to kick-start the official SV4-RS and gain international exposure within the microlight sphere. AERO2016 saw the presence of a non-flyable but complete Rotax 912-engined aircraft.
First flight and certification
Once all necessary ground tests had been successfully conducted, the SV4-RS prototype made its maiden flight on 28 December 2016 at Büllingen airfield (EBBN), close to the Belgo-German border. Its first flight successfully completed, Raoul and his team quickly initiated the vital process of gaining the relevant official aircraft certificates in the markets of interest (Belgium, France, and Germany).
The first target was German certification of the SV4-RS, powered by the Rotax 912. Since this country’s regulations, tests and verification were the most elaborate in number and detail, achieving this in Germany first would enable Ultralight Concept both to evaluate its own design and development skills in depth and also to use the German certification as the basis for a similar process in other countries.
Starting in February 2017 some sixty structural tests were executed−and validated by the inspectors−on the airframe and its various components (wing, ailerons, seats, sticks, harnesses, undercarriage etc). To pass German microlight weight limitations the SV4-RS could not exceed 297.5kg with a 472.5kg maximum takeoff weight. For the structural tests, two complete spare fuselages and wings were manufactured and tested to their limits. Initially planned to be +4/-2g-capable, the aircraft limits were increased to +6/-3g.
Every three to four weeks German inspectors travelled to Ultralight Concept’s homebase to check a prepared list of aircraft components. To complete the ground certification tests, various test-flights were flown by Raoul and a German university student, recorded and monitored by GoPro cameras to certify onboard instruments (e.g. airspeed indicators) and flying characteristics (stall-test). An inspector would re-confirm these results during two test flights of the aircraft during the various testing profiles, assisted when needed by Raoul Severin, flying ‘P2’ in the front-cockpit.
During Aero2017 Ultralight Concept’s SV4-RS replica received its German permit to fly, conditional on completing a minimum of fifty hours’ overall flying time and successfully passing a noise test. Simultaneously, the process of obtaining Belgian and French type certifications was initiated, and the official permits for each were received in November 2017.
Pros and cons of operating an original Stampe
The French-built Stampe I owned for around a dozen years was one of very few aircraft that could operate safely from my 300-yard hillside airstrip (it could make very short takeoffs and landings). It could compete − and win – at Intermediate-level aerobatics, so, for instance, was able to fly rolling circles, negative spins, and a quarter-vertical roll and fly-off. It was a superb airshow performer too. It was rather slow in cruise (around 80mph) but very comfortable and relaxing on long journeys.
Perhaps its biggest plus was that it was a genuine ‘classic’ at a reasonably affordable price; it turned heads wherever I flew it.
Also, I enjoyed (most of the time) working on it, and my word, did it need a lot of work to keep it flying. The Renault engine was always needing a cylinder stripped for a valve to be re-seated The carburettor and magnetos required regular attention, and the engine couldn’t be expected to fly more than around 300 hours without a bottom-end overhaul.
The airframe suffered from oil getting into the wood, fittings going rusty and looseness in anything that could work itself loose – such as every part of the undercarriage. Nothing was easy or straightforward to work on and it was all very labour-intensive, although fairly basic in terms of know-how. The Annuals on its C of A included a great many arduous Airworthiness Directives.
Today Stampes are Permit aeroplanes under the LAA, and the amount of work that needs to be done on individual aircraft will depend on your Inspector. Spare parts were near-impossible to come by. These days, under the LAA system you can at least get someone to make them − but it will be expensive.
Expect to pay at least £60,000 for an original Stampe in reasonable nick, and I’d advise a budget of £20,000 a year for running costs unless you’re into DIY and have the skills. The purchase price has not kept up with inflation, largely because the cost of getting someone to work on old aeroplanes has escalated − it’s the ‘White Elephant’ syndrome.
If you have a sympathetic LAA Inspector and a ‘nice old boy’ (yourself?) who does the work as much for love as for money, you’ll have a good, practical classic. If you don’t have these advantages, you had better have a deep pocket.
Finally, although largely viceless by the standards of its day, the Stampe does require skill to fly it safely. It’s one of those aeroplanes that kill clumsy pilots. − Nick Bloom
Factory- or kit-build
In order to market its SV4-RS successfully as the only ‘full-scale vintage biplane’ replica on the market, Ultralight Concept (UC) can supply the aircraft as a factory-built item or as one of three kit options for customers to choose from.
Kit 1 is for those fully able to build the microlight on their own, including all building drawings, documentation and materials. It is supplemented by two four-day workshops at UC’s hangar, during which clients will be helped to build their own fuselage, four individual wings, wingspars and ailerons.
Clients must prepare for the workshops by building various components at their home base before heading to Kelmis for assistance and instruction if needed. A UC staff member will still need to inspect the bare frame before applying the fabric and, once fully assembled and ground-tested, the maiden flight will also be flown by a UC representative.
The more elaborate Kit 2 option includes everything in Kit 1, but comes with wings and fuselage ready built.
The more-encompassing Kit 3 version delivers a finished but uncovered aircraft structure, leaving the owner/customer installing his own engine (generally a Rotax 912), avionics and instrument-wiring. Whichever kit option is chosen by the customer, all halfway-inspections must be performed and the maiden flight flown by a Ultralight Concept staff member.
Depending on the previous taildragger experience of the client, a short type-conversion instruction flight can be given by Ultralight Concept to demonstrate the various flying and landing characteristics of the SV4-RS. The aircraft has proved popular.
By mid-2017 fifty-two SV4-RS kits had been sold to clients in Belgium, Germany, France, Poland, Czech Republic and Lithuania. The future SV4-RS pilot and active builder is typically in their early/mid-sixties. With the planned build likely to take around 1,000 man hours (depending on the kit selected), the first customer-built SV4-RS may well take to the air in 2019. Future modifications or options include an ‘SV-4B’ model with closed canopy, and a glider towing connection underneath the aircraft. In future, two additional engines will be certified for the SV4-RS.
Aerobatics a grey area
So what about aerobatics, for which Stampe aircraft are well known, and many have been used as mounts for aerobatic championship competitions? The aircraft is capable of aerobatics, but the engine isn’t cleared for them and, in any event, ultralights are not authorised to perform aerobatic flights.
Only in France is there a grey area where aerobatics in an ultralight are not forbidden. However, if customers register the aircraft as ‘Experimental’, then aerobatics are authorised…
The current (and increasing) cost of PPL and GA flying, and new more stringent national regulations (especially medical requirements), may well see a shift by current and future ‘weekend flyers’ to the microlight segment.
Time will tell if the Ultralight Concept offering of a 100% scale vintage aircraft replica, aimed at ‘young pensioners with a budget and some ability’, will be an overall success in this market. However, the sales to date of fifty-seven SV4-RS may well hint at that ultimate answer.