A long time ago gliders for RC-flight were RC-assisted gliders – free flight inspired gliders equipped with electronic to make it look like you had control of the gliders flight. The aerodynamic layout was not made for active thermal searching but for longest flights in dead air conditions. As people began exploring slope flight, the need arose for models that could fly in higher wind speeds. Richard Eppler approached his computer. In the words written in Aeromodeller in 1965 he says: “You’ve got to get hold of a computer and carefully calculate pressure and velocity distributions, if you want airfoil sections which are properly matched to their specific working conditions”. With these words he started to define the needs (= working conditions) for flat field thermal flight, slope flight and very fast slope flight and aerobatic flight. In his words a thermal soarer needed an airfoil that permits the model to have a “low sinking speed when circling slow in thermals yet enables the model to fly at high speed and very small gliding angles with very high L/D ratio (= flat gliding angle) in straight flight.” Remember that this is Richard Epplers pre-1965 words! Would you define the airfoil needs for a thermal soarer different today? The airfoil to full fill Epplers needs in the mid-sixties was Eppler 385. For slope soaring low sinking speed wasn’t important back then, and the resulting Eppler 387 was a 50% improvement over the Gö 796. None of them were though suited for aerobatics. For this purpose and for very fast slope flights he made the Eppler 374 that was superior to the Gö 795 in slow flights and equal to it in fast flights. These airfoils were used but I think that their popularity was held back due to the thin trailing edges of the E 385 and E 387. If my memory serves me right the E 387 was on Multiplex’s Alpha. The E 374 was used widely on slope gliders of the 70’ties in Scandinavia. A special Norwegian/Danish modification of the Graupner Cirrus won numerous Nordic championships in thermal (pre-F3B) and slope competitions (pre-F3F?) in the mid and late seventies with the airfoil E 374 and ailerons in the hands of among others Preben Noerholm (known from F3F and Viking races).

  This is the picture and the drawing from the danish mag. "RC-information" where Preben Noerholm published the information about this modification of Graupners Cirrus which originally had an airfoil like the Aquilla.

E 374 was also the airfoil in Stuart Blanchards Calypso 6 from around 1985 where he used it with good success at the WC in F3B in Australia. Although Eppler gave us these airfoils more than 35 years ago the news spread slowly or maybe the pilots were conservative? 25 to 30 years ago the most well known and used airfoil for normal gliders were still Aquila or airfoils that looked like it i.e. common flat bottom from leading to trailing edge with a curved top, together with the same airfoils as those used by free flight pilots (can you be piloting a free flight model?). The free flight airfoils were highly under cambered airfoils without many thoughts of penetration. For a long time the flat-bottomed Aquila airfoil was a winners airfoil in radio control thermal competitions because compared to the free flight sections it had penetration ability – this statement is of course only true when compared to the under-cambered free flight airfoils.

It's me in the center with a Blue Phoenix. The two others are fellow pilots with Risers from SIG. All three gliders have an airfoils of the Aquilla type.

 Remember the Cumulus and the Cirrus from Graupner, which won numerous trophies with their pilots? These planes airfoils were also of the “flat bottom and curved top” - family. When ballasted they could penetrate. If you build heavy or pour in some lead, any plane will be able to fly pretty fast. The Cirrus was introduced in 1969. A flat bottom airfoil was also the basis for the Aquilla Grande from Airtronics (hence the airfoil name), with which Skip Miller won the very first F3B World Championship in 1977. Skip did though modify the leading edge on his version; he raised the entry point and thereby lowered the effective camber. These flat-bottomed airfoils were the best we thought we had back then, but slowly as we got more experienced in thermal seeking we began thinking about aerodynamic efficiency and better airfoils. As Dave Thornburg put it in his construction article of Bird of Time in January issue of MAN 1979 “We have lift to burn” with which he meant that we had to use thinner airfoils with less camber to produce less lift to be able to fly faster and search larger areas for thermals to gain more flight time. A moment ago I said,  “the best WE had…” because I sometimes have an Einsinish look at pilots and unite all model glider pilots in history as one group through time – time is relative. This can of course not be true (well, maybe for DS and turbine jet pilots flying close to the speed of light). I, for one thing, was really not part of this evolution since I was born the same year as peace, love and understanding became a big hit among our parents, and I was mostly into “Indians and cowboy” - games when Skip Miller became F3B world Champion in 1977 – (does children play “ US Marines and Taleban militia” today?). These airfoils were the best THEY thought they had back then. In the middle of the seventies Richard Eppler came up with the E 193, which ruled the skies around 1980. Just try to remember the AME team from Austria who developed the Dassel in the late 70’ties. It actually started out as an aerodynamic thought in a book, about a glider with a constant chord wing and 2-metre span. Made by the best materials available, it soon became the weapon of goods. This high-tech glider made in moulds had the E 193 in the wings, and the same airfoil was spotted on the Multiplex Flamingo from 1978. The Flamingo had a larger span (around 2,5 meters) and a double taper wing form instead of the constant chord wing of the Dassel. The Flamingo had a glass fuse, a fully balsa sheeted wing with balsa ribs and a spruce spar, it had ailerons and brakes and it was a plane everybody could build and it was pretty good for the rather new glider class – F3B (1980). Also Sean Banisters Algebra for F3B had the E 193 in its swept back wings. The Dassel and the Flamingo had pointed noses introduced and famed by the AMA team. A lot of people thought that it was a fast fuse (=less drag) and therefore copied it. Very few are aware that the reason for the pointed nose of the Dassel was that the AMA team often flew in the alps were the snow lies all year and the pointed nose made it easier to land! Remember the “E 193”-story when you get to the “Clark Y”-part. At the beginning of the eighties Eppler brought us the airfoil to follow – the E 205 which is still used today on many designs.

This is the Optima that Simprop kitted from Ralph Deckers original F3B glider from around 1980. It wasmy first REAL glider and it taught me a lot.

It wasn’t just because the name was Eppler. Another reason for the popularity of the E 205 was that the underside is flat from 30% behind the leading edge and backwards. This makes the E 205 very easy to build since your average DIY-store doesn’t sell building boards with a RG 15 or SD 7037 bottom surface curl in the surface. Unfortunately the performance gain from the E 205 over E 193, was not as great as was achievable with the other airfoils made at the same time by then infamous airfoil designers – guess who they are? In the eighties the biggest development in F3B was the change from build up models to foam/glass models and further on to the composite moulded-in-negative-moulds models in glass, carbon and kevlar reinforced epoxy. At the same time the airfoils changed, from Aquila/Eppler to HQ and RG 15 on the majority of designs. If you are still wondering about the funny abbreviations: HQ is short for Helmuth Quabeck from Germany and RG for Rolf Girsberg from Schwitzerland). These were the “new” airfoil designers – then mostly unknown, but do their names ring a bell for you today? Today most glider guiders have heard of “RG 15” as a magic word, and in places all over the world people bow in respect when the name “Helmuth Quabeck” is mentioned. Helmuth Quabeck is also the designer of Graupners Soarmaster and Soaring Star. Especially the RG 15 gained great popularity on anything from state of the art F3B machines to standard slope soares and slope pylon models. From mid-eighties to mid nineties it was the airfoil to choose if you had any doubt, and still today it is a good one. In Denmark we had two new national F3B speed records in one day in the autumn 2000. The first was Jesper Jensen. The second and fastest was Brian Dylmann who flew the course in 14.42 seconds with an Ellipse 2. There must be a few out there who have flown at F3B speed times close to this with an RG 15 equipped glider. The Ellipse 2 F3B/F3F glider design from Jaro Müller first saw light in 1991-92 with an airfoil designed about 10 years before! The world record today (Christmas 2001) is held by the four-times-in-a-row F3B world champion Daryl Perkins (1995, 1997, 1999, 2001), with a run of 14.07 with a Cobra in South Africa in 1999. The Cobra was designed in 1997 with MH 32 and is equally good in F3B as F3J. I’ll get back to this airfoil later. By the way: We had a new Danish record on the 9^th of September 2001 – Jesper Jensen flew 14.00 (fourteen flat) with a Cobra – MH 32. A few months earlier in 2001 this was also the airfoil on the Eraser flown by Lubos Pazderka to win the European F3J Championship in Slovakia. In which box do we put this airfoil – is it suited for fast flight or is it a duration airfoil? In part 3 you’ll hear Reinhard Kaufmann say: “We are getting closer to the optimal airfoil”.

Back to class: Rolf Girsbergs famous creation: The RG 15 can be and has been modified to suit a variety of different tasks, you can modify the camber from 1,5 to 3,0% without problems and at the same time you can change the thickness from 7 to 13%. RG 15 is also the airfoil that has been modified (how?) to take place in the wings of the Pike in all its first versions (=Pike, Pike Plus, Pike WR). In the mid and late eighties it was though still Epplers airfoils that were widely used on plain thermal soares for general flat field soaring over Open class soarers to electric gliders of any kind. In mid-eighties Michael Selig sat on his side of the pond and wondered about what really happened around glider wings at the chords and airspeeds we fly at – this is called low renoylds number airfoils and means airfoils that fly at low speeds on narrow wings (compared to full size planes). According to Selig, anything below 500.000 is a low renoylds number. As part of this test Selig also made new airfoils and one of the first to gain popularity was his improvement of the E 205, the S3021. Even recently he has tested and made new airfoils for gliders and among others, it’s these I’ll tell you a little about. If you want more information about his tests and his and others airfoils take a look at the UIUC homepage: http://amber.aae.uiuc.edu/%7Em-selig/ and www.nasg.com/afdb/list-airfoil-e.phtml.

Besides the Selig airfoils, I’ll present or introduce you to some often used airfoils from Germany and some that is not so well known yet. Later I’ll tell you that they’re all the same, they just look different, but lets take one thing at a time. I’ll also show you an airfoil that I dislike and some older ones that look a bit like the new ones – one is from Epplers hands and one is from the “This is Houston – we have a minor malfunction – KAPAW” – organisation: NASA (National Aeronautic and Space Administration), the former NACA (National Advisory Committee for Aeronautics). Quite often I’ll talk about the airfoils ability to fly slower or faster, sink slower or faster, and do please remember that these conclusions will be based on two identical models were only the airfoil differ. My conclusions are based on the airfoils camber, thickness and of course their polars. If you want to know more about how you make you gliders polar better – consult Martin Simmons articles from the August/September issue of QFI and forwards (thank you Martin). If you want to know more about how to read the polars given by airfoil designers I guess that the new book from Traplet / Denis Oglesby can help you if you haven’t got the guts to dive into German literature: “Understanding Aerofoil data” £14.95 / $ 24.00.