A Tailless Tale: the design evolution

The design Evolution

The inspiration came from the SWIFT foot launched glider, that still remains the most succesfull tailless ultralight glider that reached the market. I wanted to see if it was possible to design a better streamlined sailplane, still keeping the advantage of the foot launch method.

Year 2000: the main inspiration was coming from the Swift design

Year 2000: first conceptual rendering for a foot launched version

At this stage i started with a quite conservative aspect ratio and a thick wing section. One of the biggest issues was to find the right compromise for the pilot position respect to the wing spar, and minimizing the center of gravity shift between the pilot "running" and the "seated" configuration.
The lift distribution over the wing was close to elliptical, and two big winglets were implemented.

Year 2000: preliminar study

 The swept angle was limited to 15°. The wing surface was good enough for a low stall speed, making foot launching possible.

Year 2000: a very tight and streamlined fuselage pod.

 In 2001-2002 i was focusing on running some aerodynamic and stability simulations. At that time, there was no "easy to use" software for that. Searching on the web, i was able to find some freely available basic VLM code (vortex lattice method) in FORTRAN. Those codes were mainly coming from NASA and some US Universities. No GUI and quite complex to be used. Nevertheless i was able to prove the concept.

Year 2002: Panels setup for VLM code.

 In 2004 the design evolved in an higher aspect ratio wing, and the swept angle increased to 22°.
The winglets were very nicely blended with the wing. The first free flight scale model was built and flown.

Year 2004: that wing was very sexy!

At that point in time, a great source of inspiration was Martin Hepperle's Website, and the wing section choosen for the wing was the MH-78. This wing section was specifically developed for footlaunched gliders.

Year 2004: MH-78 wing section.

In 2010-2011 i started investigating the prone pilot position: fascinating configuration, but there are several drawback to this. The most annoying one is to find a good streamline for the fuselage.

Year 2011: prone pilot position study.

After several studies, i still prefer the traditional seated position.

Year 2012: fuselage study.

After a stop that lasted a couple of years, i focused in optimizing the fuselage shape. I thought it was good to take as a reference some well known fuselage designs. The one below is belonging to the Rolleden Schneider LS6 (the glider that i actually fly):

Year 2014: LS6 fuselage and pilot position - side view

Year 2014: LS6 fuselage and pilot position - top view

The LS6 is quite an old glider, but this fuselage design has been used on several sailplanes, from LS4 to LS8, proving a very good performance.
The difficulty with my design, is due to the fact that, more than a fuselage, i just need a pilot pod, since the glider will be a tailless one. So, i needed to optimize the shape in order to provide a good pressure gradient recovery on a reduced longitudinal length.

Dream 2700 - A tailless tale: where it all started from

I've been always fascinated by flying wings and tailless sailplanes.
They look beautiful and simple, but reality is different. They own some very specific advantages, but at the same time there are several issues that must be mitigated with a very careful and complex design work.

Advantages.

• Their reduced directional stability allows to get on the other ends a very good spiral stability, and this is a plus for thermal soaring.
• A well designed tailles sailplane can reach good stall performances and can be very resistant to spins.
• Friction drag can be minimized.
• The design architecture is ideal for a motorized version. An engine can be easily installed in a pusher configuration (getting as well a stabilizing effect)
• It can be cheap to build, not having a long fuselage and tails.
• A flyign wing is absolutely a fascinating and very attractive design.

Disadvantages.

• In order to achieve good stability and control performances, several compromises needs to be taken, leading to a potential reduction in pure performance.
• The center of gravity allowable range is small, and must be precisely defined
•  Any control surface movement will affect the ideal lift distribution on the wing, producing an increase in induced drag
• Adverse yaw can be a big issue (but here there are new development helping us)
• Pitch damping is an issue, due to the very small inertia on the lateral axis. PIO (pilot induced oscillations) are not rare for flying wing designs
• Lateral stability can be an issue
• It is true that there only a wing to be build but, when it comes to swept wings, difficult aero/structural challenges are coming into the picture.

 I'm convinced that some of those critical factors can be overcome by a very critical design optimization.
In a tailless wing design, is very difficult to get the right trade-off between good performances, easy handling, and low production costs, when compared to traditional designs.
I'm very happy to see that this architecture is a bit revitalized nowadays (see Prandtl wing study at NASA), but the number of airplanes that will use this configuration will be still niche compared to the traditional architectures.
Nevertheless, the interest on some of the advantages given by that architecture, and the fashion connected to it, makes flying wing and tailless gliders far from disappearing from the scene.
I've been always attracted by both the design and the challenges connected to this configuration, and this is the reason why a started dreaming of my own tailles glider design.
The one in the picture below was my first concept.

My first design concept. (2000)

Dream 2700 - A tailless tale

I decided to open this page to share my passion about sailplanes, and in particular about tailless gliders. Since i was a child, flying has been my dream. Airplanes are my passion since ever. I started with control line models, moved to rc models, and after i started flying for real, with hangliders, paragliders, ultralights and sailplanes. Today i'm owning a beautiful LS6 sailplane, and a Niviuk Ikuma paraglider. I've been always dreaming about designing my own aircraft. This page is dedicated to the evolution of my ideas along the years. Today i'm finalizing the design of the last evolution of my concept. It's name is Dream 2700.

Old ideas being revisited: design nr. 4

Let's now have a look at something completely different:

 Call it as you want: joined wing or box wing is probably the most appropriate definition. I would suggest "canard" joined wing design.
As usual, the idea is to make a foot launchable sailplane, easy to transport, light weight and with a reasonable performance level.
The fuselage is reduced again to the minimum, just streamlining the pilot, with an opening on the belly for foot launching it. Lateral stability should be provided by the vertical surfaces joining the fron and back wings at the tips.

 The elevator is on the front wing and the ailerons on the rear wing. The idea was to keep the wingspan below 10 meters. That was probably too optimistic, since it is giving a very small wing surface. One solution could be to increase the wing chord...

The front view is sexy, isn't it?

Old ideas being revisited: design nr. 3

Today i would like to share another "conventional" solution:

When i sketched that sailplane, the main idea was to design something similar to the Genesis concept.
What does it mean?
Well, i wanted to reduce parassite drag to the minimum by designing a very short fuselage. The wing is equipped with a low pitching moment profile, and that allows to use a short lever arm for the stabilizer. Fuselage length is below 4 meters, making the glider easily transportable. The fuselage has an open floor to allow foot launching. At first i thought about an open cockpit, but also a closed canopy should be feasible. For safety reasons, the sailplane is equipped with a ballistic parachute positioned on the back of the pilot and connected to the main wing spar.
As usual, comments are more than welcome!

Old ideas being revisited: design nr. 2

Let's have a look into a more conventional solution.
The dream is always the same: being able to foot-launch from a hill with the highest possible gliding performance. In other words, that means reducing drag to the minimum, and in order to do so, wetted area must be reduced to the minimum in order to reduce parassite drag. Profile and induced drag are to be minimised by working on the right wing section selection and wing platform configuration. In that specific case, since the architecture is close to a traditional one, wing platform should be optimised in order to get closer to an elliptic lift distribution.
In the next pictures, i've sketched some design variation of the same basic concept:

Picture 1: v-tail

All those design variations are probably too aggressive in terms of wing area. I'm quite sure that a bigger wing surface is required to reduce stall speed to a reasonable value. In comparison with a tailless design there is one advantage: the CLmax of a traditional design can be significantly higher respect to an equivalent tailless design. Should also be easier to implement a flap system that can maximise CL during take off and landing. The fuselage pod has been pushed to the minimum wetted surface: probably needs to be enlarged a bit. An amazing concept is represented by the pilot prone position, giving an outstanding visibility. The biggest drawback is that no-one will feel comfortable having is nose being the first part crashing in case of ground impact...

Picture 2: v-tail

The second picture is more or less showing the same concept.

Picture 3: traditional tail configuration

Third picture shows a bit more traditional configuration for the tail. One of the potential design issues is connected with the short tail harm. This can be achievable only using low Cm wing sections and a big tail area. Unfortunately a low Cm sections usually is also having a low CL max....
A solution could be to increase tail authority by designing a quite extended vertical fin.
Comments are more than welcome!

Old ideas being revisited: design nr. 1

Let me share with all of you some old designs i was drafting some years ago when i was still at the University. Even if most of the courses were exiting (at the end it was aerospace engineering :-) ), some of them were quite boring, and so i was spending my time drafting my dreams.
The one attached below was again related to a foot launch-able tailless glider. In that case, i considered the option to reduce wingspan, wing surface and weight to the real minimum. The design was drafted around a pilot lying in a prone position.

One of the issues to be solved were connected with the wing spar positioning relative to the pilot. The idea was to shape the spar in a way that it was surrounding the pilot body (see the small section view). Sincerely i do not know how feasible it is, but for sure is a potential solution.
From a structural and transport perspective, the idea was to split the glider into 5 parts:

• fuselage pod
• 2 half wings
• 2 winglets

Wingspan was supposed to be 11 m. Considering a 1 meter wide fuselage pod, it means max 5 meters per each wing half, that makes the glider easily transportable on the top of a mid size car.

Intriguing, right?

I hope i'm able to find the time to post all the other designs i was drafting, and would be nice to open a discussion on them. I really want to move forward in building at least a radio controlled model of the concept we will judge as the best one.

Stay tuned, and have good flights!