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Discussion Thread: The ultimate 120kg SL-sailplane

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ypsilon

Well-Known Member
Joined
Mar 1, 2016
Messages
325
Location
Austria
Last year the german authorities gave in, and allow all European registered UL aircraft to operate under LTF-L rules in Germany (as long as you can prove that it weighs less than 120 kg). This basically means that the LTF-L certification is dead, since in most European countries the 120kg class certification is a lot cheaper (and simpler) than LTF-L. Operating under LTF-L rules makes things a lot easier as compared to the other UL or Sailplane rules. (E.g. you don't need a medical, you're responsible for airworthiness yourself (check it as you see fit, after all it's your life that depends on it), you get more easily permission to launch on private sites etc.)

In a nutshell having a sailplane that falls into this category would make things a lot simpler cheaper. But how could such a sailplane look like?

I think that for (light) sailplanes electric selflaunch makes a lot of sense. We have an Alisport Silent 2 FES in the club where I am flying, and it works like a charm (provided you know the limitations of the system). It's a lot less hassle than any combustion engine I came across in the sailplane world.
Let's assume ~35-40 Kg for the whole system (including batteries), which leaves us with 80-85 kg for the structure.

Not much. But if you look at Windward's sparrow hawk, or Dariusz Lewek's Axel glider, then it seems to be certainly doable (in fact Darius built an electric SL-version that falls into the 120 kg class). There is also the foaldable Aerola Alatus, falling into the same category.

All these examples come with relatively low span (Sparrowhawk 11m, Axel 12.2m). As discussed elsewhere in this forum, there are reasons to believe that longer wings can actually be lighter. So what would be feasible if we didn't have restrictions concerning span. Could a 120kg SL sailplane (80 Kg pure sailplane) be build with say, 15, 18 or even 20m span? What would happen structure wise (monocoque wing), what about aerodynamics (low Re-numbers)?

Due to the low weight 7 m² wing area should do, so at 18m span the MAC would only be 38 cm, the average thickness maybe ~4cm!
Finally what performance would we get out of any such configuration?

Just a pipe dream, or actually feasible?

Let us know what you think!
 
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