1
$\begingroup$

I want to build for myself an ultralight aircraft as it's my dream project since I was young. I plan to build the aircraft as a 10 years project so I want to plan out everything and know if it will be even possible first.

I live in Germany so I'll follow the European aviation regulations. The specs for the aircraft are: 200 kg MTOW, 120 kg empty weight, 80 km/h cruise speed, 50 km/h stall speed, 90 km/h max speed, 10 m wingspan, the aircraft use an electric turbofan engine provide 7 hp thrust. Currently, with the wind tunnel test I got L/D ratio of 15.22. Combine these elements give my aircraft estimated performance of 1.08 m/s climb rate and cruise range of 100 km.

So my question is: will this aircraft be suitable to fly in Germany? Since I've been here for quite a while, I understand how complex the German laws are. So I would also like to ask: if it's possible to register a complete self-build aircraft? My flight plan is quite simple, a local flight in VFR for recreational purpose. So the aircraft will fly mainly within unregulated airspace as for experimental aircraft. But my worry is also if it's possible to even register this aircraft for flying at all. So if anyone familar with this topic, I would appreciate the help.

Edit: So for the commends and the answer I recieved, I found many ask why I use a turbofan instead of a propeller. The aircraft I want to build will resemble a fighter jet, the F-117N Seahawk, that's why I want to mount the engine internally. At first I actually want to use a jet engine, but given the budget limit and the problem come with thermal and strutural of an ultralight, I decide to go with 2 turbofans for total of 12hp(I decide to add some margin for safety to the engine rated power of 7hp). Yes, I understand this design is very complex, will not as efficient as already established design and potentially not as good as I expected, but it's my dream project and if it meet at least the safety factor and have good enough performance, then I'll take it. I tried with many methode to increase the performance like: sharkfin winglets, blended body design, mainly use composite material like carbon fiber laminate,... which should help the final design performance to match the small prototype design I tested in CFD and wind tunnel.

Improve this question
$\endgroup$
11
  • $\begingroup$ Related: Are there experimental aircraft regulations in Germany? From the question it seems LTF-UL applies for MTOW < 600kg $\endgroup$
    – mins
    Commented Jul 27 at 17:05
  • $\begingroup$ @mins thanks! yeah, as I though, it's as complicated as I expect it will be. I might try to ask my laywer, I'm not sure he will know about this topic though. thanks for the help $\endgroup$
    – Sairext Irkaris
    Commented Jul 27 at 17:11
  • $\begingroup$ A 10 meter biplane might be interesting, and maybe a propeller rather than a turbofan. 7 hp may give marginal performance, but 2 of them may make for an excellent recreational aircraft. You need to be able to climb in downdrafts. $\endgroup$
    – Robert DiGiovanni
    Commented Jul 27 at 22:31
  • 1
    $\begingroup$ Is this an aircraft that you're also designing yourself, that you'll then build, or is the design from someplace established? The challenges involved in designing an aircraft are far beyond the reach of a first-time DIY project. The challenges in building from an established design are significant, but surmountable, given the right resources and guidance. $\endgroup$
    – Ralph J ♦
    Commented Jul 28 at 0:59
  • $\begingroup$ the aircraft I would like to built would resemble a fighter jet, particularly the F-117N seahawk, that's why I want to use turbofan as I can put them internally. with current setup I can have range of 100km at 80km/h cruise speed and moderate maneuvers which fit my requirement for local flight as I only fly for fun, not much for travel. I understand that it will be lots of work to build an ultralight, but it's my dream and I've calculated the budget, the only problem is the legal part. With advice from mins and the answer I recieved, if the laws checked out, then build it is't a problem. $\endgroup$
    – Sairext Irkaris
    Commented Jul 28 at 5:50

1 Answer 1

Reset to default
3
$\begingroup$

Get in touch with the Oskar Ursinus Vereinigung (OUV). They have experts who will guide you through the process. The full name of that association adds its purpose: "Deutscher Verein zur Förderung des Eigenbaus von Luftfahrtgerät e.V." (German Association for the Promotion of Self-construction of Aircraft)

The association supports work on self-built aircraft in a variety of ways. The OUV is financed by membership fees and donations, and self-builders can become members.

The OUV is:

  • a recognised assessor of self-built aircraft,
  • advises the self-builder and prepares the 3 expertises which you will need during the process,
  • is a recognised noise measurement centre
  • and mediates between the self-builder and the Luftfahrt-Bundesamt in Braunschweig.

It's best to contact them before you start - every aspect of the work on your design needs their oversight, so adding them only later in the process complicates things.

Your specs seem reasonable, except for the "electric turbofan". If you choose electric propulsion, please make best use of the little energy your 120 kg budget allows and fit a large, slow-turning propeller.

Improve this answer
$\endgroup$
3
  • $\begingroup$ Thanks for the advice about the propulsion system, but I already decided to follow my dream project so it will resemble a fighter jet, the F-117N seahawk. the turbofan I use can be put internally, it provides enough thrust for a comfortable level flight and ~1m/s climb. with this design it will not be efficient as the L/D ratio is 15.22 which is quite low mainly due to the swept wings for aestetic which need surface area to conpensate. but it fits my requirements as I only fly local flight and want to experience flying feeling, so I'm fine with that efficiency if it looks like what I dream of. $\endgroup$
    – Sairext Irkaris
    Commented Jul 28 at 6:08
  • 1
    $\begingroup$ @SairextIrkaris If you decide on such an inefficient platform, the propulsion will not make much of a difference anymore. However, then I doubt that the 12 hp will be sufficient. $\endgroup$
    – Peter Kämpf
    Commented Jul 28 at 17:42
  • $\begingroup$ that's one of the problems I have with the design I chose, currently I'm still trying to fine a way to go around it, with the battery I have I can supply my engine 15kW or around 20hp which is sufficient for the 2 engines at max power. A rule of thumb I've heard is 100W/kg, so mine may not be enough. It's the challenge to go with this design and I'll see what I can do to overcome that. For now I'll clear the legal part first, then I'll try to fix the problem later after I know it's possible to get a airworthiness licence. thank you for the advice. $\endgroup$
    – Sairext Irkaris
    Commented Jul 28 at 19:14

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .