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Glasflugel H301 Libelle

quorneng

Active member
#1
I have just realised I originally posted this in the wrong place!

The Glasflugel Libelle (Dragonfly in German) was an early all glass fibre 15m open class glider.
At the time it had a performance quite a good as any glider around.
Compared to equivalent wooden gliders it was quite a bit lighter and was extremely easy and quick to put together. Most of the controls connected automatically as the wings and tail were put on. It was also 'clever' in engineering terms as the wings were fixed in place by a single pin and the tailplane by a single 5mm bolt!
The Libelle like all high performance gliders has a very high aspect ratio wing which means that at even 76" span the wing chord is only 5" at the root and half that at the tip.
Small-3view.jpg
As the canopy covers the wing it allows the use of a one piece wing so the challenge is a true scale 76" span 'electric' Libelle and just for fun built in Depron! ;)

The fuselage is built in two halves using a former and plank construction.
FormersA.JPG
Slow and tedious as each plank has to be shaped to fit.
Fuseplank.JPG
but you get there in the end.
RHplnkcmplt.JPG
To be continued!
 

quorneng

Active member
#2
With one half of the fuselage complete the other half of the formers are added.
Before the planking is started the elevator servo is installed in the tail.
ElevtrServo.JPG
The inside skin of the cockpit.
CpitInside.JPG
A box to house the radio.
RadioBox.JPG
The tailplane is built up with 2mm Depron skins over a hard balsa spar and a balsa leading edge. The elevator halves are joined by a glass fibre tube.
TailAdded.JPG
For scale appearance the wing is true scale section at the root but quicky changes to a much thinner section outboard. To ease construction the wing is made in 3 sections. The centre portion creates the dihedral and incorporates the change in wing section.
FuseWings.JPG
It is an all Depron built up structure with wide (25mm) but thin (1mm) balsa spars set in to the wing surface.

The real structural problem will arise in the long and thin section outer panels.
 

zev

lumpy member
#4
fantastic stuff! I have never seen people building with foam that way before. one question, isn't depron very bendable? why do the fuselage out of so many pieces when you could just bend it? is it because of the compound curves?

awesome!
 

quorneng

Active member
#5
zev
Depron will bend but only by so much and only the most gentle of double curves can be achieved. As far as I am aware there is no process that could form a flat Depron sheet into the required fuselage half.

The outer wing panels are built up from the 3mm Depron bottom skin which is preformed to the correct shape and has the wide thin lower spar already inserted flush with the surface.
RHwing1.JPG
The spar web is continuous so the ribs are divided front to back.
With all the ribs in place the top skin is added back to the spar to create a D box. In this state the wing is rigid enough to be handled.
RHwing3.JPG
The aileron servo is mounted at the inboard end of the 18" long narrow strip aileron.
AileronTop.JPG
Even this far inboard from the tip the wing is so thin that the tiny 3.7g aileron servo has to mounted flush with the under surface.
AileronUnder.JPG T
With the wing attached to the centre centre section does give an idea of just how 'skinny' it is.
WingOnCntr.JPG
Very light but there is still a question on its ultimate bending strength and flutter resistance. :confused:
 

quorneng

Active member
#7
The cockpit canopy is a planked Depron structure like the fuselage.
Canopy1.JPG
The result is very light and strong. It is held on by a front 'tongue' and small rear magnets.
The power train components.
MtrBatESC.JPG
The 120W Blue Wonder motor.
MtrMnt.JPG
By pure chance the spinner is very close to the original fuselage profile. The prop is unmarked but I think is a 7.5x6.
Spinner.JPG
The 1000mAh 3s in the cockpit with the ESC along side.
BattForward.JPG
The nylon wing hold down bolts go through the spar.
It is not really possible to get a gloss finish on Depron without a significant weight penalty but it has a coat of white emulsion which is then 'sealed' hair spray!
CompleteA.JPG
It has an impressive set of wings for a plane that weighs just under 12oz!
 
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quorneng

Active member
#8
Despite my reservations if flies quite well. Of course it is very sluggish in roll and drops a wing very easily but the recovery is almost instantaneous. I haven't really explored is envelope but it will loop well enough.
[video=vimeo;57452719]https://vimeo.com/57452719[/video]
 
#11
Yes it was and its on the sound track as well!
It came off because I put the Libelle into a significant side slip as a result of a climbing steep turn.
As I was using a head mounted cam you can see after a few more seconds I checked to see where it had landed.

I am waiting for better weather before flying it some more.
 
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#13
The conclusion to this thread is my Libelle is no more - or rather I don't know where it is, it is lost! :(

I suppose the only comfort is it demonstrated that it does thermal quite well.
At about 600ft I was in formation' with a local hawk and I was just thinking it was time to bring it back when I lost sight of it when it was 'edge on' to my line of sight.
I did not panic as I reasoned its big wing span would be easily visible as it continued the circle however I never saw it again!
I can only assume it did not continue the circle but remained edge on for a bit longer.
The problem is that I have no idea of its direction and from 600ft the possible area is huge (1 square mile?).
I have searched what I can but access is limited in the down wind area with many fully grown trees and tall hedge rows.
The final blunder? - it had no address label! (all my planes do now!)

It was not an expensive plane but it did take quite a few man hours to make and getting lost is so frustrating.
I would have been happier with a write off crash. At least I would know what happened to it!

Still if you can't afford to lose it - don't fly it.