NHI Kolibri N-3, scale 1:48, scratch build

Whilst progressing the construction of the torsion box, I became more and more concerned about the torsional stability of the center box. Evergreen is a rather easy material to work with, easy to cut, easy to connect, using adhesive, but it doesn't provide much stability. I think that it's due to the geometry of the center box; the box is rather narrow and slender and due to the envisioned build sequence, I need to have one of the sides of the box open for as long as I can. This means I don't have much of a resistance against torsion. Long story short, I restarted the build of the torsion box, using brass as material for the RH web and the closing panels, upper and lower, fwd and aft.

Also some progress was made with the rotor mast; I added provision for the attachment of the rotor head/gearbox and drilled a number of holes for the feed through of the tail rotor shaft and the cross tube of the landing gear.

Iso view of torsion box and instrument panel:
IMG_0951.jpeg

Iso view of rotor mast assembly :
IMG_0863.jpeg

My interpretation of the torsion box and the rotor mast (btw, all is CA bonded):
IMG_0202.jpeg
 
RDN1954 said:
Whilst progressing the construction of the torsion box, I became more and more concerned about the torsional stability of the center box. Evergreen is a rather easy material to work with, easy to cut, easy to connect, using adhesive, but it doesn't provide much stability. I think that it's due to the geometry of the center box; the box is rather narrow and slender and due to the envisioned build sequence, I need to have one of the sides of the box open for as long as I can. This means I don't have much of a resistance against torsion. Long story short, I restarted the build of the torsion box, using brass as material for the RH web and the closing panels, upper and lower, fwd and aft.

Also some progress was made with the rotor mast; I added provision for the attachment of the rotor head/gearbox and drilled a number of holes for the feed through of the tail rotor shaft and the cross tube of the landing gear.

Iso view of torsion box and instrument panel:
View attachment 488197

Iso view of rotor mast assembly :
View attachment 488198

My interpretation of the torsion box and the rotor mast (btw, all is CA bonded):
View attachment 488199
Click to expand...
A well thought out re-do, Johan. That looks very promising. But still a complex structure.
Regards, Peter
 
Peter Voogt said:
A well thought out re-do, Johan. That looks very promising. But still a complex structure.
Regards, Peter
Click to expand...
Thanks, Peter.
It's a darn complex build, I really underestimated the complexity of this little (humming) bird, but it's still a very fun thing to build, with a lot of learning.
My guesstimate is that it'll take longer to build than my Bluenose...

Regards, Johan
 
RDN1954 said:
Whilst progressing the construction of the torsion box, I became more and more concerned about the torsional stability of the center box. Evergreen is a rather easy material to work with, easy to cut, easy to connect, using adhesive, but it doesn't provide much stability. I think that it's due to the geometry of the center box; the box is rather narrow and slender and due to the envisioned build sequence, I need to have one of the sides of the box open for as long as I can. This means I don't have much of a resistance against torsion. Long story short, I restarted the build of the torsion box, using brass as material for the RH web and the closing panels, upper and lower, fwd and aft.

Also some progress was made with the rotor mast; I added provision for the attachment of the rotor head/gearbox and drilled a number of holes for the feed through of the tail rotor shaft and the cross tube of the landing gear.

Iso view of torsion box and instrument panel:
View attachment 488197

Iso view of rotor mast assembly :
View attachment 488198

My interpretation of the torsion box and the rotor mast (btw, all is CA bonded):
View attachment 488199
Click to expand...
That is some very nice metal work you have going on there Johan. Will you be reinforcing the CA only bonds?
 
Daniel20 said:
That is some very nice metal work you have going on there Johan. Will you be reinforcing the CA only bonds?
Click to expand...
That's currently not foreseen, but it heavily depends on the bond staying intact while under load. I don't expect that under display circumstances it will be an issue, but handling forces applied during the build are cause for concern.
On how to reinforce/repair a faulty bond I don't have an answer for as of yet.
 
Dear Johan. I am very late to this build and I apologize for that. I obviously have no idea of the mechanics and workings of such a craft, but I can only admire your efforts. With your known resilience and quest for finding answers, I have no doubt that it will be a great success and I fully admire and endorse the filial connection of the build.
 
Heinrich said:
Dear Johan. I am very late to this build and I apologize for that. I obviously have no idea of the mechanics and workings of such a craft, but I can only admire your efforts. With your known resilience and quest for finding answers, I have no doubt that it will be a great success and I fully admire and endorse the filial connection of the build.
Click to expand...
Hello Heinrich,
No apologies needed: it's good to see you found some time to return to SOS; your presence and contributions are sorely missed.
This little humming bird might be a bit more than I can stomach, while I initially thought it to be an easy build, I now have to come to the conclusion that despite it's deceiving simple looks, the Kolibrie is a true helicopter with inherent complexity. It doesn't help matters either that I intend to implement working flight controls. The good thing is that I have no intentions to make it speed build.
In the meantime, feel free to visit my blog anytime.
 
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