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

A few parts were added to Kolibrie model: the rotor mast has two lateral shock absorbers. These were fabricated from a sheet formed gaff, 1,6mm and 1,0mm tube and are now temporary attached to the rotor mast and the landing gear aft spar. Also the tail boom was made; again I used brass sheet for the side panels and brass c-section for the top and bottom of the tail boom. For shims I used Evergreen sheets; the tail boo should npbe about 3mm wide, but the c-section is only 2mm wide. The brass sheet has a thickness of 0,25mm, so I needed to shims, LH and RH, to eventually get a boom thickness of 3mm.
The usage of brass results in a robust, albeit heavy model. I think stepping away (partially) from the usage of Evergreen was the right choice in this case.

IMG_0449.jpeg

IMG_0450.jpeg
 
You know that nagging feeling in the back of your mind something is amiss? Well, I am all too familiar with that feeling and this project has little gremlins allover the place, with plenty of opportunities to get reacquinted with that feeling.
A while ago I was busying myself with the fuel tanks, adding a battery in one tank and an on/off switch in the other tank. I performed a dry fit and what struck me at that time was that apparently the measure between the aft of the tank to the tank attachment on the aft cross brace of the skids appeared to be somewhat too small.
For one reason or another I dismissed my observation, since I couldn't positively position the tank relative to the fuselage, stored it for later evaluation and went my merry ways. Yeah, right, that decision came back to haunt me big time. Last weekend I joined the tank with the battery to the tank with the on/off switch and again performed a dry fit. Lo and behold, the same phenomenon could be observed. Either the distance between the fwd cross brace and the front of the tank was way too large or the distance between the aft of the tank and the aft cross brace too small. Initially my idea was to make it work somehow, but that didn't sit right. Instead, I started taking some measurements. Too may great dismay I found that my initial sketch I used to produce the torsion box sidewall was rather spot on, but... my transfer of the sketch to the hardware wasn't!
The torsion box ended up being 5mm too long and the pitch between the front and aft cross brace watch 3mm too large, the length of the fuel tanks was spot on, by the way. After some days of contemplating, I decided to take apart the torsion box and make a new one, now (hopefully) correct. That's were I'm currently at, again making a torsion box... Sick

These were my observations: the aft tank attachment was too much aft on the fuel tank.
IMG_0949.jpeg

The findings after checking the actual dimensions with the sketch:
IMG_0951.jpeg

And these are the sorry remains of my little hummingbird, after demolition of the torsion box:
(In the mean time work on the new torsion box started.)
IMG_0476.jpeg
 
RDN1954 said:
You know that nagging feeling in the back of your mind something is amiss? Well, I am all too familiar with that feeling and this project has little gremlins allover the place, with plenty of opportunities to get reacquinted with that feeling.
A while ago I was busying myself with the fuel tanks, adding a battery in one tank and an on/off switch in the other tank. I performed a dry fit and what struck me at that time was that apparently the measure between the aft of the tank to the tank attachment on the aft cross brace of the skids appeared to be somewhat too small.
For one reason or another I dismissed my observation, since I couldn't positively position the tank relative to the fuselage, stored it for later evaluation and went my merry ways. Yeah, right, that decision came back to haunt me big time. Last weekend I joined the tank with the battery to the tank with the on/off switch and again performed a dry fit. Lo and behold, the same phenomenon could be observed. Either the distance between the fwd cross brace and the front of the tank was way too large or the distance between the aft of the tank and the aft cross brace too small. Initially my idea was to make it work somehow, but that didn't sit right. Instead, I started taking some measurements. Too may great dismay I found that my initial sketch I used to produce the torsion box sidewall was rather spot on, but... my transfer of the sketch to the hardware wasn't!
The torsion box ended up being 5mm too long and the pitch between the front and aft cross brace watch 3mm too large, the length of the fuel tanks was spot on, by the way. After some days of contemplating, I decided to take apart the torsion box and make a new one, now (hopefully) correct. That's were I'm currently at, again making a torsion box... Sick

These were my observations: the aft tank attachment was too much aft on the fuel tank.
View attachment 498356

The findings after checking the actual dimensions with the sketch:
View attachment 498357

And these are the sorry remains of my little hummingbird, after demolition of the torsion box:
(In the mean time work on the new torsion box started.)
View attachment 498363
Click to expand...
That a big Aai …….:(
These are the pros and cons of scratch building. But you have the guts and energie to rebuild it.
Regards, Peter
 
And the beginning of a new, hopefully correct, center torsion box.
Method:
- Cut two rectangular shapes, 8x3cm.
- Wrap both pieces in tape.
- Bond the two pieces together with ordinary woodglue.
- Transfer sketch to one of the two surfaces.
- Drill all holes through and through.
- Cut out circumference.
- Separate the two sidewalls, it's a walk in the park.
- Remove the tape.
- Deburr the two sidewalls.
- Run a preliminary fit check.

I choose to slightly alter the attachment of the fwd cross brace; whereas the original drawings show the cross brace being suspended from the torsion box, I added two eyelets to the sidewalls to positively attach the cross brace to the torsion box. Looks promising.

The new side panels with the fwd cross brace and the floor- and seat supports temporarily installed to check position and alignment:
IMG_0479.jpeg
 
Last edited:
RDN1954 said:
You know that nagging feeling in the back of your mind something is amiss? Well, I am all too familiar with that feeling and this project has little gremlins allover the place, with plenty of opportunities to get reacquinted with that feeling.
A while ago I was busying myself with the fuel tanks, adding a battery in one tank and an on/off switch in the other tank. I performed a dry fit and what struck me at that time was that apparently the measure between the aft of the tank to the tank attachment on the aft cross brace of the skids appeared to be somewhat too small.
For one reason or another I dismissed my observation, since I couldn't positively position the tank relative to the fuselage, stored it for later evaluation and went my merry ways. Yeah, right, that decision came back to haunt me big time. Last weekend I joined the tank with the battery to the tank with the on/off switch and again performed a dry fit. Lo and behold, the same phenomenon could be observed. Either the distance between the fwd cross brace and the front of the tank was way too large or the distance between the aft of the tank and the aft cross brace too small. Initially my idea was to make it work somehow, but that didn't sit right. Instead, I started taking some measurements. Too may great dismay I found that my initial sketch I used to produce the torsion box sidewall was rather spot on, but... my transfer of the sketch to the hardware wasn't!
The torsion box ended up being 5mm too long and the pitch between the front and aft cross brace watch 3mm too large, the length of the fuel tanks was spot on, by the way. After some days of contemplating, I decided to take apart the torsion box and make a new one, now (hopefully) correct. That's were I'm currently at, again making a torsion box... Sick

These were my observations: the aft tank attachment was too much aft on the fuel tank.
View attachment 498356

The findings after checking the actual dimensions with the sketch:
View attachment 498357

And these are the sorry remains of my little hummingbird, after demolition of the torsion box:
(In the mean time work on the new torsion box started.)
View attachment 498363
Click to expand...
From the looks of your demolition, I would conclude the torsion box was a sturdy stout structure that you can at least feel confident of its stability when remade in the corrected dimensions. I agree with Peter, 'you have the guts and energy to rebuild it'.
 
Daniel20 said:
From the looks of your demolition, I would conclude the torsion box was a sturdy stout structure that you can at least feel confident of its stability when remade in the corrected dimensions. I agree with Peter, 'you have the guts and energy to rebuild it'.
Click to expand...
You're right Dan, the torsion box is rather robust and can take a lot of handling forces. I changed one detail, see my post #147 above, to enhance the robustness, but other than that, I'm quite pleased with my decision to go for a CA-bondend, brass torsion box. Thank you (and of course Peter) for your vote of confidence, but I couldn't live with the faulty torsion box and hey, if I can build and finish the YQ Bluenose, I can do the same with this little bugger.
 
Johan you know that I am not new to redo's and if something does not sit right with one, there is only way. I have built tow WB's and twice have I stripped the planking from one side to redo them. As to the pros and cons of scratch building, I believe that is all part of the discovery process - a process that I will be part of or partly part in the not too foreseeable future （hopefully）. In the meantime, respect!
 
Heinrich said:
Johan you know that I am not new to redo's and if something does not sit right with one, there is only way. I have built tow WB's and twice have I stripped the planking from one side to redo them. As to the pros and cons of scratch building, I believe that is all part of the discovery process - a process that I will be part of or partly part in the not too foreseeable future （hopefully）. In the meantime, respect!
Click to expand...
Thanks, Heinrich.
Scratch building, as I discovered, is a totally different pastime than building from a kit. To be sure, I don't have anything against building a kit, with or without personal customizations, but no matter what subject, scratch building poses an almost overwhelming challenge. From obtaining drawings and specations to material selection and build sequence, you're left to your own devices.
That's not to say you can't learn from other modellers experiences (see the various scratch build projects on SOS), but still...
Scratch building and redo's are almost synonyms, at least for me, like the engine for the Fokker Spin, which was build three times before being acceptable. And now with the Kolibrie, I find I am facing similar challenges; I am now working on torsion box number three and I won't give it a rest until I'm satisfied with the outcome.
Having said that, while challenging, scratch building can be very satisfying and worth the effort.
 
Johan,
I like your scratch build a lot. Your last version of the torsion box with the instrument panel was great! It’s unfortunate that dimensionally it was incorrect…sigh! But I am certain you will eventually end up with something satisfactory and dimensionally correct, that only us in the know will realize is your third attempt. ;)
But as mentioned, redos happen on kit models as well. It is commendable that you are willing to do the research and work from drawings. Too many times we are lazy and take the easy way out with a kit, or we just aren’t afforded the extra time it would take to do the research to scratch build. I fall in the latter category.
Once I retire, I hope to do a scratch build. My goal is to design my own ship, either 17th or 18th century and see what I would have done as a ship designer, the deck layouts, levels, cannon locations, shape of the ship, ornamentation, etc. and let my creativity go wild! ROTF
 
Dean62 said:
Once I retire, I hope to do a scratch build. My goal is to design my own ship, either 17th or 18th century and see what I would have done as a ship designer, the deck layouts, levels, cannon locations, shape of the ship, ornamentation, etc. and let my creativity go wild! ROTF
Click to expand...
So looking forward to that moment!
My guess is we'll be pleasantly surprised...
 
The rebuild of the torsion box is well under way. I did a couple of dry fits and this box seems to be a lot more to scale than the previous one. Still don't have the foggiest what happened with the previous one.
I was able to use parts of the previous box. What I also did was to add some pins to more positively locate parts relative to one another and it also gives a little more robustness to the box.
The pins were use to locate the top- and bottom skins to the side panels. Also the aft lower skin attachment to the mast boom has now been relocated to sit inside the box, instead of on the outside and was located to the box with a pin.
For the LH side panel I am waiting for an Evergreen order; there's an idea I want to try, not sure if I can get it to work.

View looking fwd and to the left, the bottom mast boom attachment can be clearly seen:
IMG_0501.jpeg

View looking aft and to the right:
IMG_0500.jpeg

I started adding "rivets" to the tail beam; that now gives a real sophisticated look:
IMG_0499.jpeg
 
RDN1954 said:
Scratch building and redo's are almost synonyms, at least for me, like the engine for the Fokker Spin, which was build three times before being acceptable.
Click to expand...

Many times I have had to have 3 attempts at something. Once to see how to do it, a second attempt to do it properly, and a final one that passes inspection. So I know how it feels.
 
RDN1954 said:
The rebuild of the torsion box is well under way. I did a couple of dry fits and this box seems to be a lot more to scale than the previous one. Still don't have the foggiest what happened with the previous one.
I was able to use parts of the previous box. What I also did was to add some pins to more positively locate parts relative to one another and it also gives a little more robustness to the box.
The pins were use to locate the top- and bottom skins to the side panels. Also the aft lower skin attachment to the mast boom has now been relocated to sit inside the box, instead of on the outside and was located to the box with a pin.
For the LH side panel I am waiting for an Evergreen order; there's an idea I want to try, not sure if I can get it to work.

View looking fwd and to the left, the bottom mast boom attachment can be clearly seen:
View attachment 499237

View looking aft and to the right:
View attachment 499238

I started adding "rivets" to the tail beam; that now gives a real sophisticated look:
View attachment 499239
Click to expand...
‘3x = Scheepsrecht’ ……. Well done, Johan. It’s looking very nicely detailed.
Regards, Peter
 
RDN1954 said:
You know that nagging feeling in the back of your mind something is amiss? Well, I am all too familiar with that feeling and this project has little gremlins allover the place, with plenty of opportunities to get reacquinted with that feeling.
A while ago I was busying myself with the fuel tanks, adding a battery in one tank and an on/off switch in the other tank. I performed a dry fit and what struck me at that time was that apparently the measure between the aft of the tank to the tank attachment on the aft cross brace of the skids appeared to be somewhat too small.
For one reason or another I dismissed my observation, since I couldn't positively position the tank relative to the fuselage, stored it for later evaluation and went my merry ways. Yeah, right, that decision came back to haunt me big time. Last weekend I joined the tank with the battery to the tank with the on/off switch and again performed a dry fit. Lo and behold, the same phenomenon could be observed. Either the distance between the fwd cross brace and the front of the tank was way too large or the distance between the aft of the tank and the aft cross brace too small. Initially my idea was to make it work somehow, but that didn't sit right. Instead, I started taking some measurements. Too may great dismay I found that my initial sketch I used to produce the torsion box sidewall was rather spot on, but... my transfer of the sketch to the hardware wasn't!
The torsion box ended up being 5mm too long and the pitch between the front and aft cross brace watch 3mm too large, the length of the fuel tanks was spot on, by the way. After some days of contemplating, I decided to take apart the torsion box and make a new one, now (hopefully) correct. That's were I'm currently at, again making a torsion box... Sick

These were my observations: the aft tank attachment was too much aft on the fuel tank.
View attachment 498356

The findings after checking the actual dimensions with the sketch:
View attachment 498357

And these are the sorry remains of my little hummingbird, after demolition of the torsion box:
(In the mean time work on the new torsion box started.)
View attachment 498363
Click to expand...
EISH!
 
Alan Smith said:
Many times I have had to have 3 attempts at something. Once to see how to do it, a second attempt to do it properly, and a final one that passes inspection. So I know how it feels.
Click to expand...
Peter Voogt said:
‘3x = Scheepsrecht’ ……. Well done, Johan. It’s looking very nicely detailed.
Click to expand...
Sounds about right, building parts 3 times to get it right, Scratch building is very similar to building prototypes: a lot of trial and error.
 
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