Tigger L-39 Conversion

[daveculp]

With the dorsal hump done I'm starting work on the intakes.  The splitter plates need to be scratch built from styrene card.  I added a thin spacer where the splitter plates attach in order to move them outboard just a bit.  Here I've painted the fuselage and the inboard side of the splitter plates with a primer that closely matches the final color of this area.  I also clearly marked the splitter plates to avoid stupid mistakes

 

 

After the splitters are installed I'll sand the intakes down on the sanding board until they fit flush.  I left some extra material at the intake opening for now to keep the part strong while I sand it down.  After that more putty and sanding.

 

 

The tail end is progressing slowly.  This end is complicated and requires several interations of putty and sanding.  I used Milliput to get the basic shape of the area above the exhaust opening.  I'm using Tamiya gray putty for filler work, and I use Bondo glazing and spot putty for the final shaping.  The Bondo is very easy to use but it doesn't handle scribing very well, so you have to use it only for small touch-ups.

 

 

Eventually it'll all come together.  The control surfaces are 3D printed, and I printed them with 0.4 mm thick trailing edges.  I could go even sharper than that, but I don't want them to be too delicate. 

 

[LSP_Kevin]

Excellent progress, Dave. Love what you're doing here.

 

Kev

[daveculp]

10 hours ago, LSP_Kevin said:

Excellent progress, Dave. Love what you're doing here.

 

Kev

 

Thanks Kevin.  I recovered quickly from the wing shock, and am taking it as a blessing.  Now I have time to make progress on the fuselage while I await the new kit from Tigger.  There are three areas which I still haven't decided on a solution for:

 

1)  The tailpipe - I have an acrylic tube that's the right size but too heavy.  I'm still searching for a thin-walled alternative.

 

2)  The cockpit glass is going to be tough.  I might have to build up the canopy frames to get a good look and fit.  I plan on making the aft canopy closed and pilot's canopy open.

 

3)  The gear will be 3D printed.  The question is will they be strong enough?  We'll see.

 

-- Dave

[daveculp]

So I tried Kevin's trick of freezing parts to make the CA glue brittle, and it definitely helped.  After a lot of cutting, sawing, prying, twisting and snipping I managed to extricate the original fuselage belly from the wing structure.  This will save me a lot of time later.

 

 

 

 

I had believed that the L-39 vertical tail was close enough to correct height for an L-159 that I could leave it alone.  Upon further review it just looks too short, so I cut off the tip and am building a new one.  This is the kind of thing I'm supposed to figure out earlier in the process.

 

I'm going to print a small extension for the rudder since the geometry is already set in CAD.

 

 

[Oldbaldguy]

On 9/27/2021 at 1:26 PM, daveculp said:

 

Thanks Kevin.  I recovered quickly from the wing shock, and am taking it as a blessing.  Now I have time to make progress on the fuselage while I await the new kit from Tigger.  There are three areas which I still haven't decided on a solution for:

 

1)  The tailpipe - I have an acrylic tube that's the right size but too heavy.  I'm still searching for a thin-walled alternative.

 

2)  The cockpit glass is going to be tough.  I might have to build up the canopy frames to get a good look and fit.  I plan on making the aft canopy closed and pilot's canopy open.

 

3)  The gear will be 3D printed.  The question is will they be strong enough?  We'll see.

 

-- Dave

I have found very thin-walled tubing for tailpipes in the most unexpected places.  I have no idea what diameter you are looking for but you might want to check out your local cigar/tobacco store and your local big box hardware store.  High end cigars often come in exquisitely thin aluminum tubes that just beg to be made into tailpipes.  Drill bits, router bits and even faucet aerators often come in thin walled plastic tubes of various diameters.  You might have to buy something you don’t need in order to get the tube you want, but…

 

[Flight Line Media]

Great progress, Dave. I look forward to seeing this build completed.

[daveculp]

Working on three areas now:  The exhaust, the inlets, and the canopy frame.

 

The exhaust area is a bit complex, and I'll post a photo later when it looks more presentable.  Now it looks mostly like a clump of Milliput.

 

The other bits look more presentable at this point, so here are pics of the inlets and canopy frame between front and rear cockpits.

 

 

 

 

 

I've decided both canopies need to be open.  This means I have to cook up some "electronicsey" looking stuff to put into the rear cockpit.  I only have one distant photo of the electronics bay to work from.  The sun shade over the equipment is actually attached to the rear canopy, so I can't hide anything under it.

 

I pre-painted the inside of the inlets, including the bare metal anti-iced inlet lip.

 

The canopy frame is 3D printed.

 

[daveculp]

The tail end is well enough along for a photo.  Still some final shaping and smoothing needed.  The only photo I have of the L-159 tailpipe is a still from a youtube video, but it's enough.  It looks like a tailpipe within a tailpipe, so the first tailpipe I installed, made of 3/4 inch O.D. clear acrylic tube, is actually an inner wall of the fuselage.  I 3D printed the actual tailpipe and associated parts as a single piece:

 

 

 

 

This is one of the most fragile and complex pieces I've printed, and it didn't come out quite right.  I'll thicken up some walls, support it better and re-print.  When installed it looks like this:

 

 

 

 

The two ducts are probably cooling ducts to carry away some of the tailpipe heat, fed by air coming from two large NACA inlets on top of the fuselage:

 

 

 

 

 

[daveculp]

My new wings arrived today in record time!  This time there will be no mistakes   NOTE:  Once you cut off the L-39 style tip tanks the wing parts look very similar.

 

 

Edited October 7, 2021 by daveculp
added bit about tip tanks

[daveculp]

Club meeting tonight, so I brought the project along and took a picture of some parts with their general layout.  Tail feathers are installed, engine inlets installed.  I'm taking this opportunity to try different colors for the Honey Badger's light tan color.  The under-wing fuel tanks are painted with a previous color choice which I've since decided is a bit too yellow.  The fuselage is now wearing my next (final?) choice of tan - Mission Models MMP-010 Gelbbraun, yellowed a bit with some Vallejo Beige and darkened with some Vallejo USAF Tan.

 

 

[allthumbs]

Great looking project Dave. I love it!

[daveculp]

After staring at the vac windscreen for a while I decided I'll have to print a windscreen frame and worry about how to get the clear part to fit later.

 

Making 3D printed parts can be an iterative process, especially when fitting to a curved or irregular surface.  Here are three photos showing three of the four print iterations I had to do in order to get a good fit.  The first print is a basic "geometry checker".  The other prints are progressive tweaks to the part to get to the final form.

 

 

 

 

 

 

In the second photo I was checking that the instrument panel, cowling and HUD didn't collide with the frame.

 

Now I'll just putty in the gaps and prepare for more painting.

 

 

[daveculp]

The wings are progressing.  Here I'm replacing the flap fairings with 3D printed versions.  The wings are almost ready for attachment to the fuselage.

 

 

 

Three different putties in use here.  The pink is Bondo two-part resin.  The red is Bondo Spot and Glazing putty.  The silver is Tamiya Gray putty.

 

[Jeff T]

Looking good Dave!

 

Jeff.

[daveculp]

Well, it came time to attach the wings to the fuselage and that's when I discovered that the wings have different dihedral angles.  The right wing has a little more dihedral then the left.  I thought I had measured this enough times that it was foolproof, but it made a fool of me.  All is not lost though.  I attached the wings with the right side shimmed upwards a little.  This will hide the error by moving the error to the bottom of the airplane where all the errors can accumulate unseen.

 

 

 

 

 

 

I can fair it a bit, but I expect it will always be noticeable from underneath.  I'd previously decided that I'm not going to worry about the fit of the control surfaces on the bottom, so the errors are already accumulating there.

 

-- Dave