Thulin types N and NA - prototypes

[Torbjorn]

edit:  title was ”Thulin NA” - about halfway I got the impulse to add the N type the NA was derived from as well

 

From the ceiling in a room filled with rotary engines and airplane models at the Landskrona town museum hangs a small biplane of 1919 vintage. The room displays a small exhibition dedicated to Enoch Thulin and his Thulin works (AETA) - a short-lived aviation company which went bust after Great war surplus flooded the marked and the demand fell. Despite its relatively short lifespan, Thulin laid the foundation of Swedish aviation industry, produced a dozen or so types, some license-built, some own designs. The preserved plane in the ceiling is the Thulin NA, the last of the lot. 

 

Only one prototype was built. First flight in April 1919, made a respectable 215 km/h powdered by its 9-cylinder Thulin G rotary. A bare month later, Thulin crashed fatally during a practice flight with an older design. With the market saturated and Thulin dead, the company was gone within a year. The NA ended up in the Landskrona museum as one of a few preserved Thulin aircraft.

 

A photo here:

 

https://digitaltmuseum.se/021018827355/flygavdelningen-pa-landskrona-museum-i-taket-flygplan-modell-thulin-na

 

The museum measured and produced drafts of the plane, now available at the public Swedish digital repository. So, courtesy of Mr Göran Lundin and the Landskrona museum, I printed these drawings to produce the model from:

 

 

After once having built a significant part of a model only to discover the drawings were scaled wrong, I now measure all drawings after printing and mark them with the actual scale as extra verification…

 

The model will be built from plasticard and the usual scrap metal and, if I’m lucky, parts from the spares box.

 

Edited January 21, 2023 by Torbjorn

[Corsairfoxfouruncle]

Welcome with an interesting choice, in fact Ive not heard of it so off to research it. 

[Torbjorn]

19 hours ago, Corsairfoxfouruncle said:

Welcome with an interesting choice, in fact Ive not heard of it so off to research it. 

Thanks - I hardly expect anyone to have ever heard of this plane. It didn’t achieve anything exceptional, or introduce anything new. I’m only making it due to a certain fascination of Thulin, and this marks the end of his work. And the GB supplied the extra mojo I need to make a prototype, which I otherwise have little interest in.

 

 

I’ve started. The fuselage will be built up by flat pieces of sheet for the bottom and linen-covered aft section. By printing two drawings, I use one to cut out panels and cross-sections that I glue directly onto the plastic sheet. I usually try to make some cut exactly, while the rest are cut overly large, to be trimmed to size after attached.

 

The front side panels were wooden panels, bent to transition from a straight side to circular, to conform to the circular engine cowling. This is a construction that Thulin had  used for many previous types, and I could reuse the moulds I had previously made for a Thulin D.

 

The topside will be trickier.

 

Anyhow, here are the pieces. The port side side panel hasn’t been cut. The used mould on the right. A surplus Le Rhone from a Roden Camel will be used for dryfitting and aligning the front parts. The NA used what was basicly an 11-cylinder version of this engine of almost the same physical dimensions.

 

 

Glued all but the port side front panel. Need to leave access for construction of internals, but need one panel in place to keep the front firewall in place and avoid warping.

 

This will be the smallest two-seater I’ve built.

Edited October 16, 2022 by Torbjorn

[pheonix]

I too have never heard of this type (although I do know of some Thulin types). Thanks for the background to the man and his company - very interesting.

 

You have made a good start - especially the moulds which look super. Good idea to use an engine from the spares as they can be awkward to scratch build.

 

Looking forward to seeing more of this one.

 

P

[Courageous]

Got to love a nice bit of scratch building. I know nothing of the type, so this'll to interesting to watch.

 

Stuart

[Shorty84]

Great to see a quite unknown type covered by a good scratch build 👍

 

Cheers

Markus

[Col.]

You're off to a flying start on this one and a deserving subject.

Edited October 17, 2022 by Col.

[bigbadbadge]

Great start   not heard of the type either , very intriguing how you quickly it is building up. Cracking work 

Chris

[Torbjorn]

On 10/16/2022 at 10:28 PM, pheonix said:

I too have never heard of this type (although I do know of some Thulin types). Thanks for the background to the man and his company - very interesting.

 

You have made a good start - especially the moulds which look super. Good idea to use an engine from the spares as they can be awkward to scratch build.

 

Looking forward to seeing more of this one.

 

P

Thanks - though I still have to do something about the engine since it lacks two cylinders. I’ve never scratch-built a rotary or radial as I could not match available aftermarket, but since that bulbous spinner will block almost everything I don’t think it’s worth the money to buy a resin, even if one can be found. I’m considering just to find two spare cylinders (I have several Smallstuffmodels engines, and they usually have at least one spare cylinder) and rearrange the one on the picture.

 

13 hours ago, bigbadbadge said:

Great start   not heard of the type either , very intriguing how you quickly it is building up. Cracking work 

Chris

Thanks - but so far it’s only cutting plastic, I assure you that I’ll slow down soon enough  

[Corsairfoxfouruncle]

Do you have a drawing of the front of engine or cowling ? It probably doesnt show too much. I think round stock and a piece of wire would match the engine you have. If you build one use the round stock wrap thread around it tightly and soak in C/A. This will give you the cooling ribs. 

Edited October 18, 2022 by Corsairfoxfouruncle

[Torbjorn]

10 hours ago, Corsairfoxfouruncle said:

Do you have a drawing of the front of engine or cowling ? It probably doesnt show too much. I think round stock and a piece of wire would match the engine you have. If you build one use the round stock wrap thread around it tightly and soak in C/A. This will give you the cooling ribs. 

Strangely I cannot find any photos of the Thulin G engine (annoyingly the Thulin works used the same alphabetic naming system for planes and engines and even cars - at least they switched to a Roman numeral system for the motorcycles!), but there are plenty of highly detailed Thulin  A photos, which look almost identical to the Le Rhone they were reverse-engineered from. I suspect the G looks the same but with 11 cylinders.

 

Here are some photos of the front of the NA: you can see details on 2-3 cylinders at the bottom, the rest is pretty much invisible.

 

https://aeronavium.wordpress.com/2016/03/28/enoch-thulin-pa-landskrona-museum/

 

What you suggest is an option, but I wanted to try the method outlined by Woodman in his book: tightly wrap metal wire around plastic, bake it, and the plastic should partially smelt and fill the voids between the metal wrappings, thus creating cooling gills..

[Torbjorn]

Apologies in advance for a long picture-heavy post.

 

Finished most of the cockpit. Most internals were built up with scrap and plastic strips. The front underside had a curved fairing of sorts (to get rid of castor oil splatter?), almost identical to that of the Sopwith Camel. I sanded a block of plastic to its approximate shape and glued in on the deck: the outer underside can now be sanded out of this block to shape at some later date. As the photo shows, I’ve filled the aftermost section to make it robust.

 

 

Not too happy with the wood paint: too much contrast, although the photo has exaggerated it. Since it will barely be visible I’ll leave it.

As opposed to earlier Thulins, the NA was built with a metal tube frame, which I depicted with stretched sprue. The curved wooden frame were just to hold the curved wooden side panels in place.

 

 

Currently waiting for the Milliput leather imitation in the seats to cure before I can do more. Douglas Bader is anxiously waiting to have a go. He’s my go-to sanity check regarding seat and control placement. He’ll likely have to remove his prosthetic legs to fit in the observer’s seat though: I’ve never seen such a cramped cockpit, but I have checked and double-checked and it seems to be as built. The foot-rests for the observer can be seen next to the stearing stick! 

 

—-

Waiting for that I decided to make use of the rare sunshine…

 

 

 

 

…by starting on the flying surfaces!  I arrange a poor man’s drafting table by taping the drawings and some rulers to the window and rely on sunlight for translucency.

I follow Woodman’s method of embossing ribs on a thin sheet and wrapping this ”skin” on an inner core. I’ve been dissatisfied with one part of my earlier builds and this is an attempt to fix it. The ribs look good on the upper side, but on the underside the linen will sag and the ribs look sunken rather than raised. Tried something slightly different now.

 

I first embossed the upperside ribs with an ink pencil, like previous tries, but then flipped the sheet and *lightly* embossed theunderside with a ball tool (giving wider and flatter imprints) from the outside, so the ribs will be pushed in rather than out (but only slightly). Photo below shows the underside getting embossed:

 

The result is this:

The upper side has a reasonable wavy appearance while the underside (shadowy lower sude in the image) is flatter. This sheet was folded over a .6mm plastic core sanded and bent to an aerofoil shape. Here it is with the lower wing ”skin” freshly embossed:

 

 

 

The underside isn’t perfect, but better than my previous tries so I’m happy:

 

 

 

 

The reason I filled the aft fuselage is that I want to saw a slit for the empennage,  made in one piece for the sake of robustness. This part is made by embossing .3 mm sheets (because Eduard Nieuport empennages measure 0.6 mm and I have no better input on the thickness) and gluing them together. This has the downside of having the leading and trailing eedges to repair, but I prefer that over having to add rib structure to a single piece. Here it is, glued, with the two rudder/fin halves made in the same way (I cut to shape only after joining the halves):

 

The elevators will be cut away I think, haven’t decided yet.

Edited October 22, 2022 by Torbjorn

[bigbadbadge]

Oh wow, what excellent work , the cockpit is looking fantastic as are the wing and empenage too.  

I have seen this method before, but can I ask what you use to secure the embossed skins to the inner core? Do you secure it at the leading edge or just the training edge?

Thanks in advance 

Chris

[pheonix]

Excellent progress with very good details. I have never tried the core method of wing construction as I tend to use single sheet plastic.

 

P

[Torbjorn]

2 hours ago, bigbadbadge said:

Oh wow, what excellent work , the cockpit is looking fantastic as are the wing and empenage too.  

I have seen this method before, but can I ask what you use to secure the embossed skins to the inner core? Do you secure it at the leading edge or just the training edge?

Thanks in advance 

Chris

Thanks Chris.

 

I’m gluing the entire contact surfaces. Or rather, trying to.

 

Out of laziness I’m using what’s available in my desk, which is Tamiya green label liquid glue, which is not ideal for the task. If you put too much, it will locally dissolve the thin sheet resulting in a start-over-from-scratch situation. If you use too little, it evaporates before you have time to press the surfaces together. I start with one side, glueing the leading edge, then little by little working my way aft. The upper surface is convex so it doesn’t matter much if you miss a spot as the sheet will be stretched, but if you don’t glue everywhere on the concave underside, you might end up with airpockets - you can see examples of this on the photo above - I was sloppy. With linen-covered wings like this you can sort of get away with that though (maybe a superflous observation - I guess this method wouldn’t be useful for non-clothcovered wings anyway ). 

 

 

1 hour ago, pheonix said:

Excellent progress with very good details. I have never tried the core method of wing construction as I tend to use single sheet plastic.

 

P

Thanks - I’ve seen your wings and they all look the part. I have only tried that method for tailplanes, but only because I don’t have the patience to place all those strips on a full wing, and I find it difficult to sand one-part wings consistently (cores to be clad do not need to be nearly as pretty). 

 

[Torbjorn]

Small update.

 

Wings almost done, still need to finish the edges and cut off the ailerons. That however makes them fragile (esp. the trailing edges if I make them thin, which I intend to) and delicate to handle, so I’ll wait with that. Looking at this photo, the outboard edges are too fat and needs trimming too.

 

Chairs are in place, Douglas fits perfectly. The observer would need to straddle the pilot’s chair, but should be able to fit unless too stiff. Rather intimate and claustrophobic though. 

 

I made an instrument panel based on this photo: https://digitaltmuseum.se/021018816542/thulin-na-thulinavdelningen-pa-landskrona-museum

 

 

 

 

 

Soon the fun begins!

Edited October 25, 2022 by Torbjorn

[Col.]

Nice progress. If the pilot and observer were not good friends before they certainly would be after a flight. Or mortal enemies.

[Torbjorn]

I like to start with the most difficult task so that if I fail, I don’t hve to throw away something half finished. This time I had to wait since I needed to finish the fuselage first.  
 

I’m talking about the windscreen/skylight, which has a smooth form curved in several directions. It’s very prominent, rather unique and defining of the type, so it’s important to get it right. Due to its complicated forn I decided to mould the whole topside with clear plastic - the clear parts can the ”simply” be masked.

 

 

A male mould was made from round stock with the same diameter as the cowl mould to ensure an identical curvature, with a block of wood glued in place of the windscreen and sanded to shape. The pencil marks show the approximate location of the cockpit opening.

 

 

 

The first try was a complete failure. I got some plastic from a food container - it turned an opaque white upon heating 😩 

 

Guess I overheated it, or R-PET isn’t ideal. Or both.

 

Will have to do some research and steal the secrets of the vacform canopy alchemists.

 

Edited October 27, 2022 by Torbjorn

[pheonix]

It may be more expensive but try using 30 thou clear acetate. I moulded some canopies for a fellow modeller recently and was surprised how easily it moulded, especially when compared with white styrene which I usually use.

 

P

[Torbjorn]

On 10/27/2022 at 10:58 PM, pheonix said:

It may be more expensive but try using 30 thou clear acetate. I moulded some canopies for a fellow modeller recently and was surprised how easily it moulded, especially when compared with white styrene which I usually use.

 

P

 

Thanks for the tip. Local craft shop seems to have 10 and 15 thou, but I fear that may be too thin.  Will try the interwebs.

 

edit: had to source it from abroad, like basicly all other model supplies. This will be dormant as that parcel travels.

Edited October 29, 2022 by Torbjorn

[Torbjorn]

I got tired waiting so I got a bit side-tracked. 
 

Although type NA would be the final Thulin aircraft, and argueably the most advanced in terms of construction and performance, it was not, in my opinion, the most aesthetically pleasing of the lot. That price goes to the type it was based on, the N:

 

 

Rather smooth for 1917.

The N differed in the following:

-Wooden frame vs Metal tube skeleton in the NA

-Rounder fuselage - steamed and formed plywood all the way, while the NA had a lighter linen-clad aft section

- One-seater (still unknown why they crammed a poor observer into the NA)

-Aileron cables going to visible and exposed actuators in the upper wing just above the pilot

-110hk vs 150hk engine, made her considerably slower (160 km/h vs 215)

 

 

Only one prototype was built, so it coincidently fits in this GB! 

 

The rounded fuselage makes the built-up method ill-suited, so I’m trying my first all plunge-moulded fuselage.

 

The male mould was made from two pieces of balsa glued together to mark the centreline. First step, glue the drawing to the top and sand down the sides on the disc sander, then repeat with the side drawing (you can stretch is a few percent to account for curvature).

 

Balsa is really too soft for this, but it does go quick to form it. I had one dud (too large - I forgot to account for the plastic thickness! and figured starting over would be quicker than to evenly remove material). I sanded as much as I dared on the machine and finished with disposable nail files. Those are flexible which makes them suited for sanding rounded shapes out of soft wood.

 

 

Had 3-4 moulding failures before I found the right sheet thickness (0.8mm) and fogured out how not to fasten the mould. I did not want to separate the halves out of fear of damaging the soft wood, so I fastened the mould on a base with bluetack while moulding.

 

The mould looks really streamlined. Thulin did his phd in aerodynamics, and had a high- and low-speed wind tunnel for testing out prototypes - his early types were essentially copies of French aircraft, and the changes he did to them was usually aerodynamic in nature.

 

Anyway, I added a cockpit, entirely on conjecture. Although N still exists, it too hangs under a ceiling and I have not been able to find photos of the cockpit.

 

 

Edited November 14, 2022 by Torbjorn

[pheonix]

Two lovely fuselage halves. Congratulations on your first attempt to mould parts for a scratch build.

 

I used to use a hard balsa for moulding but my source gave out a long time ago so now I use basswood. It is soft enough to sand/file easily but hard enough to make a good solid male mould. I also use 30 thou card - thick enough to be rigid but not too thick to make heating the plastic to make it maleable too difficult. Having several failures before you get a satisfactory piece is not uncommon!

 

P

[Col.]

The N is certainly has a pleasing set of shapes to it and you've made a great start to modelling it  

[bigbadbadge]

Looks wonderful,  great work on the mould  and the fuselage sides look the part.  Cockpit details looking good too.

Great work 

Chris

[Courageous]

On 11/14/2022 at 5:25 PM, bigbadbadge said:

Looks wonderful,  great work on the mould  and the fuselage sides look the part.  Cockpit details looking good too.

 

Stuart