de Havilland Aeronatical Technical School T.K. 4 from 1937

[Timo Starkloff]

Hello everyone!

After about one year of research and half a year drawing, I'm finally at the point to start building the TK 4. Despite the 1/4 scale, the model itself will be relative small with about 150 cm of wing span. It is constructed from balsa and plywood, since that are my prefered materials.

It's an interesting plane from a time of great air races, although nearly forgotten. Since it was a students project, it's not one of the well known de Havilland planes. It flew first in 1937, took a promising part in the Kings Cup race but sadly crashed in autumn same year while preparing for a 100km record.

I got some help from Britain during the search for drawings and details. I come from South-West of Germany and I normally write only in German forums. Considering this rare plane, I think this project is interesting for an English forum, too.

Best regards, Timo

[Timo Starkloff]

Several weeks ago, I couldn't resist building a 1/72 version for the showcase. Fits perfectly to the Airfix Comet.

Timo

 

Edited By Timo Starkloff on 29/12/2015 10:40:14

[Bob Cotsford]

That's an interesting and unusual subject Timo, and a nice size at 1.5M. How do you intend powering it? There was a TK4 plan being listed years ago for control line - here

Did you find out what caused the prototype to crash?

[Timo Starkloff]

I found a picture and two articles about the crash, but not the reason:

**LINK**

**LINK**

Of course, the plane was ambitious and very small. But planes of the Formula 1 class of Reno Air Races fly until today in the same size and with not too different power.

I will try the Himax 4022-0510 and a 6s accumulator, probably 3000mAh depending on the takeoff weight and center of gravity. I have some 3S3000 from smaller planes which are suitable.

Edited By Timo Starkloff on 29/12/2015 11:31:16

Edited By Timo Starkloff on 29/12/2015 11:31:32

[Bob Cotsford]

To me, that cowling is crying out for a 90 size four stroke. I look forward to hearing how it goes.

[Timo Starkloff]

A 91 FS should also work. But this TK4 should be able to land on a relativ short landing field. I found a small club very near, but they are only allowed to fly electric models and they should be below 5000 grams.

For improved handling and flying characteristics, I made small changes compared to the original. Vertical and horizontal stabilizer are slightly increased, I install slotted flaps instead of split flaps and I'll use a tail wheel instead of a skid. A model with 150cm wing span and low drag is not easy to slow down and land without a flip over. Weight has to be low as possible and flaps have to help.

I start with wing and tail. My brother made me the plywood parts with his cnc. All ribs are glued to the lower and rear part of the wing covering.

[Timo Starkloff]

[mightypeesh]

Interesting project, lovely 1/72 scale too. Did you make it as a solid carved model? Keep the photo's flowing please!

Cheers, Simon

[Peter Miller]

Are you planning on usung washout on that wing?

[Timo Starkloff]

Thanks for the compliment, the 1/72 model is from soft plywood and much filler. After sanding it looked much better than expected.

Washout is 2.5°. I normally use 2° on standard warbird wings. But the TK 4 has a shorter outer wing, so it will get a little more washout.

I have some more detailed pictures from building. I make part of the plywood ribs of balsa for easier cutting out the flaps (first try). And I use just plain paper as a template for cutting out balsa ribs. Needs a good hand, but works fine for me.

[Colin Leighfield]

Congratulations Timo on a great and interesting choice. It looks potentially difficult but your small changes to tail areas and including wash-out may make all of the difference. I will follow this with great interest.

[Simon Chaddock]

Timo

Do you know if the original had washout?

That is a wonderful picture of the original under the DH Alnatross on the German site.

Look forward to the build.

[Timo Starkloff]

I had contact to the School and to someone who built a small model of the TK4 as a student in the fifties. But sadly no one was able to find the original drawings from 1937. So all I had was a good 3-view and many photos, which is enough for a good semi-scale model but not for a true scale one. It would have been interesting, to copy their way to build the fuselage. So my focus is to have a plane that clearly looks like the original, but is easy to build and fly. Changes are made as small as possible.

I don't know if the original had washout. But such wings either need washout or a change in airfoil from wing root to tip to improve stall characteristics.

I'm a bit further with the wing. I started placing all ribs on the lower balsa cover. Then the wing is fixed on the work bench with a underlayed balsa strip to get the correct washout. After placing the top longeron and the spar webbing, I let all parts dry.

[Timo Starkloff]

[Timo Starkloff]

After all reinforcements and parts for servo mounting are implemented, the rear section is covered with balsa. The front section is left open to install the main board for the landing gear. More will follow next year.

[Colin Leighfield]

You obviously know what you're doing Timo, this is looking very good.

[Timo Starkloff]

I thought about the construction the whole last year. If everything fits, it's like building a kit. Of course it's an airplane and many things can go wrong, so it's still exciting. But I made the experience that it is best if all problems are solved before building starts. These kind of planes with high wing loads should work right from the beginning.

Next topics are elevator and preparing the installation of the landing gear. Hopefully my brother will cut out the fuselage parts next week. Otherwise I need two evenings to saw them out manually...

I'll use two elevator servos. Easier to build than a linkage between both parts and it means higher redundancy.

Edited By Timo Starkloff on 01/01/2016 19:40:16

[Timo Starkloff]

Not much space for the retractable gear. It's height is only 20mm.

[Timo Starkloff]

Needles and pins. I use as much pins as possible and much wood glue. The glue dries and becomes very light. And every pin works a bit like rivet, since the glue wanders along the pin into the wood. And if wood is bent, it's better to keep it down uniformly.

[Timo Starkloff]

Rudder is finished, wing tips prepared and the wing itself completely covered with balsa. Tomorrow it should be dry for sanding.

[Timo Starkloff]

[john stones 1 - Moderator]

Good subject Timo and excellent building

John

[Timo Starkloff]

Thanks! Actually it's the same procedure every day: pulling out all needles and then placing them into the next parts. I'm really looking forward to the fuselage.

[Timo Starkloff]

Adding the leading edge.

It is built from two parts. The first is just 3mm balsa for easy sanding of the ribs. The actual and second is 5mm balsa and applied after the wing is covered with 1.5mm balsa.

The hole in the right wing is for the connector to the wing servos.

Edited By Timo Starkloff on 05/01/2016 19:42:24

[Timo Starkloff]

The two wings are connected with a small piece of plywood. Additional strength will come later from fiberglass.