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Preface | General description | Housing

How I build my own cockpit ?

We just started a new year. In November 1998 I started gathering information of the DC-3 with the idea on building a cockpit. It is hard to believe time went by so fast. In the mean time we constructed already a lot of things, but there is still a long way to go. I didn't yet think on giving it up, at the contrary. The fire is burning like never before. Although we encountered some hard times and seemed to be stuck. Like the story of the radio stack. On this part we have spend already a lot of time and effort. we had the necessary set backs of electronic parts that wont work, materials who couldn't be found so we had to make them ourselves. For over six months we were looking in the wrong direction, we made a lot of test prints and bought the electronics for it in vain. But finally the light is beginning to shine and the end of the tunnel seems to be nearing. The joy of the victory can't be described when it finally comes together. This is the drive to go on. The story of the radio stack will be divided in to three articles. The first part will clarify the general features of the radio and the housing and inside works. The second part will tackle the input to the computer. The last part will describe the output from the computer to the 7 segment displays. This last part hasn't been realised yet, but all looks fine, it is just a matter of time and sandwiches.
Have fun.


Radio stack in general:

To be able to let the mouse and keyboard disappear completely out of the cockpit, this has always been our objective. Therefore we obviously need a radio stack to set all the necessary frequencies for the COM1, 2 and NAV1,2 as well as for the ADF(automatic direction finder). A DME (Distance measuring equipment) would also be welcome to find the distance to a station and a XPDR (transponder) to put us on the radar. The last feature, it would be nice to have a autopilot for the very long flights. Although a DC-3 never really had a autopilot but only the predecessor called a Sperry-Pilot, I decided to put one in anyway because this cockpit is adapted with modern avionics. You could say I made a new upgrade for the DC-3.
As basic model for the radio stack I have chosen for the Bendix/King.
The following types are included in the radio stack.

KN62 A
KT75 C
-  Digital ADF
-  DME system
-  Transponder
-  Auto Flight Control system.

All the different receivers and transmitters are included in 1 radio stack and won't be build separately. This would be much to difficult because of the small size of the real instruments, the mechanical and electronic parts would never fit in such a small housing. Besides there will be electronic parts who have multiple functions for several instruments.
A small review of the functions of the different instruments.

COM/NAV KX  165 TS0 :

20 Displays :

5 displays COM frequency Use
5 displays COM frequency Standby
5 displays NAV frequency Use
5 displays NAV freq Standby or 3 displays to indicate the radial

4 Selection buttons: 1 Selection button for the whole numbers COM
1 Selection button for the fraction COM
1 Selection button for the whole numbers NAV
1 Selection button for the fraction NAV
2 Swap pushbuttons: To change the Standby and Use frequency for NAV and COM
2 Ident pushbuttons.  

Digital ADF KR87 TSO :

9 Displays: 5 displays for the ADF frequency
4 displays for the Flight timer/ Elapsed time
Power/volume switch: ON or OFF/VOL
Frequency selection buttons 1 selection button for the tuning of 1’ en 10’
1 selection button for the tuning of 100’ en 1000’
until a frequency of 1799
5 Selection buttons: ADF (Automatic Direction Finder)
BFO (Beat frequency oscillator)
FRQ (Frequency) not applicable
FLT/ET (Flight timer/ Elapsed Timer)
SET/RST (Set/Reset)

DME  KN62 A:

8 displays with three possibilities:  

Frequency mode:

the distance in NM is displayed along with the selected frequency

3 displays  for distance in NM.
5 displays for NAV freq of your choose.

GS/T mode:

Ground speed.  The distance in NM is displayed or ground speed and time-to station of a frequency of your choose.

3 displays distance in NM
3 displays ground speed
2 displays minutes to station

RMT mode:

Remote mode.  The DME takes over the frequency selected on the NAV 1 radio

3 displays distance in NM
3 displays ground speed
2 displays minutes to station
On/off switch:
3 Position function switch: for FRQ, GS/T, RMT
2 Frequency selection buttons: 1 selection button for the whole numbers NAV.
1 selection button for the fraction NAV.

Transponder KT75 C:

7 Displays: 3 displays for altitude.
4 displays for Xpdr.
Selection switches: OFF: power off.
SBY: (standby) transponder is on but doesn't transmit.
TST : (test) internal testing, not transmitting.
ON : Transponder is transmitting but gives no altitude information.
ALT : Gives altitude.
IDENT : Is pushed in when ATC ask for "Ident" or "Squawk ident" of the plane.
VFR : sets the pre installed VFR code.
CLR : clears the identification code.
0 to 7: to set the transponder code.


Automatic Flight Control System KFC 225:

5 Display: 5 displays for altitude or 3 displays for vertical speed.
Selection buttons: YD
yaw damper.
Autopilot engage/disengage button.
Flight director.
Navigation mode selector.
Back course approach.
Altitude hold.
vertical trim buttons.
altitude arm.
Vertical speed hold mode.
Rotary switch: Pre instal lation for altitude.

Like you can see it is quite a lot. A whole range of selection and display possibilities that is not available on the FS radio stack. So it will be quite a job to make all the functions work on this radio stack if possible.

house1 house2


The housing:

For the housing I choose for a acrylic plate of 4mm. Because first of all it is a electrical isolator, what is very important because it will house a lot of high sensitive electronic equipment. The front panel will be made out of a 2 mm white acrylic plate and a 4mm acrylic plate. So we have a standard thickness of 6 mm the same as in the real planes. The white acrylic plate will also diffuse the internal light. The measurements will be 300 mm x 334 mm x 138mm (l x b x h).
Why so big you will think. Because of the amount of print boards, cables, rotary switches and gears for the double selection buttons we need a lot of space to put it all in.
The displays will be covered from the outside with a thin 1 mm transparent acrylic plate to protect the them from damage.


To change the frequencies, a Bendix/King uses double rotating selection buttons. This means you have one small selection button on top and a bigger button at the bottom. All of this is positioned on one axle. When you turn them clockwise the numbers will increase and vice versa.
To make this work we need two rotary encoders, one who's fixed on the center axis and a second who will be connected via a tube and two gears to a second axle. The first problem I encountered was to find gears. I looked in the yellow pages for all kinds of suppliers. You would say an easy job. After some phone calls I found some who could make them for me. But after hearing the prices. Luckily I was sitting on a chair otherwise I would have fallen down. There was only one possibility left, this was to make them myself. I contacted a firm of polyester resin and after a small calculation I very quickly found out I could make them myself for only 1/10 of the price. So the decision was very quickly made. After making a flexible silicone rubber mould from a existing gear of a old printer. I reproduced the gears with a two component polyester. After hardening out well we centered the ruff gears with a lathe and drilled in a center hole. In the shaft of the gear we drilled a hole and taped in thread to fix the gear to the axle with a set screw. The last thing to do was to turn the selection buttons from aluminium with the lathe.
The hardest part was to make the holes in to the three acrylic plates and the front plate. The holes have to be in the right distance from each other otherwise the gears wont turn properly. To accomplish this I made a mould out of an iron plate from 1 cm, I drilled in all the holes and tested it. Then I fixed the mould on to the front panel and the three acrylic panels, after that I drilled all the holes. This is the only way to make sure all the holes are in the right position. After cutting the rest of the acrylic side panels. I put everything together, so the mechanical part of the radio stack is finished. Now we can start thinking of the electronic heart.
Read more in article 2 and 3.


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© Verley Jan 2007-2017 original text from 2003 translation Jan Verley