Effective rudder control in the Spitfire is a must. In the immortal words of Mary Ellis who flew more than 400 Spitfires and sadly passed away recently at the age of 101, the Spitfire was “a lady in the air, but a bitch on the ground”.
Anyone who has flown the Mk.IX Spitfire in DCS World can attest to this fact. It is only with very accurate rudder action that the beast can be tamed.
Thus we have spent the last two weeks redesigning the rudder pedal action. Originally this was a simple spring based system. We looked at incorporating cams but given the data on rudder forces in the Spit we wanted to do better. At rest the Spitfire rudder pedals move around freely but with some inertia, you are moving a fair bit of weight, cables and pulleys around in the real thing. We thus settled on a pulley system with elastic bungees. Not only did this give the correct feel of inertia, it also opened up new possibilities.
Force feedback is something only the bravest will attempt. All the models I have come across are hugely complex designs with stepper motors and a multitude of pulleys, belts and gears. With the use of a bungee, all that is needed is to stretch it to apply greater force. The stretching is also quite simple with a relatively cheap electric linear actuator. I had previously used one of these in the design of my trim system for my replica Fieseler Storch (70% scale) and they are available with installed potentiometer to provide precise feedback on their position.
So by incorporating a 200mm stroke 12V linear actuator into the design we have provided a very simple means of accurate force feedback on the rudders. There is fortunately precise data on the stick and rudder forces of the Spitfire from tests conducted during WWII. For the rudder pedals which move some 100mm either way, this amounts to 12lb or 54N at full deflection at full speed. By using a 10mm bungee which provides 46N at 50% stretch and adjusting the moments appropriately, we can achieve the exact force with the actuator at full retraction. Conversely, at full extension the pedal forces are minimal but should give satisfying clunks and inertia when waving them about.
DCS-BIOS will provide the speed reading which will be interpreted by one of the Arduino’s. This will send a signal through a motor controller to handle the 12V and around 3A required for the actuator.
After the fiasco with the Melexis sensors we have now incorporated the Bi-Tech 6127 rotary Hall Effect sensor. This comes in an easy to use potentiometer format and is preprogrammed for various angle ranges. In our case we have selected the 60 degree unit for the rudder. This gives a very nice full range given the rudder pedal’s 57 degree full deflection.
Next we start looking at what can be done for the elevator.