World war one aeroplanes had the wheels fixed in place with a split pin across the end of the axle,to reproduce this feature on your model then is easy,on the axle slip on a piece of brass tube which extends just proud of the end of the axle,drill a small hole at the end to take a split pin of required size,next halfway down the brass tube file a small 'v' and slip the tube back on,flood the 'v' with some solder to lock the tube in place on the axle,file smooth,slip the wheel back in place and place a washer then insert the split pin to secure the wheel.