I use this to help dirt and grime come off my cars (used it when I raced motocross and it works there as well)

Fill a squirt bottle with:
1/8 simple green or a detergent type cleaner
1/8 rain-x
3/4 water (preferably distilled)

You can vary the detergent/rain-x level but if you get too much it will foam up and actually leave a soapy haze.

Spray a decent coating on the plane BEFORE YOU FLY. Watch those electronics! Let it air dry.

You will be suprised how easily the grime comes off at the end of the day. The Rain-x makes liquids want to roll off the surfaces and the detergent keeps mud on RC off-road cars from getting a good seat.