by angib » Thu Sep 28, 2006 11:47 am
Sorry, Arne, I read this late at night and forgot to answer the next day.
Aerodynamics of road vehicles is a tricky subject - I know just enough to know that I know little. So, with that caveat.....
I don't think the Airliner would be any worse than a conventional teardrop of the same size and it may be better (lower drag).
A few, limited aero thoughts on teardrops and similar-sized trailers:
- A teardrop sits (wholly or partly) in the wake of the tow vehicle. Design features suitable for cars/trucks may not be at all relevant to teardrops. The 'best' design of a teardrop will only be best for one particular tow vehicle.
- Drag is made up of cross-sectional area (roughly, width x height) times drag coefficient. Getting a good drag coefficient isn't easy, so reducing the cross-sectional area is the easiest way to cut drag.
- Even more important than overall cross-sectional area of the trailer is any cross-sectional area that sticks out past the tow vehicle - eliminate this if at all possible. This includes area sticking below the bottom of the tow vehicle - do not lower a teardrop if its bottom will then be below the bottom of a truck towing it. Small trailer wheels/tires will have less drag than large trailer wheels/tires - don't fit wheels any larger than your ego requires...... If you can make your trailer fit 3-6" inside the tow vehicle's cross-section (top, bottom and both sides), that will probably be even better than being the same width/height, etc.
- Length is free - a longer trailer won't have any more drag than a shorter one (at least to a first order of magnitude). However, it will be heavier!
- The traditional teardrop shape is simply styling. It is not a low drag shape, either as a trailer or as a solo vehicle. The rounded top front may do some good if the tow vehicle is fairly low, but that sloping back end is absolutely useless at cutting drag - it is there to look racy, according to 1930s fashion.
Lecture over - there will be a test on this tomorrow.
Andrew