Drag and rolling resistance formula

Turtle n Peeps wrote:
The problem with these formulas is you don't know what numbers to plug into it.

Here is a real example of what little change can make a big change in the numbers.
Back in the day I used to work on airplanes. I guy came into my buddies shop and wanted to change all the button head rivets on his plane to flush mount rivets. It was a big job but my buddy did it. The plane picked up 7 or 8 MPH. I would never have believed such a little change could make such a big difference in drag.

My point is, you can plug in any numbers you want on the front end and the program will spit out any numbers you want on the other end. Cool to play with but of no real use unless you have a wind tunnel at your disposal.

This kind of thing is not uncommon. For people that own sailboats that race real competitively, they will use 3-4' long hand sanders to make sure the bottom is really smooth. Along with remove the typical thru hull fitting which is a mushroom with 1/4-1/2" off the hull to a flush thru hull. Take and figure out the shape of the keel, again fair it to the correct shape with molds....gain can be upwards of .2-.5 knots of boat speed. When you figure some boats have a max speed of 5-6 knots, that is a 5-10% gain on a competitor. Enough to put you from middle to the front of a pack!Or back to middle, then with a few more improvements, you are at the front.

I have some charts that show HP needed to move a given load, but, notes say, the HP needed can vary by plus minus 30% based on many factors. Some include tire type, design, rubber of tires, road type, aerodynamics of the rig itself. The info these charts come from, have a formula that has upwards of 15 variables to add or subtract HP needed from a given rig or load.

At the end of the day, these things can be fun to play with, and for one to realize, you can get better mpg with an 18K load, vs a 15K load, as it is pulling my bobcat trailer vs my old TT. The bobcat trailer weighs 3K lbs more, but due to a lower aerodynamic, it got better mpg being pulled than the travel trailer. Many have commented that going from a TT to a 5w that weighs more, gained mpg too, do to a better aerodynamics of the setup.

Marty