Quote:
Originally Posted by Frank Lee
It's quite simple; you are assuming the duct has no drag. Well, it does. So you are now ADDING, yes ADDING surface area and thus more skin friction to the vehicle [...]
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'Duct drag' is a good point. It also seems to be something that came up on some of those other ducting conversations, and rightfully so. However, I think that is where many of the topics broke down. Personally, I think it's a big misunderstanding. Allow me to explain a little more about how I envision the ducting idea...
First off, I am 100% confident that there will be drag within the duct, that the drag will be significant, and that the drag will increase exponentially with speed. What I'm hypothesizing is that, up to a point, the drag within the tube/duct system will be less than the total drag of going around the whole car. Nature calculates this nicely and the proof would be whether or not air would actually take the path of the tube. If it does, then it proves that it is the path of least resistance, and has increased efficiency... if not, then it just doesn't work. I'm not claiming that there will be zero airflow around the outside of the vehicle (that it would all go through the tube). Nature will do the calculations and go through the path of least resistance, which would lead to air moving both through (hopefully) and around the vehicle.
The energy saved can be calculated easily, as far as I can tell. Take the vehicle efficiency (easier said than done... lol, but can be approximated), measure the airflow through the tube (I just happened to do professional commercial HVAC systems testing while at college), then use a lil math to calculate the energy it would use (in fuel) to generate that multiplied by the inverse of whatever the efficiency factor is. Boom, there is the exact savings (at that speed). Then, just take readings at several speeds (and maybe some more data, like temp, elevation, time of day, etc.) and do a regression analysis. Then boom, a nice little equation that gives savings at any speed (or given variable), to be used to plot long-term savings, or whatever you like.
Quote:
Originally Posted by Frank Lee
[...] while a top chop REDUCES surface area, skin friction, and more than likely, form drag.
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I would like to clarify something... I have not (and don't intend to) attack the idea that chopping reduces drag and increases fuel efficiency. In fact, I'm confident that that concept works just as you (and others) say. I take back whatever I said that made you think that
