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Ford Ranger 11 degree Kamm-cap
Hello,
I was inspired to build an 11 degree Kamm cap last year and built one this spring. I recently gave it a highway test and achieved 12.087km/L with a tonneau cover and 13.19km/L with the cap over the same 100km stretch of highway and identical windless conditions, for an efficiency increase of about 9% at a 100km/h speed.
Tonneau 6.718L/81.2km no wind, included climbing 500' Niagara escarpment on 401 in Ontario.
Kamm 8.512L/112.3km. Same as before + traversed two large river valleys.
In Ontario Canada we have "up to" 10% ethanol in fuel which worst case has 96.7% of the energy content of pure gasoline. I'm assuming my fuel was identical on both test runs. On the test run with the cap I filled up later and included two large river-valley hills. I think more fuel is lost uphill than is saved downhill. Anyhow, I think 9% is believable. I have a fisheye backup camera wired to the ignition.
For ice and snow I designed the closure to drain water out, and although it is not visible, I also have a flap at the cab end of the cap which drapes below the top of the box and ensures no water comes in (standard problem with all caps I have seen). The trailing overhang keeps the camera and caplock dry and extends the tail somewhat. The cap is solid but not beautiful: there are numerous design and construction improvements I would make on another one.
I look forward to the day when truck cap companies catch up and make these commercially.
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