lightheir wrote:

That’s super interesting regarding the lack of importance of tail position. You should start a new thread on it as it’s that counterintuitive

I was bored this morning, speculating is no fun and I don't have a wind tunnel :-)

So, this morning I went out and did 3x out&back. Each out&back is 11.4km (5.7 each way). Lower than usual traffic, maybe 10 per out.

In Green is the profile of the terrain. Rolling hills
In Blue is the wind, about 1km/h. The white is the average for the out or the back so you can clearly see the head/tail.

The bars show the CDA for the out & back. First one .248, then .248, then .246. Not bad.

Now. During the 2nd O&B I would do, 20seconds head down which for me raises the tail a bit, 10 seconds look up which flattens my tail. No difference in CDA.


So zoom into test 2 and 3, and I turn on the raw signal from an IMU we put in the helmet (in Grey). This way you see the difference between my intentional moving of the head and my natural head movement. I was not trying hard to hold my head

Plotting and explaining "instantaneous CDA" would bring us down a rabbit hole, so I plot Virtual elevation in red, setting it to .248. If the moving of the head produced a change in CDA we would see elevation step up or step down every time I did it. The "intentional" head movement O&B tracks the same as the "natural" one.

You see the VE rise on the turn arounds, as well as the helmet IMU as I sit up. VE re-syncs to elevation at test start.



In my case, flattening the tail does slightly raise my front area (we measured that) as DD suggest. Next time I get bored I'll show that :-)