Login required to started new threads

Login required to post replies

Prev Next
Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [NickD1] [ In reply to ]
Quote | Reply
NickD1 wrote:
I suspect most people haven't gone for that variant of the Compton Challenge because the most obvious way to check a method for determining CdA is to change the CdA and see what can be detected (I‘m assuming the majority of people that are using your method are doing it to get a CdA estimate).
Yeah, I'm sure that's true. It seems backwards to measure precision in CdA by looking at precision in measurement of mass -- but in all these cases we're just measuring differences in drag. In fact, if we had a truly accurate way to measure height you could measure how small of a difference in elevation you could detect, so an alternative I'd been thinking of was building a little ramp of known height, maybe 15 cm high, and rolling over that. If the data and method estimated the ramp as X cm, that would be a way to assess precision. But once again you run into the problem that people think they should be altering CdA, not ramp height. So I haven't done that experiment. But I'm reasonably sure it'd work.
Quote Reply
Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [RChung] [ In reply to ]
Quote | Reply
How does mass affect drag? Through inertia and gravity and friction but not shape of a body. What is gained from altering mass?
Last edited by: BergHugi: Aug 21, 20 14:33
Quote Reply
Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [BergHugi] [ In reply to ]
Quote | Reply
BergHugi wrote:
How does mass affect drag? Through inertia and gravity and friction but not shape of a body. What is gained from altering mass?

You're altering mass by a known amount without changing the shape of the body so the drag should change by a known amount. So we measure the amount it does change and compare it to the amount it should change.
Quote Reply
Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [RChung] [ In reply to ]
Quote | Reply
And if you alter the mass by the amount 0 you actually know how drag should change and compare it to the amount drag does change.

There are easier ways to measure mass, just compare it with a known mass.
Quote Reply
Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [RChung] [ In reply to ]
Quote | Reply
Not replying to anything in this thread in particular but just want to check a few things before I start my own testing for the first time ever. I have a lot of things I want to try.

1. How important is a separate speed sensor vs GPS? Don't currently have one but don't mind buying one if it's going to drastically improve results.
2. I know the rule is absolutely no braking and hold position, but does that also apply to the turnaround if doing a half-pipe? If I'm testing in aero position, do I need to find a course with a spot wide enough to turn around in aero or better yet, a loop? Or is the turn around slow enough that it shouldn't affect the data.
3. Is there a minimum elevation gain/loss required for the course? I can think of a fairly nice stretch of road but the dips are very minimal.

Thanks all.

Benjamin Deal - Professional - Instagram - TriRig
Deals on Wheels - Race reports, pictures, sponsors, and more!
Most recent blog post: Takeaways from spectating Kona 2019
Most recent video: $20 photochromic cycling glasses review
Quote Reply
Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [realbdeal] [ In reply to ]
Quote | Reply
realbdeal wrote:
Not replying to anything in this thread in particular but just want to check a few things before I start my own testing for the first time ever. I have a lot of things I want to try.

1. How important is a separate speed sensor vs GPS? Don't currently have one but don't mind buying one if it's going to drastically improve results.
Depends on how good the GPS signal is. I prefer test venues that have some shelter from trees to dissipate the wind, but trees can block the GPS signal. If your test venue is a straight road, the signal is less important than if there's a curve (especially if the tree cover is right at the point where the curve is located). In addition, some older head units are smaller, so the size of the GPS antenna is smaller, so the positioning isn't quite as good. From a practical perspective, I'd do a quick non-critical ride on the course and come back and look at the GPS trace and especially the speed changes from second to second. If the trace is good and the speed changes look smooth rather than jumpy, you might be okay without a dedicated wheel sensor. If not, you're probably going to have to get one if you want acceptable precision.

Quote:
2. I know the rule is absolutely no braking and hold position, but does that also apply to the turnaround if doing a half-pipe? If I'm testing in aero position, do I need to find a course with a spot wide enough to turn around in aero or better yet, a loop? Or is the turn around slow enough that it shouldn't affect the data.
Sometimes you have no other choice than to use brakes (not just for the turnaround, but for cars or dogs or other obstacles). The #1 rule is don't get hit, and don't hit anyone else. That's also rules 2 and 3. That said, I've used test venues where I had to brake at the turnaround but I'm sorta used to snipping out that part of the data and stitching the parts back together. That might be too advanced for most people, at least with current tools. I would say that *if* you are going to use the brakes, don't feather them, hit them hard so that it's clear where you did use them. What you don't want is to wonder where you used the brakes.


Quote:
3. Is there a minimum elevation gain/loss required for the course? I can think of a fairly nice stretch of road but the dips are very minimal.
Not really. People do this on velodromes, where the change in elevation is maybe a few inches. The real reason why a half pipe course is handy isn't because the elevation change is necessary, it's because it's handy to get a wide range of speeds and the climb at the ends slows you down enough so that you don't have to use the brakes (much) at each end.
Quote Reply
Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [RChung] [ In reply to ]
Quote | Reply
Appreciate it Robert. Thank you.

Last question because I couldn't find a solid answer anywhere, should the start of each run be rolling or from a standstill?

I realized the best thing for me to do will just be go out there and give it attemps and start learning, but I just want to make sure I'm not making any obvious mistakes.

Benjamin Deal - Professional - Instagram - TriRig
Deals on Wheels - Race reports, pictures, sponsors, and more!
Most recent blog post: Takeaways from spectating Kona 2019
Most recent video: $20 photochromic cycling glasses review
Quote Reply
Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [realbdeal] [ In reply to ]
Quote | Reply
realbdeal wrote:
should the start of each run be rolling or from a standstill?


It doesn't matter all that much, but I usually do rolling so I can already be locked into position when I hit the lap button rather than fiddle around getting into position. For a half-pipe course, Tom A. has talked about hitting the lap button a few seconds before the lap "start" as he approaches the first turnaround, and he hits the lap button again a few seconds after the crest of the last turnaround. He doesn't hit the lap button during the test so he can stay in position all the test without moving his hands. I do the same, even when the course isn't a half-pipe: I hit the lap button once before the point where I'm going to start, and then after the very end. Usually it's pretty easy to spot the laps so you don't have to mark them explicitly with the button. Hitting the button before the "official" start of the lap and then after the end gives you two extra well-defined peaks to line up.

An oddity that I've had is that the data from my very first lap is often noisier than subsequent laps. I used to worry about this a lot and tried to track down why that was but, in the end, I decided it was more practical just to plan on doing an extra lap at the start (for example, if I planned on 3 laps for each test, I'd do 4 laps instead for the very first one). Then, if the data are noisy, I just toss that first lap. This is one of the reasons why I try not to make my laps 2 or 3 miles long; shorter laps let you do more of them, and if you have to toss one lap, not only for noisiness but also for a passing car or a chasing dog, it's not so painful.
Quote Reply
Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [realbdeal] [ In reply to ]
Quote | Reply
Question for the group:

For half pipe testing can I get out of aero for the turnarounds? So few course options around me but if I'm allowed to do that for a tighter turn around I think I have a spot.

Benjamin Deal - Professional - Instagram - TriRig
Deals on Wheels - Race reports, pictures, sponsors, and more!
Most recent blog post: Takeaways from spectating Kona 2019
Most recent video: $20 photochromic cycling glasses review
Quote Reply
Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [realbdeal] [ In reply to ]
Quote | Reply
realbdeal wrote:
Question for the group:

For half pipe testing can I get out of aero for the turnarounds? So few course options around me but if I'm allowed to do that for a tighter turn around I think I have a spot.

That's what I do. Since you're travelling slowly (or should be) at the turnarounds on a "half-pipe" course, the effects on the total run of getting out of aero are extremely small, so being able to quickly sit up, look around, and make sure your turn is safe to do is what is paramount.

http://bikeblather.blogspot.com/
Quote Reply
Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [realbdeal] [ In reply to ]
Quote | Reply
I concur with Tom A.... slow down, sit up, look behind, then turn.
Quote Reply
Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [RChung] [ In reply to ]
Quote | Reply
I have a course that is a straight road with a cul-de-sac/lollipop at one end. It doesn't have enough elevation change to really slow down using only gravity so I coast for a bit and then I sometimes turn aggressively if I haven't slowed as much as anticipated at the lollipop. It seems that the aggressive turn is scrubbing off quite a bit of speed almost as if I were lightly applying the brakes through the corner. When I thought about the original set of equations in the presentation, there isn't anything to account for cornering forces or lateral acceleration. Are there any general rules about how much "cornering" is too much or is it really important to limit any hard cornering?
Quote Reply
Re: Platypus Thread: Aero Virtual Elevation Testing Protocol [grumpier.mike] [ In reply to ]
Quote | Reply
You can generally see the hard corners. I have a venue that is sort of like what you're describing, with a wider turnaround at one end and a narrow turnaround at the other. I coast at a softpedal as I approach, then often have to feather my brakes. I try to do that in the same spot each time and then either snip or "re-tare" the VE profile at that point. It's kind of a pain so I don't do that in Aerolab and instead use my own analytical routines.
Quote Reply

Prev Next