Would this test set-up be informative?

[freebeard]

As always. It got a better reception than last time.

[j-c-c]

Originally Posted by Piotrsko

In freebeards defense, he was spitballing the solution he presented

I see no need to defend another, and I totally mentioned Freebeard's suggestion had merit.

Besides, I thought this whole forum was nothing but a spitballing session. Was I wrong?

But I do try and not get hit.

[freebeard]

What radius would obviate the 'adverse aero yaw and other forces'? 100ft is an industry standard. A quarter mile would be possible on a salt or dirt flat.

Also high speed drones change things. 40MPH used to be a stretch.

[j-c-c]

I have no idea, but not to lose sight of the filming problem of using a drone unable to keep pace with a straight-line high speed tufted vehicle, using two different radii for the vehicle and the drone IMO helps to alleviate that potential speed differential issue, but adds the unknown aero yaw factor.

The suggested 1/4+ mile radius would likely alleviate the yaw issue within test limits, but the drone camera shot/quality/resolution at the needed reduced radius with conventional drones would rather be suspect.

[aerohead]

Our vehicles are at super-critical Reynolds number by 20-mph ( 32.2-km/h ). That's all a drone would have to do in order to 'observe' tufts or smoke.

[j-c-c]

Originally Posted by aerohead

Our vehicles are at super-critical Reynolds number by 20-mph ( 32.2-km/h ). That's all a drone would have to do in order to 'observe' tufts or smoke.

Then why are most tuff tests at multiple speeds faster on the road and/or in a tunnel?

It's IMO a lot easier to securely fasten a camera for 20? mph tests than messing with a drone and nearby traffic.

[freebeard]

Signal to noise. Without still air, crosswinds are amplified.

Traffic.

[j-c-c]

With tuff testing we only need effectively a brief snapshot of the tuffs to gain insight, the problem is with a drone, straight-line testing on the open road, it only takes one wayward drone encounter with another vehicle to at the minimum ruin one or more's whole day, and still outdoor air testing is possible. "Crosswinds" on a circular skid pad are a 100% given because of yaw effects, albeit at least consistent when in still air, and reduceable by enlarging the testing radius.
All of the above is overcomable, and circling back to testing it only needs to be at 20+ mph as claimed?

[Piotrsko]

Well to shoot that down: disregards the reynolds theory particularly for critical and transition speeds where stuff can be turbulent, laminar, or "we dontknow" which will affect flow and subsequently drag.

The only scenerio I see with a cross traffic is being high enough to avoid the disruption a high profile vehicle moving at speed makes to the local area. Could tumble a 'quad. Now you get into focus and adequate resolution.

[aerohead]

Originally Posted by j-c-c

Then why are most tuff tests at multiple speeds faster on the road and/or in a tunnel?

It's IMO a lot easier to securely fasten a camera for 20? mph tests than messing with a drone and nearby traffic.

The Cd will be 'fixed' at around 20-mph.
A laminar boundary layer becomes unstable at Rn 500,000.
Turbulent boundary layer is firmly established by Rn 1,000,000.
The Cd 0.495 VW Beetle, reported by Hucho/ Hoerner, Figure 4.119, Page-200, Hucho, 2nd-Edition, presents the VW at Rn 11,000,000, which is associated with 85-mph ( 137 km/h )
The Beetle achieves supercritical Rn at 7.738-mph ( 32.2-km/h ).
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Higher tunnel and CFD velocities are associated with pitch, yaw, and roll moment magnitude, and the lift and lift coefficients for each axle, all of which come into effect at higher speed. Overkill for Cd measurement.
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Everyone here at the Aero Forum would benefit from knowing how to calculate Reynolds number, and why it exists.
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A Go-Pro at 20-mph is just fine! Just practice situational awareness when you're testing. Calm conditions away from traffic is your friend.