Class a motorhomes aerodynamics

[j-c-c]

I can't make that leap.
However, under "features" I only accept outright its cooler/more airflow to the axles/tires. The pic included of an "aero' in the wet shows IMO more spray, and they also mention what a regular flap adds in drag but not what the aero flap adds, it changes airflow almost randomly, and that does not seem to be a sound method of reducing drag.
I rate the sales pitch one notch above bogus.

[freebeard]

That would be an example of a sem-permeable membrane perforated panel, AKA 'speed holes'.

[j-c-c]

Meaning it changes airflow but changes it less than a solid mudflap?
Its IMO nearly defeating the original purpose regarding reducing spray, the best solution for that goal is a whisker style tire side mudflap or say 1/2"? vertical channels/groves, with no claim of reduced drag or cooling. The aero style does reduce those prone to draft semis in the rain though I suspect..

[freebeard]

Meaning ...?

Not a high momentum mudflap. The various types need A-B testing.

[aerohead]

Originally Posted by sregord

I know I need to build a scale model. It may convince me that no extension is doable. I get back to my shop next month.
No argument that its a long ways back there from the drivers seat with even move wag, but...
When I see things like this quite often, hanging off the back of RVs
https://letsgoaero.com/blackbox-slid...losed-carrier/
It seems that +32" suspended a foot from the RV..(=44") is an exceptable extension... attach it high enough to provide the 10-degree SAE 'departure' angle. I'm just putting on a "roof" the shape of The Holy Template.

You'd be going down the same road as with the 'THINK FLIGHT' Subaru Imprezza experiment. He got the Subie from Cd 0.29, down below Cd 0.18.
Side gust sensitivity would be an unknown quantity, so you'd want to start out with conservative driving speeds until your confidence builds up.
Modern accelerometer sensor technology, software, and actuators would be capable of deploying aerodynamic countermeasures nearly instantly, to compensate for yaw-moments; however, that's beyond my expertise.

[sregord]

Originally Posted by aerohead

You'd be going down the same road as with the 'THINK FLIGHT' Subaru Imprezza experiment. He got the Subie from Cd 0.29, down below Cd 0.18.
Side gust sensitivity would be an unknown quantity, so you'd want to start out with conservative driving speeds until your confidence builds up.

Side gusts on a 4' long addition to a 32' - 18,000# Moby was not something I would've had on my radar.
Was there a noticeable side-wind redirect with your boat-tail trailer? Is there less opportunity/worry of side gust sensitivity because of wheels on the ground?

[aerohead]

Originally Posted by sregord

Side gusts on a 4' long addition to a 32' - 18,000# Moby was not something I would've had on my radar.
Was there a noticeable side-wind redirect with your boat-tail trailer? Is there less opportunity/worry of side gust sensitivity because of wheels on the ground?

* So far, I've never experienced any stability issues with any of the trailers, but that's in the context to two of them at the old 55-MPH National Speed Limit the USA had for twenty years, and only Viking has seen duty at up to 65-mph ( I was cleared by the USFRA to pull her at Bonneville, but after running Spirit there in 2014, I new it would be a waste of time; as I'd never be able get beyond the one-mile course ).
* The aerodynamic 'mass' ahead of the trailer axle, producing any yaw moment is transferred to the ball hitch.
* The aerodynamic 'mass' rear of the axle creates an impotent 'weathervane', as it's cross-section continues to decrease, the further it projects to the rear, and the radical tumblehome and upper radii don't really allow for much of a yawing force. The air just bleeds over the top. The full belly pan doesn't allow for anything to grab hold of the underbody. Any crosswind gust experiences a 'wing section' of such tiny aspect ratio as to be laughable, as far as generating any meaningful lift. The streamlining is generating such pressure recovery that, at the trailing edge, the static pressure is nearly equal to that at the forward stagnation point. We lose pressure only equal to what kinetic energy is lost to the turbulent boundary-layer.

[freebeard]

Maybe a flying tail with micro-controller active aero?

[sregord]

Originally Posted by aerohead

* The aerodynamic 'mass' ahead of the trailer axle, producing any yaw moment is transferred to the ball hitch.
* The aerodynamic 'mass' rear of the axle creates an impotent 'weathervane', as it's cross-section continues to decrease, the further it projects to the rear, and the radical tumblehome and upper radii don't really allow for much of a yawing force.

Ah... wheels on the ground.
So an extended (Mair 1.9 diameter) boattail should be a trailer...a la

If it only starts the flow in the right direction (<3-4')..a la Ahmed

[sregord]

Greetings
Sorry I dropped the ball here.
Pesky prostate distraction has had me surfing elsewhere.
...and Moby has been on the CL for most of the summer.

I was curious what you all thought about something like this as a option for an undertray. As mentioned earlier I have several "billboard covers" ...really tough "fabric"... with an appropriate support/frame, of course.

https://www.youtube.com/watch?v=tm1Kn_X0i8Y