Class a motorhomes aerodynamics

[freebeard]

...or is one step (or diffuser) behind the I-beam acceptable?

Properly sized and shaped, it could become a Coanda nozzle that energizes and speeds up the underbody air flow (in whole or in part[s]). This may or may not be the Meredith effect, but it's blown, hot air when compared.

Some sources suggest a beveled step instead of curve (abaft the air dam or in a venturi).

[sregord]

A or B



C or D

Coandă effect is an interesting tool

[j-c-c]

Definitely D

[freebeard]

Thanks for asking. I thought about a sketch, flatbed scanner and USB transfer; and I overcame the inertia to finally install the GIMP on this machine.



In front, the stepped plate overhangs the stagnation point for downforce instead of an air dam. The step accelerates the underbody airflow to lower the pressure.

This might be broadly spread over a flat underbody, or channeled into a central jet. See the cowmeat[IIRC] Civic.



The engine air exhaust depends on the shape of the firewall (and front radiator. ) It's a good place to control the airflow through the compartment and/or radiator.



Emphasis on sealed ductwork.

[freebeard]

I see from Permalink #16, that the victim is a '02 Rexhall Aerbus XL3100. In that case an intake snorkel is unlikely, but the duct to the radiator could be offset and have two 90 degree bends.

[sregord]

Originally Posted by freebeard

I see from Permalink #16, that the victim is a '02 Rexhall Aerbus XL3100. In that case an intake snorkel is unlikely, but the duct to the radiator could be offset and have two 90 degree bends.

Thank you all,

Actually, I can see the possibility of your attachments




If the frame of the radiator was extended/sealed to the sides of the inner body, mostly below the MH floor, in front of the front wheels.
The rear of the engine compartment would be more difficult to fashion/shape... to get below/around the transmission.

[aerohead]

Originally Posted by sregord

Hangers & sturdy L-sections... Do you use aluminum or galvanized steel?

What is there is steel storage boxes(33" deep) supported by light weight steel square tube to the truck frame and... the perimeter frame(of the MH) which is heavier angle-iron & is supported vertically & gusseted between outer hatches.
Attachment 34758
The other side has the cat, LP tank & muffler. no steel storage boxes supported by light weight steel square tube. Actually the "hole" behind the rearend... between the fuel tank & rear bumper looks sorta like a parachute.

The airdam, or leading pan from bumper... could be as low as the I-beam
Lowering the whole bellypan to the I-beam(front susp sitting on wood blocks) height would be the goal- correct? or is one step (or diffuser) behind the I-beam acceptable?
Attachment 34757
Perhaps a chin airdam & side skirts would be more in order?

The BoB is a fun spot. The RedDog across the street & north is a usual hangout, also.

* Years ago, I scored a fair amount of aluminum angle section in Waxahachie, TX. Many recycling centers no longer allow any material to be recovered and purchased, and this may be the 'end' of accessing used structural light metal for me.
* Working with steel, the added weight difference vs aluminum, considering the all-up weight of your RV, probably wouldn't be a deal breaker.
* If the beam axle is 'isolated', compared to the rest of underbody components, and an air dam and skirts would increase frontal area, you might consider just streamlining the axle. I did this on the Viking 2-wheel trailer. It's 'invisible' when pulling, and maybe the trouble to create the low drag exposed axle was worth it ( all F-1, INDYCARs, and many Bonneville lakesters take advantage of faired suspension bits).
* Koenig-Fachsenfeld ( 'KAMM') completely faired in the underside of an omnibus in the 1930s, including aft of the rear axle, fordramatic drag reduction.So did NASA and Freightliner( Daimler-Benz ), with their semitrailers. It was also one of the tricks Subaru employed to get their XT down to Cd 0.29 in 1985.

[aerohead]

Originally Posted by sregord

Attachment 34759

A or B

Attachment 34760

C or D

Coandă effect is an interesting tool

* I'd want to see an actual technical drawing ( blueprint) of your rig, with exact dimensions ( 'x-ray' if necessary ) before I commented.
* The fact that 'Coanda effect' is essentially not used by anyone ( except Dyson, for his bladeless fan ( it has an embedded, hidden, electric-powered turbocharger compressor section inside its base which 'blows' the ring-slot) might help inform your decision making.

[freebeard]

Call it Meredith Effect then?

Many recycling centers no longer allow any material to be recovered and purchased, and this may be the 'end' of accessing used structural light metal for me.

That's really sad, local to me BRING recycling is flooded with diamond plate and architectural aluminum sheets in 4x4ft and larger sizes. Priced in the hundreds of dollars.

I just scored three 10ft corrugated steel sheets that have holes around the edges but none through the field so new you can see the Zinc crystals on the underside. $24 each, and I'm going to try spot welding two sheets together to reroof the breezeway.

[sregord]

Originally Posted by aerohead

*
* Working with steel, the added weight difference vs aluminum, considering the all-up weight of your RV, probably wouldn't be a deal breaker.
* If the beam axle is 'isolated', compared to the rest of underbody ...

I've thought the weight of the RV certainly wouldn't be affected by much with steel...or 1/8"(or even 1/2") plywood as the skin of the belly pan.
the Billboard cover idea seems to required more frame construction than I want to deal with.

The idea of the Coandă effect (I didn't know it was called that)design was already in the works. A shaped undertray between the fiberglass nose of the RV and just in front of/below the I-beam.
This discussion has helped greatly on how to "blend" that low point to the (behind the front wheels) bellypan that is higher from the ground.