Class a motorhomes aerodynamics

[Piotrsko]

Comments: unsure if containing water will ever ecceed the psi limits of any aircraft fabric, but you also put holes to let that water out. I do know that screaming through a water puddle cannot distribute the loads sufficiently enough to preclude failure. Water is rather like a brick wall at high speeds.

There were WW2 and beyond aircraft that had fabric moveable control surfaces.

[j-c-c]

Originally Posted by aerohead

A client has a 55-foot Prevost motorhome.
* 'Chord' = 55' ( 16.764-meters )
* 'Wingspan' = 8.5' ( 2.59-meters )
* 'Aspect ratio' = 0.154
* 'Wing area' = 467.5 square-feet gross ( 43.432-sq-meters ) [ we can ignore the wheel house areas for simplicity ]
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A cubic-foot is 12-inches on a side, with 1728- cubic-inches volume.
A cubic-foot of 60-degree F water weighs 64.2-pounds.
There are 7.707- gallons in a cubic-foot of water.
Each gallon of that same water weighs essentially 8.33-pounds.
A one-inch 'slice' of a cubic foot of water weighs 5.35-pounds.
One square foot contains 144-square-inches.
One square-inch of water, one-inch 'deep' weighs 0.0578-pounds.
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The World War-II, Waco Aircraft Co. CG - 4G 'Hadrian' assault glider, ( featured in 'Saving Private Ryan )' is cloth-covered, reaching up to 150-mph ( 241.4 km/h ) while towed behind the Douglas C-47, 'Skytrain', then glides to it's target landing zone at around 75-mph ( 120.7 km/h ).
The cloth-covered wings have a design wing loading of 8.33-pounds per square-foot.
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A 'cloth'-skinned belly pan, built to the specification of the Hadrian's wing would support 8.33-pounds per square-foot, at normal loading.
8.33-pounds per square-foot requires a live-load of 1.557-inches of standing water, netting 3,894-pounds of water on top of the pan.
If the Hadrian is designed to a 4g safety factor, positive and negative, then specifications would allow a survivable depth of 6.22-inches of standing water on 'top' of the belly's membrane, still short of structural failure, be it the membrane, ribs, stringers, or 'wing spar'; yielding a live-load of 15,577-pounds of standing water without failure.
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I'm not advocating for allowing 'any' water to make its way onto the top of any belly pan, regardless of materials chosen.
The wheel-houses and inner fender wells will be the focus, as this is where splash and spray originate.
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Most homes and apartments I've experienced have 'ceilings'.
And they're typically constructed with paper-sheathed gypsum board ( Sheetrock' if you will ).
And even though their complete and total destruction is just one, leaking roof away, we continue to construct them, while inspecting, and maintaining roof integrity.
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Seems like a stretched-fabric membrane, securely fastened to it's supporting structure, could function reasonably well as a belly pan, as long as its weaknesses are respected in the 'build.'

I guess if we ignore concentrated ponding effects, constant turbulence/buffeting on both surfaces, repeated dynamic road induced unknown g shock loads, it should fly, so to speak.

[freebeard]

Does this mean we can get back to Cold Plasma Actuators?

journals.sagepub.com: Aerodynamic drag reduction for a truck model using DBD plasma actuators

Abstract
In this study, the effect of DBD plasma actuator based active flow control for a truck model was investigated. Two different electrode shapes which are linear and comb-shaped plasma actuators, are considered. The two DBD plasma actuators are placed at the leading edge or the trailing edge of the trailer, respectively. First, the drag reduction for the DBD plasma actuators at input voltages varying from 6 to 14 kVpp are compared. At a Reynolds number of 25,000, the maximum drag reduction using three comb-shaped plasma actuators at the trailing edge of the trailer is 8.7%, while the maximum drag reduction of three linear plasma actuators is approximately 6%. Then flow visualization behind the truck is performed. At a Reynolds number of 3500 and an input voltage of 14 kVpp, the results show that three comb-shaped plasma actuators installed at the trailing edge of the trailer produce a significant reduction in the wake region. In addition, the PIV measurement is used to quantize the flow field. It is observed that comb-shaped plasma actuators change the slope of the wake region more significantly than using linear plasma actuators. Therefore, this study shows that the use of DBD plasma actuators qualitatively and quantitatively reduces aerodynamic drag.

[aerohead]

Originally Posted by freebeard

Does this mean we can get back to Cold Plasma Actuators?

journals.sagepub.com: Aerodynamic drag reduction for a truck model using DBD plasma actuators

I think this is a 'prank', perpetrated by someone with a greatest sense of humor, perhaps only just to see if those out in the community who are 'looking' can still fog a mirror.
It's immediately 'stupid', and any 8th-grader in algebra class would pick up on its bogusness 'hiding in plain sight.'
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'Reynolds number' ( Rn ) is the product of a vehicle's length, multiplied by it's velocity, with the product divided by the air's kinematic viscosity.
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Rn times kinematic viscosity = Length X velocity
--------------------------------------------------------------------------------------Rn X kinematic viscosity / length = velocity
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1) We're given some Rn 25,000 and Rn 3,500
2) An 18-wheel, conventional tractor/semi-trailer has a length of 74.35-feet.
3) The kinematic viscosity of SAE International 'Standard Air' is 1.578 X 10-to-the negative 4th power, or, 0.0001578.
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I won't spoil the fun by giving the computational results.
Solve for velocity, in feet per second.
Then, convert to miles per hour.
You'll be astounded by the absurdity of any notion of the viability of DBD plasma actuators.
Truly 'Unicorn Corral' material.

[freebeard]

I think this is a 'prank', perpetrated by someone with a greatest sense of humor...

The 'prank' extends to Wikipedia. en.wikipedia.org/wiki/Plasma_actuator

Contents hide
(Top)
Introduction
Power supply and electrode layouts
Influence of temperature
Influence of Rain
Flow control applications
Toggle Flow control applications subsection
Vortex generator
Active noise control
Supersonic and hypersonic flow control
Flight control
Heat transfer
Forced cooling
Film cooling
Modeling
See also
References

Modeling
Various numerical models have been proposed to simulate plasma actuations in flow control. They are listed below according to the computational cost, from the most expensive to the cheapest.

Monte carlo method plus particle-in-cell;

• Electricity modeling coupled with Navier-Stokes equations;[39]
• Lumped element model coupled with Navier-Stokes equations[40]
• Surrogate model to simulate plasma actuation.[41][20][42]

The most important potential of plasma actuators is its ability to bridge fluids and electricity. A modern closed-loop control system and the following information theoretical methods can be applied to the relatively classical aerodynamic sciences. A control-oriented model for plasma actuation in flow control has been proposed for a cavity flow control case.[43]

[aerohead]

Originally Posted by freebeard

The 'prank' extends to Wikipedia. en.wikipedia.org/wiki/Plasma_actuator

Since Wikipedia relies upon, and requests vetting of the materials they carry, by viewers, you could be the one to 'correct' this BS.
A used, $5 pocket-calculator is all you'd need to supply the necessary quanta.
An un-regulated internet has it's downside.

[freebeard]

...you could be the one to 'correct' this BS.

As could you.

[sregord]

Originally Posted by aerohead

You could experiment with 'tension', and determine how close you'd have to space support ribbing to maintain an acceptable level of 'sag' in between supports.
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A local trim or upholstery shop would be able to sew in reinforcing strips with brass webbing eyelets, at any chosen location, which would allow you to lace the fabric onto your skeleton anywhere needed.

Sounds like a big trapeze.

Originally Posted by aerohead

I'm not advocating for allowing 'any' water to make its way onto the top of any belly pan, regardless of materials chosen.
The wheel-houses and inner fender wells will be the focus, as this is where splash and spray originate.
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Seems like a stretched-fabric membrane, securely fastened to it's supporting structure, could function reasonably well as a belly pan, as long as its weaknesses are respected in the 'build.'

All, even aluminum sheet, would...should have some focus'd protection from the wheel wells, well secured leading edges that face especially forward, but also left, right & the rear and keeping it away from catalytic converter & other exhaust piping heat.
...as Piotrsko mentioned IF a "pond" were to develop, a first inspection drain hole?
One more thing to ponder is ease of drive-train maintenance.

[aerohead]

Originally Posted by sregord

Sounds like a big trapeze.



All, even aluminum sheet, would...should have some focus'd protection from the wheel wells, well secured leading edges that face especially forward, but also left, right & the rear and keeping it away from catalytic converter & other exhaust piping heat.
...as Piotrsko mentioned IF a "pond" were to develop, a first inspection drain hole?
One more thing to ponder is ease of drive-train maintenance.

yes, the actual 'bottom' of the 'pan' should be 'flush' with the bottom of the airdam and rocker panels, requiring any splash or spray to make it vertically upwards and through the 'maze' between the perimeter
box' inner surface, and any 'gap' in between the pan superstructure and this boundary.
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Any exhaust component with a heat flux strong enough to compromise the fabric would need to be wrapped with thermal insulation, and, or, provided with enough heat-shielding ( multiple layers if necessary )to buffer that flux.
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As to 'ponding', a $7 leather punch can provide drain holes, centered on any fabric span, reinforced by a brass grommet from a $7 grommet kit from any hardware store. As soon as any ponding conditions were to occur, they'd immediately begin to self-drain by gravity.
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Over time, you're going to need access to the entire underbody, so constructing the pan in handy sections allow for partial, or entire removal. I use vertical tension hangers, attached to the frame rails, extending down, with stubby L-sections bolted to those, creating a horizontal attachment surface hardpoint, with spring-steel, 1/4-20 female speed-nuts clipped to the pre-drilled holes that stainless-steel, 1/4-20 hex-bolts are inserted and tightened into; which hold my belly sections. And I use 2-inch fender washers under the hex head of the bolts to distribute the holding force over a larger area to reduce 'point-loads.'
The speed-nuts have a slight interference thread, and bolts cannot loosen until you put a breaker bar or end wrench to them. And they can't fall 'off' as they 'clip' themselves onto the host hole until forcibly removed.
Don't use the cheap, crappy, zinc- electroplated bolts. They almost immediately begin to rust, create Galvanic corrosion, and will want to 'seize' in the speed-nuts, even if you apply anti-seize compound.
PS
When you're in town give my regards to the folks at the 'Bucket of Blood Saloon.' I had a nice lunch there with my brother a few years ago. Had I known you lived there, we might have droppd by to pester you.

[sregord]

Originally Posted by aerohead

....I use vertical tension hangers, attached to the frame rails, extending down, with stubby L-sections bolted to those, creating a horizontal attachment surface hardpoint, ....
PS
When you're in town give my regards to the folks at the 'Bucket of Blood Saloon.' I had a nice lunch there with my brother a few years ago. Had I known you lived there, we might have dropped by to pester you.

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.

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?

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.