Hard-Side Truck Camper Nose Aerodynamics

[ReluctantTraveler]

Here is my non scientific take:

We settled on version one of your nosecone design. Reason: having another slope on the bottom would greatly reduce the inside bed area.
Another thing I personally noticed on several thousand miles of road tripping with a TC truck camper and flatbed camper: at certain speeds the air from oncoming traffic creates massive "shockwaves" and seriously rocks your rig. Now imagine having the down slope on the bottom part of the cabover and imagine the lift/upforce that wind buffer will create. View attachment 910563View attachment 910564

Always appreciate your insights as a builder! Thanks!

 

[ReluctantTraveler]

One of the most effective modifications reported in that NASA monograph for the “shoe box” (square experimental test box/vehicle) was rounded corners:

View attachment 910631
The whole monograph is a really interesting and worthwhile read.

I think a previous discussion of that report here noted that the pull quote misrepresents the impact of that modification? I could be misremembering, but read through it recently.

Planning to have rounded corners nonetheless.

 

[Peter_n_Margaret]

My views,
1) is that the trailing end is at least as important as the leading end.
2) making any assessment by looking at a drawing or model is (almost) a complete waste of time.
3) What works at one speed might be a disaster at any other speed.
In the "real world" aerodynamics is not easily predicted and a wind tunnel, at least, is needed.

My build options in the past have been determined by aesthetics and practicalities (much like Victorian's), not some pretense of improving fuel economy, and that approach will continue with my current new build.
Fuel economy is best reduced by reducing speed (massive), choosing a better motor for the job (massive), choosing better tyres (significant) and reducing weight (about 1L/100km per Ton) and probably drive train choices.
Cheers,
Peter
OKA196 motorhome

 

[rruff]

....speed has an outsized impact on aerodynamics.

It is an outsized impact on drag and fuel economy, but the Cd (drag coefficient) is not greatly effected. Power to overcome aero drag is proportional to V^3, or a V^2 impact on mpg.

For instance, the aero component of mpg at 80 mph will be 78% higher than it is at 60, assuming that the engine and drivetrain efficiency is unchanged in this range.

 

[ReluctantTraveler]

Y'all are impressively knowledgeable about this!

 

[rruff]

My views,
1) is that the trailing end is at least as important as the leading end.

Reducing the trailing edge area is very helpful provided that it can be done with smooth attached airflow. It needs to be a gradual taper.

2) making any assessment by looking at a drawing or model is (almost) a complete waste of time. 3) What works at one speed might be a disaster at any other speed.

Oh, not really. Putting large radius rounded edges on the leading edges, or a rounded nose (for instance) are universally good practices. Also, Cd doesn't change much over the smallish speed differences we care about.

The problem is that a squared box is the most space efficient enclosure, and width is limited. Shaping is usually expensive, reduces volume, and interior spaces are more difficult to utilize. Plus a lot of stuff sticks out like solar panels, vents, awnings, etc that make it impossible to create a clean shape.

Fuel economy is best reduced by ...choosing better tyres (significant) and reducing weight...

Yes, if the government wanted to do something useful, measuring the rolling resistance of all truck tire models would be a big help. It would force manufacturers to at least consider this when designing their compounds.

 

[rruff]

One of the most effective modifications reported in that NASA monograph for the “shoe box” (square experimental test box/vehicle) was rounded corners

U-Haul did exactly that for their truck boxes. I wonder if there was any testing of the impact of this?

 

[rruff]

I can say that it has low mpg impact and handles crosswinds very well, but... it was a PITA to make the roof and nose, and there is an obvious reduction in interior space for the HxWxL envelope.

 

[ReluctantTraveler]

I can say that it has low mpg impact and handles crosswinds very well, but... it was a PITA to make the roof and nose, and there is an obvious reduction in interior space for the HxWxL envelope.

View attachment 910680View attachment 910681

That looks like it was really annoying to shape! Looks really nice, though!

 

[Pntyrmvr]

Driveway build. Originally an empty area over cab. Swayed by passing transports. Roof over cab would oil can! Suspect remaining flat verticals below air dam are an impediment. Also mirrors and roof deck railing bases.

Better with it installed, but headwinds still rule the day. 31% overdrive transmission just won't let engine stay in power band. Direct drive 3rd gear fine, but mileage goes down. 79 chassis, 94 transmission, 2007 Hemi.

Will cruise all day at 63 mph. Has done 85, but that's just not "right".

6-8 mpg

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