Breakfast with Phil Knox

[aerohead]

Originally Posted by miket

Given the vehicle lengths dropping the rear bumper 2" would raise the front bumper 0.4" and change the rake less than a single degree. Honestly a 4" drop would make it easier to load/unload the bed and definitely the ladder racks and a 2" drop is really all I can get out of the front. The hood would stay in positive pressure, might have to check the wipers. Its hard to tell if the roof of the cab peaks in the front or middle, its relatively flat. I think the undercarriage would be presented with the undertray. I think even with the body dropped the axles are still the lowest point.

I just realized that the back is always sagging down bad from the constant load lol. Its already lowered. I think i should add a leaf or a helper spring, especially since i plan on adding a few hundred more pounds. I think supercars are raked for downforce more than anything.

Do you ever have problems with snow or dirt flying up through the gaps around the wheel wells or in front of the axles and filling up the cavity above and weighing down on the undertray? Ever have any problem with vertical undertray components when they'r pushing through deepish snow either driving forward reverse or turning?

If you do the drop,you might consider some time to familiarize yourself with anything new and quirky which might show up in handling.
I had air-shocks on an El Camino and they were great for load leveling.Something like that,or air springs might help with load stabilization when she's buried in pipe or tubing.
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I have experienced material buildup on top of the pan,as I've never invested the extra time to detail out the wheel wells.After a good rain,I can usually chase everything out with a blast from the garden hose.
I've never had a clearance issue with the pan until the floodwater,when I struck a submerged hazard and it rip the diffuser off.And it struck me that the racing tires were partly responsible for that,as the truck rides a little lower.
The times I've driven in snow,traffic had already knocked down significant accumulations so it wasn't an issue.My pan is pretty strong and could support quite a 'load' and doesn't deform.The leading section is the fiberglass skin from a Mustang trunklid and is radiused well,not a 'snagger.'
If you're 'trail-blazing' on un-plowed streets or roads in heavy snow,you'll have to be mindfull of clearance.

[miket]

How much difference is there between a boat tail or kamm back with the back end closed or open?

[miket]

Originally Posted by aerohead

miket,the full skirt was for proof of concept.It was 'fixed' and did limit the wheels range of motion,although not much of a problem.
The 'final' skirts will attach to pantograph/hinged parallelogram mechanism which allows the tire sidewall to engage inline skate rollers attached to the mechanism,swinging it out and up to clear the 'steering' wheel,then stow flush against the fender when centered.
....
In HUCHO's book you should find a great inflatable design by Fachsenfeld,done for Omnibus at FKFS around 1936.

I dont quite understand. I would think that a pantagraph would be used if you wanted the skirt to pivot at the front edge or the back edge when the wheel turns outward but if the skirt swings upwards instead then a simple hinge at the top would do.

I find it interesting in huchos book p184 he dismisses eliminating the rear wheel arches because of it only having less than .01cd improvment even on a streamlined vehicle.

The inflatable boatail on p456 has an underside that is rounded with much steeper angles than 4deg?

Is 6959958 the patent you were refering earlier to on semis?

[aerohead]

Originally Posted by miket

How much difference is there between a boat tail or kamm back with the back end closed or open?

miket,Sepp,(I believe he lives in Belgium) reported that closing the back on his Nissan Frontier aeroshell made a definite improvement compared to an open tail.
My neighbor Bob ran an open boat-tail on his VW Vanagon and it returned less MPG than what I experienced with my VW Transporter.
Bob never enclosed his,so I have no comparative data to share.
I've never run an open tail,so I have no data to offer.
Perhaps others will come forward with some supporting data.Good question!

[aerohead]

Originally Posted by miket

I dont quite understand. I would think that a pantagraph would be used if you wanted the skirt to pivot at the front edge or the back edge when the wheel turns outward but if the skirt swings upwards instead then a simple hinge at the top would do.

I find it interesting in huchos book p184 he dismisses eliminating the rear wheel arches because of it only having less than .01cd improvment even on a streamlined vehicle.

The inflatable boatail on p456 has an underside that is rounded with much steeper angles than 4deg?

Is 6959958 the patent you were refering earlier to on semis?

miket,my setup provides for the skirt to remain always parallel to the side of the vehicle,moving away and up as the steering tire/wheel moves off center.
There are 4-links,to which 8-pivots,4 at the attachment to the wheel arch,high and low,and also 4 at the carrier framework,high and low ,to which the molded skirt attaches.
A roller,fore and aft on the inside frame is what is contacted by the turning wheel,displacing the frame/skirt until re-centered.
I don't have any materials with me,so I'll have to wait to respond to Hucho's comment on wheel arches.A casual thought would be that for any 'low-drag' car,the arch would be superflous,as it would be hidden behind a streamlining skirt.
I'll have to re-visit Hucho to look at the inflated tail.I hope we have the same book!
The one I like best,I'm pretty sure is from Baron R.von Fachsenfeld around 1936,that he did for Omnibus at FKFS.I have a U.S.Patent which is similar to it,I'll have to ferret that out.

[miket]

I would need to see a picture to understand exactly what you described. I do see the advantage of going up like that instead of a simple hinge on top because the bottom edge of the fairing wouldn"t swing out much farther than the wheel. As a practical matter how do you make the pivots?

I was interpreting what hucho meant by elimination of the rear wheel arches he meant no arch around the wheel well just a flat across fairing? I have the fourth edition of aerodynamics of road vehicles. The Fachsenfeld is what i was refering to, the bottom of the boat tail curved almost as much as the top curved down.

I have concerns with a totally solid hub cap concerning brake cooling and snow buildup. Obviously not at the same time lol. Tundras have been know to warp rotors. Solid hubcaps might prevent snow from getting in from the outside but all the snow that gets in from the inside might not be able to get out.

[aerohead]

Originally Posted by miket

I would need to see a picture to understand exactly what you described. I do see the advantage of going up like that instead of a simple hinge on top because the bottom edge of the fairing wouldn"t swing out much farther than the wheel. As a practical matter how do you make the pivots?

I was interpreting what hucho meant by elimination of the rear wheel arches he meant no arch around the wheel well just a flat across fairing? I have the fourth edition of aerodynamics of road vehicles. The Fachsenfeld is what i was refering to, the bottom of the boat tail curved almost as much as the top curved down.

I have concerns with a totally solid hub cap concerning brake cooling and snow buildup. Obviously not at the same time lol. Tundras have been know to warp rotors. Solid hubcaps might prevent snow from getting in from the outside but all the snow that gets in from the inside might not be able to get out.

miket,I almost had your questions addressed yesterday,then computer crashed before I could enter.( we think Verizon FIOS is the new term for FECES ).I'll take your questions one at a time in case the computer is looking for a repeat performance.
The pivot point 'outers' are created from steel C-channel welded to the outside of the fixed-frame and inside of the floating-frame.
The frames are joined by 4-steel tube double-T-bone links,through which hinge- pins are inserted and secured,creating the pivot articulation.
The floating-frame simply dangles from the 4 links,and it is in this position that the skirt is fitted and secured by Zeus fasteners

[aerohead]

miket,our books are different vintage so I'm going to need some help on the wheel arch issue.

[aerohead]

With respect to diffuser angle limits beyond a cars original rear bumper I have no data.
Hucho,in his section on racing cars shows some long-tail configurations along with lift/drag comparisons.
Hucho also has a full-boat-tail drag tabulation for the Daimler',M-B C-111 record car,and you'll notice that this car also has the upsweep.
Ditto,EV-1/Impact LSR car at Ft. Stockton,Tx.
The only thing that I would throw out,is that a 'track' car would require special considerations that a 'road' car would not.And I believe an upswept tail is a concession to cornering downforce ( say 257 mph around a curve in the Olds AEROTECH ).
The other 'clue',is from GM's display at EPCOT Center in the 1980s,where they displayed an 'active' diffuser which went 'flat' at highway speeds.No upsweep!
On the road,there would be no concern for approach/ramp/break-over clearance,so a 'flat',or 2.5-4.0 degree diffuser wouldn't pose an issue.
My streamlining template reflects a 'flat' diffuser as used by Jaray,Klemperer,Lay,Kamm,GM,etc. which would require the 'active' approach,something I don't feel to be a big deal.
Why Fachsenfeld did what he did died with the man.I would not,and will not design as he did,however,what he did remains a very high bar,better than anything I've seen to date.

[aerohead]

No doubt your concerns have been shared by many over brake-related issues.
The 'answer' was to provide some 'minimum' aspiration to the wheelcover.
Renault,for it's Vesta-II,provided one streamlined opening in the disk which coincided with the valve stem position.
On Ultralite,GM had very small penetrations near the outer extremity of the wheel.
GM's Pontiac Div. used larger ones on Trans Am Firebird.
There's a long list of concessions to 'practicality.'
As to snow issues,I have little to bring to the table.I've driven in white -out conditions over Raton Pass into Colorado,with snow all the way to Colorado Springs without event.And plowing County Line road,east out of Palmer Lake.
I would let safety be the over-arching priority.High mpg is kinda meaningless when you're dead amidst the twisted remains of your car at the bottom of a ravine.