racing wax

[jons999]

A store around here sells "racing wax," guaranteed to make your car go faster by reducing drag. My question is, would this stuff really make a difference on a vehicle traveling below a couple hundred miles an hour? I can't imagine the the paint finishes on new vehicles are rough enough to cause a noticible decrease in speed and fuel efficiancy.

-Jon

 

[sciguyjim]

I agree. This is just another way for someone to separate you from your money. There are many larger obstacles to airflow on cars than dust.

 

[sprintcar]

It can have an effect when you get up around 180 mph on something like a Winston Cup car but as the CD of these vehicles decreases, so does any surface effect. Most of the wind tunnel testing for R&D is done in primer.

We did testing a few years ago on boats and found the reduction in hull friction made a difference with drag boats made a difference on the clock. The slower te boat the greater the effect, since the faster classes had less hull surface in contact.

We also tried it on golf balls - got 5 to 10 yds longer drives. So there's something to be gained by surface treatment in certain cases, but I doubt the 'guarantee' has much data behind it Keep the wheels on the ground
Bob
showshine@aol.com

 

[sciguyjim]

Bob,
The boats I'm not surprised about because of water's density, viscosity and surface tension.
The golf balls though, sounds like there's $ to be made with that idea. Maybe some kid wanting a summer job can polish golf balls for his neighbors. He'll have to understand what's going on though because he's going to have to convince them it's worth it.

 

at low reynolds numbers, it's better to have a slightly rough surface to keep the boundary layer energized so it doesn't build up too quickly, causing more drag. so, unless you're going around the track at 180 mph, all by yourself, it won't help. profile drag is your nemesis.

 

[astroclone]

That's why I prefer to keep a fine layer of grit on my car at all times. Sometimes the airflow gets disrupted by the "Wash me" written by some helpful (But obviously not an aerodynamicist) person.
Tony

 

Nice one!

 

[WKTaylor]

OK guys, stop being so cynical.

Don't forget that the wax really does multiple duty:

(1) fills-in pits/pores within paint finish caused by impact damage and paint irregularities, that can appreciably "smooth-out" an overall "rough" finish.

(2) makes the surface relatively "non-adherent" for bugs, dust, debris, rain/moisture, etc.

(3) adds a thin layer over the paint finish for improved abraision resistance and a provides a temporary "wear-away" surface.

In aviation I've experienced the following:

(a) A very rough paint job reduced cruise speed of an O-2A acft by up-to 18-Kts [was ~150Kt with a glossy finish... reduced to 132-Kts at 75%-pwr with a rough "flat-camoflage" finish]. Sand-off and repaint "to spec" "improved" overall cruise airspeed up-to ~142kts!!!

(b) Many experimental or high performance airfoils have seen disasterous performance reductions due to roughness [especially on airfoils, due to premature/irregular flow separation]. Sailplane and "racing" pilots learned years ago that a "clean waxed" exterior provides a "winning-edge in contests... simply because of the improved micro-finish and reduced adhesion that "wax" provided.

(c) Boeing pays attention to minor exterior details... a 0.5% decrease in drag is probably worth several hundred-thousand $$$ in fuel expennse over the life-time of "heavy" [transport sized] acft!!!!

NOTE: on a dirty racing auto the improvements may be very slight... but between high speed racing vehicles, win-loss times are generally measured in 1/10s of seconds over an entire race! if the wax just keeps a few bugs from sticking, it may make a "winning" difference.
Regards, Wil Taylor

 

[jgm]

Is the paint on an aircraft aerodynamically necessary, or necessary for the protection of the skin of the aircraft? I'm just wondering how much a typical paint covering for, say, a 747 weighs. Are the passengers paying so that the airline can fly a ton(?)of advertising hoarding on every trip?

 

[sciguyjim]

jgm,
To give you some idea of paint weight, when the space shuttle was first built NASA painted the big liquid fuel tank under the shuttle white. Shortly afterwards they stopped painting it because they realized the paint weighed 300 lbs and every pound they launch is expensive.

 

[WKTaylor]

jgm...

Surface roughness is the key here. Polished metal and waxed paint are about the same.

Paint is there for (2) reasons.

Engineering: corrosion protective organic finish [primer] over inorganic-finish surface preparation [anodize, alodine, platings, etching/passivation, etc].

Decorative [or camoflauge]: "pretty" finish over corrosion protective finishes to please the customer's needs.

Paint adds considerable weight. For a small fighter [F-16], the primer and camoflauge paint [specialized heavy pigments] add up to about 80#. Large transports [747-400] can gain close to 1000# for a full primer/paint job [huge surface area]. Also, primer and paint touch-ups have been known to severely affect the ballasting of a large balanced flight control surface [transport elevator].

Note: highly polished "ALCLAD" skins have good corrosion resistance and low skin friction. Maintenance is easy IF the polished apearance is NOT allowed to deriorate... and repainting costs are obviously minimized***. ON-GOING MAINTENANCE is very critical if corrosion sets in, maintance.

American airlines has choosen bare-skin and decals as their "finish scheme" of choice. This approach is high maintenance on a daily basis [maintaining highly polished "pretty appearance" is demanding] ... but saves lots of weight and re-repaint cost/time.

Other airlines have choosen the opposite approach, since a majority of primary structure skins*** [IE: wings] are machined and cannot be successfully ALCLAD and/or polished... and still maintain good corrosion resistance on critical structure [they are generally anodized, primed and painted]. These Airlines choose the minimum daily maintenace approach... followed by on-going touch-up and occasional de-paint/re-finish every 6--8 years.

The drag affects and maintenance affects of ACFT finishes have LOTS of economic affects!!!!
Regards, Wil Taylor