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Old 06-02-2007, 09:01 AM   #11
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Solid response, lca13. I also knew from reading that the dimples did not apply to automotive applications, but couldn't find a handy reference.
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Old 06-02-2007, 09:19 AM   #12
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So I have a work in progress, but when closer to done I'll post for all you to give me feedback on. It is a spreadsheet with calculates predicted aerodynamic force plus rolling resitance and allows input of coasting deceleration times to compare predicted versus actual drag on the car. By varying the Cd, weight, Cr, etc, you can get a pretty good match of what is really going on with a particular car, and then start playing with things to see what the predicted effect would be, and also entering new coast down data to verify or dispute it. Force and Power are graphed giving you a good idea of your match of experimental data to predicted.

So far, I am showing a "measured and calculated" CD of about .30, a weight of about 2486 lbs, and an overall RR Cr of about .011 ... all this has my actual data lining up with my predicted quite nicely. The CD survives the sanity test.... a stock Civic VX is listed at .31 and I have my pass outside mirror off. The weight was interesting... heavier than I thought but after analysis the car actually should be (stock dry VX: 2094... but mine has AC, full of gas and fluids, etc.... me.... need to find a weigh scale to verify). Rolling CD appears low, unless my tires are pretty good (cannot find any Cr values on the web but I did find a level surface and started pushing my car a ways.... by hand... with a bathroom scale in the middle.... not very scientific but the readings I got were in the 25-30 lbs range.... plus or minus 10-15 ibs... but enough for me to say, somewhere in the 30's maybe.... and the measured is coming out at 27 lbs.)

I need to get the spreadsheet cleaned up and posted so you folks can find my errors.
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Old 06-02-2007, 04:10 PM   #13
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Wow. Cool.
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Old 06-02-2007, 04:18 PM   #14
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Here's a pic anyway.
As soon as I get my 5-wire O2 blues out of the way I'll start working on it again.
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Old 06-02-2007, 06:21 PM   #15
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Quote:
Originally Posted by lca13 View Post
There's a few articles on the web documenting how auto surface conditions basically do nothing for aerodynamics. This makes sense to me after all of my digging. Dimples on golf balls work, but the same correlation cannot be made on larger surfaces due to different aerodynamic effects (flow separation is partly a function of surface length.... a not often quoted fact is that small scale wind tunnels do not accurately reflect full scale unless the pressure in the wind tunnel is increased corresponingly). For the vortex jets and maybe the rougher surfaces on planes and jets... the velocities are so much higher that things like that can make a difference.

For a car, 20 feet long at 60-80 miles per hour, neither would likely have a measurable effect... you need to affect the air flow more dramatically than you can with such passive means. Look up synthetic jets however. These look more promising if you are looking for something measurable, yet not altering of vehicle shape characteristics in a large way.

Dig further. Read the first two paragraphs closely. The paint finish caused numerous crashes of this aircraft. The bold italics I added for this reprint. I hold all copyrights to this article. No reprints without permission other than at "www.gassavers.org" in posts related to this series of posts. All rights reserved.

This is from the article that I wrote in 1989:

MIG-29s AND RUSSIAN CARGO AIRCRAFT APPEAR AT KALAMAZOO, MICHIGAN AIR SHOW.

By Max W. Cottrell, YCIS news service.

"During the late 1960's, (but not in time for the end of the Vietnam war) the Russians started a study for a "Perspektivnyi Frontovoi Istrebitel" (Advanced Tactical Fighter) which was a tactical fighter paralleling the development in the United States for the first designs that became what we know as the F-15. However, there were problems with the initial release of the fighter, the "Fulcrum A" as NATO called the aircraft when it first appeared or more commonly known as the MiG-29. These problems, while similar to the American F-14 "Tomcat" or F-14A had several dissimilar aspects. I'll note right now that the MiG-29 was not a copy of the F-14 "Tomcat". It is a duplicate of the F-15 "Eagle". Many of the design characteristics were stolen from the United States during the cold war, which has recently ended with the fall of the Berlin wall. The F-14A suffered numerous engine stalls at low speeds from a lack of engine inlet air flow. The MiG-29 as you will read in this article suffered from an actual physical defect in the airframe due to its design.

It was discovered during early flights that the unique doors on the MiG-29's engine inlets were not stopping debris (such as rocks, metal bits or birds) from getting into the engine ducts. These ducts (this problem has apparently been solved according the designer of the aircraft whom I interviewed for this article) tip up during takeoff in order to prevent debris from entering the inlets. Since the doors retracted "up" into the inlet, debris that were kicked up by the nose wheel lodged on or at the bottom of the door seal and then were ingested into the engine when the door opened during the nose gear lifted off the ground during takeoff. Most of these ingestions were due to the unique paint that the MiG-29 carried which has a "pebbled" finish. I examined this finish but was prevented from photographing it by Russian security guards during the air show. This finish was due to what the designer, Rostislav Belyakov told this reporter was "a lack of our ability to refine the fit and finish to western standards". The so called 'pebble' finish allows the mach 2+ speeds of the airframe to be possible. Belyakov would not elaborate on the type or construction of the paint. This finish allows the high (above 1000 mph) speed airflow over the airframe to proceed past the poor fitting panels and finished sections of the airframe. Belyakov stated that without this type of revolutionary type of paint and finish, the MiG-29 would not be able to achieve the speeds that it is capable of.

General Designer and recognized academician, Rostislav Apollosovich Belyakov, took over the MiG Bureau in 1970 following the death of its founder, Anushavan Ivanovich Mikoyan. Belyakov was a graduate of the Moscow Aviation Institute while the Russians were fighting in World War II. He received the State Prize for design in 1951, and was the chief designer of the MiG-23. Mr. Belyakov ran the Mikoyan company with four Chief Designers and fourteen deputy Chief Designers."

Now, I've seen and touched this finish. It is pebbled and the ports and access panels were indeed poorly fitting. Since this aircraft is indeed capable of flying in excess of mach 2 for short periods one has to assume that Mr. Belyakov was not lying to me.

As an aside, this is the same air show that a Blue Angel pilot traded planes with one of the MiG-29 pilots and created quite an uproar.

One of the aircraft was a two seater "training" aircraft that was fitted with a specialized radar with an "artificial" aperture radar. Shortly after the air show in Kalamazoo after the military was alerted to this the aircraft were "removed" from the United States due to "maintenance problems".
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Old 06-02-2007, 06:35 PM   #16
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I forgot to mention: theclencher suggested it and I made it.

http://www.northernmichigansolar.com/webernator2.wmv

Another item about the MiG-29. A guy named Don Kirlin, has a MiG-29 that he purchased from Kyrgyzstan. It is at the Quincy Regional Airport in Illinois the last I heard. He can't fly it because according to the state department it lacks "registered avionics", whatever the heck that means. Apparently "look-down-shoot-down" Russian radar isn't allowed in the U.S.. If you're close by you might be able to photograph the paint on them if you contact him. I don't have his phone number any more.
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Old 06-02-2007, 06:56 PM   #17
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Richard Petty had an unusual black vinyl top installed on his blue Plymouth at the 500 that year[1968]. Petty crewmen were whispering in other team members ears the vinyl roofs pebbled surface helped diffuse the air flow and made the car quicker. Other teams began scrambling to install vinyl roofs on their cars. Petty was seen rubbing baby powder on his roof and again his team whispered the baby powder helped the car slip through the air. Other teams began rubbing baby powder on their cars. In later years Petty would admit it was all a prank, to play on the ?monkey see-monkey do? attitudes other teams had taken towards the Petty crew after the way they dominated in 1967. Others still claim Richard?s guys did some surgery to the roof area of his Plymouth to make the car more aerodynamic and used the vinyl roof to help cover their treachery.
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Old 06-02-2007, 07:21 PM   #18
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Some of those guys also had an amazing amount of fuel lines in their cars. Enough to hold a few gallons of gas. The Petty baby powder story is amusing.

I knew a friend that used to race on Saturday nights. He had a large friend that split his winnings with him. What he did was disconnect one spark plug and pull a hidden plug on his exhaust that made his car sound like crap. Then he'd act drunk and bet some outrageous sum for a race. As soon as the bet was taken he would open his hood, bang on a bucket with a hammer, reconnect the plug and open the headers from in the car. The large friend was to collect the bets after the races. Oddly, he won a lot.

Another story: I had one of the original Petty Kitcars in 1978 (hence my nickname) with the black valve cover race engines. There was another guy in town with one who was famous for cheating, ("One....Two - and he'd take off before anyone said "three"). Well, I met up with him one night while buying Union 76 racing gas right after I put a 1,000 cfm carb on mine and I was dialing it on I-94. Another buddy of his was there with this crapped out Camaro with a luggage rack on it. Well, stupid as it was I agreed to race him and his Camaro buddy tagged along. Sure enough Leonard went on "two" and I went with him. As we passed 100 (I was ahead) or so this Camaro BLOWS by us amid a shower of sparks and flames. Actual flames shooting out the exhaust. Turns out it was his dad's car that he had bought and put a 427 with twin turbos in it. Once those things spooled up that thing took off. Darnedest thing I ever saw. Of course he blew it up a week later but that thing scooted right along until then. Our Kitcars would break 100 in under 10 seconds. And this thing just blew by us after 100. It was one of those deals where you just look at the other guy and say, "What the heck was that supposed to be?!"
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Old 06-02-2007, 08:40 PM   #19
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>> Dig further. Read the first two paragraphs closely.
>>The paint finish caused numerous crashes of this aircraft.

I must be missing something. My only comment was that surface conditions don't really matter much at auto velocities.
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Old 06-03-2007, 05:42 AM   #20
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Sorry, I should have been more clear. The relatively slow landing and takeoff speeds of the MiG-29 at 161 to 170 miles per hour, the ingestion of the particles into the engine inlet and the root cause being the bumpy paint causing vortexes around the engine inlets show the stuff worked at near automotive speeds but is the effect detrimental to the energy needed to propel the vehicle?

We can't use the golf ball analogy here because it isn't correct.

A perfectly smooth ball suffers from a flow separation around its surface, a large wake and this causes large pressure drags. A smooth ball has low skin friction, but really really high pressure drag, because even though the flow is straight, it separates from the ball very early in flight during its acceleration. If you put dimples on the ball to roughen the surface, the pressure turns turbulent and the resulting higher energy flow stays "attached" to the ball longer, making a smaller wake and reducing the pressure drag. What you have done is traded friction drag for a drop in pressure drag which allows the ball to go further through the air. Spheres are very special cases in aerodynamics and simply can't be applied to vehicles.

What I'm actually refining the theory into is a way to reduce the wake of the vehicle by the use of irregular surface areas by using a turbulent boundary layer. I.E., reducing the pressure drag (wake) of the vehicle.

I guess I could have been more technical in explaining the concept for turbulent boundary layers but this stuff can glaze eyes over and make grown men weep in confusion:

We know that the air stream follows the curves (shape) of the vehicle as it passes through the air. Conventional wisdom says that the smoother the surface the better the vehicle slips through the air (closing of gaps, removal of wipers, etc.). In the same vein, an introduction of a surface with less surface area would produce less wind resistance. It should be a matter of degrees. If a Mach 2 aircraft needs tiny bumps to achieve this (which it turns out worked at 161 to 170 mph), then vehicle with a lower terminal velocity (say 60 mph to keep the formulas as simple as possible) would need larger bumps. However, that is the problem with fluid stream dynamics; logic doesn't always apply. Over the years, I've thought about the concept a lot since the interview and on the surface it makes all the sense in the world. What you're attempting to do is make the surface that pushes through the air irregular in that the surface area varies with the use of protrusions into the fluid (air) stream which in turn causes the air that you travel through to "think" that your vehicle is smaller than it really is. Taken to the n th degree, that is what we do with air dams, side skirts and such. We're taking away surfaces that the air would normally be traveling over and thus making the air "think" that the vehicle has a smaller aspect area or cd than it really does. Boiled down, let's reduce the pressure on the vehicle by introducing a lower pressure boundary layer of air in certain areas of the vehicle.

Now I wish we had a way to put formulas into our posts. That would be handy at this point. However:

This is called the boundary layer and what we are looking at is called turbulent boundary layer effect, which is expressed as the RANS (Reynolds averaged) formula. This is assuming that the density of the air is constant (which we know it isn't but we can simplify the entire deal a lot by assuming it is). What we are looking at is a combination of force, viscous stress, isotropic stress and apparent stress due to a fluctuating velocity field (which is what the irregular surface - or bumps - is) and for that we can use the Reynolds stresses formula; (Re)= ((fluid velocity*distance from leading edge)/kinematic viscosity).

How's that for a convoluted explanation to my silly little idea?

Maybe I'll just stick with canards on the wheel wells.
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