This is a very low drag car and extremely low consumption..there are cars with 0.07 drag coefficients ( believe it or not ). This is the only one with 4 seats.
This not meant for speed...is 55 mph really a "speed" ?

I btw counted the g force affecting a golf ball; it is 16 100 G:s in that less than an inch distance where it accelerates from 0 to 160 mph.( Sadlowski hits the ball to 216 mph ).

A properly designed airfoil"
According to what criteria?
All of the shapes are compromises
every last one of em
As weight us reduced or the power is increased ,the criteria for the
properly designed airfoil changes shape.
Also a flat plate may be as good as ANY shape - depending on the flight criteria .
You aint working with a trained squirrel ,buddy.

[quote]A properly designed airfoil"
According to what criteria?
All of the shapes are compromises
every last one of em
As weight us reduced or the power is increased ,the criteria for the
properly designed airfoil changes shape.
Also a flat plate may be as good as ANY shape - depending on the flight criteria .
You aint working with a trained squirrel ,buddy.[/quote]

LOL. That's a new one on me, but you aint dealing with no chipmunk either friend.

But back to the topic, the "properly" designed airfoil, in the case of most planes, would give the desired amount of "lift" at a given speed with the least amount of drag and weight possible. As you stated, each is a compromise of some sort, you give up speed or effeciency to accomodate lift, weight, power, structural integrity, etc. The point of the original question about the dimples is whether they actually would reduce drag enough to make a difference. I think they would, but I'm not sure it would always be desired in a plane. I can see where reducing drag along the fusalage and other surfaces would be beneficial if it increased fuel ecomonmy. But I'm not sure in the case of the wing. In the example given by some one above about the Cessna gaining 5mph due to hail damage, I have to wonder if this also increased the stall speed of the craft? If so, this might not be desirable under some conditions.

If I feel an airfoil is not correct - I just take a time out and have a drink-
Usually the airfoil has now improved
If not - I lighten the plane -smaller batteries etc-
that usually fixes it.
It's all VERY subjective.

I guess everything is subjective after you have a couple or twelve "time outs" then huh?

well sorta -but I also get a chance to look for the real problems -which never seem to be related to the airfoil selected.
weight , balance, bending under load etc., are the usual suspects.

On JEOPARDY tonight , the following question was asked
Question-When a batter hits the ball - he hopefully produces backspin on the ball.
>The backspin cause the air over the top of the ball to travel faster than the air under the ball<
The air on the underside then produces this.
Answer - lift-

I have never seen this wording to explain the pressure difference.
I guess I have led a sheltered life.

Actually, if a dimpled wing would work, you'd see them on full-size aircraft. Just because it works on a golf ball doesn't mean the application is universally adaptable. Aero engineers have looked at almost everything to try to get more efficiency out of aircraft designs. If dimpling would work, you'd see them on the newest airliners, where efficiency is a BIG DEAL.

This discussion kind of reminds me about the "story" where an aircraft design kept having wing failures. They finally solved the problem by riddling the wing with holes. After all, when you tear off a piece of toilet paper or paper towel, it never rips at the perforations. So, by inference......

I never heard of that one, I'd like to see that plane with the holes in the wings!

Pattern designs for years have used a "compromise" airfoil. Dick, you can likely support me on this and fill in any holes since I sure don't have your background in pattern models.

As I read different arcticles about pattern models over a number of years in the old model magazines it soon became apparent that they did not want the airfoil to perform TOO well. Just well ENOUGH. It's a fine line between a model that flies smoothly and turns well in pitch but that can snap roll cleanly on demand. "Detuning" an airfoil by sharpening up the leading edge or selecting a less than ideal choice from a low stall speed standpoint was done often to get the model to achieve just the right charactaristics. And as the focus on the style of manuevers shifted the choice of airfoil shifted along with it. Now we have 3D models that use a much thinner airfoil with relatively poor, by normal sense, stall charactaristics. But they are the right tool for the job the model is designed to do. But this choice presumes that the maker will be able to meet the rest of the criteria to let the package fly as it was intended. So along come a bunch of ARF companies or builders of kits that don't know that the model needs to be kept down to a target weight and suddenly we get lots of compaints about models that stall and snap roll when doing loops or during landing approaches.

The point is that a "proper" airfoil IS a very highly subjective call in a lot of cases. In other flying tasks it can be more sharply defined but even in those cases there's seldom a single track, single solution. Look at world class F3B sailplane designs. There's gobs of slightly differing airfoil choices that put just a hair of emphasis on different aspects. Even commercial airliners have a number of various airfoil and flap options yet all seem to manage to top the bar that is set for them.

Anyhow, back to dimples. If it's true that those Cessnas did gain some top end then it's because the surface finish or the choice of airfoil was less than optimum for top speed use. It still comes back to the idea that using turbulators is a "bandaid" for a bad design or to fix an issue at some point where the gain gives back more than the cost in other modes. In the case of the golf ball the shape is mandated and the dimples are a fix to get more out of it. With an aircraft the pluses and minuses have to be weighed and a decision made to use turbulation or change the airfoil design to achieve the goals without using add on fixes.

In some cases the cost enters into the issue. The old A-4 Skyhawk uses outer tip turbulation to delay the stall at the tips or to gain some aspect of this sort during high G loads and during landings. The Aermacchi Delphin uses the same style turbulators on the lower leading edge of the stabilizer to gain more "lift" or lower drag or better control stick feel during larger applications of up elevator. But both of these gain what they get at the expense of adding drag. Perhaps both would have gained more by switching to a different airfoil or going with an alternative airfoil modifying device such as leading edge slats. Or perhaps not. But doing so would definetly have cost a lot in terms of time and money.

The efficiency of a surface treatment is surely dependent on the speed at which the object is moving through the fluid mass. Also the density/viscosity of that fluid mass. Airliners through high altitude/thin air at 500+ mph vs sharks through water at 20mph or nuclear subs at 50(?).

Terry in LP

I'm sorry Dick, we needed that in the form of a question.

Exactly what I said in a prior post. Are we the only ones who've picked up on that.??

No, you're not the only ones. I implied that when I said there's such a variety in the type of turbulators or invigorators or whatever they call them in the full sized craft.

At one point it was popular in the free flight glider class to use forward supports to suspend an elastic thread in front of the leading edge to turbulate the flow before it even hit the leading edge. Quite a few FAI world class models used this option for a few years back in the 50's and early 60's. That's one option that I've never seen on a full sized airplane but that worked just fine on our models.

So yeah, there's certainly more than one road to Rome as the old saying goes.

Matter of fact, full scale designers experimented with wings that had arrays of holes all over 'em. The holes were pressurized. If I remember correctly, whatever they were trying for they got, but they were too difficult to mfg and maintain.

Of course, I know about the "blown" wing, but my story came from a different source...(heh, heh).

I did see a series of pictures that showed the Boeing 707 prototype with blown flaps. The airplane landed as slowly as a lightplane. Trouble was, the equipment for that mod was heavy-enough that the carrying capacity of the plane was compromised to the extent that is really wasn't useful. I'd still LOVE to see a B-707 (or equivalent) get in and out of a 2,100-foot strip, like lightplanes do!

Would you settle for a Hercy doin' it?

Don't remember which, the 707 or the 720 had the paint rubbed off the instrument panels where the pilots' shoes ground away when they were pulling the yokes to flair........

Dimples work on a golf ball because the shape of the ball is not aerodynamicaly efficient. The dimples cause the air to break free of the back side of the ball. this is good because the ball (if it were smooth) is asking the air to follow the surface of the ball all the way around to the back. This pulls back on the ball more than if the air were to break free. A tear drop is an aerodynamically efficient shape. Think of what the air looks like if it were to break free of the back side of a ball. The air breaks free of the ball and gradually closes in to itself some distance behind the ball. This patern looks just like a teardrop.

Hi Louis9624,

Actually, the situation is the opposite of your description. Without dimples, the flow at the surface of the ball tends to be laminar, which allows it to separate, or break free, earlier. This causes high drag, because the area on the back of the ball (behind the line where the flow breaks free) is subjected to low pressure. Dimples cause the flow to be turbulent, which delays the separation, thus reducing the amount of area on the back that is subjects to low pressure.

Low pressure on the back of a moving body increases the drag. Engineers who design airfoils sometimes refer to the rearward portion of the top of the airfoil as the "pressure recovery" region, because on a well-designed airfoil, the pressure will be "recovering", or increasing. The minimum pressue tends to occur near the thickest part of the wing, and failure of the pressure to recover toward the trailing edge results in increased drag.

banktoturn

<p style="MARGIN: 0in 0in 0pt" class="MsoNormal"><span style="FONT-SIZE: 7pt; FONT-FAMILY: Arial">The Myth Busters are chumps. If you take three identical cars off the assembly line and test the mileage of each they will all be slightly different. They have done this before.<span style="mso-spacerun: yes">  </span>FAIL. They should stick to myths they can handle like teaching an old dog new tricks.</span></p>

Based on the wind tunnel tests I have done using golf balls, the reduction in drag occurs only at higher reynold's numbers. There is a lot current research going on to include such flow control techniques in the latest aircraft but the problem is there is not enough data on how they will perform in actual flight. dimples on a wing will surely reduce drag but it would have increased icing effect which could lead to a catastrophic crash.

For one, dimples don't cause a turbulent flow they induce a turbulent boundary layer that reduces boundary layer seperation for high reynold's number ( higher velocities) . The flow is still smooth . I have some velocity and turbulence intensity graphs to back this up if you want.

[img]file:///C:/Users/shiva/AppData/Local/Temp/moz-screenshot.png[/img]

Geez be careful -you could upset some faktz, stated by some of me most larnerd masters of advanced aerodynamics

Sorry , dint know I only had to state facts . I will only stick to the facts from now on.

Nahh!!! Don't do that. I wouldn't laff as hard then

MattK

Golf balls spins and vibrates while travelling through the air - look at high speed photography. When hitting the ball, it changes shape drastically, and while it return to a sphere, it is still vibrating, getting rid of the excess energy, thus the dimpled surface is not the same as in a static condition in a wind tunnel.

Whilst dimpled wings may work in a wind tunnel, practically it would be difficult to keep a plane clean for optimum performance (air pollution), micro debris deposits i.e. soot, exhaust gas, bugs etc. I don't see a pilot wiping the whole plane clean top and bottom after each flight - becoming "wing wipers" ......[sm=red_smile.gif]

Dimpled wings will push the production cost up a lot - extra manufacturing cost (press dimples in duraluminum sheets, then NDT it for stresses, overlapping sheeting on frame, rivetting sheeting etc.. Investor's money rules everything......

On the other hand, F1 racing car designers have looked at it and discarded it in their 300 km/hr plus carbon fibre cars - closest they come was tossing out the wind screen and making that little lip deflector in front of the driver and directing the exhaust gas directly onto the lower back wing - but that was to create extra downforce, esp at lower speeds. Probably the same for air racing - I've not seen any "gatorback" planes in world cup racing - maybe it is a matter of speed range too....

Some jet fighters had "pores" in the wing through which hot exhaust air is forced but it is limited for various reasons.

Darn, THAT WAS what Tiger Woods trying to do to his Cadillac........trying to put dimples on it...? [sm=spinnyeyes.gif]