AERODYNAMICS (Fluid Dynamics)

[SHY]

Let's open up the mother of all cans of worms...

Firstly anyone interested should read Elvo San's article:
http://users.pandora.be/elvo/8/1.html

We had a VERY long and very interesting discussion about this on myTSN back in 2001/2002 (?). The good old myTSN is sadly gone with the wind, but I managed to save some of the stuff:
http://www.ymr.no/bilder/aerodynamics_discussion.pdf
(this is mainly for 1:8 TR, but still much can be learned)

Here is a super cool presentation from a university on the topic:
http://www.ymr.no/bilder/race_car_aerodynamics_evolution.pdf

I learned a LOT from my master Elvo here, and I must say this is extremely fascinating stuff!

For the real lazy people you can read the "conclusion" here:
http://users.pandora.be/elvo/8/9.html

Here's a more recent debate:
http://www.one-ten-rcforums.com/4wdrc/viewtopic.php?id=1333

Now let's talk turkey!

One of my big surprises was that open wheel cars are extremely inefficient as to aerodynamics. Closed wheel cars are faster. I.e. F1 cars would have been faster with a CanAm style bodyshell...

But for us RC people my biggest "revelation" was when Elvo pointed out that inverted aerofoils etc does not work for our scaled down cars. It's simply a matter of deflecting air for us...

Narrowing it down to 1:10 OR I think we could still gain from having lighter cars and much bigger wings.

2501
This would have been ideal! Extremely low weight, high grip, extreme agility... :lol:

But we need something to propel the thing, so then comes a chassis with some sort of motor +++ and so we need 4 wheels to keep this thing stable... still I claim the basic idea is to keep the weight at an absolute minimum and maximise downforce, but it's gotta be balanced and stable to drive and jump of course. Since we have so much power in excess we don't really get a "drag penalty" like real cars!

When some say that adding weight is better, I don't argue that it's right. I'm sure it can be faster. I still think that more downforce genereated from a shell, wings or ground effects could do the same and be even faster. Very slippery slopes is different though, with low speeds wings don't do much and adding weight may be the only solution for more tyre load/grip...

Share your ideas guys!

[Lee]

I agree that a lighter car is faster over a single lap but i think people add weight to make the car easier to drive, i personally never add weight , i like the car to feel sharp. (i did add 20g to the front of a losi cr though to make it steer:lol:)

I know a british company actually had someone work with them from mclaren on this sort of stuff, it obviously cost them a fair bit of money and the result was, they learned nothing because RC is very different to 1:1 cars.

Just because the cars are 1/10th scale it doesnt mean gravity and air particles are 1/10th scale:thumbsup:

[SHY]

Yup, you can't simulate or calculate as to fluid dynamics for RC cars. So you can't tell if a shape is good or not...

From track racing we've tested so many bodyshells you wouldn't believe it! I remember one season I painted, cut out and tested 10 different new shells... and all were slower than the old ones...

Some even look totally equal, yet perform totally different on the track. And some are good on one track, but not the next...

Furthermore a boxy shape can even be more smooth to drive than a round shape... so you just gotta test, test, test...

You might wonder when you see F1 if they are sure as well... there so much winglets and stuff going on, and the cars are very different from each other these days...

[Zedman]

Read the conclusion, there is a big mistake

"The reason is quite simple: R/C cars are too small and go too fast"

RC cars do not go too fast they do 'scale' speeds and weight has nothing to do with it.

They actually go relativly slowly cornering at under 40 miles an hour (do they even get up to 40mph on the straights on some tracks)

Aero dynamics only come into effect at SPEED, (google inverse square law), this is the reason you only see race cars running spoilers, yes a formula 1 car can theoreticaly stick to the ceiling upside down at 200mph BUT the spoilers would have virtulaly no effect at 50 mph, its the same with plane areo foils, for a jet to take off it has to go very FAST due to having small wings, for slow speed take off ie gliders, planes employ massive wing spans and still need a reasonable speed.

Spoilers look cool but dont really work, when was the last disscusion you saw regarding wing angles on a car doing under 50 mph ?

[SHY]

Come on people! Give us your views, experience and ideas!

[glypo]

What should we be sharing our opinions on? I don't understand the question, sorry.

[Scouser]

Personally, the only time I think about air flow is when I am cutting venting holes. I dont think about downforce, I am making sure enough air is getting into the shell to keep the hot bits cool! IMO the main purpose of the rear wing is to protect my shock towers when I crash!:lol:
I think worrying about downforce provided by the shell and wing is, to some extent, a moot point. The benefits of high downforce wings and bodyshells are most noticable at top speed which is only attained for maybe two seconds a lap? Not really enough to worry about for me.

[glypo]

Spoilers look cool but dont really work, when was the last disscusion you saw regarding wing angles on a car doing under 50 mph ?

That's not correct. A light aircraft can take off at around 50mph with a small wing. You can't consider jets at all, they are designed totally differently. Firstly have large swept or delta wings, so that the sweep delays the critical mach number. The aerofoil is much thinner, as it's designed to be efficient during cruise at 500mph, not to take off at 50mph. The reason people think gliders wings are so big is because of the span. The truth is, they aren't big. They have a very small chord, to give a large aspect ratio, it's more efficient which is important in the unpowered world.

Another good example is could be my RC airplane that weighs around 4kg (big beast) and that can take off at just 10-15 mph, on a wing smaller then 2m span. A good way to see just how strong airflow is by just sticking your hand out of a car window when you're travelling 30-40mph and feel the resistance, it's mad.

Formula 1 cars don't use spoilers, so I'm not sure how to comment on that. But even at low speed aerodynamics is important. In 1/18th scale classes where some corners are taken at speed, it's amazing the effect it has. In in rallycross, if you loose a wing you certainly notice the difference in handling on tracks with fast! However for 1/10th off-road, we could be talking too slow.

[SHY]

Thx lads, now we are getting somewhere!

I just find this topic very interesting, and it has so many facets. Let me first comment on Zedmans post...

Read the conclusion, there is a big mistake

"The reason is quite simple: R/C cars are too small and go too fast"

RC cars do not go too fast they do 'scale' speeds and weight has nothing to do with it.

They actually go relativly slowly cornering at under 40 miles an hour (do they even get up to 40mph on the straights on some tracks)

Aero dynamics only come into effect at SPEED, (google inverse square law), this is the reason you only see race cars running spoilers, yes a formula 1 car can theoreticaly stick to the ceiling upside down at 200mph BUT the spoilers would have virtulaly no effect at 50 mph, its the same with plane areo foils, for a jet to take off it has to go very FAST due to having small wings, for slow speed take off ie gliders, planes employ massive wing spans and still need a reasonable speed.

Spoilers look cool but dont really work, when was the last disscusion you saw regarding wing angles on a car doing under 50 mph ?

1) Speed: RC cars are on the contrary in my opinion insanely fast relative to scale. I'll stick for now to 1:8 TR which I know from many years of racing the class (only raced 1:10 OR one year ). They normally reach 110 km/h top speed. Which would have been 110*8 = 880 km/h for a real car (or is it ^8??? Don't recall...) So they are way too fast relative to scale. And cornering speeds are actually insane! I'd love to see some G-force recordings from these cars!!!

2) IMHO wings, shells and spoilers DO work even at very low cornering speeds. I've tried without the shell many times (1:8 TR), and there's absolutely no grip at all! The car's just sliding around from standstill! And bodyshell differences are highly noticeable even in low speed chicanes.

3) Spoilers, diffusers, splitters - all of it works, believe me! (The whole shell of a 1:8 track car is one big diffuser btw)

4) Buggies have open wheels, which create massive turbulence. So you can't do anything there, only over and between (wings and shell). And ground clearance is high, so ground effects won't come into play. I still think there is yet some to be gained by optimizing aerodynamics. RC competition is getting closer all the time, it's the tiny details that often decide the outcome these days. Does the EFRA rules specify that the wheels must be open?

Question: In cases where one adds weight to a 1:10 OR car, when does it help the most? When accelerating out of a slow corner?