Aerodynamics.

[Yalson 514]

1 hour ago, TurnipJF said:

An interesting approach, but it would probably be simpler and lighter to use an inverted Jedelski wing. We know this works very well at model scales. 

A what?

*Googles.*

Oh. Wow. That answers a lot of questions.

[Mad Ax 9310]

Really wouldn't be that difficult to make a Jedelski wing from balsa and stick it to the back of a car.  Cover it with resin and it might be tough enough to survive a buggy race.  Better on F1 or touring where cars don't go upside down that often.  I don't own an RC F1 but I'm pretty sure they have moulded plastic wings, not lexan.  I don't know if the moulded plastic has the right airfoil shape or if they just rely on angle and Newtonian physics.  Moulded plastic would be the right material for longevity in racing once you had the right wing profile worked out.

Maybe strength is why proper airfoils didn't catch on in buggy racing?  I could probably make a Jedelski wing without too much trouble but I can see it getting snapped or ripped off when (not if) I go upside down...  Lexan wings survive crashes extremely well and when they do break they're cheap and easy to replace.  I don't race buggies often but I've got 4 or 5 unused lexan wings sitting around that I've just acquired from others who have hundreds of them lying around.  AFAIK one of the reasons racers don't bother to paint their wings is because they get changed out so often.

Like I say, I could make a Jedelski wing, but I'm nowhere near a good enough driver to actually tell if it actually makes any difference on track.

Just thinking aloud, maybe there's also the case that the air over the back of a buggy is already so turbulent from having passed the body, suspension towers and big wheels that it can't work effectively over an airfoil, but it can still hit a great slab of angled lexan?

[Yalson 514]

40 minutes ago, Mad Ax said:

Really wouldn't be that difficult to make a Jedelski wing from balsa and stick it to the back of a car.  Cover it with resin and it might be tough enough to survive a buggy race.  Better on F1 or touring where cars don't go upside down that often.  I don't own an RC F1 but I'm pretty sure they have moulded plastic wings, not lexan.  I don't know if the moulded plastic has the right airfoil shape or if they just rely on angle and Newtonian physics.  Moulded plastic would be the right material for longevity in racing once you had the right wing profile worked out.

Maybe strength is why proper airfoils didn't catch on in buggy racing?  I could probably make a Jedelski wing without too much trouble but I can see it getting snapped or ripped off when (not if) I go upside down...  Lexan wings survive crashes extremely well and when they do break they're cheap and easy to replace.  I don't race buggies often but I've got 4 or 5 unused lexan wings sitting around that I've just acquired from others who have hundreds of them lying around.  AFAIK one of the reasons racers don't bother to paint their wings is because they get changed out so often.

Like I say, I could make a Jedelski wing, but I'm nowhere near a good enough driver to actually tell if it actually makes any difference on track.

Just thinking aloud, maybe there's also the case that the air over the back of a buggy is already so turbulent from having passed the body, suspension towers and big wheels that it can't work effectively over an airfoil, but it can still hit a great slab of angled lexan?

I think you could easily make a Jedelsky wing and fit it to an RC car, but anything made of balsa is going to have a useable life you can measure in minutes. You can mould plastic in any shape you want and it's the shape that's important, rather than the material it's made out of (although you obviously want something that is stiff enough to maintain that shape).

I think the problem with moulded plastic F1 wings is not shape, but scale. As I said earlier, aerodynamics does not scale. If you build a 1:10 F1 car, you do not get 1:10 scale downforce, you get 1:1 scale downforce with tiny, tiny wings. And remember that these wings are not 1:10 the size of the original – they have been reduced by a factor of ten in all three dimensions, so they are actually 1000th of the size of the original. Given the difference in materials, comparative lack of chassis stiffness, bodywork flexibility and lack of any aero underneath the car and I doubt a 1:10 F1 car gets even a tenth of the downforce you would expect if the car had been perfectly scaled down. They are also heavier than scale by about 50%, which means anyone wanting to drive one across the ceiling is going to be waiting for a while.

[Pata76 501]

But take a look at the Top Force, is that a good design? Looks more like a take of ramp to me  Dont get me wrong here i love my Top Force.

[Juls1 1661]

While you might have some valid arguments, you actually need to go try drive some racing rc cars minus they aero aids and with them back to back.  

Maybe the downforce doesn’t perfectly scale, regardless of that, you do need it and you will be destroyed on the track by the people who have the aero aids if you choose to go out minus your body, or just minus your wing. 

Whenever im using my Tamiya f104, once I get up to speed you can see the front wing bent down in a slightly U shape, as the speed increases this gets more pronounced as the whole car tucks down. 

Now the car may not be as efficient as a full scale model at creating downforce but I can say without it’s wings, it’s impossible to drive once you get past 15-20km/h. 

Instead of making theory’s why not go put them into practice. Fact is we do need the wing on our RC cars, but no one is being forced to use them.

[Palfertronic 74]

as well as building and driving RC cars since 1979, I have been flying RC aircraft (especially gliders) since the early 1970s.the one thing i have not seen mentioned in all of this thread is Reynolds numbers...its used to describe the viscosity of any given fluid (air being the main one)  It had a great effect on aerodynamics, especially when we get down to the sizes of wing we are using on out 1:10 cars..  To make any aircraft fly, the wing must generate as much lift as the weight of the aircraft.

I doubt whether the down force generated by any RC buggy is more than a few grams, 10 at most...and we would be better off just sticking a few grams of lead in the right place to sort out the balance of the car, and sort out understeer/oversteer issues. 

If we scaled up the our cars to 1:1 scale, they would be extremely heavy! even with a LiPo! A Nicad/Nimh would virtually double the weight of the car...

1:1 scale cars are extremely light for their size/speed, making aero packages virtually compulsory above about 100MPH/160Km/H. we have all seen the videos of Le Mans type cars lifting off at high speed!

in short, aerodynamics at 1:10 scale have little or no noticeable effect unless we are going in excess of 100 mph ACTUAL SPEED... So thats about 90% of us out of this discussion already!

But if it makes you feel better,...enjoy!

[Yalson 514]

1 hour ago, Juls1 said:

While you might have some valid arguments, you actually need to go try drive some racing rc cars minus they aero aids and with them back to back.  

Maybe the downforce doesn’t perfectly scale, regardless of that, you do need it and you will be destroyed on the track by the people who have the aero aids if you choose to go out minus your body, or just minus your wing. 

Whenever im using my Tamiya f104, once I get up to speed you can see the front wing bent down in a slightly U shape, as the speed increases this gets more pronounced as the whole car tucks down. 

Now the car may not be as efficient as a full scale model at creating downforce but I can say without it’s wings, it’s impossible to drive once you get past 15-20km/h. 

Instead of making theory’s why not go put them into practice. Fact is we do need the wing on our RC cars, but no one is being forced to use them.

I have driven cars both with and without aero aids, as I mentioned earlier. I also specifically said that I was interested in whether the aero aids on 1:10 off road cars were effective. I know that the circumstances for on-road cars are different and I accept that their aero aids will be more efficient as the environment they work in is more stable. They are also more likely to be genuine aerodynamic devices, with all the benefits that entails. They may not work as well as their full-sized counterparts, but they probably do work.

However, if you have more experience than me of running Tamiya F1 cars, then I will take your experience into account. It certainly seems that there are more people with anecdotal evidence that aero aids work with circuit cars than with off roaders, as you might expect.

[Yalson 514]

2 hours ago, Pata76 said:

But take a look at the Top Force, is that a good design? Looks more like a take of ramp to me  Dont get me wrong here i love my Top Force.

The Top Force is a lovely looking car and one of the few which appears to genuinely try to use aero in its design. The upward sweep of the body from front to rear and the little fences along the edge of the body upper surfaces, plus the biplane rear wing, show that someone has actually thought about how it's laid out and tried to maximise downforce from what is an inevitably compromised platform. Unfortunately, it probably doesn't work, as the front end is still so cluttered with suspension mounts, shock absorbers, turnbuckles and huge spiky tyres that everything behind it will be operating in hopelessly turbulent air that will not be coherent enough to do anything useful. The wing might be high enough to stay out of the way, but I wouldn't count on it.

Also, as an owner, can you tell me if there is a reason for the big, square air scoop on the roof? Does it cover the receiver, the ESC or something else, or is it just there for show?

I do like the Top Force, though. Great-looking car and I gather they are pretty good to drive, too.

[Yalson 514]

58 minutes ago, Palfertronic said:

1:1 scale cars are extremely light for their size/speed, making aero packages virtually compulsory above about 100MPH/160Km/H. we have all seen the videos of Le Mans type cars lifting off at high speed!

For anyone who hasn't... ouch. Astonishingly, he walked away from this. Although I imagine he had to radio back to the pits for some brown trousers.

 

[Yalson 514]

1 hour ago, Palfertronic said:

as well as building and driving RC cars since 1979, I have been flying RC aircraft (especially gliders) since the early 1970s.the one thing i have not seen mentioned in all of this thread is Reynolds numbers...its used to describe the viscosity of any given fluid (air being the main one)  It had a great effect on aerodynamics, especially when we get down to the sizes of wing we are using on out 1:10 cars..  To make any aircraft fly, the wing must generate as much lift as the weight of the aircraft.

I doubt whether the down force generated by any RC buggy is more than a few grams, 10 at most...and we would be better off just sticking a few grams of lead in the right place to sort out the balance of the car, and sort out understeer/oversteer issues. 

If we scaled up the our cars to 1:1 scale, they would be extremely heavy! even with a LiPo! A Nicad/Nimh would virtually double the weight of the car...

1:1 scale cars are extremely light for their size/speed, making aero packages virtually compulsory above about 100MPH/160Km/H. we have all seen the videos of Le Mans type cars lifting off at high speed!

in short, aerodynamics at 1:10 scale have little or no noticeable effect unless we are going in excess of 100 mph ACTUAL SPEED... So thats about 90% of us out of this discussion already!

But if it makes you feel better,...enjoy!

Interesting to hear from someone with experience of RC aircraft and the aero knowledge that goes with it. I have been reading up on aero terms while this thread has been developing, but I hadn't got to Reynolds numbers yet!

Do you reckon that aerodynamics don't work on 1:10 off roaders because they are so cluttered at the front end, because the wings are simply no good or because aero effects just don't scale very well? Or is it a combination of some or all of the above?

[Yalson 514]

5 hours ago, Mad Ax said:

Just thinking aloud, maybe there's also the case that the air over the back of a buggy is already so turbulent from having passed the body, suspension towers and big wheels that it can't work effectively over an airfoil, but it can still hit a great slab of angled lexan?

This is what I reckon, too.

[Mokei Kagaku 2706]

24 minutes ago, Yalson said:

The upward sweep of the body from front to rear and the little fences along the edge of the body upper surfaces, plus the biplane rear wing, show that someone has actually thought about how it's laid out and tried to maximise downforce from what is an inevitably compromised platform. Unfortunately, it probably doesn't work, as the front end is still so cluttered with suspension mounts, shock absorbers, turnbuckles and huge spiky tyres that everything behind it will be operating in hopelessly turbulent air that will not be coherent enough to do anything useful. .

Isn't it entirely obvious that the designers at Tamiya must have acknowledged this before they started on the design of the body? In other words, the body was most certainly designed like it is purely for cosmetic reasons only (and of course the lower edge for sealing against the undertray).

[Yalson 514]

8 minutes ago, Mokei Kagaku said:

Isn't it entirely obvious that the designers at Tamiya must have acknowledged this before they started on the design of the body? In other words, the body was most certainly designed like it is purely for cosmetic reasons only (and of course the lower edge for sealing against the undertray).

Probably. But the annoying thing is that if the front end didn't have so many bits interfering with the airflow, it might have actually worked. Or at least helped.

[Yalson 514]

Of course, you don't have to have massive shock towers and shock absorbers cluttering up the front end at all. The Schumacher Top Cat had its suspension system hidden within the body and even had some of its suspension components made with a more aerodynamic cross section. No idea if this was done specifically for aero reasons, but it's unlikely. Probably had more to do with keeping them out of harm's way. Was the Top Cat also the one with the rubber band at the front, which allowed the suspension to snap backwards if it hit something, then snap back again afterwards? Can't remember now.

Although it ultimately won't have made much difference to the amount of downforce generated by the wing at the back, it would be interesting to put this in a wind tunnel alongside, say, an Ultima or RC10 from the same period, to see how much extra turbulence and drag the suspension system created.

This would obviously be extremely difficult to do with a 4WD car, but it worked perfectly well in the 2WD Top Cat, and looked great too. The Marui Hunter also had an inboard system, but that was housed within the nose, rather than in the chassis. But if you're driving a Marui Hunter then aerodynamics are the least of your problems.

[Juggular 4964]

I like that suspension!  

For F-1 cars, aerodynamics is important.  Fokker DVII stalled at 34mph.  F104 could easily do the same speed as the real airplane.  Since F104 is like 650 grams (I'm guessing), several grams of downforce would be like adding 10% of its weight.  Entry level buggies would be going at half the speed (15-17mph), which means it encounters only 1/4 of air resistance.  Even 1/8 buggies going at the same 34 mph won't be affected as much as F1 cars, simply because 1/8th buggies weigh 3.2kg.  Momentum is about 5 times, wind resistance is 4 times.  So 1/8th should behave similarly to entry-level buggies when it comes to aerodynamics.  

That is not to say it's completely ignorable.  Imagine flinging a 2 gram lead weight onto the rear wing of a buggy while it's jumping.  That could alter the pitch just a bit.  

So, as Yalson already stated, F-1 (or equally light and fast on-road) cars are probably most affected by aerodynamics.  Other types of RC cars, not so much.  (Yet, all this talk of wings made me want to put a wing on my Konghead...)  

I had seen other people put a wing on it.  While looking for it, this popped up.  All wheels turn at the same rate, how does it work with smaller front wheels?  Oh, to slide around?  Wings might not be functional, but these are cute.  

 

[Mad Ax 9310]

19 hours ago, Palfertronic said:

I doubt whether the down force generated by any RC buggy is more than a few grams, 10 at most...and we would be better off just sticking a few grams of lead in the right place to sort out the balance of the car, and sort out understeer/oversteer issues. 

I think the issue with adding weights is they contribute to the mass of the car in every direction.  If you go over a bump with a weight in the back of the chassis the mass is thrown upwards, so it will take weight off the tyres.  Aerofoils or sloping wing sections only add downforce in the direction they are mounted and only when moving at speed.

@Yalson, I wonder if your question has almost answered itself - proper aerofoils don't scale well enough to be effective on a 1:10 model.  To make them effective may either make them too big for the car or would compromise the rest of the chassis design so much that the end result isn't worth it.

And yet, a big slab of lexan, which would be woefully inefficient on a 1:1 car, actually works perfectly well at 1:10 scale for the exact same reason that aerofoils don't - the big angled surface of the buggy wing is effective at adding downforce without creating the excess drag that it would create on a 1:1 car.

This is pure speculation on my part - I don't have the maths to back that theory up.

With a number of people already engaging in a Tamiyaclub Top Speed Shootout, we could easily test the drag theory - let someone do a speed run with their Top Force on a smooth tarmac road, then do the same run without the wing.  There might need to be various runs with different gearing to get a solid result but from that we could see how much drag the wing adds and estimate what effect that downforce would have on a dirt track.  We might also find out if the chassis becomes unstable during high speed runs with no wing, even on smooth tarmac.  There's a possibility that the car would need a completely different suspension setup to even get a top speed run without a wing (you'd definitely expect this with a 1:1 drag car).

[ThunderDragonCy 7876]

31 minutes ago, Mad Ax said:

I think the issue with adding weights is they contribute to the mass of the car in every direction.  If you go over a bump with a weight in the back of the chassis the mass is thrown upwards, so it will take weight off the tyres.  Aerofoils or sloping wing sections only add downforce in the direction they are mounted and only when moving at speed.

This is only true of unsprung mass. Actually the bigger the difference in sprung to unsprung mass makes the suspension work more effectively and the car more settled, i.e. a heavier chassis will ride bumps more effectively than a lighter one for the same wheels/arms/shocks. When the bump force is transmitted to the sprung chassis through the shocks the inertia of the heavier chassis prevents it being moved as much as a lighter chassis. It's not a no cost option in terms of performance though as you rightly point out. It has to be accelerated and braked which takes more effort/power or takes longer for a given power output, and the same inertia preventing it from being unsettled by bumps also prevents it from turning up quite so effectively (more force wanting to plough straight on) but it's less of an issue if the extra weight is around the centre of mass of the vehicle. 

I have been reading this with interest as I am fascinated by aerodynamics but it is the one branch of engineering physics which really eludes my understanding. For buggies intuitively I think @Juggular has it about right. On jumps that air dam on the back is bound to have an effect on the attitude of the car.

I would really like to know if these aero shells on race buggies actually do see some CFD or a wind tunnel at all. You read a lot about people preferring one body to another, but as mentioned above I suspect it's the actual mass distribution of the body at work rather than aero. A cab forward 2wd race body has more of its weight at the front which is a better weight distribution. 

[Yalson 514]

6 hours ago, Juggular said:

So, as Yalson already stated, F-1 (or equally light and fast on-road) cars are probably most affected by aerodynamics.  Other types of RC cars, not so much.  (Yet, all this talk of wings made me want to put a wing on my Konghead...)  

I had seen other people put a wing on it.  While looking for it, this popped up.  All wheels turn at the same rate, how does it work with smaller front wheels?  Oh, to slide around?  Wings might not be functional, but these are cute.  

 

Ha ha! Love the F1 conversion, but they should surely have gone with a March 2-4-0 or Williams FW08B instead of a Tyrrell P34, as the Tyrrell had four wheels at the front and two at the back.

I had a look for weights for the F104 and it is surprisingly difficult to find any figures. However, a site I was looking at a while back suggested a chassis would have a racing weight of 1100g, while another site suggested the F104 Pro in standard spec weighed in at 1010g, which is about 250g over scale.

[Mad Ax 9310]

On 9/9/2018 at 7:55 AM, ThunderDragonCy said:

This is only true of unsprung mass. Actually the bigger the difference in sprung to unsprung mass makes the suspension work more effectively and the car more settled, i.e. a heavier chassis will ride bumps more effectively than a lighter one for the same wheels/arms/shocks.

Another disclaimer: I'm far from being a chassis dynamics / suspension expert so the below is based on my layman's understanding - I'm quite prepared to be wrong and corrected

So I'm sure the above is true when concerning bumps in the surface that can be absorbed by the suspension, but what about when the bump exceeds the suspension travel?  On a buggy course, for example, what about a jump?

As far as my understanding goes (and temporarily excluding the effects aerodynamics - assume we're testing in a vacuum ) if I jump a heavy car and a light car off the same ramp at the same speed, they'll both follow the same arc, jump the same distance and land at the same point.

Given that buggies typically have to cope with jumps, and a lot of the talk about wings on buggies relates to handling in the air, I think there's still a place for aero over mass.  The other benefit of aero is that it only really comes into effect at speed - so you don't have the trade-off in acceleration, braking and changing direction that you have with adding mass to the chassis.

FWIW I've seen some modern 2wd buggies have little wings on the front shock towers too.  I've heard these are to keep the nose down during jumps, although I've also heard they're to stop the towers from damaging the astro and/or the marshals if they land upside down...

[Juggular 4964]

Good point about having no trade-off in acceleration, braking, etc.  

Here is something I found interesting... 

We all know that if you drop a steel ball from the tower of Pisa, along with a rubber ball of the same size, they land at the same time.  Gravity accelerates things at the same rate, no matter the mass.     

But...  momentum is different.  If you throw a steel ball and a rubber ball horizontally, they don't go the same distance.  I find that odd. But true.  I have BB guns.  0.12g plastic BBs don't fly well at all. They are useless. 0.2g is the standard, they do okay. I have 0.23g, 0.25g, 0.28g, 0.3g, even 0.33g.  The heavier they are, the more accurate they fly.  Heavier things fly truer due to momentum.  Air has to exert more force to alter the course of heavier projectiles (or cars).  This is why 1/8th cars weighing 3.2kg, won't be affected by air as much as light F1 cars.  The force air gives is the same.  Just that 1/8th buggy is a freight train when compared to F1 cars.  

In the air, however, even small amount of force can decide nose-up or nose-down.  Like you were saying, Mad Ax, tail wings could work like feathers of an arrow. (That statement actually changed my understanding! You just put it out there, but I kinda feel like I owe you one)  Only when the rear wing is going through the air already punched through by the front of the car, would it encounter the least resistance.  If the tail goes up, it will be hit with more air.  If tail dips down, it will be hit with more air too.   So it can work like a badminton shuttle.  It comes at you with the heavier nose first. You hit it with your racket. The shuttle changes the course, because the nose is heavier, and has more momentum than the feathers.  The rear wing of an RC car can work like the direction-correcting feathers of the badminton shuttle.  

Front wing, I'm not so sure if it's a good idea when jumping.  Once in the air, it can aggravate the pitch.  If the car is nose up in the air, the front wing can make it even more nose up.  If the car is nose down, it can make it even more nose down.  I suppose, the point of a nose wing is that it will keep the nose down until the jump, so the departure angle could be stable.  I think the angle of the ramp and the weight distribution of the car dictates the pitch more, and rear wing can correct a bit.  If both front and the rear work ideally, they could keep the jump shallower by keeping the car lower. (at the risk of landing a few inches shorter)  

 

 

 

[Yalson 514]

13 hours ago, Mad Ax said:

As far as my understanding goes (and temporarily excluding the effects aerodynamics - assume we're testing in a vacuum ) if I jump a heavy car and a light car off the same ramp at the same speed, they'll both follow the same arc, jump the same distance and land at the same point.

Given that buggies typically have to cope with jumps, and a lot of the talk about wings on buggies relates to handling in the air, I think there's still a place for aero over mass.  The other benefit of aero is that it only really comes into effect at speed - so you don't have the trade-off in acceleration, braking and changing direction that you have with adding mass to the chassis.

FWIW I've seen some modern 2wd buggies have little wings on the front shock towers too.  I've heard these are to keep the nose down during jumps, although I've also heard they're to stop the towers from damaging the astro and/or the marshals if they land upside down...

Downforce increases proportionally with speed, but then so does drag, and the latter potentially has a greater effect on overall performance. Now that you can get battery packs of up to 5000mah and brushless motors, which are much more efficient, you can more or less write your cheque in terms of speed and acceleration. But back in the days when 1200mah SCRs were the best cells available and battery performance was marginal, to say the least, anything which sucked any life out of those precious cells was a big deal. You'd trim the wings down as much as you dared and mount them as flat as possible, as we didn't know how much downforce they were giving us, but we knew they were causing drag and that literally is the equivalent of adding weight to your car as it will drain your battery just the same.

Nowadays, not so much. You could attach a kite to your car and it'd still last five minutes.

And just to show there is nothing new under the sun, I give you the Brabham BT26 from 1968. These high-mounted wings were banned shortly after this as the mounts were prone to fail and cause accidents. Nobody at this point really had any idea how aerodynamics worked, so the teams generally just mounted the wings as high as they could to get them out of the cluttered airflow caused by the car body and suspension components. The front mounted wings were normally only used for qualifying as the added enough downforce to the front wheels to make them physically difficult to steer for long periods, which was a result of them being added in an ad hoc fashion to cars originally designed and built without them.

[Yalson 514]

BITD we used to fold bits of Lexan over and screw them to the tops of the shock towers, although this was to protect the cars from the tarmac surface we raced on in the winter rather than anything else.

[Yalson 514]

Or, you could use cable guides, as can be seen here on my Lazer's shock towers from the last time it was used.

 

 

[Yalson 514]

7 hours ago, Juggular said:

Good point about having no trade-off in acceleration, braking, etc.  

Here is something I found interesting... 

We all know that if you drop a steel ball from the tower of Pisa, along with a rubber ball of the same size, they land at the same time.  Gravity accelerates things at the same rate, no matter the mass.     

 

If both front and the rear work ideally, they could keep the jump shallower by keeping the car lower. (at the risk of landing a few inches shorter) .

Wings do have a trade-off in braking, but they generally improve it.

Also, do you remember the other experiment from school physics classes which involved things falling? It may have only been our Physics teacher Mr Budd who had one of these, but I remember being fascinated when he brought out a vacuum-filled* glass tube which had both a coin and a feather in it. Obviously, because they were in a vacuum, when he turned it upside down the feather and the coin fell at the same rate – very quickly. Air is surprisingly dense stuff when it comes at you quickly and it is only the density of air counteracting the force of gravity which creates the concept of terminal velocity, or the fastest an object can fall in Earth's gravity and atmosphere.

The only thing stopping the feather falling as quickly as the coin under normal atmospheric conditions is drag. The force of gravity is countered much more easily with the feather as it is lighter and the drag of the air can pull comparatively harder on it to hold it up. The coin is smooth and heavy, so suffers far less impedence. Cars are much more like coins than feathers, but that drag will still slow you down.

The risk of landing a few inches shorter is no bad thing. If you are on the ground you can accelerate and potentially come out quicker. This is why BMX and Moto X riders try to stay on the deck if they can. If you are on the ground you can travel quicker than a rider sailing gracefully through the air on a longer and slower arc.

 

* I know, I know.

[Juggular 4964]

Yep, "hang time" in the air looks cool, but you lose time.  You cannot accelerate in the air by turning tires really-really-fast.  

Air pressure is often underestimated.  Human experiment shows how my wife sleeps all day if the air pressure is less than 1 bar (rainy days).  She's out gardening all day, if it's above 1 bar.  (no animals were harmed in the experiment)  

Jokes aside, if you try to fan with a flat piece of something, and blow a piece of crumpled paper at 30mph, it takes some force.  RC cars are facing that kind of force.  The cross-section of an RC car is like A5 size paper, and RC cars are not brick shaped, but that still has to go through air.  Wings are not negligible.  But as Yalson said, I wish there was wind tunnel data.  

At 30 mph wind, how much does an RC car gets pushed back, with/without a shell.  

How much down force can a shell with wings generate, at 30mph, etc.  Of course, momentum cannot be measured this way, but at least it will be a good starting point.  I don't like math, but I would love to see an exact number like how many grams of down force, etc...

That's why I like videos like this.  (going off tangent warning!)  This Japanese guy does a good job comparing between bushings and a bearing.