Speed aerodynamics

[Frh076 2]

Would this design increase the top speed of the car, or should i do something else/ change it? I took inspiration from the McLaren speedtail.

[wilsonian 41]

If your trying to break speed records etc then probably. :-)

[Superluminal 3750]

I would imagine the front end of that, what looks like the zakspeed capri body shell, probably isnt going to do it any favours if you are going for speed runs. 

Also, I have one of those shells too and its quite weighty.

[markbt73 5310]

I doubt it would make much difference at all, really. Aerodynamics do play a role in RC cars, but full-size designs often don't scale well. Usually what works for RC is something that would look ridiculous in real life, and probably not work at all.

For example, when I was racing pan cars on an oval track, we all cut almost the entire rear panel of the body away and left it open. Why? Because otherwise air would get trapped in the giant empty space behind the rear axle and the back of the body, create a high-pressure area inside the body, and the car would lose traction and slow down or spin out. In addition, we added large rear wings mounted directly to the rear pod (not the body) so the airflow would press the rear axle down and add even more traction. Try to run a car with an intact rear panel and no wing (as people often did who were only interested in the concours competition and not racing), and you'd be a good 10% slower.

Another thing to consider is that you have to look at the airflow over the car as a whole, not just one spot. The McLaren has that long tail, but it also has almost no frontal area, and is shaped so that air is directed smoothly over the top (and underneath) and over the tail. Adding the long tail to what looks like a Tamiya Capri body won't have the same effect, because the air hits that brick wall of a front grille before passing over the car. In fact, it might be slower overall, because it no longer has the rear spoiler to keep the rear end steady.

But never let it be said that I discouraged someone from trying weird stuff to see what happens. Go for it. Keep trying things, keep a log of what you try, and go back to the way things were if it doesn't work. Experimentation is a big part of the fun of this hobby.

[Frh076 2]

40 minutes ago, Superluminal said:

I would imagine the front end of that, what looks like the zakspeed capri body shell, probably isnt going to do it any favours if you are going for speed runs. 

Also, I have one of those shells too and its quite weighty.

Yeah. I also have made the front less steep, and have reduced the air under the car from putting a piece of thick paper(?) To almost rub against the ground. It works very fine. However, want to know if this or a similar sort of mod on the rear can get my car to hit somewhere around 100mph.

[WillyChang 1814]

If you really care about aero... you'd need to be hitting above 60km/h to matter.  

Air gets under the shell... you'll gain speed by chopping off whole rear panel (look at rear end of any pan car or 1/8th racer) rather than pasting on even more obstructions for the air trying to escape.

No point building a underbelly pan until you can seal the wheelwells too. 

There's a fair bit of "downforce" when air hits the windscreen of a sedan car. We needed to put a 5th bodypost in the middle to support the roof, otherwise it caves in and squashes down onto the tyres. 

Stiffen your suspension to resist the downforce (unless your bodyshell is mounted directly onto wheel knuckles - that's why suspension pan cars do that). Otherwise you're losing power if your bodyshell or chassis keeps scraping the ground. (Plus they wear off sooner than you think too, even 3mm carbonfibre chassis can grind away to knife edge in 1 run!)

Make sure your tyres are belted or solid, you don't want them ballooning out into skinny discs giving no grip.

 

As mentioned above... might be more aero to mount that Zakspeed BACKWARDS  looks more wedgey at the tail than its blunt front end.

 

[Superluminal 3750]

At 100mph I wouldnt have thought body mods made of paper would not stay attached for very long. The air resistance at that speed is huge. I would think on an rc car that some form of down force would be better than aeordynamic aids because of how light they are.

If your chassis is set up for the Capri bodyshell it will have a 251mm wheelbase and there are not a lot of other body shell options at this size (martini porsche and 240z?)

What chassis is it you are anticipating for your high speed runs? If its the tt01 or tt02 that used to come with the capri body sheel the rear arms are reversible so you can lengthen the wheelbase to 257mm which means a whole range of shells will be available. The longer wheelbase will also make it slightly more stable in a straight line.

I would then try and find a pan car style body or one of the smooth jelly mould racing touring car bodys (ie protoform, bitty, mon-tech etc) as these are shaped to have low air resistance and are lightweight.

[WillyChang 1814]

13 minutes ago, Frh076 said:

....get my car to hit somewhere around 100mph.

What chassis?

Are you throwing it off a tall cliff?

If Gravity is not involved... you'd be hard pushed to get a TT01/2 reliably above ~60km/h with "normal" RC electronics. 

Chassis parts slop is mega bad trying to keep it in a straight line at any speed.

Approaching 100km/h you'll need about 4X the power of 60 above. That's both making the power (batts/ESC/motor that won't blow up) AND getting that power onto the road (drivetrain, tyres, suspension). 

100km/h is only 62mph. You want 100mph? Quadruple that power & more.

 

End of the day, speed costs money. How fast can you afford to go?  

[Frh076 2]

The chassis is the 4tec 2.0 vxl, with castle "something" kv motor. I know the car is 1cm too wide for the body, but I had this body left after a flip over (le mans-style crash, almost burning through the roof at 100kmh that is why I attached the front cardboard).

[nbTMM 433]

Will it increase the top speed? There's one certain way to find out: try it!
 

56 minutes ago, WillyChang said:

If Gravity is not involved... you'd be hard pushed to get a TT01/2 reliably above ~60km/h with "normal" RC electronics. 

stew_mac on this forum has his TT02's running close to 200kmh with nothing too abnormal:

https://www.tamiyaclub.com/forum/index.php?/topic/80775-tamiya-club-official-top-10-fastest-rcers-list/&page=99

Personally I have a TT02 with a trackstar 5130kv motor on 2S and that runs 100kmh with a lancia delta body (as aerodynamic as a brick and with a near vertical rear wing). I don't run a gyro, just 1million cst oil or a lock block in the front diff, 7k in the rear and lots of caster angle and I find above 50kmh the car actually gets more stable. It's below 50kmh that is the problem because of traction (torque steer and drifting). The only part that required modification was cutting a hole in the gear cover to fit a big spur gear. https://www.youtube.com/watch?v=8WF4LDK9WRo

 

 

[WillyChang 1814]

12 minutes ago, nbTMM said:

Personally I have a TT02 with a trackstar 5130kv motor on 2S and that runs 100kmh. I don't run a gyro, just 1million cst oil or a lock block in the front diff, 7k in the rear and lots of caster angle and I find above 50kmh the car actually gets more stable. It's below 50kmh that is the problem because of traction.

meh, might've noticed I steer clear of speedrun thread... 

main thing is "reliably" maintaining that speed  if your rig blows up before it can make 2 runs in opposing direction, it won't pass them World Records recording judges 

GPS gizmos all have their own eccentricities too... "instantaneous" measured velocity ain't always a me as proper distance travelled over time.

 

But I'm mainly into the engineering part of things  all ye lawyers & politicians feel free argue amongst yourselves how you want to measure & certify; I'll stick with wrenching. 

If there's no limits as to motor/battery/drivetrain... heeeey Elon, can I borrow some Tesla parts?!?  

Back to 1/10 RC. Don't think gyro would help, haven't ever wanted to stick one in. I just turn steering EPA down to about 10% or so, that's more than enough steering to negotiate a 400m banked oval track. 

Shaft vs belt on a 1/10 tourer... I like shaft better, seems more efficient at higher rotational speed. Comes a point though, I'm estimating it around 90-110km/h, that the drag from a 4WD drivetrain becomes a liability vs a simpler direct-drive RWD even though you lose 2 driven wheels. Fair trade to wide sponge on rear of a pan car.

FWD M03 mini is surprisingly stable at speed too, for how tiny it is. Been wanting to try a FF03 for top speed dash but haven't gotten around to it.

 

Then sanity kicks in & asks why we're still trying to get RC cars going fast, when a plane or quad can do "GPS speed" quicker & cheaper.  

[nbTMM 433]

I did about 5 runs back to back once without checking temps, at that point the motor can was about 100c so I called it quits. No damage was done. I've installed a motor fan since then and now the ESC hits temp protection (>85*c) first. 
A lower kv motor on 3S geared for the same speed would probably run a full pack without overheating due to higher efficiency but where's the fun in that? It's more fun when not blowing it up or crashing it is part of the challenge  

[TurnipJF 9181]

5 hours ago, WillyChang said:

Then sanity kicks in & asks why we're still trying to get RC cars going fast, when a plane or quad can do "GPS speed" quicker & cheaper.  

True that - when RC gliders are going at 800+ kph, even our fastest cars seem rather pedestrian by comparison.

But then the same can be said of full-size. Many 1:1 scale aircraft can go significantly faster than a car, but people still try to build fast cars.

[WillyChang 1814]

Weird thing is... I once tried a free rolling chassis with wheels and bolted a motor and prop on top. It made a hecka lotta noise but didn't go particularly fast... why?! 

Stick a wing on it & it'll taxi just as fast  then with my luck the moment it gets airborne gravity sucks it back down quick smart 

 

[El Dougo 326]

The amount of Meh in this thread saddens me deeply .

Bottom line is that just about anything you do to a Capri would improve the Aero and hitting 100Mph is not easy.   If you are serious about hitting that magic number you will need a body designed to be aerodynamic from the get go. Then add a 7000kv+ motor and a high capacity high discharge 3s battery and give it a go (other combinations are available).

I would go with the Bugatti Chiron approach (drop off with open back), they are only going for 250Mph with Speedtail and I suspect the “Tail” branding may have influenced the design.

[Fabia130vRS 2098]

I always wanted such a 1/8 nitro racer with electric conversion.

I think this chassis or similar ones are perfect speed run rockets.

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F352617627269

4wd, 8s, sponge tires, pan car body only and full go!

 

anyone owns one of these?

[WillyChang 1814]

21 hours ago, Fabia130vRS said:

I always wanted such a 1/8 nitro racer with electric conversion.

I think this chassis or similar ones are perfect speed run rockets.

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F352617627269

4wd, 8s, sponge tires, pan car body only and full go!

 

anyone owns one of these?

Power Racing made XR80 over 12-15yrs ago afaik... looked like a decent 1/8th aimed at entry level club racing; don't know whose design they imitated. 

Biggest drawcard was that it was cheap  vaguely remember it got sold as either RTR or kit with engine; the XR80 was a third or less of Serpent Veteq chassis kit only at that same era. Half the price of HPI Proceed.

No idea what's the benefit of shoehorning modern Traxxas power into ancient racer chassis... does it even go any better than the whole Traxxas car it can me from?  

[Wooders28 4718]

I think the extra weight would undo any gains, as @El Dougo says, start with an areo body to start with and/Or follow @stew_mac, and modify your own with carbon fibre.