Gravity Racing - Improving Aero to Beat the Best

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jimcroisdale
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Joined: Wed Nov 09, 2016 11:47 am

Re: Gravity Racing - Improving Aero to Beat the Best

Post by jimcroisdale » Fri Oct 06, 2017 8:12 pm

The one issue that gravity racers have (at least on the track in question) is that they need to be incredibly stable. The gradient is 18% for the final drop and sidewinds are not uncommon, as well as a less than perfectly even road surface. Looking at the eco racers, you'd have a job on getting anyone to drive them as they look as if they could fall over :-) If the body needs to be an "elongated egg" shape, i think outboard wheels (the wheels used are only small) are unavoidable.

I'm unlikely to ever have access to a wind tunnel, and even getting some CFD is going to be a bit of a leap, so in my case it's really going top be a case of "broad stroke" improvement. If the elongated egg shape (on paper at least) is a good improvement on what's gone before, then it would make sense for me at least to try that. As far as the construction of the body goes, at least its a fairly "uniform" shape, that shouldn't be too hard to make.

What do you think?

For reference, you can see Fast Donnie Schoettler's 99mph run here: https://www.youtube.com/watch?v=CeZTOi-yAUM

Greg Locock
165
Joined: Fri Jun 29, 2012 11:48 pm

Re: Gravity Racing - Improving Aero to Beat the Best

Post by Greg Locock » Fri Oct 06, 2017 8:31 pm

I'm not going to argue with what works but his suspension seems pretty rigid. Sidewinds are a concern, any shape you use should have some sort of fin, at least initially.

We did a fair amount of work with a flat tray bolted on top of a car and 1/5 scale models.

jimcroisdale
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Joined: Wed Nov 09, 2016 11:47 am

Re: Gravity Racing - Improving Aero to Beat the Best

Post by jimcroisdale » Fri Oct 06, 2017 8:49 pm

None of the cars there this year used suspension at all. :-)

As regards a fin, if you mean a long sharkfin type thing then yes, I have thought that also.

It's not rocket science.... (oh wait... )

Greg Locock
165
Joined: Fri Jun 29, 2012 11:48 pm

Re: Gravity Racing - Improving Aero to Beat the Best

Post by Greg Locock » Fri Oct 06, 2017 8:54 pm


Greg Locock
165
Joined: Fri Jun 29, 2012 11:48 pm

Re: Gravity Racing - Improving Aero to Beat the Best

Post by Greg Locock » Fri Oct 06, 2017 9:14 pm


jimcroisdale
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Joined: Wed Nov 09, 2016 11:47 am

Re: Gravity Racing - Improving Aero to Beat the Best

Post by jimcroisdale » Fri Oct 06, 2017 9:21 pm

Yes, those are well known on the scene, or well, at least to me. A whole host of car manufacturers made some, but unfortunately they were only around for a short time before being sold to collectors and never took part in any serious racing or speed attempts. GM, Volvo, Nissan, Bentley, Aston Martin and Audi all made them, to name the ones I can remember off the top of my head.

To be honest, looking at the better ones, and the eco marathon cars, what I can never understand is why the current super fast G Cars dont try and copy what they did.

I see this as a golden opportunity. If the aero of the record holding car(s) is quite poor at the moment, someone like me with relaitively modest fabricating skills has a chance to beat them, hence the OP. The big players are going to realise this at some point and the opportunity is going to disappear.

Anyone wanna join team GB? I have a top driver who did 90+ this year and has crewed on the top team.... (I myself have never been...)

jimcroisdale
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Joined: Wed Nov 09, 2016 11:47 am

Re: Gravity Racing - Improving Aero to Beat the Best

Post by jimcroisdale » Fri Oct 06, 2017 9:28 pm

(and my driver mate is actually the guy in the blue car at the top of the page you linked to... :-) )

Tommy Cookers
511
Joined: Fri Feb 17, 2012 3:55 pm

Re: Gravity Racing - Improving Aero to Beat the Best

Post by Tommy Cookers » Sat Oct 07, 2017 10:41 am

you sketched a 4 wheeled car with a central body and outrigged wheels - ie symmetrical, like a trimaran

why not have the body incorporating 2 wheels (like a LSR 'motorcycle') at one side and the other 2 wheels outrigged and ballasted ?
like an outrigger canoe

this picture is Tarf 1 having 2 bodies (like a catamaran) but Tarf 2 exists - either a 1 body outrigger or such was proposed by Taruffi ?
http://www.conceptcarz.com/z21595/Piero ... d-Car.aspx
https://www.rmsothebys.com/mc12/monaco/ ... ar/1049711

HorsfallRacing
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Joined: Sun Oct 08, 2017 8:04 pm

Re: Gravity Racing - Improving Aero to Beat the Best

Post by HorsfallRacing » Sun Oct 08, 2017 8:18 pm

This topic has brought me out of retirement... It's been so long since my last post that I neither remember my login credentials, nor do I feel I can even use the name I went under before (it's quite clear that I was only ~16/17 when I came up with it)

The "Over and Under or Around the Sides" topic was initiated by myself and this forum was a great help in all of the incremental steps taken to become the 2012 F24+ Champion, so, If at all possible, I would like to return the favour.

I have a couple of pages to catch up on, but I'm sure I can be of service, I have a modest, but proven, CFD setup and reasonable CAD surfacing skills. So what I would propose is we look at trying to get a baseline, from the BodRodz car, and working it all back from there. Do you have and decent, side, front, rear and plan shots?

Preferably with some method of scaling at least one of them? be it assuming that they've built to certain dimensions or if there's other things in shot that are of a known dimension.

roon
440
Joined: Sat Dec 17, 2016 6:04 pm

Re: Gravity Racing - Improving Aero to Beat the Best

Post by roon » Sun Oct 08, 2017 10:50 pm

Find an Olympian, someone with good lung capacity. Use them as your driver. Incorporate a boundary layer control feature in the bodywork. Arrays of fine holes coinciding with detachment-prone areas of the surfaces. Or, at known intervals along the bodywork where the boundary layer thickens to a detrimental degree. Port these holes through a bodywork cavity to the driver--it is how they will breath. Hermetically seal the rest of the driver compartment. A respirator face mask can be used. Port exhalation tubing to the trailing edges or any bluff trailing surfaces.

The general shape of these sorts of vehicle probably aren't too radically different from what is in the OP. Human-powered-vehicle/faired-bicycle speed record racing reveal similar forms. No surprise as they are operating around the same speed. So performance gains will be found in the small details, I think. Taping or eliminating seams, lower drag bearings and wheels, weight reductions to optimize ballast locating, packaging of the parachute.

Image

Might look into steering as well. Being able to steer both axles could permit holding a yaw angle while in crosswind, therefore the optimal shape is always presented to the wind. I bet crosswinds are a major factor in performance for this type of racing. You'll also be a hero holding an angle down the straights as you barrel along at 100mph.

Tommy Cookers
511
Joined: Fri Feb 17, 2012 3:55 pm

Re: Gravity Racing - Improving Aero to Beat the Best

Post by Tommy Cookers » Mon Oct 09, 2017 8:30 pm

you'd need good aerodynamic stability as the crosswind wind component is variable
laminar flow and aerodynamic stability are mutually antagonistic
ie laminar flow bodies have large variation of CoP with AoA

and laminar flow bodies of course don't work better (than traditional streamlined bodies) if a crosswind is ignored
ie the LF body will only have lower drag at small AoAs

Greg Locock
165
Joined: Fri Jun 29, 2012 11:48 pm

Re: Gravity Racing - Improving Aero to Beat the Best

Post by Greg Locock » Mon Oct 09, 2017 11:02 pm

What %age of races are in crosswinds? Add a bigger fin on windy days, sure, your performance will suffer, but you won't be a dent in the Armco.

roon
440
Joined: Sat Dec 17, 2016 6:04 pm

Re: Gravity Racing - Improving Aero to Beat the Best

Post by roon » Tue Oct 10, 2017 3:03 am

If there are turns there will be crosswinds.

Armco denting not really a problem. Vehicles are too light.