81 replies to this topic

[NeilR]

Time has come to plan for the wings on my car and I have a couple of options. Multi-element wings are the usual wear for hillclimb cars and the professionally made wings are beautiful, I just cannot afford $2000. Then I can make my own - I have made carbon wings in the past and have the means for making moulds, but knowing the combination of main foil and flap for best L/D up to 180kph is not something I have experience in. Today I found an interesting program - has anyone used it before?

http://www.hanleyinn...com/mefoil.html

[Greg Locock]

I used microcfd for a while. That's a lot cheaper. Look at the list of exclusions in the lite version of Hanley s program. If you want to get serious look at open foam. Bear in mind that your rear wing will be operating post stall, conventional aircraft oriented programs may not be expecting that.

Edited by Greg Locock, 11 July 2016 - 10:01.

[NeilR]

Thanks for the link and your thoughts Greg. I think at this point I just need to get a basic F/R wing plan together and open foam will take too much time and frankly may be beyond my capabilities. The Micro CFD looks good though and I like the pricing! Formula Libre in hillclimb is open in many respects and the wing can be much larger than any other formula currently running.

[MatsNorway]

Is there no size limitations on the wing? How much downforce is desirable?

[Greg Locock]

I was intending to say that if the wing is large enough you may be able to run it in the linear range, not stalled,so you'll get less drag.

[NeilR]

There is a practical and structural limitation to the wing of course. So 1600-1800mm span rear wing - wider will be problematic for transport and more effort will be required for stiffness. The mainplane will be fine but second and third elements (if used) will require care.  The front wing will match the car width 1650mm or so - wider will be inconvenient in practical terms in pits and at some tracks. Wing chord is free.

I have a limited amount of power/torque, so drag is an issue, but most local events are low speed i.e. well below 160kph and at the champs coming Bryant park is a very different venue given the down/up nature of the course - see below.

[NeilR]

This was recommended as well: http://www.flowsol.c...ducts/newpan2d/

[NeilR]

I was intending to say that if the wing is large enough you may be able to run it in the linear range, not stalled,so you'll get less drag.

 

Mainplane chord at 300mm and effective speed range from 50kph cornering to 160kph max, roughly Re should be from 950,000 down to low of 300,000.

Sorry MatsNorway I've been meaning to answer your post but have not been able to check some details, so I'm only guessing when I say 120kg, split 45/55 @ 100kph

Edited by NeilR, 14 July 2016 - 21:57.

[Fat Boy]

I was intending to say that if the wing is large enough you may be able to run it in the linear range, not stalled,so you'll get less drag.

 

Wing size should just be a packaging thing. Run as big of a wing as you can and run it stalled. To hell with drag.

[Fat Boy]

How much downforce is desirable?

 

All of it.

[Fat Boy]

There is a practical and structural limitation to the wing of course. So 1600-1800mm span rear wing - wider will be problematic for transport and more effort will be required for stiffness. The mainplane will be fine but second and third elements (if used) will require care.  The front wing will match the car width 1650mm or so - wider will be inconvenient in practical terms in pits and at some tracks. Wing chord is free.

I have a limited amount of power/torque, so drag is an issue, but most local events are low speed i.e. well below 160kph and at the champs coming Bryant park is a very different venue given the down/up nature of the course -

 

Everyone has a limited amount of power/torque. If you can make the entire run without lifting off the throttle, then we can start talking about drag. Until that happens, though, keep adding.

[Greg Locock]

Are you specifically talking about low power to weight ratio cars? And or non GE cars? After all F1 cars certainly back off the aero for high speed circuits.

[Fat Boy]

Are you specifically talking about low power to weight ratio cars? And or non GE cars? After all F1 cars certainly back off the aero for high speed circuits.

 

Primarily, I'm talking about a relatively small car with enough HP to be frisky on a course that has no sustained high speeds and lots of relatively slow corners. Also, I'm taking into account that it's only going to be driven strictly on cold tires by amateur drivers on courses with which they are only moderately familiar.

 

A good example of this is any competitive Time Attack car. They've got more wings on those cars than you can find at Hooters.

Edited by Fat Boy, 16 July 2016 - 04:34.

[Greg Locock]

Ta, yes that makes sense. I was really thinking of sprint cars where the wing is the size of the car

[Lee Nicolle]

Primarily, I'm talking about a relatively small car with enough HP to be frisky on a course that has no sustained high speeds and lots of relatively slow corners. Also, I'm taking into account that it's only going to be driven strictly on cold tires by amateur drivers on courses with which they are only moderately familiar.

 

A good example of this is any competitive Time Attack car. They've got more wings on those cars than you can find at Hooters.

Time Attack cars though half of it is 'bling' Some work, some just drag, a lot. Look at Drifters who want to unhook the car but all use giant wings!!!

I agree though with an amatuer operator though. More downforce even at the expense of drag [within reason] will make the car go faster. When,,, you get very good then start trying to lose drag for those extra tenths.

[gruntguru]

Look at Drifters who want to unhook the car but all use giant wings!!!

Drifters do not want to unhook. They get scored on angle and speed. If the following car can't keep up - it loses. If the following car can overtake - it wins.

[NeilR]

That idea, of as much DF as possible, does simplify the process a little.

You can see Malcolm Oastler's car below:

Edited by NeilR, 16 July 2016 - 08:57.

[gruntguru]

One thing that surprises me - why the open-wheel design? (I assume formula libra doesn't mandate open wheel?) If maximum DF (and minimum drag) is the object, you would choose an enclosed design with full underbody aero.

[NeilR]

Formula Libre is an open, 'bring anything' sort of a formula - a catch all sort of a class. Light weight is very important and Malcolm's car is considered very light weight.

Unconventional cars do occure e.g. Bill Norman's GEK

 

Bill changed direction and made a 'conventional' car as seen at the start of this video: It is still fabric covered and weights less than 250kg

Edited by NeilR, 16 July 2016 - 12:40.

[Greg Locock]

http://www.consultke...ttack_Chart.png

That's the graph I wanted, max lift is off the chart to the right, well beyond optimum l/d.

[Fat Boy]

http://www.consultke...ttack_Chart.png

That's the graph I wanted, max lift is off the chart to the right, well beyond optimum l/d.

 

I love it when I'm at the racetrack and someone with enough knowledge to be dangerous mentions that the wing *might* be stalling. My response is always, "It damned well better be." As fun as that is, though, I like it better when people discuss laminar flow on a racecar.

[thegforcemaybewithyou]

Formula Libre is an open, 'bring anything' sort of a formula - a catch all sort of a class. Light weight is very important and Malcolm's car is considered very light weight.

Unconventional cars do occure e.g. Bill Norman's GEK

 

Bill changed direction and made a 'conventional' car as seen at the start of this video: It is still fabric covered and weights less than 250kg

 

 

Is there something in the Formula Libre regs that prevents the tyre tread width to be bigger than 200mm, as the preview picture of the second video shows "skinny" tyres. Or is the lower weight of the narrower tyres an advantage? Do they heat up faster?

 

Regarding your wings i'd be careful that they do not raise the overall weight (and CoG) too much.

[gruntguru]

Is there something in the Formula Libre regs that prevents the tyre tread width to be bigger than 200mm, as the preview picture of the second video shows "skinny" tyres. Or is the lower weight of the narrower tyres an advantage? Do they heat up faster?

Nothing in the regs. I can see several arguments for not running wider tyres on that car.

1. As you say the narrow ones heat up faster - critical for hill climbing - tyre warmers are not allowed.

2. Less than 250 kg is a very light car. Even fully warmed, a wider tyre would probably not work any better than the ones on the car.

3. Wider tyres eat into space for aero. Both of those cars have some focus on under-body aero and maximising plan area and flow area are critical.

 

I love Bill's focus on function over form. Note the (torsional stiffening of the cockpit area - later car) tubing "pyramid" on one side of the chassis only.

Edited by gruntguru, 17 July 2016 - 02:54.

[NeilR]

You can run any tyres you can afford, but avon hill climb tyres are expensive. You only get a few good runs on them before they start to turn/harden - some tried to use uncut wets as an alternative, but they did not have the grip as they were too hard. Bill himself will admit that his car is not one you want to hit a barrier in, the larger tubes in its construction being 19mm in diameter.

[Fat Boy]

 the larger tubes in its construction being 19mm in diameter.

 

Not really a fan of that.

----------------------------

 

Tires are a interesting thing to discuss. It's actually a rare thing to get to spec. In most forms of racing, the tires are spec'd and you go from there.

[NeilR]

Nor am I. I discussed this with Bill and suggested that 25mm should be used at least - he quite rightly pointed out though that there are 750cc gokarts running and they have even less protection.

[NeilR]

This may sound like a silly idea, but it's been bugging me for years: Aero testing that I see reported is done is a nice tunnel and good control of flow, with the model being tested held under tight control. However a car the aero has to function of is vibrating, moving around, inducing yaw and coping with bumps. I assume all of that motion could have some effect? If so, would there be any point in using something like a shaker rig in the tunnel simulating the known conditions of a track to refine the aero package prior to the event?

[saudoso]

Instrumentation is hard enough with everything nice and steady.

[gruntguru]

This may sound like a silly idea, but it's been bugging me for years: Aero testing that I see reported is done is a nice tunnel and good control of flow, with the model being tested held under tight control. However a car the aero has to function of is vibrating, moving around, inducing yaw and coping with bumps. I assume all of that motion could have some effect? If so, would there be any point in using something like a shaker rig in the tunnel simulating the known conditions of a track to refine the aero package prior to the event?

Makes sense. Of the aspects you mentioned yaw/crosswind effects are certainly investigated in any serious wind tunnel testing

[NeilR]

I've ordered a copy of benzing's book and am trying to get my McBeath book back (should stop lending books to people). Have found a cheap mould material. Re profiles it seems to makes sense just making one mainplane mould for front and rear. This should not be too heavily cambered so that the front centre section does not disrupt the underfloor too much.

I am estimating frontal area (with wings) ATM to multiply by a generic single seater CD figure in order to calculate BHP required to get car to 180kph. I will subtract this from BHP available to get a BHP budget for aero.

[Lee Nicolle]

Drifters do not want to unhook. They get scored on angle and speed. If the following car can't keep up - it loses. If the following car can overtake - it wins.

Anything that is sideways with the tyres smoking is well unhooked! The object of the wing is too push the car down to give more traction and stability. That does not cover drifting!

[gruntguru]

I repeat - a drift car needs both angle and speed.

 

For "angle" it needs to unhook.

 

For "speed" it needs to generate maximum cornering and accelerating force even while unhooked. So it needs as much DF as possible.

[Greg Locock]

Neil, this spreadsheet might help

http://www.mediafire...ts_car_aero.xls


Max cornering at high speed is power limited, this is an old version that doesn't include that effect.

The blue feasibility curve was generated using a Cd of o.3, then ground effect at L/D of 10, then wings at 5, I think.

If the airfoil is fully stalled does its profile matter? Isn't it just acting as a diverter vane?

Edited by Greg Locock, 19 July 2016 - 09:29.

[thegforcemaybewithyou]

Neil, have you considered starting with a simple(cheap) diffusor similar to that on Bill Norman's car? It seems to be a thin sheet flat under the car and bends upwards after the rear axle. Should be easy to produce and install and remove, even at the track.

[NeilR]

Thanks Greg, I will have a good look at that.

TheG I will be running an underfloor copying Malcolm's car. We've come up with all sorts of ideas, such as bodywork fully enclosing rear suspension and wheels etc, but who are we kidding? This is a beginner's car, think Formula Ford with wings and more revs ... just no point making 'bad' wings!

Greg what are the numbers at the bottom of column C under the graphs?

Edited by NeilR, 19 July 2016 - 11:30.

[Greg Locock]

Metres per second

[NeilR]

Thanks, did not want to assume anything. I looked for tyre data for Formula Ford tyres, but could not find anything even on the FSAE forum, so tyre Mu is a pure guess. I've assumed 1.2. It's been fascinating changing numbers and looking at the changes in the numbers in relation to Katz's data.

 

"If the airfoil is fully stalled does its profile matter? Isn't it just acting as a diverter vane?"

 

Yes, but then there are two wings. If the front stalls I imagine the effect is more noticeable? Also I assume there can be a partial stall? I really need to read more as I've been spending too much time with RC glider foils.

Edited by NeilR, 19 July 2016 - 12:36.

[Fat Boy]

Thanks, did not want to assume anything. I looked for tyre data for Formula Ford tyres, but could not find anything even on the FSAE forum, so tyre Mu is a pure guess. I've assumed 1.2. It's been fascinating changing numbers and looking at the changes in the numbers in relation to Katz's data.

 

"If the airfoil is fully stalled does its profile matter? Isn't it just acting as a diverter vane?"

 

Yes, but then there are two wings. If the front stalls I imagine the effect is more noticeable? Also I assume there can be a partial stall? I really need to read more as I've been spending too much time with RC glider foils.

 

Racing slick, right? Start with 1.6-1.7 for mu.

 

These wings are the polar opposite of a glider. Think cargo plane on final approach. Lots of chord, Lots of thickness, lots of elements. A diffusor is a given, but you don't have rules, so run tunnels...it's a no-brainer. They're much easier to make than wings and more effective.

[NeilR]

Formula Ford's in Australia use Avon ACB10's, a treaded 'slick', though they are moving to Yokohama AO48's (which I don't like), so I might have to start using small Hoosier slicks just like some of the FSAE guys. Problem with that is local supply of Hoosier is not great, will bump up the mu and see what it looks like. With the number I put in I seem be well in the range of Katz's results and below the blue line

The glider foils have some similarity in considering that attached flow is a priority and they are low Re foils, but yes I take your point that we're talking a low aspect, flapped section.

[Greg Locock]

When I get back to the Bat Cave I'll dig out an old NACA paper on mu!tielement wings, it is pretty neat.

[thegforcemaybewithyou]

I will be running an underfloor copying Malcolm's car.

 

If that is the current version of Malcom's car, i would suggest to extend the floor, ie let it start right behind the front wishbones and maybe also add a few cm at the back. Make sure you still can enter the cockpit

 

http://rotaryhillcli...mt-cotton-2015/

[thegforcemaybewithyou]

Another thought on the car, not aero related. The bearings at the lower front wishbone are placed under the chassis ( http://forums.autosp...-3#entry7552759 ) and will be the first part to come in contact with the track/curb if the front dives down too much.

 

Do you plan to add some protection for those bearings?

[MatsNorway]

You can make a tunnel/venturi towards the wheel too. No point having that area flat.

In fact, no point having anything under the car flat if not neccessary. Probably smart to have a wall/separation between the rear diffuser and the side tunnel.

Edited by MatsNorway, 20 July 2016 - 14:11.

[thegforcemaybewithyou]

If one would start from scratch then yes, you probably would end up with something like the Porsche 956/962, the new Aston Martin Red Bull car or a Lotus 79 type open wheeler with skirts.

[NeilR]

TheG there will be a skid ramp just before the front bearing on each side, but it's really there incase of off-track excursions and rejoining the track over a kerb. I cannot envisage how they could meet the track surface itself unless we lost a front wheel - the chassis will ground out way before they get close.

I cannot find any images of really extensive underfloors on the british hillclimb cars, which is interesting.

[saudoso]

There isn't a lot to be gained with foreplay in ground effect, it's throat and diffuser.

[NeilR]

I spoke to a previous Australian hillclimb champ about his wings, as his car had been tested in the Monash wind tunnel (a fairly basic tunnel). His car produced 140kg of downforce front and rear at 100kph.

[Fat Boy]

I spoke to a previous Australian hillclimb champ about his wings, as his car had been tested in the Monash wind tunnel (a fairly basic tunnel). His car produced 140kg of downforce front and rear at 100kph.

 

I'm curious what his weight distribution is? You'd expect a higher percentage on the rear for an open-wheeler. The numbers sound legit, though.

 

It's important to quote the speed at which you're measuring the downforce, but don't worry much about 'low-speed' downforce vs. 'high-speed' downforce. A lot of people seem to worry that measuring DF at one speed is invalid for a different one. It's a V^2 relationship. Ride heights will matter, but those can be measured on their own.

 

Having said this, I will say that big-ish gurney's seem to keep the wings more DF stable in nasty (i.e. bouncing, side-flow, dirty air) environments. They're draggy, but they work.

[gruntguru]

How big is "big-ish"?

[Canuck]

Smallish,compared to a 737 wing.