Aerofoils

[MiNiTiCi]

Anyone got any good low speed aerofoil profiles?
Or tips on manufacture.
I have made a couple of sets of front aerofoils for the Hawke, which were copied from a Van Diemen Vauxhall/Opel Lotus.
Construction being 0.7mm aluminium skinned on formers beaten from sheet. I have made one set with pre-formed polystyrene foam inserts and a second with expanding polyurethane foam applied after construction.
The later method has bulged slightly - I think I need intermediate formers at about 250 mm intervals in order to keep everything straight.

The righthand side was 'replicated' by me after taking out the finish banner at Doune!

This is the new front wing, for Angus's Hawke, which I have been fabricating today (another copy of Opel Lotus profile).
Doug.

[Cita]

Hi Doug,
I just sended you an email but i'm not sure if it worked so i'll try to repeat it on here.
Let me know the chord,the desired thickness and the size of the spar you are using and i will draw up a 1/1 scale airfoil for you in autocad.
Do you have any idea on the origin of the airfoil (Eppler-Gottingen-Selig-NASA etc...) as there are hundred's of under cambered airfoil designs around.

Just let me know what you want and i'll try to be of any help to you.

Cheers Cita.

[MiNiTiCi]

Hi Cita,
Did you send your message to my e-mail address or did you post a private instant message on this forum? (I don't see any e-mail or message).

Anyway - thanks for your offer of Autocad drawing of the profiles.

My problem will be selecting a suitable low speed aerofoil section.
Do you have any links to useful resources?

I have also been considering using foam core and epoxy construction for aerofoils - the Autocad data would come in most useful as I know a fellow competitor who has a flatbed CNC mill - ideal for machining cores.
Doug.

[Cita]

Since some of the critical dimensions are preset by design,chord-length of the wing and thickness and size of the spar (the beam which carry the wing) it will not be too difficult to draw an airfoil shape.
Glider airfoil sections offer the best result i guess since they are designed for low speed.
If you have acces to a CNC mill the foam can be shaped almost perfectly but i'm not too sure how to make that into a sturdy wing.
Flexing (torsion) of the wing is most unwanted as it destroys the characteristics (negative lift in your case) and becomes unpredictable, so i would go for a metal (aluminum or aluminium) wing.
Let me know the rough sizes (chord-max thickness) of the wing you like and i will draw up some airfoils so you can choose and from there on we will work something out.

I dont know if there are any sources on the net for racecar aerodynamics but i'm sure there are,question is are they of any value to the amateur constructor.
If you have enough ribs there's no need for foam filling.

I used the messenger to send you a mail Doug but i obviously did something wrong (as usual in my case ;D)

[MiNiTiCi]

Hi Cita,
My current front aerofoil has a chord of 350mm and a combined span of 1000mm. The section is 45mm deep at its thickest at about 110mm from the leading edge. The wing has a 6mm fixed 'Gurney' flap on the trailing edge. The wing has a slightly concave upper surface and runs at a maximum angle of attack of 10 degrees.
My rear wing is a bit more complicated as it is of the slotted flap design. I will need to take off an endplate and measure the dimensions.
Currently, my rear wings span is a little short (900mm) I think that the UK regulations allow a maximum span of 1400mm. This would get a lot more of the wing to run in clear air ;D
Doug.

[Cita]

Hi Doug,
since i dont know how to post pictures i have sended you an email with a drawing of the wing and a possible construction technicque.
It's an all metal wing.

Cheers cita.

[allan]

Aerofoils still a black art. Look at current F1. But I wrote a simple man"s guide to the basics in Race and Rally Car Source Book. The masterwork on airfoil shaps and what they do in terms of lift and drag is probably Abbott and Doenhoff"s "Theory of Wing Sections" a massive tome funded originally by US space programme money. Model aircraft literature also good. Foam filling a metal outer skin very good IF you pour the mix in with one end completely open , do it in more than one mix, and as fast as you can manage. Extending front wings with flaps to largest are you can get in also works well.Hope this is a bit of help. Regards to all Allan

[MiNiTiCi]

Cita said:

Hi Doug,
since i dont know how to post pictures i have sended you an email with a drawing of the wing and a possible construction technicque.
It's an all metal wing.
Cheers cita.

Thanks Cita,
I got the e-mailed image of the wing section.
The folded spar looks like it would give immense rigidity along the span. I think this may be a bit over-engineered for my use
Certainly, for my front wings the span is only 500mm per side. The foam filled alloy skinned wings seem pretty rigid and are attached to a 25mm pole through the wing at the widest point. The wings pivot on the pole to give easy adjustment and are easy to replace when my co-driver nudges straw bales ;D
I would have replied last night but I ended up surfing the web for aerofoil resources - there appears to be very many, here are a couple which seemed useful:
www.desktopaero.com/appliedaero/airfoils1/airfoilgeometry.html
www.ae.su.oz.au/aero/naca45/naca45.html
www.sm.go.dlr.de/SMinfo/HGAinfo/applets/NACA.html
Doug.

[MiNiTiCi]

allan said:

Aerofoils still a black art. .....Extending front wings with flaps to largest are you can get in also works well.Hope this is a bit of help. Regards to all Allan

Thanks Allan,
Yes - I was thinking of putting flaps on my front wings, I presume that there is not much of a drag penalty due to the placement being in front of the wheels which already contribute considerable drag?
As for my foam filling, I'm sure I will get the hang of it on the next set I make
Doug

[Cita]

;D
I thougth something along similar lines Doug.I designed this spar techniqcue a few years ago and aldo very light in weigth you probably are right that it's over engineered for this purpose.
It could perhaps be used on the rear wing.

Let me know how i can be of any help.

Cheers Cita

[MiNiTiCi]

Thanks again Cita,
For the rear wing (1400mm) it will have to be a bit stiffer. My current rear wing is only 900mm and vibrates wildly on its central mounting pillar - I notice this when I am towing the race car on the trailer.
Doug