19 replies to this topic

[NRoshier]

I've been looking at the transition of wing mount design from the under-wing to 'top-wing' or goose neck designs favoured over the past ten years. The products in the after-market for road and racing cars seem to vary widely in their quality and adjustability. Most do not allow for any adjustment of the flap elements relative to the main airfoil, regardless of the flap/airfoil used. Some are also so flimsy looking that they are probably more for show than an airfoil that will produce any downforce. The reason for this is that I need to make some of my own mounts for two and three element wings of 1600mm span for single seat use. Has anyone seen any mounts that looked to be good designs and that allowed for quick adjustability?

[PayasYouRace]

Sounds interesting.


Mounts on the top of the wings are preferred because they do not put a disturbance on the underside of the wing which carries the adverse pressure gradient - the low pressure side of the wing - which is where airflow is easier separated. The top of the wing has a favourable pressure gradient so the airflow is less easily disturbed.

For adjustability usually the easiest option is to use the endplates as mounts.

Do you have any links to the sort of things you've been looking at? Perhaps images of what you're working on too? The more information you give us the better.

[mariner]

Tony Rudd, the BRM chief engineer and later Lotus technical Director told a relevant tale in his autobigraphy.

 

The designers had come up with big front wings on the BRM GP car claiming 150lb downforce per wing.

 

He then proceeded to step onto one of the front wings wing to stand on it with his 180lb or so. Howls of protest om the designers to which he replied " well it you don't think it will take my weight you cant have designed it right for the claimed downforce"

 

A crude but valid  test. 

 

 

If you go to any good designers autobiography ( Len Tery, Tony Souttgate, John Barnard etc) you will find descriptions of their methods of wing mounting and adjustment. 

 

The new swan neck mounts are aerodynamically sound but a horrible piece of structural design. For any serious wing downforce I suspect they need very good design analysis 

[GreenMachine]

Don't forget that one mount is in compression, the other in tension, aside from other differences.  That may have implications for the size/shape of the attachments on the wing, the mount also to ensure it has the necessary strength.  The swan necks are longer and have that cantilever section to which the wing attachments, raising stiffness issues.  I agree that endplate mounts would be a good solution, have you assessed and rejected that option?

 

I agree that 'over-the-top mounts should be better, but for all but the highest tech designs I wonder how much difference there is between the two.  And whether they are worth the complications.

[Fat Boy]

I've been looking at the transition of wing mount design from the under-wing to 'top-wing' or goose neck designs favoured over the past ten years. The products in the after-market for road and racing cars seem to vary widely in their quality and adjustability. Most do not allow for any adjustment of the flap elements relative to the main airfoil, regardless of the flap/airfoil used. Some are also so flimsy looking that they are probably more for show than an airfoil that will produce any downforce. The reason for this is that I need to make some of my own mounts for two and three element wings of 1600mm span for single seat use. Has anyone seen any mounts that looked to be good designs and that allowed for quick adjustability?

 

You might try looking at the Ligier LMP3 car. It has relatively simple pair of angle AL brackets. The brackets come in 1 deg. increments of wing angle. The P3 wing is a single element.

[NRoshier]

https://photos.app.g...p8j6eguUuTxDN98

 

Thanks for all of the replies.

I don't know why but I cannot get an image to show in this forum. Please follow the link and you'll see a setup to help me visualise the wing in real-life.

The mounts to the car will be 5mm thick solid 6061 T6 flat alloy extrusion, which will go into the end of 6061 T6 airfoil shape alloy extrusions. At the other end there will be a solid 5mm beam, again slotting into the airfoil extrusion.

I have considered under-wing mounts - they would be in a region of the wing that is in relatively 'dirty' air and realistically I've built a solid, sturdy car for fun times, so it probably would not make much difference. The whole thing is really for me to have fun and experiment.

The only airfoil regulation is that the top-most part of the wing (or any aero device) cannot be more than 900mm from the track surface.

I have considered end-plate mounts but they would be harder to attach to the car.

This will give you an idea of the type of cars (all home made) and the track conditions.

Edited by NRoshier, 31 July 2019 - 09:01.

[Fat Boy]

I don't think you need to make the mount that stout. If there were 2 pickups on the main element and the endplates located the flap, I think you'd be fine and it would definitely be tidier.

[GreenMachine]

FB, you know more about this stuff than me, and I admit this is a WAG, but I would think that at least a mid-span support for the secondary airfoil would be desirable, if not necessary.  I would mount this support to the mainplane, for lightness, simplicity and minimising drag.  You would be more likely to get away without it on slow speed climbs, but where the crossover came might only be found by a collapsed secondary, and damaged endplates.

[PayasYouRace]

I'll second what the guys above me are saying. Use a simple twin under wing support for the main plane. It will be simple, strong and stable. Then mount the flap(s) via the endplates, with various bolt holes for adjustability. Use one or two spacers between the elements to stop them collapsing onto each other, but they only need to be resting and not fixed.

 

Do you have any windtunnel time available or is this just back of the envelope type stuff?

[NRoshier]

Thanks for the replies - the full-size drawing was simply musing about how a top mount could work - just pen on MDF thinking.

Wind tunnel time?? - surely you jest! 1hr in the local wind tunnel (we only have one in this state) would cost a small fortune!

No this is strictly rule of thumb with a bit of help from Hanley's multi-element airfoil program - a 2D solver. All very low key stuff.

I have a CNC hot-wire cutter for cutting blue from (from another hobby) so I can accurately cut foils and make moulds/bucks etc.

[PayasYouRace]

It's only good to ask. I didn't know how much resource you have available.

 

I'd go with the mantra of keep it simple and keep it safe. 

[NRoshier]

No problem with asking at all. I could get tunnel time, but as indicated - not really a cost effective solution for this project.

Cornering is in the 40-110kph range, top speed around 160kph for a very short time on any of our local tracks.

My car is power and rubber limited ... and driver limited.

I'm following FB's prior observations - if I have to lift going around the track then I don't have enough downforce!

Working on mounts this week

[PayasYouRace]

Please share your progress. Most interesting!

[mariner]

When John Barnard did the Chaparral 2K indy car which introduced ground effects to Indy he used a very unusual rear chassis wing layout. 

 

Basically there were two large vertical  slabs at the full width of the car and the rear wing was mounted between them, what was unusual is that they also took the rear spring/damper loads.

 

https://historicmoto...sworth-indycar/

 

The was a logic in that he knew to keep the spring/dampers right out of the tunnel air flow so tucking them into the  verticals made sense. Also the rear wing loods did go directly into the sprigs and not through a series of posts and gearbox casings.Ditto  the outside edge tunnel loads.

 

Its not my right to criticize somebody like Barnard but one drawback I can see is the difficulty  of working on the rear end with such large slabs of structure in th way. Maybe for a one off Indy car that mattered less.

 

 

On a lighter note his biography reveals the entire ground effects design was based on one phone call to Patrick Head who gave him a few sentences on tunnel design!!

[EngineeringArt]

This drawing may be of interest, it's Benito Belli’s layout and stress and strain calculations for the rear wing of a March 88C Indy car.

 

 

https://engineeringa..._poster_quality

 

 

https://engineeringart.uk.com/

 

 

 

 

[GreenMachine]

That is interesting.  I find the mainplane intriguing, almost a rectangular section with rounded nose, and a recess for the lowest of the flaps - which are of more traditional airfoil section.

 

Was that the state of the art at the time, I think the mainplane these days a traditional airfoil section?

 

Looking at that drawing a light went on, and I realised that the arrangement looks like a fowler flap only upside down.  the use case is similar, up to a point - maximum lift at the lowest airspeed, and drag is not a consideration.

[Fat Boy]

FB, you know more about this stuff than me, and I admit this is a WAG, but I would think that at least a mid-span support for the secondary airfoil would be desirable, if not necessary.  I would mount this support to the mainplane, for lightness, simplicity and minimising drag.  You would be more likely to get away without it on slow speed climbs, but where the crossover came might only be found by a collapsed secondary, and damaged endplates.

 

It's pretty common to have little spacers to make sure the flap gap stays consistent across the span. So, ya, a good idea to put in place from the start.

[Fat Boy]

No problem with asking at all. I could get tunnel time, but as indicated - not really a cost effective solution for this project.

Cornering is in the 40-110kph range, top speed around 160kph for a very short time on any of our local tracks.

My car is power and rubber limited ... and driver limited.

I'm following FB's prior observations - if I have to lift going around the track then I don't have enough downforce!

Working on mounts this week

 

Lol, I'd forgotten writing that, but I stand by it. Incidentally, if you don't have to lift then you need to make more power.

[gruntguru]

[NRoshier]

ah, well more power, like more rubber, is an expensive proposition!

I used Hanley's multi-element airfoil software  - darn the rest of my post got cut when I included a link. Anyway the software did not seem to have enough resolution to accurately show the differences between some widely different airfoils - or that there really was little difference when a flap is added to the mainplane. I tested airfoils on the UCIC database including S1223, E423, FX63-137 etc. The Churchill Hollinger CH10 was pretty good and will likely be used once I plot all of the other information. I did get a bit carried away looking for differences, but as I noted I think the tool is perhaps not too refined, but more of an issue is the fact that I don't think chasing the last 1-2% is really going to be noticed.

Edited by NRoshier, 21 September 2019 - 12:50.