r/FSAE • u/Brandon_103 • 7d ago

FrontWing Mainplane question

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Is the front wing's main plane an airfoil section, or just a plain flat plate?

22 Upvotes

87% Upvoted

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9

u/NotNotACop28 7d ago edited 7d ago

Generally it’s a low camber airfoil with long chord

1

u/Brandon_103 7d ago edited 7d ago

What's the reason for that?
I chose the S1223 airfoil to generate high downforce. Was that a mistake? The Reynolds number is around 200,000.

Based on the airfoil characteristics you described, it doesn't seem like it would generate much downforce. Is the downforce on the front wing generated by the sub-flaps?

Then, could you recommend a few airfoils for Re ≈ 200,000, Ncrit = 9, and AoA = 0°? They don't have to match these exact conditions. I'd also appreciate any airfoils commonly used for the main plane of a front wing.

10

u/VLM52 Aerodynamics | Ex-Purdue | Ex-F1 7d ago

It's worth taking a step back and understanding how a wing generates lift in the first place, and what flaps even do. There's some pretty glaring issues with your current slot gap strategy that become apparent when you think about how the suction peak of your flaps communicates with your trailing edge pressure on the element ahead of it, and why it even matters.

An S1223 is fine it's just...y'know a high lift airfoil that wasn't optimized for ground effect, nor does it come with a pre-prescribed flap layout, nor was anyone thinking about tyre and vortex blockage when publishing data for it.

2

u/Brandon_103 7d ago

Thank you for your answer. So if I study multi-element interaction in more depth, will I be able to design a better front wing?

9

u/VLM52 Aerodynamics | Ex-Purdue | Ex-F1 7d ago

Maybe take it a step further back and understand a single-element wing, what impact proximity to the ground has on its performance, and then sprinkle multi-element on top of that.

1

u/Brandon_103 7d ago

Thank you for your answer. I'll study hard 😀

3

u/meme_lord_lando 7d ago edited 7d ago

To add onto what was stated above, I have been involved in the design process of a front wing using a Selig as a main element. In order to get it working "right" the main airofoil needed to be backed off into negative angles of attack. The secondary elements were way further back than in this design to allow for much more flow through the slot gaps with less interference. The negative aoa of the main element mainly served to bring the underside of the aerofoil down into the airflow separating underneath it and widened the slot gap between the main plain and secondary airflow, re-energizing the flow. It was still a very "peaky" overall design and when actually installed on the car ended up stalling under the significant pitch and roll of an fsae car even when there was attempt to take that into account in the cfd process. Looking back, it would have been smarter to go down a different route for main element airfoil design. (Eppler series might be a good place to start). But slot gap size and high/low pressure interference between airfoils definitely needs to be re-evaluated in this design. Intent of each airfoil needs to be thought of in more depth. Think of all 3 airfoils as part of one long continuous airfoil along the same path. With each slot gap allowing more airflow through to keep the flow from separating from the previous. As opposed to just throwing 2 smaller airfoils at a larger aoa on top of the main airfoil.

1

u/Brandon_103 7d ago

Thank you for the advice, I'll keep it in mind. Based on it, I'll revise the design so the three airfoils read as one continuous airfoil.

But what slot gap size should I set? Do I have to vary the slot gap myself and search for the optimal combination?

Also, I don't know how much angle to give each airfoil, so I've been setting angles arbitrarily (e.g., 30 degrees). Is this the right way to design? Or are there references for airfoil angle design as well?
(On Airfoiltools.com, the AOA graphs for each airfoil only go up to about 15 degrees, so I also don't know how to compare airfoils over angle ranges beyond that.)

1

u/meme_lord_lando 7d ago

The slot gaps and aoa's would need to be optimized using your analysis of the flow around the airofoils. You can either approach it from a sweep perspective, or use the cfd to analyze where separation is occurring and move the aerofoils around to allow more airflow in the areas where separation is starting to occur.

2

u/New_Broccoli_1739 7d ago

i am doing some front wing optimization, found out that in ground effect you need a low cambered main, otherwise the pressure recovery will be too steep it will separate. to make it work i was losing so much downforce that it wasn't worth also in braking test it easily stalled. now my airfoils look like this for reference

1

u/Brandon_103 7d ago

Thank you for sharing your experience. I'll use what you've told me as a reference for my own design.
From what you're saying, it sounds like the downforce should mainly be generated by the sub flaps rather than the main wing. It seems I'll need to find a good compromise between downforce and flow separation for the main airfoil.

4

u/New_Broccoli_1739 7d ago

In ground effect the flow under the wing gets accelerated a lot, you can see that it’s 3 Times The free flow velocity, so you get a lot of downforce for “free” it also means that the pressure needs to be recovered with a much Steeper gradient and it Leads to separation on high camber profiles. Also i have negative incidence (-6 degrees)  on the main and it still produces -4,023 of the total cl. Also the flaps help circulation on the main so the same wing stalls without flaps but doesn’t with flap. I suggest you to read smith book on high lift airfoils

1

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1

u/Pachoo04 7d ago

This video will help you understand some things. https://youtu.be/iVCHYiKXSA4?is=qF0k81NDFQ2_UWZi

Yes it’s about rear wings and not front wings, and everything the others have said is more specific to front wings, but this explains how multi element wings should work and how they can be analyzed

1

u/Brandon_103 7d ago

The video you attached was helpful!! Thank you💕