I am currently doing a school research project attempting to find the effect of single-slotted flaps and slats on an airfoil's (NACA 2412 or similar) lift coefficient. I will be using a small homemade wind tunnel to see the lift force that a small airfoil model generates with and without the use of high-lift devices, and backing the claims up using CFD data. The model will be a simple wing that is essentially an elongation of a 2D airfoil.

When designing the slotted flap, there seems to be very little information on how the geometry of the flaps is created nor is there much data on existing designs. There are many research papers investigating the effect of high-lift devices, but almost none explain how their designs were produced or why they used the flap that they did. Essentially, how the flap takes its shape. For example, in Theory of Wing Sections, various slotted flaps were tested for their max lift coefficients, but the book does not specify how these designs are created (see image). The same goes for slats.

various flap designs in Theory of Wing sections

My question is, how are these various designs of flaps and slats produced mathematically and how can I replicate this design process for my airfoil? The flaps and slats do not need to be perfect, but I will have to justify what led me to the design that I will be using in my experiment.

Alternatively, I can also use proven designs of high-lift devices from existing airplanes such as a C172 or experimentally optimised ones. Unfortunately, I was not able to find any of those. If anyone is aware of existing single-slotted flap and slats schematics, it would also be very much appreciated.

I am aware that someone asked a similar question but it was deemed too broad. Hope this isn't.


1 Answer 1


High lift flow and high lift design is really complex. If you choose to become an expert aerodynamicist, you could spend your entire career working on high lift flow.

The most important paper is "High Lift Aerodynamics" by AMO Smith. It is 30 pages long and I had to read it many many times before I started feeling like I understood many of the ideas. That was half a lifetime ago -- if I was to need to get into high lift aero again, I would start there.

I have access to wind tunnel data for several high lift tests. These tests were performed to be used to test, calibrate, and improve CFD codes. The documentation I have provides all of the information you would need to either build a similar test section for your wind tunnel or to conduct your own analysis of the foils. If you want, we can figure out how to share this data with you.

There are several high lift airfoils you could choose from.

A2, a Farnborough High Lift airfoil. This one comes in three configurations, but all include a slat as well as flaps. Farnborough High Lift airfoil

A5, a McDonnell Douglas aileron test originally conducted at relatively high Mach number (around 0.7). McDonnell Douglas aileron

A9, an NLR airfoil NRL High Lift airfoil

Boeing TR-1332 airfoil Boeing TR-1332 High Lift Airfoil

I would probably recommend A9, the NRL airfoil. It avoids the complexity of the multi-element systems (including flaps). Similarly, it avoids any transonic flow effects that the aileron test case is designed to go after.

  • $\begingroup$ Thank you so much for this information! I would love to have a look at the data that you mentioned if possible. $\endgroup$
    – bob
    Commented May 27, 2023 at 20:12
  • $\begingroup$ I have just downloaded these, really appreciate your help. I still have a couple of follow-up questions regarding the airfoil that you recommended. Would you be so kind to answer them? $\endgroup$
    – bob
    Commented May 27, 2023 at 21:16
  • $\begingroup$ Happy to help out. $\endgroup$ Commented May 27, 2023 at 21:18
  • $\begingroup$ Here we go: 1. Since this airfoil has a max thickness of 16.5%, will I be able to apply thin airfoil theory to it for lift calculations? (or which other theory should I use to calculate a theoretical lift value?) 2. If I 'borrow' the NLR airfoil design, do you advise me to ditch the slats in the investigation to simplify things? 3. To change the angle of the flap, can I simply rotate the flap at that point or do I have to do additional translation to it? 4. I understand that this is a supercritical airfoil, how different are its properties to something like a 2412 at really low airspeed? $\endgroup$
    – bob
    Commented May 27, 2023 at 21:41
  • $\begingroup$ Just for clarification as I forgot to mention in my original post, my investigation is about how the angle of flap/slat deployment changes lift coefficient (hence question 3). I do not have access to research-grade facilities, so I will just be using what looks like PC fans as a source of air flow (hence question 4). I have proven with a really simple setup that a simple 2412 model actually does generate some lift, so I was wondering how much it could change with the NLR. $\endgroup$
    – bob
    Commented May 27, 2023 at 21:45

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