Introduction to Aerodynamic Analysis using AVL

[@philippefrancois2097]

Hi everyone. Its been about three busy years since I made this video. I apologize for not being able to answer everyone's questions but a lot of it can be found in the guide on AVLs website. I will be finally making a new airplane (a small one) where I will be doing the conceptual design in XFLR5 first so I'll get a chance to compare some results. I am not sure if this has always been the case but, you can export the geometry and mass file from XFLR5 to AVL. This is especially useful if you are designing an airplane from scratch or you have sweep and dihedral in your wings and I would greatly recommend using XFLR5 first since you won't have to muck about with geometry files. In the project in this video, alot of the conceptual work was already done for me so I only needed to start from AVL. Hope you all are getting through/got through your projects.

[@uc3729]

Thank you for the tutorial. It was excellent. Hope we get a full tutorial on developing a simple rectangular model from scratch to full aero analysis. It would be appreciated. No much material is available out there about AVL.Once again thank you.

[@zephyr7912]

Thanks! A great material for learning AVL.

[@calinsa3880]

Thank you very much for this video!

[@kathrynrada]

Hello, I’m having trouble understanding how to create twist on the wing of my aircraft. Also, if I were two have two sections on my wing would I be able two implement a different twist angle on each respective section? Thank you for your help!

[@nitheshkumar9886]

hello ma'am, were u able to figure out how to create a twist on the wing of the aircraft? I hope I will learn something from your reply. with regards

[@vancouver2014]

How do you get to the "Upper Menu" to pull up the geometry plot?

[@alejandrocoser6785]

Thank you! this was very useful.

[@antoniosanchezjimenez5401]

Hi! Is there an option to change the velocity under which the analysis have been made? I mean, to calculate the coefficients, can we do it under 10, 15 or 20 m/s? Thank you :)

[@muhammadfahadzahid7202]

Hi Philippe, Why doesn't AVL show induced drag coefficient in the .run file although it calculates it (as it shows in avl.exe window) ? Any suggestion for how to save CDi value in the .run file...

[@muhammadfahadzahid7202]

Hi. This is the only video on KZbin about AVL and is very informative and helpful. How can I find the neutral point of Aircraft using AVL?

[@azharcassim2795]

Hi. Not sure if this reply will help you now but for the sake of providing an answer here it is: After exciting a run AVL outputs Neutral Point location as part of the .st output file. The variable to look for is : Xnp

[@muhammadfahadzahid7202]

@@azharcassim2795 Lol thanks...I did actually figure it out 4 years ago. Thanks.

[@willtsing3000]

Hi there, very good vedio, currently I want to use AVl to perform some calculation, only about the lift coefficient, but in the .avl file there seems no way to change the unit from default(don't even know the default units) to SI units, is there a way to do that?

[@michasuchons1713]

Is it possible to make lift coeff. drag coeff and pitching moment coeff vs alpha plots using AVL? Or do I have to change the alpha manually each step?

[@alejandrocoser6785]

Could you do it? I'm interested in doing the same but I don't know how to proceed.

[@CottonCookie]

How can you download AVL for Mac? What is the Quartz Library?

[@adriandolsgutierrez]

Hi, one question, how did you get (or set) the viscous drag? is it a constant? Thank you.

[@philippefrancois2097]

Hi, in case you haven't found already. After you load the .avl file and type 'oper' and enter to get into the OPER menu. Type M and enter to access the run case parameters. You should see CD CDo which you can put in the CD0 coefficient for parasitic drag. This is not computed for you . You will need to research parasitic drag estimation equations to compute it. then you enter it here.

[@lucianogreyck8590]

Hello friend, is there any tutorial or handout that teaches you how to use the other AVL features?

[@jefflim7020]

Hi, I tried running aerodynamics simulations on AVL and VSPAero but the results do not tally. Can u help me with it? Thanks.

[@guidodalessio9267]

do you know wich are the unit of measurement for lenghts? feet or meters?

[@JgekZ]

If I wanted to have a sweep angle of 45 degrees at the quarter chord on say the wing.avl file from the runs zip file, would I just change the xle parameter to 45 or is there something else I need to do?

[@philippefrancois2097]

Hello, Yes, in this case because, the wing.avl only has 2 sections you only need to change the 2nd section's Xle parameter. But you wouldn't change it to 45, I think it will be around 7.5, from basic trigs. Remember that the Xle, Yle and Zle are coordinate points defining the start point of each section, in an arbitrary frame usually where 0 ,0, 0 is at the nose of the aircraft. Hope that helps

[@JgekZ]

Awesome! Thanks! I was wondering, would you know how to go about editing the wing file to be able to use a particular NACA airfoil so that avl could create the airfoil?

[@MZ-tl3ib]

maybe this is a silly question. Could i input a solidworks geometry file into AVL and get result from AVL. I want to compare the hand calculated result vs the result from AVL. Thank you very much!

[@alejandrocoser6785]

You can't. AVL generates the geometry through a text file with a specific format. It isn't hard. There are many examples of this taht you could use to learn.

[@rebecasampaio2211]

how to put the Geometry Input File - xxx.avl?

[@3purplesectors]

I wish to add alpha vs Cl data points as run cases to calculate the total CL of the wing and the lift distribution at those specified angles of attack. How would I proceed with this?

[@alejandrocoser6785]

Could you do it? I'm interested in doing the same but I dontt know how to proceed.

[@SaintNate1]

How to do you add a winglet at the tip of the wing?

[@philippefrancois2097]

Hi. You can model a winglet by adding another section on the end of the wing surface. However, the new section will have to have a z-component that is above the z-component of the rest of the wing's sections. I would be cautious when modelling winglets. Check your spanwise lift distribution to ensure you are getting what you expect. I personally would consider leaving them out unless you are sure of how AVL is computing the lift and aero-derivatives and they agree with what you would expect.

[@akshaym9358]

Hii sir.....How to install the aileron control surface on a wing.....U have explained the geometry plot by using a example....But u have skipped to explain the control surfaces on geometry plot.....Pls help me to get into this....!!!!

[@arpitparashar9519]

How to make geometry file and run case file from XFLR5?

[@gustavolins6683]

Good afternoon, how can I vary the CDo on avl?

[@gabrielleweis5963]

How does aileron work?

[@muammarfaruq9054]

please compare AVL vs XFLR 5 ?

[@Tyw7]

Can you do AVL without doing the mass file?

[@philippefrancois2097]

Hi. If you mean without a mass file.. . So you dont need to load a mass file. You can use the M command in the oper menu to manually put in the mass and inertia data. If you meant do Avl without mass and inertia data then, it is possible.. I think your stability derivatives will be reasonably ok. But of course your trim conditons will be off. Using the C1 command might not make alot of sense and your eignenmode analysis will also be wrong.

[@muhammadfahadzahid7202]

Hi Philippe, Can AVL be interfaced with MATLAB optimization toolbox ?

[@philippefrancois2097]

Hi Muhammad. I doubt you would be able to do it directly. I know it is possible to run .exes from MATLAB through the command line using the dos() function in MATLAB e.g. [status,result] = dos(strcat('.\avl.exe < ',basename,'.run')). You would have to create the .run file and specify the case files to load and parameters you want to change and then run the case file with AVL through the dos function. You could then write the results to a file and then import the data back into MATLAB, read it and analyse it and then update the case file parameters from MATLAB and then repeat the process again until you achieve some optimal criteria. You would have alot of MATLAB code to write but it should be possible to do something like that. But to be honest I do not know much about the Optimization Toolbox.

[@muhammadfahadzahid7202]

Philippe Francois Thanks for your help. I too had anticipated the same (the case file thing).

[@arfieerissonia8319]

What if I dont have the .mass file (i dont have the data for the mass)? how can I make it?

[@philippefrancois2097]

Hi. If you don't have mass data, then you can make a best estimate. For the inertias, I believe there is a Roskam method that may allow you to generate Inertias with very little data or you can even simply get data from similar aircraft to start with or even simplify the geometry to something that has known standard equations for. Once you have this i.e. Mass, Ixx, Iyy, Izz, Ixz ..etc do to the "Sample Inputs File" Section on AVL website and find the Allegro.mass example. you should be able to modify it, just have one entry for you entire aircraft. The most important part I believe is knowing the CG, if you do not have this, your results may be garbage, especially any eigenmode analysis. Good Luck :)

[@arfieerissonia8319]

Philippe Francois thank you very much...I have the c.g for the aircraft. Allegro.mass, I will modify it. Thanks again...

[@meddimarcy]

How do you define that circular fuselage bit in the middle ?!

[@philippefrancois2097]

Hi. This is defined using the BODY tag in the .avl file. If you look in the sample input files you will see a file called bd.avl. Under the body section you will see BFIL fuseBD.dat. This calls in the fuseBD.dat file (fuselage) which is just two columns. To be honest I cant remember what the two columns are for....See if you can load the db.avl file and play around with it and you should get it. I really don't have much experience with the effect it has on the aerodynamics so please take care when using it.

[@rafalsz]

Your comment is 11 months old now so probably this is too late for you but if anyone else is trying to figure this out - AVL generates this fuselage from a .dat file that is not much different from an airfoil .dat file. The .dat airfoil file format is a txt with a bunch of coordinates, though they are not normal x-y coordinates. It's the coordinate system that's sometimes used in classical aerodynamics, where X = Xmax stands for the trailing edge (and corresponding Y coordinate), then you move towards through a top surface to the leading edge where X = 0. Next you move through a bottom surface towards X = Xmax. The major difference is that for most airfoils the coordinates are scaled down to be between 0 and 1, and for the fuselage you need to use non-scaled dimensions in your preferred unit. This website could be helpful as well: tracfoil.com/airfoils/index.php?page=en_file

[@marcomarin1196]

Would I have to make a detailed geometry and case file myself?

[@philippefrancois2097]

Hi Nick, you do not need to start from scratch, there are some examples under the "Sample Input Files" section which you can modify to suit your needs. They are in the " runs/ directory zip file" on the main AVL page. The best way to get the coordinates and dimensions for the geometry file is from a CAD model but you can also make a sketch in any drawing software that you can draw to scale and that has the ability to measure distances. I used Visio in this video as an example.

[@guidodalessio9267]

are the units of measurement for lengths given in "feet" or "meters"?

[@rafalsz]

it's not important as long as you're consistent with them

[@guidodalessio9267]

@@rafalsz ok. So, if I set an INPUT file .avl with distances in" m" and surface in "m^2", for the only geometric parameters of a Wing, the results should be the same ?

[@rafalsz]

@@guidodalessio9267 I don't think there is any place in .avl file where you set surface areas, only distances

[@guidodalessio9267]

@@rafalsz yes ^.^ The reference surface you Need to calculate CL, CD and CM. In the file .avl, the 4th line: Name of file 0.0. Mach 0 0 0 iYsyk iZsym Zsym 154. 4.47. 36.87. Sref Cref Bref reference area, chord, spam... the .avl file continue so you can define all the Wing geometry, flaps, slats, ailerons... Than for the tail and fusolage. Find " AVL - MIT" on Google

[@rafalsz]

​@@guidodalessio9267 yes, of course - my mistake. having consistent units like you mentioned is probably fine. if I find out otherwise over next few days I'll let you know here

[@marinabarahona97]

we want the cruisecase.run file pleeease

[@philippefrancois2097]

--------------------------------------------- Run case 1: -unnamed- alpha -> alpha = 0.00000 pb/2V -> pb/2V = 0.00000 qc/2V -> qc/2V = 0.00000 rb/2V -> rb/2V = 0.00000 aileron -> Cl roll mom = 0.00000 elevator -> Cm pitchmom = 0.00000 rudder -> Cn yaw mom = 0.00000 alpha = 0.00000 deg beta = 0.00000 deg pb/2V = 0.00000 qc/2V = 0.00000 rb/2V = 0.00000 CL = 0.00000 CDo = 0.02132 bank = 0.0000 deg elevation = 0.00000 deg heading = 0.00000 deg Mach = 0.6 velocity = 177.900 m/s density = 0.39760 Munit/Lunit^3 grav.acc. = 9.81000 Lunit/Tunit^2 turn_rad. = 0.00000 Lunit X_cg = 18.8660 Lunit Y_cg = 0.00000 Lunit Z_cg = 0.99200 Lunit mass = 75335.0 Munit Ixx = 2000000 Munit-Lunit^2 Iyy = 4800000 Munit-Lunit^2 Izz = 6600000 Munit-Lunit^2 Ixy = 0000000 Munit-Lunit^2 Iyz = 0.00000 Munit-Lunit^2 Izx = 0217000 Munit-Lunit^2 visc CL_a = 0.00000 visc CL_u = 0.00000 visc CM_a = 0.00000 visc CM_u = 0.00000

[@philippefrancois2097]

Please note this is just a template. Note you might want to trim the AoA at some non-zero value at start of cruise and around 0 at end of cruise depending on your CL/CD.I hope this helps

[@prakashmishra9480]

could you be able to provide me this geometry file

[@philippefrancois2097]

Hi, my apologies the aircraft is a company project and unfortunately I would not be able to. There are however many examples of geometry files and other stuff if you download the 'runs/ directory zip file' on the AVL website under the Sample Input Files section. Good luck.

[@prakashmishra9480]

thanks ... and thanks for this video..it helped me alot... i got it..

[@0xpurn]

Comment here if you are from MEiL. O boy!!! :D

[@rafalsz]

:

[@FliBaleon]

Aaam

[@lucianogreyck8590]

Hello friend, is there any tutorial or handout that teaches you how to use the other AVL features?

[@philippefrancois2097]

Hi sorry for the delay, unfortunately I have not seen any other videos tutorials. There is however the full documentation: web.mit.edu/drela/Public/web/avl/avl_doc.txt . This video is intended to be a simple intro that will allow you to make some progress before tackling the full documentation. The full documentation has alot of information that may help you, it is a good read but I suggest you look there. If there is some specific part you would like more explanation of I would be happy to make this a series. Just let me know which particular other features you would like some help with.