# How to create an Airfoil (MH 30)?

• I'd appreciate if anyone can guide me on how to modify the Airfoil of glider "Surprise" from "MH 32 8.7%" to "MH 30 7.84%".

Carlos

• If you know the real difference among the two you can modify and rename your airfoil in the "airfoil.tmd" file.
But I really doubt that you will feel a difference in flight.
An other way is to edit the values in the models airfoils and save the model as modified.
RGDS Jürgen

These two airfoils seems indeed very similar to each other so I agree with you that it won't make much difference in flight; but anyways I'd like to understand a little bit more about how the airfoil's parameters in Aerofly relates to the real data provided by specialized sites like http://airfoiltools.com/

• Official Post

No the airfoil.tmd file does not have any affect on the flight phyics of the individual aircraft.
You will need to edit the .tmd file of the aircraft itself with a text editor like Notepad++. Create a backup of that file first, than find the "AirfoilRoot" and "AirfoilTip" in the code.

Here is a quick version of how I'd generate the desired airfoil...

To change the airfoil you first need to know its measured parameters. For the MH 30, you can use this link:
http://airfoiltools.com/airfoil/details?airfoil=mh30-il

Check the checkboxes for the appropriate Reynolds-Nr. here it could be about 50 and 100,000 and update the plots.

Now one by one fill in the fields in the similated airfoil.
Cl0 is the lift coefficient of the airfoil at zero angle of attack (AOA). For the MH30 I read about 0.2 from the Cl/alpha graph.

Cd0 is the drag coefficient at zero AOA. Thats about 0.012 for that low Reynolds number (air gets sticky here...)

Cm0 is the moment coefficient at 0 AOA. Thats about -0.055 if you extrapolate the linear part.

ClAlpha is the increase in lift with the AOA. I'd say its about 0.67 increase in about 5deg that 0.67/5 * 180/Pi = 7.7 cl/radiant - Id take that down a bit to 7.2 or so. 6.28 (about 2*Pi) is the theoretical value with zero drag for all aircraft...

CdAlpha is a bit more tricky, I'd leave it at 0.4, maybe increase it a bit if the airplane cornes without enough loss in speed. (higher value more drag in high angle of attack)

CmAlpha is equivalent to the lift but for the momentum coefficient. The increase is about 0.045 in 10deg thats 0.045/10 * 180/Pi = 0.2578.. That makes the airfoil pitch up more as you increase the angle of attack, which is good for turning without much elevator back pressure, but also adds instability, so the CG has to be right.

Now to the flap.
I've calculated the increase in lift per radiant deflection (ClFlap) for small deflections for NACA airfoils to about 2.1. For split flaps you can use 2.8 and for double fowler flaps that would be 3.0 and higher.

CdFlap comes from experimenting. I know that some aircraft also have a fake butterfly drag build in, so that will interfere here, if you try to adjust the drag coming from the flaps in butterfly configuration.

CmFlap is the moment coefficient that the flap adds to the airfoil per radiant (57°) of deflection. While -0.2 is the default, -0.4 would make the nose go down more when you add flaps. 0.0 would make the nose pitch up quite a bit if you set the flaps at high speeds.

Leave Cd0Base, ClAlphaBase, CdAlphaBase, CmAlphaBase, AttachedCenterFlap and ClFlapBase where they are, that just affects stuff in the stall itself. You could make it spin differently with lower ..AlphaBase values for lift and drag, but not as important if the cg isn't set correctly. ClFlapBase could increase the flap effectiveness in high angle of attack.

Now to the stall:
AttachedCenter is the midpoint between stall in positiv and stall in negative angle of attack.
Here its about 7deg I'd say, that makes AttachedCenter -7 * Pi / 180 = -0.122, but I'd set that to -0.1 or slightly higher, could feel odd...

AttachedRange is the angle between center and stall begin... thats about 5deg (only!) thats 0.0873 rad

And finally StallRange is about the width of the stall range - I'd say about 4deg or so... thats about 0.07.

And thats it. Copy paste the code below as replacement for the AirfoilRoot, and do the same for the AirfoilTip, but set the name correctly again afterwards!

After testing, if you feel the aircraft stalls to quickly, increase the StallRange and AttachedRange... move the AttachedCenter closer to zero, if the stall is too asymmetric.
Cheers,
Jan

Regards,

Jan

• Thank you, Jan!

I followed your instructions and I'm very happy with results.

I really appreciated your time and efforts to explain in details all that I wanted to know about Airfoil setup in Aerofly.

Carlos

• Official Post

Hi Carlos,

that wasn't even that much detail, I just brushed over the parameters. I could write pages of information about the aerofly flight physics (wiki ), especially the airfoils because I spend so much time with them. But I am happy, that I could help you!

Cheers,
Jan

Regards,

Jan

• to the expert:
surely the airfoil is an important item for flight behaviour of the plane in the simulator.
But in the editor there are items / values which IMHO are also very important for this but nowhere explained:
FuselageAero / RumpfAerodynamik
What are realistic values here? Just trial and error?
Kind regards
Jürgen

## Images

• Official Post

Hi Jürgen,

Thats also already described in the wiki with nice pictures and stuff I even mentioned some values there!
http://wiki.aerofly-sim.de/bin/view/Main/AeroFuselage

The aerofuselage has a defined geometry and shape in the tmd file. The aerofly calculates the area seen from top, side and front and uses them for lift and drag calculations.

Cdx: The drag in forward/flight direction (x) is calculated using the formular for drag: D = rho / 2 * v^2 * FrontArea * Cdx;
With flight direction I mean direction the body is facing not the actual path through the air... With zero lift those should be the same direction... The value you enter here is somewhat comparable to the drag-coefficient of a car - gliders can be quite low, 0.01 or so....

[Blocked Image: http://wiki.aerofly-sim.de/pub/Main/AeroF…FuselageCdx.png]
Cd...
Perpendicular to the "flight direction" Cdy affects the drag by the side-to-side velocity, e.g. in a knife edge or side-slip.
And same for the up down motion: Cdz

Cl...
For the side-to-side and up-and-down-motion the fuselage can create lift. Aerodynamically efficient fuselages like those of F3A aircraft there can be quite a bit of lift. Here I'd go as high as 2.0... Glider fuselages usually only have a tube like shape, those don't create that much lift, maybe 1.0 is enough here, could be lower... comes down to testing.

Cly changes lift side-to side and Clz does the same up and down.
[Blocked Image: http://wiki.aerofly-sim.de/pub/Main/AeroF…oFuselageCz.png][Blocked Image: http://wiki.aerofly-sim.de/pub/Main/AeroF…oFuselageCy.png]

Again, just take a look at the images I created: http://wiki.aerofly-sim.de/bin/view/Main/…ge#Coefficients

I found that the drag does play a big roll when doing spins. For an aerobatic glider I used a drag of about 1.8 and a lift of about 1.3 to get it to spin slow enough but without giving to much lift. Also take a look at the Katana unlimited modification... Those values were set by hours of experimenting in the aerofly 5...

Cheers,
Jan

Regards,

Jan

• Many thanks indeed!
Up to now this Wiki was entirely unknown for me.
And I fear not only to me...
Some promotion would be positive, but how and where? :confused:
Kind regards Jürgen

• Official Post

Well if you google: aerofly aerofuselage the first result that does come up is the wiki page!
I've mentioned it as many times as I could so far and linked it from my homepage and I have it in my signature here in the forum...
But I guess thats not quite enough to promote it to anyone. I've spoken to the developers about the wiki and they very much liked the idea of publishing information and help about their simulator to future developers. We didn't yet descide what the best format for that would be, if we keep a wiki or do something else, like a book or pdf document etc... I guess when the next aerofly developer tools are on their way I will have more information...

So long, have fun whilst studying the wiki

Cheers,
Jan

Regards,

Jan