# BF-109 Aerofoil Question

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#### Shayde

##### Well-Known Member
Bringing up an old thread...

In my ongoing adventure into designing a BF109 replica, I fell down the rabbit hole of 109 wing profiles, and this thread came up during a search on previous investigations into them. So I thought I'd document the results of my research in case it's useful for someone.

From the factory blueprints the F through to K wing supposedly uses a 2R1 14.2 profile at the root, a 2R1 12.9 profile at rib 9 (60.5% along the wing), and a 2R1 11.35 profile at the tip. However, when matched to the detailed wing ordinates from the blueprints, this profile deviates a fair bit (on the order of just under a centimetre at widest chord).

Interestingly the profiles are closest at the tip, but at the root the profile "sags"; the top and bottom edges go lower than the 2R1 profile. I've wondered if this is an interesting take on wing washout as presumably the root would experience slightly less lift than the tip (despite the presence of slats on the 109).

Anyway, after lots of playing around I finally managed to produce a profile that matches the factory 109 ordinates within an error of one millimetre around rib 4 which I figure is probably better than 40's manufacturing tolerances.

So, the root profile of the F - K wing is:

Code:
    [0, 0, 0],
[1.25, 2.65, 1.86],
[2.5, 3.59, 2.58],
[5, 4.96, 3.45],
[7.5, 5.97, 4.03],
[10, 6.71, 4.4],
[15, 7.81, 4.85],
[20, 8.51, 5.08],
[25, 8.91, 5.13],
[30, 9.05, 5.13],
[40, 8.81, 4.89],
[50, 8, 4.52],
[60, 6.78, 4.01],
[70, 5.29, 3.37],
[80, 3.66, 2.56],
[90, 1.91, 1.51],
[95, 1.02, 0.88],
[100, 0.09, 0.09],

The profile at rib 9 (60.5%) is:

Code:
    [0, 0, 0],
[1.25, 2.41, 1.69],
[2.5, 3.31, 2.35],
[5, 4.56, 3.1],
[7.5, 5.49, 3.59],
[10, 6.17, 3.93],
[15, 7.21, 4.29],
[20, 7.91, 4.45],
[25, 8.26, 4.5],
[30, 8.42, 4.48],
[40, 8.21, 4.27],
[50, 7.43, 3.93],
[60, 6.29, 3.51],
[70, 4.9, 2.98],
[80, 3.35, 2.28],
[90, 1.74, 1.36],
[95, 0.94, 0.78],
[100, 0.12, 0.12],

The profile at the tip is:

Code:
    [0, 0, 0],
[1.25, 2.12, 1.48],
[2.5, 2.97, 2.08],
[5, 4.08, 2.68],
[7.5, 4.93, 3.06],
[10, 5.53, 3.36],
[15, 6.51, 3.61],
[20, 7.14, 3.7],
[25, 7.48, 3.74],
[30, 7.65, 3.7],
[40, 7.48, 3.53],
[50, 6.76, 3.23],
[60, 5.7, 2.93],
[70, 4.42, 2.51],
[80, 2.97, 1.95],
[90, 1.53, 1.19],
[95, 0.85, 0.68],
[100, 0.17, 0.17],

So, finally, to produce the profile at any location on the wing, blend smoothly between the root, rib 9, and tip profiles.

I did reduce the deviation down to half a millimetre by introducing a curve to the chord thickness, but that gets complicated.

All this, of course, assumes the factory ordinates are in fact what were actually used on the real planes. And it also assumes I typed in all the numbers correctly from the blueprints - there were a lot of numbers!

For reference, the blueprints specify the E wing's profile as being; root: 2R1 14.2, 60.1%: 2R1 12.84, tip: 2R1 11

#### WINGITIS

##### Well-Known Member
The BF-109 2R1 airfoils are generated, BY A CAMBER LINE FORMULA, from base NACA 00xx symmetric airfoil THICKNESS DISTRIBUTIONS of the desired thickness.

Airfoil tools has the FORMULA for the thickness distributions, so you can check your airfoils against these dimension for whatever Camber line you have ended up with.

You can get the camber line from the the 2R112 airfoil on BIGFOIL which has the correct camber line, because Mike has updated it with the correction I gave him a week or so ago after I found a single typo error in it.

Attached is the Airfoil tools generator PAGE on Airfoil tools you can use to get your thickness distributions. I did the 14.2 one there in the example.

You have to also remember that blueprints and drawings may have errors such as this one which has a fold that puts errors in it.....

Photos of blueprints and plans also have Parallax errors....

#### Attachments

• NACA 0014.2.png
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• BF-109_1.png
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BJC

#### WINGITIS

##### Well-Known Member
OK, I added negatives to your lowers and compared the 11.35 to the original NACA 2R112

Your camber line is VERY close, but your Trailing Edge is thicker 0.34 compared to 0.26, but that could have been a BF-109 mod at the factory...

The thickness looks good as well.

I increased the points to 299 and ran an analysis at a couple of speeds and Reynolds Numbers(attached)

#### Attachments

• SHAYDE 2R111.35.txt
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• SHAYDE BF-109 AIRFOIL COMPARISON 2R112.xlsx
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• SHAYDE CAMBER LINE.png
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• SHAYDE COMPARATIVE ANALYSIS.png
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• PROFILES AT 299 POINTS.png
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#### Shayde

##### Well-Known Member
The BF-109 2R1 airfoils are generated, BY A CAMBER LINE FORMULA, from base NACA 00xx symmetric airfoil THICKNESS DISTRIBUTIONS of the desired thickness.

Airfoil tools has the FORMULA for the thickness distributions, so you can check your airfoils against these dimension for whatever Camber line you have ended up with.

You can get the camber line from the the 2R112 airfoil on BIGFOIL which has the correct camber line, because Mike has updated it with the correction I gave him a week or so ago after I found a single typo error in it.

Attached is the Airfoil tools generator PAGE on Airfoil tools you can use to get your thickness distributions. I did the 14.2 one there in the example.

You have to also remember that blueprints and drawings may have errors such as this one which has a fold that puts errors in it.....

Photos of blueprints and plans also have Parallax errors....

The ordinates I got from the blueprints were from a table of values (sheet 8-109.590 Bl.2), not a drawn rib profile, which I checked against a similar table of values produced by the Czech factory (you could say, it was Czech checked ) where the writing became hard to read. They're accurate to a 10th of a millimetre. So folds and parallax errors don't affect the results as they're produced from typed values.

The 2R112 airfoil I used for the comparison tests matches exactly the values from BIGFOIL. They do not match the Messerschmitt factory values when scaled to the correct thickness. The profiles I listed in my previous post were computed from the actual factory values.

#### Shayde

##### Well-Known Member
OK, I added negatives to your lowers and compared the 11.35 to the original NACA 2R112

Your camber line is VERY close, but your Trailing Edge is thicker 0.34 compared to 0.26, but that could have been a BF-109 mod at the factory...

The thickness looks good as well.

I increased the points to 299 and ran an analysis at a couple of speeds and Reynolds Numbers(attached)

Hey thanks for those analyses. As noted, though, the tip profile you used (11.35) is the one closest to 2R1 so the results should be similar. If you check the root profile (14.2) you'll notice the curve sags compared with 2R1.

Interestingly the profiles are closest at the tip, but at the root the profile "sags"; the top and bottom edges go lower than the 2R1 profile.

Here are the root and tip profiles scaled to 12% thickness to match 2R112 if that helps:

Code:
[0, 0, 0],
[1.25, 2.25, 1.57],
[2.5, 3.03, 2.19],
[4.99, 4.2, 2.92],
[7.49, 5.05, 3.41],
[10, 5.68, 3.73],
[14.99, 6.61, 4.1],
[20, 7.2, 4.3],
[24.99, 7.53, 4.34],
[29.99, 7.65, 4.34],
[39.99, 7.46, 4.14],
[49.99, 6.76, 3.82],
[59.99, 5.74, 3.39],
[69.99, 4.48, 2.85],
[79.99, 3.09, 2.17],
[89.99, 1.61, 1.28],
[94.99, 0.86, 0.75],
[100, 0.07, 0.07],

Code:
[0, 0, 0],
[1.25, 2.24, 1.57],
[2.5, 3.14, 2.2],
[4.99, 4.31, 2.83],
[7.49, 5.21, 3.23],
[10, 5.84, 3.55],
[14.99, 6.87, 3.82],
[19.99, 7.55, 3.91],
[24.98, 7.91, 3.95],
[29.98, 8.08, 3.91],
[39.98, 7.91, 3.73],
[49.97, 7.14, 3.41],
[59.97, 6.02, 3.1],
[69.96, 4.67, 2.65],
[79.96, 3.14, 2.06],
[89.95, 1.61, 1.25],
[94.95, 0.89, 0.71],
[100, 0.17, 0.17],

Again, not saying these are correct for the real planes, just what the blueprints indicate.

#### WINGITIS

##### Well-Known Member
Ok that makes sense if there were ords on the sheet, as you have found you cannot just scale the thickness, that makes another shape.

The key thing is that the camber lines are more or less the same.

I have added the IMAGES of the profiles at 299 points above.

#### Shayde

##### Well-Known Member
Ok that makes sense if there were ords on the sheet, as you have found you cannot just scale the thickness, that makes another shape.

Okay that's a good point. Scaling from the wing centre line isn't the same as scaling from the camber line. Interesting, maybe that's why they differ. I'll be back....

#### WINGITIS

##### Well-Known Member
I do have the ACTUAL formulas for generating any thickness but have not coded them yet.

Where in NZ are you?

#### Shayde

##### Well-Known Member
Eesh, well that was it. What a newbie error. I was scaling from the centre line and not the camber line. Definitely explains the slump. There's still some anomalies around the 1.25% mark at the root, but these anomalies aren't more than 1.5mm out. Otherwise the rest of the wing follows 2R1 within a margin of .5mm. That's close enough for me.

Nothing to see here folks, move along.

Thanks to @WINGITIS for showing me the error of my ways.

Now I can go ahead and compute the E wing profile using 2R1.

#### WINGITIS

##### Well-Known Member
I think we have likely all done that at the beginning!

#### raymondbird

##### Well-Known Member
Supporting Member
Eesh, well that was it. What a newbie error. I was scaling from the centre line and not the camber line. Definitely explains the slump. There's still some anomalies around the 1.25% mark at the root, but these anomalies aren't more than 1.5mm out. Otherwise the rest of the wing follows 2R1 within a margin of .5mm. That's close enough for me.

Nothing to see here folks, move along.

Thanks to @WINGITIS for showing me the error of my ways.

Now I can go ahead and compute the E wing profile using 2R1.
Thanks so much for sharing all that. I used Profili for mine which has the naca 2r1 in it and glad to learn it's correct. Went a bit thicker than scale though just to help fit the gear.

#### Shayde

##### Well-Known Member
Thanks so much for sharing all that. I used Profili for mine which has the naca 2r1 in it and glad to learn it's correct. Went a bit thicker than scale though just to help fit the gear.

I'm always happy someone can make use of my inane calculations.

One thing to note is the airfoil thickness isn't linear between root and tip. When I tested the 2R1 airfoil against the factory values I used a curve function for the thicknesses. By using a linear function, 2R1 deviated by as much as 7mm from factory. This drops down to around 2mm when you do a linear blend between the root, 60.5%, and tip thicknesses. Choose whichever method for how close you want to get to the factory values I guess.

#### raymondbird

##### Well-Known Member
Supporting Member
I'm always happy someone can make use of my inane calculations.

One thing to note is the airfoil thickness isn't linear between root and tip. When I tested the 2R1 airfoil against the factory values I used a curve function for the thicknesses. By using a linear function, 2R1 deviated by as much as 7mm from factory. This drops down to around 2mm when you do a linear blend between the root, 60.5%, and tip thicknesses. Choose whichever method for how close you want to get to the factory values I guess.
Are you are saying it doesn't taper linearly from 14.2 root to 11.35 tip? Very interesting and that would sure make it difficult to skin. Would that not need skins with a compound curve?

#### Shayde

##### Well-Known Member
Are you are saying it doesn't taper linearly from 14.2 root to 11.35 tip? Very interesting and that would sure make it difficult to skin. Would that not need skins with a compound curve?

Not really, as the difference is only in millimetres over a more than four metre span. You wouldn't even notice the curve if you sighted along the wing. I only mentioned it for accuracy sake.

Speaking of curves, it's interesting that Marcel Jurca maintained the rear fuselage of the BF109 was straight in his MJ9 plans. It's not (again, according to the factory blueprints), but the curve is subtle. Makes me wonder if Mr Jurca sighted along the back of a real BF109 and decided it looked straight. But he knew better than all the available literature of course.

#### raymondbird

##### Well-Known Member
Supporting Member
Not really, as the difference is only in millimetres over a more than four metre span. You wouldn't even notice the curve if you sighted along the wing. I only mentioned it for accuracy sake.

Speaking of curves, it's interesting that Marcel Jurca maintained the rear fuselage of the BF109 was straight in his MJ9 plans. It's not (again, according to the factory blueprints), but the curve is subtle. Makes me wonder if Mr Jurca sighted along the back of a real BF109 and decided it looked straight. But he knew better than all the available literature of course.

View attachment 129996
Well, I had noticed that too and built mine with the correct curve. Good eye you have! Put a curve in the bottom too if you can make it out in this pic.

#### Attachments

• IMG_20220528_195619.jpg
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• IMG_20220528_195630.jpg
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#### Shayde

##### Well-Known Member
Well, I had noticed that too and built mine with the correct curve. Good eye you have!

Thanks. I've been researching building this plane for some time.

After you mentioned you were building one I found the pictures you posted. She's looking very nice! Is that an MJ9 design? I thought the Jurca plane used one piece wings? It appears you've deviated quite a bit from the plan, if so.

It'll be exciting when she becomes airworthy.

#### raymondbird

##### Well-Known Member
Supporting Member
Thanks. I've been researching building this plane for some time.

After you mentioned you were building one I found the pictures you posted. She's looking very nice! Is that an MJ9 design? I thought the Jurca plane used one piece wings? It appears you've deviated quite a bit from the plan, if so.

It'll be exciting when she becomes airworthy.
MJ9 design and yes, three-piece wing is quite a deviation. Lost my big shop so it was either that or give up. Carbon rod spar now though so weight is okay and even less actually. Ran the engine this summer. Was really exciting with that 88" prop!

#### Shayde

##### Well-Known Member
MJ9 design and yes, three-piece wing is quite a deviation. Lost my big shop so it was either that or give up. Carbon rod spar now though so weight is okay and even less actually. Ran the engine this summer. Was really exciting with that 88" prop!

Nice. After giggling maniacally at seeing the prices for locally sourcing the wood for spruce spars for my BF109 project, I've opted to start again from scratch using metal. I hadn't considered carbon fiber. That's a neat idea.

So your design is going to be quite different to the Jurca one. That'll be interesting.

#### raymondbird

##### Well-Known Member
Supporting Member
Nice. After giggling maniacally at seeing the prices for locally sourcing the wood for spruce spars for my BF109 project, I've opted to start again from scratch using metal. I hadn't considered carbon fiber. That's a neat idea.

So your design is going to be quite different to the Jurca one. That'll be interesting.

Hey, going all metal will be even more different and God love ya if you can do that. Great plan I think though too and hope you'll share your progress. I have Mustang ii plans and Harmon rocket if you're interested. Might help for mixing and matching.

#### Shayde

##### Well-Known Member
Hey, going all metal will be even more different and God love ya if you can do that. Great plan I think though too and hope you'll share your progress. I have Mustang ii plans and Harmon rocket if you're interested. Might help for mixing and matching.
Ha, thanks, I think I need all the love I can get. Let's hope it's not a huge mistake. The Mustang II and Rocket are metal planes? I never say no to useful references.

I admit to curiosity about how you're placing the ribs around your CF spar? Are you still using wood for them? Do you now have a round cut-out for the spar instead of Marcel's box one? Too many questions?