Wing pylon alignment

[daveculp]

This is a cross-post from my L-159 project.  The question is a general one so I'm posting here to get more opinions.  The issue began after I was studying photos and found one that surprised me:

 

 

(original photo credit:  Jan Kouba Czech republic 2013.  All rights reserved.)

 

 

I added the green lines and text.  What surprised me is the pylons are perpendicular to the underside of the wing rather than being aligned with the vertical.  In this case I figure it's about a 4 degree difference.  The best explanation I've read for this comes from forum member Oldbaldguy who figures it's done to keep the pylons from being handed, so they are interchangeable left and right.  That sounds like a fair explanation to me.

 

I'm pretty sure I've seen pylons on other airplanes that are aligned with the vertical, and I'm currently pouring over my books looking for examples, but it's hard to find photos taken at just the right angle.  I suppose it could vary from one airplane to the next.  It might depend on the dihedral angle - too much dihedral and you have to go with handed pylons.  It might have to do with weight limits on the pylon - above a certain weight the pylon needs to be vertical.  Maybe it's an option for the buyer.

 

Are there any general rules for this, or do you just have to study each airplane?  I've learned that you can't trust 3-view drawings, which are really just artist's conceptions.

 

[Oldbaldguy]

Dave, you need to be aware that what Jennings and I have said is by no means universal. Airplanes with anhedral wings rarely have pylons that cant inward but are perpendicular to the ground - the F-104 comes immediately to mind, for example.  If necessary, the angle of the pylon can be changed with spacers and/or adaptors between the attach points in the wing and the pylon itself, but, if the design and mission allow, it is much easier, more cost and aerodynamically effective and less expensive to simply use universal pylons that mount flush to the wing without adaptors and such, particularly on airplanes that employ a lot of pylons.

[Dave Williams]

An interesting thing about the F-104 is that in the early A-D models, the wing pylons were perpendicular to the underside of the wing.  That changed from the G/J/CF models to be perpendicular to the ground.

[Rainer Hoffmann]

1 hour ago, Jennings Heilig said:

The F-104 is a notable exception, which probably had to do with stores separation in the very limited space available on that tiny wing.

 

Well, there is also the Tornado. All pylons aligned with the local vertical, not perpendicular to the wing surface.

 

Cheers

Rainer

[Sepp]

Alpha Jet also has pylons that are normal to the horizontal, rather than the wing.  As can be seen here.

 

 

 

 

Edited September 23, 2021 by Sepp

[allthumbs]

Great topic. The Skyhawk is an interesting example. As you can see in this photo, its wing pylons are noticeably splayed and, as far as I could tell, not handed resulting in a larger inboard gap at the wing interface.

 

[daveculp]

A couple photos from my airshow/museum folders.  The F-84F and the F-86.  Both appear to be handed.

 

 

[Dave Williams]

From the photo above, it doesn’t look like the F-86 is handled.  The tank looks like it’s angled to the pylon, which is usually a sign that the pylon isn’t perpendicular to the ground.

[LSP_Ron]

2 hours ago, Dave Williams said:

From the photo above, it doesn’t look like the F-86 is handled.  The tank looks like it’s angled to the pylon, which is usually a sign that the pylon isn’t perpendicular to the ground.

 

I think the F-86 picture looks handed. The pillion appears perpendicular to the wing but the bottom of it is angled so the tank sits horizontal to the ground. 

[LSP_Ron]

Yet in this image the pillion appears to be perp. to the ground??? I'm guessing this could be a Canadair verse North American thing??

 

[allthumbs]

These pylons are off by 180 degrees!

[MikeC]

23 hours ago, daveculp said:

or do you just have to study each airplane?

And there we have it in a nutshell - that's a big "Yes".

[Rainer Hoffmann]

9 hours ago, allthumbs said:

These pylons are off by 180 degrees!

 

Well, British design. What did you expect? 

 

Cheers

Rainer

[Stevepd]

32 minutes ago, Rainer Hoffmann said:

 

Well, British design. What did you expect? 

 

Cheers

Rainer

Efficient use of available space.. Every drop counts you know.

 

other examples, take the Harrier in all guises. Canberra, etc….

[LSP_K2]

16 hours ago, allthumbs said:

These pylons are off by 180 degrees!

 

Ah yes, but when flying upside down, they're correct.