Fuselage Bulkhead/Rib question; Curved flanges

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

Chlomo

Well-Known Member
Joined
Oct 8, 2014
Messages
120
Location
Seoul
Hi forum!
Good day to build airplanes! Or to design one.. Or maybe just to think about designing one.
Some food for thought;
How does one create professional looking(and correspondingly strong) curved flanges?
When a flange is straight like the ones in Sonex there is little issue in designing such flanges.
But suppose we have some fairly graceful lines maybe more suitable for composite fuselages(and we're trying to do it with aluminum).

My observations so far;

-984002212284532864.jpg img_0519.jpg

for the more curvier or less load carrying areas you split the flanges into multiple segments. Left image is a bulkhead from a Piper and we can appreciate the clever clever reinforcement. And note the smoothness of corner flange. It's more elegant and looks stronger than segmented flanges found on RVs.
What does a homebuilder should do to duplicate such piece?

Turning our attention to the image on the right it is evident that the flanges are not perpendicular to their bulkheads.
Would there be any strength or stiffness related issues compared to 90 degree flanges? Or must we use stiffners?
The photo below demonstrates an effort to align rib flanges exactly perpendicular to rib as the wing is untapered. This is going to be more difficult for non 90deg bends.



And for gradual curves more like a straight line flanges typically have ripples(?) between rivet holes thus not making full contact with the skin. I assume some rv wing ribs incorporate this for added stiffness.



This is from a Spitfire cockpit. It's not super duper high res but all the flanges seem to bend very very smoothly without any ripples or segments. I wonder how they fabricated those parts..


Large structures don't seem to have such issues as those flanges can be bent almost linearly with channels segmenting them.
 

kent Ashton

Well-Known Member
Joined
Aug 15, 2008
Messages
797
Location
Concord, NC
Pazmany has some good books on scratch-building ribs and various metal parts.
Amazon.com: Light Airplane Construction for Amateur Builders sold by Author eBook: Ladislao Pazmany: Kindle Store
or
Pazmany Aircraft Corporation - pazmany.com

Mr. Lazze has some good youtube vids on metal shaping--mostly for cars, but it will lead to other metal working vids.
lazzemetalshaping - YouTube

Below is a bender I made for bending BD-5 wing leading edges from a Pazmany idea. Sort of over-kill using a 6" "I" beam but it did a nice job
skin bender-2.jpgskin bender-1.jpgskin bender-3.jpg
 

bmcj

Well-Known Member
HBA Supporter
Joined
Apr 10, 2007
Messages
13,948
Location
Fresno, California
The ripples in the wing rib flanges are to allow for the extra material that wants to bow the flange out. That is because before the flange is bent, it measures larger (longer) around the outside edge... longer than it needs to be once it is bent down to the size of the rib. The ripples give that extra metal a place to go in a controlled manner.

When you see curved flanges that don't have ripples, it is because they have either stretched or compressed the metal to compensate for the change in length. You can buy tools that stretch or squeeze metal, but the ripples are the easiest and work fine.
 
Last edited:

WonderousMountain

Well-Known Member
Joined
Apr 10, 2010
Messages
2,455
Location
Clatsop, Or
Sorry to inform you about this,

It is not a homebuilt procedure. The best ribs (continuous curves) come not from crimpers but metal presses and stamps rated in tons. If you can find a template that suits your needs, or parts from a production run it's not necessarily costly.
Sometimes sheet is bent in soft state and then heat treated or annealed, much lower pressures are needed in that case.

LuPi
 

Matt G.

Well-Known Member
Joined
Nov 16, 2011
Messages
1,266
Location
Kansas, USA
That Piper bulkhead is probably hydroformed.

Much of what you show in that last photo of a commercial aircraft is far beyond what is practical for a homebuilt. They have stretch-formed skins and frame chord extrusions, roll-formed stringers, and things like that.
 

Marc Bourget

Well-Known Member
Joined
Feb 28, 2011
Messages
411
Location
Stockton, California
That Piper bulkhead is probably hydroformed.

Much of what you show in that last photo of a commercial aircraft is far beyond what is practical for a homebuilt. They have stretch-formed skins and frame chord extrusions, roll-formed stringers, and things like that.
A third opportunity to comment on the wisdom and experience of John Thorp. I am blessed!

That comment, while accurate for production aircraft, would benefit from the techniques taught me former Prototype Shop employees of North American and Lockheed. There are many ways of forming flanges shown above. Hydroforming is cost effective for production, but a well trained and diligent builder can produce parts that would "fool" all but the most experienced observer.

To get a bit more accurate in the "warp" that evolves from forming, it's not so much stretching the flange (unless you're heavy-handed and impatient) - the "warp" arises from the compression of the material at the inside of the angle (usually 0.090" radius for sheet thicknesses used with small aircraft)

If forming a rib it will cause it to "potato chip" if bending a 3/4" x 3/4" 0.025 stiffening angle on a leaf brake, it will form a "reverse curve" arch. Fluting (as shown) or shrinking are means for straightening, but proper forming technique eliminates the need (most times) for shrinking. As far as area contact on the flange is concerned, it's not that significant. Rib loads are generally in compression.

Finally, during construction, you want to over-form the flange to 87 deg or so (sometimes 85 deg) as well as "roll" the outer, 1/8", edge of the flange. The flanges will "relax" in reaction to riveting forces. If you fail to "roll" the outside edge of the flange, or fail to use good forming technique, the formed flange will generally take a concave profile and with riveting and load cycles - after you fly it, the edge of the flange can/will "print" through the wing skin giving a very unsightly line - evidence that your forming technique was below standard.

Much more on this topic, but I popped into this thread in the wee hours of the morning, and now wish to go back to bed.

Thanks, again, for the opportunity to share.

mjb
 

mwflyer

Well-Known Member
Joined
Jul 16, 2014
Messages
87
Location
St. Louis, MO USA
It is not a homebuilt procedure.
Couldn't be more wrong. There are car rebuilders who can manufacture a fender in steel. Aluminum is much easier to work with. My father's Airframe & Powerplant books (from the '40s) went into great detail on forming complex aluminum parts including flanges. Strangely, my A&P books (from the '70s) didn't as much. Alas, all of those books died in a wet basement.

Making aluminum parts that look like they were stretch formed or pressed is certainly doable without stretch formers or presses. But its a serious skill. Artistry wouldn't be overstating it too much. Be prepared to go through a lot of scrap before useable parts start to show up.
 

WonderousMountain

Well-Known Member
Joined
Apr 10, 2010
Messages
2,455
Location
Clatsop, Or
Okay, fair enough,

it's a homebuilt procedure for those willing to diligently learn a skill. I read a couple books on such advanced sheet work they were full of tables on the springback of various metals, ductility, bend radius' tooling differential, and more still on proper layout.

I've not see anything built in such a manner since pre-WWII. Certainly you would have my respect as a metal sculptor if you went this route. Please anyone who is accomplished please write a book on it, I've not seen anything remotely new on the art.

LuPi
 

Chlomo

Well-Known Member
Joined
Oct 8, 2014
Messages
120
Location
Seoul
I am very eager to learn more about such metalworking skills. My design requires fabrication of some of the more curvier flanges.
 

4trade

Well-Known Member
Joined
Nov 1, 2010
Messages
527
Location
Lahti/Finland
Remember that all of metal forming that you might see in internet, is not aircraft quality approved because stretching or shrinking is too hard or leave marks or bends on metal that might weaken part too much. Bingelis books are good source of any builder.

Find out every material minimum bend radius and make tool for check that. Never use part with tighter radius than minimum.

Here is something basic forming methods:

Metal Forming 101 - The Biplane Forum

https://www.tinmantech.com/

Rib Forming
 

kent Ashton

Well-Known Member
Joined
Aug 15, 2008
Messages
797
Location
Concord, NC
I am very eager to learn more about such metalworking skills. My design requires fabrication of some of the more curvier flanges.
In the U.S., EAA offers workshops on aircraft building. Might be worth a trip.
EAA SportAir Workshops: Build Your Own Airplane | EAA

Have you looked at EAA Webinars?
EAA Video Player - Hints for Homebuilders: Sheet Metal

Otherwise, Ron Covell and Kent White give metalworking workshops and sellDVDs
Ron Covell Creative Metalworking Workshops
https://www.tinmantech.com/

DVDs and Youtube will teach you a lot.
 

Marc Bourget

Well-Known Member
Joined
Feb 28, 2011
Messages
411
Location
Stockton, California
Having served as a tech counselor in the EAA 1/2 day (Osh) and weekend workshops, they do not teach forming like shown above.

Generally, in the homebuilt community, there is a dearth of knowledge about the processes involved in forming. Kent "The Tinman" White is just about the pinnacle for the US (this does not disparage other good guys) but he is the only one I know currently giving classes. Having attended one, and assisted in another of his workshops, my original opinion that they were pricey was wiped away. If you go there with an open mind, ready to listen - and learn, (leave your insecurities behind) you'll leave with more knowledge and insight than you can haul away in a dump truck. IMHO, Kent is metalshaping's "Renaissance Man".
 

Chlomo

Well-Known Member
Joined
Oct 8, 2014
Messages
120
Location
Seoul

Chlomo

Well-Known Member
Joined
Oct 8, 2014
Messages
120
Location
Seoul
Having served as a tech counselor in the EAA 1/2 day (Osh) and weekend workshops, they do not teach forming like shown above. Generally, in the homebuilt community, there is a dearth of knowledge about the processes involved in forming. Kent "The Tinman" White is just about the pinnacle for the US (this does not disparage other good guys) but he is the only one I know currently giving classes. Having attended one, and assisted in another of his workshops, my original opinion that they were pricey was wiped away. If you go there with an open mind, ready to listen - and learn, (leave your insecurities behind) you'll leave with more knowledge and insight than you can haul away in a dump truck. IMHO, Kent is metalshaping's "Renaissance Man".
Thank you! Dearly appreciated! As much as i'd love to attend his classes I do have a 5000mile distance between him so a dvd will be helpful. Will look for dvds.
 

Dan Thomas

Well-Known Member
Joined
Sep 17, 2008
Messages
6,374
Couldn't be more wrong. There are car rebuilders who can manufacture a fender in steel. Aluminum is much easier to work with.
Steel is more forgiving. Excess metal, such as the flange on an outside curve, can be heated red and tapped flat, compressing that extra metal, and it will also pull tighter as it cools. Can't do that with aluminum unless you're willing to totally ruin the heat treatment and start intergranular corrosion caused by precipitation of the alloying elements.

When working on large aircraft, I watched the structures guys make complex parts from -O material which were then sent off for heat treating. That's how many manufacturers make those nice curves. When I made the cowl for my Jodel I used a set of stretcher/shrinker tools for the curved flanges, but those tools leave lots of marks, and 2024-T3 ends up tearing at some point if you stretch it much. Softer alloys like 5052 are more what they're intended for.

Dan
 

WonderousMountain

Well-Known Member
Joined
Apr 10, 2010
Messages
2,455
Location
Clatsop, Or
I know this is thread drift, but could someone compare the qualities of roll form vs. extruded as used in longerons and stringers?

Thanks,

LuPi
 

gtae07

Well-Known Member
Joined
Dec 13, 2012
Messages
2,196
Location
Savannah, Georgia
Extrusions will typically be a fair bit stronger (in absolute terms) than a formed section. That's why you'll see them used for major fuselage longerons, for instance. But if you don't need all that strength, the formed section is lighter.
 

Matt G.

Well-Known Member
Joined
Nov 16, 2011
Messages
1,266
Location
Kansas, USA
The answer to that is highly dependent on the alloy. A 7075-T6 or -T62 roll-formed section is generally going to have better ultimate strength properties than a 7075-T73511 extrusion, for example. The -T6511 extrusion temper is stronger, but has some other issues.

What qualities are you wanting to compare?
 

WonderousMountain

Well-Known Member
Joined
Apr 10, 2010
Messages
2,455
Location
Clatsop, Or
Do roll forms resist plastic deformation near point loads like rivets bolts and notches better, or do they experience less corner stress risers due to bent radius?

I suppose they're comparable for the most part, which would explain mixed construction.

LuPi
 

Matt G.

Well-Known Member
Joined
Nov 16, 2011
Messages
1,266
Location
Kansas, USA
Material properties depend on the alloy, not the cross section.

For a light aircraft that isn't going to matter that much anyway, as stringers and longerons should be sized by buckling. If your structure is so stable as to be able to load up structure like that to Fcy, you are probably carrying around a bunch of extra weight.
 
Top