Sopwith Baby Project

[brinesharks]

Originally Posted by Nick

Joe,
...The radius on all the Snipe fittings is 1/16". ...

Cheers, Nick

The Sopwtih Triplane is the same - most of the radii are 1/16" which we have discussed at length on another post - seems too tight. Sopwith still drew it that way.

[Joe Perkel]

Originally Posted by David Paule

Typically now and I believe back then, steel was formed in the annealed or normalized condition. If annealed or if heat-treating was needed, it would then be done. Cold working would only be performed under somewhat controlled conditions and avoided for general work.

David Paule

Good question, Nick...how did you do this?

The 1918 reference is a bit lax in the description of field replacement for one of these fittings Aeroplane Construction and Assembly - Google Book Search

I read this to mean, "Hack it out and hammer away Charlie".

Of course, we wish to be a bit more precise.

[Joe Perkel]

Originally Posted by brinesharks

The Sopwtih Triplane is the same - most of the radii are 1/16" which we have discussed at length on another post - seems too tight. Sopwith still drew it that way.

Bryan,

I've not yet found a call-out for this radius on any of my drawings.

Truth be told, 1/16" is bothering me a bit, and 3/16" is much too big. I will look into this further. Hard to do when all I really have is a couple hours late at night.

[Joe Perkel]

Stumbled on something of interest doing archival research today.
A direct reference to my aircraft by an American pilot who apparently flew in a British squadron.

Page 370 towards the bottom

Testimony of Capt Kindley to

Aircraft Board
Office of The Judge Advocate General
Washington D.C. February 14, 1918

United Air Service ... Hearing[s ... - Google Book Search

Looks to me like testimony to help establish the American Air Service???
Not much said but, it adds a little something of a personal nature somehow.

[brisfitworks]

My Camel drawings show 1/16"R as the inside radii of the bend on 18g spar box.

Radii is a function of thickness and alloy. You'll see "rules of thumb" like: "minimum radius is 1/2 thickness or 1/32" whichever is larger for low carbon steel". The other rules of thumb you see is recommended bending radius is metal thickness (T) or that times a factor - 1xT through 3xT is often seen. Aluminums are larger - even 10xT. At 18ga (0.048" BSWG) the Sopwith dwgs implied recommendation is 1.3xT.

When Brit dwgs refer to mild steel they typically call a spec like RAF9a. This is a medium carbon steel (.20-.25c) and thus the bend radius is larger than that "1/2 thickness or 1/32R" rule.

The RAF9a spec also states: "Bend Test - The steel, when cold, is to be capable of being hammered double in any direction to the fibre without fracture, or the development of cracks in its outer surface."

This raises another issue and that is the grain ("fibre") direction of the sheet. Grain direction is along the rolling direction. Some mills will print an arrow to indicate this but it is parallel to the grade printing. The normal recommendation is the have grain direction across the bend because grain parallel to bend is more likely to crack as would a piece of veneer split along the grain. In reality, few of us pay attention to this and you don't read of horror stories about failure because builders ignored this grain direction rule.

With 4130 the radius likes to be larger. You will see 3xT factor recommended for 4130N. The stuff is tough to bend. Bending spar boxes where the edges of lightening holes are close to the bend has been putting the stiffness of our big bending brake near the limit of the beak's ability to hold the material tight enough for the bend.

The spar box halves I just bent and getting ready to trim for welding ended up at very close to 1/16"R and there is no signs of stressing on the outside of the bend. There is no cracking at the edges. (N.B. there is an edge cracking allowance that states something like: "an aggregate cracking of not more than 1/16" in length is not a cause for rejection")

The 4130 we get is 4130N which means normalized. This means the internal stresses have been relieved. (Cold working imparted by rolling to thickness is a source of stressing). Being normalized means the material can withstand the cold working of the forming operations we do (just don't try fixing a bending mistake by hammering it flat again and rebending it several times!)

Cold forming 4130N is basically a must. Here are some practical reasons:

- 4130N is pretty much at the full strength of the alloy 90,000psi. (this is the state we want, the full heat treated stuff they use in modern undercarriages is about 200,000psi but not ductile enough for what we need) Hot forming is hard to control and will result in heat treatment. It is very difficult to evenly heat thin sheet, so you really don't know what state the material is when your done. Thus you don't know its properties and you are into unkowns much worse than cold working;

- full annealed 4130 sheet is hard to find and has lower properties. With full annealed, you can be confident using tight bending radii but you might as well use mild steel sheet due to the other issues;

- the issue of uneven heat makes hot forming much more difficult than it sounds. I gave a tool and die maker and a sheet metal guy the task of forming 4130N strut sockets for the ctr-section cabane sockets for the Camel. They got into such a bind they decided to heat it with torch and hammer it around the CNC machined forming buck/jig we were using. The result was ugly - wavy, lots of hammer marks, scale deposits from over-heating, and poor fit. Tossed the part and the damaged jig and cold formed the rest myself;

- the scale mentioned above is a bad sign! A poorly adjusted torch or a part played upon by the wrong part of the flame will "carburize" the metal. This is dissolving extra carbon into the metal and thus the surface properties change and now hammering and cold working it may be a bigger source for cracking or brittleness in that area.

Yes, I know I've been forming to tighter than the recommended radius, but I haven't found much in the way of good information as to bending radii data on 4130 is and have seen lots of 4130 parts bent very tightly and show no signs of cracking after years of service. The two-fold stronger 4130N bent to make a part that was mild steel is an additional safety factor. Furthermore, these tight bends only occur on items like the corners of spar boxes, and as such, are well supported by the spar and not subject to the bending loads of other parts where bending radii can be and are much larger like rigging wiring plates.

Then there is this ... the RAF9a spec outlines a Bend Test. 4130 has a very simlar requirement and it is stated the same in some texts or as an alternate test of a 180 degree bend over a strip of the same thickness which implies a x1/2T radius. Thus I am not really that worried.

The only real issue is the power it takes to bend a tight radii in 4130N.

[David Paule]

In general, if the 4130N hasn't cracked, it's okay.

Use a 10x magnifying glass to look for cracks. None are acceptable. For more assurance, have the parts checked at a qualified non-destructive inspection facility. But the 10x glass is a very good inspection and should normally suffice.

It's just another routine shop tool.

David Paule

[Joe Perkel]

Originally Posted by brisfitworks

My Camel drawings show 1/16"R as the inside radii of the bend on 18g spar box.

Radii is a function of thickness and alloy. You'll see "rules of thumb" like: "minimum radius is 1/2 thickness or 1/32" whichever is larger for low carbon steel". The other rules of thumb you see is recommended bending radius is metal thickness (T) or that times a factor - 1xT through 3xT is often seen. Aluminums are larger - even 10xT. At 18ga (0.048" BSWG) the Sopwith dwgs implied recommendation is 1.3xT.

When Brit dwgs refer to mild steel they typically call a spec like RAF9a. This is a medium carbon steel (.20-.25c) and thus the bend radius is larger than that "1/2 thickness or 1/32R" rule.

Bill,

Another truly valuable response to go in the build file, thank you!

Intuitively knew about "grain direction" issues if I had not maybe read that before. The cold working test is helpful, will do that with any batch orders.

It is very satisfying and comforting to know that there are individuals and groups out there to help with these interpretations when they arise.

Will proceed now as per above with drawing these radii per these "rules of thumb." Really, slow going, my CAD sessions seem further spread apart in recent weeks.

Thanks so much!

[Joe Perkel]

Based now then upon independent confirmation of a 1/16" radius as per Nick, Bill and Bryan. I quickly used that as the "inside" radius and offset the curve to come up with the outside. Here is the result.

This now looks right to me and matches my non dimensioned section drawings. Good enough now to proceed.

Thanks to all!

[brisfitworks]

Joe:

While searching for references of extant F2b documentation, I stumbled across a document: "Records of the British Aviation Industry In the RAF Museum: A Brief Guide"

It goes on to describe the document content in this way:

"Brief details of the records, the relevant accession numbers and any limitations on access are given. Where the records have been listed this is indicated"

"Copies of Sopwith Baby drawings (MPC 74/33, listed)"

This may be worth storing away for future research

Bill

P.S. Do you have a copy of Mick Davis' book "Sopwith Aircraft"? Lots of detail of the history of the company and aircraft and especially the lineage of the designs and design details. Discussion of the linear of the Baby as well. Photo of the "Folder" in it too!

[Joe Perkel]

Originally Posted by brisfitworks

Joe:

While searching for references of extant F2b documentation, I stumbled across a document: "Records of the British Aviation Industry In the RAF Museum: A Brief Guide"

It goes on to describe the document content in this way:

"Brief details of the records, the relevant accession numbers and any limitations on access are given. Where the records have been listed this is indicated"

"Copies of Sopwith Baby drawings (MPC 74/33, listed)"

This may be worth storing away for future research

Bill

P.S. Do you have a copy of Mick Davis' book "Sopwith Aircraft"? Lots of detail of the history of the company and aircraft and especially the lineage of the designs and design details. Discussion of the linear of the Baby as well. Photo of the "Folder" in it too!

Excellent!

I will look into this further! Not familiar with the MPC 74/33 reference. Most of what I have, is original Schneider except one float drawing and one main planes drawing.

I picked up the Mick Davis book immediately!

Thanks a bunch Bill!