Sopwith Baby Project

[Joe Perkel]

Originally Posted by brinesharks

Although it doesn't have wooden struts, the EAA Acro Sport (II) has a similar set up. I'll email you some pics of the open structure. The cabane struts are actually bolted to the fuselage which could easily be adapted to wooden struts that have steel end fittings.

I also have an idea regarding floats - I'll include it in the email as well...I ramble a bit much for forum posts!

Brinesharks,

My (over full) inbox is now purged, look foward to seeing that.

Don't like what I read about float durability as originally designed, so original idea for changing the internal structures to more modern design is most likely. Look forward to that as well.

Thanks!

Nice project! Great thread! Excellent web site!

FYI: I voted for the Blackburn color scheme too. More colorful.

Cheers,
WF2

WF2,

If I have to cut a "deal" with the "boss" about say,... a little larger workspace for example. Then I just might end up with the Blackburn version!

Thanks for the compliment, modern website development tools now eliminate html competency, a real plus for the amateur webmaster!

Thanks!

[Joe Perkel]

Ending another late night session and nearing completion of aileron details as originally drawn. Before proceeding further, a couple of things just,...don't seem quite right. At least, my interpretation anyway.

1) What is the purpose of this diagonal strut and did I fit it correctly at the forward end? All I have of this is a plan view which specifies 1/2" sq spruce. No real dimensions or coordinates for placement, just a plan view.

2) I've checked the dimensions and placement of the lightening holes and ribs several times but, it seems to me the ribs should land on solid sections forward? It just doesn't look quite right but, the drawing details seem to match it up like this.

Thanks!

[ulpilot]

The diagonal may be to strengthen the end rib from bowing inward when the fabric covering is shrunk. Many aircraft have that feature.

[brisfitworks]

Joe:

You have it correct as I see the image.

It is interesting how nearly identical in details this is to the Camel.

ULPilot is correct, the diagonal is to brace the end rib against loads especially the fabric shrinage (I saw a Cub with improper wing tip bows, over heated ceconite and tautening dope bend the tips up to almost being giant winglets! Fabric shrinkage can be powerful). There does not seem to be any clear definition on the rib end location vertically for this 1/2"sq. strut, but the convention would be to center it on the spar vertically. Yes the spar is thinnest there but the engineering practice is to aligne lines of force to intersect on centerlines. Furthermore, the glueing of the rib to the spindled out spar will supprt the end AND it is a hell of alot easier to trim end to fit.

The carpenter on the line would interpret it on the fly so there was, undoubtedly, variation; the engineer would have taken the center-line of the 1/2" square and had it interstect the spindled face of the spar at the center-line of the rib. Ends bevelled to match rib and spar surfaces.

The original Camel Blueprints I have show the ribs fitted into the spindling in the same manner. It works from an engineering standpoint as well - the cap strips and the ply butted against the outer, unspindled, sections of the spar provide the most significant portion of strength. The portion contoured and glued to fit the spindling just adds to the attachment strength of the rib AND because it is so deep fore-and-aft, is stronger than a straight vertical joint. (engineering eligance versus complication to frustrate the guy that makes and fits it)

The solid sections exist entirely for the passage of the aileron hinge bolts and the hinge loads and at the ends to avoid splitting.



[QUOTE=Joe
1) What is the purpose of this diagonal strut and did I fit it correctly at the forward end? All I have of this is a plan view which specifies 1/2" sq spruce. No real dimensions or coordinates for placement, just a plan view.

2) I've checked the dimensions and placement of the lightening holes and ribs several times but, it seems to me the ribs should land on solid sections forward? It just doesn't look quite right but, the drawing details seem to match it up like this.

Thanks![/QUOTE]

[Joe Perkel]

The diagonal may be to strengthen the end rib from bowing inward when the fabric covering is shrunk. Many aircraft have that feature.

Thanks Vet, you certainly know your way around Tube & fabric aircraft!

"...the convention would be to center it on the spar vertically. Yes the spar is thinnest there but the engineering practice is to aligne lines of force to intersect on centerlines"....

"....the engineer would have taken the center-line of the 1/2" square and had it interstect the spindled face of the spar at the center-line of the rib. Ends bevelled to match rib and spar surfaces..."

Excellent!, now that I know what this is for, I can look to place it better. One quick question though,...Centerline to centerline alignment will give this a slight diagonal vector as viewed from the wingtip. I suppose that is better than offsetting forces by offcenter placement?

"...The portion contoured and glued to fit the spindling just adds to the attachment strength of the rib AND because it is so deep fore-and-aft, is stronger than a straight vertical joint. (engineering eligance versus complication to frustrate the guy that makes and fits it)..."

"...The solid sections exist entirely for the passage of the aileron hinge bolts and the hinge loads and at the ends to avoid splitting..."

Terrific! Little bits and pieces of the puzzle now made more clear. Only thing better would be having you standing next to me in the workshop!

Thanks William!

[Michael Scheetz]

The diagonal bracing keeps the framework from racking, or going out of square. So not only does diagonal bracing reinforce and strengthen the framework of the wing, it increases the lateral strength against shear forces
| | | ---> / / /

Imagine a scaffold without a diagonal brace, the square framework would lean over into a parallelogram and eventually fall over and break under a load.

observing,

Fee2b
Michael Scheetz

[Joe Perkel]

Originally Posted by Fee2b

The diagonal bracing keeps the framework from racking, or going out of square. So not only does diagonal bracing reinforce and strengthen the framework of the wing, it increases the lateral strength against shear forces
| | | ---> / / /

Imagine a scaffold without a diagonal brace, the square framework would lean over into a parallelogram and eventually fall over and break under a load.

observing,

Fee2b
Michael Scheetz

Thank you all for the input. Based on this new bit of info on this one strut, I've repositioned it as follows.





By the way Micheal, I think the FE.2b and DH1 are good looking myself!

[brisfitworks]

Joe:

Looks excellent!

I was uncertain as to whether I was understandable, but you got it dead on!

The next confusing part of this is that any production sample will have variation in the way the bevelling is done for fitting the ends - some guys on the line would likely make the bevelled faces equal and others the way you have drawn and others find another varaition. I have found variations in details in photos on the Camel and F2b in many spots. One photo I have of the F2b production in 1924 for Spain shows many fuselages side by side. Two fuselages, right next to each other, have minor differences! Undoubtedly, because there are different people on each. Many details on drawings say "fit on job"

When building the Camel we found many details that had to be made like what we thought it should be and we could see in photos and ignore the drawings because what was "engineered" either didn't work or was overly cumbersome.

Moral: "Perfectly engineered is often less correct than interpretation, because that was the way manufacturing works!"

I just realized I was thinking mostly about the wing tip bow bracing when writing about fabric and now realized that your model does not have the 1/2" sq. brace at both ends. On the Camel there are two - one as you show and one mirrored at the other end but butting the joint between AP121 and the aluminum rear spar. The brace is attached with an aluminum clip similar to those at TE on ribs.

Also, for comparisons, the aluminum tube spar is squashed flat, sectioned out and wrapped around the AP121 and rivetted through. This was a 1" dia. tube. I have tube dwg B-2059 that shows this detail. If needed, I can scan.

Also at each ply rib, there were ply doubles fitted around tube, from capstrip to capstrip on both sides.

I am throwing in these Camel details just in case the Camel is more like the baby than we might know and thus helpful to you.

There is a few very old images of the ailerons on our Camel thread (Replica Sopwith Camel Construction Process)

I really should set up an account somewhere so I can post images @#$%%^ What I "should" do is revitalize our Camel thread since we are just finishing up the wings and getting ready for covering. I'll do that quicker if any of these details are critical to you.

I just checked Jim Keiger's dwg's for the Strutter and some aileron details are more similar to what you have modelled than Camel but there is no internal diagonals because it has external wire diagonals like Sopwith's earlier seaplanes. Jim shows the aluminum tube as 3/4" dia. and squashed similar to Camel. Since AP121 is 1/8"R on large end, Baby likely similar - squashed,wrapped and rivetted.

[Joe Perkel]

William,

Thank you for taking an interest in my project and the time to help me out, it is much appreciated.

“…The next confusing part of this is that any production sample will have variation…”

I have noticed this opportunity for variation in a few places, the airfoil for one had original coordinates that interpolated in a rather unfair curve. I suspected as you note, shop floor corrections during manufacture. Still, if I don’t know what something is for, I do need to find out. Your explanation about alignment of forces was my clue for this strut.

“…When building the Camel we found many details that had to be made like what we thought it should be and we could see in photos and ignore the drawings because what was "engineered" either didn't work or was overly cumbersome…”

I need a bit more experience before I can make that leap, I‘ll ask you folks first. And here lies the main reason for my CAD modeling this initially. Cost of materials is a bit cheaper this way!

“…I just realized I was thinking mostly about the wing tip bow bracing when writing about fabric and now realized that your model does not have the 1/2" sq. brace at both ends. On the Camel there are two - one as you show and one mirrored at the other end but butting the joint between AP121 and the aluminum rear spar. The brace is attached with an aluminum clip similar to those at TE on ribs…”

The wing tip bows do have this on the Baby as well, but the aileron does not have another strut, at least not this drawing anyway. I have to check some of my other drawings and the Pup (Baby‘s closest relative). My CAD model is not yet complete in all details, still need to do fittings wires,…etc.

“…Also, for comparisons, the aluminum tube spar is squashed flat, sectioned out and wrapped around the AP121 and rivetted through. This was a 1" dia. tube. I have tube dwg B-2059 that shows this detail. If needed, I can scan…”

I have this wrong on the model, that detail is the same on the Baby. Where I went wrong is the AP 121 section, which I made too large, (guessing), so I can’t pinch and wrap the tube. I did however, get the outside dimensions correct in plan view. So I figure since manufacture of this TE is likely to mimic contemporary designs (Skybolt, Pitts, Hatz,..et al), I figured for the CAD model, to just let it go for now. If you have a dimensioned detail of AP 121 in section, I could use that to correct the model.

“…I should just revitalize our Camel thread since we are just finishing up the wings and getting ready for covering. I'll do that quicker if any of these details are critical to you…”

No need to hurry on my account, I’ve got time. This planning, research, and CAD work in phase one of my project, is all done late at night after a long day at work with my head bouncing off the keyboard. This while I await my home renovation to be completed sometime in October.

The resulting small workshop will then allow me to commit one day weekly to start ribs, bombs, guns, small components, and eventually floats, that can all be crated for later assembly at another location. Another reason for the keen interest in CAD work first, increased chance of proper fit for assembly down the line.

Thank you so much, and look forward to seeing the Camel!

[brisfitworks]

Joe: I was just editting my comments for the 20th time because I saw your note about bracing the strut at spar end. Was adding a sentance when you replied. So I'll say that bit here.

I am not sure about an extra block. I didn't notice any in dwg's and we used T-88 epoxy so such was unnecessary. I'd suspect screws installed through from front of spar into end of brace to secure it for glueing. Now you have me curious. I'll look some more but suspect the answer is, from other examples, no blocks and screws installed aftward through spar.

The variations from engineered perfection is something that makes many of the debates about details seem likely pedantic. Your airfoil example is a good one - I've had this discussion before with people asking about what section was used. When you take the coordinates for the throetical section and map it onto a CAD model of the wing you often find the spars don't fit. This is the engineers compromise of locating spars to line up with structure on the fuselage and finding balance between the needs of engine, undercarriage, cabanes and all that. He gets to needing an aft spar in a certain place to make things work out simpler and then calculates the bending loads on the spar and squeezes in a little more material and voila the section is slightly thicker than theory at the aft spar. Or he designs a spar, spends three days confirming the strength calculations and realizes the fuselage change he just made need sthe aft spar to move back an inch.

I have applied the design principle of forces intersection and centerlines in many cases to get the job done when dimensions or photos are missing only to have the documentation show up after the fact to confirm what I "guessed" at. If you remember and trust that these guys were very good design engineers and that basic structural engineering theory hasn't change all that much in a 100years, you can reverse engineer missing details with confidence.

CAD modelling is a huge help. I did that for the Camel and am working through my Brisfit that way. It shows mistakes and fills in missing or hard to read dimensions. I always described the process, to our museum members this way: "In the war, a Sopwith would sub-contract to a Ruston Proctor. Sopwith would deliver dwg's and a pattern ship. The Ruston shop would, as the Sopwith shop probably did, curse the engineers that made the drawing while they would make about one and a half airplanes worth of parts that were wrong. Then they would work out the details and corrections in their tooling. All the corrections would be pencilled onto dwg shop copies (which usually don't survive) or not documented because the tooling and tooling dwg's had the corrections built into it. We can't afford to waste that much effort and materials so we will make our mistakes in CAD!"

I made the same explanation to some workers from DeHavilland Canada and they laughed and said nothing has changed in 80 years for they said the same basic thing to their engineers when asked about the idea to sell a construction license to another country for the Dash8: ".. dumb idea, WE could barely build it from your drawings!"

With all that engineer bashing I should sign this post more formally...

Wm. K. Batter P.Eng BSc.aero
(aka Bill ;-)

P.S. glad to help! all the effort I have put into other projects is more worthwhile if a larger group benefits from the cinder block wall scars I have from frustrating over lack of drawings and conflicting details that makes me beat my head against a wall.

P.P.S AP121 is 1/2" chord, 1/8"R leading edge, 3/64"R trailing edge, straight flat sides along tangent between these two radii. Don't remember where I got these dimensions from but they are a period source. I suspect that the 3/64" is rounded down for the only round tube that fits making this part is 10mm OD!