Sopwith Baby Project

Joe Perkel · 12 February 2008, 12:39 PM

Someone please check my figures.

Sitka Spruce Density = 450 kg/cubic meter, converts to 28.034 lbs/cu ft

Calculated volume of lightened rear spar for Sopwith Baby = 487.69 cubic inches

487.69 cubic inch = 0.2822 cubic foot

Therefore…..

Calculated weight of this spar is 28.034 x .2822 = 7.91 lbs

Does this seem correct? Seems a bit light to me.

Thanks!

Leatherhead · 12 February 2008, 12:56 PM

Your value for spruce density (@12% moisture content) agrees with "Softwoods of North America", by USDA, Page 51.

If you've determined the spar volume correctly, then I'd say it's ok.

brisfitworks · 12 February 2008, 01:49 PM

[quote/] There must be some technical trick to rolling long lengths of A & P 121 without the twisting you mention. I recall Achim keeps the tubing in tension as it pulls, rather than rolling it out with the rolled end free. Did your trials keep the tube in tension or was the rolled end free?

Thanks.
-pete[/quote]

I have made A&P 121 with a rolling mill to both make the section and, by installing a 3rd roller, to roll the curves for such items as the outline to the Camel fin. I also have a set of rollers for A&P 5 and the "clown smile" section of the cowl ring used by Sopwith.

It is a lot easier with mild steel, 4130 is tough stuff!

One of the challenges is that the best fit for A& 121 is 10mm dia tube. 3/8" dia. is a reasonable compromise.

Yes, the trick is to do it under tension, you do not drive the material with the rollers you pull through the rollers, as Baldeagle described. My rollers are geared together to make them always spin equally.

After making the rough section you have to have a drawing bench so you can pull the stock through a drawing die to finalize the section and straighten.

I have been using a long bed lathe to make the shorter sections required for tail feathers.

I am still tooling up a drawing bench for longer lengths, so to avoid waiting for the longer lengths of A&P 121 for wings, our museum used 1/4"dia. 4130 tube for the wing TE's on our Camel.

It is all doable if you make the tooling. It is the same way as was done to make it in WW1.

Cheers,
Bill.

Joe Perkel · 12 February 2008, 01:49 PM

Quote:

Originally Posted by Leatherhead

Your value for spruce density (@12% moisture content) agrees with "Softwoods of North America", by USDA, Page 51.

If you've determined the spar volume correctly, then I'd say it's ok.

Years ago when Light Miniature Aircraft was in Miami, I visited their operation in Opa Locka. I remember thinking then, "boy that sure does look skinny!"

I best be getting used to it I suppose!

The volume is calculated by the CAD software. Best way to check this then is real time with a scale. Calculated weight of solid spar is 8.9 lbs. All that routing seems like an awful lot of trouble to save a pound. I wonder then, if adding "surface area" by means of these lightening channels,.. adds stiffness to the structure? Which then brings the question of why specify solid for the top rear spars, and lightened for the bottom rear?

Just trying to understand the mind-set behind the design.

Thanks Leatherhead!

Joe Perkel · 12 February 2008, 01:57 PM

[quote=brisfitworks;367900]

Outstanding information Bill. I've been mulling over what Rick had said about mild steel as well. I'll be taking a closer look now at what is done by flying museum examples,... where I can see it. The memorial flight Strutter in France has nice construction pics.

Will save this for future reference!

Thanks!

brisfitworks · 12 February 2008, 02:10 PM

You're more than welcome Joe!

I have more details on the A&P sections somewhere in my files. I am just trying to unpack my office after a busy three years to find things again and organize it so I can know where things are. As I find stuff I can post more details.

I have the outlines of some sections, as used on the Camel, drawn in Autocad.

I have listing, somewhere, of many A&P sections.

The other thing you likely need is SL fitting outlines and details. In building the Camel for the museum I CAD modelled in 3D and flatform most of the parts. Sopwith being smart, used the SL fittings on many aircraft. I know that many are common from Pup through to Snipe. Likely you will find them on a Baby.

Cheers,
Bill.

Joe Perkel · 12 February 2008, 08:44 PM

Quote:

Originally Posted by brisfitworks

You're more than welcome Joe!

I have more details on the A&P sections somewhere in my files. I am just trying to unpack my office after a busy three years to find things again and organize it so I can know where things are. As I find stuff I can post more details.

I have the outlines of some sections, as used on the Camel, drawn in Autocad.

I have listing, somewhere, of many A&P sections.

The other thing you likely need is SL fitting outlines and details. In building the Camel for the museum I CAD modelled in 3D and flatform most of the parts. Sopwith being smart, used the SL fittings on many aircraft. I know that many are common from Pup through to Snipe. Likely you will find them on a Baby.

Cheers,
Bill.

Bill,

I had a suspicion that may have been the case and ordered Pup and 1 1/2 Strutter drawings from Replicraft at the same time I did the Baby from WW1 Aero. Pretty sure I do in fact have all of the fittings. Most of those are nice clear copies of the originals.

What I am missing, is tail float detail and empennage. I can extrapolate both from what I have but, would be better not to have to if at all possible. Knut Erik from Norway is offshore at the moment but, has been kind enough to forward a non-dimensioned but scale side view of the empennage.

I can convert AutoCad (.DWG) into a readable Rhino file (.3dm), If you would like to forward me the A&P Section file, I will do a 2d drawing, dimension it and post it here. In scanning over the drawings that I do have,... I have not yet found a dimensioned section drawing for that tubing.

I did however find a fitting shaped to that section and planned to scan that then trace over a bitmap in the software. Close enough I would think.

Speaking of Brisfits, I love the story of the 5 fuselages found used as trusses for a barn in Great Britain! Was that really true?

Thanks Bill!

John Masters · 12 February 2008, 09:40 PM

It looks like 'Hull' or 'J.McHull'...

JM

drrivah · 13 February 2008, 02:55 AM

Hi Bill:
Could you kindly post a photo of the geared dies/drawing table set up used to do the streamline tubing?

Also, a chart of A&P streamline dimensions would be great, or a published reference where these might be found.

Thanks very much.

-pete

brisfitworks · 13 February 2008, 07:48 AM

Joe:

As soon as I get a few of the files back in order, I'll sort out A&P information and disseminate in one batch.

The F2b fuselages used as part of a barn are referred to as the WOTG (Weston on the Green) Fuselages. There were six and for years one was thought to be mysteriously missing. Funny you should mention the WOTG's I was recently trying to trace F2b serial numbers and doing a literature search about the WOTG's and found many interesting new bits about them. They have been something I've wondered about for 30 years. But that is all for another thread to be.

Pete:
A&P info to come as descibed above.

Images of the set-up for tube shaping will have to wait a bit, the whole set-up was torn down for other jobs and right now our customers have swamps us with orders and all requesting half the quoted delivery.

I will make postings as time becomes available.

Bill.