Sopwith Baby Project

[Bookmaker]

Joe, I would recommend you stay away from salt water. That is if you want your plane to last any time at all. There's just no way to clean it out of every nook and cranny.

Just ask the guys at Chalk's.

Dale

[j ferguson]

I thought of this because I used to rent a J-3 in northwest Illinois. After the owner got comfortable with me, I received permission to take it anywhere I wanted but clearly because it had no nav lights, be sure to get home before dark. Usually he propped it for me when I was leaving. I found if I went somewhere else and shut it down, I could prop it by standing in front of the wing struts and swinging the prop from behind. the idea was that if it developed any thrust, I'd prevent it from going flying without me by preventing it from moving since I was in the way of the struts.

One time this didn't work. It was a very hot day and maybe I'd flooded the carb. I just couldn't get enough leverage to really swing the prop and I wasn't comfortable being in front of an unrestrained plane and turning it even with the mags off. so I tied the tail to a tree with one of the tie-down lines, pulled it forward til the rope was taut and then cleared out the carb and got it started, set it to an unaggressive idle, untied it and flew home. But then I wasn't standing on a float.

Are you sure you want floats?

best, john

[Joe Perkel]

Originally Posted by Bookmaker

Joe, I would recommend you stay away from salt water.
Just ask the guys at Chalk's.

Dale

Dale,

I hear you, it's battery acid and I've waged war for years as a boater! I'll be very tempted though, ......depends on what I learn from other float pilots.

Sad thing about Chalk's, I should look it up on NTSB, loosing a wing just has to be someone's fault.

Are you sure you want floats?

John,

I always did, never got around to it though. I figure here's a way to have it all.

Just found a private seaplane base a stones throw away from my build-site!

As for the water ops issues, don't really know enough yet for an educated reply about start, run-up, and taxi procedures, just conjecture on my part at this point.

[Joe Perkel]

I am having a bit of trouble interpreting a detail. I've done what I think makes sense but would like some confirmation of my thoughts before proceeding.

The drawings are not quite clear as to whether or not these load struts are embedded into the ribs like I show here, or on centerline back to back, flat side to flat side.



I am favoring this only because it seems to make sense to transfer loads from longitudinal to longitudinal. Still, I have to wonder about a centerline mount with an appropriate backing plate???

[j ferguson]

Joe,
a clue that embedding the vertical strut midst the ribs might be wrong is that the ends of the upper horizontal "gusset" aren't doing anything - not load carrying except as transferred through glue shear connections. True, glue is very strong in shear, but what you have shown is a segmented beam. If you move it out of the plane of the ribs, it doesn't need to be interrupted.

beautiful drawing by the way.

You might assume that with all the glue you're going to use, you will get good shear connections in that interrupted horizontal "plate", but it would be a whole lot more sure if it was adjacent to the ribs. also it would be a whole lot easier to build.

another clue might be the width of the top and bottom longerons. they should be wide enough to accommoate both ribs and vertical struts if what I'm suggesting makes any sense at all.

We used to have a real wood wizard here who was building a Spad. In my ignorance, I would think it a good idea to build, when in doubt, so you don't absolutely depend on glue as structure, but more as a method to retain structural elements in place.

best, john

[Joe Perkel]

Hi John,

Thank you very much for your analysis.

I have to tell you,.... I'm truly conflicted here. Mind you, this would never be built like this but, I want to try and understand the original thought process.

the ends of the upper horizontal "gusset" aren't doing anything - not load carrying except as transferred through glue shear connections.

another clue might be the width of the top and bottom longerons

Part of the "confliction". The drawings seem contradictory in that dotted lines are shown behind the struts in one view, but not where you would expect in another. This eluded toward centerline. However, the dimensions as you note, (3/4" gusset, 3/4" longerons) elude towards outboard panels as I have them. The radii of the ribs at the bottom panel, rules out placement of these solid pieces immediately adjacent to them.

Still, the "plan" view does not show these on centerline ....and likely hidden, under the same dimension longerons.

Like you, ....I don't like this "splitting" of the ribs but the "side" view drawing shows complete ribs the entire lenth at 3" spacing, along with the above mention "dotted lines". But, "dotted lines" usually mean structure behind something, or maybe a continuation of a path??? (Did I mention conflicting info?)


Another clue is this quote from a float kit manufacturer in Canada....Kits and plans for ultralight floats

Outside panels

The outside panels carry most of the float loads. They provide panel stiffness and resist point loading when mooring or beaching. They are exposed to the environment and of course keep the water out. They are the most important wood material involved.

The 3 mm plywood supplied in the kit will provide ample panel stiffness on floats 12 to14 feet long.

Anyway John, I'm sure you can appreciate that regardless of the details, it's looking like I'll be building three little "boats" on strongbacks! I sure do like this project!

[j ferguson]

Joe,
it could be that you do have it right and the extra wood is intended to stiffen up the 3 ply vertical skin near the struts. sometimes parts get designed to do one job and the fabricator doesn't really understand what's happening and makes them look like something else. seems like just adding vertical fillers between the ribs would have been simpler. why the diagonal, unless these were also intended to carry the plane load down to a cradle which supported the floats at these offset points.

I like what you're trying to do here. it is vital when you're doing sometnhing like this to try to understand why everything is the way it is. this might protect you from design "features" which either don't do anything constructive or are actually not good.

Was this plane actually engineered or simply designed?

john

[Joe Perkel]

why the diagonal, unless these were also intended to carry the plane load down to a cradle which supported the floats at these offset points.

Brilliant! .....There is a cradle. I have to check the position of this when I get home tonight, it's a simple affair but it is designed to lift the plane with two levers / handles on either side. A quick check of the internet shows a couple of cradles but, not close enough to see the exact position.

Was this plane actually engineered or simply designed?

I'm not quite sure.

I know that the Schneider prototype was specifically built in 1913 to race the following year. I'm a bit confused as to how the Tabloid fits in here but, I believe the Tabloid was designed first and specifically as a two-place "Sport Biplane." Everything else seems to follow the path of the Tabloid.

Pretty sure it (Tabloid) was Harry Hawkers "Baby" ....as it were.

Thanks a lot John, the cradle hint is most helpful!

[Joe Perkel]

John,

I want to thank you again for putting me on the right track.
Note in this museum display, the angle of the triangular mounting brackets...which matches the underlying wooden struts! So there's my answer,..these are just inboard of the side panels!



The cradle assembly does not appear related to these as I look at various other images.

So to venture an educated guess, I am going to postulate that these are roughly aligned to take advantage of grain alignment to the expected forces of T.O and landing????

Thanks again John!

[drrivah]

Joe-Image below from the web: a Heath Model V Parasol from ~ 1930s (?), with wheels attached to floats that look similar to your dwgs. Internal diagonals may follow LG for float wheel mod: are there wheels detailed in Sopwith float plans?
-pete