Sopwith Baby Project

Joe Perkel · 18 November 2007, 12:14 PM

Gentlemen,

I'm now a bit more used to the forum's set-up and as such will keep this thread for any future questions, statements or other issues regarding my intended Sopwith Baby project, so as not to post quite so randomly.

Step (1) of Phase one is completed as of today, as follows.....

The decision to go 4130 tubing for the airframe is solidly grounded for many reasons and is therefore permanently decided.

As for the issue of Al.-vs- wooden wing structures. In speaking with many of you both on and off-line along with the many flying examples out there, the decision in favor of wooden wings is therefore also made.

However, Airfoil section is "tentatively" decided as a NACA 4 digit section as per the following reasoning......

In order to maintain some degree of authenticity but, yet take advantage of better lift / flying characteristics, I don't see another section which can be manipulated to match the original as closely and still do the job.

......Any comments / observations regarding the airfoil choice are very welcome and encouraged.

Regards

jumpinjan · 18 November 2007, 01:37 PM

I don't think you can go wrong using the NACA 4412, just about every small aircraft uses it. Its a good dirty airfoil.
Now that you decided on 4130, your next "big" decision will be what to weld it with....TIG...MIG....or gas??????
Jan

Joe Perkel · 18 November 2007, 02:38 PM

Quote:

Originally Posted by jumpinjan

....... your next "big" decision will be what to weld it with....TIG...MIG....or gas??????

Jan

I'm not sure on this one yet Jan. I was trained plenty in gas back in A&P school but, I still have to evaluate the options carefully. Will look at TIG closely.

Thanks Jan!

Joe Perkel · 20 November 2007, 06:46 PM

Gentlemen

Knowing that most who post and read in this replica section are likely certificated airmen and may not look at the historical sections as much. I just posted an identity request in the "People" section of this forum.

Please take a moment to look at that post as I am hoping that perhaps someone here might be affiliated with or have access to old FAA airmen databases.

Please help ID this airman

Thanks a lot!

Joe Perkel · 5 December 2007, 07:55 PM

I hope all are enjoying the Holiday Season so far! Myself, I've been pecking away at the main floats late at night here and there. What I have so far is the overall perspective while I work on the interior structures in detail. (Quite the Dinosaurs in there I must say, ....canvas bulkheads for one thing?!.) I am drawing these up as original in order to expose areas for improvement / re-design.

At this point, some issues are now apparent and I would like to elicit comments from those who may have float experience (I have none) as to the following items.

- It is immediately apparent that there is no step in this design. However, the short dimension and placement of the floats puts the aft end right about where a step should be. Comments as to the issue of "un-stick" and it's ramifications are encouraged.

- The 270 deg ash beading is clearly designed to protect the bottom for beaching / ground handling. What kind of spray pattern and it's effect on the prop can be anticipated? Suggestions for spray control while remaining true to original design?

There is much documentation as to the general unsuitability of these designs for rough water. However, I would not be deployed against enemy shipping / zeppelins in open ocean and so be restricted to inland bays, lakes,..... protected waters. Still....I look at this flat bottom and the three float configuration and wonder about nose over in an inadvertent oscillation (porpoising). So the following operational issues then come to mind.

-Take-off would appear to be straight forward. Allow the tail to come up at its leisure, come up on plane to flying speed and un-stick....correct?

-Landing is a question though. Main floats first and allow tail to settle,..... or three point? Simply curiosity at this point.

Thanks!

Jeff Brooks · 6 December 2007, 02:44 AM

Joe, you're gonna bend 1/4" plywood? Or are you going to laminate several smaller piceds to get to 1/4"? How sure are you of those plywood thickness dimentions? They seem thick .. and heavy.
also, 1/4" 3 ply plywood is not aircraft grade. I think my 1/4" has 5 to 6 ply.

ulpilot · 6 December 2007, 03:41 AM

Based on my extremely limited knowledge of float design and theory, here is why you don't see that style float anymore.

Glassy or calm water operations. They stick like glue, due to the surface tension of water. You would need lot's of horsepower to get off the water. Glenn Curtiss figured that out back in 1911, and came up with the step design to help break that surface tension. Float design hasn't changed much since.

Rough water, rough ride, very very rough ride. The best riding pleasure boats have a deep vee hull, flat hulls, like rafts, ride pretty bad.

Directional control, they are like ski's, just as happy to go sideways as straight. Which can easily induce a water loop (not a good thing, think ground loop), and some nasty side loads on the struts and attachments.

By the way, how did they steer with these old floats? I don't recall seeing a water rudder on any of these older floatplanes. Then again, maybe because of the flat bottoms they didn't steer too well.

But it's your plane, so try the old style, you can always update the floats after some taxi testing.

Joe Perkel · 6 December 2007, 06:20 AM

Quote:

Originally Posted by Jeff Brooks

Joe, you're gonna bend 1/4" plywood? Or are you going to laminate several smaller piceds to get to 1/4"? How sure are you of those plywood thickness dimentions? They seem thick .. and heavy.
also, 1/4" 3 ply plywood is not aircraft grade. I think my 1/4" has 5 to 6 ply.

Jeff,

These are in fact the original dimensions, although a later improved version over an earlier design. The earlier design may have had thinner ply, I don't know for sure but, this one also has closer rib spacing at 3" vs 6" for the earlier design. The documentation says the earlier ones weighed 72 lbs, no word yet on this one since I've not completed the CAD work yet.

As for actual construction, I would mimic modern wood float methodology, I see your point on bending 1/4' bottom to the radius specified.

Thanks

Joe Perkel · 6 December 2007, 06:33 AM

Quote:

Originally Posted by ulpilot

Based on my extremely limited knowledge of float design and theory, here is why you don't see that style float anymore.

Glassy or calm water operations. They stick like glue, due to the surface tension of water. You would need lot's of horsepower to get off the water. Glenn Curtiss figured that out back in 1911, and came up with the step design to help break that surface tension. Float design hasn't changed much since.

Rough water, rough ride, very very rough ride. The best riding pleasure boats have a deep vee hull, flat hulls, like rafts, ride pretty bad.

Directional control, they are like ski's, just as happy to go sideways as straight. Which can easily induce a water loop (not a good thing, think ground loop), and some nasty side loads on the struts and attachments.

By the way, how did they steer with these old floats? I don't recall seeing a water rudder on any of these older floatplanes. Then again, maybe because of the flat bottoms they didn't steer too well.

But it's your plane, so try the old style, you can always update the floats after some taxi testing.

I suspect as much, that's why I do want to hear about these issues from other sources.

There is a linked water rudder on the Baby's tail float, just fine for taxing I suspect. I cannot speak to as to whether or not the beading would provide some directional stability, I simply do not know for certain but, I suspect they might do so at speed.

Internally, I expect to go modern as in these from Muk Tuk....Kits and plans for ultralight floats

Externally, I will try to stay as true to original as is practical. Perhaps I may take a bit of "creative licence" and make some modern concessions while still maintaining some degree of authenticity...will have to see what develops.

Thanks!

Joe Perkel · 9 December 2007, 06:42 AM

I made some offhand remarks a few posts back about the Sopwith floats being "Dinosaurs" in terms of structure. Last night I finished the ribs, rendered the results and had a chuckle to myself..... they look like bones!

CAD Page

Sopwith apparently had a lot of trouble with an earlier version of these coming apart. The earlier versions had rib spacing of six inches -vs- the three you see here. There is a lot of brass screw use for assembly but, no word on assembly adhesives. There is mention in the documentation regarding varnish coatings and continuing problems associated with water saturation.

So I have a basic question as to what adhesives were in use at the time, was it Recorcinol glue?

My thoughts are along the lines of liberal use of West System epoxy to solve bonding and saturation issues but, weight gain is a worry. If I can save material weight in the interior structure re-design, then the hope is to have some elbow room.