Sopwith Baby Project

Joe Perkel · 7 November 2008, 02:03 PM

Quote:

Originally Posted by j ferguson

Well that's pretty expensive air, isn't it.

It's a little like the Titanic. Without something like the ping-pong balls, a long slit in the bottom spanning your compartments would sink that float. This does make putting the kevlar cloth around the bottom and sides very attractive.

The discussions in themselves are so helpful in that it makes me ask myself questions. Case in point from your post here....

1) Is one compartment likely all that can be flooded and remain upright for towing, where two would result in capsize? I can answer this better with a completed model, the software has hydrostatic and stability capability.

2) I need to more closely evaluate seaplane accident data.

3) If it turns out that puncture accidents happen with some degree of regularity, then the hidden Kevlar layer on the bottom panel is a given, and will justify the consultants fee.

Thanks again John!

brinesharks · 12 November 2008, 01:50 AM

Joe, this is starting to sound a lot like a Reliability study!

Joe Perkel · 12 November 2008, 03:35 AM

Quote:

Originally Posted by brinesharks

Joe, this is starting to sound a lot like a Reliability study!

Bryan,

I hadn't thought of it this way, but yes the whole project to date is a reliability study!

Since you've been following my thought processes from the start, then you're noticing the same tendency to "run home to mama" and trust in the original engineering. This has happend on all of the major components, wings, fuselage, and floats.

The addition of this single kevlar layer hinges upon seaplane accident data. Are F.O.D incidents enough to be bothered? Likely yes, but I can't seem to gleam the information easily from the N.T.S.B database.

David Paule · 12 November 2008, 06:50 AM

Quote:

Originally Posted by Joe Perkel

Are F.O.D incidents enough to be bothered? Likely yes, but I can't seem to gleam the information easily from the N.T.S.B database.

I'd guess probably not, actually. I've got a sailboat and have rarely hit anything, nothing big enough to cause damage to a float. On the boat, forward visibility to the water is poor for close-in things, so the liklihood of not spotting something and hitting it is real. Mostly, I've bumped lobster floats and such. Those are side impacts more than bottom impacts, and I've only had a very few of them.

I've sailed in Florida, California, and Colorado. Also Lake Mead.

I think the odds of hitting anything, using normal care, are very low. However, unless you've got watertight bulkheads, the hazard of doing so is possible loss of the plane.

j ferguson · 12 November 2008, 07:19 AM

Joe,
Another way you could look at this:

What size object would the kevlar protect you from better than wood alone?

Clearly if it was a large object, like the phone poles we see from time to time in the ICW, you would still have a real problem, and if it was small, the wood alone might go unpunctured.

So the kevlar would protect you from a limited range of object sizes - maybe so small a range as to not be worth the weight.

this might be a little like having a seatbelt on a car which only works in collisions at speeds between 22 and 24 mph.

best, John

Joe Perkel · 12 November 2008, 07:52 AM

The delay in commencement is serving me well in that I can contemplate these issues carefully.

Likelihood of impact puncture and from what?....

I hear you both on the probability factor, and it's that very thought that has me questioning the value of this in the first place, along with the mentioned weight gain.

My experiences in my cabin cruiser over the years that I owned it had been a bit different. Moving along at 15 -20 kts, I bent the prop on all manner of garbage from coconuts to floating boards. My concern for the lakes in Florida, is muddy water, submerged logs, and alligators.

Still, I have zero float time, and I have to defer to what I have yet to learn from the float instructor. An inquiry with the Seaplane Pilots Association, yielded no results, and I can't find relevant accident data.

Interesting to watch what's happening to me here, something bristfitworks had predicted. You go round and round with proposed changes in design, and if prudent, you end up back at square one "trusting" in the previous engineering!

Thank you both for the discussion. I will proceed with the thought in mind that there must be significant relevant accident data to support this change in order to implement it. Perhaps a better trade is a light layer of glass on the bottom for abrasion resistance, this would be beached and run up to ramps plenty.

John, I will be doing test pieces for weight analysis of epoxy coatings -vs- varnish at my earliest opportunity. I'm thinking about drying out the components in a climate controlled environment, then sealing them from absorption. The initial weight advantage afforded by wooden floats is traditionally lost later to absorption.

Thank you both!

David Paule · 12 November 2008, 11:59 AM

If you still have the boat, you could build some test floats, stock, and load them up to about the same loaded weight. Then tow them or pull them and see how they survive....

sheppo · 12 November 2008, 03:15 PM

Consider also that where they were designed (UK) many beaches were of the rocky variety. I can imagine the damage they could recieve there on a regular basis!

Have you considered having the floats filled with a lightweight floatation assisting expanded polystyrene (or similar, its not my speciality) If you are using epoxy then the foam should not be adversely affected and it would serve to block more than a small amount of water entering if you were cunning about how it was inserted into the floats.

Even a large gouge could be negated for long enough to make the shore.

This way, for a negligable weight you could have some assurance that following any holing of the float you will not be sinking for a start and ingress of water would be dramatically reduced?

There are a surprising variety of foams out there, some that can be expanded in situ from constituents, which would allow you to fill the tank post construction...

Just a thought.

Chris

sheppo · 12 November 2008, 03:28 PM

US composites Ph # 561 588 1001 sell a 2LB and 4LB pour in place marine flotation closed cell foam.
The 4LB mix is designed to add some structural strength to frames.

The basic math they offer on the 2LB mix is as follows:

2 feet x 2 feet x 4 feet = 16 cubic feet
at 60lbs buoyancy/Cube = 960 lbs of buoyancy...

Its a 2 part pour in place system but you would need to protect any exposed areas which it may expand over with a plastic like lexan as this stuff sticks like S@*# to a blanket.

If yor floats are 10 x 1.75 x 1 (or so) thats around 1000Lb flotation guaranteed for each float regardless of small holes, larger ones are still not likely to be any real issue with buoyancy. If the all up weight is about 1700lbs loaded, then you should be sorted.

chris

Joe Perkel · 12 November 2008, 06:06 PM

Quote:

Originally Posted by sheppo

Consider also that where they were designed (UK) many beaches were of the rocky variety. I can imagine the damage they could recieve there on a regular basis!

Have you considered having the floats filled with a lightweight floatation assisting expanded polystyrene (or similar, its not my speciality) If you are using epoxy then the foam should not be adversely affected and it would serve to block more than a small amount of water entering if you were cunning about how it was inserted into the floats.

Even a large gouge could be negated for long enough to make the shore.

This way, for a negligable weight you could have some assurance that following any holing of the float you will not be sinking for a start and ingress of water would be dramatically reduced?

There are a surprising variety of foams out there, some that can be expanded in situ from constituents, which would allow you to fill the tank post construction...

Just a thought.

Chris

Chris,

It's an idea that has precisely the advantages you state. Additionally, It negates a potentially dangerous "free surface effect" of any missed volume of water shifting on take-off.

The problem with the foams, (aside from any weight gain), is interior inspection, and getting the stuff back out again for maintenance. Johns idea regarding the ping pong balls if not so expensive, would have been a relative snap to get out.

It would appear, (according to the texts I'm reading), that the designers address these issues best by the addition of watertight compartments. The idea being that a single flooded compartment on one float will allow for recovery of the aircraft while remaining upright.

A completely flooded float, is supposed to allow recovery of the aircraft via the 100% reserve buoyancy of the remaining float, but likely inverted and wet.

The problem with the three float Baby (pre float design rules), is that each float is only 71% reserve buoyancy,...oops! The tail float offers 300 lbs, but that and one float still fall short by about 194 lbs buoyancy,....oops again!

To make up that 200 lbs, I could consider the ping pong ball idea (or similar) for the center compartment of each float. (This thought, prompted by this discussion).

I'll know more as time goes along, but I certainly am getting a handle on what to look for and the questions to be asked as a result of this participation.

Thanks guys!