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Replica Aircraft Topics related to the construction of WWI replica aircraft

View Poll Results: Finish Options for Sopwith Baby
Serial Number 8165 Sopwith Factory Built Baby 37 63.79%
Serial Number 2071 Blackburn Factory Built Baby 21 36.21%
Voters: 58. You may not vote on this poll

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Old 12 November 2008, 05:25 PM   #501 (permalink)
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an idea

"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."

Thats a fair comment,the accessability of the float is achieved by inspection ports I assume? How large are they?
If inspection was performed by removing the top panel either as a whole piece or in sections could the foam be applied to the inside of the float inside a heavy duty plastic liner and still allow for its removal? If the foam is the buoyancy do you need to worry about waterproof barriers?

The issue with ping pong balls is that a badly split float could scatter the balls far and wide thus negating any flotation assistance in exactly the circumstances you want it. Even adding the balls inside a bag or in each seperate compartment would not be a sure fix.

The foam would survive taxiing impacts in a largely intact manner, only a serious prang would cause it major issues.

Inspection is a different story.

There is the ability to cut cavities in the foam to allow an inspection camera to be used inside the float. Cast the foam insitu using a bag. Remove the bag and foam from the open float, cut out channels where required and reinstall the foam un bagged. Fix the top down as per usual. If you are cunning about the cavities positioning you can have a dry compartment area below the inspection ports with access holes running where you want them. This way you could well still have 75% of the foam acting as guaranteed buoyancy and sufficient access for regular inspection.

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Old 12 November 2008, 05:46 PM   #502 (permalink)
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I still like the ping pong balls @ 144/$14

There's a lot of merit in Sheppo's idea, but inspectibility does seem like it would be more difficult.

Maybe the whole issue of back-up flotation is another one of those things where you have to imagine the circumstances of the need.

What would you have done to damage the float enough to rip it open and turn the ping pong balls loose? Can you imagine your Baby floating happily on it's floats but inverted like an overended catamaran?

I found ping pong balls on the web for a dime each which would bring the flotation bill to under $3,700. My thought was that the protection you are seeking is for the plane tethered to a mooring while you go for lunch, not as an aid to locating the wreck after an unfortunate meeting of float and large foreign object.
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Old 12 November 2008, 05:54 PM   #503 (permalink)
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Quote:
the accessability of the float is achieved by inspection ports I assume? How large are they?


Chris, They are hand sized holes, (I forget the diameter at the moment, 5 or 6 inches I think).

Quote:
If inspection was performed by removing the top panel either as a whole piece or in sections could the foam be applied to the inside of the float inside a heavy duty plastic liner and still allow for its removal? If the foam is the buoyancy do you need to worry about waterproof barriers?
An interesting suggestion. First question to mind then is structural integrity of that top deck for walking on. Crossbeams attach to the frames and the load path is vertical through those, so that's not a worry.

Second thing I have to consider on the top deck, is watertight integrity. Look how nicely they get a bath on take-off....



Quote:
If you are cunning about the cavities positioning you can have a dry compartment area below the inspection ports with access holes running where you want them. This way you could well still have 75% of the foam acting as guaranteed buoyancy and sufficient access for regular inspection.
In order to make up the missing 200 lbs of reserve, I need to guarantee about 3.1 Cubic feet of volume in each float in seawater, slightly more in fresh. I will look at this from this perspective now to see what options are presented.

Thanks Chris!
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Old 12 November 2008, 06:09 PM   #504 (permalink)
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an idea with piccies.



Bear in mind this is not to scale, it is an idea being visually expressed while looking over my shoulder for the boss ....
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Old 12 November 2008, 06:19 PM   #505 (permalink)
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3 cubic feet

Simultaneous posts apparently. Gday Joe

3 cubic feet in a float the size you are looking at is very little really, given the length of the float you could get the required amount with a tall vertical block glued roughly down the middle. The interference for inspection is going to be absolutely minimal. Could you fix the foam block on some risers or suspend the block altogether to clear the lower skin?

I would not do away with the watertight compartments at all, but this could be a solution. Perhaps a very light ply box to contain the foam in each chamber and pour the foam insitu, then just carry on building the float as if it wasnt there....

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Old 12 November 2008, 06:38 PM   #506 (permalink)
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suspended quickie

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Old 12 November 2008, 07:06 PM   #507 (permalink)
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Here are three alternatives and a few comments. There's probably more alternatives that would make you more comfortable with the operation of the floatplane, and it would be interesting to see them.

My sailboat is a trimaran, with large floats on either side. Each float has three compartments. The end ones have one or two 6" inspection ports each, and this is adequate to get an arm in with a sponge, or a pump in to pump it out. The marine hatches do leak somewhat at speed. But 6" hatches are acceptable for access; 8" would be easier.

The trimaran is made of a composite sandwich, glass on the outside and inside faces, and PVC foam core. There's enough of it that the boat can't sink. The structure is vastly different than your Sopwith's, and the point is that a new airplane can be designed not to sink. But perhaps the old designs ought to remain authentic.

Now for the alternatives....

1. If you must add foam, add it as low as possible. Perhaps glue it to the inside of the bottom surface, form-fitting it to the structure. That way it won't allow water under it, and will sink the least.

2. Another alternative to adding weighty foam would be to slightly increase the size of the floats, of course. It wouldn't take much of an increase for that, keeping the proportions and shape the same, and increasing all the lengths by the cube root of the increased volume.

3. In your home waters, you can go out with a small boat before a take-off and check out the conditions. And you can look over the water before landing. Both of these would minimise the hazard. This is what I'd do, I think. That and checking the floats for water as part of the preflight inspection. This is a third alternative, using operational procedures to reduce the hazard.
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Old 12 November 2008, 08:30 PM   #508 (permalink)
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David has a point

1. If you must add foam, add it as low as possible.

If the float is holed badly so that it has no integrity below the 'normal ' waterline, having the foam on the bottom means you will sink less before the foams' buoyancy kicks in. If it is suspended in the middle etc you have say another 6 inches to sink before it even begins to work. This adds difficulty to taxiing etc , so having the foam down low may well leave you with far fewer problems in an emergency.

I suppose that you to balance the need for routine inspection against the need for immediate effect in case a float is holed where/when you least need it. If its a routine inspection, 5 minutes of difficult fiddling is a small price to pay (to see inside) if it means the foam float offers more buoyancy at an instants notice.

And I thought the Albatros had some curly problems...

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Old 12 November 2008, 10:31 PM   #509 (permalink)
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I do this sort of design decision making at work. We look at the possible Failure Modes, the Effect and how Critical that is to the system. Ranking the critcality means you can then make design decision with some confidence that you know what is the most important consideration. An example would be:

Failure Mode: Float holed after collision with foreign object in water
Effect: Loss of boyancy of float (can quantify it here eg. '900lb')
Criticality: High (or give it a rank once all the other failures have been decided on).

As David says, you can treat the Criticality with operational procedures (doesn't always have to be a redesign). Then go back and compare your treatment with your mission profile and see if it still works. Then go and recheck the weight limitations you have (important to set a hard and fast not-to-exceed weight!). This might sound complex but it's essentially what you are doing but list it in a spreadhseet and record your design decisions. Helps keep track of all the ideas and ties the decisions together into a solution.

One thing to consider is how you will predict a Failure. Ie. will you notice a crack, delamination, vibration, etc before failure? If you do, then this goes in to your maintenance or pre-flight inspection checklist. If you don't get external warning, will an internal inspection be needed? If so, how and what tools/skills will you need? If you don't get much warning, maybe two sets of floats are needed. Swap out the suspect pair and take your time inspecting the old set. This means your aircraft is available for flying without the worry of sudden failures. It may mean your design can be more original and still be flown fairly often. Simplifying maintenance or having a sensible inspection process means more time flying!

I'd be happy to help out if I can.

Now - on to the fun stuff. Does anyone know if a Nieuport 17 was tested on floats? I've just moved to Pt Cook (home of Australian military aviation) and the original Pt Cook aerodrome (10min from my house) has a flying boat ramp! My brain is skipping ahead a bit here.....
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Old 13 November 2008, 02:19 AM   #510 (permalink)
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Criticality & Expected failure

Quote:
look at the possible Failure Modes, the Effect and how Critical that is to the system. Ranking the critcality means you can then make design decision with some confidence that you know what is the most important consideration

Failure Mode: Float holed after collision with foreign object in water
Effect: Loss of boyancy of float (can quantify it here eg. '900lb')
Criticality: High (or give it a rank once all the other failures have been decided on).
Bryan,

This has to be why I'm not seeing mention of additional flotation merntioned in the design texts. Even going back as far as my earliest text (1928), flotation material was available to them. Risk benefits having been examined, the watertight bulkheads have been the response.

Quote:
One thing to consider is how you will predict a Failure. Ie. will you notice a crack, delamination, vibration, etc before failure?
This is however, mentioned quite clearly in both of my texts. The issue of interior inspection is mentioned various times quite promenently. I have a high degree of confidence in the glue joints, holing via impact moves up the criticality ladder as a result of that confidence, so am fighting the impulse to over engineer, (a typical amateur response). I've read about this response on a number of occasions now!

Quote:
As David says, you can treat the Criticality with operational procedures (doesn't always have to be a redesign). Then go back and compare your treatment with your mission profile and see if it still works. Then go and recheck the weight limitations you have (important to set a hard and fast not-to-exceed weight!)
Precisely! I have already seen that "back taxi" and "dragging the landing zone" is a recommended operational procedure. I wonder what the actual mathematical reduction in probability of an incident is by implementing this simple procedure. I'll bet it's measureable!

Quote:
Now - on to the fun stuff. Does anyone know if a Nieuport 17 was tested on floats? I've just moved to Pt Cook (home of Australian military aviation) and the original Pt Cook aerodrome (10min from my house) has a flying boat ramp! My brain is skipping ahead a bit here.....
Now that is truly neat! There have been a number of WWI seaplanes that caught my eye, here is one of them, a Nieuport IV....



Done nicely, this would be another spectacular project, and in the absence of drawings, could still be replicated using contemporary design models, photos / drawings, and standard aeronautical practices.

Care to join me for a swim?......

Chris,

Fabulous little drawings, thank you for taking the time to do those! The discussion has been spectacularly helpful!!!!
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