Miss Galveston - Land, Water or In the Air

[larry cottrill]

Here's my latest idea -- fly as a U-control stunt plane from land, water, snow or ice OR remove the wings and "fly" as a two-pointer hydro.

All right, guys, don't try to talk me out of it -- I've already ordered the float set at considerable personal expense ;-) The only thing that will basically change the plan is if Pyro Joe suddenly conquers the challenge of carbureted liquid fuel. Then, everything becomes simpler. The floats are from an outfit called Classic Aero, and can be seen here (the 28-inch ones, second from the top):
http://www.classicaero.com/floats/

Everything else I have as scrap wood lying around, except for sheeting to cover the exterior of everything (including the wings). Those (the wings) will be cannibalized from an unfinished R/C stunt plane kit a friend of mine gave me. Wish me luck. I don't have the time to do anything like this, of course. Ha.

By downloading the PDF, you'll get to see the basic layout dimensions (approximate, for now) and the interior structure and fuel setup. Basically, the engine and its heat shield mount to a sliding rail. The engine thrust pushes the rail forward against the miniature valve toggle, holding the valve open as long as thrust exceeds about .75 kgF -- if thrust falls below that for any reason, the spring in the valve forces the toggle back and cuts off fuel. The entire thrust force is applied to the toggle through a replaceable wood dowel "shear pin" -- in a crash, the G load of the engine sliding forward snaps the shear pin, so the toggle snaps back and cuts off fuel flow.

Due to the cylinder orientation and "centrifugal force", Propane leaves the cylinder as liquid and expands in the evaporator tube, thus putting a lot of the expansion cooling outside the cylinder for longer duration of adequate pressure. Delivery pressure to the engine is stabilized via the miniature regulator. A "third hand" device (not yet designed) is needed to hold the engine forward during starting, until enough thrust is achieved to hold the toggle valve open. Simplicity itself.

L Cottrill

[metiz]

Haha oh man, yet one more step further into the ridiculous - I love it!

[larry cottrill]

... ridiculous - I love it!

Man, I know that feeling!

L Cottrill

[larry cottrill]

Having purchased the float kit, I was able to make actual measurements of the parts, which allowed me to revise the drawings to a more accurate depiction and even create the beginnings of full-size plans. The main revision is that the real floats are much deeper and more "fish bellied" (and a lot wider, too) than my earlier estimate, which was from photos only. There should be plenty of flotation here, even for a fairly heavy model. I also figured out the ducting for ventilating the float step, and most of the design for the wing attachment scheme (not visible here).

Here's the revised external view plan. I'll try to get some photos as I build the floats and make my mods. Things should get more interesting at that stage.

L Cottrill

[larry cottrill]

Here's almost the whole basic parts set for ONE float (the whole kit has parts for both floats). All of this is sheet balsa, the first laser cut balsa I've ever seen.

The top row is the series of what would usually be called 'formers', from front to rear as seen left-to-right. The next row is the four pieces that form one side. The third row is the float top, and the fourth row the other side (the two sides are identical, and each float is perfectly symmetrical as supplied). The next row is the bottom of the float's basic box structure (mostly lightening holes!). This is significantly wider at every point than the top sheet. The next row is a set of little triangular pieces that go across the bottom of the box, i.e. essentially 'formers' for the inverted roof-like bottom of the finished float (there are more of these for one float than I show here). At bottom left are two rows of bottom sheets -- the actual sheets that will plane on the water (each two pieces -- the smaller nose piece is cross-grain to the larger section). At bottom right is the sheet of laser cut keels (in this case, one sheet of laser cut parts for BOTH floats in the kit) -- I left these in place in the sheet to lessen the chance of breakage.

Note that on the longest side piece in the middle row, you can see a little 'soot' smudge above the right-most lightening hole. The laser cut edges are all a rich brown color from the cut. Very interesting. Extremely precise forming, of course. These floats supposedly build up to 3 OUNCES each (before any covering or mounting hardware is applied), even though they are 28 inches long. My mods will increase weight significantly, of course. Six ounces for 70 bucks US -- but it's beautiful stuff, I have to admit.

L Cottrill

[larry cottrill]

Stage 1 Buildup of Floats

The basic structure of the floats is built up without the bottom sheet, and with central formers absent where the plywood platform for landing gear and wing mounts will be fitted, from the bottom side. At this stage, only minor mods have been done: The nose is extended about 1 cm to give a slightly longer, leaner appearance. The top deck is built as nearly perfectly flat as possible, instead of curving down slightly toward the nose and tail. The center section of the top deck sheet has been cut away to make room for the wing mount structure. At the rear, a pair of carefully cut sheet balsa gussets have been glued to the interior faces of the side walls; these are basically not for strength, but rather as guides for exact positioning of the fin spar mount structure.

So far, so good. Some real modification work comes next: forming and fitting the fin spar mounts and the interior plywood pieces and torsion bar assemblies for the main landing gear. All these will have edges carefully carved to fit the tapered and/or slightly curved side sheets.

L Cottrill

[larry cottrill]

I wanted to provide a ventilated step on the floats, to minimize suction in moving forward through the water. Though this preliminary form of the detail drawing doesn't have any text notations, you should be able to figure out what's what. On the drawing, yellow is balsa, orange is plywood or hardwood, grey is metal. Bright blue indicates epoxy -- either filling gaps or coating wood surfaces. The torsion bar bearing for the main landing gear shows up here, also -- it's half of a standard steel 2.5-inch butt hinge with a 3/16-inch brake line bearing glued in to support the 1/8-inch music wire torsion bar / trailing arm.

The air is tunneled rearward through a main plenum of 3/4-inch OD metal tubing (slightly flattened at the rear), then turned downward by a carved elbow block and immediately split between two 1/2-inch OD tubing stacks that slant down toward the step. These tubes are heavily flattened before they emerge through both sides of the step. The photo shows the modified balsa step formers with slanted oval holes where the tail end of the flattened stacks go through. The formers are also shortened at the top, for the plywood platform to pass over. Front of former at left, rear surface at right. Note the upward and inward slant of the holes (as seen from the rear surface). For the oval holes to work, I had to inset small "bridges" of scrap balsa across the bottom edges of the step formers; these can barely be made out in the photo. These were needed because of the vertical grain direction in the balsa formers.

L Cottrill

[Chadly33]

Looking good Larry! Cant wait to see it finished, theres something about pulse jets on water that really intrigues me. I watched a vid. on youtube that had a RC hydrofoil with a valved pulse jet on it, they lost control of it just after launching it but man it was moving! they probably had the thrust point to far back or to far forward, I know from building RC airboats that this is very critical when running on water. In fact I still have my airboat sitting in the garage, it has a 33cc brush cutter motor, ported, polished, tuned exhaust and runs on 2 stroke avgas!!

[larry cottrill]

Some of the formers -- new plywood ones ( 1/4-inch plywood ) and balsa formers modified from the kit parts. The drilled holes in the plywood parts are for the control system (left float only). Most of the wing root plate is also shown -- the two big holes are where the tubular steel "spars" go through, and the long slot is for the control system fork which will protrude from the root of the removable left wing.

L Cottrill

[Irvine.J]

Update please larry ?

[larry cottrill]

Progress is slow. I got some of the plywood pieces cut -- when they're ALL cut and smoothed up, I'll get another photo to post before I glue them all in. Of course, I still have to do the hardest part: Bending the music wire landing gear struts / torsion bars.

L Cottrill

[Irvine.J]

Is it just me or does music wire blunt everything you try to cut it with.

[Al Belli]

Hi Irvine.J,

Music wire is high carbon steel which is pre - hardened during the drawing process, and is about as hard as any tool steel tool that You might use to try to cut it.
The best method for cutting it is to use an abrasive cutoff wheel or the corner of a grinding wheel.

Al Belli

[larry cottrill]

Our (model plane wackos) favorite tool for this is the little Dremel abrasive wheel that's about as thick as two or three business cards. Quick and easy. Wear your goggles, as with any grinding task!

Actually, it isn't quite tool steel hard, but it has to be hard so you can get music out of it. ;-) You can bend it to a sharp angle in a bench vise, but you have to take it slow -- get in a hurry and it will SUDDENLY fracture at the tightest part of the bend, usually in a "green stick" fashion, interestingly.

For landing gear strut material (ESPECIALLY if you're forming torsion bars), music wire has no peer. I only wish it were rustproof. Stainless wire is too soft to use, unless you want to keep re-bending it back to shape after hard landings (I'm talking about the normally available alloys, of course -- there might be some SS you could get that would work fine, for all I know).

If you look at the latest full-size patterns I posted (in reply to Ozzie James), you'll see 'ghost' images of the main torsion bar assembly: A steel butt hinge (half) with a soft steel sleeve epoxied in (brake line), and then the 1/8-inch diam music wire running through that. The bent-over end is HEAVILY anchored with epoxy; the other end goes straight over thru the outside wall of the float, where it bends down at an angle to form the landing gear strut. Simplicity itself, but a bear to make; especially if you need two that are (very close to) exact mirror images of one another.

L Cottrill

[larry cottrill]

Rats -- double posted it! See next post ...