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WHAT TO LOOK FOR IN AN AMPHIBIAN
For those of you who are trying to decide on what airplane to buy, you should first decide on your typical mission.  Here are a few statistics:
  • Most general aviation aircraft log less than 100 hours a year, with the average flight being one hour, including taxi time.

  • Most private pilots log about 6% of their time flying IFR with less than half of that, i.e., 3%, under actual instrument conditions.

  • Most flights are with two or fewer people, yet 85% of the pilots want a four-place aircraft.  About 5% would like more than four seats.

  • Chances are you use only two seats 85% of the time. That makes the other 15% of the time a real problem if you have only a two-seater.

Most statistics do not consider a five-place aircraft with three of those being for children. We estimate that half of the 5% who want six seats would be happy with five.

The Seawind has the widest cabin in its class. The forward seats have 52 inches of shoulder room (most people are narrower at their hips). That is 10 inches wider than the Lake Renegade.

The rear seats have 54 inches of shoulder room. The seats can be configured for three children or for two adults.

If future resale value is an important criteria, then we suggest that you consider only a four-place aircraft. If comfort is a big consideration, then the Seawind will come out on top.

How does your mission compare?

  • What speed do you prefer?

  • Do you want a high-performance, retractable-gear aircraft, or a less challenging, two-place, fixed-gear aircraft?

Obviously, we want to look at how the Seawind stacks up.  Let's go item by item.

  • For a one-hour flight, you have a radius of 180 miles. That's a lot of territory (101,780 square miles to be exact) using only 19% of the fuel in the mains.  So why even have the long-range fuel tanks?  But then, why not?
  • For three or fewer hours a year of actual IFR, why spend the money for all those expensive instruments?  That extra $8,000 to $16,000 can pay for a lot of hotel rooms.
But, if you just want to have them or must be equipped to fly IFR, then you will be pleased with the panel space available on the Seawind.  You will also be pleased that the Seawind is such a stable instrument platform.

You can comfortably set up a 90-knot approach and set your rate of descent with about 14 to 16 inches of manifold pressure.
  • SPEED

That is either the first or second question asked.  Let's take a look again at your mission.  The Seawind will cruise at 75% of power at 190 MPH, or 165 knots. However, most pilots fly at a lower power setting between 55% and 65%, seldom using the power and speed available.

We get a few inquiries about turbo-charged and turbine engines.  Of course, if you are frequently crossing high mountains, then there is a real advantage to these engines.  We will be developing a turbo-charged or turbo-diesel installation when we have sufficient customers lined up.  In the case of the diesel we are waiting for a certified 300 to 330 h.p.

As for a turbine installation, we will not be exploring that option until there is a 300 to 350 hp turbine engine available.  As we have said many times, a high thrust line amphibian must have the power plant in harmony with the pitch control of the horizontal tail. The Seawind is designed for 300 hp +/- 10%.

Again, let's look at your mission.  Even if your average flight is 360 miles (320 n.m.), that is two hours in a standard Seawind, and you will burn about 34 gallons of fuel.  A turbine doesn't really begin to get efficient until you start to breath oxygen at 16,000 feet.  Deducting the extra climb and descent time from the time saved by the 20% increase in speed, the same trip will take 1:45 and burn 53 gallons of fuel.

That high-priced engine saved 15 minutes in time.

Another significant reason not to use the Allison turbine is the down exhaust, which is overheating the tail and causing structural damage.  A top exhaust discharge would be better.

  • Now you must decide if you want the ability to land only on land, or on both land and water.  If you want a fast land plane only, you have a choice of a Seawind, Mooney, Cirrus, Cessna 210, or a number of fast home-built aircraft.

If water flying is in your future, you have to make a choice between straight or amphibious floats or a flying boat such as the Seawind or Lake.

There is a big difference between a float plane and a flying boat.  Float planes sit very high and are easier to dock.  They are also better for crosswind water landings.

That is where the advantage ends.  Flying boats are much more stable on water and can be step-taxied crosswind or downwind.  Besides being susceptible to capsizing, float planes are much slower and carry empty seats.  The additional weight of the floats usually equals that of two passengers.

If you do not want a purely utilitarian, cramped, slow aircraft, then you have only one choice.  Guess which?

WHAT NOT TO LOOK FOR IN A SEAPLANE
Just as important in your evaluation is what not to look for.

Is salt water in your future?  If the answer is yes, your options become very narrow.

Salt water and aluminum are not compatible.  Even infrequent splashes in salt or brackish water will lead to major corrosion repair in a few years on an aluminum airplane.  A fresh water rinse will slow the process, but it will not remove the salt at every rivet or those nooks and crannies.

Now, you should rule out everything but fiberglass.

NOT ALL FIBERGLASS IS CREATED EQUAL
There is a reason that sailboats and yachts use polyester resin, and it's not just because it's a little less expensive.  Epoxy resins take on considerable moisture (in the range of 4% to 6%).  That moisture can cause blistering or, when frozen, can cause delaminating and cracking.  If that isn't enough, when the moisture is heated by solar radiation, it severely reduces the allowable strength of the structure.  It is called the hot, wet condition, and it comes from solar heating or exhaust from turbines over a wide area.  Epoxy is not as fuel-compatible, and requires special coatings or fuel tank liners.  Epoxy is also known for causing contact skin rashes.  Once susceptible, a person can never work with epoxy again.

Vinyl ester resin is a hybrid resin with nearly the strength of epoxy, but without the disadvantages.  It takes on virtually no moisture (less than 2%).  It is compatible with all the fuels and requires no special treatment for the fuel tanks.  There have been no recorded health problems in either the aviation or the much, larger boating industry.

So, the main structural item remaining is the fiber.

KEVLAR is a high-priced, hard-to-work-with fabric that is poor in compression.  It is not recommended for amphibians unless you are concerned about bullets being shot at your plane.

CARBON FIBER is a high-priced, lightweight fabric.  It has a very limited market and limited weaves.  As a result, the weaves commonly used in aircraft are very coarse compared to those weaves available in E-glass.  So, to acquire a smooth surface, much more filler is required for carbon fiber.  That reduces the weight advantage.

THERE ARE MANY MORE DISADVANTAGES

  • Carbon fiber is not as compatible with vinyl ester resin.  It should be used with epoxy resin, which is not compatible with moisture, i.e., boating.
  • Carbon fiber requires sophisticated electronic inspection because defects are not visible due to the color.
  • Every bolt hole requires an isolated patch of E-glass to reduce catalytic corrosion between the carbon fiber and the bolts.  The presence of moisture and salt make this even more serious.
  • Overly stressed carbon fiber will splinter, emitting many little spears that have been known to cause injuries.
  • Carbon fiber, when hit by lightning, will sustain much more damage than E-glass.
  • Finally, you cannot build in an antenna beneath carbon fiber as you can with E-glass.  So, that beautiful bird just became a porcupine with antennas as quills.


E-GLASS OR S-GLASS
S-glass is about 15% stronger and stiffer than E-glass and costs almost twice the price.  Like carbon, since its use is limited, there are few weaves available.

E-glass fabric is most commonly used in the industry, and the most cost-effective.  For flying boats, it is the best for a water environment.

To a great extent, the resin and fiber criteria apply to all aircraft, not just amphibians, even though the moisture condition is greatly reduced with land planes.

SPECIFICALLY FOR SEAPLANES
All aircraft require attention to maintenance.  All boats require attention to maintenance.  With flying boats, you guessed it.  In this case it is the worst of all worlds, especially if you enjoy the salt water environment.

WHAT DO YOU LOOK FOR?

  • Make sure that stainless steel hardware is available.
  • Are all aluminum parts anodized?
  • Are all the bolt holes anodized?
  • Are all the cables stainless steel?
  • Are all the nav. and landing lights protected behind plexiglass?
  • Are the exhaust pipes stainless steel?
  • Are the wheels and brakes designed for salt water use? Some amphibs carry 8 to 10 pounds of grease to protect wheel bearings, and they only last 100 hours. The Seawind special design system has logged 740 hours between bearing replacement.

 


This article was originally written for experimental aircraft.

CARBON/GRAPHITE VS. FIBERGLASS
We occasionally receive inquiries from potential customers about having their Seawind parts fabricated in carbon fiber/graphite due to the emphasis placed by the aerospace, military and high-performance manufacturers.  A published article by Martin Hollmann, comparing wet lay-up to prepregs, has brought a few more calls.  Although Martin's article has placed some emphasis on his use of graphite prepregs and his comparative refers to non-vacuum bagged, wet lay-up of fiberglass, the carbon/graphite issue is most regularly addressed by our callers. The Seawind, as with every other aircraft, is the result of compromises that the designers and engineers toiled over to attain their ultimate creation.  The Seawind team correctly chose to apply a very strong, but economical approach to material selection.  The materials and the fabricating processes now used for the Seawind are considered "advanced composites".

Surface finishes are applied to reinforcing fibers to allow handling with minimum damage and to promote the fiber to matrix (resin) interfacial bond strength, water resistance and optical clarity. Since graphite is almost exclusively used for aerospace and military markets, where expensive epoxies are utilized, the manufacturer's finishes have been optimized for epoxy.  This is the reason that vinyl ester resin is not normally recommended for use with carbon fabrics.  Exceptions would have to be tested and close attention to the manufacturer's Certification should be specific regarding the applied finish.

It is very difficult to properly wet out graphite woven cloth, because there is little change in appearance when resin is introduced. Since carbon is opaque even when completely wetted out, visual inspection for air inclusions is impossible.  This makes inspection either very difficult or expensive (ultra-sonic equipment) and reject rates are unquestionably high.  The danger is in what you can't see.  For that reason (and others related to aerospace requirements), the most common fabrication process for carbon parts is elevated temperature curing, performed with expensive epoxy prepregs.

To fabricate a graphite part, epoxy resin impregnated, graphite fabric reinforcements, core, peel-ply, breather ply (perforated sheet for resin control), and bleeder cloth (for excess resin and a vacuum path) are placed into or on a prepared mold, covered and sealed with a thin impervious sheet of plastic material, drawn down with vacuum, placed into an oven, and cured at high temperature (typically 250°-270°F) for several hours under precise controls.  A standard for many years in the aerospace industry, this process presents many negative issues relating to cost, handling and quality control, making it practical only for the military, the aerospace industry, and a few other specialized and high priced products (sporting goods, race cars, etc.).

After it is manufactured, shipping and storage of the prepregs in a frozen-state also requires a high degree of quality control.  The material has a limited storage life but, most importantly, a short out-life.  This means that after bringing the material up to room temperature in sealed storage bags (to avoid moisture, one of prepregs' major problems), the clock starts ticking. 

Carbon fiber has the highest specific stiffness of any commercially available fiber and very high strength in both tension and compression.  It's impact strength, however, is lower than glass with particularly brittle characteristics being exhibited by high modulus fibers.  The graphite laminate tends to shatter, with very sharp, stiff needles and shards around damaged edges.  The racing industry must provide crash "cages" of Kevlar to protect the drivers from dangerous pieces.

Like metals, graphite is opaque to radio signals.  Antennas cannot be installed within the carbon skins, so they must be attached outside, interrupting the smooth, flowing, composite surface and, of course, causing drag.  Fuselage and wing skins of carbon are normally electrically-grounded to each other with jumper wires, as are the control surfaces to the wing, so that the hinge bearings are not damaged if forced into service as electrical conductors.

Since carbon can be greatly affected by corrosion due to galvanic reaction, special care and time must be taken to insulate dissimilar metals, e.g., aluminum, steel, brass, etc., from the carbon.  This would involve placing a sacrificial piece of fiberglass between the graphite laminate and all metal hinges, brackets, tracks, etc., and dipping rivets, bolts screws, and bushings in primer resin before installation.

Surface finish of a prepreg is extremely porous. Epoxy resin has an affinity for moisture, as does the freezing and thawing process, and any moisture lay-up will produce water vapor (steam) under vacuum and elevated temperature, which is evident in the finished part as porosity, a rejection factor.  The solvents used in the manufacturing (prepregging) process can also produce voids during curing.  The predetermined resin quality is sufficient to wet-out the fibers but not to fill in the coarser graphite fabric weave patterns.  That process is left for the builder to do — squeegee filler into the porous surface and sand.  Then repeat the process for any remaining pinholes.  Some of the weight-savings is certainly lost with the addition of fillers.

Expensive honeycomb core materials and film adhesives, used to bond the core to the face sheets, require additional labor and associated expense.  Any assembly of carbon prepreg parts must be accomplished with more expensive structural adhesives, compatible with the graphite/epoxy components.  If the ribs, bulkheads, webs, etc. are attached or reinforced with a wet lay-up process, graphite fabric and epoxy must be used and, again, a good visual inspection will be impossible.  Be careful — epoxies are toxic and could cause serious and lasting reactions.  Dry graphite fabric must be handled with more care than fiberglass. Fibers can break and loose particles can be inhaled. Also, cured carbon splinters will not work their way out of the skin as would glass or wood.

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