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Dolphin stitch & glue plywood flying boat project

Posted By:
William Hodges
Young Eagles Pilot or Volunteer
#1 Posted: 6/20/2010 09:56:35

Hello everyone. 

For several years now I have been tinkering on the drawing board for a new seaplane.  I have recently made some design decisions that are solidifying the project and I am looking for people near and far who might be interested in a project like this.  So here goes. 

I am looking to scratch-build a stitch-and-glue plywood, wood & fiberglass 2+2 flying boat that will duplicate the performance parameters of our 1968 Cherokee 140.  I think of this airplane as an elongated version of a Coot Amphibian or Osprey2 Amphibian with 2+2 seating, folding wings, a 500NM range, and that is trailerable, so we could tow it behind our truck-camper or RV. 

My wife and I, our luggage, and our dog routinely fly 400 NM from EZF to HXD for visits with family.  We are right at 2150 lbs gross in our Cherokee with 40 gal of fuel and make the trip in 3.8 hours with 1 hour reserve.  We have the ability to take two couples, no luggage and a light load of fuel up for a joy ride, and our airplane cruises at 110 Kts at 6500 ft while burning 8.0 GPH, and 100 kts at about 7.5 GPH. 

I want low speed maneuvering so that we can use the airplane to spot dolphins from the air, land and maneuver around with them quietly.  This boat will be equipped with an inboard 1.5 HP electric propulsion system with a folding prop and a Kitchen Rudder control system.  The Kitchen Rudder allows a single screw vessel to maneuver like a twin screw vessel, with a single lever control and a constant throttle setting.  It is an old system and it works.  The folding prop will reduce drag on the prop for flight and high speed water operations. See  http://www.oldmarineengine.com/discus/messages/1/95580.html 

 The aircraft/vessel will have a 2.5 HP 12V DC Auxiliary Power Unit  driving a charging alternator.  It will likely be rope start, and mounted below the main engine so it can act as a pre-heater in the winter time as well as battery a charger to provide power for the battery and electric propulsion drive system.  Should the main engine quit over the water, after landing on the water, the APU can provide power to the electric propulsion system as long as the fuel supply lasts, allowing the vessel to navigate to the nearest port.  The APU can also be started without the battery, and can recharge the battery should it go dead while camping in the wilderness. 

I expect the aircraft to have a gross weight of 2400 lbs, fly at 100 kts at 6500 feet and burn 8.5 GPH.  It must hold 44 gallons of fuel in the wings, and have a 5 gallon automatic reserve tank in the main hull. The battery should provide enough reserve power to drive the electric motor at 1/2 throttle for 15 min, and start the engine after that.  It should have a useful load as equipped of 800 pounds. 

I have been looking at the stitch-&-glue plywood method of building boats, and I think this method is the way to go for the hull portion of this boat.  It is reasonably fast, it is reasonably priced, it is flexible to different designs, and Devlin's book shows you how to apply this method to building any type of boat. 

So I am asking any of you who may be interested in a project like this to contact me.  I am hoping this will be the ultimate fun airplane for me and my wife, and maybe for some of you as well.  Thank you for taking the time to read about this project. 

William “Pete” Hodges
The Quixote Airman
Spotsylvania VA 22553


Greg Young
Warbirds of America MemberHomebuilder or Craftsman
#2 Posted: 6/28/2010 17:06:07

Have you done any preliminary design work yet? The design goals seem awfully ambitious. Try assembling specs on all the single engine amphibs you can and scale them up or down to your needs. Then estimate if you can do it any better. The Skimmer/Teal/Lake family would be an interesting comparison. I'd also suggest getting a copy of X-Plane. It's got all the aerodynamic calculations built-in so it's a really good way to model a design. I'm using it on a Corsair replica project.

Greg Young

Richard Warner
Homebuilder or CraftsmanAirVenture Volunteer
#3 Posted: 6/28/2010 19:49:57

Hey Pete,

    I had built an Anderson Kingfisher back in the 80's and sold the plans for several years to it.  It was a fairly good performer(better than my 180 h.p. Lake),, but I often wonder if using "Stitch & Glue" would make it possible to build it light enough that it would qualify as an LSA.   I have built 3 Stitch & Glue boats and the construction is easier than conventional and lighter, but more expensive than conventional.  If it could be built 180 to 200 lbs. lighter, it could be LSA legal.  I know you are not talking LSA, but the type of construction should work for both of out "wants".  I'm still just in the thinking stage on mine.

Richard Warner, EAA 22313 Lifetime

Covington, LA

William Hodges
Young Eagles Pilot or Volunteer
#4 Posted: 7/9/2010 17:49:23

I have been reading the COOT plans and "Devlin's Boat Building..."  I am not sure if stitch and glue is the right way on this or not, but I have made signifigant progress towards the layout of the aircraft.  If I follow the plans on the COOT bulkheads, but space them 15% farther apart and add one station in front of the step, the hull lengthens nicely to provide enough room for the 2+2 seating arrangement, and the majority of length is added right where the majority of weight is concentrated, where the hull is widest in the water.  I have discussed this with Richard Steeves somewhat.  This makes the overall length about 28 ft, (instead of 22.5) and 12 ft to the step (instead of 9).  It will be 25% longer. 

Devlin's book sugests building a 1/16 floatable scale model (3/4 inch = 1 foot).  At this scale 1 penny has a scale weight of 25 pounds, and the hull hydrodynamically behaves like the full sized hull at 1/4 speed.  So the model can be weighted and tow tested from a powerboat on a lake.  5 kts acts like 20 kts, 10 kts acts like 40 kts, 15 kts acts like 60 kts and so forth.  100 pennies has a scale weight of about 2500 pounds, and they can be placed to simulate the actual weight of the aircraft components and loads.   This is the plan I am taking. 

Camper first:  I spent the day cutting the old windows out of my truck camper.  Next I'll cut up the hulk and send it to the dump, then lay out the camper on the custom truck bed.  The camper is going to be my learning tool for the processes I'll use on the Long-Coot.  Pete

Dan Malone
Homebuilder or Craftsman
#5 Posted: 7/9/2010 20:40:51


Have you ever looked at the construction technic used by Muk Tuk Floats? http://www.ultralightfloats.com/index.htm

They use a slot and tab arrangement to align and clamp the parts.  Might work for your project.

I am currently building a composite Seastorm amphibian but was looking for a wood 4 place amphibian.  I own a wood working company that has some cnc routers.  If you are interested on having parts cut on a cnc, maybe we can work a barter deal.


Dan M