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It has been nearly two years since my last entry. Two things happened to slow the project. A partially reassembled Coot Amphibian N29DW came up for sale. This aircraft had been flipped, causing the main and aux spars to be cracked. The spars have been replaced but the ribs and skins were not reassembled on the airplane. The price was acceptable and my A&I mechanic agreed to open up some space in his shop for us to work on it together. So N29DW was crated in a container truck and shipped from Minnesota to Virginia.
I started by laying out an ordinate table for the GA35A415 Long Coot (LC) wing at 75 inches long. This information gave me a maximum wing thicness of 11.244" at station 26.25", or 35% of wing chord length. Subtracting 1/8 for each wing skin gives me a maximum main spar height of 10.994 inches. This is the outside dimension the spar is to be made.
So the garage is built, but still needs some items... The camper is on hold for now... I am proceeding to start construction on the wings. This is where Molt Taylor suggested starting the Coot, and since the Long Coot is going to need a new wing anyway, this is a great place to start. The wngs take up less space than the hull or the camper, and I can work on them as I finish other things necessary around the shop.
The Coot wing chord is 5 feet and the Long Coot chord will be 25% longer, 6.25 feet long. Using the basic idea of increasing the length by 25% and increasing the weight by 50%, puts design gross weight at 2800 and the overall length at 28 feet. Using a designed empty weight of 1800 leaves 1000 pounds of usefull load. Rounding weight up to 3000, gives a useful load of 1200 pounds. So 3000 is the desiged gross weight. The standard load test of 3.8Gs would give a test load of 11,400 pounds, and load testing a the utility category of 4.5Gs puts the test load on the completed wing assembly at 13,500 lbs. At this rating the wing will be overbuilt by 18.4%. A nice overbuild for safety.
I have taken a stab at modeling in clay and wood sculpture because a 3d object is very descriptive to the mind. I want to build a 2 stage, nested, progressive Vee hull as the basis of the Long Coot Amphibian's high speed water handling characteristics. I have some 2D sketches of the step that appear to channel the outward flow of water properly to create lift and separation thus reducing the cantact footprint of the hull to about 25-33% of total hull volume and reducing power required as the boat accelerates to flying speed. The nested hull has proven difficult for me to duplicate in clay or wood carving (likely due to my lack of skill as a sculptor) so as to create a decent hull form capable of extrapolating templates. This led me to look for alternative methods of modeling.
The letter below is a result of discussions and research on the Riblett wing as applied to the Coot amphibian. I am trying to select a modern airfoil for use on the long coot. I now see that I overlooked that the GA30-615 was used and have therefore looked seriously at the GA37A615 instead of the GA37-315. I will consider scaling the 615 down to 614, but I think this is the airfoil I want for the Long Coot. There are drag and moment reductions compared to the NACA 4415 used on the Coot and drag reductions compared to the GA30-615, with about the same lift available.
Dear Mr. Riblett
I have been reading your book GA Airfoils and was wondering if you could help me to better understand the airfoils and apply them to my application. I am writing you because I feel like you can see the air flow on the wings, just like Dale Earnhart was able to see the air flowing around a race car. That type of insight is rare and I like to consult with the best.
I had a discussion recently with Coot enthusiast about hull bottom design for the Coot Amphibian. I had suggested going to a progressive V hull like we talked about and using strakes to increase the lift. He warned be to be careful with strakes because they can be dangerous when landing in a crosswind. If the airplane is moving sideways when it touches the water, the outside edges of the strakes can dig in causing the airplane to yaw and roll violently perhaps resulting in an accident. He offered specific examples of this and suggested that I reconsider.
So I spent some time drawing bottom profiles at the step and hit on the idea of one-sided strakes. I have later come to realize that the progression of the hull would form a type of nested V design that could allow the aircraft to slide sideways somewhat during a crosswind landing before settling out and tracking straight. There is a sketch of this idea attached to this email.
Do you think the general idea is sound and that my proportions are about correct?
The upper drawing shows the inside intersection at 8" left and 8" right and the outer intersection at 9" left and 9" right.
The garage construction was completed in March. We got busy at work and I started working on the garage again off & on in September. I have buit a workbench and purchased a new table saw. I have insulated and sealed the ceiling and am now working on the walls. I want to keep the humidity at 50%. I just got a used Shopsmith Mark5. I am considering inviting my neighbors to help as a community boatbuilding project. Maybe I'll get lucky and find one or two people who can help me occaisionally.
Saturday, October 16, 2010
Since the last log entry I have done a LOT of research into Aircraft Diesel engines that are or will soon be on the market. The main move to the diesel was prompted by my observation at Kentmorr marina and Kent Narrows marina that diesel fuel was available at both, but 87 octane pump gas was the only gasoline available. Also, at Bay Bridge Airport Jet A was selling for $3.30 per gallon while 100LL was $4.55, and highway diesel in our area is $2.90-3.30 depending on where you buy. Unlike gasoline aviation engines, which cannot tolerate lower octane fuel easily, diesel engines designed & rated for Jet A can tolerate #2 diesel fuel with only slight modifications to the fuel supply system. In fact running these engines on #2 diesel will provide slightly better power and fuel economy. When you consider that diesel fuel or jet A are available nearly everywhere, it makes sense to go with diesel.
Friday, September 03, 2010
Sunday, August 01, 2010