Originally Posted by Jeremy_H
Your wife's cam should have a setting to reduce the quality/file size.
Ok, thoughts...Quick ground rules. This is a forum, and the written word carries risk when the delivery is not heard, please understand that what follows from me throughout your build is me enjoying being part of the discussion of your process, not anything negative or intended as rebuke.
There's a lot of dialogue about the right shape for the front of sponsons. Some say curved, some say straight angles. To me it's about what's doing what, so where it's wet under full power it needs to be flat, what's in front of that dictates how it reacts to differing depths. A straight path increases in lift proportionally as more surface area enters water, as does the drag. a curved surface's lift increases exponentially, so does the drag. All of that stuff applied to boats having to penetrate water by design, hydroplanes only do this to get going, so to me flat angled sponsons are easier to make, but any suggested advantage of one over the other is academic because if that area is in the water enough to care about such efficiencies you've got a bigger problem that having the right shape to deal with it! So in essence you've done what I do, curved entries followed by a lift plane which is flat in the wetted area, in my case because I think it looks better and is stronger.
A tapered tub I'm troubled by. This means a lot of the hull pressure will be exiting the sides of the tub, this will be fine if there's enough thrust to simply overcome the loss and the CoB allows it, but I'd need to know your CoB before harping too much on that. Whatever, I'd be looking at parallel personally.
I've noted on a lot of airboat riggers that there's a little too much adherence to established water prop designs in some areas. This works, but two things come to mind which I'm considering for my own rigger project (this is a gift engine I've been given, a small Pylon racing engine, so not in the league of yours). The sponson supports are the usual two parallel shafts, and I think these need to be as high as possible as keeping them clear seems to be something of a challenge even on water propped boats, in my case I'm thinking of arches: [ATTACH=CONFIG]1985766[/ATTACH]. The other thing I've not got to yet is prop protection, One of the quiet benefits of Chris Selph's design is the massive deck which keeps spray off the tub and sponson away from the prop. From my experiences with the little red hydro limited protection means intolerant to rippled water. So I'm coming at this aspect again and methinks those arches are going to grow a bit if I want to be able to run it in other than millpond conditions.
Thanks Jeremy, appreciate the input. I do respect another's opinion and am not offended in the least, I don't think any of us in this forum wish's to see another fail. I know what your saying about the written word but, when is it enough, that's what questions are for I guess.
As for the sponson design I'm only following my previous experience and the latest developments that are made public. Previously I had built a hydro 4' and I noted it took til about half throttle to get up on plane due to the water adhesion and my best guess is it may have been attributed to the curved ride pads. Please observe the enclosed pic of the sponson with the straight edges aligning the bottom in the following posting, as I mentioned the bottom is essentially two angles and I have just removed enough material to appear curved so the impact on transitioning from one plane to the other should be minimal, I hope. Also I have drawn a horizontal line on the sponson template to indicate the bottom of the hull so I will have 1 1/8th" clearance under the hull and the boom tubes are an additional 1 1/8th above that bringing the total tube to water clearance to 2 1/4" above the water line.
The tub itself I mulled over for quite some time and here is the reasoning behind that madness. I recall when holding an airplane by the midsection at full throttle the prop has a definite control of the direction in which it is directed (can't explain it any better than that) and as you move the tail up and down it follows the direction of the pull of the prop so in my thinking the only lift I want is controlled lift thus the standard I guess front end and to taper the aft part of the hull to expel the lift rather than holding it. To my understanding of the dynamics of the whole thing a high percentage of blow overs are caused by uncontrolled air pressure lift. Another point to this is the Japanese air boat basically has no lift surfaces at all except for a rear stabilizer and is one of the worlds fastest to the best of my knowledge.
I have given the thought of spray a little consideration and if the boat runs as expected there shouldn't be any issue with the sponson's set out at about 24"s so if that becomes an issue when this beasty goes for a run I'll have to address it at that time. I have come up with a tentative design for an air inlet scoop because of your similar issue, whether it'll work or not?
Is the above drawing a rendering of what you propose to build? pretty sharp looking, I like the arched sponson connection. The water I'll be running is a major river with lots of current so that is how I came to the clearance between the tub and water surface.