Jeremy_H

Some more video to contemplate

Here's some footage from last evening, choppy on the left side, but with the curved fin I was able to start introducing snippets of straight run sections, squaring off the circle I've been doing. Dodgy in that chop on the left though. I need to wait for calm conditions to take the next step with fins.

http://youtu.be/PTFkx-pUk7E
In this short slowed clip the guy with the vidphone was sent down the side to capture the effect I was seeing if I hit the chop too hard. If it had no fin it would lose it normally:

http://youtu.be/ywhNBz8i2Xw

arcdude

That is interesting it seems to be just landing on the far side of the wakes in the water causing it to buck up and down. That is what I'll be facing running on a major river, glad to hear the curved fin assists in keeping it from lift off, I may be doing the same.

Jeremy_H

Whilst the fin seems to stop it from stepping out, I'm wondering if it's turned that into a bunny hop through the slight pull down angle I have on it. I don't think there's any merit in pursuing it specifically though, the turns on the right are clear evidence that the fin is gripping hard on flatter water, so it's that degree of surface ripple here that matters I think, the stuff that a boat creates on a flat lake is just enough to release the boat a bit. On the first run I was caught out by it biting too much resulting in it turning closer in than thought, hence the right/left jink that resulted in the roll . By the last few laps the water was a bit better and straight sections were achieved on each side of the course, pretty much the last lap shown on the vid. The rooster tails tell all with what the boat's doing.

From here it's time to look at the thrust output too. My son's boat on the same engine is revving much higher with his MA 12X6, I still have an APC 12x8 on mine and I'll be fitting an APC 12x6 tomorrow if the weather's OK. It'll be interesting to see the RPM to Pitch to thrust output the two props give. I figure it's best to get the engine up to full chat first, then I'll start moving the fin rearwards, and perhaps increasing the chord length again back to what is what, or more. The pivoting fin is nearly there, I will try that in this position whilst I'm at it.

arcdude

You know Jeremy you may very well be onto something, possibly the fin is causing it to lift and weight bringing it back down causing the bucking effect. I've considered a complete 90 degree fin for my creation to prevent it from blowing over all of a sudden should it get to high speed. One thing for sure that does deserve merit is continued experimentation.

Jeremy_H

In my head we are a long way away from what could be the best for this boat. To me the key is the CoB positioning, it just makes so much sense when you think of the mass of the boat and how a fin too far forward could not be loaded up too much, it's like going into a fast sharp corner in a car with the front wheels braking.

Take look at this, it's the dims for the JAE Rigger, .21 size engine!:



Considering the mass of such a boat is far less than this SI3, it's a big lump that fin, about four times the surface area of mine. If we add the higher CoG we have, a need to pull down will be higher perhaps. I'll speak to the hydro boys tomorrow and see how they tune them, what they are looking for. Maybe that will help configure the next fin which will be aft of the existing one, and yeah, bigger.

arcdude

It may be due in part to the length of the hull that is making it hard to find an accurate pivot point, just a thought but maybe ahead of the actual CoB. Other models I'be constructed including 1/12th scale planes they are quite twitchy on balance and rather than using the actual balance point it's in some instances has proven more effective to have weight aft of the balance point. I would like to see one of these boats up close, that would help for sure. Are we having fun yet?

Jeremy_H

Oh yes, all along the way

Some pics from today, the best session yet. Vids on the way

Jeremy_H

Some tighter turns with straight bits in between on our small course:

http://www.youtube.com/watch?v=_1wEL1LwKQk&feature=share&list=UUw8b4mq7g44FwvGq97q6aKw
And today I had the confidence to go to the far corners of the course for the first time:

http://www.youtube.com/watch?v=YNC6vBOLDvM&list=UUw8b4mq7g44FwvGq97q6aKw&feature=share&index=1

arcdude

That's zipping along nicely there Jeremy, but work on that confidence level, those banks came up close a couple of times.

Jeremy_H

It may look like that on these phone vids but it was fine.

arcdude

It sure did in the video, love the pond though I wish there was one in my neighbourhood at least there isn't 2' wakes to deal with.

Jeremy_H

Yeah I've looked at the original vids and I'm no closer than about four feet to the bank at any time. It's confidence in the boat I was referring to, it's sliding tendency is fine to work with when the buoys are on the inside of the turn, it's the outside ones I was nervous about.

arcdude

I was in no way questioning your abilities there mate! Depth perception in video compared to in person is a whole lot different for sure

Jeremy_H

Yeah I know that, my grammar should have been better. My abilities are not great, and my eyesight makes that ever more of a challenge, but I spent ten years following 1/8th Serpents around circuits at up to 80 mph on our track, the problem there was usually other people LOL! That's much easier on grippy tarmac with four wheel drive and rail like abilities, so what I'm alluding to here is that the boat was a handful in a bit of chop, but with this fin fitted it feels more rail like, and so I have the confidence to direct it around the pond much more now. My experience with RC boats has been airboats of my own design since dot, always with water rudders, but still carvers which were all pretty stable, and submerged water prop boats, this SI3 is light footed and flips out in a blink of an eye if it's choppy or you get the control wrong. Frankly that's happened so much I'm genuinely surprised that the boat is unharmed so far. The CoM is very high because of the upright engine and resultant high tank, that makes sense for build ease, but there's no doubt that an inverted engine is on the cards to help it along.

arcdude

I've only built 4 boats and all have been inverted engines, once the tricks such as priming are learnt it really makes no difference in starting and so on. I can definitely relate to the eyesight issue at least in the last couple of years I have one pair for reading and another for 3-4' and bifocals are out of the question I figure I still have another 15 years before that Lol (the pride thing).

Jeremy_H

I quite like the idea of the engine at an angle, where it naturally falls when you hold the end of the crank. Of course that means the CoM of the engine is at its lowest, so if it was really on the cards to get the weight lower that does seem to be a way to go, the only problem is that a mount for such an angle is that much more awkward, and to make it strong enough possibly a risk to the weight lowering exercise in the first place. A light radial mount is probably best I'd imagine. Easier to get to the glow plug though

Jeremy_H

Take a look at this, at least an hour after posting, whilst I go eat some humble pie

http://youtu.be/bdnoWgUf6dM

arcdude

That looked like a half spiral, is that all it's got Lol. Thankfully little damage! Hope that was a big pie there mate

asmithnc

Hope you liked the pie.... Keep at it! The more practice the better you will get. Don't mind the scratch and remember.... If you're not flipping, you're not going fast enough even if you hit the shore?

Jeremy_H

Class huh? I'm still blaming the rock

This model remains far better than I am, probably a good thing as that means it'll always be interesting

arcdude

Out of curiousity there Jeremy what was the final weight on your SI3?

Jeremy_H

Ah hah! You've asked the golden question.

It's up to 2 lb over weight at 9lb 7oz