Rigger design question

[Simon.O.]

Update.
I have a length of CF tube on the way and and sealing the sponsons and tub with a nice poly'varnish.
The motor is here. A nice little Reedy Radon 17t that has already spun a few laps on the OB tunnel.
I have to source a mini servo and maybe an esc as I managed to nuke one today with the Cat and hydro trials.

I will begin a new thread for the rigger as soon as I have some pics of progress.

[Simon.O.]

I'm back again to pick the brains here.
As we know I now have a 8S on 6 cells in the balsa rigger that was built for a hot 05 brushed can.
At speed the front is very flighty and with all of the CoB, strut and AoA changes I have come to the conclusion that my sponsons are too fat on the water. They are 2" or 50mm wide at the ride surface and seeing Brians N2 Saw boat with 5/8 wide sponsons confirms my belief that mine are too wide.

Now I am not going for any records as we know but I want some more speed out of this thing and am confident that I have the power there to achieve this.

Looking at the sponsons in this thread you can see they have a fat butt.
http://www.offshoreelectrics.com/for...ead.php?t=3984

I can easily rework them so that they look the same from the top but taper down to 1.25 to 1.5" at the ride surface.
To achieve this I will remove the outer skin and shave the bulkheads so that the outer skin will then have an inwards slant on them like the attached sketch.

Thoughts, ideas, pointers anything but flames please.

[raptor347]

The wider ride surfaces were perfect for the lower power of the can motor. You'll need to narrow them up a bit for the faster combo.

Here's an example.
The boat in the pictures is my N2 2 lap/heat race boat. Ride pads are 1 5/8" wide set at 4 degrees. It is 26 7/8" long and has run over 65 mph and is absolutely rock solid. She's just shy of 5 pounds fully loaded.

It holds the NAMBA 2 lap N2 record at 23.35 seconds.

I can stuff a 1515/Hydra 240/2S2P 5000 pack in the poor little thing

You won't have the power of this combo but you also won't have near the weight to carry. My old NiMH boats ran 1 5/8" wide pads as well (I measured an old sponson). Thosse boats were pretty quick on a 6-7S feigao.

I looked at the figure of what you're planning for the sponson mod. If I were going to do it, I actually narrow the top the same amount. If you put too much angle on the sides it will tend to grab a bit more air if it does get unsettled while running (think easier blow off).

Don't know if any of that is useful or not.

[Simon.O.]

Brian that is VERY useful information. Thank you.
1,5/8" it will be !!
Now for the next bit given that your hull there has given me a lot of food for thought.
I am at 24" in length and I see that you are over 26".
My homework tells me that longer is more longitudinally stable at speed, so great for a saw boat.
Given that I run a sort of loose oval with the emphasis on the front straight as it is only me and the birdlife at my local pond I guess my boat is a little more like a saw boat as opposed to a true oval or heat racer.

I am considering increasing the distance between the sponson and the prop to hopefully prevent some of the loosness in the tail. I am aware of the problems caused by the prop riding up the blade and have read your pointers on cupping props etc, unfortunatly I can not do that with the 431 and 531 plastic Octuras.
Given the high fatality rate of my props due to floating debris on the pond I am not ready to pour money into metal props yet.

My options for lengthening are.
1. Move the sponsons forward
2. Extend the tub by adding a section in the middle.
3. Add a longer strut standoff with the required strengthening of the transom.

This will naturally require component movements to adjust CoB etc.
Is this a viable idea to help tame down my loose tail ?

[raptor347]

Simon,
Realize that my boat is running about 1000 watts. It's actually smaller than I'd like it for the power.

Your boat is about the right size. Figure you're going to see a max of ~400 watts.

Before you start moving things around, I've got a couple things you can try:

#1. Add some prop weight. Tape an ounce or two of lead on the transom and see if it gets the prop to bit a bit better. My N2 SAW boat has 2 oz stuffed in the radio box.

#2. Heat up the plastic prop blades until you can mold them a bit and add some cup to the plastic props.

[Darin Jordan]

Someone responsible for this site ought to setup a rigger-tech section and capture this incredibly detailed and insightful information Brian is providing on making riggers work!

I know his goal is to get MORE people running Hydros... This info helps a TON!!

[Flying Scotsman]

Seconded.
Right on Darin, plus the help he has given Paddy (Xasperated) is what FE brotherhood is all about. You will not find many other sports/hobbies that offer this sharing of technical info

Douggie

[Ub Hauled]

"Thirded", Brian is a very helpful guy.

[detox]

Brian has been helping me some also...Thanks Brain. If I ever experience blow over I may try this sponson mod.

[Flying Scotsman]

Danny, please move this to a rigger setup sticky
It is great info

[Eyekandyboats]

I will send you some new sponsons if you want with a mod in them if you would like to try it?

Brian has been helping me some also...Thanks Brain. If I ever experience blow over I may try this sponson mod.

[detox]

HECK YES! I would love to try them out. Thanks

I think I saw a glimpse of your new shape sponsons installed on a new larger rigger you are working on.



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[Eyekandyboats]

thats them.

HECK YES! I would love to try them out. Thanks

I think I saw a glimpse of your new shape sponsons installed on a new larger rigger you are working on.



........................

[Simon.O.]

Before you start moving things around, I've got a couple things you can try:

#1. Add some prop weight. Tape an ounce or two of lead on the transom and see if it gets the prop to bit a bit better. My N2 SAW boat has 2 oz stuffed in the radio box.

#2. Heat up the plastic prop blades until you can mold them a bit and add some cup to the plastic props.

After I narrow my sponsons I will report back with my findings.

I will hold off on any LOA extension until after the narrowing is done.

I like the fact that some riggers are carrying lead in them. I am off to the pond in the morning if it stops raining and will have a play with idea of loosening the rear and then feeding it ballast in small ammounts at a time.

I also have a crawler project on the go !!

[Simon.O.]

Back again as this is a good place to keep all this info.

Balance question. Cg, Cog, CofB, Where to put your fingers call it what you want.

I see some riggers such as the Xcess Crabs III and indeed Joergs beasts that have the sponson trailing edge almost in front of the tub. How the F@rk to you get the hull to balance 1"to 2" behind the sponson trailing edge in that application. Or is it further back for a good reason such as tub lift or prop lift ??

I see the Rigged Insanity from Taylor and some of Brian B's hulls have the sponson much further back, indeed further back than on my Balsa rigger and can easily see how a CoB 1-2"aft of the sponson is achieved.

No one is right and no one is wrong. Many are quicker than me and I want to tilt the table a little to get up there in speed.
50mph will be good for now but my long term aim is for 100 kmph about 65mph. I will need more water for that so for now I am testing designs and hull forms as some of you who follow my endevours are well aware.

So where is the Balance point on a Rigger that has the long forward sponsons??