Slayer-RCU

Here are some pics of the boat in its current state.

Cheers

Slayer

Mikie888

This boat should fly... Slayer , good paint job mate....

rsieminski

Has it seen the water yet?
If so, how did it handle the turns?

pro27

Good job Slayer.
Inginuity at work.
What's for power?
Overall weight? (approx)
IMO you'll have your hands full................of fun

Update us after she runs.

maik

Cool Boat Dude!!

I built one myself, but i preffered to do an everglades type of boat.

I'm dying to find out how your boat runs!!!!

by the way a freind of mine has the same type of boat he ran it with a water rudder. He had some problems with turns. it keeped turning turtle.


I thought it was just a cg problem but he insist that the design was wrong.

He built a new boat, This time a tunnel hull!! Thats right and now it runs great. I'm going over to his haus now maybe i can get some pics. And include it later.

Maik

Slayer-RCU

Well finally an engine run,

Got sick of painting and decals.. thought what the hell its time to run the sucker in.

What can I say.... The GMS engine fired straight up, the cline fuel system worked a treat (the lower tank was filled with fuel, it sits approx six inches below the engine) and let the engine run until both tanks were emply... The boat sailed around the lawn (3 inch high grass) and had to be throttle down once moving...elevators had good authority... Turns were a bit sluggish but this will improve with speed and less friction ( water instead of earth) I think.

Roll on the weekend....off to some water I go. must rember to fix the Tx first.

woo hoo

Slayer

pro27

Slayer-

If possible, get some pics of it on the water.
I like to see how it rides.

Fluid

Great looking boat! The reason that hydro hulls are faster than other designs is because they have less hull in contact with the water. With a water prop, the transom is held up out of the water so that only the front sponsons touch the surface. This limited contact allows much higher speeds. The problem with a hydro airboat is there is nothing to hold the transom out of the water when it is running. Depending on how the boat works, you can probably increase the speed noticeably by using small auxillary sponsons under the transom to hold the transom up. These are common on many nitro and electric hydros.

The only potential problem with the small "shoes" is the possiblity of degraded turning. This may not happen at all, but if it does it can be reduced by having non-trip surfaces on the rear shoes. Good luck and keep up posted!!

Slayer-RCU

Pro 27 and all the others with questions and comments,

Yes it works, as the engine is still being run in, it was not tuned for max rpm. I have about 20 meg of video (MPEG format) but no where to host it. The attached pic shows it sitting in the water for the first time (yay).

Lets see... The boat came up onto the plane, however had alot of trouble with LH turns - no rudder authority (might look at replacing the dual rudders with a larger single rudder)- RH turns no problem. First semi high speed run, the boat was on the plane lifting, lifting.. flip over we go..SPLASH..bugger.. o'well mental note remember to adjust the elevator to trim next time.

Damage Report - RH Rudder hinge points ripped out, LH rudder hinge points loose... no elevator control. 10 mins latter with damage repaired off we went again.

Apart from the flip (x2) the boat went very very well for a prototype design, looked good up on the plane and sinking back into the water as it was throttled down, requires a little more water proofing for the radio bay and rudder rework, then watch this space.

See Ya

Slayer

rsieminski

That looks great man! You have an adjustable elevator? Where's it at? The rudders are air rudders or water rudders? Thanks for the flight report.

maik

I think your boat is perhaps too nose heavy ???

I had the same problem. My boat would nose down and flip on a high speed pass.

I moved my engine pod back 5 inches and lowered it 2 inches.

I also inverted my engine to lower the cg down so that i can carry more speed through the turns without worrying about flipping.

How do you paste pictures into your post. I want to show you pix of my boats.

Slayer-RCU

maik,

The boat did not 'nose in' before it flipped, it was on the plane and the front just kept lifting until it reached an angle that caused it to come out of the water and back flip.. I guess trim plates would fix this or adjusting the elevator to compensate for the lift generated by the hull and keep a nose level attitude.

As to pictures, there is an "upload images" link at the bottom of reply to message box - don't know if this is only for the thread owner ?

Cheers

Slayer

pro27

If it back-flipped on you, that can be fixed............to an extent.

Basically, you have reached a critical speed at which the boat suffers from the oops.
I think you are on the right track by proceeding to trim the boat with the elevator you have installed. Whether or not it will be enough only more test runs will show.

I'm sure the hull is heavy enough already, so adding weigh to the bow would do more hurt than good. Trimming it by other means would be more benefitial. Maybe even a small wing (spoiler) between the front sponsons that could be adjusted with a turnbuckle or clevis on a threaded 4-40 rod (don't use the std 2-56 size, it'll bend under the loads it is sure to see).

The other alternative would be to play around with the engine angle. More time consuming than a movable aerodynamic, but do-able.

The final outcome you want is for it not to blow over at max speed. Keep in mind, the faster you go the more sensative the aerodynaics becomes. Proceed in little steps and increments.

Slayer-RCU

pro27,

I hope I have not reached the hulls critical speed as the engine was not run in and it did not reach peak rpm (I know it can go faster). I will increase the size of the elevators thereby increasing the amount of downforce that can be applied to the nose of the boat.

A couple of other points

The cline fuel pressure system - very impressed, no trouble with drawing fuel from the lower hull tank and the boat ran for about an 45 mins without refuelling on a 24 Oz tank.

Is there an air/water filter that fits over the throat of the carbie to prevent the ingress of water, I was think of using a peice of garden hose and a bit of oil soaked foam (sort of like a car air filter).

pro27

To clarify...
You may have reached the hulls critical speed for the way it is currently set up!.
We always hope it can go faster. It's the aerodynamics/hydrodynamics that limit the possibilities do to unknown limitations. That is what makes it so FUN!

I think by increasing the down force will help. It may take numerous tries though to get it just right. Once you have reached the point where you think the engine is maxed out (rpm) and is gonna go as fast as it's gonna go, then it can be fine tuned for the optimal ride.

Getting there is only half the fun.

I haven't heard of the Cline Fuel pressure system until I came to this forum. Where can I get more info online? Sounds interesting.

Bruline makes some carb filters with different size throats which are pretty small diameter so they don't interfear with the prop. Almost all car type filters are too big . However, it won't stop the injestion, but just make the drops much smaller. In the past, I have rigged up small shields over the carb with some thin clear plastic/lexan to deflect any water heading towards the carb. Not fool-proof, but usually cheaper.

Slayer-RCU

Pro27,

Here is the link to Jim Clines web page, the actual fuel system is called a Proportional Control Fuel System (PCFS). As stated above it worked a treat and I would recommend it to anyone looking at placing fuel tanks in unusual locations. This boat has the 24 oz main tank located about six inches below the engine with a 2 oz header tank behind the engine.

[link]http://www.billsroom.com/pcfs/[/link]

Back to the aerodynamic issues with downforce etc.

pro27

Slayer,
Thanks for thr link, I'll be checking it out.

If you have any questions about your aerdynamic problems, you know you can ask them here.

maik

Slayer

when do you click upload images do you do it in between the [img][/img] ???

pro27

When you click on 'upload image' another box should pop up with four boxes inside. If you click on 'browse', you can then look anywhere in your computer for the item you want. You then select the item and open the item, and it will be downloaded to the post. You are able to uplaod 4 images per post.

Slayer-RCU

Hi,

I have just thrown together a quick web page and have some video footage (2 Meg) and the begining of a construction guide. The link is [link]http://home.iprimus.com.au/psguy/[/link]. I am extending the rudders and fixing up the control problem I had, as stated above.

[8D] Slayer

pro27

Just threw this site together?????????????

Good job on it. Liked the vid and your construction info. Building the hull was obviously more involved than just building the kit as stock. Good job on the mods.
Hopefully you will post another vid once you have your latest mods finished.

Nice watering hole too.........

Fluid

I could not get the video to work, so my comments may not be 100% spot on - but they should be close. A 3-point hydro does not operate at all like a flat-bottomed airboat. Operating correctly, it is balancing aerodynamic and hydrodynamic forces and the balance can be rather "touchy". I've built and run a lot of water-propped hydros, and IMO attempting to 're-invent the wheel' with a 3-point airboat is a set-up for frustration. There are basic design and rigging parameters which just cannot be ignored if success is desired.

Blowovers are very common to 3-pointers if their air/water balance is not correct. The usual reason is an improper ride attitude, with the transom too close to the water. This packs air under the nose and results in a back flip. With a water prop the ride attitude is adjusted with the prop depth, usually running the transom 1/2" to 1" above the water surface ( depending on the front sponson depth ). IMO a rear airfoil or elevator simply cannot supply a consistent running attitude, and when the model achieves a certain speed, if the transom drops a bit the boat goes over - seen it happen dozens of times. What is needed is a small ride surface at the rear of the hull to establish the ride attitude. Even the world's fastest boat, the 3-point Spirit of Australia with its jet propulsion used a small rear sponson for just this purpose. At full speed the rear sponson may be out of the water so there is no drag, but as the boat slows a bit it comes back in touch with the water to keep the boat from flipping.

The second reason for a 3-pointer to flip is the wrong CG. This is usually placed 1" to 4" behind the front sponson transoms. Pro27 is right, adding weight is not the preferred solution, but moving the radio, batteries, fuel tank, etc. forward until this CG is achieved will not only reduce the incidence of blowovers, but by lightening the transom it will make the boat come up on step much faster and stay on step better.

If the boat is really moving at high speed, then a blowover is always a possibility - the 3-pointer is fast because it is essentially flying over the water and is not the most stable of models. But properly setup I believe it is the fastest type of airboat. Just don't try to reinvent the wheel - instead rely on proven trimming and rigging techniques. [8D]

pro27

Fluid..........
Do you think a mod as I will describe would help Slayer?

The latest thing for outriggers, ( at least to me), that use rear sponsons is to have them located completely under the hull at the transom, vs out the sides AND under.
If he were to measure the difference between the front sponson bottoms and the hull bottom, and create this difference at the transom using , say 2" x 3" tapered blocks, so the static attitude is level or very close. This I think would also help the ride attitude under power.
But I still think that playing with the CG is well worth the effort and would show some positive results.

Comments ????????

Slayer-RCU

Fluid and Pro27,

Firstly, thanks for all the info and feedback, it has helped alot.....sorry about the site..some problem with uploading the index page (it forgot the hotspots) however that is now fixed and the site works. Here is the link again [link]http://home.iprimus.com.au/psguy/[/link]

Do you have any pics of a transom with rear sponsons or a drawing of the shape required.

When the boat was running it appear that the transom was approx 1-2 inches out of the water and as the boat accelerated the front sponsons started to lift and over a distance of about 60 ft the boat backflipped, I did notice the elevators has some effect a keeping the nose down. The CoG for the boat is approx 30% forward the transom, I really don't want to add weights.

The Boat now has larger dual rudders and elevators, both about 30% bigger, hopefully this will fix the rudder authority problem and just may be help with the back flip problem.

Fluid

Looking at the video I can't determine if the transom is out of the water or not - I know that the boat is running slow there, but it seems to be dragging. Pro27, riggers are using three types of rear sponsons; the "traditional" larger ones mounted on the sides of the tub, twin smaller ones under the tub, and a single one in the center. But, riggers have different dynamics than a three-pointer does, and successful scale hydros usually run "shoes" or ramps mounted under the hull on the outside edges. These are usually deep enough to keep the transom up a 1/2" or so and are 4-6" long, tapered from zero depth in the front to about 1/2-3/4" at the transom. I'll try to find a pic...

If the transom is indeed 2" out of the water when running, then the lifting/blowover is probably due to the CG being too far back. I know that it is tough to change the CG now, and adding weight is not the best option. Many scale ( and full-sized ) hydros use a canard wing in the picklefork between the front sponsons to supply some downforce, and as suggested this may be the easiest option. Below is an example: