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1st R/C Airboat build

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Old 05-08-2011, 12:58 AM
  #26
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Default RE: 1st R/C Airboat build

Got a new engine on the way for this boat.. Super Tigre S90K! I think this should get 'er moving better than my poor old K&B Sportster .65...




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Old 05-21-2011, 07:11 AM
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Default RE: 1st R/C Airboat build

Mounted the SuperTigre .90 on my Kamikaze airboat. Even with the engine stupid rich, it ran far better for me than my K&B .65 did. I know the K&B just needs a new carb to run right, but the .90 was the right price and it'll swing the same 13x6 prop 2000rpm faster than the K&B will. Seemed to be a no-brainer for me.

K&B .65 next to the ST .90 - both engines are about the same size but the mufflers are obviously different.


When the weather clears up around here, I'll get some videos up.
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Old 04-10-2012, 05:39 PM
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Default RE: 1st R/C Airboat build

I'm in the process of dusting off the Kamikaze, and decided it was time for a new rudder. Much like the one I made for my Minikaze, I laminated strips of Black Cherry and added some Black Walnut in for color. I need to make the blade and finish putting coats on the rudder strut, but this thing should work as well as my other rudder and help with handling too.

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Old 04-12-2012, 07:17 PM
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I finished the rudder assembly for this boat. I might have to put a different control horn on it, but I wont know until I get off my keister and mount it up. The next one I make I'm going to experiment with different cutting techniques to get the grain of the wood showing in just the right way to give a really neat 3D effect.

Anyway.. here's a picture.
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Old 04-13-2012, 03:47 AM
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Default RE: 1st R/C Airboat build

That is just the ducks nuts man !

It looks awesome, and would work great.

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Old 09-29-2012, 10:09 AM
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So I've been experimenting with my .60 4-stroke engine on my big Kamikaze... The problem I'm encountering is porpoising. The age-old wisdom (not that old, LoL) has been, AFAIK, to have the prop at 1/3 the length of the hull measured from the transom. I have the prop in this location. 32 1/2" long hull, prop is at about 10.75" from transom. The boat weighs about 8lbs with engine, full tank of fuel, Battery pack, etc. Lifting by the prop, the boat is very bow heavy. Moving the engine forward any more than it is will involve raising the engine even higher so the prop clears the hull. Not ideal. Instead, I strapped my 8oz GPS on top of the fuel tank and this helped it balance much better, nearly perfect. It still porpoises. I had the same problem with my .90 2-stroke, but worse since that engine is a lot more powerful. There isn't much I can do to lighten the bow much except using lighter servos but that isnt going to save more than an ounce or two. Not enough to make a difference. So.. Since there isnt a How-to in the Jigs/how-to section, I ask here to find out from the veterans (if any of them still visit the forum) as to how I can correct the bouncing up front. The 4-stroke .60 weighs just grams less than the .90 2-stroke, and the original engine (bushed crank .65 2-stroke) was installed about 1.5" further rearward than the engine is mounted currently. What does a guy do? I can't get a good speed run if the bow is bouncing like a pogo stick... Need some input, please.

Empty fuel tank, but RTR otherwise:

Empty fuel tank, with GPS on top of fuel tank (+8oz) - sorry I cut off the rearmost section of the boat in this picture. You should get the idea though..

Static picture of boat as I ran it last.


This is an older vid from a couple months ago, but you can see and hear it porpoising. This is without the GPS on it, but a total of 12 Standard alkaline batteries in the radio box for ballast. 4 of which power the receiver and servos.
http://youtu.be/fANKIgoe65Q
I dont really want to have to add that much more ballast... Is my only option to move the engine? Angling the prop up didnt change much. The GPS on the fuel tank helped some, but not enough.
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Old 10-11-2012, 02:55 AM
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Default RE: 1st R/C Airboat build

Instead of adding weight, change the motor's thrust angle. Shim the motor or motor mount to raise the front of the motor, that will help hold the bow down without weight.




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Old 10-11-2012, 05:21 AM
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Default RE: 1st R/C Airboat build


Quote:
ORIGINAL: Got RPM

Instead of adding weight, change the motor's thrust angle. Shim the motor or motor mount to raise the front of the motor, that will help hold the bow down without weight.




.
I ran it a couple weeks ago and tried a few different things and the results of that require the engine to move forward. I've shimmed the thrust angle already with little change. Too high of AOA ends up causing a drop in speed which I don't want. I'll have to make a new engine mount allowing 2" of forward movement which will make the boat balance.

I've been running my 3-pointer lately so this boat has been idle. I may work on it over the weekend if I have time.
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Old 11-17-2012, 08:17 PM
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Default RE: 1st R/C Airboat build

I'm in the process of making a new engine mount, in the mean time I shimmed the thrust line up quite a bit to smooth out the porpoising. It runs far better now, although not quite perfect. I think the prop will have to move forward at least 1.5" if not 2". I'll incorporate some adjustment as I have 3 engines I can run on this boat.

A couple short vids I made today running my Enya 60-4C on the Kamikaze
http://youtu.be/qAgUyZDCx1I
http://youtu.be/tHgkyInh1J0
http://youtu.be/zKZaxLuuzRw

Nothing special, it just sounds cool. The engine ran pretty well today. I'll try a few other props and test with the GPS.
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Old 11-18-2012, 07:30 AM
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Default RE: 1st R/C Airboat build

CG is based on weight. Move the engine to the rear and balance 1/3 the length of the hull, measured from the transom. Looks's like the engine is too far forward. Also, Put the silver spinner back on for the gold spinner is quite a bit heaver. The gold is used for adding weight for balancing purposes.
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Old 11-18-2012, 04:01 PM
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Default RE: 1st R/C Airboat build

Quote:
ORIGINAL: rcairboater

CG is based on weight. Move the engine to the rear and balance 1/3 the length of the hull, measured from the transom. Looks's like the engine is too far forward. Also, Put the silver spinner back on for the gold spinner is quite a bit heaver. The gold is used for adding weight for balancing purposes.
If the prop was put at 1/3 length from transom, it hops real bad. The proper balance AFAIK is when holding the boat up by the prop that the hull stays level. This boat is not level holding it like this, it is very bow heavy. Moving the engine forward will balance it. Moving it back makes it worse.

My SI-3 .20 size hydro balances perfect at the prop and runs out perfectly.

The brass spinner nut is the only 7mmx1.0 nut the LHS had. Being a 4-stroke, it likes to have a little extra flywheel effect on smaller props. I have little to no intention of changing it.
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Old 11-18-2012, 04:41 PM
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Default RE: 1st R/C Airboat build

Get a piece of round stock longer than the width of the hull. Lay the stock on a flat surface, and level as well. Mark on the hull on either side the balancing point and line up the round stock and see where the hull balances. You can move the hull back and forth on the stock to achieve your balance point.

Another method is to tape the round stock on the top of the hull at the balance point and lay either end on a end of a table or similar.
Give this a try and see.

Let me know how you make out.
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Old 11-22-2012, 07:35 AM
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Have not heard from you. How did you make out on the balancing issue?
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Old 11-03-2013, 05:20 PM
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So I did the crazy and stuck my new 1.20 4-stroke on my kamikaze. No water testing yet, but it flies in the grass. Here's pics of the entirely new engine mount:






Ran it in the grass getting chased by crispyspa's Brushless E-Maxx... He will have to post a link to the video, I'm having a hard time grabbing the link through my phone.


It did a loop de loop, landed right side up, *still running*, but unfortunately the prop hit the hull in the process... Minor damage here but still a bummer.

Later on I somehow hit a stick and took a chunk out of the prop... Goodbye $7 prop (13x10)!

This 4-stroke has some serious power. 14x6 APC @ 10,800rpm, 13x10 APC @ 9,400rpm. All on 5% nitro 25% castor fuel. Love these things!
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Old 11-04-2013, 03:47 PM
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Classy motor, looking forward to seeing this
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Old 11-04-2013, 05:07 PM
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Quote:
Originally Posted by Jeremy_H View Post
Classy motor, looking forward to seeing this
Crispy posted a link to the video over on my build thread at RCAW. Enyas are really nice engines. Wish I could afford a VT-240. (Drool)
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Old 11-05-2013, 12:08 PM
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Cool I'll check it out
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Old 11-07-2013, 06:55 PM
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New grass video. Cold and breezy and frosty grass. The boat didn't go for crap but sounded great. Needs more nitro and a different prop and let the pig fly.

http://youtu.be/CeIub2cAsYE
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Old 11-08-2013, 06:34 AM
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Plenty of potential. Liking the paths the boat left in the leaves
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Old 11-08-2013, 08:30 AM
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Quote:
Originally Posted by Jeremy_H View Post
Plenty of potential. Liking the paths the boat left in the leaves
If my second video didn't get cut off youd see I cleared a circle about 8 feet across in the middle of the leaves. The leaves really fly when you run right into the pile! LoL. I am still testing props to find the right one. With a 13,000rpm limit on the engine and 14" props being a touch too big for the boat, I'm stuck with 12-13" props with high pitch to keep the rpm at bay. I think a 14x6 might make enough thrust to flip this 18" wide boat right over. The all-up weight RTR is 10lbs. The 14x6 APC makes about 15lbs thrust, the 13x10 is about 7.55lbs.
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Old 11-09-2013, 06:55 PM
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Two new videos from today. Tried two more props, mixed up some new fuel with more nitro and went to the park.
13x9 APC prop at around 9,600rpm rich 23.3mph top speed - http://www.youtube.com/watch?v=Rvoe05B2ZY8
13x8 APC prop at 11,500rpm+ rich gave 28.8mph top speed, not enough room to top it out. I'm sure this boat will hit 45-50mph given enough space. http://www.youtube.com/watch?v=R8qOm3eBBs0

13x8 prop giving up about 11.55lbs thrust (Thats 2.5hp!), 13x9 gives up 8.5lbs thrust. I may have to revert to the 14x6 APC (2.1hp) and shim the engine up. That prop gives up close to 15lbs of thrust. I really need to get it on the water with the wet rudder........ Next summer is going to be interesting....

Last edited by 1QwkSport2.5r; 11-09-2013 at 06:58 PM.
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Old 11-10-2013, 05:46 AM
  #47
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You're having to much FUN!
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Old 11-10-2013, 08:46 AM
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Hello 1QwkSport2.5r
Your engine sounds fantastically.
We are curious how it will float.
What model of GPS do you have ? ? ?

Greetings from Poland
Marek&Wojtek
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Old 11-10-2013, 10:21 AM
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Thanks guys! Here's a video of this boat with my Enya 60-4C powering it on water. http://youtu.be/fVadTr40eQw

And this is from 3 or 4 years ago when I built the boat originally. Powered with a K&B .65 Sportster and 12x8 MA prop: http://youtu.be/pwdsXcMDSMA , http://youtu.be/4ujAO4lfElc

I was having a lot of fun. It's a blast when you ridiculously overpower something. Enya engines rock! GPS unit is a Lowrance iFinder Expedition C. The boat hangs dead level without the GPS on board so it should ride really nice with the R120 on it.
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Old 11-11-2013, 01:11 PM
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Hello.
Thanks for informations about GPS. AirBoat on water is jumping too much. You must to change the center of gravity and will be ok. Can you drift on this boat ???


Greetings from Poland
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