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Design a fast airboat outrigger

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Old 10-13-2019, 07:05 AM
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critx
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Default Design a fast airboat outrigger

I am looking to design and build a fast airboat rigger.
What would be best power plant combo to achieve really good speed for a slim boat long of 800-900mm (~32") and estimated at 2kg (4.5 pounds)?
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Old 10-13-2019, 02:08 PM
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Originally Posted by critx View Post
I am looking to design and build a fast airboat rigger.
What would be best power plant combo to achieve really good speed for a slim boat long of 800-900mm (~32") and estimated at 2kg (4.5 pounds)?
I don’t build anything with electric power - I run glow power only. The fastest engines are Jett, Rossi, Picco, etc. You need a fast engine with a lot of rpm to make an Airscrew rigger go fast. Search YouTube for “rigger airboat”. You should come across a video by ‘crispyspa’ with my rigger running. The engine was slow for that boat, it’ll get a Jett .56LX on a pipe next season.
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Old 10-14-2019, 09:47 AM
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Thanks, sounds nice but I still have to stick to electric.
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Old 10-14-2019, 10:01 PM
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Get ready to puff some LiPo packs then. One problem with FE boats - the batteries do not last real long. Also, USE STRONG GLUE to hold the boat together.

crispyspa is a FE guy I know. Send him a PM or message through YouTube. He might be able to help you on the electric side of things.
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Old 10-15-2019, 04:57 PM
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Get ready to puff some LiPo packs then. One problem with FE boats - the batteries do not last real long....

This is simply not true. It’s exactly like me saying that nitro boats always burn out plugs in the middle of the lake, they lean out and die all the time, and the fuel goes bad fast. Clearly you don’t have much if any direct FE experience, just what you read on the internet.

I’ve been racing LiPos for over a decade and have never puffed a cell. This is with over 50 packs, I lost count. Some packs have been raced for four years and are still running strong. The dozens of FE boaters I raced with have similar stories. These are high amp national-level race setups, not hopped-up RTRs.

True, cheap packs don’t last that long, but the OP wants fast, so at least mid-range quality packs will be needed. Packs puff because folks don’t understand what setup to use and over-amp them, or run them until they are under 3 volts per cell. If the OP will tell us how fast he wants to run and what hull he is planning on copying, someone with FE experience can help him get there. Lots of successful air-prop hydros out there, I’ve had a few.


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Old 10-15-2019, 09:13 PM
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And when you are 2mph from something crazy, you push it that much farther and something goes wrong. Your comment reminds me of the guys who say that electric is as safe as anything else, yet they bring home charcoal once in awhile. I’ve seen posts like this before - you can recommend a bulletproof system, but people never buy the bulletproof system you recommend. They get some hobbyking crap and wonder why they smoke their ESC or batteries. Not all electric boats blow batteries, but the systems people seem to flock to are cheap and nowhere near as robust as they should be.

I can tell you that a 27 pound wood 3-pointer takes at minimum a $1000 power system from hobbyking (part of that is a 300A water cooled ESC) to run 70MPH; and this run smoked the 300A ESC to hit 70. Perhaps better quality electronics components wouldn’t have failed, but when you’re trying to go as fast as humanly possible, all bets are off. They just are. No one can argue that.

I agree the OP needs to share their intentions and budget. This could confirm or deny my suspicions.
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Old 10-17-2019, 02:30 AM
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I had a look at Dan Jones airboat. Very fast and nicely built.
But I am thinking to have a smaller/lighter configuration - also made full out of carbon fiber. I will look for short straight line runs.

I cannot progress much before I decide on - motor and prop.
I am not good in selecting motor/prop to get best out of them.
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Old 10-17-2019, 05:28 AM
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So after some search and estimats I got thinking I could start with this:
Prop: 10x8 or 10x7 ( some good quality supplier for testing)
Battery : 10S / 2200mAh / supporting up to 100C - buy 1S packs and make wiring myself with good quality and enough thick wires to ensure deliver of current
Motor: 10S-12S / 600..700 rpm/V

According to some thrust calculators this could deliver:
- 9000g static thrust ( static efficiency ~80%)
- prop. absorbed power ~ 4400W
- prop. tip MACH speed ~ 0.8

The plan is first make prop/power tests and build the ship after.
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Old 10-20-2019, 12:18 PM
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I’m not sure how you calculated the results posted, but PropCalc* shows closer to 6500 grams of static thrust and 2200 watts of mechanical power with my best guess of your components and a 10x8 prop. Pitch speed is high (good), but the prop is stalled statically, meaning you won’t reach max thrust in static condition.

Most concerning is with the motor temp having a risk of overheating depending on the exact motor used. Not so important if all you do is make two long passes. The 2200 mAh pack may be on the small side for many runs so that may mitigate the heat issue. I’d start with a 10x6 prop and judge speed and temperature from that before propping up.

* I’ve used PropCalc for years with my airboats and find it to be pretty accurate, sometimes surprisingly so. Like any modeling software it is only as good as the inputs.

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Old 10-22-2019, 09:00 AM
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@GotRPM thanks for your input.
The first important topic is to have a good sizing of battery-controller-motor and later will have to test different propellers for best performance.
Below is a rough design of the boat. I'm still working to figure out if I can build it with in 2kg weight. I am not actually sure how much installed kW power I need in order to get relevant high speed.
Actually the reason I opened this topic is to get support in sizing the power plant and propeller.

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Old 10-23-2019, 07:48 AM
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What speed are you wanting to achieve?



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Old 10-23-2019, 09:21 AM
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Originally Posted by Got RPM View Post
What speed are you wanting to achieve?
First step - 60 mph - with this design
Final target - 100+ mph - with a next design build based on lessons learned
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Old 10-23-2019, 10:30 AM
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Then a 36-42mm motor with a Kv around 600 on 10S spinning a 10x6/3 APC Electric prop should get you to 60 mph with reasonable amp draw - assuming the hull design works. The better the motor and cell quality, the better the chance of high performance.

Your hull design is rather unconventional, most riggers have a tub wider than it is tall to lower the CG and to help keep most of the sponsons well above the water at rest. You don’t need the T-tail as it adds complexity and drag, but the vertical may be a good idea. So is the rear shoe, it defines the hull’s aoa.


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Old 10-23-2019, 09:25 PM
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The unconventional design with taller than wider tub is to reduce the air lift created by the hull. This rigger is not supposed to be too maneuverable, I can increase distance between sponsons for stability.
Regarding T-tail I was thinking to test if at higher speed the T-stab will lift the rear shoe out of water and run only on front sponsons. Anyway if not efficient or troublesome can be removed.
The CG is about 70-80mm obove water while gliding.
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Old 10-27-2019, 01:02 AM
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Can you please suggest a suitable motor supplier that is of good quality and performance?
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Old 10-27-2019, 06:46 AM
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I have used numerous motor brands, and while most performed okay, the highest quality I used were by Scorpion motors. Powerful and durable, they are not cheap But worth it for most projects. The best “budget” motors I’ve used were the NTM PropDrive motors sold by HobbyKing. They appear well made and performed well although I don’t know how durable they are in the long term. However they are currently in short supply and I don’t know if they are still being made.
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