Building an airboat around an engine

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Alex A.
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Building an airboat around an engine

Post by Alex A. » Fri Dec 23, 2016 9:32 am

Greetings, gentlemen. As the topic says, i've got my hands on an engine ez30 (220hp/6000rpm as i was told) and a task to make an airboat out of it. Therefore i have to figure out how much of a mass i can move with it so i can make a hull order in our local workshop. They haven't made any yet, so i would have to draw it. After some research i got the idea of a hull building, but at the same time got confused of how big it can be.

Let's say i would divide my rpm by 2.2 and get to around 2700 rpm. How do i calculate the next step? I understand that i can get a tons of different props, and the result will vary dramatically. My concern here is that my given engine is 220hp versus 500hp everyone else seem to use. It would be nice if you guys show me a direction i need to research. :roll:

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Re: Building an airboat around an engine

Post by AirRanger » Fri Dec 23, 2016 12:20 pm

http://www.motorreviewer.com/engine.php?engine_id=54

If this is the engine you have it will be unique in an airboat. I see lots of custom components in your future.
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Re: Building an airboat around an engine

Post by John Fenner » Fri Dec 23, 2016 1:01 pm

Welcome to the forum, I would start by what will the engine and gearbox weight combo be, then I would figure on what you intend to run said boat in, marsh, lakes or canals, open water or dry ground, then what do you plan on hauling around and with how many folks you intend to carry.
That said, surely there are experimental aircraft using the Subi platform for a power plant in which I would do research on to find out what is the best climb prop combined with gear ratios, and in comparison to an aircraft engines performance on similar airframes would give you the best idea on what size hull to build to give you best power to weight ratio possible in your build.
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Re: Building an airboat around an engine

Post by swamper2 » Sat Dec 24, 2016 11:06 am

For starters I would look at hull and prop using the 215hp 360 continental . Then you need to figure out how to adapt a gear reduction to it. Either a 2.38 or 2.68 which I would talk with the prop company of your choice for input. looks like fun.
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Re: Building an airboat around an engine

Post by goldhunter_2 » Sat Dec 24, 2016 11:48 am

Alex A. wrote: My concern here is that my given engine is 220hp versus 500hp everyone else seem to use.
Don't get caught up in "Hp" its all about the torque! There are allot of continental pe-150 commonly called gpu 220 ground power the are probably starting off stock with around 400lbs torque curve @ 2700-2800rpm compared to that 500hp carmotor you mentioned that must have a gear box and turn the engine 5400-5800 to produce maybe 350-400lbs torque (stock) we see up to the 500lbs range on some built engines on the dyno (and your probably not looking at spending the money to build the engine) Allot of people get disappoint when their engines don't produce the numbers they expected from the ligature but fail to understand that the advertisements numbers are for absolute best case situations.

Just for another torque comparison a four cylinder Continental Pe-90 with just 470anggle valve swap will produce more torque an swing a bigger prop @ 2700-3000rpm then a a direct drive small block chevy 350.383,400

The point is you need to think about your engines "torque" above all else if your going to use that engine I'd subtract 10-15% of the posted torque numbers and look for a gearbox that will work for you (you'll probably have to make a adapter plate, but experimental aircraft market may have one already to) and remember not all props turn 2700 rpm you mite want one that runs a lower rpm

Happy building keep us posed with how your project turns out
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Re: Building an airboat around an engine

Post by OneBFC » Sat Dec 24, 2016 5:32 pm

Well, as nicely as I can say this, it is all about horsepower and not torque.

The higher power engine will always make more thrust if setup properly to match propeller appropriately.

I wouldn't worry about a 220hp engine. I think that is quite enough to have a good performing build if you don't try to haul 5 people around with it on dry ground all the time.

With a good propeller choice to go with your chosen gear reduction, you will make around 800lbs of static thrust.

Keep boat weight to thrust ratio at least 0.5:1. That is, 2 lbs of boat weight to 1lb of static thrust. Boat will perform reasonably with that ratio.

Talk to prop manufacturers. They will steer you in a good direction.

Good luck with your build!
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Re: Building an airboat around an engine

Post by Alex A. » Tue Dec 27, 2016 2:54 am

I agree I owe you some clarifications I should've posted earlier:
1. I intend it to run on lakes, shallow rivers, snow and ice.
2. Yes, there will be a lot of custom components.
3. I think I will use a custom belting instead of a gearbox. Fortunately, I have means to construct it.

Now I did some research and calculations, and I would like to know what you think of it and how bad is it (or not) =D.

As the first step, I found this program called prop selector. And here's what i got out of it:
Image

But I was warned it's results are very, very rough. Nevertheless, I set it up to get the above mentioned 800 lb of force, and it looks like it can be done. What I don't like is 190 hp, which means I will have to go on full power, and there won't be any reserved power (to get the boat started, for example, which requires a lot more power than actual running). But... it's a rough calculator, and it's designed for air flights. The problem is - I have no idea how the real life results will differ from this.

As the second step, and after some more talks, I decided to assume the weight of my boat as follows: 440 lbs for 2-3 people, 880 lbs for the hull and 880 lbs for the engine, prop, metal parts, fuel and chairs. I had to assume something, I thought, to provide the prop manufacturers some input info. But it already looks like my prop is going to be a big one :arrow: . But the bigger prop requires more power to turn, meaning more hp :banghead: .

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Re: Building an airboat around an engine

Post by CarMotorBarge » Tue Dec 27, 2016 7:49 am

Alex,

I have a few questions and observations that will help with providing answers:

1. Where are you located? This info will help people better understand how you will use the airboat.

2. Given that you are using a 200 HSP engine, I would recommend building a 11'x7' hull. This is the size of hull that is normally ran with a 200 HSP A/C.

3. The 800 lb estimate for the hull is extremely high. The hull needs to weigh under 400 lbs. Do you know what type of material you are going to use? Also how thick of material.

4. You want the total boat weight to come in around 1200 to 1300 lbs. This is with no fuel, gear, or passengers. Just hull, rigging, and engine.

5. For the prop, I recommend a 68 or 70 inch prop using a 2 to 1 gear ratio. This size of prop is what 200 HSP A/C engines use. The difference is that you will be using the 2 to 1 gear ratio to allow the engine to get to the usable HSP. There are 3 primary airboat prop manufacturers. Just tell them you need a hill running prop for a 200 HSP engine. Also make sure you get the correct rotation for the prop.
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Re: Building an airboat around an engine

Post by mojoe » Tue Dec 27, 2016 7:54 am

1) in shallow water, snow and ice, almost any airboat will do.

2) Your targeted weight is way wrong. I have a "typical" 260 hp 400lb AC motor on a boat that I have lifted up and slid a trailer under. Maybe 300lbs. The cage I can take on and off easily. Maybe 40lbs. The rest of the rigging can easily be lifted with 2 people. One can do it but it's awkward. Maybe 125lbs. Add on the rudders and other assorted crap and the complete rig is right at or under 1000lbs. This is "typical" power vs weight for a strong running AC boat. Passengers and fuel vary, but I love how it runs with just me and a half tank of gas.

The car motor boats can get away with more weight as long as they have more HP. You have less, so if you want it to run strong, you gotta cut weight.

260 hp pushing 1000lb boat= runs good!

220 hp pushing 1700lbs = stuck or sunk!

3) if you want to know what prop to run, delete that on line airplane calculator and call one of the airboat prop manufacturers. They will tell you the right prop.

4) We shouldn't use an AC motor to compare hp to your car motor. Since an AC motor generates max hp at MUCH LOWER RPM than a car motor, the correlating torque generated is significantly more in an AC motor for the same measured HP.

http://www.calculatoredge.com/new/horsepower.htm

I have seen varying formulas to calculate hp to torque, so I don't claim that one to be accurate for airboat applications. I put it there because the one thing every formula I have seen says, the higher RPM required to generate said Hp the lower the correlating torque.

So you will likely need to set up your boat similar or lighter than a typical 220gpu to get it to run well. Or add hp.
Mark 7:9

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Re: Building an airboat around an engine

Post by Alex A. » Wed Dec 28, 2016 10:00 am

Wait, wait, wait... so thrust should be = weight?

Now that i think of it, there is something wrong with this:
OneBFC wrote:Keep boat weight to thrust ratio at least 0.5:1. That is, 2 lbs of boat weight to 1lb of static thrust. Boat will perform reasonably with that ratio.
>>> delete that on line airplane calculator and call one of the airboat prop manufacturers

I did, and here's what I got: at 200HP/6000RPM and a six-bladed 80'' prop rotating at 2140RPM i would get around 900lbf. It almost made me cry :o

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Re: Building an airboat around an engine

Post by D.M. » Wed Dec 28, 2016 10:54 am

https://www.youtube.com/channel/UCLe2Op ... QvYIgcM65g
That check out my video. I've built with EZ-30. maximum weight of 800 kg
Statistical Thrust 370 kg

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glades cat
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Re: Building an airboat around an engine

Post by glades cat » Wed Dec 28, 2016 11:54 am

Some good numbers have been used in the past. 4 lbs of thrust per Hp for a correctly propped power plant is about what is to be expected. Weight to Hp ratio numbers in the neighborhood of 5:1 have been in the ballpark. 1000lbs needs about 200 Hp.
Torque and Horsepower will always be equal at 5252 RPM. If an engine is designed to operate below 5252, its torque will always be higher than its horsepower. If it's designed to operate higher than 5252 the horsepower will be higher than the torque...because the RPMs in the formula factor favorably towards horsepower. Horsepower is the true measure of work and it is the number propellor manufacturers will be concerned with.
The gear reduction will match engine and propellor operating ranges.
The terrain and payload will dictate the hull requirements. A weight calculation should be made of the completed package and this will dictate power requirements. This would be a forward progression of a build. You are coming in sideways. :D You are starting with your engine...and hence, its limitations.
With these numbers, you should be able to calculate the load you intend to move based on the horsepower you have and the reduction drive needed for the intended propellor.
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Deano
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Re: Building an airboat around an engine

Post by Deano » Wed Dec 28, 2016 12:12 pm

glades cat wrote:Some good numbers have been used in the past. 4 lbs of thrust per Hp for a correctly propped power plant is about what is to be expected. Weight to Hp ratio numbers in the neighborhood of 5:1 have been in the ballpark. 1000lbs needs about 200 Hp.
Torque and Horsepower will always be equal at 5252 RPM. If an engine is designed to operate below 5252, its torque will always be higher than its horsepower. If it's designed to operate higher than 5252 the horsepower will be higher than the torque...because the RPMs in the formula factor favorably towards horsepower. Horsepower is the true measure of work and it is the number propellor manufacturers will be concerned with.
The gear reduction will match engine and propellor operating ranges.
The terrain and payload will dictate the hull requirements. A weight calculation should be made of the completed package and this will dictate power requirements. This would be a forward progression of a build. You are coming in sideways. :D You are starting with your engine...and hence, its limitations.
With these numbers, you should be able to calculate the load you intend to move based on the horsepower you have and the reduction drive needed for the intended propellor.
X2. Very Nice.
I tried to attain a similar end, but abandon the effort as it was turning into a book.

For an airboat application, that 'Prop Selector' has a lot in in common with Hogan's Goat.
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but it is not the path to knowledge; it has no place in the endeavor of science."
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Re: Building an airboat around an engine

Post by Alex A. » Wed Jan 11, 2017 9:08 am

glades cat wrote:Some good numbers have been used in the past. 4 lbs of thrust per Hp for a correctly propped power plant is about what is to be expected. Weight to Hp ratio numbers in the neighborhood of 5:1 have been in the ballpark. 1000lbs needs about 200 Hp.
Ok, but how about this: a crazy russian aero-sled on 300 hp diesel, two five-bladed props, wieghts about 6000 lbs and runs 40 mph on water. Here's the video. What is this? Magick? :scratch:

Sure, it's diesel, but if
glades cat wrote:Horsepower is the true measure of work
then there should be no difference... right? Or am I missing something again?

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glades cat
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Re: Building an airboat around an engine

Post by glades cat » Wed Jan 11, 2017 4:25 pm

Yea. You should be good to go. Get a nice hull built, put your engine on with a nice prop, get it all rigged up and you'll be running in no time. Take some pictures along the way. It will be a cool build. We'll follow along.
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Re: Building an airboat around an engine

Post by CarMotorBarge » Wed Jan 11, 2017 8:18 pm

That Russian airboat is the best running airboat that I have ever seen! The video definitely proves that. I think you should build an exact duplicate and use your 200 HSP motor. Given how well that Russian boat is designed, you will have plenty of power.
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Re: Building an airboat around an engine

Post by Olf Art » Wed Jan 11, 2017 11:03 pm

Airboaters tend to build their craft just the opposite of aircraft and yacht designers ...... they tend to say OK, I've got this 0-360 Lycoming, so how big can I build my boat?
An aircraft or marine designer will say, OK, I want my boat or airplane to be this size, and I want it to be capable of doing this and this, so how much engine will that take to get that done?
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Re: Building an airboat around an engine

Post by D.M. » Sat Jan 14, 2017 2:44 am

Russian airboat, Cummins Engine 6L torque 1000N · m at speeds digatelya 2000. A mass of 700 kg

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Re: Building an airboat around an engine

Post by Alex A. » Mon Jan 16, 2017 1:48 am

CarMotorBarge wrote:I think you should build an exact duplicate and use your 200 HSP motor.
That would be impossible.

Now I get it, it has everything to do with diesel. Also, I think using hp as primary input for designing is wrong. Speaking of that massive russian airboat, it's engine has approximately 2 times more torque comparing to equivalent 200-300 hp gasoline one, so there is no magick there, really. It just pulls 2 times more mass due to x2 propellers. While my gasoline 220 hp won't be able to pull two 6 ft props, most probably.

I think I need a solid 3d models of some working propellers to see if i can get the right numbers with solidworks simulaion.

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Re: Building an airboat around an engine

Post by glades cat » Mon Jan 16, 2017 4:48 am

It's amazing how the old time Gladesman built their boats out of wood and powered them with model T engines...and hauled all their building materials to build their camp. We certainly have a world of resources available in this day and age.
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Re: Building an airboat around an engine

Post by D.M. » Mon Jan 16, 2017 1:15 pm

EZ30 my craving 320-350 kg.sm.
https://www.youtube.com/watch?v=JPtHYSGPKLc

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Re: Building an airboat around an engine

Post by Olf Art » Mon Jan 16, 2017 1:59 pm

glades cat wrote:It's amazing how the old time Gladesman built their boats out of wood and powered them with model T engines...and hauled all their building materials to build their camp. We certainly have a world of resources available in this day and age.
It is, isn't it. One of the ways they got that done was to build a 'cargo' sled and tow that into the worksite behind their airboats. It was probably slow going at times, but it gotter' done. Good stuff.
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Re: Building an airboat around an engine

Post by OneBFC » Mon Jan 16, 2017 4:22 pm

Also, I think using hp as primary input for designing is wrong
Well, to be quite honest, power is the important factor, not torque, when designing a complete system.

Do not get fooled into thinking a low RPM / high torque engine will produce more thrust than a high RPM / low torque engine.

200hp = 200hp

Doesnt matter how you get there.

Now, if engine A is 200hp at an RPM that works such that it can directly drive a propeller without the need for a speed reducer (or speed increas), then it will potentially make a few % more thrust than engine B at 200hp that does require a speed reduction due to losses incurred at the reduction device of choice.

This is not to say that more torque is bad. Just that torque, by itself, is meangingless.

That 1000Nm torque diesel would be a terrible airboat engine in my opinion. Especially at 700kg? (Is that really its weight?)

Yikes if so....who here would advocate for the use of a 1400lb av540 as an engine?! :shock:

After looking at the last video posted, they measured around 330 kgf (approx 730 lbs of thrust). That is pretty close (but less) to the documented 800lbs of thrust a 220 GPU put out in a thrust test a few years ago.

Wish you the best in your build still....just trying to arm you with proper information!

Edit: had some posts mixed up. Fixed a few statements.
-Russ
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400+hp Ecotec, 12x7.6 DBDO, 80" 3B Maximus, 2.3 OX,85+mph, water = purely optional
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Re: Building an airboat around an engine

Post by CarMotorBarge » Tue Jan 17, 2017 7:38 am

Alex A. wrote:
CarMotorBarge wrote:I think you should build an exact duplicate and use your 200 HSP motor.
That would be impossible.

Now I get it, it has everything to do with diesel. Also, I think using hp as primary input for designing is wrong. Speaking of that massive russian airboat, it's engine has approximately 2 times more torque comparing to equivalent 200-300 hp gasoline one, so there is no magick there, really. It just pulls 2 times more mass due to x2 propellers. While my gasoline 220 hp won't be able to pull two 6 ft props, most probably.

I think I need a solid 3d models of some working propellers to see if i can get the right numbers with solidworks simulaion.
Put a turbo on that EZ30 and let her rip. Also you need to look at gear ratios and how they multiply torque. It isn't torque at the engine that matters. Ultimately it is torque at the prop after the gearbox that matters.
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