Airboat propeller

[Who BootParticipant @whoboot]

Hi

I have recently built an airboat from scratch, made from balsa wood and it weighs 2.6kg with all the equipment in situ. I would like some help to try to make the airboat faster.

Here are the equipment I have fitted it with:

• Proboat 25-inch 3-bladed propeller (the same as in a commercial built model airboat called Aerotrooper)
• Hobbywing Quickrun 10BL60 60A ESC
• Leopard Hobby brushless motor, LC3536-1520KV
• Li-Po 2200mAh, 11.1v battery

I have so far only given it one run on the water, and after having waited for the right weather for several weeks, I was delighted to just see it have a run. Initially I was pleased with its fastest speed, but I discerned that it was losing speed as the minutes ticked by. I am not very knowledgeable about the nature of batteries, but I believe a craft will slow down as the battery capacity drains away, right? Through being cautious with a new Li-Po battery, I had not fully charged the battery, that’s for sure, and I wasn’t surprised that its duration was not long – it lasted about 10 minutes when I was intermittently on full throttle. I slowed down or came to a stop when navigating between other boats on the pond, but put it on full throttle when the going was clear.

I would not say I was disappointed with the initial speed of the airboat, but it was not as fast as I had envisaged and slower than some other airboats I have seen. Not that I want mine to fly at 90mph. A more experienced modeller than I talked about all kinds of permutations I could do to improve performance, this through combining various motors, batteries and propellers together, and even different ESCs. However, he said that the cheapest way to start experimenting is with different propellers. I wonder would anybody who knows more about airboats than I care to look at the equipment inventory above and see what they think, especially as regard to propellers as that is the cheapest item to buy? I am only beginning to understand how important a propeller is to an airboat, as also to aircraft, and that it is not just about the battery and motor. A propeller can even make or break an electric motor; if its an unsuitable one it can overwork the motor and drain the battery too quickly.  I’m not knowledgeable about propellers but I know more than I did a week ago. I have no other propellers at the moment to swap with the one I have attached.

 

 

 

 

 

 

 

 

[Dave ReedParticipant @davereed72029]

Hi,

I’m no prop expert but as you have no replies yet, here’s a thought to get you started.

If you look at your motor manufacturers web site you will see a recommendation for a 9×4.5 inch prop at 11.1v. That’ll be 2 blade, so if you want 3 blade it’ll be about 8×4.5. Not sure the diameter of the prop you currently have but would guess about 6.5 inch? If there’s not enough room for 8 inch you could try smaller with more pitch (eg 7×5) but until you get advice from someone more knowledgeable, it’s trial and error.

Dave

[Who BootParticipant @whoboot]

Hi Dave

Thank you very much for replying, very thoughtful of you. Your reply is a starter, a very good starter. I had not thought of looking to see if there were anything said about propellers on motor manufacture web sites. It doesn’t say on my propeller or its packaging what size it is, but I’ve measured it from one blade tip to another as 5 1/2 inch. Is that how you get the size? I believe that 7 x 5 means the 7 is the length of the prop, and the 5 is the pitch size, am I right?

[Dave ReedParticipant @davereed72029]

measure from centre to one blade tip then double it for diameter. Blade tip to blade tip only works for 2 blade props. First number is diameter, second is pitch.

[Dave ReedParticipant @davereed72029]

Take a look at the “Cajun Commander” airboat for ideas, it has a similar size motor and decent performance.

[Who BootParticipant @whoboot]

Thank you very much, Dave. With the information you have given me, I’m growing more confident in my knowledge of props. My 3-bladed prop is 3 inch from centre to tip, double it, and therefore it is 6 inch. It’s getting late tonight, so I’ll have a look at the Cajun Commander tomorrow and let you know.

[Ray Wood 3Participant @raywood3]

Hi

I fly aeroplanes with the 3 cell Lipos 11.1 volts I think your doing well if you get a 10 minutes motor run 🙂

Regards Ray

[Who BootParticipant @whoboot]

Hi Ray

Thank you for sharing that. I haven’t flown a model aircraft, so I have no idea. I’m guessing that your aircraft is quite a performance one as its duration is so short?

My battery was not on full charge when I gave my airboat its first runabout. But quite how far charged it was, I don’t know. I’ll find out more about my airboat’s system next time.

[Who BootParticipant @whoboot]

Hi Dave

I have looked at the specifications of the Cajun Commander airboat you mention. As you say, the specifications is similar to mine, about the same length, beam, height and weight.

One difference in equipment is the KV of the motors: Cajun is 1800KV : mine is 1520KV.

The Cajun’s propeller is 9×7 3-bladed FRP : mine is 6 inch long but don’t know its pitch value.

Battery is not included with the Cajun but recommends a 2200-5000mAh : mine is a 2200mAh.

So there is scope for a slightly stronger motor and a battery with more capacity. The propeller is still the unknown factor for me. I am awaiting a reply from a company called 4-Max who advertise model aircraft things in the RCM&E magazine, where I have asked for advise on propellers. They sell propellers and wondered whether they could suggest a better prop. I would buy one off them.

 

[Colin BishopModerator @colinbishop34627]

As one of our other members Ashley, would recommend, you would find a wattmeter very uiseful in measuring and calculating current consumption and running times using different motor/ prop combinations. Otherwise it is just hit and miss guesswork.

Colin

[Ray Wood 3Participant @raywood3]

Hi Who,

Give George Worley a call at 4 Max he will tell you straight away what prop / motor combination to use , my electric aeroplane is a Chris Foss designed Acrowot moulded in polystyrene I’ve been flying it for 10 years, I know when its running low on power it won’t climb, so time to land 🙂

Regards Ray

[Dave ReedParticipant @davereed72029]

Hi, It looks like George Worley at 4 Max could the “more knowledgeable” person I mentioned earlier. I still think you need to go bigger than your current prop but bear in mind that if you go too big, you’ll end up turning power into heat in the motor and ESC.

Dave

[ashley needhamParticipant @ashleyneedham69188]

As Colin says…use a wattmeter…instant visibility of how much load you are putting on the motor.

Try using a smaller pitched prop as well. Air boats don’t go as quick as aircraft so will benefit from a lower pitch.

Say….7×4 rather that 7×5…or 6×3 instead of 6×5.

It will allow the motor to rev more. Wattmeter…buy one now!

Ashley

[ashley needhamParticipant @ashleyneedham69188]

Who.

Can you post a picture please and tell us some dimensions.

2.5kg is very heavy for an airboat and may be your issue.

Fitting a bigger prop has issues of its own, like increasing the torque reaction and turning the boat over!

Ashley

[Author]

Posts