AirBoat build

[Scott T]

Looks good, I like airboats.

Can you turn the fan around though? I mean just the fan on the motor shaft, not the entire fan unit. The way it's shown won't be efficient at all, so if you can't turn the fan, you'll need to turn the whole fan unit around. Personally I would have gone with a prop, but I'm a traditionalist.

Looking forward to your progress

[j.m.]

Your fan unit is mounted backwards!! Turn that sucker around, and you'll be good. Make SURE your turning vanes are securely mounted, that fan has some POWER. Not having them directly in the airflow is probably a good idea, thats a lot less strain on the servo(s). Have you bench tested it yet? Make sure it won't go anywhere...

Don't forget to balance the fan, just like a boat prop.

Lookin good!
Jon

[Chop]

oops

Your fan unit is mounted backwards!! Turn that sucker around, and you'll be good.

I don't know what you're talking about.
Do you really think it will work better if the fan is installed right?
Funny how it helps with the Center of Balance too.

Make SURE your turning vanes are securely mounted, that fan has some POWER. Not having them directly in the airflow is probably a good idea, thats a lot less strain on the servo(s). Have you bench tested it yet?

No, haven't tested it yet. That's my next step.

Don't forget to balance the fan, just like a boat prop.

The only balancer that I have is the Octura Boat Propeller Balancer, and the fan is too big for it. A quick check with a .25" rod showed the fan to be pretty close to balanced. I'll have to cobble something together to do it better. Maybe a trip to the LHS is in order.

[calcagno45]

What ducted fan is that?

Looks killer and to be a cheap and fun setup! What battery do you plan on running?

Or what brushed ducted fan setup would work in a boat that size?

[j.m.]

I wasn't sure if you knew whether the fan was backwards or not, but I will have to check with the engineer who designed it on whether it will work better the way it was designed to run... :P

You can use a GWS 60(?)mm fan on a boat that size if it's about 1/8 the weight of Chop's. I have an airboat made from a slab of 3/4" insulation foam 10"x24" with rounded bottom edges running off a GWS fan I got at my LHS. It was $10 for the fan and motor. It has a 380 size plain can brushed motor and I'm running it on a 3s 800mah lipo. Weight is around 8 oz, and it scoots along pretty well.

I wouldn't buy another brushed fan again though, because you can get a fan and brushless motor for the same price I paid. Check above, there should be a link to some fans.

[Chop]

Link to the fan I used.

[j.m.]

Just now looking at the pics on my pc, (was on my iPod earlier) and it's looking great!! The fin mounts look perfectly adequate, and very smooth. Awesome design!

The magnetic balancer from TopFlite should work good. It'll also work on boat props, car wheels, anything you need done. (most likely to be available at a hobby shop)
http://www3.towerhobbies.com/cgi-bin...&I=LXHY61&P=ML

Can't wait to see a video of this thing, it's going to SCREAM! Reading the first review of the fan, a guy reached 1080 watts with a 540L on 6s at 50 amps. You may want to fashion a foam (or other soft material) shroud to go over the fan. Something that adds an intake lip like this:

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=8686&Product_Name=EDF30_with_9000kv_Motor_Assembled__

And smooths out the mounts and ridges around the fan. No nice fans come with this option, mostly because they get mounted inside an aircraft that has a tunnel for the air to flow through (think fighter jet), but it shouldn't be too hard. Again, it's only optional and not necessary to make a shroud and intake lip.

[calcagno45]

Whats the rule on # of blades here?

[j.m.]

The more the merrier!

As long as the motor can handle it and the blades are reasonably sized. (Most of the times you get more blades with an increased aspect ratio [better efficiency] on higher quality and performance fans)

Look at this:

http://www.airplanegeeks.com/wp-content/uploads/2008/07/jet_engine.jpg

They wouldn't be thin if it wasn't good. (real airplane if you didn't catch that)

But with more blades you do get:
-More fragility
-balacing becomes much more difficult

[Chop]

Whats the rule on # of blades here?

I think the same rule would apply to blades pushing air as to blades pushing water – A 3.5” fan with 4 blades will push less air and draw less amps than a 3.5” fan with 7 blades.

[j.m.]

If the total surface area of the blades is the same, then the 7 blade fan will have much skinnier blades. A high aspect ratio (length to width) airfoil is much more efficient than a short stubby one.

The 4 blader would probably draw about the same as the 7 blader, but the 7 blader might spin at 1000 more rpm.

[calcagno45]

I'm thinking of a 5" EDF, KB45-10XL 1200kv on 10s. Should have some thrust! I'll either adapt it to a TC31 hull I have or make a Airboat like chop is.

Any thoughts?

[j.m.]

THERE ya go!! That's probably more appropriate.

[calcagno45]

Should have more thrust than 2 3.5" edf's.

[j.m.]

You gotta remember though, water has a lot of friction on the bottom of the hull, and using an EDF that's designed to be run with an airspeed of at least 50mph, your going to be overstressing it.