oceansfiftyseven

Hello, I am building my first airboat. I have come to the part where I need to choose an engine so I can make the stand and rudders. I origionally planned on putting in a TT .15. But now I think it may need more power. I also have a .25FX available too. I would like to use a 7x4 3-blade on the .15 or an 8x6 3-blade on the .25. Both these engines turn these props at about 15,000 rpm. My boat is built up from 1/16 balsa. Double sheeted all around. Then 1 layer of 1.5oz glass cloth. 2 coats of epoxy, the primer and paint. Dimensions are 21x12. Weight as pictured is 19 oz. Which engine would you choose and why? Will the .25 make it too top heavy? Also, what about thrust angles and balance? Thanks, Richard

saleens7

looks pretty good, i would say use the .25.....boats that big have been used with .46's with good results....

but they have a wider running surface, yours looks to be about 7-8" of flat on the bottom, it may be a bit unstable, but i would try it anyway....you can mount the engine upsidown or sideways(with the exhaust under the engine), to lower the CoG....

the balance point should be around 25-28% the length of the boat from the transom....or around 5-6" from the transom....

it doesent need to be precise as the balance point can be adjusted by changing the AoA of the engine...(youll want a bit of a downward angle to keep the bow a little in the air, but i would start out with it level and then adjust it and see wether it runs better like that...

ive heard that the engine should be pointing to the right a few degrees to counteract the effects of the tourque, but i find it easier to just make the engine mount square with the hull and trim out the rudder until it keeps it strait....

oceansfiftyseven

Thanks for the great advise. The flat part of the bottom is only 6 inches. Then it angles up 15 degrees for 2.5 inches on either side then a sharper angle for the sides. Origionaly I was going to use a 6x4 prop so I only made the flat part 6" wide. I used the shallow angle on the bottom as I thought it might help it to slide rather than dig in to the water or grass. It should have stupid power with the .25. At least 1 to 1 thrust to weight ratio. hmm...

air-madness

Yeah, saleens7 is right. The few degrees (2-5 degrees) right is recomended, but, I too have just used the rudder and trims to counter this phenomenom.

saleens7

only 6" wide?

the rule of thumb for an airboat is that the bottom running surface must be atleast 2" wider than the prop (1" on each side)

your will still work, but there is a chance it will be unstable in turns....there is also a chance that you WILL flip this boat at one time or another, so make sure you have the radio box sealed up....

vamp131

Hi looks fantastic angle the engine down a little bit nose cone towards the front mount the engine as far back as possible use an air filter stops water getting into the engine and stopping it i have not had any problems since fitting an air filter when you 1st try it use swallow water grease up the servos make sure receiver is water tight too put it in a nice sealed box a fishing rod is handy too lol to get it back

The advice given on here is very good helped me a great deal

with my boats but it is great fun!! better take more pills lmao

oceansfiftyseven

Yeah, 6" is pretty narrow but I thought with the shallow angle on the bottom the running surface will be 11" as the deadrise is only about 1/2 an inch. I thought a little rise would help keep it from rolling over on grass. Our flying field gets pretty soggy at times so I thought I would build a couple of these little airboats for me and my buddies to race around when it is too soggy to fly. It will also be run on water as a coworker of mine is building a tiny little tunnel hull with a TT .12 inboard engine and we have this competition thing going. We both work on yachts for a living so we are around water all the time. Should be good fun. It sounds as though my boat will be a little unstable so I will probably mount the .15 on this one and change the bottom design a little for the next one. What is the recomended hull shape for an airboat? Should It be flat all the way across the bottom? Or is a little deadrise good just not so much? Thanks.

rickburnout666

looks good O`s57, but i would fill the hole ,flip it over and use it as a tunnel hull, but i do like to do things different as you might have seen in my thread.
http://www.rcuniverse.com/forum/m_5220872/tm.htm
No its not finished yet , i`ve broke my collerbone again, and working on the boat is a bit tricky at the moment.
The .25 engine will hardly add much weight, the boat with everything attached, will probably just sit on the water rather than in it, get all your parts you will use, put them on the hull, and see how it floats, plus you can do the balancing and get the ride level right .

oceansfiftyseven

I thought about turning it over too but nah. I will finish it and see how it goes. Here are some more pictures of the motor pod.

oceansfiftyseven

Well it is finished. I used the .15. I have run it on both water and grass. It works alot better than expected. There is a video of me running it on grass for the first time in "the other" forum in the boat video section. Rich

rickburnout666

Have you got a link to the video, as i can not find the "other forum" ?

oceansfiftyseven

Sorry guys. I didn't know if the would let me post this but here it is: http://www.rcgroups.com/forums/showthread.php?t=681794 Thanks, Rich

rickburnout666

That`s pretty good for your first airboat build, it should really fly when you get it on the water [sm=thumbup.gif]

codtongue

great boat !!! I love running on the grass, that one of the things I like most about the airboat, you can run them anywhere, I took one of mine to a party at my brother inlaws, it was the hit of the party, everyone got to try it, everyone wants one. its the best.

Mr Cajun Gator

They can build their own or they can get one of these.

codtongue

I threw in a plug for ya, gator. One of the guys there said that my boat was'nt to scale, and that the real airboats look different than mine. ( i bit my tongue and said " i guess I'll have to build another") so we went online
and I showed him some your boats, to which he replied "thats what I mean".

Mr Cajun Gator

Thanks Man Get'um all invovled, build buy, it don't matter, just get them into the airboats.Then watch the fun unravel.

oceansfiftyseven

Well after playing with my air boat for a while I was racing a Revo 3.3 in the grass when my boat was run over. So I decided to do something different. I pulled off the engine and mount and set it up for a wemotec Midi Fan. It is now running a Mega 22/30/2 with 5s3700 lipos. Initial test results with the wattmeter put it at a little over 940 watts. The boat now weighs 3lbs 10 ounces ready to run including the battery installed. What do you guys think?

saleens7

i think i need to see a vid of this...

TERBObob

My Feedback: (21)

[sm=50_50.gif] Don't think you'll be as happy with the EP . Think the little 15'er will do better[sm=what_smile.gif]

oceansfiftyseven

Well, I ran her in the water today! Steering was much better than before and the power was insane. I could only advance the throttle to full and imediatly back her down. It will start to catch air as it spools up. The last run I was going pretty fast and spun it around and ran into a customers Cobalt while going backwards. No damage to the Cobalt but I broke off both rudders though. I will repair her and make video. But I wont have any video until this weekend. Mr. Terrobob, It was alot more fun on EP. Sorry. Rich

vamp131

Get the biggest you can get I have just fitted a 61 wow nearly flys lol try get a nearly new engine stay away from the unkown ones Irvine is a very good engine i have 3 lol

oceansfiftyseven

Well I managed to get some video of her on grass today before I fried the Pheonix 80 esc. Rich
http://www.rcgroups.com/forums/showt...15#post7599773

Tommy gallagher

WOW im speechless Ocean, that thing be out in a jiffy

I think you got a winner there. If i were you i wouldnt even go back to the .15 engine no way. Imagine what that thing will do on water.

Anyway what happened to the ESC. Did it burned down because of this setup or what.?

Tom

Tommy gallagher

And most of the airboat guys here say ohh it wouldnt work well enough its not efficient enought. Look at that thing, as long as your boat is light enough and theres a good fan on top powering it your good to go