brewski

Hello, I am fresh into boats and I am building a Swamp Buggy. To give some background on myself, I am active in airplanes. I have 10 in the hanger from 4*'s to a 25% Pitts Special and from speed to 3D. This airboat bug fits well in that I have all of the necessary R/C equipment and I live across the street from 2 small lakes. I started this build on Sunday and I am getting close to being ready to paint. I did a 2 rudder mod and now ready to work out the engine mount. My question is does it matter, performance wise, if the boat is a pusher or puller. I am putting a freshly broke in Fox .40 on the boat. The obvious advantages are things like starting and better prop choices for pullers. I like the thoughts of the muffler pointing to the rear on a puller also.

crispyspa

welcome to the sport. I prefer pushers myself, but I do believe that a puller will outperform a pusher (nitro) just for the reason you stated....larger selection of props, and I believe there is a greater chance of overheating with a nitro pusher. Gassers are another story.

Mr Cajun Gator

I also rather the pusher. On nitro's with small cooling heads will have more chances of over heating, more so durning ground running, the same can go for some gas engines. At the same time gassers with fins on the flywheel with a shroud can run all day hard with out too much worry about heat.
There is a better selection of props for the pullers than the pushers, but If you match your hull to the engine the props that are available for the pushers you will get a quick boat. The MABA has been in contact with APC and MAS in efforts to get more selection in pusher props. The newer pusher prop is the 12" x 6" 3-blade works great on the .75 nitro. I GPS my Cajun Gator .75 nitro at 32.4 mph with the 12 x 6.
I don't have experience with the .40 fox engine. If it is a ball bearing engine, the MAS 9x7 3-blade prop would more than likely be your best choice.
edited prop size

brewski

Thanks for the replies. I have it mounted to see how it worked out. I like the looks as a pusher and will probably go that way. The Fox is a ball bearing motor. The only prop at the LHS for it was a 9X6 but that is going to turn up too much. I'll order a 3 blade MAS as you suggested. DO you guys run higher nitro to help with engine temperatures or is it even an issue?

Selph-Inflicted

Brewski,

I prefer puller set-ups. And in my opinion, they out perform pusher set-ups. For one, the prop runs in "clean air", it doesn't have anything obstructing the air flow to the prop, thus, making it more efficient. I have seen a puller flat bottom with a .46 run 40+mph. I have also seen .46 pullers out perform .61 pushers. With my SI3, we have seen 49 mph with a .46 and 53.3 with a .61, all are pullers.

Running higher nitro percentage will add heat. You can add castor oil to your fuel to boost the oil content to aid in cooling. I run 20% oil in all my engines. In my OS motors I run 15% fuel. In my Rossi's, I run 10% in my .40 and 5% in the .61.

joe2011

i am all most done with mine i will be running an os 25la this is the 2nd one ive had the frist one i ran an os max 35 with a puller on it and it booked i am going with a pusher set up this time i also he 2 of the 31" dunas air boats there a lot of fun good luck with yours here are some pic's of mine

asmithnc

Brewski, To answer your question I would have to say the pullers have the performace edge over pusher.

Why you may ask.

1 all if not most have cages.....extra weight
2 cage boats use air rudder. You lose the ability for straight line running. But they look great sliding around.
3 cooling issues.
4 prop selection poor. Finding the right prop for your boat is important. Small selection = possible performance issues
5 I have never seen any good speed 's posted with pushers
6 Look at the manufactored airboats on the market. All are pullers... this to me tells the whole story


I would only recommend pushers with gas engines.

Below is a picture of a flat bottom puller flirting with 45 mph. She is running a OS .55 AX.

brewski

That is FAST!

I have mine ready to run today. It is pretty fast inthe grass. Should be fun on water. I still have cosmetic work to do like filling in lines in the wood and repainting. Also going to add white stripes or a checker board. I have the motor setup so I can turn it around as a puller to see the difference. I don't have enough prop on it now with the APC 9x6. I have a 9x7 3 blade on the way. I will try to get pictures of it running today. This has been a really enjoyable project and will certainly not be the last of the boats for me.

asmithnc

I gald you have had fun on your project. I hope you have many hours of enjoyment in the future. Happy boating.

brewski

I ran the boat this evening. Went well but the engine is running to hot and not very reliable. I turned it around and made it a puller after I got home. I'll try again tomorrow.

http://www.youtube.com/watch?v=9-juxEs9OvA

jesupslanding

nice.. now for the dry run vids

asmithnc

Too bad she is running a little hot. Looks like she a very good attitude on the water.

brewski

I turned the motor around and it is much better. Runs right now. The next mod I am going to do is widen it a few inches on each side. I am going to angle it fom the bottom to the outer edge maybe 15 degrees so the extensions will not drag until I am in the turn and hopefully make it more stable.

Selph-Inflicted

Glad to hear that Brewski!

I know your gonna like the puller set up better. For one, you won't wear your motor and it'll last a lot longer for you. With a pusher nitro set up, you don't get the prop wash over the head to cool like it should. And since the airboats have more drag than an airplane, you get more static load on the engine, which generates more heat. And not having an engine that is cooling properly, its life and performance is shortened.

On my flat bottoms, I like to use 45* on the sides of the boat. This keeps the boat from digging in when cornering and keeps the boat flat when cornrning. Turn chimes allow the boat to drop one side of the boat and rock up the other side when cornering, which can cause your boat to "flip-flop" when taking a corner. Stay with 45* sides, you'll like how the boat stays flat when cornering, it makes for some nice controlled slides.

Keep us posted on your progress. And as Andy stated........Have tons of FUN!!!!

brewski

Been working on widening the boat. I am adding 4" total plus 45 degree sides. I have the side extensions built. I am going to glass the seams before mounting them to the boat. I am also going to replace the 40 Fox with something a little stronger. Maybe a Webra 40, Magnum 52 XLS or an OS 46 AX.

crispyspa

Nice mod....I assume those are chunks of balsa?

brewski

Thanks,

They are 1/32" light ply and top and sides. 1/16" on bottom.

crispyspa

WOW! That's some woodworking...making it look like a solid chunk. snaps. [8D]