Me and my friend are having an arguement on where to put the prop on an airboat we are building. Which is better to put the prop facing towards the front of the boat where it will have an undisturbed air supply (my opinion) or to put the prop facing backwards where (supposedly in my friend's words) it will be better. which is better and why

Which is better.... Puller or pusher? The motor are designed to pull so the prop wash will cool the head. Pusher relies on movement to cool the head. It's your call.. .. .. Puller are easier to build, Pushers need a prop cage to mount the rudders. Keep us in the know if you do a project. Andy

good point for me, but the arguement continues, anyone have any other reasons? it is electric, no head

Puller props are a dime a dozen. Pusher props can be very hard to find in your size. The right answer to your arguement may be who can find the right prop!

i think you may have just won the arguement for me, my friend is one of those people that always argues with me on things like this but if he cant find the right prop. but we are useing an electric motor, i dont know if he can reverse the direction, it is brushless and when he had it in his car it could not reverse. thanks for the reply but if you have any more please send them ... The arguement lives on...

I have a couple outrunner brushless motors with 3 wires and if you switch one of the wires it should run in the opposite direction . Then mount the motor backwards and turn the prop so the markings are to the front . On an electric you still have some cooling issues so the puller is the best option IMO .

I prefer puller props myself.

Good luck trying to convince your buddy. The best thing to do is just have a build off and race what you build.

also, he says that with the brushless there is less heat (i dont know why) so that might not convince him, if anyone still has some reasons , please send them

Pusher looks more original .... pullers look like someone got things backwards ...
IMO - pushers run better since they are directing the thrust at the rear-most postion on the hull rather than more towards the center , and since you want the hull to plane as good as possible , then with the thrust being applied to the rearmost section of the hull , it is easier to set ( prop thrust angle ) and plane out .

I build and run both styles of hull. The puller set up keeps the motor cooler while running under a hard load. The pusher has a better handling, due to the prop being closer to the rudders, given the rear of the hull better lifting. The puller will give more power while running the ground or other hard loads, because it will run cooler. Then again heat is an issue on the pusher set ups, but, not a realy big one.
As stated above, best way to solve the arguement is to each build and race.

Sorry Terbobob,
Check your physics, thurst does best when running through the COG. Whether it is pulling or pushing, the most efficient use of thrust is through the COG. some exceptions do exist, especially when there are more than one force being placed on the craft. For a standard boat, the best setup is a mid engine with a straight driveshaft (the engine sitting on the COG) The same goes for airplanes (although the engine is not on the COG on most planes, it is in the same line of thrust). With Airboats, the engine aloft works because there is a counter force of the hull pushing into the water, similar to having a multi engine setup on an airplane(where the force is balanced between the engines). This is what leads to most blow-overs, when engine force is suddenly decreased, and the force on the hull takes over. http://image.rcuniverse.com/gallery/...humb-33413.jpg is my latest boat. take a look at the engine mount - yes, there is a nut under the front motor mount. the COG of this boat is about where the radio box meets the fuselage (and in line with the engine thrust) http://image.rcuniverse.com/gallery/...humb-33405.jpg is my first boat, pusher, clearly the AOA on the Cowling can be seen. Although the engine thrust misses the COG (where the 'nose'meets the 'struts' - under the chin) it is only by a couple of inches, and still worked very well. Neither boat has ever blown over, and the yellow boat has only rolled (sideways) on dry land.

Try this - take an airboat, if a puller, hang it from the propeller hub, and look and the angle she hangs. Is the thrust line (gravity)where she wants to go (where is the bow pointed?) Conversely, with a pusher, balance the boat onthe prop hub, is the thrust line the way the boat wants to go?(again, where is the bow pointed?) Again some offset is ok due to the counter force of the water, but try to get the thrust to go through the COG. Most other concerns are for the build - where to attach the ruddres, heat concerns for the pusher, and of course personal preference. Personal Opinion - the pushers will handle better, due to the distance (leverage) between the thrust point and the COG, but this is the reason the yellow boat has the tail it does, leverage for turns. At this point, I would have to agree with the Cajun Gator, the best way to know for sure, is to experiment (build and race).
Sean

Pusher or puller????? The answer is in the engineering. You can make either/or out-perform the other, its all in how you want it to run and what you are expecting out of the boat. I like the puller set up personally, and I have no problems with heating or with the handling on my set ups. I can turn them in any radius I want...tight water-nuts or long sweeping turns. The key is finding what works best for you and how you want it to run. Some build for performance, some build for pleasure. I guess what I'm trying to say is....just build and tweak, you'll find what works best for you. The other factor is getting to know your boat and how it acts and reacts.

Good luck with your projects....Have FUN!!!!

what about for running on snow, me and my buddy live in michigan, half the year it will be on water and the other half it will be on snow and ice.

Watch out ...... they are the fastest on ice.

Myself....I am more of a ......."true looking" model guy. How many real air boats have a puller set up?
Although I am jealous of the performance that a puller set up seems to have.

I don't spend a lot of time around full size airboats, and I've never seen a picture of a full size puller, but that doesn't mean they aren't built.

I've been around full size boats alot, and there isn't a puller setup for them...JUST NOT SAFE, for the occupants. Although I wish it was possible....for I believe the pullers give better performance, but a pusher prop will move heavier weights easier.

I have seen my .46 puller outrun a .61 pusher. For me, I like performance, so I prefer the puller setups.

Side by side 2 boats built the same one puller the other pusher, the only thing different is a little more weight from the roll cage, they ran side by side, with the pusher having a quicker responce time in the turns. The next advantage of the pusher, it is easer to make a roll cage/prop guard look better.
Either set up, the main thing is to learn your boat, know what its going to do and when. If your going to race your boats, a good driver of a slower boat will out run a faster out of control boat on a course.
it may have been seen, a 46 puller out running a 61 pusher, I know of a 61 pusher that, flat out walk right over a 46 puller.

Sean , you can NOT apply water prop driven boats "rules" to those of an airboat ( when talking CG and thrust ) . TOTALLY different forces being apllied . And whilst an airplanes engine is FAR from being close to the CG and a water prop boat is right on it , how can you state what you have ?
The thrust created from an air-prop dictates MORE than JUST the angle of ride for an airboat . It also dictates LIFT ! ( if the speed is there ) JUST like strakes on a water propped boat ! And based on WHERE the air thrust is being apllied , as to HOW much lift is created as well . For an airboat , if there is any negative thrust ( prop angled down towards the front ) the hull will not plane , hence , there HAS to be created a certain amount of POSITIVE thrust angle ( front of prop angled upwards ) when the engine is mounted more center , to create LIFT to get the hull to plane out
If you honestly think this does NOT apply , the try flying one of those HYDRO foamies .... OR , over powering ( larger engine ) on an airplane .
THIS will show/explain/prove , my statements on prop thrust angle , position/location of engine and lift effects

Sorry Bob,
physics is physics, regardless of which craft it is applied. It applies to Ballistic missiles, as much as human body movement. to apply force to an object, not directed through the COG( and absent of any other force) will cause the object to spin. as I said before, airboats have two forces, the thrust from the engine, and the hull pressing on the water( the hull lifting out of the water is not a function of the water propeller pushing the hull up, rather the force of the water on the rake/strakes lifts the hull, or, how else do surfboards plane with no propellers?), which will conteract the 'spin' if it is not accounted for otherwise. This does leave problems, such as blow over, and less efficient use( read speed ) of engine power.
the Dragon ( my boat) is not the only one with negative AOA, http://www2.towerhobbies.com/cgi-bin...=LXBTC1**&P=ML of course is commercially made boat, assumeably with professional engineering, and also clearly shows the negative AOA. Positive AOA works very well with pullers ( again my boat, the yellow one) utilizes a positive AOA, but to pull through the COG. The negative AOA will work if with a pusher, due to the point of thrust being in the rear, but still thrust goes through( or is parallel to, ) the COG. although the aquacraft is a puller, the AOA is still parallel to the line through the COG. to look at it a different way, it is also parallel to the water, when the boat is at plane.

To relate one manufactured hull is not an example ...
Take a look at some others ... I have one where the thrust in VERY negative . AND , its manufactured !
but , none the less ....
All , in all , there are general rules of thumb , and then there are the exceptions .
Either way .
And FTR - comparing a surfboard , which utilizes an external force , also , can not be compared or exampled to/against airboats which are self-powered .

Gravity is a force too, just as much as the force from an engine, or sail.( what about water skiing? The force undoubtedly comes from an engine, but the water skier planes from the force of being pulled by a rope, balanced by the planing lift of the ski - no prop lift there) the point is, the surfboard planes without 'lift from the prop'.
I suppose you are saying the 'manufactured' boat you have does not plane? you say the thrust is VERY negative; does this imply the craft does not perform? because you also said that any negative angle will keep the boat from planing. which is it? you seem to have contradictied yourself, or passed it off as an exception; while I see two examples of 'manufactured boats' with negative AOA. this would seem to support that the 'manufactured boats' do it for a reason. One would assume that a manufacturer would do some research to give a modicum of performance, if nothing else to retain customers who are satisfied with the performance of the boat, rather than produce a dog of a craft that will give the company a bad name.

What I should have stated about it was ENGINE LOCATION. On an AIRBOAT , if the engine is mounted at the furthest back area possible , then YES , a NEGATIVE thurst WILL cause BLOW-OVER ( front raises up - transom gets pushed down ) With the hull I am referring to , the engine is mounted more towards the center and is tractor driven . ( and I was NOT contradicting myself ) And seeing as to HOW the hull does NOT sit "flat" in the water , then , yes , by all means , THIS is how you have to adjust the ride attitude of the hull . ( which ALSO applies to ski'ing and surfing - hence the reason WHY the rider(s) have to keep shifting their body weight and or position )
And back to the surfboard and now ski's . Since the source of movement is CONSTANTLY changing on ski's ... it does NOT relate . And with a surfboard CONSTANTLY having its CG relocated , this too , does NOT relate .
I was not trying to get this into a crapper session , but , one last note ... if the thrust angle and engine postion and location does not have a direct effect on the hulls ride attitude , then kindly explain to me WHY , there are SO many airboats that HOP ( porpoise ) whilst , others do NOT !
And FTR - do NOT compare REAL life-size airboats to the little guys we run .

Sure you can. As long as it is scaled down in perportion to the full size it is modeled after it will show the same characteristics. The lil boats use the same physics as the full size just on a smaller scale.
Try telling that to engineers, developers, or an architect. NASA, our government, construction companies, car companies, bridge builders, full size airplane developers, boat builders, etc., etc...... all use models for development and research.

The difference with the little guys is that we don't have occupants onboard the boat. That allows us to try different setups. Some of which would really jeopardize the safety of others.

I use knowledge from the full size world to build my boats and make modifications. I have friends that build custom airboats for a living, they also drag race them. They also build lil boats and use the same technology they use in their full size boats.

In the family business we have built 757 full size boats from 10' flats, up to 65' crew boats, speed boats and cruisers, I have built approximatly 150 R/C airboats (pullers and pushers) and about 75 of the R/C race boats(mono's, hydros and outrigger hydros). The little guys do have some comparison (just the simple basics/the looks) to full size boats. The only true way that the little guys can be compared to full size, is if you slow the little guy down to about 8mph. Example: trim tabs on a full size(15') may only extend 3" to 6" beyond the transom, which is very little when compared to 1" of trim tab on a 24" boat. the hp to weight/size ratio also has a large margin of difference. Now with this said, comparing a full size to the little guy can give you a small starting point.
Back to the little guys, you can place your engine just about any where you like on your boat as long as it is on or very near the center line of the boat, if the engine angle is matched to the placement location, this does not mean the preformance will be the same.
Starting points of the little guys, would be match the prop to the engine to the boat, then match the placement location of the engine to the boat, then the AOA to the way you want the boat to handle. Next you call up your buddy for a race and blow him out of the water.