LOL yeap that was a wild answer on my part, had my head up my butt figured I get a answer while I was there. With almost 700 post, ya'll need to let me have one wild answer.
Ok lets get back to why this boat has to be run with a hard right rudder. All of the answers so for play there on little part. First is torque, the prop looking from the transom to bow is turning clock wise, making a counter clock wise force on the hull. Keep in mind that this force becomes less as the boat begins its forward movement and the engine/prop reaches its top rpm's. Now add in the weight of the piston and cylinder plug and maybe the coil on the port side of the center line of the boat. Thats so for 2 down forces on the port side. Now add in the extra cavitation on the bottom side of the prop as it passes, below the transome gunnel. Now add in a little twist of the engine stand as the engine is powered up(looking at the pics, if does give any, it will give so that the prop will slightly move towards the strbd side) adding to a left turn.
If the engine must be on its side, mount it on the opposite side, cut the transom down like you plan to in the pic above, install rudders that are a little larger. Place the battery pack on the strbd, side of the radio box. Set the engine so that it will make the boat turn a little towards the right(looking down turn the engine, counter clock wise)
All in all you built a fine boat, that just needs a little tweeking

No problem, Hal,
Everyone makes mistakes, guess it was just your turn. We'll let it slide, this time. LOL
I agree, it sounds like balancing and tweaking as you mentioned should do the trick.
Crispy - you should have one heckuva boat, be patient and try balancing the boat as Hal suggested. The results will be well worth it. Sean

WOW ! That's a lot to absorb,
Hold on.....[&:].......[][X(]..................[&o]............................................. ..............................................[8D]
O.K.
I did cut down the transom, (check out the "hay field" video's first couple of seconds) . so part of what you are saying is that the port side is too heavy, right? so,,,,what if I'd throw a couple of rocks in the strdb. side just for the sake of testing? If you remember, I did temporarily elongate the strbd rudder by 2" which seemed to only amplify the list of the boat while trying to turn ( although it DID turn a little better, not much ). as far as mounting the engine plug up/down/strbd, those actions might be a fabricators nightmare...but I think it could be done, which one would be best? I'm thinking piston down to lower the CG.

I have to say that if it weren't for you guys and this forum....I probably would've packed my hobby away, not for good, but i would have ignored it for a long time. Thanks!

Sounds like someone knows there PHYSICS. While other _ _ _ ' _ .[:-]

The only 'problem' with mounting the head down (or so I've read) is the possibility of fouling the plug faster. Putting some rocks in the starbord side may help, it may give you a good idea of whether you are on the right track. Keep in mind, the rocks will be a constant force, where the engine torque varies. This is why I suggested flaps(much like roll control with an airplane); with flaps in the propwash, the higher the RPMs, the more force the flaps exert(to counter the engine torque). Probably, a combination of balance and flaps will do best. Otherwise, let the experimentation begin! Good luck! Sean

Dogmoat,
I guess i misunderstood when you said "flaps" before. I now see what you are saying, did you have anything/place specific in mind of how and where to place flaps? would it be possible for you to "MS Paint" one of my pics and re-post it? would the flap have to be ran along with the throttle or be fixed ? would the flap need to have an airplane wing type curve ? or wouldn't it make a difference?

http://image.rcuniverse.com/gallery/...s/lg-38398.jpg is my latest boat. she has 'flaps' just under the 'armpit' ( behind where the stantion meets the fuselage) for the same reasons. for your boat, being a pusher, I would suggest attaching adjustable flaps onto the prop cage, or even on the rudders. They can be on the fly adjustable, but that would require a 3rd channel on the radio. simply make them adjustable, as you would trim tabs for the hull, and do a series of test runs, adjusting the flaps in between each run. See what works best. http://rcairboats.net/v-web/bulletin...pic.php?t=1337 this thread shows (somewhere) similar flaps. these are on the fly adjustable, if I remember correctly. as far as shape, I would say neutral lift (symetrical top to bottom). Good luck! Sean

Hello crispyspa
One of my first boat hulls twisted a little in the construction period.This led me to having to adjust the air rudders about 10 degrees to the left to correct the drift.
You mentioned that your first stage of hull construction did not go directly to plan.
May be you need to try a water rudder . Or just angle the engine in the opposite direction as to counter act the prop walk.
My theory is there is no such thing as a problem ! Just fix IT . And show us some Vids.Please! . That thing looks like it could kick AAAAARRRRRSSSSS

Actually ... no .. it is not incorrect .
I did NOT mean that the engine would rotate in your hand ... but rather the "feeling" you get of the engines power stroke .
If you doubt what I say , then do a simple test ....
Take that engine ... set it on a axis ( sideways - like the way that engine is mounted ) and watch that sucker spin sideways in a circle .
( sorry ... but it DOES happen . I JUST finished doing exactly thie with a TANAKA 16 cc engine )
Now , take the SAME engine , and place it up-right ... and it does NOT rotate like it does when placed on its side .
( tested and proved - sorry ---- need a video ?????? )

pretty much perfectly desribes the forces exerted by a gyroscope. If this is not what you meant, then perhaps you should brush up on communication with the english language.
Video? Yes, that would be entertaining. The last video you posted to 'prove your point' showed a boat that was either very difficult to handle (due to porpoising) or being controlled by someone with little experience. The second vid showed the same boat, involved in a horrendous blow over. Hardly inspiring, and not good for your arguement of stability in your boat.
On second thought, do nothing. I remove myself from you. Trying to bully and intimidate people into leaving threads, or even a website completely, (are you trying to ruin this website?) does not prove your point in any way, it just means people do not wish to deal with you. Yelling louder from the treetops, and saying it more often does not make it correct. I refuse to converse with someone who attempts to change the laws of nature and physics to suit his own ego.

I'm not exactly sure of what your saying about your experiment. Could you give us some more specifics.


What axis's did you use in your experiment?

Could you give us some diagrams of how each axis was set up and tested?

When you say the motor was then placed upright, is that indexed around the crankshaft? Or is the crankshaft indexed to another axis?

Did the motor have a prop attached or not?

If the motor spun, sideways in a circle; was the motor mounted to anything? Or did you crank an unmounted motor and set it down on the ground?

If it was an unmounted motor, was the fuel supply kept attached?


Yes, if you have video...lets see it.

I was undecided on what to try first, [&:] so...I tossed the proverbial dice and came up with re-mounting the engine with the spark plug down. started yesterday, about 1/2 done today, took a day of vacation for tomorrow to see if I could finish. Hopefully I'll have video of the " new and improved " model posted on sunday.....maybe even saturday, if all goes well.

We really need some snow up here so I can freeze my face off again. the last hull with this engine did an unconfirmed 42 MPH on snow,(see [link=http://www.rcuniverse.com/forum/m_3642333/tm.htm]speed test[/link])......I'm itchin' to see what this one will do.

The dice could not have rolled on a better place to start. I have no doubt that you will get this boat running well. It can be seen that you take pride in your work, keep up the good work, and try to stay away from the quick fixxes.

Excellent! Keep after it Crispyspa. I want to see what this bad boy can really do!

Crispyspa,

Good luck on tweaking your boat. Stay at it, don't give up. That is another "Fun" phase of rc airboats....getting the engineering right to get the boat to run like you want it to.

My latest step hull went through several trials before I got the step right....almost threw it in the garbage at one point. It pays to experiment.

Let us know how your progress goes.

Crispyspa,
Good luck! Hope you can get her dialed in quickly. Can't wait to see pics and vids!
Sean

Hey DOGMOAT ....
Do you even know what the heck you are talking about here ?


get the people you are referring to straight BEFORE you start flapping thos lips of yours ... since it is QUITE obvious YOU know nothing about what YOU are talking about ....
( boats flipping over AND porpoising ????? - you are a TRUE piece of work there DOGMOUTH )

I went and bought some toys today. a new digital camera, a fish scale, and,..............a radar gun . had to order radar gun online, but it was on sale with free shipping. $79.99

I also got the engine turned (pic 1) but it had a terrible glitch after doing so. had to sheild the throttle cable and ground it to the cage to get it to stop. (pic 2) *green wire* After I got the glitch solved, I went down to the water to test her out, I didn't take the camera along because it was raining. I hooked the fish scale to the stern and throttled up......anyone hazzard a guess on the pounds of thrust???

But it is with a heavy heart I say: "still won't turn right" [:@][:@][:@][:@][:'(][&o] *stomping feet-throwing things-having a general fit* soooooooooo I ran it in the hay field to make myself feel better. LOL

Maybe tomorow, weather permitting, I can shoot some video.

Can I see a pic of the motor mounts and how the engine is connected?

Chris, I also found some specs on my engine:
YEAR INTRODUCED: 1986
YEAR DISCONTINUED:
ENGINE DISPLACEMENT: 2.4 cu. in. (39.3 cc)
NUMBER OF CYLINDERS: 1
CYLINDER BORE: 1.563 in. (40 mm)
PISTON STROKE: 1.250 in. (32 mm)
CYLINDER TYPE: Aluminum with chrome plated bore
INTAKE METHOD: Reed valve
MANUFACTURER ADVERTISED H.P.: 2.16 SAE @ 8,000 RPM
WEIGHT : 9 lbs. 12 oz. (4.4 kg.) powerhead only

any guesses on pounds of thrust? anyone.......anyone.....?

12x10 prop @ 8700rpm = 4.81 lbs of thrust aprox .( static test)
Max prop speed (Dynamic Thrust test ) 12x10 @8700 rpm 87 mph.
These figures are from rc airplanes tests. Not my own. Anyone else

Just for the fun of it, add some weight in the front of the hull, about 5lbs. Try to keep the weight in the center. Run the boat and see if it makes any difference. Looking at the close up pics, it looks like there is a lot of weight on the transom. If too much weight on transome and the bow is lite, this will cause the hull to sink to much in the rear. For the extra weight it takes extra displacement to float the boat, the less displacement the greater chance of rolling. The 5lbs of added weight to the front is just a quick way of testing, if it helps in the problem, then move the engine and cage forward. The 5lbs is just a rough weight, testing with different weights may be needed.
Hopefuly this will remove some of the leverage the engine has gained from the displacement.
Off subject just a little, reading back over the post here, it proves that the airboats are not just fun boats, there is a lot too them, that many do not realize. This statement comes from hearing in the past, that airboats are just fun boats.

Is it possible teh rubber mounts allow the engiine to twist when powered up? If so this can change the orientation of the prop to the hull while under power. If the prop is parallel with the transom at low rpm's, then when powered the prop walks a bit causing the undesirable condition.

Try this. Keep the boat stationary, get on one side of the boat. Power the motor up and keep an eye on the prop. Notice if it moves in orientation.

got some video today,
[link=http://www.rc-airboats.com/gallery/view_photo.php?set_albumName=new-quarter-scale&id=test_with_flaps]test with flap[/link]
[link=http://www.rc-airboats.com/gallery/view_photo.php?set_albumName=new-quarter-scale&id=street_crash]street crash[/link]
[link=http://www.rc-airboats.com/gallery/view_photo.php?set_albumName=new-quarter-scale&id=pounds_of_thrust_002]pounds of thrust[/link]

nope... at least very minimal ( maybe 1/8 " )

Mr. cajun, did not try the weights thing yet, but I did put a flap on, did no good[:@] .

the boat weighs 29 pounds, thrust is at 17 pounds, what is the ratio supposed to be? and is mine too much? Maybe I am overpowered