shem

I am trying to figure out some handling issues with a RCMK Stealth hull powered by a RCMK R254 engine.

1) While making a right turn with a constant rudder input on the radio, the turning radius of the boat will tighten by it self while maintaining the constant rudder input on the radio. Have tried reducing steering EPA, but with same results only the radius is larger. This is more pronounced when the hull leans over to the side of the hull "V". In real extreme cases, while full steering input the boat will just hook and make a really really tight turn.

2) While the boat is turning, when the steering on the radio is release to return to the neutral point, the boat will continue turning for a while before it straightens out. Have tried opposite steering input at the radio but does not seem to react, but when it does the boat direction scarily snaps over.

Initially its thought to be a weak servo causing this, check and rechecked, and checked the battery level all good. Its a Hitec HS-7955TG.

Typically what causes this kind of ill handling?

martno1fan

If you say you have checked your servo and pushrods then all i can think of is prop walk,is the drive offset to the right or central?.Are there any bends in your rudder pushrod that can flex under load?.Prop walk makes boats veer right especially if you have a very blunt unbalanced prop? or the prop is too big etc.Usually on a mono we offset the drive 1/4" to the right of the keel to overcome any prop walk or torque steer.Spinning out is usually caused by too much rudder throw,you only need arround 20-30% travel on the rudder blade sometimes even less a lot depends on the hull as all boats are different ,turn fins can help make turns smoother not sure if you have those or not?.How about a few pics of your setup and especially of the prop and pushrod etc?.
Mart

dicko

Is your rudder kicked forward or back? and how far back off the transom is it? A few guys at my club run the stealth with out any issues. They run them without tabs or fins & they run quite well. You could try emailing the guys at Adelaide Model Boat Center as they've had a bit of setup time with that hull & have it running quite well.

http://www.adelaidemodelboatcentre.com/

I know they run the stinger in the center with it slightly angled to prevent prop walk. They are also running through hull water pickups on their hulls as well as rudder pick ups.

danielplace

Sounds like you don't have enough steering servo torque. As the boat slows down it is finally able to add the rest of the steering input you actually told it to initially because the hull speed dropped enough to overcome the force of the water. Try moving the steering pushrod closer to the screw on the servo horn and it will increase it ability to turn the rudder a speed. Nothing is binding? Running 6 volts?

Daniel

shem

Martno1fan,

We tried to fix the propwalk by tilting the stinger, it did help on the straight line but not much on the steering characteristic problem. Pushrods are straight, props sharpened and balanced. I dont think the rudder throw is excessive because this problem happens even with very little steering input. It becomes pronounced the moment the hull leans over even without maximum rudder input. Its not spinning out, but rather the turning radius tightens by itself. Its impossible to hold the boat to turn on a constant arc.

While the boat is turning, the bow comes down and the hull is wet. It appears that while its turning there is a lot of lift at the transom causing the bow to bite and the transom loosing traction. Could this be it? How to fix this?

We will be trying with a larger turn fin this weekend to see if it helps. I will try to get a picture of the boat.

Dicko,

The rudder blade is neutral. The rudder and stinger are from RCMK. Not sure of its length. However the length of the stinger has been fully extended so the rudder LE is about 3mm behind the LE of the prop. We have tried to have the rudder LE just after the LE of the prop but it did not help.

I will try to reach out to the guys in Adelaide Model Baot Centre and see if they could help.

Danielplace,

The servo is 333oz(24kg) torque and running at 6V. Nothing is binding.

dicko

Daniel,

I was just there & had a chat with Dale about it. He doesn't run the strut in the center any more. He runs it offset almost 8mm to the right & uses th longest stut & rudder mount that RCMK sell. This has solved the problem that he had with steering issues. I've attached a pic of the back of Dale's Stealth for you to see where his mounting holes are. I forgot to ask what prop he was running.

Hope it helps

Cheers
Jason

Scott Schneider

What your describing is referred too in model boats as "Hooking"
Typical causes are ......

*Prop NOT sharp enough, causing a prop walk issue that lifts the transom.
*Too much down trim tab angle, again lifting transom allowing prop to walk.
*Rudder kicked back excessive amount, again causing transom lift and prop walk & bow dig in.
*CG of hull to far forward having the bow of boat dig in as hull leans over.

** In part or combined, ALL of the above will have degrees of this effect.

martno1fan

Id look at what Dicko posted thats the typical position for the tube to exit on most monos,this will help a lot and also as Scott says a sharp prop and having the correct angle on the prop and or Rudder are good places to start.My stepped vee used to do it i solved it by tilting the rudder in a tad this will lift the bow and keep it up in the turn better.Also check your cog you want it arround 28-32% ,any more than that you might find it hard to get the nose up.
Mart

Ron Olson

My Feedback: (1)

I'd go with the fourth one on Scott's list as the possible problem but the one that I'd want to fix last as it involves more work. The first 3 are the easy ones to check.

shem

There is lots of good info here, really appreciate it.

I think CG is the main culprit and to try it out, we will add some weight at the stern and see how it goes.

Thanks again guys.

danielplace

Didn't quite pickup on the issue at first.
Yep, now that I read more it sounds like the all to familiar hooking and bow steer that mono's like to have. Seducers do that a lot till you get them just right. The bow digs in and steers the boat tight.
Lower lift props and more positive strut or even Cg back some can all help stop it. All as already mentioned.

Glad your getting her worked out. Really tough to drive when their doing that.
I've messed with plenty of mono's but just recently purchased my first one in almost 25 years. Just got a new Lazer 45 and have a full mod RCMK in it.


Daniel

martno1fan

Another thing to check is the hull itself,check there arent any hooks or rockers in the ride surface,lay a small straight edge along the ride surface starting at the keel and work out towards the chines where the bottom meets the sides.If there are any gaps under the straight edge then you have a hook but these usually suck the hull down not what you describe, if you have a rocker or raised spot that is your probelm,this can be fixed by sanding flat.My money would be on a rocker in the last few inches of the bottom near the transom creating lift and pushing the bow down,make sure its dead flat and a sharp edge not rounded seeing as you seem to be bow steering.Just check the hull ,hopefully its not your problem and just a cog issue.I know a mate of mine had similar problems with one of the forabuck monos called the cobra and it was put down to the hull not been true.Good luck!
Mart

dicko

Mart, not sure if you've seen an RCMK hull, they're pretty straight, I doubt it would be that. It's more likely a COG issue or rudder kicked back issue.

martno1fan

Nope never seen one not that i even knew what the heck a stealth was,but that said no two boats are alike you cant be certain its straight just because most are .Wasnt saying this one isnt just giving another example of what could be wrong so he can cover all bases so to speak.I also mentioned before i felt the cog could be the problem,on some hulls its critical and even 1% out can make all the difference.
Martt

shem

This is great info here. Some of which did not cross my mind and the info provided serves as reminder. This will keep me and my buddy busy this weekend at the lake. Will update you guys our findings.

Thanks again.

shem

Its CG problem. We gradually added weight at the transom and each time when weight is added the problem was less pronounced. We went on adding weight until the the problem went away! By that time the total weight was 180grams.

We now know where the CG point(26cm from transom) is on this hull and will use it as a reference point for the future RCMK Stealth builds.

My buddy now drives the boat with a big smile on his face.

dicko

Glad you got it sorted.