rudder problem 21 mono

[petdos]

Hi to all,i have a 21 mono (in aus its called a delta style hull),1/2 throtle or so no probs but open up it digs in like it grabed the water and does donuts(left or right dosnt matter) ,back off, straighten up and your off again, then do it again ,have changed props,changed servos,turn fin- off/on, dosnt matter,only thing havnt done is change pos of rudder,at present it is 15mm behind prop (towards transom)any sugestions greatly appreciated thanks peter.

 

[Tall Fella]

Hello Peter .

I noticed that you have the same question on the AMPBA Forum ( Australia ) and this time you included a picture . While not having run a mono in many years , my guesstimation is that the rudder mounting bracket is flexing on your boat . I leave it the other members to provide you with some more input . Due to the activities of some people after the end of the 2009 AMPBA Nationals in Penrith on last Sunday afternoon , our club no longer has a motor for the rescue boat , generator or air compressor , which was noticed on Monday morning . Our next scheduled practice / race day is June 14 / 28 , unless we are granted a extra day this month . So why not bring it out and show us your problem boat .

Regards

Ian Baas

Tall Fella Racing

Australia

 

[petdos]

Hello Peter .I noticed that you have the same question on the AMPBA Forum ( Australia ) and this time you included a picture . While not having run a mono in many years , my guesstimation is that the rudder mounting bracket is flexing on your boat . I leave it the other members to provide you with some more input . Due to the activities of some people after the end of the 2009 AMPBA Nationals in Penrith on last Sunday afternoon , our club no longer has a motor for the rescue boat , generator or air compressor , which was noticed on Monday morning . Our next scheduled practice / race day is June 14 / 28 , unless we are granted a extra day this month . So why not bring it out and show us your problem boat .

Regards

Ian Baas

Tall Fella Racing

Australia

Thanks ian,put it on both ,get the broad spectrum of ideas,see ya at the next meeting,peter.oh ye,the upload of pics is different on ampba site.

 

[Ray Sametz]

Peter, rudder bracket looks fine, but that 90 degree bend in the push rod is a problem. Flexing too much!!! MHO. B) B)

 

[Sean Bowf]

When you changed the rudder servo, did you swap it out for the same model of servo?? Which model of servo are you using?? I had a similar problem (would not come out of a turn too well) and it was the servo...I swapped for a stronger one and have not had the problem since.

Sean

 

[Mike Hughes]

Are the trim tabs flat with the underside of the mono? They kind of look like the start flush with the transom but than they go below the ride plain of the boat. This will push the bow down. One looks to more than the other. These should be flat with the boat of the boat and just slightly above. 1/32 or so. Where is the strut in realation to the keel? It to should be level with it or a little kicked up in the back. If it is kicked down, it will push the bow down.

Mike

 

[Mark Bullard]

Hi to all,i have a 21 mono (in aus its called a delta style hull),1/2 throtle or so no probs but open up it digs in like it grabed the water and does donuts(left or right dosnt matter) ,back off, straighten up and your off again, then do it again ,have changed props,changed servos,turn fin- off/on, dosnt matter,only thing havnt done is change pos of rudder,at present it is 15mm behind prop (towards transom)any sugestions greatly appreciated thanks peter.View attachment 13143

I disagree with all the answers that have been posted. They were all good answers but everyone look at the size of those turn fins. Remove the turn fins and try and run the boat. If this works reduce the size of the turn fins. About 1/2" long and 1/2" deep and about 0.032 thick would be all you need for a 21 mono.

 

[SayMikey]

Hi to all,i have a 21 mono (in aus its called a delta style hull),1/2 throtle or so no probs but open up it digs in like it grabed the water and does donuts(left or right dosnt matter) ,back off, straighten up and your off again, then do it again ,have changed props,changed servos,turn fin- off/on, dosnt matter,only thing havnt done is change pos of rudder,at present it is 15mm behind prop (towards transom)any sugestions greatly appreciated thanks peter.View attachment 13143

I disagree with all the answers that have been posted. They were all good answers but everyone look at the size of those turn fins. Remove the turn fins and try and run the boat. If this works reduce the size of the turn fins. About 1/2" long and 1/2" deep and about 0.032 thick would be all you need for a 21 mono.

Mark ya beat me to it. Id at least remove the right one as its next to the rudder

 

[camaroboy383]

He had already stated he tried it with no turn fins and still does the same thing.

How is your cg 30%? To much wieght in the nose will cause this when the prop has lifted fully.

Also what props you try??could need a lower lift prop??

Then like mike said,, check your strut angle.

Alden

 

[Mike Hughes]

Saw that too. Reread his post. Turn fin on/off.

Mike

 

[P THOMAS]

If that tube running up past the strut is the antenna, move it off the transom. RF noise from the shaftor pipe can cause boats to do strange things.

 

[Ron Olson]

I see a case of a wimpy rudder linkage not to mention the bend in it which had already been covered. Nothing but 4-40 with anything .21 and over.

 

[petdos]

I see a case of a wimpy rudder linkage not to mention the bend in it which had already been covered. Nothing but 4-40 with anything .21 and over.

Thanks to all for your input,pretty much all the sugestions have been done ,will change wimpy linkage,servo was not the same,its actually the metal geared 20+lb off my outbard,used just to eliminate source of problem,after all everyone has said,i to am starting to look at the linkage,goes flat out straight no prob,long arching turn,no prob,just quick turn at full speed,anyway, again thanks to all, will keep trying" WE WILL TRIUMPH".

 

[M@MRacing]

20lb servo is not evn close to enough on a 20 mono

 

[nitrotwin]

320 ozs wow!

 

[Michael Costanzo]

20lb servo is not evn close to enough on a 20 mono

hey bro, do not evn use a 200oz servo in my 90 mono! i think maybe he was trying to say the newer servo is got 20oz more tq than other servo?

 

[petdos]

Sorry fellas i beg to differ a little on this one ,12.5kg or 27.5 lb of torque should be more than adequite for a 20 mono,anyway thanks again ,will see what hapens on the weekend ,have put a straight peice of 3ml music wire,lets watch that bugger bend,see what happens hey,all the best ,and thanks again,peter.

20lb servo is not evn close to enough on a 20 mono

hey bro, do not evn use a 200oz servo in my 90 mono! i think maybe he was trying to say the newer servo is got 20oz more tq than other servo?

 

[David Kingston]

Are you using 440 pushrod or larger.

when you have the radio box locked into position, grab the rudder and twist side to side. Notice any flex i the push rod.

Try stiffen it up where possible. 1/8th brass tube i think is the nice size that fits 440 push rods through, adding a sleve in will stop any push rod flex...

flex under pressure can cause radical hooking - ive had that issue.

change to a MG digital BL servo 15kg and that made a difference also in my mono.

Does sound like it is riding to wet. Push the COG back a bit and try that also...

Dave

 

[shadow]

Hi to all,i have a 21 mono (in aus its called a delta style hull),1/2 throtle or so no probs but open up it digs in like it grabed the water and does donuts(left or right dosnt matter) ,back off, straighten up and your off again, then do it again ,have changed props,changed servos,turn fin- off/on, dosnt matter,only thing havnt done is change pos of rudder,at present it is 15mm behind prop (towards transom)any sugestions greatly appreciated thanks peter.View attachment 13143

In your post it said you had tried everything, but it says nothing about trying another receiver. Try another receiver and or try cleaning out the one that is in the boat now.

Cliff

 

[M@MRacing]

27lbs isnt close enough either i am running 64lbs on my seaducer and a 440 rod