MHZ Lizard Xtreme

[cacofonix]

hello

here are some pictures :


on this one, rudder is .... not as it was, i reduce width during session, trying to reduce rolling effect .....


another one :



few ideas i have :

- change rudder to reduce widht and thickness
- add a turn fine

just also wondering if having rudder so close to propeller, is really good ....

herve

[ozzie-crawl]

mite be the camera angle but it doesnt look like you have much rudder below the prop

[cacofonix]

i measure from transom to:
- begining of DD : 82 mm
- rudder rotation axis : 92 mm
- back of rudder : 120 mm

rudder width : 25 mm

propeller and rudder are lined up .... i think that flow create by each blade is disturbed by rudder
and create rolling ....

herve

[Flying Scotsman]

mite be the camera angle but it doesnt look like you have much rudder below the prop

I agree, how long is the rudder and if you look at the centre of the prop what is the length of the rudder that is below this centre line?

Douggie

[cacofonix]

horizontaly or verticaly ?

ok i will draw some thing

thanks

herve

[Flying Scotsman]

Vertical position as viewed on the horizontal prop placement

Douggie

[cacofonix]

ok, so when propeller axis is perpendicular to transom
from this axis to hull V = 10 mm
from V to rudder bottom = 35mm

so 45 mm from prop axis to rudder bottom

rudder with is 25 mm, i think too much

herve

[Flying Scotsman]

Herve, I still do not understand but your rudder length looks way too short and is causing your problems. Buy a longer one and try it, as it is very easy to shorten. The width and thickness should not cause your problems. Trim tabs are another option, but from viewing your photos the rudder length looks like the culprit

Douggie

[cacofonix]

hi douggie

what did you not understand ?

i measure again, total rudder lenght : 110 mm
from bottom V to rudder end : 35 mm

i'm not lucky, i reduce rudder lenght last week ......

herve

[Flying Scotsman]

Ok, how did the boat perform prior to cutting the rudder. Pour moi je pense qu'est votre probleme....please excuse my bad French

Douggie

[cacofonix]

yes great french !!!

in fact i did'nt try it before cutting rudder ..... what a shame !!

herve

[DISAR]

I also think that your rudder is too short. I had similar problem with longer rudder though but each boat is different. What I would suggest is:a
a) Place your batteries in the boat so that there is more weight on the left side as you look from behind and test
b) Put a longer rudder and test
c) Add trim tabs and adjust as this thread describes posted by Jeff

Your rolling is caused by the proppeller torque, the motor has the tendency to roll the boat on the opposite side that the prop rotates

http://www.rumrunnerracing.com/feforums/showthread.php?t=28536

[cacofonix]

pfffioouuu, ok i will take time to read this, thanks !!

@disar : lipo pack is already on the left, so i can't do more.
for you the fact that , horizontaly, propeller and rudder are aligned , don't cause any trouble ?

i also tested a K45 and K48 : same

if possible, i will test a 3 blades prop, hope steven has stock.

but first i will rebuild a new rudder.

thanks folks

herve

[cacofonix]

hi

here is a video done last we : http://www.vimeo.com/4985907

orange one is mine.

herve

[cacofonix]

hi guys

new runs last saturday with a brand new rudder, longer, thicker and i also reduce width.
steering is more sensitive, but it don't solve the problem.
when hull start rolling ..... i must reduce throttle to avoid.............crash

i think problem is lipo pack position, i use a 6S1P pack, stick on the left. i think this made CG to high .

so lot of work to come ..... because i must move back motor also.

herve