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Old Jul 02, 2014, 08:49 AM
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United States, NC, Chapel Hill
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Question
Float rudder question

I am having a very hard time keeping the plane flying straight during take off from water, and I am wondering if the water rudder is the problem.
I got this plane in a trade, and came with no instructions at all. It is an old Cub .40.

These are three pictures showing the water rudder all the way down, mid way up and all the way up. Which one is the best position?
Thanks for your help.
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Old Jul 02, 2014, 03:53 PM
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Joined Jun 2005
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Usually this type of problem caused from too much float in the water ahead of the step. This causes drag in front of the step and the "snaking" occurs. The proper setup for take off is just the step in the water, the nose of the floats high, and the rear of the floats in the trough cut by the step. To achieve this, if the floats are set up correctly, keep a little up elevator during the take off run. This will push the tail down, the rear of the floats down, and raise the nose of the floats. Keep in mind, that too much up elevator may cause the plane to leave to water too soon and stall. To back up what I stated, go to Youtube and enter "float plane take off" and watch many videos of full size float planes taking off, and especially watch the attitude of the floats. Lake Hood in Anchorage, Alaska has a great viewing area for take offs and landings, so also in Youtube look for " Lake Hood take offs".

Hope this helps................Ralph
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Last edited by Seaplane; Jul 02, 2014 at 04:16 PM.
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Old Jul 03, 2014, 06:18 AM
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Thank you. Looking at the videos, it seems that the rudders are close to the up position... The problem I was experiencing was the plane turning to the right, so that when I finally take off I am flying almost at 90 degrees relative to the start of the run, with the wind to the left of the plane...
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Old Jul 03, 2014, 09:31 AM
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I have the identical rudder on my GP .40 J-3 Cub. Your installation appears correct. One thing you might check is float alignment and toe-in. First, center lines of floats should be accurately parallel to the fuselage centerline. Then I, and many others, have found that a small amount of toe-in is desirable at the float noses to eliminate the "veering" at step taxi. In my case, a total of about 5/8" (each float toed inward toward the fuse centerline at the noses about 5/16") cured the tendency. It seems that toe-out really accentuates the veering problem on the step, so this check is worthwhile.

I recommend you carefully check current alignment to see how they are. Let us know what you find.
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Old Jul 03, 2014, 09:56 AM
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Quote:
Originally Posted by Lambro View Post
I have the identical rudder on my GP .40 J-3 Cub. Your installation appears correct.
Which one of the three pics shows the correct installation?
I will check the alignment of the floats as well.
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Old Jul 03, 2014, 10:58 AM
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Quote:
Originally Posted by ululi1970 View Post
Which one of the three pics shows the correct installation?
I will check the alignment of the floats as well.
Well, after checking my rudder vs your photos more carefully, I found my rudder is the same, but the mounting isn't. Yours is mounted lower on the transom, and I cannot discern the rubber-band "kick-up" function. Your photo showing the rudder fully down would be the proper operations position, but the depth of the low edge of the rudder is deeper than most would install. Generally, you do not want too much rudder in the water when on step.

I have attached a couple of so-so photos. This arrangement has been flawless for hundreds of water operations for me on this CUB.
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Old Jul 10, 2014, 11:06 AM
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I think you need to hold up elevator while taking off to prevent the front of the floats digging in and squirreling the plane. Release the up just as the plane is about to take off, of course!
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