Seaplanes Aircraft that typically take off and land on water...radio control seaplane discussions are in here.

Where should the step be?

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Old 07-08-2012, 05:56 AM
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goirish
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Default Where should the step be?

Putting floats on my 60 size stick. Where should the step be in relation to the CG?
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Old 07-08-2012, 09:59 AM
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Default RE: Where should the step be?

Theres a formula for figuring that out, but the easy answer is about a half inch behind the CG. Thats what I was told when I started. I have used 1/2" on all my float planes and it works good. Keep the CG the same as for wheels and if you have to add nose weight add it to the float tips.
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Old 07-08-2012, 10:31 AM
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Default RE: Where should the step be?

http://www.smilesandwags.com/Floatsite/FAQ2.html
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Old 07-08-2012, 11:07 AM
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Default RE: Where should the step be?


Thanks bunch!!! I printed that out to put in my notebook.

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Old 07-09-2012, 07:17 PM
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Default RE: Where should the step be?

I have always put my step about 1/2" behind the CG and never had a problem. I just recently got a Goldberg Cub (77.5" span) with the Goldberg floats and they are set up to Goldberg specs which is the step 1/2" ahead of the CG. I have found this to work even better at least on the Cubs. It handles well and lifts off the water without the the "pop" or "breaking" off the water some of the float planes will do. I will start experimenting with the location of the step on my future float planes. I currently have a Sig 1/4 scale Cub I'm recovering and it came with a set of Sig 1/4 scale floats made for it. I am going to look for the location of the step on those to see if they are set up like the Goldberg ones.
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Old 07-13-2012, 05:34 PM
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Default RE: Where should the step be?

Step in front of the C.G., around 1/4". Ask any powerboat.
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Old 07-16-2012, 10:51 AM
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Default RE: Where should the step be?

Definitely step should be slightly behind the CG. When planing and about to lift off, the plane is supported on the small area just forward of the step and should have slight positive angle of attack.

If step is too far forward, the plane will sit tail-low, at a too-high angle of attack, and may have too much drag to get up to speed and to a relatively level liftoff attitude. Have seen many "taxi queens" cured by moving the step aft. Of course, if you have enough power you can take off regardless, but high attack angle gives a fierce takeoff.

This assumes you have a single-hull seaplane or conventional plane supported on 2 floats. If you also have a tail float like some oldtimers, then you have essentially a hydroplane (think "Miss Budweiser") and will want the mainfloat steps a bit forward so the plane will be supported at 3 points.

-Dave
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Old 07-16-2012, 03:11 PM
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Default RE: Where should the step be?

Bob has probably forgotten more about models than I ever knew, but I will disagree with him about the location of the step-with a small caveat. 
Having the step under 40% of the mean Aerodynamic chord has always worked well for me.  All my references put the step behind the CG, And it's easy to see that it would be a little more stable on the takeoff run with the contact patch behind the CG.  I have never even had to add balance weights when adding floats.
Caveat: As long as it's not too far forward, Bob's method will probably work,. It has worked for Bob, and that's why Bob swears by it.  It's like taildragger landing gear.  From a stability standpoint, it's suicidal,but lots of airplanes have survived it.  You'll notice videos of Spitfires taking off from nice slippery grass next to the grippy paved runway.......
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