Oct 22, 2014, 07:30 PM Registered User United States, CA, Sacramento Joined Feb 2010 75 Posts Discussion step location not sure if this has been covered before but i was curious where the step should be on a seaplane in relation to the center of gravity? thanks in advance carl
Oct 22, 2014, 11:27 PM
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Slightly behind CG.
Too far forward will likely cause instability when planning and will result in uncontrollable swerving. It will also cause porposing on landing
Too far back will restrict rotation during takeoff that allows the wing to achieve enough lift to get off the water. Although if all of your decalage angles are correct this should be less of a problem since flight attitude should be similar to planning attitude, meaning your aircraft should transition from planning to flying with little to no pitch change.

This is one of my favourite vids showing a great CG, step location and angles. Notice how there is very little difference between flying and planning. It also helps that the wing loading is very low.
 Martin Mars Bergen -Low and Slow- (4 min 51 sec)
 Oct 23, 2014, 03:38 AM Slip the surly bonds... Christchurch,England Joined Aug 2004 2,892 Posts My favourite video on RC Groups! Another way to answer the question might be to say 10 - 15 degrees behind the CG, taking your vertical from the wing undersurface. Nice flying Arvid!
Oct 23, 2014, 08:02 AM
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Vienna
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Quote:
 where the step should be on a seaplane in relation to the center of gravity?
Slightly behind the center of gravity, seen from a side view. The step is the point where the airplane can rotate to lift its nose during take off. If the step ist ahead of the CG it will cause instabilities as described before, if too much aft the speed at which it can rotate will increase. This is not necessarily a bad thing as it prevents a take off with too slow speed.

Also important is the angle of the float behind the step. If, for example, this angle is 8°, this is the max. angle the aircraft can rotate. (Yes, you can rotate a bit more, but then the end of the floats is pressed into the water causing drag). If the wing is parallel to the float construction the aircraft must be fast enough to generate enough lift with this 8°.

regards
Andi
 Oct 23, 2014, 08:39 AM Registered User United States, CA, Sacramento Joined Feb 2010 75 Posts ok thanks guys. flying off water is on my r/c bucket list so i think i might draw something up. would it be at all possible to do a twin boom seaplane?
Oct 23, 2014, 09:11 AM
Slip the surly bonds...
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Quote:
 Originally Posted by carl holtz ok thanks guys. flying off water is on my r/c bucket list so i think i might draw something up. would it be at all possible to do a twin boom seaplane?
Try the Naardi Riviera here but I think there are also some Sikorsky 1930's seaplanes that werre twin-boomed.
Oct 23, 2014, 09:31 AM
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Quote:
 Originally Posted by Sopwith Mike I think there are also some Sikorsky 1930's seaplanes that werre twin-boomed.
Kinda like this one?
Wormboy's blog
 Oct 23, 2014, 12:56 PM Registered User United States, CA, Sacramento Joined Feb 2010 75 Posts kinda like those but foam! lol and something im not gonna get depressed about if i wad up :-)
 Oct 23, 2014, 01:05 PM Registered User United States, CA, Sacramento Joined Feb 2010 75 Posts wormboy, just read the blog . what a beautiful plane!
 Oct 23, 2014, 05:50 PM Registered User Australia, WA, Madeley Joined Jul 2011 736 Posts Thanks Carl The only other twinboom seaplanes I can think of is the sister to the one I built, the S38 as well as the BV138. I understand about wanting a foamy to have a go with. Good plan. If you are set on building a twin boom seaplane it wouldn't be that hard. Start with a wing from a cub or similar. Whack a couple of carbon rods for booms out the back of it and stick the elevator and tail(s) to that. Just some Depron profiles should do the job. Then all you have to manufacture is the pod and maybe some tip floats. Stick a motor on top and you're sorted.
 Oct 24, 2014, 04:30 AM Registered User Norway Joined Jan 2009 101 Posts The step position relative the airplane centre of gravity is not set in stone. The full size Beriev Be103 has the step forward of the airplane CG and seem to work ok. A number of free flight models where designed with the step forward of the CG too. These would rise of water without any pilot input. But notice, if you are to deviate from common practice the challenge of making a well working seaplane hull rises considerable. This have been discussed before on this forum, last time here: http://www.rcgroups.com/forums/showthread.php?t=2238362 Twin boom seaplanes? Have a look at Andy Lennon’s Sea Loon. http://www.rcuniverse.com/forum/seap...-sea-loon.html A full size with twin boom’s are the Sea Era designed by Paul Weston.
Oct 24, 2014, 04:47 AM
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Two more twin boom and twin hull seaplanes:
The Privateer: http://www.privateerindustries.com/
Dewy Eldred's Flyer:
 Dewey Eldred 'Flyer's Dream' light seaplane (1 min 12 sec)
 Oct 24, 2014, 06:36 AM Registered User Australia, WA, Madeley Joined Jul 2011 736 Posts Heya Himat, Yes I should have included your information from that thread, I was just trying to present the conventional arrangement rather than the exceptions that proove the rule. Thanks for including it I love the Flyer's Dream, what a great litle plane. It looks like someone has strapped a VW beetle to a corsair and some floats! There are a couple more designs presented in the Float plane pictures thread if you have a look at the attachments you'l find them. The old Talespin Seaduck is also a subject that has been modelled, and the thread happens to have been recently resurrected. Although fictional it does seem to have been flyable.
Oct 24, 2014, 06:45 AM
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Quote:
 Originally Posted by Wormboy Heya Himat, Yes I should have included your information from that thread, I was just trying to present the conventional arrangement rather than the exceptions that proove the rule...
A wise approach.
To develop the unconventional arrangements always brings greater challenges. Have a look at my avatar. Also once posted in the seaplane pictures thread.
 Oct 24, 2014, 11:25 AM Slip the surly bonds... Christchurch,England Joined Aug 2004 2,892 Posts The HobbyKing Skipper aka Joysway Dragonfly has the step in front of the CG. I have wondered whether this was deliberate (and if so, why?) or just a design error.