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Some Float Issues - 7/11/2003 6:15:35 AM   
jdorsh


 

Posts: 18
Joined: 11/11/2002
From: Waltham
Status: offline 		First Off I wanted to thank those of you who replied to my previous thread askign for some float help, most notably Seaplane. I have attached a picture of my GP 60 J3 Piper Cub with my floats attached. I tried to take a scale approach with the floats by glassing them and using my new HVLP paint system with Dupont Chroma System Paints.

After my first attempt to fly last week, my floats ripped off the cub due to the poor mounting system that GP provides. With some welding and reinforced fiberglass, I have designed a much more robust mounting platform. However, I am worried about the weight of the plane now. I am using a OS 70II Surpass swinging a 12X8 APC prop. My second attempt last night to get the plane in the air was unsuccessful though, as I allowed the plane to get to speed for quite soem time before lifting off. However, after in the air for a brief period about 5 feet in the air the plane quickly twisted to the left (due to the torque) and into the drink. My guess is that the plane is now too heavy for the engine, and thus did not have enough wind speed coming over the wings for proper lift - resulting in my crash, which seemed to be a result of my forcing the plane up. Any thoughts?

Thanks,

Jed
       Post #: 1

Picture of Plane - 7/11/2003 6:19:51 AM   
jdorsh


 

Posts: 18
Joined: 11/11/2002
From: Waltham
Status: offline 		I am having problems with my file sizes!

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       Post #: 2

Some more details - 7/11/2003 6:22:16 AM   
jdorsh


 

Posts: 18
Joined: 11/11/2002
From: Waltham
Status: offline 		A glimpse of the rivets and panel lines

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       Post #: 3

Some Float Issues - 7/11/2003 10:11:12 AM   
JohnBuckner



Posts: 3999
Joined: 12/23/2001
From: Kingman, AZ, USA
Status: offline 		The power you have is entirely suffficient for that airplane even if it may be a little heavy although you never said how much you added by abandoning the GP struts.

Always difficult to tell from pictures but from the photo and description of the takeoff it appears you have inadaquate float incidence. The wing must be at three or four degrees positive incidence to the float top decks in other words when the airplane is sitting on the bench and the top deck of the floats is proped up level the tail will be slightly low with the wings leading edge raised slightly.

What happens is the airplane will accelerate to a point on the step just below flying speed and as you try to rotate for take off by adding elevator to increase the angle of attack of the wing the heels of the floats will hit the water and just put on the brakes preventing take off. Now you are motor boating along just below flying speed and if you hit a little wave or you force it off with full elevator it will bounce into the air with to little speed and she stalls and rolls over.

The GP struts setup is actually a good arrangement and it make it very easy to make small float incidence (float decaladge) adjustments at the lake by carrying some simple plywood spacers under the wire clamps and adjust the incidence.

John

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       Post #: 4

Some Float Issues - 7/11/2003 10:19:48 AM   
Wayne22



Posts: 4433
Joined: 4/10/2002
From: Edmonton, AB, CANADA
Status: offline 		How much does the cub weigh? Nice detail on the floats!!

On a surpass 70, I would use a 13-6 or even a 14-6. It will give more static thrust for takeoffs.

Your configuration looks like it should take off just fine (although my preference would be to lower the tail in relation to the floats a couple of degrees). It could be you just need a little more experience on floats to acquire the finesse your cub requires. With the 70, you can't just fly through problems on brute power, so it will demand more flying skill, especially at low speeds.......but, once you get the hang of it, it will be worth it!!!



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       Post #: 5

Some Float Issues - 7/11/2003 11:57:13 AM   
4*60


 

Posts: 1267
Joined: 3/10/2002
From: Blind Bay, BC, CANADA
Status: offline 		Cub does appear a little nose down on the floats(an amateur opinion), but it's those rivets that are causing all the drag and weight problems!

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       Post #: 6

Some Float Issues - 7/11/2003 6:04:29 PM   
CheezWhiz


 

Posts: 13
Joined: 11/20/2002
From: Canada
Status: offline 		I'm a rookie at RC, but I am also building the same kit with floats and am watching this thread closely.

I notice in your photo that you don't have the ventral fin (under the rear fuselage near the tail) installed. My understanding is that this component is required for the aircraft to fly properly with the installed floats.

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       Post #: 7

Some Float Issues - 7/11/2003 6:36:58 PM   
jdorsh


 

Posts: 18
Joined: 11/11/2002
From: Waltham
Status: offline 		Nony - If I need more positive incidence as JohnBuckner points out, wouldn't I be increasing the distance between the tail and the floats?

John - currently I have 1 1/2 degrees of positive incidence between the wing and the top of the floats. There was minimal weight added by my strut modifications - just some welds and stronger plywood (guessing a 3/4 of a pound at the most). Some additional weight is from the use of a fully redundant Li-Ion battery system and the use of more robust linkages to the rear control surfaces that include a pull/pull system for the rudder, and separate controls for left and right elevators (I was worried that with the extra weight the added stress would snap the original setup if I was to try any aerobatics). I believe the whole setup is weighing in the high teens but that is just a guesstimate on my part.

Finally, I would agree that the cause of my crash was my inexperience on water - I forced the takeoff. However, after watching the video it did not seem as though the plane was accelerating anymore, which is why I started up on the elevator.

My vacation has ended at the summer house so it is back to the workshop to make the proper repairs. I appreciate all of your advice and comments!

thanks,

Jed

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       Post #: 8

Some Float Issues - 7/11/2003 7:41:07 PM   
Wayne22



Posts: 4433
Joined: 4/10/2002
From: Edmonton, AB, CANADA
Status: offline 		[QUOTE]Nony - If I need more positive incidence as JohnBuckner points out, wouldn't I be increasing the distance between the tail and the floats? [/QUOTE]

nope..the wing would have a positive angle relative to the floats which would put it slightly nose high / tail low while sitting in the water......

If the cub weighs any more than 10 or 11 lbs, you are asking too much from a surpass 70...

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       Post #: 9

Some Float Issues - 7/11/2003 8:49:41 PM   
JimCasey



Posts: 1570
Joined: 3/4/2002
From: Cookeville, TN, USA
Status: offline 		Ditto on the weight. Things like redundant battery systems are supposed to make you NOT crash.

Your tail is too high by a good 2 inches.
Take a look at this Maule:

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       Post #: 10

Some Float Issues - 7/12/2003 7:26:25 PM   
jdorsh


 

Posts: 18
Joined: 11/11/2002
From: Waltham
Status: offline 		Thanks guys - I think I made a rookie mistake on the incidence of the plane (I have negative 1 1/2 degrees of incidence). I am currently making the mods now! Also, I believe my apprehension regarding the weight has been confirmed - I am replacing the OS70 with a 91 too. Thanks for all the help!

Jed

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       Post #: 11

Some Float Issues - 7/12/2003 9:04:42 PM   
seaplane



Posts: 334
Joined: 6/15/2002
From: Gibraltar, MI, USA
Status: offline 		Jed, I have the same plane on GP floats and I have a 91 four stroke in mine and I think it is a perfect combination. Glad you are going to a 91..............Seaplane

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Some Float Issues - 7/13/2003 12:53:59 AM   
JimCasey



Posts: 1570
Joined: 3/4/2002
From: Cookeville, TN, USA
Status: offline 		don't beat yourself up about the float incidence: The Great Pains catalog photos have showed the floats with about 10 degrees too much nose up for ten years. I don't know how they ever got the GP Cub off the water. It is probably contributing to the myth about floatplanes needing a bunch of extra power.

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Dittoos - 7/13/2003 1:08:03 AM   
JohnBuckner



Posts: 3999
Joined: 12/23/2001
From: Kingman, AZ, USA
Status: offline 		And 'myth' it is.

John

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       Post #: 14

Some Float Issues - 7/15/2003 6:35:31 PM   
shv2sail


 

Posts: 113
Joined: 8/21/2002
From: Odenton, MD, USA
Status: offline 		I've just mounted a set of fiberglass floats on my WM Cub, and have been doing the mental debate over float to wing incidence angles.

I believe I've read that for flat bottom airfoils (which at least the World Models Cub has) there should be a 0 (zero) degree incidence angle between the float and wing. I've since ignored this and mounted my floats with about a 1 1/2-2 deg positive angle (mostly because my existing struts just fell into place that way). Does anyone have an opinion on no angle vs up to 2 deg positive on a cub? Which do you think is better for a novice float plane pilot?

I'll be spending 9 days on a quiet lake in central NY and am bringing the Cub along...just want to make sure I have all the build/mounting details down before I travel 250 miles from my workshop!

Thanks!

Steve

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       Post #: 15

Some Float Issues - 7/15/2003 7:41:38 PM   
JohnBuckner



Posts: 3999
Joined: 12/23/2001
From: Kingman, AZ, USA
Status: offline 		[QUOTE]Originally posted by shv2sail

Does anyone have an opinion on no angle vs up to 2 deg positive on a cub? Which do you think is better for a novice float plane pilot?
Steve [/QUOTE]


Steve 2deg positive float dacaledge is an absolute minimum and your suspicions were correct. 0 deg and even worse a minus figure is the reason so many folks can,t get off the water. In my opinion four degrees is better. Make some simple spacers to put under the front mount for adjusting at the lake. I always carry spacers and usually end up giving them away to folks who can,t get off the water.


To visualize why 0 deg won.t work just set the airplane sideways on a table in front of you and block it so the top of the floats are level. now just let it rock back on the step untill the float heels hit the table. This is the maximum angle the aircraft can assume on the water. Look at the wing, is this a sufficient angle to lift the aircraft off? On top of that those float heels contacting the water is like putting the brakes on.

John

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"Keep your controllines tight"

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       Post #: 16

Some Float Issues - 7/15/2003 9:45:19 PM   
shv2sail


 

Posts: 113
Joined: 8/21/2002
From: Odenton, MD, USA
Status: offline 		Thanks for the advice, John! I especially like the spacers idea - I'll make sure I bring a bunch to the lake with me.

I'm headed there this Sat...will post some pics and a 'first flights' report when I get back!

Thanks again-

Steve

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