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

Some Float Issues

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Old 07-11-2003, 12:15 AM
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jdorsh
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Default Some Float Issues

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
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Old 07-11-2003, 12:19 AM
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jdorsh
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Default Picture of Plane

I am having problems with my file sizes!
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Old 07-11-2003, 12:22 AM
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jdorsh
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Default Some more details

A glimpse of the rivets and panel lines
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Old 07-11-2003, 04:11 AM
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JohnBuckner
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Default Some Float Issues

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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Old 07-11-2003, 04:19 AM
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Wayne22
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Default Some Float Issues

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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Old 07-11-2003, 05:57 AM
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Default Some Float Issues

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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Old 07-11-2003, 12:04 PM
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CheezWhiz
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Default Some Float Issues

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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Old 07-11-2003, 12:36 PM
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jdorsh
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Default Some Float Issues

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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Old 07-11-2003, 01:41 PM
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Wayne22
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Default Some Float Issues

Nony - If I need more positive incidence as JohnBuckner points out, wouldn't I be increasing the distance between the tail and the floats?
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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Old 07-11-2003, 02:49 PM
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JimCasey
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Default Some Float Issues

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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Old 07-12-2003, 01:26 PM
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jdorsh
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Default Some Float Issues

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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Old 07-12-2003, 03:04 PM
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Default Some Float Issues

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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Old 07-12-2003, 06:53 PM
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JimCasey
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Default Some Float Issues

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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Old 07-12-2003, 07:08 PM
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JohnBuckner
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Default Dittoos

And 'myth' it is.

John
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Old 07-15-2003, 12:35 PM
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shv2sail
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Default Some Float Issues

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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Old 07-15-2003, 01:41 PM
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JohnBuckner
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Default Some Float Issues

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

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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Old 07-15-2003, 03:45 PM
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Default Some Float Issues

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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Old 07-15-2003, 04:13 PM
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JohnBuckner
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Default Some Float Issues

Looking forward to hearing of your adventures and pics.

John
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Old 07-16-2003, 01:13 PM
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Default Incidence angle

I am just about finished building the Goldberg J-3 with the Goldberg J-3 floats. I just read the instructions last night and it specifies that the bottom of the wing should be level with the top of the float. Does what you say mean that on this model I need to add the spacers for a couple of degrees of incidence? Also I did not see above where you need the fin under the tail. I live on the lake and a friend of mine has a real J-3 on floats. I have flown it about 20 hours and it is really easy especially taking off on one float. I have never looked at the incidence and he doesn't have the tail fin. Is it required for RC?
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Old 07-16-2003, 02:17 PM
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Default Some Float Issues

Phantom
Concerning the instructions calling for zero incidence all I can say is yea sure, this is the number one reason so many have so much trouble. The fact is you need a minimum of two degrees positive and more normally four.

In reguards to the Cubs ventral fin Yes it will fly without it Perhaps with a bit of a butt wiggle during a steep turn as you pull elevator.

On a Full scale cub the requirement for the ventral is entirely dependant upon the STC used for that particular manufacturers and model float also you will find differances in the various STC's on float instalations for J-3, PA-11 and PA-18 Supercubs as well as the many differant long and short wing pipers.

John
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Old 07-16-2003, 04:28 PM
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Phantom II
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Default Floats

Thanks for the info John, I really appreciate it. I have a couple of more questions if you have the time. My 75 engine calls for a 13x6 prop preferably wood. On the real plane you really have to be careful not to add the power too quickly otherwise it will suck water up into the prop and damage it regardless of whether it is wood or metal. You can even see a small vortex at idle. Do you have to see if the prop is too close to the water to decide on the size prop? I have a 13x6 nylon and a 12x6 nylon prop also. I checked with pilots at the local field and the only thing that they told me is to really add the power slowly to9 keep the plane from veering to the side. If you have any other tips, I would really appreciate them. I plan on breaking in the engine tomorrow, but I am going to do a lot of research before I fly it. It is all done with the exception of parallelling the floats and adjusting the water rudders.
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Old 07-16-2003, 05:14 PM
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JohnBuckner
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Default Some Float Issues

Phantom the glassy water/high density altitude full scale technique you are talking about I have no doubt will aid a struggling ship get off but is a rather tricky technique in RC part of the problem is most takeoffs that may be marginal are done left to right or vice versa due to the need to visually see the floats water line angle, which is fine but now the needed cross control technique becomes difficult to judge. If you takeoff straight out from the beach the cross controling becomes easier but telling the waterline angle is difficult as the airplane gets smaller and smaller. There is one fun thing that is great fun and an attention getter that is actually easy to do if the float installation is decent. That is a circular single float touch and go.
It is not cross controlled like a straight single float t/o but mearly flying a big circle pattern holding a steady coordinated bank and just powering down and holding some power to a contact point in front of you just as the inside step makes contact apply slightly more aileron and you will be in stable single float step contact with the aircraft still flying in a big circle and at any point if the water is smooth just apply full power and your fully airborne agine in the turn. Sounds complicated but much easier than straight single float flight and will make you the hero of the float fly.

Normal takeoffs are as you know are just like full scale but in a way easier because you can watch the floats water line as you climb onto the step and rotate, you can even see if you start to drag your heels. Just with as with full scale with a heavy wingloaded airplane landings need to carry a little power and a lightly loaded ship can land power off fine. Of course full elevator on the water. RC's can be sailed just like full scale with idle power or dead stick buy control surface positioning in the wind just like full scale.

Float RC is not hard and is extremely satisfying once you get over the fear. Now possibly the most euphoric experiance you can have in RC is night float flight, it is magical. Probably my favorite activity in RC athough I only have the opportunity to do it at the London Bridge float fly each year. The airplane in my Avitar will be my lastest night float flyer at this years event in November.


Happy sailing

John


Almost forgot, Forget the wood props and yes prop clearance will decide how long you can use and with your type airplane longer and flatter is always better.
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Old 07-16-2003, 06:17 PM
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Phantom II
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Default Floats

Thanks John, I am going to print your suggestion up and file it away for the time when my knees are stable enough to try it. I have done circling on the step take-offs for areas that have only a small area of water. That is the only thing that I did not enjoy about float flying. I felt like going the speed that I was going that all's that I would have to do is add just a little aileron to the outside and the outside wing would dip and catch the water. I have read all the other posts and that should hopefully do it. I guess I am headed to the hobby shop to get some longer bolts so that I can add the shims. I have just finished siliconing all around the cockpit and wing. I understand that you are better off wrapping the battery and receiver in saran wrap and putting it in a plastic bag and taping that as well. I will send pictures when I get it all together. Thanks for the help John. I used to fly the f4-Phantom and I would fly over Lake Havassu quite a bit, but have never been there by land.
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Old 08-26-2008, 02:49 PM
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Default RE: Some Float Issues

had a great first few flights with my cub last week-end heres a link to some video

http://www.youtube.com/watch?v=GWlwCnjg2_g
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Old 08-26-2008, 05:23 PM
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Default RE: Some Float Issues

If you set the bottom of a Clark-Y airfoil or similar, flat bottom airfoil, at zero degrees, the actual incidence, measured from the leading edge to the trailing edge, will be 2-3 degres. This is more than likely the reason it was indicated to make the bottom of the wing parallel with the top of the floats.

For a symmetrical airfoil, you'll need to use an incidence meter or measure and calculate the degrees.
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