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Once on step plane whips around and dunks

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Old 05-18-2012, 08:51 AM
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Taxus812
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Default Once on step plane whips around and dunks

So Ibelieve I have a number of possible issues but I want to get opinions from experiance.
I am not experianced and that has a lot to do with it im sure. I have time and like to experiment (school of hard knocks life student) Ok so here is what happening. I can throttle up, Theplane goes in a straigt line until I get on the step and just about at the pointof lift off,itwhips around 180 Deg. If I try to compinsate say with left rudder it will whip around left. If I compinsate right it whips right.


Iput floats ona E-flight Alpha 450 Sport. I seen a you-tube video of a person using supercub floats http://www.youtube.com/watch?v=-IOebqDvHis). I had a set realily avaliable so I used them( http://www.redrockethobbies.com/Hobb...-p/hbz7390.htm)


I verified that the floats are paralell with the centerline they are also paralell with each other.
The step is on the CG (mabie just a little aft of it)
The CG is clean with the floats installed


I dont have a water rudder but was thinking it was not comming into play at that point . the Alpha is about 2 lbs so at slow speeds I can turn without one.
I noticedon the waterthe floats can flex\piviotup and down a little bit at the tips.
These floats are short for this bird but it didnt seem to affect the alpha in the video.

I used the exisiting main gear to mount the floats and a wire "T" to make the front mount.

I have my guess but again I am looking for your thought and experiance.

I love trying this stuff


Terry


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Old 05-18-2012, 10:02 AM
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Default RE: Once on step plane whips around and dunks

I may be wrong and I am not too experienced, but I would say that it is light plane and just as soon as one float comes out of the water, the drag on the other float pulls it around. With a light plane, the resistance to twisting around would be minimal. I saw a video of another plane, a foam cub type that as soon as it got up to speed and pulled one float off the water, would spin around.
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Old 05-18-2012, 11:03 AM
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Default RE: Once on step plane whips around and dunks

Post up some pics and we can maybe see something,, my first guess is you need too much speed before it lifts off,, this could be as simple as the angle of the floats holding the tail up too high,, that is the floats don't let the plane rotate and it won't lift off at a slow enough speed.

post pics of it sitting on the water as well
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Old 05-18-2012, 02:09 PM
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Default RE: Once on step plane whips around and dunks







I measured the angle (incidence?) using a digital angle gauge. With the top of the float at 0 Deg I have Aprox +2 deg at the bottom of the wing (flat bottom trainer) and on the horizontal Stabilizer. I tried moving the floats forward to see if it made a difference (no difference). >>



I also tried to stiffen up the floats by adding some cross wires (eliminating flex). It did stiffen them all up a lot but no real improvement in takeoff. >>



I did a LOT of taxing and watched what happens. This is what I think is happening is its not tracking straight in the water sloshing left or right. Unconsciously I am using a lot of rudder to correct the drift. When I get up to speed and start to break water it was WAY too much causing me to tip one float in (then spinning out.). >>



I may try to add a waterrudder to see if thatwill help. My gut says the floats are just too short and it will never be as clean as it is shown on the video.

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Old 05-18-2012, 03:25 PM
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Default RE: Once on step plane whips around and dunks

The floats have too much incidence.  At liftoff speed your fuselage goes horizontal and the plane rides up on the nose of the floats-way ahead of the Cg.  You have more incidence in the wing than you realize...incidence is not the bottom of the airfoil, it's measured from the most-forward point of the leading edge, to the trailing edge.  You have plenty of reserve incidence  to become airborne.  Meanwhile the plane is acting like a grocery cart pushed backward. 

Rework the front strut and raise the noses of the floats 3/4 to 1"


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Old 05-18-2012, 04:20 PM
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Default RE: Once on step plane whips around and dunks

That made a HUGE diffrence. I was able to take off and do a few circuits and bounce a landing in . Very weird flying with floats I felt I was always flying just above stall speed.


Not sure but I think I still have to fine tune the nose gear. I have to hold back elevator until it just about takes off. it will stay straight and clean. Once up tospeed, Ilett a little elevator off. to much and it spins out. (to long well you know it stalls). It took a LONG time to get up to speed. Pehaps I went to far in the other direction ?


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Old 05-19-2012, 03:51 AM
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Default RE: Once on step plane whips around and dunks

I'm glad it helped. I may have misjudged the scale of your plane and suggested too much correction.  I should have just expressed an angle.

 It is necessary for the plane to be supported by the step at planing speeds.  On  planes with flat-bottom airfoil it usually works to have the bottom of the wing parallel to the top of the float.  There's a pretty wide range of angles where it "works". Since the forward planing surface has 4 degrees incidence, as does the afterbody. With the step, the float can usually rock about 6 degrees back.  Optimal is to have the top of the float flat at takeoff speed, then you have ~6 degrees of rotation  for the transition to flight. 
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Old 05-19-2012, 07:09 AM
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Default RE: Once on step plane whips around and dunks

Works like a champ now! Iran through twobatteriesand got in somereal flying intoday (first real float flights at all for me honestly). This morning It got on thehump in a few feet and took off clean in a few more.Once I trimmed it out, it flew nice (went through battery power quicker however). I was able to landwith no real bounce so I think the incidence may be where itwants to be for this plane and float combo.

Last night I think the balsa was a bit watter logged making the plane a bit heavy (so it flew like a slug). Today it flew no problems.Surprizing thing was that it flew better and seemd to get morealtitudeat half throttle? I will have to investigate that more.

The Shopping cart anolgy made sooooo much sense. thank you
With thesupercubfloats I end up with top of the floats -2 deg relaitive to the bottom of the wing and it works there (just the opposite of what I had before)

A water rudder is definatly not needed. With all that dunking practice. Ilearned taxi it on the hump and the air rudder can turn it tight even in the wind.

Well thanks for the help. I will take a video and post it later. (just dont laugh at my flying skills, I only have a few water flights under my belt and mabie a handfull more on land )

Terry
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Old 05-19-2012, 08:55 PM
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Default RE: Once on step plane whips around and dunks

Here is a video

youtu.be/gUQEs4wKEFA
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Old 05-20-2012, 06:14 AM
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Default RE: Once on step plane whips around and dunks

Probably the most professional video I have seen-even from vendors. Thanks for the mention in your credits. 
I'm glad I could help with getting to a working setup. Your son will learn to fly more easily than you did.  He is at the age where kids learn quickly, and his part of the brain that would be involved with flying is doubtlessly highly advanced from playing video games. 


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Old 05-20-2012, 03:13 PM
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Default RE: Once on step plane whips around and dunks

Thanks I worked on that until 1:30 am last night finnishing it up. We had a blast this weekend flying. The best part is it was in our back yard. Now I have the proper setup im going to build a better mount (now I have the geometery). I broke off the landing gear mount this morningafter a slightly hard landing. That made me realize that there is just to much stress on that once point. So im going to build a new mount using 1/8" music wire. The rear mount will attach to the front support (so it looks like an "N"). I still have to figure out how to "weld" the peices together.
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Old 05-21-2012, 01:59 AM
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Default RE: Once on step plane whips around and dunks

Make your diagonal strut with small bends at the end so they line up with the main legs. Grind the contavt points at least flat if not a little concave. Polish all the contact areas with steel wool or fine sandpaper. Wrap with uninsulated copper wire. Get silver solder at your local hobby shop or ACE hardware. Flux, heat, solder. Hints here: www.smilesandwags.com/Floatsite/FAQ3.html
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Old 05-22-2012, 01:02 PM
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Default RE: Once on step plane whips around and dunks

Looks like you have it pretty well figured out there, Taxus. For future reference, you might want to have slightly longer floats (typical length is 75-80% of overall fuselage length) so that you can have about 2 inches of float in front of your prop, and put the step behind the CG.

You have two things to think about with the fore-and-aft location of the float. One (which has been mentioned) is that when the plane is "on step" you want it supported by the step, which means that the step must be no further forward than the CG. The other point is that on the water, you want the floats to sit level or slightly bow-up. This means that the CG of the plane + floats should be at or slightly aft of the center of buoyancy of the floats.

Given the design of most floats, the center of buoyancy will be somewhat forward of the step, but it isn't always easy to determine its exact location unless you are good with trigonometry (or CAD software). This is why most people recommend putting the step slightly aft of the CG - you will likely be in about the right place for both parameters that way.
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Old 05-23-2012, 07:28 AM
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Default RE: Once on step plane whips around and dunks

Thanks Imaysee if perhaps http://www.seaplanesupply.com/ can make a 30" set of its Light Electric floats.

The alphais okwith the supercub floats but I am sure the takeoffs and landings would becleaner with longer floats.I justtried these because they were, proven, available localy, pre-finnished and $25. I know I can teach myself how to "adjust"for deficiancies but If I decide to teach my son how to fly it I will have to get longer ones (my long term goal).

I decided to make a better mount. It cost me about $10 to make using 3/32 music wire (the same size that the original mount used). Using the exisiting laning gear andnose gear allowed the landing gear mount to break off (I am sure pilot has something to do with it). I was going to add a drag link but decided if im going that far why not just build it out.





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Old 05-23-2012, 08:39 AM
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Default RE: Once on step plane whips around and dunks

yes,, as sugested before the 30" float will give you more room for error,, how long are the hz floats you're using?
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Old 05-23-2012, 09:10 AM
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Default RE: Once on step plane whips around and dunks

The supercub floats are about 23". So they are about 7" inches short. Being only 2lbs it doesn't seem to have that much effect.
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Old 05-23-2012, 09:55 AM
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Default RE: Once on step plane whips around and dunks

I have an old article that recommends the floats be 75% of the fuselage length. 

Here's a reprint of that article:

http://www.seminolerc.com/EZ-Float-Design.html
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Old 05-23-2012, 01:19 PM
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Default RE: Once on step plane whips around and dunks


Quote:
ORIGINAL: Taxus812

The supercub floats are about 23''. So they are about 7'' inches short. Being only 2lbs it doesn't seem to have that much effect.
Not saying what you have won't work,, you've proved it will. But you'll notice the water handling improvement if you get closer to that 75% mark,, espcially if you want to fly in a little wind chop.

good luck
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Old 05-25-2012, 02:04 PM
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Default RE: Once on step plane whips around and dunks

i had the same setup on my Alpha before it met it's demise. I flew mine on the water with a 12x6 APC prop, made a huge difference in it's climbing abilities. The 12x6 may be a little over kill but I have them on hand for my piper and it worked.
Just thought I'd throw that at ya, looked like you were using the stock 10x6.
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Old 05-25-2012, 05:32 PM
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Default RE: Once on step plane whips around and dunks

I am using the stock prop. I will have to give that a try thanks
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