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Direction problem?

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Old 11-26-2004, 12:04 AM
  #1  
Guy
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Default Direction problem?

I put a Tiger Trainer 60 on floats and when I make a take off full throttle often the plane turn 180 right or left. If I make the take off half power it is ok.
It is Niagara floats 36 inches long and I put the step about 1/2 inch back C.G.
Plane span 73 inches , 58 inches long, .60 OS FX engine, prop 12/6 8.5 lbs with floats.
I check everything and I not found the problem.
Please help me.
Sorry I am not very good in english.
Thanks Guy[:-]
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Old 11-26-2004, 07:34 AM
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Ross Kean
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Default RE: Direction problem?

Sounds to me like the floats are twisting one way or the other in the slipstream. It would be more likely at higher power/speed. How firmly are the floats mounted and can the mounts twist? If the mounting is very rigid and the rotation can be in either direction than I can't figure it out. If the rotation was always to one side I would think that there is an alignment problem.

Ross
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Old 11-26-2004, 12:01 PM
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Default RE: Direction problem?

I've seen the same thing happen when the floats are setup such that the wing has too much incidence angle when the floats are planed out. The plane is trying to level out which drives the front of the floats down into the water. You should have the tops of the floats about parallel with the bottom of the wing. Also, your floats should be around 44 inches long. Do you have any float ahead of the prop? There should be a couple inches..........Seaplane
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Old 11-26-2004, 12:07 PM
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Default RE: Direction problem?

Seaplane is right, but if reducing the incidence doesn't do it, consider this; Your trainer has a lot of downthrust built in. When you use full throttle for take off, the downthrust forces the front of the floats deeper into the water. The resulting high pressure on the front of the floats causes the airplane to dart off to one side or the other.

The solution is to move the floats forward. Put the step 1" in front of the CG. I've done it and it helps.

Jim
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Old 11-26-2004, 12:21 PM
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Wayne22
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Default RE: Direction problem?

It could be that the Tiger is running on the front part of the floats. It is directionally unstable under this condition and will turn either left or right as you discribed - usually quite suddenly..

Could be a couple of causes:
-pilot technique perhaps...too much down elevator forcing it up over the step and making it ride the floats in front of the step
- floats are too short with too much relative area ahead of the step location (ie not enough afterbody to stabilize it on the water at high speed)
-too much downthrust with full power forcing the front of the floats deeper in the water. Without seeing your particular float installation, and knowing that the Tiger is very well proven design, it is possible that there is not enough positive incidence between the plane and the floats..it should be between 1 and 3 degrees positive (nose slightly high).

Just throwing ideas out that may be the cause of what you describe....without seeing your particular installation and watching the takeoff, these are only educated guesses at this point...
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Old 11-27-2004, 10:08 PM
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Guy
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Default RE: Direction problem?

I check the incidence and it is about 2 degrees negative.
It is the first things I correct to give about 2 degrees positive. If it is not the solution I put the step 1 inch in front of the C.G.
I cannot make a test because the lake is now frozen ,the next test in may 2005
Thanks very much for the help.
Guy
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Old 11-27-2004, 11:15 PM
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JohnBuckner
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Default RE: Direction problem?

I would be willing to bet three burned out glow plugs that your negative wing to float incidence is indeed the problem compounded a bit by the CG at a half inch to the rear of the step. Most seem to work well with the step either at at or a quarter inch aft of the CG. As most of the responders have indicated one to three degrees positive wing to float is about ideal and I usually shoot for around two degrees.

Putting the step ahead of the CG will not provide those pretty float plane lift offs we all love so much and in my opinion will only agravate your t/o directional stability. This works in exactly the same way that a land plane with taildragger main gear when the wheel footprint is too far forward and the result is directional instability. The area immediately in front of the step when on the step is in effect of the wheel footprint. Move it further forward and always the result is instability.

John
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Old 11-28-2004, 12:17 PM
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Default RE: Direction problem?

ORIGINAL: JohnBuckner

Putting the step ahead of the CG will not provide those pretty float plane lift offs we all love so much and in my opinion will only agravate your t/o directional stability. This works in exactly the same way that a land plane with taildragger main gear when the wheel footprint is too far forward and the result is directional instability. The area immediately in front of the step when on the step is in effect of the wheel footprint. Move it further forward and always the result is instability.

John
Unlike a wheel plane, where the center of pressure is the bottom of the wheel, the initial point of water contact and total wetted area of a float is variable depending on the angle of attack of the float. You can change the point of contact and thus the center of pressure and yaw stability of the plane on the water by using the elevator to change the angle of attack.

In this case, if the downthrust (or excessive negative incidence in the float) is forcing the nose of the float into the water, the point of contact will be far in front of the step, causing the instability. If that is the case, moving the float forward, thus increasing floatation in front of the CG, can allow the point of contact to move rearward to a more normal position. I've done it on many trainers and it seems to help.

Jim
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Old 11-28-2004, 01:39 PM
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Default RE: Direction problem?

Yes Jim agreed, precisely as you described and as that foot print expands forward when digging in the aircraft will become more directionally unstable just exactly like it will with a wheeled taildrager when the footprint is to far forward. So except for that one small point I agree to disagree and like you I am not speculating causually but from experiance with a lot of aircraft over the years both my own and observation of others. The most consistantly successful conversions of my own and others is with the step at or just slightly behind the CG.

John
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Old 12-01-2004, 09:09 PM
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Default RE: Direction problem?

Only a test to post an image






[img][C:\Documents and Settings\Propriétaire\Mes documents\Mes images\Nikon View HTML\page4.htm]
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Old 12-02-2004, 04:14 PM
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Default RE: Direction problem?

I give 3 degrees positive angle incidence with a block 3/8 inch see the image below and you can look the airplane before .
Guy




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Old 12-02-2004, 04:24 PM
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Default RE: Direction problem?

And did that solve the problem? Or make it worse?

Jim
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Old 12-02-2004, 05:02 PM
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Default RE: Direction problem?

Presntely the lake is frozen I post an answer in May 2005
I make test to import image . gGuy

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Old 12-02-2004, 05:15 PM
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Test to transfert an image
Thanks Guy
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Old 10-20-2019, 03:00 PM
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Question More on Direction Problems

I realize this is a very old thread, but as it seems pertinent to my recent experiences, I'll post here with my problem, which seems very similar to Guy's. I'm probably an intermediate level RC flier, semi-competent with taildraggers; but float flying is a new experience for me. I've recently added an E-Flite 15e float set to my Pulse XT 15e, and have probably flown it 8-10 times off mostly glassy water conditions. Most--say, 75%--of my takeoffs are smooth and graceful, but every once in a while I get a nasty diversion from a straight takeoff run that sets the adrenaline running and causes me to jam the throttle wide open and horse the thing into the air. I have come to consider that perhaps my setup isn't optimal, and reading through this thread has given me some ideas I'd like to run by the experienced residents here.

The float kit, being intended to snap on to an Apprentice or some such, isn't readily adjustable. While the floats' angle of incidence seems just about right, the step is just about dead aligned with the CG, which I see isn't ideal. As moving the floats aft a half inch or so is going to be challenging, I'm wondering if it makes sense to add some foam filler blocks behind the existing step to effectively move it aft. Has anyone here had any success with such a modification? Am I asking for trouble?

Thanks in advance for any advice.
Rob
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Old 10-20-2019, 07:21 PM
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JohnBuckner
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Hi Mudbay, indeed this a very simple method albeit effective one and yes I have done exactly that with one ship that some years ago was proving troublesome. It was an old Bridi pattern ship that I set up and flew on a fifty three mile cross country flight down the Colorado river from Laughlin Nev. to the London bridge Lake Havasu Az.

The problem was the need to carry 72 ounces of fuel in four tanks running atop the fuselage from the nose pretty far aft which resulted in a CG in the most aft position when fully fueled for takeoff. The takeoffs were by necessity quite long and yaw instability during the run showed up. The solution was proved to be two two half inch wide balsa blocks were glued behind the step. After this the long extended takeoffs proved easy with no directional problems during the runs.

Do feel free to experiment as you described and I am sure it will help.

John
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Old 10-23-2019, 03:06 AM
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Thanks for the input, John. I'll certainly give it a go.
That long-distance Colorado River flight sounds like one heck of an adventure, BTW! There must be photos!
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Old 10-24-2019, 06:14 AM
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Old 10-24-2019, 08:00 PM
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There ARE photos! Bloody genius!!
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