Question about angles

[antslake]

Well, this seaplane of mine is making me sick. I have had some successful flights with it last year, but because it is a cub with a very short tail moment, she likes to snap on take-off. So last year, I beat her up a few times in the drink.

I removed all the covering this year, and recovered her in NAVY colors. DId a lot of work to her to get her up to snuff. But I crashed again on take-off. I think I had too much down elevator in it, and when I pulled up, she looked like she wanted to snap, so I let off, and then she violently went down into the drink.

I got her all apart drying her out, but my question is, how should the plane sit relative to the floats? I know I have the steps in the right place, and the balance is good. I mean she should take herself off if everything is right. I am not a beginner flyer, but with seaplanes, yes.

Should the plane have a slight up attitude, and if so, how much?

I included some pictures, just of the plane, nothing telling. There is a video of the crash, but you can't see it go in. Before take-off, she was like a magnet to the water.

[Art Schmitz]

It looks like the steps are too far forward. They need to be rearward of the fully fueled CG by about an inch on the size of plane that you have.
The plane should be slightly nose low..about 4 degrees.. to be balanced. It sounds as though the Cub is tail heavy.
The GeeBee floats leave alot to be desired.
You may wish to add to the vertical area to compensate for the added side areas of the floats that are forward of the CG. A ventral fin is the easiest way to do this.The area equal to the rudder is a good place to start.
The wing needs a slight amount of positive incidence. Comparing the leading and trailing edge measurements as taken from the top of the floats usually suffices.
The floats need to be rigidly mounted, level with one another, and slightly toed in. 1/8" should do it.
The Sig Cubs tend to be prone to snapping on take off.[ wheels or floats ] Setting the elevator trim half down and the rudder trim half right helps alot, in my own experience.
Ironsides has a very comprehensive and helpful water flying web page.

[antslake]

Thanks for the advice.
A ventral fin is that fin that sticks down below the stab?

Also, I confused about the nose low, and positive incidence at the same time.

There may be too much flex in the mounting system they give you.

I must have read the instructions wrong concerning the placement of the steps. I am about an inch forward of the cg.

[happypappy]

All of the information given so far is good information. The cub, by the nature of the beast, should not be lifted off the ground (or water) before it is ready to fly or what has hapened in the past will continue to happen. BOTH wings must attain flying speed in order to lift the additional weight and drag you have created. When a Cub snaps on take-off it is usually because proper take off speed was not attained. I fly a Cub regularly and destroyed the first one the same way as you. Many of us have! I also fly real J-3 Cubs as well and purposely stall/spin the aircraft for fun and practice. When one of the wings quits flying "ain't nothing you can do about it" unless you know the simple procedure for getting out of a spin. Bad part of a snap during take off is that you don't have the altitude to react fast enough and damage usually occurs. More speed during your take-off run should help along with the checks and changes mentioned earlier.

[antslake]

I should have been more specific. It was last year that I snapped on take off, and learned that lesson.

Today, I was moving very well, and the plane did not drop a wing, it went straight down and in. It was either one of three things. I had too much down elevator to start with, since I just rebuilt it, and didn't really check it before I took off, a radio glitch, because I spilled some fuel inside the fuse, but cleaned it before flying, or my incidences are wrong.

I also double checked, and the trailing edge of the step is indeed 1/2 to 1 inch behind the cg of the plane. Not exactly sure, because the wing isn't on, but it is definately behind the cg. The plane was balanced properly.

The floats did hook to the right, right before take-off, don't know if that had anything to do with it, and I might have been heading with the wind. I couldn't tell which way the wind was blowing, there was hardly any. IT may have been going right over us, as we live next to a big mountain. There seemed to be wind out further on the lake, and that would indicate a tail winded take-off.

I personally think it was too much down elevator dialed in. The plane was like a magnet to the water as I was gaining speed, and I had to pull way back on the stick to get her to launch. When I saw her jump out of the water at too steep of an angle, I feared snapping her, and let go of the stick, but there was too much down elevator, and she just dove, hard. Ripped the floats off.

I am just running this by everyone, so that I can get good advice, and double check everything before I go up again.

I think I also understand why these floats hook on take-off's. The mounting seems to be too flimsy, and I think I will be beefin it up, so that the float cannot curl under itself as easy. I will give these floats another shot, then I will can them. I did have two great days out last summer, with many take-off's touch and go's, and landings, so I know it works. Just really have to watch the wind, and the take-off speed.

I think I will also add a ventral fin, as this has got to help anyway, then rebalance the plane.

I ahve the plane balanced perfectly so that I can switch between floats and landing gear.

Thanks again for the advice.

[Art Schmitz]

When they stay 'glued' to the water on take off and then 'pop' off, the relative wind is deflecting off the upper surface of the wing. Hit a ripple and the floats bounce causing the wing to suddenly ( rather than gradually ) have positive incidence and at a much higher speed.
The wing needs to have a degree or two of positive incidence relative to the floats.

[antslake]

When they stay 'glued' to the water on take off and then 'pop' off, the relative wind is deflecting off the upper surface of the wing. Hit a ripple and the floats bounce causing the wing to suddenly ( rather than gradually ) have positive incidence and at a much higher speed.
The wing needs to have a degree or two of positive incidence relative to the floats.


That's what I was thinking, then the plane will take itself off, if it is trimmed right. I think I will shorten the rear struts of the floats by 2 degrees.

[canadagoose]

I have buddy that built one of the Great Planes cubs and the GP floats for it.
His cub on takeoff 95% of the time would hook severly to one side when it got to a certain speed. I tried it as well and the same thing would happen so i knew that it wasn't him as he was new to float flying as well. We checked and double checked the step location, float to wing incidence, whether the floats were parallel and straight with the fuse. Everything checked good, but the plane got wrecked before we ever did find what the problem was. I had a Goldberg cub on floats quite a few years ago that sometimes would do that too, not near as bad as my buddys though. I'm sort of under the impression now that cubs don't really make the greatest seaplanes. I designed and built a plane called the VeeBee from the ground (or water) up to be a seaplane with alot of the TLAR (that looks about right) rule , anyways i must have unwittingly done what makes a good seaplane with the design because it is pure pleasure to fly from water. It never hooks a float and hardly needs any right rudder as well, it will take off without much of a run and will land slow without wanting to snap into the water. This plane will make a novice float flyer look good. Maybe you too have one of those planes that just doesn't want to fly off water.
If it were mine i would place the step 1/2" behind cg, make sure floats are parallel and straight with the fuse, build a sub fin to mount uderneath the fuse at the rear and either mount them so that the tops of the floats are even with the bottom of the wing (if the wing is flat bottom) or with a the tips of the floats down slightly to give the wing a bit of positive incidence. You won't need much with a clark y or flat bottom airfoil. Maybe get rid of those floats and get a better design. If all those things don't help, i'll can sell you a set of plans to build mine :D

[canadagoose]

The three things i notice in you photos that i don't really like the looks of is: floats too far forward, look to be very wide apart and hanging quite far below the fuse. Having the floats too wide apart places more weight out towards the wing tips. It's better to try and keep the weight as close as you can near the center. That helps create a more stable flying plane.
With the floats too far below the fuse that creates a bigger pendulum effect when combined with quite a bit of extra weight located quite far out from the center line of the plane especially on a high wing plane could very well be the culprit in the plane wanting to swing and snap after lifting off.
One rule of thumb for spacing the floats apart is 1/4 of the span.

[antslake]

Rodger on the spacing, I will check it out.

The pictures aren't very telling, and I installed them as per the instructions. The end of the step is 1/2" behind the cg. The step is vee shaped, and you can't see that from the photos.

[Seaplane]

I've been flying off floats for around 10 years now and here's my experience on hooking. When the plane is taxiing the floats are in displacement mode and they dictate the attitude of the plane, although up or down elevator will change the attitude somewhat. When the plane is at or near take off speed, the plane will dictate the attitude of the floats. If the floats are set up correctly, with the plane at or near take off speed, the floats wlll ride on the step with very little surface ahead of the step in the water and no surface behind the step in the water. If your plane is at the proper attitude for take off and too much float ahead of the step is in the water, it will cause the floats to veer right or left. This is due to too much drag ahead of the step. If one float is deeper in the water than the other (more drag ahead of the step) the plane will veer to that side. A little drag behind the step, like a tail on a kite, will produce a straighter take off run. Too much drag will slow the plane down.

This uncontrolled veering is usaully caused by too much positive incedence of the wing in relation to the floats. That is, with the plane in it's level flight attitude, the front of the floats are too low. For a CUB, set the top of the floats parallel with the bottom of the wing. If you still have problems, either trim in a little up elevator or hold a little up elevator on the stick during take off. This will raise the front of the floats up, decreasing the drag ahead of the step. Too much up elevator may cause the plane to leave the water too soon. So experiment with the amount of up elevator. When I fly my Beaver on floats, I always trim in a little up, then retrim in flight.

I hope I explained it properly.................Seaplane

[jpgilbert]

Seaplane,
This is the best explaination I have seen of this problem. I was having this problem with my Bonnie 20 and finally gave the plane to an experienced float builder and told him to replace the floats with his design and set it up correctly. What a difference! Now the plane is a pleasure to fly.

Joe

[antslake]

Got it.

[Art Schmitz]

A little 'toe in' will cure the veering.
Think it through...any instance of assymetrical deviation will self correct back towards the original take off direction.
I used 9/16" on my 6' Beaver....1/16" on my GWS Beaver. HTH art

[antslake]

The instrutions for these floats say no toe-in.

I think the problem arises when one wing is trying to lift off. I am thinking of canning the piper cub on floats idea. I will give it one more try. Getting tired of drying out radio equipment.

I have one of those READY plastic planes that resemble a cessna .40 size, that I should probably be putting my efforst into.

[G.P.]

I have two cubs on floats and they make excellent float planes. I did have the veering problem that you discribed on my latest one. I did what Art has suggested and added some toe in and it tracks very straight now. It's the same as a car or a tail-dragger needing toe in. As the plane tries to veer the outside float will have more drag, bring the plane back into alignment.

As you have stated, I have been given advice and seen instructions that indicate that no toe in is required. This could possibly be true if it was absolutely perfect, but I don't have the skills/tools required to get that level of perfection. A little toe in will eliminate any chance of error.

The other thing that has worked for me is to use a little aileron when doing high speed corrections or turns on floats. Doing a coordinated turn with both the ailerons and the rudder will help with your corrections by creating more drag on the inside float. It doesn't take much, so be gentle and work your way up.

Hope this helps,
Greg

Also, I've never tried mine without a ventral fin. That may help a little too.

[G.P.]

Here's a couple shots of my ventral fins if you are going to make one. I had a hard time finding pictures of a cub ventral fin.

Keep at it! Flying a cub on floats is the most relaxing and enjoyable flying that I have done. Trust me, it will be worth it.

[canadagoose]

Hello G.P., nice looking CUB. What lake is that in the piture? Is Pete's Hobbies (if i remember right) still in business? Whenever i was in Grande Prairie i had to pay a visit to pick up things i needed.

[jpgilbert]

Attached is a photo of the fin on my Bonnie 20. While not a cub, I found when I started flying it from snow (and now water) it handled much better after I added the fin. Once everything is set up correctly, flying from water is worth all the effort to it done right. I am amazed at the change in behavior once it was set up by someone that knew what he was doing.

The fin is attached by a piece of MW in the rear that slides into the fuse and a front screw going into a blind nut. The Bonnie is set up for a 10 min change over to wheels.
Joe

[G.P.]

Hello G.P., nice looking CUB. What lake is that in the piture? Is Pete's Hobbies (if i remember right) still in business? Whenever i was in Grande Prairie i had to pay a visit to pick up things i needed.

That's Sandy Point on the Shuswap (spl?) lake, right by Salmon Arm B.C.. I spend two weeks there every summer and bring the float planes with me. I haven't found a more beautiful place to fly and the lake is always like glass.

Pete went out of business. A victim of Great Hobbies prices and selection. We only have Wonderland Toy and Hobbie now. There's not much for planes though, just car stuff.

Here's the full shot.

[canadagoose]

That's Sandy Point on the Shuswap (spl?) lake, right by Salmon Arm B.C.. I spend two weeks there every summer and bring the float planes with me. I haven't found a more beautiful place to fly and the lake is always like glass.

Pete went out of business. A victim of Great Hobbies prices and selection. We only have Wonderland Toy and Hobbie now. There's not much for planes though, just car stuff.

That's too bad about Pete's hobby shop, i liked going there. Usually had an RC video going to watch too.

I know what you mean about Sandy Point, i usually go to the spring and fall float flys held there.

[jimsp]

It sure looks like the step is too far forward. You show the plane resting back on the floats. Ready to fly you should also be able to rest it forward on the floats. I’m curious about the size and shape of the floats. They don’t appear to be very wide. Also the bottom corners of the floats look rounded which will make the plane seem like a magnet to the water.

[jpgilbert]

Are these the infamous GeeBee floats?

[antslake]

I love those pictures of the cub, what camera are you using?

[G.P.]

I know what you mean about Sandy Point, i usually go to the spring and fall float flys held there.

I had no idea they had float flys there! Now, how do I convince the wife that we need to change our yearly summer vacation dates?!?! :)


I love those pictures of the cub, what camera are you using?

Just using a crappy Kodak cx6445. It does stills, outside in the sun fine. Everything else is horrible. Anything moving more than a snails pace is blurry and if the suns not out the pictures are dark and grainy. I don't suggest it.

Sorry about the thread hi-jack.

[canadagoose]

Are these the infamous GeeBee floats?

Yes

I had no idea they had float flys there! Now, how do I convince the wife that we need to change our yearly summer vacation dates?!?!

Usually the beginning of June and September, don't need to change them, just take more there. There's always a good assortment of cubs there up to 1/3 scale!
I'll be the one flying my red and black VeeBee.

[G.P.]

That VeeBee is sweet!

That would be pretty cool, but I don't know if I would be able to swing it. The whole family books vacation around the last two weeks in July and we all meet at Sandy point. It would take a lot to change everyones plans. It's always the same two weeks because they claim they've never had bad weather (other than a day or two) during those two weeks, for the past twenty something years! I've only been going for three years, so who am I to suggest change!

That beach looks sooo much better with all those planes, instead of all the loud motor/jet boats. Of coarse I wouldn't be saying that if I had one! Thanx for the pix.

Greg

[lake flyer]

I have a Sig 1/6 Cub on floats , I was having the same veering problem , "Seaplane" gave me the same advice he has given you .

I did as he said and now the Cub is very good on the water , takeoff is smooth and straight.

As far as tip stall goes , be sure you have about 2 degrees of washout .( real Cubs do )

[antslake]

I have a Sig 1/6 Cub on floats , I was having the same veering problem , "Seaplane" gave me the same advice he has given you .

I did as he said and now the Cub is very good on the water , takeoff is smooth and straight.

As far as tip stall goes , be sure you have about 2 degrees of washout .( real Cubs do )

Even though it wasn't mentioned in this thread, I was going to put some washout it in anyway. Thank you :)

[JimCasey]

ANtslake: If you have the Modelfly floats for the Ready, Install them on the Cub. You WILL notice a great difference. They are MUCH better floats than you are using now. I am a big proponent of Foam-core, sheeted floats which are better yet. They are light, durable, and they work very well, plus they can't leak. The floats you are using are oft maligned. For a pointy step, the FRONT edge of the pointed part should be considered the critical dimension for step location, and this should be under the 40% chord point which is almost invariably about an inch behind the balance point with the plane level. Wiggle your existing floats and see that they are actually quite flexible. Makes you wonder how well the airplane can go straight on takeoff, no? Floats should be mounted as rigidly as possible.

Seaplane was dead right about incidence. I had a Telemaster with floats and HUGE incidence(5 degrees) that worked for me with that plane. Zero incidence with a flat bottom airfoil is commonly used (Top of float level, bottom of wing level). Basically it is as Seaplane said: Going fast, only the step should touch the water, and you should be able to rotate back to takeoff AOA without the tail of the floats touching the water.

Move the floats aft a bit more, double check that they are mounted true: Parallel, straight, rigid, and, with respect, only Art recommends toe-in but it may work for you.

[dirtstar1]

G.P., Nice looking cub! Im putting together a cub right now and it very much looks like yours.

Did you use the GWS floats? Nice finish on the floats, Very realistic

Here is a pic of my progress

[antslake]

ANtslake: If you have the Modelfly floats for the Ready, Install them on the Cub. You WILL notice a great difference. They are MUCH better floats than you are using now. I am a big proponent of Foam-core, sheeted floats which are better yet. They are light, durable, and they work very well, plus they can't leak. The floats you are using are oft maligned. For a pointy step, the FRONT edge of the pointed part should be considered the critical dimension for step location, and this should be under the 40% chord point which is almost invariably about an inch behind the balance point with the plane level. Wiggle your existing floats and see that they are actually quite flexible. Makes you wonder how well the airplane can go straight on takeoff, no? Floats should be mounted as rigidly as possible.

Seaplane was dead right about incidence. I had a Telemaster with floats and HUGE incidence(5 degrees) that worked for me with that plane. Zero incidence with a flat bottom airfoil is commonly used (Top of float level, bottom of wing level). Basically it is as Seaplane said: Going fast, only the step should touch the water, and you should be able to rotate back to takeoff AOA without the tail of the floats touching the water.

Move the floats aft a bit more, double check that they are mounted true: Parallel, straight, rigid, and, with respect, only Art recommends toe-in but it may work for you.


You are 100% correct about the rigidity of the mounting of these floats, and I was wondering about the pointed step.
Maybe I should just can these floats.

[Tom Frank]

You are 100% correct about the rigidity of the mounting of these floats, and I was wondering about the pointed step.
Maybe I should just can these floats.
I struggled with getting GWS floats to track straight, too. The stock wire LG and cross ties act like a bunch of hinged rods. The floats can easily translate fore and aft.

To correct this I first ditched the wire spreaders and replaced with CF rod epoxied into holes drilled horizontally near the float top into the sides of the wood mounting rails. I inverted the floats on a flat surface and squared up the tips to align and make them true while the epoxy set up. I then added more CF rod as diagonal braces on each float extending from the front LG wire where it attaches to the float back to the top of the rear LG wire. I used extra wing strut attachment pieces from the kit (A GWS E-Starter) to attach the diagonals. This made a very rigid and strong float platform.

I found toe-in is fine while the plane's weight is approximately equal on both floats, but if the plane tips slightly to one side for any reason and unloads the opposite float, the toe-in doesn't help as much, and in fact can accentuate the veer just as leaning on the outboard ski when snow plow skiing will cause a turn to the other direction.

It wasn't until I checked the relative angle of attack of the plane relative to the top of the floats tonight as mentioned below did I finally get my plane to track straight at high speed. Prior to this final adjustment, I had to hold in up elevator during the take-off run to keep it tracking straight. And then had to be careful to let off the elevator as it lifted off to get a normal climbout.

I had initially intentionally set up my floats so the plane was at a positive angle of attack when it sat in the water on the floats, thinking it would help get the plane off the water faster. It did do that, but in the process it forces the front tips of the floats down into the water as the motor is throttled up and the planes levels off as it gains speed. And as noted below, the added drag in front of the step is what causes the floats to hook and veer at the slightest yaw movement.

The following picture shows not only the mods to brace and firm up the float platform, but also the positive angle of incidence of the plane relative to the floats I had at first. I simply swapped the fore and aft wire LG wire to correct the incidence problem. My plane now tracks straight and glides straight when landing, making both ROWs, LOWs and "splash-n-goes" a lot more predictable and fun.

[antslake]

Good stuff!

[scratchandbash]

What a nice shot on the shoreline GP (pg1). That's add worthy. I just dug this up in a Google search, not an RCG search, which is why I just found it.

Bill

[G.P.]

Oh you, your making me blush! I just got lucky for once.

Thanks!