kegelt

Trying to run a O.S. L.A. 46 on a 40 size trainer, with AirCore Floats, will this engine be strong enough to lift the aircraft?

tailspnr

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Thats a good question. I just finished my aircore floats that I bought off of here. I put them on a Airmadillo 40 trainer powered by a Magnum 53 fourstroke. Probably about the same power as your .46LA. Its gonna be real interesting to see if it flies. I put a 1" larger x 1 degree flatter pitch prop on her. I will probably get to try her off of snow before I do water.

JimCasey

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If your trainer takes off from grass with wheels, or if it will take off ACROSS a paved runway, it probably will take off from water with floats. My experience does not support the popular notion that you need a lot more power to fly from water.

Just be sure to rig the floats so that when they are level, the wing points UP 2 or 3 degrees. Otherwise, the floats should be parallel with each other and with the centerline of the airplane.

If you use a water rudder, don't make it stick down more than about a half-inch below the stern of the float(s). If it will kick up (like an ERNST rudder), that will be that much better.

tailspnr

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Jim, as you can see I have fabricated my own water rudder setup out of coroplast that I have from all of my PBF's. I have no experience with floats and had no idea how large to make the rudder. I just measured it and it's a hair over 2" down from the bottom of the float. When installed it will not kick up but I did make it so that I can remove it easily for flying off of snow. Until just now (when I went outside and floated it in my unwinterized pool....I knew I hadent done that for a reason) I got to see just how much of the rudder would be in the water. The full 2" is completely submersed with the top of the rudder at the surface. I assume from what your telling me that my water rudder is too big and will create too much drag. I also have to consider the fact the its made of 4mm thick corplast. So thats going to create more drag than usual.

This is good information to know. Thanks and throw out any other hints that you may have.

Scott K

JimCasey

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You have a clever water rudder installation.

Full-size planes have retractable water rudders. Water rudders are only used for slow taxiing.

Since, with R/C models, we would need an extra $ervo for a retractable water rudder, we generally do without.

Imagine the airplane going fast, floats level, about to take off. You're just touching on the step. You REALLY don't want the water rudder in the water 'cause it'll slow you down A LOT. Now you're ready to take off and you haul back on the stick. The water rudder sticks in to the (30 mph) water an extra inch and a half. If you only have ONE water rudder, that drag is a pretty big off-center force trying to pivot the airplane away from a straight line. If you're quick, you can save it but it'll make for a ragged takeoff.

If the rudder is no deeper than the step, when you haul back on the stick, the airplane can rotate 4 degrees nose-up before the water rudder touches. This, plus the 3 degrees of positive incidence you should have in the wing makes for a 7 degree angle of attack. You get enough of a bite of the air to make a nice takeoff. If you find that you need more bite from the water rudder, make it stick back further behind the float(s), not farther down.

Water rudders on RC floatplanes help you taxi crosswind. It's possible to operate without a water rudder...just dial in all the travel you can get on the air rudder. If the motor is running, you get prop-blast over the air rudder and can steer with power and rudder. If the motor is NOT running, a water rudder does you no good anyway.

Technique:
To taxi into the wind, the airplane should do this with the elevator neutral and the motor at idle.

To taxi downwind, hold full UP elevator, and add 2 or 3 clicks of power. The plane should be plowing along, trying to climb up on the step, pushing a lot of water, with the floats tilted upward as much as they will. This gets you (1) max rudder in the water, (2) the center of floatation of the floats is now behind the center of aerodynamic forces on the airplane, so the plane tends to weathervane downwind around the part of the floats that are in the water.

To taxi crosswind: Hold full UP elevator, and steer the rudder in the direction you want to go. When the wind catches the air rudder, the plane will probably try to weathervane. Add power to turn downwind. Reduce power to turn upwind. Steer with the throttle. It really works!.

My buddy Donnie has a beautiful Cub with twin water rudders. We tried to fly it one windy day. The water rudders were so effective that the airplane pivoted around them. When the wind blew, the whole plane pointed downwind, and we couldn't get it to turn back around for a takeoff. At max rudder deflection, it would just go a little sideways, but still downwind. If the water rudders were not so big, he could have given it a bit of down elevator and lifted the water rudders out of the water, and the plane would have weathervaned into the wind instantly.

tailspnr

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After reading your previous response I cut the water rudder down to less than 1" tall. I also adjusted the floats so that the wings have a positive angle of attack and the floats remain parrallel to the fuse. I even went out earlier and dialed in the freshly adjusted motor. I think the power should be okay.......it pulled her around the front yard in the grass.

I appreciate all of your advise and will try to remember as much of it as I can when the time comes. I'm already itching to go fly it. Now if the warm weather would just come back I'd get to try it out.

Scott K

JohnBuckner

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Could not agree more with Jim, float set up is far more critical to t/o performance than extra power. That two to three degrees positive incidence of the wing to the float top decks is vital and this is the most common mistake folks make you see float installations all the time at events with the aircraft tail sticking up in the air like a flag and its these same airplanes driving around the lake at high speed unable to take of at speeds everybody else is already flying at and their doing waterloops snubbing their bows and tipping over. The ideal set up is when the float decks are level the tail of the aircraft is slightly low. Here is what happens if you don,t have that positive incidence. When the ship is up on the step flying speed is reached but the wings angle of attack needs to be increased to lift off but when more elvator is used before the wing reaches the neccessary AoA the heels of the float contact the water and the extra drag just slows everything down below liftoff speed and making like a motorboat! Sometimes these rigs will bounce off a wave and with the excessive up elevator the airplane stalls into the air nose way up and the resulting battle for control. At proper incidence of the floatrs the wing will reach the proper angle of attack before the float heels reach the water and lift off sweet as you please.

I would also agree that corroplast rudder is way to big and thick. sheet Aluminmum at about fifty thousanths is just fine. At a float fly one year I lost a rudder when the hinge bolt fell out and not wanting to finish the day without a rudder (important at an organized fly with lots of traffic and taxi lanes, takeoff lanes) the solution turned out to be my wallet. Out came the abused credit card and whittled down to about a quarter of the full size with a bolt hole poked in the corner. This saved the day just fine in fact I got lazy the old card attended many more float flys .

So in my opinion just get the float incidence right, get the CG just a tad ahead of the step and whatever flew the airplane properly on land will do just fine on water.

John

tailspnr

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John, I have aquestion regarding your last comment. You say to have the CG just ahead of the step? My instructions said to have the step slightly ahead of the CG. I feel this could be very critical.

I'd also like to ask how critical is it that you have no more that 4 degrees of positive wing incidence in relation to the floats. What Im getting at is if I have setup too much positive incidence will I be hurt to? As I have only eye balled the AOA for the floats/wings.

Scott K

JohnBuckner

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Scott, yes your gut feeling about the importance of CG/step relationship is very important and I am aware that indeed many float instructions (not all) as well as other flyers will tell you to have the step ahead of the CG. All I can say is watch them fly and it will become apparent that something wrong. While other airplanes lift off sedately nice and smooth conversely landing beautifully and dirctionally very stable, why? Well this is my opinion of course but is the result of a wide variety of types I have set up and simply watching others at a lot of float flys over the years. Here is what is happening: I am sure you are aware how directionally unstable a wheeled taildragger is compared to the same airplane with tricycle gear. This is simply because with the taildragger (conventional gear) the CG is behind the main gear and there is the tendency for the Aircraft CG to want to swap ends with the main wheels so it can be in front i.e. directional instability. Conversely with a tri gear the CG is already ahead of the main gear (the gear with most of the weight) therefore much more stable and a natural tendency to go straight.

Now lets talk about floats, all float planes just before liftoff and right after landing will be on the step, thats running float level and all aircraft weight not supported yet by the wing is taken entirely by the floats in a tiny little footprint just ahead of the step. The entire float aft of the step behind the step is clear of the water. Now what we have here if the A/C CG is behind the step it is exactly the same situation as with a taildragger i. e. very directionally unstable but if we run the step a tad aft of the CG we have effectively converted the airplane to a tri gear and I can assure you set up like this, that ship won,t be spending as much time nose down in the water waving its tail saying get me out of here .


Back to the wing/float incidence thing just as Jim Casey wrote in his first post the wing must be positive to the float decks and most anything in the two to four degree area works well its not super critical you just must be able to rotate the wing to suffficient AoA to take off without digging in the after float bottoms and if you just step back you will readily see this from the side. Hold the wing at what you think would be a normal lift off angle then look at the after float bottoms is it level or also tilted back and digging into the water?


If when you set up your floats if you will just use the same CG on floats as on wheels (pitch stability which is what we are talking about when we speak of longtitudinal CG and in that regard the wing doesn,t know it has floats), arrange the float step a bit aft of that CG (1/8 to a 1/4 inch works well on 40 to 60 size airplanes) and set up a few degrees positive incidence wing to float decks. Do that and you will be very successful and I might add this form of RC is very addictive.

OK whats the next step? Night float flight of course, talk about euphoria but thats a different thread.

Best of luck and I apologize for motor mouthing.
John

tailspnr

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John, thanks for the detailed explanation. I understand exactly what your trying to say with regards to the step location. And as far as being long winded....I too suffer from that problem on occasion.

But now let me ask you this. On a conventional gear craft the gear is located far enough forward to ensure that adequate weight is behind the gear, therefore giving much more distance between the CG and the LG. As we all know, the further forward the LG is, the harder the plane is to handle on the ground. And on the float setup, my step is appx 1/2" in front of the CG. In my mind that should equate to one rock solid tail dragger. As opposed to having the gear the usual 3 to 4 inches forward. Am I not correct here that the handling characteristics should less unstable than a traditional conventional gear plane........or do the floats and water add a new dimension of instability?

Scott K

JimCasey

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John's explanation was correct.
If the step is very much in front of the balancepoint, it can make the plane laterally unstable on takeoff. But I don't think it's "CRITICAL" as he said, only because the floats can slide sideways on the water as soon as the plane is on step. The rake of the floats is critical, and the alignment is pretty darned important, and the step can go +-10% of the MAC relative to the balance point. Just get 'em both the same. I use 40% of the MAC for the step location, and that agrees with what John said. When you make "rules" more precise than this you have to understand thet the particular float design, the loading of the floats, and a bunch of other parameters matter. I use V-Bottom floats with tapered sides, and I think they outperform other designs in terms of stability, light weight, ease of takeoff, and low drag.

If you're nose-heavy on the floats, or if the floats are too small, it doesn't destroy stability, it just makes the floats submarine when power is added. Some seaplanes are particularly bad about this.

planecrazy101

Hey TailSpnr, could you post some details on your coroplast floats? I'm looking for a cheap and easy way to try float flying. Thanks

JimCasey

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If you want cheap and easy, here's a link to an old Chuck Cunningham article that shows you how to make styrofoam floats that you can cover with packing tape.

http://www.flyinglindy.homestead.com/skisandfloats.html

tailspnr

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Planecrazy, what would you like to know? I bought mine from a guy on here for about $30 and spent maybe $8 on glue, took me about 1.5 hours to build and mount them. As you can see they are very simplistic flat bottom floats but hey........as long as they do the job I'll be happy. My only thoughts or concerns are regarding the seams were you have to apply alot of silicone. If they don't leak after a short bit of use I'll be happy. And of course theres the concern of weight. But I wont know the answer to any of these until I fly it. I'll be sure and post a report as soon as I do.

Scott K

planecrazy101

Hey thanks, I don't know why I was thinking that your floats were built from scratch. I had to go back and reread your posts. Anyway, the recommended article is great. Good luck with your floats.