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Old 11-19-2014, 03:22 PM   #21
av8rps
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Thumbs up Re: I still need float-rigging info

*** NOTE - UPDATED WITH CORRECTIONS ******

Quote:
Originally Posted by Lynn Matteson View Post
Sorry if this becomes redundant, but I haven't heard a word of response to a month-ago request for float-rigging info for my Zenair floats on a model IV. And I can't seem to get off a private message either. I know you float-fliers are out there, and I'm anxious to join the party. : )

Lynn Matteson
Ok Lynn, I have some info for you. I did some calculations using a variety of float install information I've aquired over the years, and then called a few people that I consider to be float experts to see what they thought about how to best float a Jab 2200 Speedster? The good news is that we all came up with approximately the same numbers. The bad news is that I can't tell you exactly how we came up with that, as we all used different methods to arrive at our numbers . But after talking about what would be best for your situation we all agreed that the best thing to do is to use experience rather than formulas. Many seem to think that float installation is a science, but the reality is that it's more like an art. So in the end the numbers we decided to use are based on our collective experience more than what you might find in some textbook. But we're confident that it's more likely to help you than if you were left to do it by the book.

But I do have to make this disclaimer; None of us are formally trained on any of this. We're just guys that have been flying these kind of floatplanes for a lot of years, and have learned mostly through our own trial and error. So don't be surprised if you find that you may have to tweak things a bit after you've installed the floats on your airplane. With homebuilts since no two are alike you almost always have to do some trial and error before you get it right. And while I'm pretty confident we can get you 85-90% accurate to where your floats need to be, it's likely that you may need to tweak the throat angle and/or step placement if you want to extract the top performance from your new floatplane. And if by some stroke of dumb luck our numbers work well without any tweaking, then you can just consider that a bonus you get to enjoy from all of our years of fiddling

So let's cut to the chase;

- First, set your spreader bars so that the floats are no more than 8 ft wide at the widest part. Typically that means that if you drew a centerline down each float lengthwise, from the center of each float (with Zenairs that would be the channel that you walk on), that measurement should be 6 ft. Our experience has shown that a lot of people put the floats too far apart, reducing their off-the-water performance of the float. Most people don't know this, but the bow wave coming off the front of each float helps to hydrodynamically lift the other float next to it in the initial part of the takeoff run.

- Second, set the floats up for about a 22 inch height from the top deck of the float to the bottom longeron on your Kitfox. That should give you enough prop clearance, while still benefitting from the use of ground effect to help make the wing lift sooner. You will notice when looking at most of Zenairs float install pictures that they tend to mount their floats further away from the airplane than what I'm telling you. That's not to say what they're doing doesn't work. But if the aircraft is kept closer to the float it typically results in having the wing closer to the water, which makes better use of ground effect (or should I say water effect?). The theory is simple, as the aircraft moves forward the air becomes slightly compressed under the wing, which helps to create lift sooner. Or at least that's what some of us believe (plus, sitting lower on the floats also helps with stability on the water)

- Third, level the Kitfox using the bottom door frame tube (this is very important). Then locate the most aft (rearward) center of gravity for your Kitfox, and run a plumb bob down from that area of wing to the floor.

- Fourth, slide the floats under the aircraft until you have located the step 3 to 5 inches aft of the rearward Center of Gravity range for your Kitfox (3-5 inches from where the plumb line is hanging). On my Kitfox equipped with Aerocet floats (which handles and performs marvelously), that positions the step directly below the middle of the 3rd (from the front) landing gear attach bracket (see the photo I attached of the float rigging dimensions for my Kitfox to see what I am describing. But note that the 23 inch measurement I am showing in the picture was done only so you could have an easy way to see EXACTLY where my step is located). Your step location should be somewhere near where mine is in the picture. And you probably will find it even further aft as the location of the step on my Kitfox is as far forward as you would want a set of Zenairs. If you put it further forward you are likely to have water handling issues (e.g. porpoising), and too much forward CG.

The Zenair amphib is about 2 ft longer than my Aerocet amphib, so when the Zenair is installed the bows with all the nosegear weight is much farther out in front of the airplane than mine, and likely will cause the aircraft CG to move quite a bit forward. So it is possible that you might need to move the float even further back than the 3-5 inches. The good thing is that having to move the step back because the float is long doesn't do much to affect water handling. The worse it does is (maybe) extend your water run for takeoff.

But have the step too far forward and you can cause all kinds of weird, and even scary water handling issues.

- Fifth, set the float angle. On an aircraft with a high power to weight ratio you can get away with just a 2 to 3 degree (tail low) angle on floats. But for most normal aircraft that number is more like 4 to 6 degrees. In the case of your Kitfox I would recomment going with a 4 to 5 degree angle (using the top of the float and the bottom of the door frame) as the Kitfox wing does generate a lot of lift for its size, and your overall wing loading is still relatively low.

The last two photos attached are just there to show you how the float should look when the airplane is at high speed on the step. Commonly a floatplane will ride on only about 4 inches of the float, the area just ahead of the step (also known as "The sweet spot"). It may look as though the back of the float is skimming too, but it is essentially that small 4 inch area ahead of the step doing all the work. That's why it is ultra critical to have the step in the right location.

One last suggestion is to study the photos of my Kitfox closely, as even though I have Aerocet amphibs and you have Zenairs, the concept is the same. So if you can just make a few minor changes to your rigging as explained above, it's likely you will get great enjoyment from your new Kitfox floatplane.

I will follow up this post with some more pics that I also feel might help you.

Paul

(please forgive my late editing - I had a computer crash earlier)

Last edited by av8rps; 11-19-2014 at 06:54 PM. Reason: Better clarity
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Old 11-19-2014, 06:14 PM   #22
Lynn Matteson
 
Join Date: Dec 2008
Location: Grass Lake, Michigan
Posts: 48
Default Re: I still need float-rigging info

Thanks VERY much for that info, Paul. Just to give you a bit of feedback, I had set my floats up exactly to the 6-foot centerline separation that you suggested, and because my floats are 24" wide, the max of 8 foot that you mention is adhered to. I went with the 6-foot centerline wheel separation that my Grove landing gear gave me, as that looked "about right for float separation." (solid engineering presumption on my part, eh?)

Next, I had rigged up a mock Kitfox lower longeron "frame" and had this spaced 18 inches above the float walkway. I had originally figured that I had to keep the overall height of the tail fin under 120" due to the height of my hangar door. Your dimensions will fit within this parameter. I'll just raise the lower longeron on my mockup. This mockup is just to give me an idea of what the struts and diagonals will look like and allow me start some of the cutting on those parts without having to actually ground the plane so soon. I wouldn't actually build to this mockup, I will just use it for getting the bottoms of the struts and diagonals cut to shape, leaving adequate length for the tops to be cut when the plane is actually hanging over the floats.

Lynn
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Old 11-19-2014, 07:25 PM   #23
av8rps
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Default Re: I still need float-rigging info

Quote:
Originally Posted by Lynn Matteson View Post
Thanks VERY much for that info, Paul. Just to give you a bit of feedback, I had set my floats up exactly to the 6-foot centerline separation that you suggested, and because my floats are 24" wide, the max of 8 foot that you mention is adhered to...
Lynn,

I had a computer crash (and a brain crash ) after a bunch of interruptions while trying to put this whole thing together for you. So please make sure to go back and read all that I just reposted. It will probably make more sense than the earlier gobbledy gook I wrote.

I like the idea of your rigging mock up. I'm not that smart, I just crawl around under the airplane while it hangs mid air from a chain while I cut struts and cables (see pic below and note wife's comment "Are you sure this is safe?)

Your 18 inch spacing between the fuselage and top of float would probably be ok because you aren't running a long prop.

But also remember that whatever throat angle you use will lower or raise the tail accordingly. And it's amazing what an inch or two off a strut can do to tail height. The original rigging I got with my used Aerocets were modified for a VW powered Kitfox , so it had a HUGE throat angle. After I figured out what I needed for struts and I got them installed the tail came up a about a foot and a half! I'm lucky I have a tall hangar...

(of course a guy can always build a cart or two to go under the nosewheels to keep the tail down when in the hangar)
Attached Images
File Type: jpg Poor mans float crane.jpg (102.8 KB, 299 views)
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Old 11-19-2014, 08:25 PM   #24
av8rps
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Default Re: I still need float-rigging info

I put at the end of this post a random bunch of old photos I had saved of Kitfoxes with Zenair or Czech floats installed. I thought if you hadn't already seen them you might like to. As we all know when it comes to building things, sometimes a picture can be worth a thousand words...

(Incidentally, the blue, red, and white Kitfox IV on white Czech amphibs is a short wing Speedster version as I recall...FYI )

In addition, just below this post you should find a mechanical drawing of my Aerocet float details with dimensions. But more importantly it shows my full scale drawing of the fuselage attach brackets you will probably need for installing your floats on your Kitfox. You might still be able to buy those fittings from John or Deb at Kitfox? But if not you can hopefully make your own from the drawings on that sheet. I traced them full scale and then scanned them into digital, so I'm thinking if you print that page on an 8 1/2 x 11 piece of paper, you should probably end up with a full size template. And if not at least the fuselage attach fitting concept is there for you.

But if you do end up making your own, I would recommend making the fittings longer (per the hashed lines I added). That way if you need to you can adjust your float rigging up or down without having to buy all new (expensive) strut material.

Paul
Attached Images
File Type: jpg 1 - My Kitfox Aerocet 1100 amphib float specs with bracket drawings.jpg (86.6 KB, 313 views)
File Type: jpg Czech 1150 amphib Kitfox IV at hangar.jpg (65.2 KB, 310 views)
File Type: jpg Czech 1150 amphib Kitfox IV in flight.jpg (20.5 KB, 314 views)
File Type: jpg Czech 1150 amphib Kitfox IV in water side view.jpg (71.9 KB, 312 views)
File Type: jpg Czech 1150 amphib Kitfox IV on ramp (blurry -sorry).jpg (56.4 KB, 311 views)
File Type: jpg Czech 1150 Amphib Kitfox IV on runway.jpg (76.7 KB, 315 views)
File Type: jpg Czech 1150 amphib Kitfox IV on runway rotation.jpg (68.5 KB, 312 views)
File Type: jpg Czech 1150 amphib Kitfox IV on the water.jpg (101.7 KB, 315 views)
File Type: jpg Czech 1150 amphib Kitfox IV water rear view.jpg (92.3 KB, 316 views)
File Type: jpg Czech 1200 amphib Kitfox IV on the grass.jpg (37.6 KB, 311 views)
File Type: jpg Czech 1200 amphib Kitfox IV on the step.jpg (49.6 KB, 314 views)
File Type: jpg Czech 1200 amphibs Kitfox IV on beach.jpg (47.3 KB, 314 views)
File Type: jpg Czech 1200 amphib Kitfox Model 2 side view.JPG (35.3 KB, 313 views)
File Type: jpg Zenair 1150 amphib Kitfox IV front quarter view.jpg (27.5 KB, 315 views)
File Type: jpg Zenair 1150 amphib Kitfox IV in hangar.jpg (75.9 KB, 313 views)
File Type: jpg Zenair 1150 amphib Kitfox IV straight on side view.jpg (26.1 KB, 310 views)
File Type: jpg Zenair 1150 amphib Kitfox IV side view.jpg (31.6 KB, 312 views)

Last edited by av8rps; 11-19-2014 at 09:27 PM.
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Old 11-21-2014, 07:17 AM   #25
Lynn Matteson
 
Join Date: Dec 2008
Location: Grass Lake, Michigan
Posts: 48
Default Re: I still need float-rigging info

Quote:
Originally Posted by av8rps View Post
I put at the end of this post a random bunch of old photos I had saved of Kitfoxes with Zenair or Czech floats installed....Paul
Thanks for the updates, Paul. I haven't re-read the original posting (with edits) nor all of the latest, but just skimmed it enough to make a reply. The one thing about rigging that Zenair DOES make available are machined fittings that fit the Kitfox IV factory-welded brackets. I already have these fittings and all the strut and diagonal brace material, and of course the plane has the 4-on-each-side float/ski brackets. Yesterday morning, after thinking of how to make the rigging somewhat adjustable, I laid an aluminum bar across the pickup tubes on one of my floats...fore and aft...to check on the feasibility of making the throat adjustable. I leveled the float so this bar was reading "zero" on a digital level. Then I placed a 1/2" shim under one end of the bar....the dig. scale read 0.5 deg. Then I removed the 1/2" shim and used a 1.5" shim (2x4) and the reading was 1.5 degrees. Swapping the shims to the other end, one at a time, and the reading were the same. In short, as luck would have it, whatever the thickness of the shim is in inches, adjusts the reading a similar number of degrees. So if I were to use, say, a 1" shim under each of the four rigging blocks that bolt to the spreader bars, then set the plane-to-float (throat angle) angle at say, 4 degrees, fly it, and if an adjustment were necessary, I could remove the front 1" shims, and the throat would close up 1 degree to 3 degrees, or remove just the rear shims, and the throat angle would open to become 5 degrees. Or, if the plane flew well at the original setting, I could remove all four shims, and still be at the 4 degrees of the original setup. Now, is this what others have done to have some adjustability, or am I all wet (no pun intended) on this theory? Using shims judiciously under what Zenair calls the "pickup fitting" which is shaped like a pillow block and to which all the fittings are attached, raises or lowers the entire rigging package...struts, diagonals, x-wires, and airplane....at once, and no changing of the struts or diagonals is needed. So, in my thinking, I can easily change the throat angle, but it's the placemant of the step in regards to the C of G that would involve drastic changes of strut/diagonal tubing length if that original step/CG placement were not made right to begin with.
Your thoughts?

Lynn
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Old 11-21-2014, 09:33 AM   #26
av8rps
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Default Re: I still need float-rigging info

Lynn,

Typically people use extended float fittings at both ends (float and fuselage) so that you can move it up and down in the other bolt holes to adjust it wherever needed. But the way you are describing yours with using shims, I can't see why that wouldn't work just as well.

And yes, I agree it is much more difficult to be able to adjust the step location. I've seen people use a c-channel mounted upside down to the top of the float (usually attached to the area where the spreader bars are) so the struts could be moved to different bolt holes in the c-channel, allowing the float to be moved fore and aft by just moving the strut fittings in the bolt holes. If you can figure out a way to do that even temporarily until you are ok with how your airplane performs, that could save you a lot of time and frustration (and probably money because you won't need to cut up so much strut material). Once you know you are happy with how the floats perform, you can always make a permanent fitting for attachment.

Half the battle with installing floats is understanding what you are trying to actually accomplish. And from what I'm hearing from you, you are most definitely on the right track

Paul
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Old 11-21-2014, 11:54 AM   #27
Lynn Matteson
 
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Posts: 48
Default Re: I still need float-rigging info

Quote:
Originally Posted by av8rps View Post
Lynn,

Typically people use extended float fittings at both ends (float and fuselage) so that you can move it up and down in the other bolt holes to adjust it wherever needed...
Thank, Paul....I hadn't thought of the C-channel idea for fore-to-aft placement, but that's a good idea. I might even be able to incorporate the shimming-for-throat-angle method into the C-channel idea, and have a more or less universal temporary flyable mount. This is getting exciting!

Lynn
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Old 11-21-2014, 03:18 PM   #28
Lynn Matteson
 
Join Date: Dec 2008
Location: Grass Lake, Michigan
Posts: 48
Default Re: I still need float-rigging info

Paul-
I have a question regarding that blue, red, and white Kitfox IV....it is the only one of the planes pictured that has the diagonal brace starting from the rear fuselage bracket and going forward and down. I have been told that the diagonal brace (on float-equipped planes)will start at the fuselage directly above where the original landing gear was mounted...or near where the original main wheel was. So, if that is true, that would make all the other pictures of Kitfoxes (that you posted) appear to have been originally tailwheel planes, and the blue, red, and white one would have been a tricycle gear plane originally? Just curious...

Lynn
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Old 11-22-2014, 08:24 AM   #29
av8rps
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Default Re: I still need float-rigging info

Lynn,

I don't think that installation has anything to do with being a taildragger or a trike gear setup.

I'm guessing the reason for that is because those floats have the spreader bars closer together than most floats. A lot of builders as well as manufacturers don't really know what they are doing when putting floats together, so they put spreader bars too far back, too far forward, too close together, etc, etc.. if you compare the blue airplane to the others, you will notice there is a lot more float forward of the the front speader bar, besides the rear spreader attach being moved forward causing that rear strut to be more vertical. So something is different with those floats than most. At one point I do know the Czech's were building a 1250 that moved the step 6 or 8 inches back to offer more forward buoyancy for the Rans S7 guys, and I know the first sets did not have the spreader bars moved ahead to match the new step location. So I'm guessing those might be a set of those floats?

The Czechs did the same thing on their first set of their CZ 1300 amphibs. They made them initially for a specific airplane that had really closely spaced attach fittings that also were way far forward. They essentially couldn't give those floats away for install on other airplanes until Ken from Harbor sport aviation modified them and redesigned the landing gear so they could easily be mounted and used on other airplanes like the Rans, Kitfox, Highlander, etc. Ironically, after the spreaders and gear were fixed, they became one of the nicest floats out there.
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Old 10-09-2015, 02:18 PM   #30
av8rps
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Default Re: I still need float-rigging info

Hey Lynn, are you out there?

I never heard back to see how your float installation turned out? I figured by now (knowing how commited you were to making a Jab powered Speedster work on floats) that you must have it all figured out or you would have recontacted me.

Hopefully you are having so much fun on your floats that you didn't have time to write but now that float season is ending I'm hoping you may have some time to let us know your results.

Paul
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