I still need float-rigging info

[Lynn Matteson]

Paul, Lowell, Dusty and others-
Thanks for all the valuable insight and ideas regarding my float installation/training.
Paul, I just found the diagram that I drew after I had the floats rigged. I checked float top, lower door sill, and wing angles with a digital level. My drawing shows the floats at 2° up, the door sill at 6.2° up, and the wing at 8.1° up. Now on the wing, I checked the level figuring the center of the leading edge and the center of the trailing edge (I used a block at the rear to achieve a straight line reference through the "center" of the wing). So from what I'm seeing, I have 4.2° of incidence, right?....top of float to datum of aircraft. Then perhaps 1.9° more throat angle, for a total of 6.1°? I'm heading for the hangar right now to recheck the datum-to-wing angle. I will get reading this time using just the bottom of the wing and forget the "theoretical center of the wing" for now. I can't check the float-to-fuse angle as the floats are off. I'll try opening up the throat angle when I install the floats after repairs are made, but it seems as though as slow as it flies (with floats on), I gotta have more than enough incidence, eh?

Lynn

[Lynn Matteson]

Holy crap, Batman....I just put the digital level on the door sill and the bottom of the wing...the door sill read 11.8°, and the wing bottom (straightedge along the bottom surface of the wing) read 10.5!! I also re-measured the chord line angle (using the point on the leading edge that gives the chord its' maximum length) and this reading was 12.8°. Now I'm confused....if the bottom of the wing is compared to the door sill, the incidence is negative 1.3°, but if the chord line is compared to the door sill, the incidence is 1° positive. And from my previous post, I said that the float-top to door sill angle was 4.2°, and with hardly ANY "built-in" incidence, it doesn't sound like I have nearly enough throat angle....no wonder this thing won't get off the water!

Incidentally, I took a flight while I was at the hangar and it took 5 seconds to get airborn...not a worlds' record by any stretch, but seems like I have enough power to get the bird up without floats.

Lynn

[av8rps]

Interesting info Lynn. I will dig out my digital protractor this weekend and measure mine to see how it compares.

A 5 second land takeoff is pretty good in my opinion. That's why I said I believe you have most of the Jabiru figured out. But I still believe it can make a lot more prop thrust with a longer blade, if there was just a way to run a longer one.

Even with my 912 that is evident, as my Kitfox on floats gets off a lot better with the longer 72 inch 3 blade than it does with the 68 inch 3 blade. But the smaller 68 inch prop makes it fly faster by probably 5 mph. My Lake amphib is much the same; I tried a later model Lake prop on my airplane once because I was told it would fly a lot better, and it did. I gained almost 200 fpm and about 10 mph, yet both Hartzel 2 blade Constant Speed props looked essentially the same. The only significant difference was that the later model prop was 74 inch diameter rather than the older prop that was 72 inches. Two inches more prop diameter did amazing things for the Lake. So I have proved to myself again and again that the longer diameter props make more thrust.

I don't meant to beat a dead horse on this subject, especially knowing that you get pretty good performance from your airplane in its current state. But bolting floats onto an airplane does tend to bring out the worse in an engine, prop, airframe combination. So even though you are getting good performance on wheels as it is, I still believe your engine probably has a lot more potential to make more power with a more efficient prop speed.

[av8rps]

Holy crap, Batman....I just put the digital level on the door sill and the bottom of the wing...the door sill read 11.8°, and the wing bottom (straightedge along the bottom surface of the wing) read 10.5!! I also re-measured the chord line angle (using the point on the leading edge that gives the chord its' maximum length) and this reading was 12.8°. Now I'm confused....if the bottom of the wing is compared to the door sill, the incidence is negative 1.3°, but if the chord line is compared to the door sill, the incidence is 1° positive. And from my previous post, I said that the float-top to door sill angle was 4.2°, and with hardly ANY "built-in" incidence, it doesn't sound like I have nearly enough throat angle....no wonder this thing won't get off the water!

Incidentally, I took a flight while I was at the hangar and it took 5 seconds to get airborn...not a worlds' record by any stretch, but seems like I have enough power to get the bird up without floats.

Lynn

Lynn,

I went to the airport today and measured the difference between the bottom of the door frame and the top of my Aerocet float - on my Model IV that door frame sits 1.5 degrees higher (or tail low) than the float top.

But that is not the throat angle from the wing to the top of the float.

Unless we all agreed to doing a wing to fuselage incidence reading EXACTLY the same way, it is unlikely we will get readings that would accurately compare. And frankly, I don't think that number matters when we have a known good flying Kitfox amphib (my Model IV) that has a fuselage exactly the same as yours to compare lower door frame measurement to the top of the float measurement. I'm not trying to minimize anyones in depth float rigging analysis, or their math. I just think it is best to follow an example that is known to work well.

The only real variable between our two very similar airplanes would be the angle in the step area on the bottom of each of our floats. Yes that could be off slightly, but it would just be diffence in the float design, and I'd be willing to bet it is minimal. And I'm sure if we compared other brands we'd find them much the same as the Aerocet or the Zenair, but likely still slightly different. (Hopefully my explanation here makes sense...)

Another thing that might help you is a recent discussion over on the Highlander / Just Aircraft forum where I have been trying to help a couple Highlander guys rig their Zenair 1450 amphibs to 912s powered Highlanders. The most recent post is interesting to say the least, as one builder just put his floats on the way Zenair said to install them on a Zenair 750 (which is something I would have never suggested as a Highlander is very different aircraft in design from a 750), but from what I can tell he hit the jackpot!

Ironically, most of his final rigging numbers were in line with what I had originally suggested to another Highlander builder, but he did locate his step differently from what I can tell in his explanation. I'm not 100% sure he said that right, but if he did then that part I find quite interesting and will probably look more into that myself. So I'm going to ask him to explain that further.

But whatever he did works very well, and he has youtube videos to prove it. I was pretty impressed with the videos, as it looks to be rigged perfectly to me (especially when he's operating from glassy water with a lot of suction issues). The only unknown would be if he might later learn of issues associated with extreme CG loading fore or aft, or something else that would be odd. Other than that, the videos show it flying on and off the water near perfectly. In my opinion, at first glance I think he nailed the rigging setup! In fact, I'm keeping his numbers and the next time I install my Highlander floats I'm going to compare my numbers against his. Maybe he has better numbers than me? If so I'm not ashamed to admit there may be a better way to do it. I'm not too proud to modify my rigging if my airplane will perform better

Here's the link to that forum subject; http://wingsforum.com/viewtopic.php?...23589&start=15
The last post has the info most valuable to your install.

And here's the separate link for the takeoff video; https://www.youtube.com/watch?v=TPDp...ature=youtu.be

And here's the landing video; https://www.youtube.com/watch?v=HEaz...ature=youtu.be

If your numbers are close to what he is doing, at least you'll be vindicated for your setup. And if not, maybe that can be the information you need?

For me, seeing is believing. So his videos are priceless to guys like us that are trying to set up a float plane for best performance.

[Lynn Matteson]

Thanks for the info, Paul, and sorry it took me so long to get back here to the forum...too many irons in the fire!
Yes, I agree that we all need to "standardize" the method of measuring/comparing angles, etc. when we discuss these matters. And in the matter of comparing our VERY similar (read: identical) airframes, the door bottom-to-float top is the one that should be used. As far as the angle of the step area on my floats is concerned, the top of the float is parallel to the bottom of the keel/skin for about the last 24" or so, so I doubt that that is very different between our set-ups. So at this point, I'll forget about the wing incident-to-float top comparison, and stick to the door frame bottom-to-float top comparison, and most likely increase that angle a bit when I reinstall the floats the next time....spring most likely.

I've been thinking lately that the most likely problem for this beast taking so long to lift off is the added weight of my CFI, (along with the short prop, low power, direct drive Jabiru power) which is about 235 lbs. If I could get my training revved up a bit in his Cub, and get his approval to cut me loose and fly the Kitox alone, I think the whole frustrating matter would be a thing of the past.

Again, thanks for all your help, Paul and others, and I hope that this thread hasn't scared off potential float flyers...my situation is kind of unique, I'm thinking.

Lynn

[av8rps]

Hi Lynn,

Knowing how busy you always are, I figured you were just off on projects.

Yes, I agree that adding a bit more wing to float incidence will help your situation. Most would probably do that with my Kitfox, as it is pretty much the least amount I would ever put on a floatplane. But I like it the way it is. I'm certain however if I increased my throat angle on my Kitfox, I would shorten my takeoff run quite a bit. So in effect, my numbers are probably not the best to follow.

I think your idea of getting your time in the Cub would be a good one. Let's face it, most of these little airplanes fly best with just one person in it. The only thing I'd suggest is to incorporate your amphib ops training into your training program, even though the Cub is not an amphib. Just pretend it is so you develop habits that include proper gear position.

On that subject, I just read an article in digital Kitplanes talking about flying a Searey amphib,and the author explained Searey's new gear position warning indicator, and I really liked what they did. Granted I am really old school, so I will probably never go out of my way to actually buy one, but if I did I think I'd use theirs. I think they have it figured out.

I too hope people aren't discouraged by any of this float discussion, as yes, you are trying to do something that as far as I know has never successfully been done before (a Speedster Jabiru 2200 Kitfox amphib). And frankly, I'm impressed with what you have accomplished thus far. I think with more angle, along with those wing extensions (which will also be much more effective with the increased angle) that you will probably be happy with your new amphib. Especially if you can limit additional weight in the cabin.

[Lynn Matteson]

Regarding my on-again, off-again training in the Cub, my instructor has me call out all the moves for landing as if we were in the Kitfox....that is: "wheels going up for water landing, pressure building ....mechanical indicators show all four wheels are up, and hydraulic pressure is maxed out on the gauges, mixture set (I've got a Rotec throttle body injector on the engine), flaps set, throttle back, etc, etc." He has me do this in the Cub even having to pretend that I'm looking at gauges...it really IS good practice.

I ordered a new front fork to replace the damaged one, and while talking to Michael at Zenair, I mentioned that I broke the top ot the bulkhead near where the rigid end of the hydraulic cylinder mounts, then told him that this is a very weak area in their design, and that they ought to strengthen that area. He said that the people who buy their floats are very weight conscious....geez, what would it cost to reinforce that area? one pound per float would be a high figure, I'm thinking. The main wheels are built adequately, as far as I can see, but those fronts are weak right at the top of the bulkhead, where the flange is formed, and this is where the stress is concentrated.

When I was building my floats, I was narrow-minded enough to just follow the instructions and build accordingly. I DID do some modifications to the main wheel amphib apparatus, but never really looked at the front wheel mechanism with an eye toward how it worked and how the design put such a huge load on a very small area, to wit, the formed top of the #2 bulkhead. It would have been such an easy matter to have reinforced that area, and spread the load out over a larger area. Well, I forgot to put my "engineer's hat" on while building them, but you can bet that it'll be on while I'm RE-building them, and mabe even use a chinstrap to insure that it doesn't blow off!

Lynn

[N213RV]

Hi Lynn,

I am building a set of 1450A's right now at 26W. I sent you an email a few weeks back regarding lessons learned from your build. I will look at the above mentioned areas, but would love to get together with you soon to get some advice from you. I can either meet you at your hangar or you can fly to 26W if you are out and about. I am on vacation all next week (Thanksgiving) except for Tuesday I have to work. I can work around your schedule. Thoughts?

Thanks