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Old 10-21-2015, 08:51 AM   #61
av8rps
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Default Re: I still need float-rigging info

A checkride?? That's funny!

I'm at least glad to know people are enjoying the thread while also learning from it.

I am a little concerned however that in trying to explain all this seaplane stuff in detail that it might appear a bit overwhelming to the average guy that is thinking about one day flying his or her Kitfox as an amphib. It's not really anywhere near as hard as this thread is making it appear. Not only does a Kitfox make for an excellent seaplane, but pretty much anyone can learn to fly an amphib well, and even though it may appear complex and overwhelming, if one learns properly and then practices it regularly, it will become second nature. And if one does it that way, it also can be done safely.

I think it is a lot like the latest trend of booney bashing with big tires and STOL aircraft flying around on sandbars and landing on tops of mountains (oh, and not to forget skimming water with your tires ). Doing that kind of flying certainly requires one to develop special skills, and an extreme ability to exercise good judgment and common sense, knowing what you and your airplane are realistically capable of.

But just like flying an amphib, when you get that all figured out just look at all the cool places you can go that the average guy with his 180 mph Spam Can can never go. I personally enjoy booney bashing almost as much as flying off water, as both require special skills that in my opinion not only makes flying more interesting and enjoyable, but the additional challenges also makes you a better pilot.

So we can beat this to death some more if there is further interest, or if people have additional questions. Otherwise I think we probably need to just let Lynn work on his floats so he can report back this spring after trying out his modifications.

Paul
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Old 10-21-2015, 11:19 AM   #62
av8rps
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Default Re: I still need float-rigging info

Lynn,

I know you are a very creative and talented guy. So I just want to plant a seed with you that might make the biggest difference ever with your Kitfox.

Think about the possibility of putting some sort of a prop reduction unit on that Jabiru so you can spin a longer, larger prop. I am absolutely convinced that if that were done to the Jabiru that it would truly be a kick-ass motor for a STOL type airplane like a Kitfox. Yeah, I know it would add weight, and it might require a bigger effort than it sounds. But I'm convinced it would produce so much more thrust that you wouldn't even notice the extra 10 or 20 lbs for a PSRU. And you'd be very happy with the extra effort to do it.

I say all that because of knowing how well my 80 hp 912ul with a gearbox reducing the prop speed works on my Kitfox IV amphib. I do cheat a bit by having an IFA IVO prop, but even if I use a fixed pitch prop setting it performs really well. As an example, the other day I was cruising around (on floats) at 105 mph at approximately 5000 rpm, which is only about 70% power with the prop setting I was using. While we probably can attribute most of that to the efficiency and performance of a 912 matched to a really good airframe, the reality is that turning a prop at a very efficient speed produces the most thrust for the available horsepower or torque. That in my opinion is where a 912 Rotax prevails over most other engines in its weight class. Turning a small and lightweight engine at high rpms so it can make the most horsepower and torque out of its size, coupled to a gear reduction that makes the propellor most efficient is why I believe the 912 does so well.

So with that said, now compare your Jabiru to the 912 ul. It is approximately the same weight as the 912ul (actually lighter), and produces about 4 hp more, with similar torque, but at much lower rpm. But then consider engine displacement. The 912ul is only 1,211 cc, or 74 cubic inches. By comparison the Jabiru is nearly 1,000 cc's more than the 912ul, with a displacement of 2,200 cc, or 134 cubic inches. So in a nutshell, the Jabiru actually has the same or more power than the 912ul (and probably way more potential for more due to more available displacement), but just doesn't apply that power to a prop as effectively or efficiently as the 912.

So imagine if you could add a prop speed reduction unit to the Jabiru that would allow it to turn a propellor at similar speeds to what the 912 does? I personally believe you would actually have as much or more power than the 912 ul.

To support my reason for feeling a PSRU would do so much for a Jabiru Kitfox, I will share a story most here probably don't know about our airplanes;

I remember Dean Wilson (designer of our airplanes for those that don't know) telling me about the first flights of the Avid Flyer prototype being a huge disappointment. It was powered with the most popular ultralight aircraft engine at the time, a Cuyuna 43 hp two stroke engine with a standard 50'ish inch ultralight prop bolted right to the crankshaft. Even though Deans calculations said 43 hp should be more than plenty HP for the very lightweight 364 lb Avid Flyer prototype, test flights returned poor at best performance numbers. Climb rate was only 200 fpm, and cruise only 55 mph. Frustrated, Dean almost scrapped the whole idea of the Avid Flyer. But after thinking about it more, even though the entire ultralight industry was using that engine and prop combination on most every ultralight, he came to the conclusion that turning that short prop at the rpm of that Cuyuna (about 6500 WOT) was making for a very inefficient propellor, resulting in very little thrust for the available horsepower.

So Dean went down to a local junkyard and bought the planetary drive out of a Ford C3 transmission. Then he machined a gearbox housing that held the ring gear and sun gears in place, and a adapter that would bolt all that to the crankshaft of the Cuyuna. Now he had himself a 43 hp Cuyuna that would spin a 6 ft diameter propellor with 36 inches of pitch at only 2200 rpm!

The test flight that followed the gearbox addition produced amazing results from the little 64 lb, 43 hp Cuyuna;

Instead of 200 fpm climb, he now had a 1,460 fpm climb rate!

And cruise jumped from 55 mph to 80 mph!

So every Avid Flyer kit was sold with a PSRU installed on the Cuyuna. And shortly after that (about the time Kitfox started), Rotax showed up on the light aircraft scene with their PSRU equipped 2 stroke aircraft engines. Of course we all know where that all went, with Rotax now being the number one aircraft engine manufacturer in the world (I often wonder if they ever gave Dean Wilson any credit for any of that, as they should have IMHO ...)

So, imagine discovering the true capabilities of the Jabiru engines by adding a gearbox that allows for a larger, more efficient prop, just like Dean Wilson did with the Cuyuna? I could be wrong, but I'm willing to bet you would see an amazing difference in your Jabiru Kitfox with the addition of a PSRU. And it would improve in all operational modes, climb and cruise, and land or sea, .

There you go Lynn...there's the seed I wanted to plant
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Old 10-21-2015, 11:51 AM   #63
Dusty
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Default Re: I still need float-rigging info

At risk of getting a little off topic,
I would agree the jabaru with a reduction would be a serious contender for one of the best power plants around.
Cooling would need to be improved(Rotec water cooled heads?)and a possible shift of the torque/power curve.
If the weight worked out ok, this would be worth considering for our type of aircraft.
Still some big boots to fill,the 912 will be top dog for a long time!
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Old 10-21-2015, 03:09 PM   #64
av8rps
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Default Re: I still need float-rigging info

Yeah, we probably should move this Jabiru PSRU to a thread of its own as there might be more interest in it where it is more obvious. But for now I guess we are still relating to float flying, so unless the moderators want to copy off this part and start a new thread, we can continue on here.

I'm somewhat aware of those liquid cooled heads from a friend that suffered at length with cooling problems with his early Jabiru 2200. But it seems that Lynn has figured a lot of cooling issues out with his Jab powered Kitfox, so I'm thinking it is possible his engine with a PSRU might actually run cooler?

Think about it, if it works like I think it might, he will immediately see more air through his cowl merely for the fact that the airplane is very likely to gain cruise speed with the same power setting. Plus, the bigger prop will probably push more air through the cowl too. I believe right now he is using his Jabiru engine to its max potential, just that the short prop isn't efficient on this airframe. So with a more efficient, longer prop he might not need to run it as hard as he does now. So again, that's why I think it could actually run cooler. I forgot to mention earlier that when Dean geared the Cuyuna on the first Avid, he saw lower temps from better cooling. Not sure all the reasons, or if the fan cooled Cuyuna would compare to the free air Jabiru that way? But maybe?

You bring up some very good points about doing this, and certainly all worth considering. But I don't think any of us will ever truly know until someone tries it.

I agree it would be a really big deal if a PSRU equipped Jabiru could even get close to what the 912 does, as the 912 is certainly the proven leader in applications like ours. But just imagine the response if it did better? Hey, maybe our Rotax prices might then finally come down
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Old 10-21-2015, 09:35 PM   #65
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Default Re: I still need float-rigging info

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Originally Posted by av8rps View Post

I'm at least glad to know people are enjoying the thread while also learning from it.

Paul
I for another am enjoying it. I once flew in the factory float equipped Series 6 and that likely is it for me, but reading a very knowledgeable conversation between two of my favorite List contributors over the years brings back great memories along with a treasure trove of new knowledge.

Landing at Cameron Park after a "Splash and Dash" at Folsom Lake

ser6apro.jpg

One of these guys was my pilot, do you recognize the guy on the left?

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Old 10-22-2015, 12:44 PM   #66
Lynn Matteson
 
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Default Re: I still need float-rigging info

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
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Old 10-22-2015, 03:46 PM   #67
Lynn Matteson
 
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Default Re: I still need float-rigging info

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
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Old 10-23-2015, 12:44 PM   #68
av8rps
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Default Re: I still need float-rigging info

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.
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Old 10-27-2015, 03:45 PM   #69
av8rps
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Default Re: I still need float-rigging info

Quote:
Originally Posted by Lynn Matteson View Post
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.
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Old 11-16-2015, 06:50 AM   #70
Lynn Matteson
 
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Default Re: I still need float-rigging info

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
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