ESTABLISHING C.G IN A UNIQUE DESIGN

[MLEVEN63]

Holden,
Sounds like you got a handle on it. If you get some prelim 3-views done I'd love to see them sometine just out of curiosity.
Been good chatting with you.
Have a good day,

Mike

 

[orion]

Hope you don't mind two more cents worth.

A tandem pusher configuration is one of the most difficult design configurations to balance. I have worked on several to date and have always run into the same issues.

First of all, in any airplane design, you must first determine the allowable CG range of the airplane. This is a function of many variables, most of which are connected to the wing/tail geometry. The aft limit of the CG range is a function of tha aircraft's "neutral" point, which is usually calcualted for the stick fixed and stick free conditions.

The forward limit of the CG range is a function of the airplane's ability to be brought to full power off stall in ground effect. The last part is very important - if you neglect the issue of downwash and ground effect, you can get a very nasty surprise on your first flight.

Once you establish these two points, then you can work with the loading of the airplane and the positioning of the main gear (assuming a tricycle layout). Position the main gear like convention dictates and the airplane may end up on its tail when the front seat occupant gets out.

Position it aft so the nose stays put and you'll end up with a very abrupt (and late) take-off rotation and heavy nose gear slap loads on landing.

This is a very challenging configuration and there are no set answers. Each case seems to be different.

If you're considering an amphib, as a few responses above mention, and the case gets even more interesting.

Good luck.

 

[MLEVEN63]

Orion,
Thanks for your input. Yeah, its a challenge made more difficult by my desire to carry my wheelchair and me. Even though it will increase my frontal area, I have considered goin to a sided by side config. but that brings in other design challenges specific to my needs,. I guess that why they keep making paper and pencils. It will work itself out eventually.
As far as the amphib., thats not my design. I was having a discussion about the needs of disabled pilots with a member whose is working on a new seaplane design.
Thanks for your input,

Mike

 

[Holden]

Orion (Bill Husa),

The issue of ground effect is perhaps one way to overcome some of your stated difficulties in a pusher design. By having a lower surface in strong ground effect that is also forward of the cg, the airplane could be made neutral in ground effect and allow easier rotation. This would require a "three surface" design. The lower surface could be the hull of low aspect ratio. In fact, all airplanes are "three surfaces", namely the main wing, horizontal, and hull (fuselage). It just depends on the shape of the hull and the relationship to the main wing, both longitudinally and vertically.

Also, the difficulties you mention can be eliminated by using a different type of landing gear. A tri gear, although popular, is NOT the ideal gear for an airplane, especially in mud and rough fields. An airplane is an off-road vehicle. Anybody who has gone off road knows that a tri wheeler is very poor for rough terrain. And then there is the tail dragger that is unstable. Would you make the airplane fly unstable? Why make it drive unstable? The small benefits are quickly gone when a brutal analysis is done on a tail dragger. On the other hand, the tri gear is worse in some situations, and therefore is still used by many "back country" airplanes that have not explored other options.

Once you can get out of those two "traps" in airplane design, and convince yourself that there must be a better way, you can see your way into a new design that is not a compromise in weight and will dramatically increase landing performance. If you use a tri gear or tail dragger it just means you have not thought long and hard about it. Gear design is critical to the airplane, and is beyond the point of Mike's questions in this thread. (Start a thread on gear design and I will jump in the discussion. That is what HBA us about!)

Also, there are several fine kits that Mike can use that would allow for a wheelchair that are already on the market, now that I think about it. The two place Earthstar could work. It is a land plane, low to the ground, with easy access. It is wide enough for a wheel chair, and the nose gear could be modified to allow front entry, or ramp drive in with the windshield modified to pivot up. The vertical distance (51") might be tight and require a mod to the floor.

Holden

 

[orion]

Good morning Holden;

You bring up some valid points but also miss the gist of my answer. The issue of ground effect and landing is more a function of stability and controlability than anything else. Ground effect reduces, or in some cases, even eliminates the wing's downwash over the horizontal tail. This makes the horizontal significantly less effective. Since it needs to bring the airplane to full stall with flaps, even near the ground, its sizing must account for the loss of downwash near that surface.

In a pusher, this problem is compounded since the windmilling prop also blankets the horizontal, further reducing its effectiveness.

Regarding your comment about getting lift from ground effect. Yes, a fore surface could be used to help the airplane rotate however your contention of it generating more lift due to its proximity to the ground is incorrect. For wings in general, ground effects are a function of three items. First, the strength of the ground's influence is a function of the wing's height above the surface. This has two functions: One is a function of the height versus the span; the other is the height versus the chord length.

In general, the height versus span ratio affects the induced drag generated by the wing. This is why some low wing airplanes tend to float. It's not that the wing is generating suddently more lift, it's just that as the airplane nears the surface, the induced drag component significantly decreases, thus extending the airplane's glide. This is what's somewhat incorrectly termed floating.

To get a lift benefit, the height of the wing must be close to the surface as a function of the chord length. To get a significant benefit, the wing's trailing edge has to be less than 15% of the chord length above the surface. So, for a five foot chord let's say, the trailing edge would have to be less than nine inches off the ground.

I agree that a tricycle airplane is a poor off-runway platform, although I fly a Cherokee Pathfinder, Piper's answer to the Cessna 180. So far I've had it in a number of less than ideal conditions and so far (knock on wood) have never had a problem.

But ground handling aside, what makes a good short or soft field gear is the ability to reach the flying or take-off angle of attack quickly. The tricycle gear requires accleration to reach a speed where the horizontal has sufficient power to rotate the airplane. It then has to generate the down-load, causing the mains to dig in further, before the airplane rotates and flys off. This is why most soft field take-offs are done with flaps down, since that way the airplane can usually take-off in a level attitude.

The tail dragger however is already in the nose high attitude and thus does not require the horizontal to force it that way. This is mainly why tail-draggers are preferred over planes with a nose gear in bush operations.

Are there other options? Probably. But the gear configurtion has to be balanced with the rest of the airplane's required operational characteristics and so all this becomes a balancing excercise of trading off one thing with another. The obvious question one must ask in a discussion of this type is why, in the last fifty years or so, have airplanes come out with primarily only two configurations of gear positioning? Is it because we, the designers, are blind or dum?

Not likely - we just tend to use what we know works. Balancing the flight requiremetns, the groundhandling requirements, and the drag characteristics, generally leads us back to the same choices.

Personally, I'm alwasys open to other ideas. In two weeks we're starting another bush-plane development project for an Alaskan pilot who now lives in Colorado. He has some really interesting ideas for his gear but boiling it all down, it still will be a basic taildragger, but with some very impressive rough field capabilities.

 

[Peter Garrison]

CG

CG position in a tandem pusher is no problem at all, because the major variable weight -- the passenger -- is on the CG. It's particularly easy if you're the only pilot.

I would suggest that you avoid the canard configuration. If you get it wrong it can be dangerous, whereas the conventional configuration is reasonably robust and tolerant of design error. There is no performance advantage to the canard configuration.

It sounds to me as if a twin-boom pusher would be the most sensible choice for your needs. It would put the pilot's station way out in front, where it could be as close to the ground and as accessible as you like.

Peter Garrison

 

[MLEVEN63]

Peter,
I looked at canards, slick looking but I'm not that smart or stupid .
I did a preliminary design on a twin boom/rear entry design but the hatch and ramp mechanism got a little complicated plus I had this recurring thought of the tie down failing and me and my chair going out the back like so much cargo!!
I've revisited the idea recently with a side entry, but lean towards why build two when one can do theory.
I am sticking to the basics, good 'ole high wing clarkY type airfoil, maybe wiith fixed slats to improve STOL characteristics.
Seems to be alot of debate on the pusher c.g. issue, but considering how many designs there are out there it can't be that large a design issue as it is a matter of preference.

Thanks for the input,

Mike

 

[Holden]

Orion,

I got the gist of what you were saying, however I disagree with the detail of what you are saying. They are incorrect, and I will leave it at that for now. Perhaps another thread on landing gear would be useful, and entertaining (very important to Jake and Homebuildairplane.com. The more entertaining it is the more members...!).

I did get the gist, but your gist is based on your "choices" which lead you to the same conclusions. You are following your trail, or should I say "tail," of choices that "generally leads us back to the same choices" or in other word nowhere. Designers of buggies knew what worked for 4000 years.

The reason "why, in the last fifty years or so, have airplanes come out with primarily only two configurations of gear positioning?" is because the choices made by the designers have lead to those configuartions. There are no dumb or blind designers, just bright people taking very high risks trying to follow a dream. They compromise their dreams in the face of risk and make their choices. The easiest thing in the world in airplanes is to make another Cub or Cessna, or Cirrus, and that is extremely difficult.

Getting out of the box offends nearly every designer I have encountered, including me. Why? Because people are known by their choices.

The issue is never with a designer's ability as an design engineer, just with the selection of choices. New choices lead to new design requirements.

My dreams in an airplane are not your dreams, and therefore you will make choices that lead you back to, in my opinion, what does NOT work for me. If my dreams in an airplane were on the market, I would just buy the bugger.

In fact, homebuilding is about the ability to make new choices. Experimenting is about trying out new choices. Staying with "what works" is NOT about experimenting and is more about being part of the group and being one of the gang.

The longing for the group is perhaps the major part of homebuilding. Experimenting and the desire to be part of the ground is at odds to each other because each experiment (design) brings with it a unique culture.

Once I get my design completed, there will be a following or adherence to the ideas. Each designers wants as many followers as possible.

As a designer (leader) in search of builders (followers and customers), the real question is "why, in the last fifty years or so, have airplanes come out with primarily" the same old thing? There are millions of customers out there to be had, but nobody wants to do what it will take to get them. That is not to say they have not tried, big time. The fact still remains that this is a market with 50-99% of the cumstomers not buying.

Why? (Why ask why?!) Simple, they do not like our choices as designers. They are not saying we are blind or dumb, just that they do not like our choices. Should we be offended by this reality? No. Are they calling us blind and dumb? No.

I would hope you are not offended by my new choices. Those choices are tempered by hard science, engineering, and data. If you want to debate the facts, that is what I am here for. The postering and attitude of "been there done that" I can do without. Why? Because you have not been there or done that. How do I know? Your choices...that lead you back to the same choices. Your stuck.

By the way, I'm stuck too! That is why I'm on HBA to get some ideas going! Maybe if we push hard enough on each other we can both get unstuck!

Respectfully,


Holden

 

[orion]

Hi Holden;

No, I'm not at all put off by your response and agree with what your are saying wholeheartedly. Thinking out of the box always presents new variables to a solution, sometimes good, sometimes not so good.

It may also be true that I and many of my kind may be entrenched in our thinking due to the length of time we've doing things a certain way.

However, in the same breath, it must be pointed out that as designers and engineers, there may be a sound reason why we've been doing this this way.

There have been many "out of the box" thinkers out there, especially during the past ten years or so. Most of those have been proven to be quacks, presenting ideas that have no technical feasibility or merit - they just look good on paper. I just shudder when someone comes along and proposes to "revolutionize" the airplane industry. 9.999 times out of ten this will be a money sink-hole and not worth a second look. Most of us now know that when we hear this sort of thing we need to run the other way, and quick.

On the other hand, "been there and done that" sometimes needs a swift kick in the behind to get it unstuck too.

Happy flying.

Bill

 

[orion]

Re: CG

Originally posted by Peter Garrison
CG position in a tandem pusher is no problem at all, because the major variable weight -- the passenger -- is on the CG. It's particularly easy if you're the only pilot.

I hope this works - this is my first try at the quote.

The statement above is dependant on the configuration but in general it's not correct. Looking at a conventional twin seat tandem pusher, the primary weight components are the fuselage, the engine, the tail and empennage, and of course the two crew. Depending on size of course, balancing the need of the airplane and matching the predicted CG travel with the allowable CG range (the latter is based on the aircraft's stability requirements) of the wing/tail combination is paramount.

Looking at the pieces, the fuselage is relatively light and will be fairly close to the CG range and so, in itself, will have only little impact on wing positioning. For an empty aircraft, the wing is on or near the CG so it too has little impact, regardless where it will need to end up. So the two major components that will drive the wing position (as a function of structure) are the engine and the tail assembly.

Even with a light engine such as a Rotax, this in itself will force the wing to be fairly far aft. Allowing sufficient room for two tandem seats, the front occupant will be sitting well forward of the allowable CG range.

The aft passenger may be close to the CG envelope but, depending on the size of the engine and tail, may also end up in front. Therefore, neither the pilot nor the rear seat passenger are likely to be on the CG. This is why a tandem pusher is such a design excercise of trade-offs.

The final position of the wing will be a combination of the structural weight driven requirements and those of the occupants. But given the historical record, it is difficult to place the occupants directly on the CG envelope, although the aft passenger may be very close.

 

[MLEVEN63]

Orion (Bill)
Thanks for the response, I'm not and engineer by any means but the concept of C.G. is basically the same as the R/C models I set up to fly... "nose heavy..add weigh to the tail and vs/vs and to much glue hear or there, battery in the wrong spot and you have to counter"
I'm not foolish enough look at my design in those simple of terms of course, and take all advice with caution when it comes with no credentials, I know that every inch of frame and covering all adds up to enough material weight to effect the C.G., let alone the placement of the pilot(s) effect.
I am going slow and cautious with my design, I don't want my first flight to be my last.
By the way you and Holden are welcome to stay on my thread, I enjoy reading your verbal fencing. Although I am still scratching my head as to exactly what Holden's fuselage down design is I have to agree with the "out of the box" thinking. I believe that for two reasons- every major technical advance in aircraft has been accompanied with the phrase "That won't work!!... its never been done." just before the thing did "its" thing. Secondly my own personal situation. I won't list the number of things people told me I couldn't do things because I'm "disabled".....yet I did get my masters in architecture, I do own and drive two 85 mph boats, flown sailplanes and now I want to build a plane that is W/C accessible. I've had plenty of people say it isn't possible, maybe, but I doubt it. It is just a matter of looking at things from a different point of view - mine happens to be sitting down looking at planes I cannot get myself into.
So onward I'll go planning and drawing and getting the correct direction and information and someday if it all comes together I'll have my plane, if facts and science prove me wrong, oh well the idea will die in my archives. I don't believe in bad ideas, if they are thought through completely and turn out to be a mistake knowledge will still be had. I was once told that if your not making mistakes, it just means your not doing anything.
I'll be posting my preliminary 3-views soon, I hope you'll put in your thoughts.

Have a good night.

Mike

 

[Holden]

Orion,

You seem to be able to be reasonable and clear thinking. I agree with your last post to me. A swift kick could save me time and money.

I am not trying to "revolutionize" the industry, just get an airplane I want to fly. Simple. I don't have a web page, nor do I post pictures of what I do. I don't want someones money. I am not a consultant, or do I provide engineering services.

All I want is honest discourse and frank opinion based on sound analysis and clear thinking perspective.

Thanks for your opinions. I learned something from you.

Holden

 

[Jman]

Melvin,

I love your attitude. It sits in such stark contrast to most (but not all) of the young people I go to school with right now. They have every faculty and advantage and yet everything must be handed to them. I have a feeling that you will succeed in what you are doing because you have an attitude of success. I'm not trying to get too philosophical here but it's true. I can't wait to see the first flight pictures! Best of luck!

Jake

 

[Holden]

Mike,

Have you ever read Alex Strojnik's book "Laminar Aircraft Technologies?" On page 39 he talks about "low drag landing gear" and shows a C-152 with the wheels inset into the fuselage.

I read that years ago and it occured to me that if the airplane were low to the ground it would also be easy to get into. A wheelchair goes well with an airplane that is low to the ground. Most gliders are low to the ground, and they work well.

You might take a look at his book(s). By the way, my gear is not like his but the ideas behind it got their start there and are similar. I am a little stuck on just what I want finally, but I do know what I don't want. Sometimes you have to back into a design by eliminating what you don't want because you cannot see exactly what it is, but only have a gut feeling where to look.

As for the low fuselage you have a hard time seeing, first go to the WIG page and read about the theory. Then try to think of ways to use that information in an airplane to get what you want in your airplane. There is a group on Yahoo (WIG) that has a lot of discussion on WIGs, including a lot of good posts from Orion (Bill Husa). See http://www.se-technology.com/wig/

Look forward to your sketches.


Holden

 

[MLEVEN63]

Holden,
I'll see if I can locate that book. Your right abouth the design process, its the same in architecture, you sometimes get so cluttered with ideas you lock up, I've literally walked away from a project in complete design block and days later been sitting drinking coffee and made a simple shape or line on a napkin and had that ah,ha moment and all became clear.
I checked out that web page on the ground effect planes. When we were talking I thought about how a sealplane could use it to help get in the air. I've taken rides in high-performance catamaran boats, which use that ram air between the hulls to help lift the hull and they operate right at the edge of flight sometimes. I thought hey, a config. like that would it would eliminate the mono hull's drag and supply what would appear to be a stable water landing system although the re-entry into ground effect might be tricky... anyways, its just a thought.

Have a good day.

Mike

 

[Holden]

Mike,

A cat hull, in short, is NOT what you want. No way, no how. Here is short list of why not:

1) The stall is a function of the chord length. The AC at the 1/4 point will move back towards the 1/2 chord during stall, and the distance will give you a very strong negative pitch, and in ice, you are nose-down dead. It makes a very bad "known ice" airplane, and for this reason alone should not be used. Ice is common where I live.

2) The ground effect on the lower side acts at the center of area. In other words, the stagnating air on the lower side works far aft of the free air AC causing the nose to DIVE in ground effect as a funtion of chord length and height. The longer the hull the worse it gets. It would be very difficult to fly in ground effect, much more so than a Cessna, for example.

3) It has all the bad points of a float plane, where one hull side can dig in and spin the airplane. Drag on one side causes a turning moment. Ever had one wheel on your wheelchair stuck in the mud, or gone off the highway at 70 mph after falling asleep? If one side of the car digs in, you will roll the car. Same applies for airplanes, but worse, far worse. Ever drive on a soft shoulder with one side of the car on hard pavement and the other in mud? Get the picture?

4) High drag due to the channel effect. (Can give good lift though)

5) Poor area rule practice.

6) No ability to bank and turn to avoid other boats. This is VERY important if seaplanes are going to be accepted into boating areas. Having to fly straight ahead on takeoff is a big deal for State Park Boating Directors. I just got done opening four lakes in my State and this issue was key on their mind. I showed them my airplane and the fact that it could bank +/-25 degrees right and left, and they (by just looking at it) went on the the next issue at hand. They did NOT like the classic float plane because of the lack of turning power, and poor forward visability, but they had no problem with my seaplane. (Very few seaplanes <10 in my State)

7) Heavy structure

8) Step turn flip over where the outside hull dives in.

9) Poor cross wave ability. If a boat creates a wave at say 45 degree, it will very often cause one side to dig in, and will cause a rolling moment, that may upset the airplane. Not good.

I think you get the picture. There is more but that is more a design subject, not a generic characteristic.

If you reread the WIG page you will notice the criteria for control in ground effect. Understand that and you will see what I was saying about a low forward hull and takeoff rotation. That criteria cannot be had with a cat hull.


Holden

 

[orion]

Hi Mike;

I agree with Holden but let me add a few more tidbits.

The AC, or aerodynamic center, by deifinition, is a function of the shape of the airfoil. It is the point at which the pitching moment coefficient of the section is constant, regardless of angle of attack. Since it is a function of the section's geometry it stays relatively constant regardless of the wing's height off a surface.

What changes is the wing's center of pressure and as Holden states, in ground effect for a fixed angle of attack that is at an approximate cruise setting, this point moves from roughly the quarter chord point to nearly the 50% point (although the actual shift magnitude is a function of about half a dozen variables). This shift results in a high nose-down pitching moment, which of course has to be trimmed for or you end up nose first in the water.

As far as one side digging in, this used to be my attitude also until it was corrected by several long time floatplane operators. Yes, a float or sponson can dig in and flip the airplane however it is not automatic. As an example, quite a few pilots (especially in Alaska) have shown the trick of bouncing a conventional wheeled landig gear off the surface of the water with no detrimental effect. Basically the wheel acts like a skipping stone. As long as the speed is above about 70 kts, it is actually pretty difficult to bury it in a way that will cause the airpalne to flip.

The same is true with a float or tunnel hull. Unless one float is forcibly buried in the water, an unsymmetrical contact has actually very little effect on the direction of flight and the bit of yaw is easily tolerated and controlled.

In a number of cases, which are taught by good floatplane schools, the pilot is trained to actually dip one float onto the surface on purpose to aid in turning the airplane when operating within a crowded waterway. I've actually seen this done in the tight harbor in Victoria, BC. The airplane I saw doing this was a twin Otter. As he was coming in, somone accidentaly enterd the landing path. He slowed down, dipped one foat in the water, and made a neat tight turn away from the boat. The turn was actually tighter than if he tried to bank.

If you follow some of the links on the WIG page you might be able to find some of the airticles that discuss the Russian WIG operations. The larger craft such as the KM and the Lun are of course massive and in normal flight mode actually take several miles to make a 180 deg. turn. What the pilots did to correct this is learned to purposely dip a wing tip into the water to increase the drag a bit on one side, creating a yaw condition, and thus dramatically reduce the turn radius.

A short practical example of this is on the Rices' web site. They make a series of WIG models and as part of their site they also include several home movies of some of the flights. In one particular case, as the little WIG nears the camera, it accidentaly dips one of the sposons into the water. The dip is long and hard enough to actually create a bit of spray.

But despite this contact, the model does not flip, nor does it even veer from its fllight path. The momentum carries it straight with no special input from the pilot.

However, unless specifically and carefully designed for, as Holden states, the tunnel hull is not a good choice for an aircraft.

In our development of the Pelican WIG (unfortunatley the same name as the Boeing monstrosity but different craft), we actualy started with a similar twin hull layout, but due to a number of other operational design issues, as you see in the picture of the Marine page within our site, we are now using a relatively standard stepped hull layout.

 

[MLEVEN63]

Holden,
I haven't had a chance to read all the website, just brushed through it this morning, but plan to revisit it. But I see your point, I dont like the way a cat. boat handles in turns compared to my v-hulls, the turns flat and can catch an edge with the outside sponson and defininately causing your heart race to increase a few clicks. I can only imagine what a wing on top would add to the fun!

Take care.

Mike

 

[Holden]

Orion,

I have to agree with most, if not all of your last post. Perhaps another way to say it is: if you make it unstable, or potentially so, a good pilot can use the instability to dramatically improve performance. The Wright Bro. did that, tail draggers do that, but insurance companies, who like stability of liability, refuse to play that game, and sadly more and more each year. This is the reality of the world today.

I was taught the float dipping technique during my float training, but I did not find it useful because it took a lot of practice and consentration before it became a reflex, and the risks of a bad move were a crash. Tail draggers are a LOT of fun to fly. I own one. But after all is said and done it must be a reflex before one can effectively exploit the advantage and do so as an enjoyment. It is an aquired taste. Also, habits take time to learn, which cost money to keep current. And then even the best pilots can get tired and the plane crashes.

I would be interested in the "half a dozen variables" as you see them. The WIG page only covers a few, from what I read. Since you have put a lot more thought into WIG design than I, where I am only interested in how it could help in seaplane design, perhaps you could give us some insights that may not be obvious.

One thing I was considering was a small trim flap that creates a "J" on the trailing edge. As I understand this helps a lot in creating stagnation under the wing in ground effect. The negative pitch moment could be offset by the nose gear panel and allow for strong ground effect (as a function of chord--as you said) during the run phase. That wing area would then lift the nose up and allow the main wheels to be more aft than they otherwise could be.


Holden

 

[orion]

Hi Holden;

Regarding WIG technology - The WIG page is a great place to get a crash course on the language and some of the issues of WIG development and flight. But of course it is far from complete. Although I've been involved with WIG research and design for about fifteen years now, I certainly would not call myself an expert. But I am comfortable that I do have the basics and that the work we've done is based on a sound understanding of the principals.

If you're interested, at our web site, under the Papers and Articles page, I posted a PDF document called the "WIG Matrix". It goes through several of the basic decision variables needed to be considered when looking at this type of craft. The very first chapter gives a brief summrizing overview of a number of NASA and NACA research papers that deal with the issue of flight in surface proximity.

The variables that drive a WIG design are also a function of the approach you are trying to develop. Our Pelican project is what is known as a Class B WIG - in other words, it operates primarily as a WIG but has the capability of briefly popping out of ground effect to overfly an obstacle, if necessary. As such, it needed to be optimized for low flight, but also had to be stable (or at least controllable) in free air.

The primary controlling variables of surface proximity behavior include the airfoil (specifically the shape of the camber line), the airfoil thickness, the foil shape distribution as a function of span, the leading edge shape, the trailing edge shape (both subsets of the camber line), the planform shape of the wing, the configuration of the wing's trailing edge in relation to the water, and to a lesser extent, the shape of the wing's underneath surface.

But to get the most benefit from a WIG type wing, it is important to carry a substantial angle of attack (6 to 10 degrees) and to have the trailing edge very close to the water's surface. The real benefits to lift don't occur until you drop the trailing edge to less than 10% of the chord length from the average surface plane.

Several years ago we were working to develop a new class of aircraft floats, based on the geometry of sponsons commonly used on unlimited hydroplanes. The operational characteristics were going to be a marked improvement over conventional floats.

The two drawbacks to this program were a function of the actual geometry. First, most operators were concerned about the lack of symmetry. The handling was going to be superb over a conventional float but the operators wanted to be able to replace a float with another they had sitting around. Our floats are of course symmetrical about the airplane's cenerline but this means there is a right and a left.

Although we were able to show reduced take-off performance (ten to fifteen percent), the operators we were discussing the project with wanted more in order to justify the different layout. We therefore developed a configuration that interconnected the sponsons with lifting surfaces that were optimized to work in ground effect. Based on our best approximation, the configuration we finally arrived at was going to be able to take-off in a distance that was over 30% shorter than any other float configuration.

But regardless of our good news, the customer was never able to complete his funding and so the program never went beyond a few models and some scale testing. Oh well - so it goes.

Bill