Float design for performance - some concepts and experiences

I guess I stuck my foot on it in another thread. How about some thoughts-comments-experiences on aircraft float design for performance? Just casual with links if available.

I can start with EDO 1400's - early models had no boosters and were often outperformed by the smaller earlier 1320's. Low powered aircraft need all the boost they can muster to get airborne. Boost being reduced friction between the water and float surfaces (sides and bottoms). So, EDO added boosters - shaped metal riveted to the aft of the forward bottom in front of the step. Apparently helped enough to improve takeoff and keep the model competitive. See image below with boosters installed from a screen grab.

Any other do's, don'ts, or comments?

Gary

Anyone know why the cast aluminum extension of the forward keel (at the step) has a hole in it? They’re round in my EDO 2000’s. Always wondered why.

What ever happened to the plastic fins mounted on the inner sides of the floats? They were supposed to enhance performance off the water.

Jim

To attach a beaching wheel assembly

55-PA18A said:

...What ever happened to the plastic fins mounted on the inner sides of the floats? They were supposed to enhance performance off the water.

Jim

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http://crosswindsstol.com they were offered by Crosswinds at one time. Looked similar to the one piece fin some attach to outboard motors above the propeller.

Edit: more on these hydrofoils: https://www.supercub.org/forum/showthread.php?42374-hydrofoil-float-design

Gary

Here's some don'ts....covering the bottoms with spray-on truck bed liner material. Local did that and found the floats liked water more than air. The floats were leakers so why not just resurface them? I recall a few days of scraping and cussing as the rough liner was later removed.

Clean the float area under water frequently. Algae and small aquatic insects like to adhere to and set up housekeeping on floats - fresh or salt water. Like the covering above it slows takeoff especially by Fall hunting season when performance is needed for a heavy plane. It can also promote surface corrosion for some reason.

Gary

I hung around Sky Harbor Mn seaplane base a little 17 years ago. Lots of ole boys who did a lot of small Continental float flying over the years. They all liked EDO 1320 over anything else. They told me that the bottoms on 1320 worked so well the EDO and every other float manufacturer tried to duplicate 1320 performance and never did. I told JJ Frey what they said and he laughed and said they were right but nobody would admit it, even EDO

Glenn

Here's some earlier threads on this subject. Just a quick search and there's lots more buried in various threads:

Why this is here: https://www.supercub.org/forum/showthread.php?61088-Aqua-1500-straight-floats
https://www.supercub.org/forum/showthread.php?36366-Rigging-floats
Float performance: https://www.supercub.org/forum/showthread.php?45418-Best-Performing-Floats
https://www.supercub.org/forum/showthread.php?22771-Hull-Float-Speed-and-a-few-other-float-questions
https://www.supercub.org/forum/showthread.php?42458-j3-on-1400-floats-rigging
https://www.supercub.org/forum/showthread.php?60658-Seaplane-Step-Location&highlight=float+design
https://www.supercub.org/forum/showthread.php?51993-PK3500-B-or-C
https://www.supercub.org/forum/showthread.php?59136-Best-floats-going-to-a-super-cub-150
https://www.supercub.org/forum/showthread.php?57840-Edo-question
https://www.supercub.org/forum/showthread.php?57159-Float-recommendations-for-Pa18-95
https://www.supercub.org/forum/showthread.php?53933-Anyone-have-experince-with-AQUA-3190s
https://www.supercub.org/forum/showthread.php?39692-Float-choice

Gary

More on boosters and added chine angles from Eddie Peck Aero Products These enhancements can help performance by getting the floats higher out of the water and reduce drag (I guess).

Gary

55-PA18A said:

Anyone know why the cast aluminum extension of the forward keel (at the step) has a hole in it? They’re round in my EDO 2000’s. Always wondered why.

Jim

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The hole is likely to save weight and material. It all depends on the whims of the designer. This is the skeg on my EDO 89A-2000 floats. Sheet metal sides with a solid keel section. More labor intensive than just a casting.



Yours are likely 89-2000 floats. What's the difference you ask? There's a story behind the answer. Long long ago in the land of Cessna when they were stamping out 150s for flight schools by the dozens, they got the bright idea to promote seaplane training as a further customer base for their 150s as well as a customer base for the students to move up to larger Cessna floatplanes. So, Cessna did a gung ho certification and marketing program for single engine sea training. EDO signed on and started building 88-1650 floats in preparation for the huge demand. Well as those of you know who have flown the 0-200 powered 150 on floats, it was a great seaplane as long as the fuel was low and the sole occupant was a lightweight. As a result the marketing program flopped. EDO had 100 or so sets of 1650s in the back room with no customers. So they certified the 1650s on the PA-18-150 and the Citabria. That too flopped since the floats were just too small for reasonable performance as well as having marginal floatation. Marginal floatation is dangerous in a heavily loaded seaplane on windy rough water. Sooo, EDO converted the remaining 1650s to 89A-2000s. My 2000s is one of those sets of modified 1650s. The A in the model number denotes the modification. This was done by inserting an 23-1/4" plug ahead of the step. The 1650 used the same skeg as the 89A-2000.

If I happened across a good pair of PeeKay B2300s I’d be tempted to put my Cub on floats!

Maintaining a float plane beached on water (lake, stream, or ocean) consumes lots of time and effort. The water rises and falls....storms with wind and precipitation come and go....the plane demands constant attention to keep it safely moored while floating. Nothing much new here but as I age I realize the benefits of parking tied next to a padded dock, on trailers set on dry land, sitting on secure ramps/parking pads, or even amphibious floats. Let storms arise and pass by then watch the traffic to the water parking area increase.

Lots of owners give little thought to ropes and tie downs then wonder why damage occurs. Something to consider - the safest parking setup before the plane is put on floats. Better than straining (at night is best) to pull and tie loose lines during a good blow or add even more.

Gary

Gary, you forgot to mention how much fun early and late season wet heavy snow is at 3AM

Glenn

When I’d be 100 miles away and see red on the radar ….yikes

cubdriver2 said:

Gary, you forgot to mention how much fun early and lat season wet heavy snow is at 3AM

Glenn

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Indeed Glenn very true. Not only does the plane start to sink from the snow load, but if asymmetric one wing will drop...usually the one downwind which can cause the float tip to dip also. Leaky floats unpumped help all that happen. Then you find that bucket you carry in the plane to throw water on the wings to remove the snow. We do carry one full of gear (extra ropes and things) just in case don't we?

Gary

BC12D-4-85 said:

Indeed Glenn very true. Not only does the plane start to sink from the snow load, but if asymmetric one wing will drop...usually the one downwind which can cause the float tip to dip also. Leaky floats unpumped help all that happen. Then you find that bucket you carry in the plane to throw water on the wings to remove the snow. We do carry one full of gear (extra ropes and things) just in case don't we?

Gary

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Needed it last October when 3 Cubs camped in the Adirondacks to remove frost from all 3

Glenn

A buddy and I were talking today about float performance. He wondered if anyone had tried thin film bottom paints used for improving boat performance (he winters where the water never freezes). Being ignorant about fast boats (I use them to catch fish and not go quick) I looked up some info. Here's a list of some commercial offerings. I'll read more tomorrow but anyone have experience with them good or bad? I'd at least try the area ahead of the step like where the boosters above are attached and maybe aft. Compatibility with aluminum with no electrolysis would be required.

PS: Something makes smooth composite floats fast on the water. Can't only be their price.

https://www.practical-sailor.com/boat-maintenance/paints/freshwater-bottom-paint-test
https://www.interlux.com/en/us/boat-paint/antifouling/vc-17m
https://www.defender.com/product.jsp?id=7873430
https://www.wholesalemarine.com/boa...ling-bottom-paint/thin-film-bottom-paint.html

Gary

[h=4][/h]

Yup, never put it on



Glenn

In Minnesota, lots of boats live on “lifts” when not in use. First time I saw one of those, I thought, wow, I wonder if one of those would work on a straight float airplane. Turns out somebody had already thought of that, nice way to store a plane, long as the lift is stable.

Stewart,
You would not like the PeeKay floats initially, but once you figure them out, they work great. The sweet spot is very small, which takes some getting used to. When I started flying the B2300s, I had the benefit of quite a bit of experience with the bigger PeeKays, which helped.

MTV

Been there, done that. B2300s are my favorite floats of those I’ve owned.

cubdriver2 said:

Yup, never put it on

View attachment 62418

Glenn

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Why not? You need my address Christmas is coming and I might have a birthday sometime.

Gary

BC12D-4-85 said:

A buddy and I were talking today about float performance. He wondered if anyone had tried thin film bottom paints used for improving boat performance (he winters where the water never freezes). Being ignorant about fast boats (I use them to catch fish and not go quick) I looked up some info. Here's a list of some commercial offerings. I'll read more tomorrow but anyone have experience with them good or bad? I'd at least try the area ahead of the step like where the boosters above are attached and maybe aft. Compatibility with aluminum with no electrolysis would be required.

PS: Something makes smooth composite floats fast on the water. Can't only be their price.

Gary

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Hers's some study material on the topic. https://pubmed.ncbi.nlm.nih.gov/20855320/
And here is an article which refutes it: https://www.latimes.com/science/sci...denticle-drag-bioinspired-20160314-story.html

I can confirm that flush rivets in the forward bottoms does reduce drag from the normal protruding head rivets. Long ago I rebuild a wrecked Lake LA-4 replacing everything from the step forward. AN427 (countersunk) rivets were used on the bottoms. Normally when making a glassy water landing with a Lake, the first indication of touching the water is when you hear the swishing of the water as the step touches. With the flush rivets, the first indication is seeing the spray out of the corner of your eye. No sound. The heads of each rivet makes a swishing sound therefore each rivet in creating turbulent water is also producing drag. Also, getting on the step is a bit quicker as is the ability to better slide sideways in tight step turns. These airplanes can make frighteningly tight step turns safely within the radius of one wing span. It can be as tight as still being on the step while going backwards. It stops very quickly. I don't recommend you try this. There can be no question the smooth bottoms of the composite floats like Aerocets and Meads are a performance enhancer.

Hmmm? I understand the reason golf balls have dimples is to reduce drag so that they ravel further? https://www.sciencedirect.com/science/article/pii/S187770581100991X

Well after reading about the friction reducing anti-fouling paint I think I'll pass for now. Compatibility of copper and aluminum can be avoided by eliminating certain chemicals. But once applied any wear will require restoration, and I'm not into painting like annual boat hulls. I earned my boat bottom aquatic degree during in the 1960's in Sitka and never went back to that marine maintenance. I can see some good non-silicone wax (or maybe the new durable ceramic polishes if they can be removed to repaint float lacquer) being applied, but any more than a day's work like that and I'm gone fishing.

Gary

My Baumanns have fluted bottoms and boosters.

Mead have double fluted

Dan, did you add the booster to the Baumann floats? I like the Mead's design.

There's a set of fiberglass floats here that were built for PA-18's that look similar. Came from Washington State and have round spreaders and struts. Rounded tops with large openings held on by elastics. I need to start taking pics of local floats to share and discuss before winter. Might as well have some photos when the time comes to see what they look like. Please post pics if you have some.

Gary

Baumanns came with boosters

Dan Gervae said:

Baumanns came with boosters

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Ok thanks Dan, just never seen a set with them installed.

Edit: Yup here's a set of boosters on B-1500's Legend Cub. Maybe I recalled their early 1420's...do they have the boosters as well.

Gary

Dan Gervae said:

My Baumanns have fluted bottoms and boosters.
View attachment 62419
Mead have double fluted
View attachment 62420

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Douten kicks my a$$ all the time, Baumanns perform

Glenn

As I suspected not all Baumann 1500's were equipped with boosters. I checked a local set this eve made 12-07 and nothing there. So maybe it's a mod that they did before or after the local's, or maybe they're just done for the better.

Now I'm thinking about my 1320's and installing the PK-style boosters there. I bought them years ago for my former EDO 1400's.

Pics of my boosters on PK 1800's below.

Gary

Here is a sketch of some representative miscellaneous bottom shapes. We can reference the sketch number as part of our discussion so that we all are speaking of the same shape. These in no particular order.



#1 Flat bottom.. more lift for getting on the step. Best in very smooth water. Takes a beating in rough water. Sometimes sticks to the surface and will not lift off from glassy water, works better with a small ripple to break the surface.
#2 Nearly flat with double curved bottoms. EDO's initial attempt to correct #1's issues. Was an improvement but still had high impact loads.
#3 Single curved section tends to smoothly roll the water sideward.
#4 Medium sloped flat skins, simple cost effective construction, a compromise for most water conditions.
#5 Deep V shape is best for rough water in that it pushes the water to one side while slicing through the waves. Low impact loads. Tends to ride lower in the water so requires more power and speed to lift off.
#6 Same as #4 with the EDO style boosters for more lift while on the step.
#7 Double fluted stretch skin provides the best combination for most water conditions. More expensive to manufacture.
#8 Like #5 with PK's version of booster angles.
#9 Like #4 with a booster on one side (for illustration) and chine spray rails just ahead of the step. The spray rails assist in capturing the side flow of water while climbing on the step in order to increase low speed lift.
#10 Similar to #7 with a double keel. Perhaps helps with low speed lift.
#11 This was the brainstorm of a fellow who tried it on model airplanes and followed through to certification on several full sized planes. Great in smooth to light chop. There were reported airframe structural failures due to rough water use. The cross struts (in lieu of wires) had shock absorbers. I have flown this on a 235 Maule. It was called Fiberfloat.

The arrows are to show the approximate direction of flow of the water in relation to the bottom shape.

Excellent post Pete! The effect of deep V hulls can be seen...like CAP 3000 and PK 3000-3500's...they throw water a good distance sideways until approaching T/O speed. The CAP's use a single small angle booster per side and single chine spray rails back to the step on the inside only. If I had them I'd run a similar spray rail (#9) on the outside of each float.

Now another couple of questions please. What about the shape of the float bottom aft of the step? Best duplicates design forward of the step?, or is #4-5 just ok? Any reason for boosters back there?

And what about ease of step turns with the designs above when you have the time? A CAP owner ran aground again recently with CAP's presumably turning on a river (not sure yet).

Gary