Sizing floats for different aircraft

[kerick]

Anyone know of a method or a website to calculate how big floats would have to be for different size aircraft? I have a couple ideas for floatplane conversions but I want to have something believable for the floats. I've checked the web and not much comes up.

I'm thinking of two floats on an aircraft about 25000 lb max take off weight. Plus maybe some WW2 fighter types.

[jcf]

You can try one of the online boat hull displacement calculators, that's the closest thing.
Note that they are very 'in the ballpark' in regards to the results.

These EDO charts might help give you a rough idea, all are for twin float installations:

[kitnut617]

Well a Dakota has a gross TOW of around 25,000 lb, so you can see here how big the floats are for that aircraft.



Then for example,  the Bristol Blenheim's max weight is around 14,500 lb



But so is the Hawker Tempest's weight -----  But a Beaufighter's max TOW is also around 25,000 lb so you would need floats that the Dakota has for it.

[jcf]

Yep, and further to what Robert said, the He 115 and the CANT Z.506 are roughly in the range of your desired weight
and they illustrate how different design approaches can have a different visual result. The floats have to do the same
job but they look quite different, the Italian floats being the more aesthetically pleasing. 

[sandiego89]

A noble effort- too many WHIF float planes slap the excess Frog spitfire floats on a much heavier aircraft   

Calculating displacement is the key, but I'm afraid math is involved. 

A simplier rule of thumb might work with the rule of thumb for float length is twin floats should be 75% of fuselage length.  Single float- 100% of fuselage length.

Here is a calculator for boat designs, giving you displacement.  May help you get a rough size.  Remember to factor in 2 floats.

http://www.blueheronwings.com/bh/comps/bdesign.html

The stats on the Edo float on the C-47:
EDO Model 78-29400 amphibious floats
Length: 42 ft
Beam: 5 ft 8 in
Depth: 5 ft
Weight: 2.234 pounds
Fresh water displacement: 29.400 pounds
Water-tight compartements: 14
Internal fuel tank: 325 gallons

[kerick]

Thanks for all the info. I have a set of vacuform floats of different sizes from Aeroclub from many years ago. Good thing plastic doesn't go bad. Trying to pick out the right size for my idea. There are many different sizes in the package to choose from. I just don't want it to look silly with too small floats.

[Librarian]

Very useful thread for my ongoing projects. Thank you.

I always thought EDO was named after the city but just googled and they are after company founder's initials. Edo became Tokyo and you have Tokyo tanks. It's all fun .

[PR19_Kit]

Thanks for all the info. I have a set of vacuform floats of different sizes from Aeroclub from many years ago. Good thing plastic doesn't go bad. Trying to pick out the right size for my idea. There are many different sizes in the package to choose from. I just don't want it to look silly with too small floats.

I used the largest set of those Aeroclub vacform floats as a basis for my build of the floatplane Dak, but with a 1" extension just forward of the step and a 40 thou styrene 'backbone' down the centre. That produces a pretty good 1/72 scale version for those 78-29400s.

[Flyer]

My current project is a seaplane based on the Spitfire, I'm building the floats from scratch so the above EDO pics are helpful with the shape. It will be trimaran like set up, large centre float with outers about half the centre's size but I have done no math, I'm going by eyeballing only so I hope the size isn't too small, if I enlarged the floats any it would look silly. Maybe I'll stick with the wing guns only and not add any external weapons like I had planned. Pics going into Flyers Projects thread soon.

[kerick]

Here's a pic of the Aeroclub floats for anyone who hasn't seen them.
IMG_1006 by kerick214

So here's the scoop. All this talk lately about P/F-82s and now a floaty GB got me to put 2 and 2 together and come up with 5. What if the P-82 was ready earlier in the war or the war dragged on? Built as an escort fighter with great performance on Packard Merlins it fullfilled that role. But pride and politics got in the way and an Allison engine version was built (this part really happened). Like every other Allison engined aircraft, it was slower and had less performance at high altitude than the Merlin engine version. It was assigned patrol and attack duties. With all those islands in the South Pacific a float plane version was created to deal with enemy shipping. I'm thinking painted up like a Ventura and carrying rockets or a torpedo would be interesting. Trick is picking the right floats. I looked at the rule of thumb courtesy of sandiego89 and found a pair that would fit that description.

IMG_1007 by kerick214

However, this is a P-82 with two fuselages and will be carrying up to 4,000 lbs of stores. I'm thinking that a longer float will be needed. The one in the pic with the fuselage scales out to about 27 feet while the next size up is more like 39 feet. I'll try the displacement calculator and see what that gives me. I just want it to look believable.

[jcf]

Go bigger.

The float mounted Beast is a good example of a smaller than a twin but heavy design that needed more floaty goodness.  

I suspect you'd be in the same situation with a P-82 on floats.

http://en.valka.cz/viewtopic.php/t/48309

[kerick]

Nice find! I'm leaning towards the same direction.

[Captain Canada]

Some great stuff here. Thanks guys ! More fodder for the files....

[sandiego89]

Go bigger.

Agree, a bit bigger.  She is a heavy airplane.  Those are a bit smallish in diameter- want about half the float out of the water.   

Awesome idea!  A float twin mustang 

That bag'o'floats is a nice thing to have in the stash.   

[kerick]

That Aeroclub set is good for any number of 1/72 conversions. Not big enough for 1/48th unless its a Cessna 150.

The displacement calculator says one 40' float would be good enough but its using a rectangular box for the calculations. I'm guesstimating that half that is lost due to the tapered front and rear of the float. So two 40' should work. At least it will look decent.

Thanks for all the help. I hope its useful for others that maybe interested.