Question,,,,when its said to make the floats 70 to 80% of the fuse, are they talking tail post to fire wall?
i am going to scratch out a pair for my 1/5 scale (great planes) cub
Falcon

That distance is from the rudder hinge line to the front of the thrust washer of the engine.
( rear face of the prop )

Thank you for the quick come back. looks like its 52 " so i gess that will make them 39 to 41" long. ill size up a set of balsa USA planes.
Falcon

Check out my foam floats @ www.seaplanesupply.com

I'd stay with the longer dimension - 41" if I were you. From my experience the longer number works out better. I like to use the Chuck Cunningham standards, then add a small amount of length forward the step. Chuck says use 53% in front of the step, I like to use 55% and work from no less than the 80% number - which for you would be 41.6". This is just what has worked out for me best. The little extra in front is just a little extra measure of insurance against nose overs.

I have a simple program that will do all the math for you. It will do both floats and a single Pylon float, included is a simple pic to show where to use the numbers it generates. If you like I can send it to you in a ZIPPED file, very small files.

Thank everyone for the quick replys. ill go with the 41", ill size a set of edo from balsa usa to size.
Falcon

A lot of float makers say "for planes 8-11 pounds {this is a 35" float} whereas they should say "this is for a XX" long fuse".

My LT-40 ARF weighs less than eight pounds, but it needs at least a 40" long float.

Another point of possible confusion- the specs. published for a given plane may say " Length-56", but that is the TOTAL length [including the rudder]. You cannot base your float length on that figure.

Shack

Hello Shack
You said you need at least 40" floats for your LT-40 ??????? When measuring for floats you measure from thr rudder hinge line to the front face of your engine's thrust washer. My LT-40 measures about 49". Then multiply this length by 75% and the results are 36" floats. The floats on my LT-40 are a tad over 35" and are just right for this plane. I have a Magnum 46 for power and it is just the right amount of power.

[8D] Hi, on my LT-40 I have Planefun 40 size floats which are 34 inches. The engine is a Magnum 46, a great combo. Also have a Kadet Sr. ARF converted to electric which I have Planefun 60 size floats. Haven't flown it with the floats yet, but flies great on wheels so should do well on floats.

I have always used Chuck Cunningham's formula with pretty good success. He reckons the length of the fuse. to be measured from the BACK of the prop to the ELEVATOR hinge line; that is 53.5" on my LT-40 ARF. Multiply by 75% = 40.125".

Mine is powered by a Saito FA-72 [four stroke].

I had a set of 36" Great Planes fiberglass floats on, but were obviously too short. They particularly needed to extend furthar in front of the prop. Keep in mind, I run a 13" dia. prop, so the mounting gear is a little taller.

Shack