gmd

Does anyone know what the proper ratio is for floats? I have been told they should be 75% of the fuesalage length. I have also been told 2/3 rds. I have a Goldberg Decathlon that I want to put on floats. The fueslage length is 53 inches. I have an extra set of Goldberg floats already built and glassed that are 36 1/2 inches. I'm guessing that they are a little small, and I will need to build some 60 size Great Planes floats to fit it.

Thanks Much!
Gary

jrf

My Feedback: (551)

Gary:

The Great Planes "60 size" floats are huge. I have a set on my 4-star 120 and they are really too big for that airplane. My floats are MonoKoted, not glassed, and with aluminum struts, they weight 4 pounds.

You do need a 40-42" float, but I'd go with one of the foam float cutters, they will be a bit smaller overall and a LOT lighter.

Actually, you might want to loosely fasten the Goldbergs on (with the step at the CG) and try the airplane in a pool. They have plenty of floatation and as long as the nose of the float is ahead of the prop and the tail of the airplane stays out of the water, you could use them.

Jim

CraigA

Here is a link to everything you need to know about floats...well almost everything. Click on the pages to the left to bring them up to a readable size.

http://flyinglindy.homestead.com/skisandfloats.html

CraigA

Antique

My Feedback: (4)

The article CraigA (above) pointed you to is right on the money. I've been using this formula by Chuck Cunningham for many years on many different planes, and they have all been letter perfect. You'll hear many different formulas for float design and step placement but none work better than Cunninghams.

CraigA

These floats were made per the Chuck Cunningham article...and work great!

CraigA

JimCasey

My Feedback: (1)

The Chuck Cunningham article is a benchmark for what you ahould know to fly floats.

Here is a link to another article I have saved over the years: http://users.rcn.com/llfc/floats/
You have to download several gif files, but it's worth it. It's the Ed Westwood article from Model Aviation.

Bill Rademacher

My Feedback: (77)

go to www.flyingcolorsky.org and click the float flying link on the left. There is a formula you can run to tell you the necessary dimensions of your floats, etc.

SKYPILOT

My Feedback: (9)

YIKES,

I'm also building the Goldberg Decathlon ARF for floats, and have the GP 60 floats that my father is building for me for the project, and I plan to use a Saito 91s for power

My reasoning for pairing these two WAS the numbers ! With the fuse being 53", the ideal float length would be 39.75 rounded to 40" if my math is right, so my thinking was that the GP 60s were the closest .

So Jim and Craig,

You guys think that these are too big, and or heavy for this plane ?, if so, what specific make/model/size float would you guys recommend ?. This is also my first effort into floatflying, so i'm looking for any and all advise and help

4*60

My Feedback: (41)

It has been explained to me by a very long time float flyer and scale builder that 75% of fuse length is a little misleading. Measure the distance from 2.5 inches ahead of the prop to the CG. Double this and that should be your float length. I like that because it places the CG relative to the floats about right.

JimCasey

My Feedback: (1)

I like what 4*60 said. The Ed Westwood Article which has disappeared from the web said to put the nose of the float 1/3 of the prop diameter ahead of the prop, and to put the step of the float at 40% of the mean aerodynamic chord. Then the rest of the float is the same length, behind the step.

jrf

My Feedback: (551)

Skypilot:

What makes the GP floats too big and heavy is their width (almost 7 inches) and depth (about 5.5 inches). They are also made from light ply and very hard (heavy) balsa. BJ foam floats in a 40" size, or a similar float from one of the custom float cutters would be smaller in cross section and (depending on your finishing method) much lighter. Jim Casey and others who post here know of several foam float cutters.

Jim

JimCasey

My Feedback: (1)

When I cut 40" floats, I only use a 5" wide blank, and since the sides are tapered the width actually comes out a teensy bit less than 5".

alasdair

The 75% fuselage length rule IS a little misleading, though it kind of works on many models.

What you REALLY want is at least 10% (at most 15%) of the float length ahead of the prop (assuming a conventional prop-at-the-front model).

My rule is to measure from the prop to the CG and multiply by 2.5 to get the minimum float length, and then put the centre of the float at the CG.
That will guarantee 10% of the length is ahead of the prop.
have a look at www.gvmac.com
go to the Beginners Section and look at the Float Construction article ( an improved version was in the British magazine R/C Model World in Jan/Feb/Mar 2004).
Alasdair