Anyone know how much weight the Hangar 9 40 size floats can carry ???

They say 40-50 size planes, but what weight would that range be ???

Thanks in advance,

Sam

Sam,
I don't know these floats in particular, but I have measured several others and discovered the following.

If you multiply the total length times the maximum width times the depth at the step to get the block volume.
Then the actual volume will be between 50% and 61% of the block volume.
Taking 55% as an average, multiply the block volume by 0.55 to get an estimate of the actual volume. The buoyancy is the volume times the density of water (1 g/ml, 1 kg/litre or 0.58 oz/cubic inch).

Example, model in photo. Floats 37" (940 mm) long, 3.25" (82.5 mm) wide, 2.7" (68.6 mm) deep.
Block volume = 324.7 cu.in. = 5.32 litres Actual volume estimate (@ 55%) 178.6 cu.in or 2.926 litres.
Measured volume was actually 3.185 litres (or 60% of block volume)

The estimate of 55% is on the safe side and would give buoyancy of each float = 5.32 kg or 188 oz estimated

If the weight of the model, with floats, is equal to the estimated buoyancy of each float then the floats will be half submerged, which is OK, and that gives you a weight limit for the pair of floats - 55% of the block volume times the density of water.

Wow !!!

Thanks,

Hangar 9 Float Specs:

SPECIFICATIONS
Length: 36 in (914mm)
Overall width of float assembly: 20.75 in (527mm)
Tip of float to the step: 19.25 in (489mm)


So you think the Hangar 9 floats should hold up 9-10 lbs ???

Sam

If you go to the very top of this forum you will find a thread called something like frequently asked questions about float flying - done nicely by Jim Casey - Jim is very informative and will not steer you in the wrong direction. The rule of thumb is to measure from the rudder hinge line to the back of your prop ( front of thrust washer ). Take 75-80% of that distance and this will give you the lenght of floats needed. I put 40 size floats on a beefed up Sig Kadet Senior yes they were a bit shorter than called for , the plane sat a bit deeper in the water than a 40 size trainer, but I had no problems with this set up.

That 75-80% of fuselage length often works.
But a better method is to measure from the prop to the aircraft's CG and multiply by 2.5 then place the centre of the float at the CG and the step just behind. This method guarantees that 10% of the float will be ahead of the prop which is important.

For details see [link=http://www.gvmac.com]gvmac[/link]
Go to Articles and read or download the Word doc. The first couple of pages tell you how to size and shape floats, then goes on to how to make them yourself.

Quote Hangar 9 Floats SPECIFICATIONS
Length: 36 in (914mm)
So you think the Hangar 9 floats should hold up 9-10 lbs ???
If each float is about 4" wide and 3.5" deep, that sounds about right. They are good for up to a 10 lb model.

Thanx Guys...

Looks like it's going to work....putting my CMP Cessna on Floats....

Once I take the main landing gear and the nose strut off this should bring her back down to around 8 lbs...

Sam

I frequently cite the 75% guideline. As Alasdair says, it usually works.
What I really think is infallible is to find the mean aerodynamic chord and to place the step under the 40% point. That's pretty easy to find with a straight wing.
The nose of the float goes 1/3 of the prop diameter ahead of the prop. Then put 95% of the nose-to-step length behind the step.

Inspect your H9 floats carefully: there is another thread where flyers are reporting fragile hulls that crack and leak. I have not witnessed such, but it's easier to check and reinforce proactively.

Yes Those are important points.
The step should be just behind the CG (often at 33% mean chord, but not always) so 40% often works
I generally make the part aft of the step a bit shorter than the front part.

1/3 of the prop diameter ahead of the prop. I'd say 10% of the float length, but I'm sure either will convey the idea - some float buoyancy needs to be ahead of the prop to lift it above oncoming waves.

The article referred to in my earlier post does these same things. I measure from the prop to the CG and multiply by 2.5 to get the float length. (That always worked - until I built the jet) Then I put the mid-point at the CG and the step about 2% of float length aft of the midpoint.

All these general rules of thumb are fine, until you encounter an oddball design, then it's back to general principles.

Enough buoyancy to support about double the model weight, distributed so that the nose is held up.
A bottom that curves up gently to a point well above the waterline so that it will climb up onto the planing position without pushing up a bow wave.
Step just behind CG.
Buoyancy ahead of the prop.
Rear angled up behind step at 5 to 7 degrees to allow room for rotation and take off.