Formula For Calculating Speed (Revisited)

[bbill1]

1.4 x 47 = 65.8mm = 2.59"
what don't you understand?
Octura props have always been numbered this way, makes it super easy to figure out what you have.

Not that I didn't understand.

For nitro I just always used the numbers on the chart. But I got it now. Thanks!

[sailr]

1.4 is the 'factor' or multiplier. 1.4 x diameter = pitch. Same is true with say a 642 prop. that would be 1.6 x 42 = 67.2mm = 2.645661".

How are you guys coming up with your prop pitches? The pitch on a raw x447 is 2.59. Yet in the example below from post #1, it is listed as 1.4.



I've been into nitro for quite awhile and have never come across any other numbers for pitch other than what would be listed on a prop chart. (in inches and are 2+ inches of pitch for any props I have ever used.)

[BHChieftain]

Thanks again for working this out. This is very helpful. But you need to add a "color" factor to your equation-- we all know red boats go faster...


Chief

[properchopper]

Good stuff. One thing, 'tho ( and in no way is this a criticism of these efforts) is that the V or voltage value used is based on the nominal starting V which changes (decreases) considerably under load, as I have found after much data collection/plotting on several brands of batteries. The +/- 3% variation likely is a result, in some part, of this phenomenon. The KV is another possibly varying value based on production tolerance and other considerations.

[Ub Hauled]

Tony, I thought about the same thing, but you had to throw a wrench in there, eh?
LOL

[carlcisneros]

good inforamtion all around.

but, it is a tool for getting an idea of about how fast the boat is going.

nice to have folks that take time and figure things out for us out in the boating world.

GOT TO LOVE THIS FORUM!!!!!!!

[properchopper]

Tony, I thought about the same thing, but you had to throw a wrench in there, eh?
LOL

Hey now, I only throw wrenches while working on my chopper - most of the time I throw hockey tape

[Shooter]

Within 3mph of my GPS reading for my Vegas running 2200KV, X642, 4S. Nice work.

[martin]

Within 1.7mph of my GPS reading for my Vegas running 2200KV, X642, 4S. Nice work.

What speed did you get with gps & from formula. Thanks Martin.

[Shooter]

Hi Martin.

Vegas (X642 S&B, 1515 1Y): (1.6 x 42 x 2200 x 14.8)/33610 = 65mph (GPS = 62)

[martin]

When ever i see someone post speeds with gps & they give relavent info like kv, volts, prop, type of hull i like to work speeds out on how i do it just to see how close or far away i am. With the info on your boat i got 60.8mph. Martin.

[Shooter]

Martin - Which denominator is correct for Hydro? 33610 or 33300. Both are listed in your first post. Thanks.

[martin]

I dont actually use that formula but either of those numbers work out quite close to one & other on calculated speeds. On say a 60mph boat both those numbers are only .5mph apart. Martin.

[penz]

Hi Martin.

Vegas (X642 S&B, 1515 1Y): (1.6 x 42 x 2200 x 14.8)/33610 = 65mph (GPS = 62)

So im curious putting that prop on that 1515 motor how are your temps?(motor/esc/batts) What c rating batts are you running, and what esc? I am planing on running a 4074 2150kv motor in my apparition, i am shooting for 50 mph on 4s. If you hitting 65 mph with good temps then i think my setup should work good.

[FloatDaBoat]

Here's a spread sheet version (XLS) that I whipped-out.