Prop pitch vs diameter & amp load

[gsbuickman]

Hello everybody :tiphat:,

Yesterday a local FE boater was bending my ear when he ran across a twin mean machine that was on fleabay that started this discussion :doh: . It was running twin leopard 3650 5400kv mills pushing 1.6 pitch 42mm props on 2s power. The seller stated that it makes 60mph runs.

This discussion led to a question being posed that I thought was pretty good.
In theory if you were running a 29" GEICO cat, on twin mystery 2200kv mills, x447 props, 80A esc's and 4s 40c power and you wanted to go to 1..6 pitch props w/o frying the esc's, how would you go about it ?.

Is there a formula to estimate when increasing prop pitch, the drop in prop diameter to maintain about the same amp draw ?.

He's pondering a twin build with 2 of the 2200kv / 80A combos from HK, might prove interesting ...... :w00t:

[srislash]

I do have said 29" Geico twin. I am running SK 120's and PB 1800kv's mind you on 5s. When I get my ET logger to work with Windows 8 I can tell you the difference between pitch and amp draw. I have pairs of 45mm in 1.3, 1.4, 1.6, and 1.8 here. Should be able to play with the speed calc a bit and get a guesstimation

[Meniscus]

Maybe I can help here. First of all, I run a lot of 2s setups with setups pulling from 20-25A up to 280A+. The easiest way to find the comparison in speed from one prop that is one pitch to another is to figure out the "total" pitch in either inches or mm. Example: an X447 prop has a pitch of 1.4 and an outside diameter of 47mm. This means that the total pitch is somewhere around 2.591 inches or 65.8mm. This is the distance it covers per revolution. A comparable 1.6 pitch prop to go the same speed would be an X640.

HOWEVER, because of the various in blade area and interaction with the water, the load can be significantly different from one prop to another, even if they are supposedly and appear to be the same. The best course of action is to start the whole process over when you look at trying a higher pitch prop, meaning go back to a small prop and work your way up while measuring heat and load put on the system.

At the end of the day, there is no magic conversion between the prop choices with regards to load because every prop is different. What you can compare is the "total" pitch to make a comparison about how water a given prop with cover per revolution. However, the prop slippage may be different from one prop to another. Hopefully that makes sense. :smile:

As a final thought and caution, as much as I love the X6 series props, especially on 4s power, they often put a very heavy load on 2s setups. In my testing, some of the highest numbers I've every seen and the most amount of heat have come when I ran an X6 series prop on 2s. Note that there is an exception when you talk about micro models.