What is BL equivalent to 0.19 to .45ci in IC engine?
Especially if driving an air propellor - this I can do!
Several ways, also If we know the power of the IC engine we can match that:
If we assumed a 0.45 is claimed to produce 1HP at peak revs - thats 0.746 Kw or say, 750watts
The BL that matches that is not, actually a 750 Watt device, but probably about 5 to 600W*
So now we only need to pic the KV, and Job Done.
This depends a little on the prop diameter available (on the airboat)
Ideal is the largest prop driven slowly (quietest, most efficient) but practical reasons will rule out the 18x24 inch prop
so the prop diameter will be set by the structure of the boat, the revs are set by keeping the tips of the prop well sub-sonic (for noise reasons), and then the pitch wants to be the coarsest consistent with the power available and acceleration required.
I don't have the figures in my mind, but if the boat will take a 12 inch dia prop it probably wants to be turned below say 10,000 RPM for noise reasons so on 10V that would be a 1000KV motor, and power is tuned by playing with the prop pitch, which in 12 inch props seems to be avaialble from about 4 inch pitch to probably 18 inch - in 1/8th inch increments (12 inch props are used by stunt and aerobatic flyers who need very fine adjustments for their (weird) requirements.
OR - if we know the prop and RPM for the IC engine (which equates to the exact power) we can use BL motor data tables to find the same RPM for the same or similar prop - and there is no more to do than that!
Example of prop data for a particular BL motor - in this case Scorpion 3026 -8 http://www.micronradiocontrol.co.uk/scorpion_data/3026-8.html
* Why would a BL motor need less power???
- Electric motors produce torque only, not vibration - less weight of supports etc to resist shaking
IC props are thick enough the resist the vibration and torque variation. less efficient than Electric props at producing thrust
Power for IC engines is quoted at peak revs - often silly ones. The 0.46 might peak at 18,500 on a 7x6 prop - not usable in practice because of prop noise, and not desirable either cos of short engine life (Ducted Fan engines are an exception - they always run WFO)
IC manufacturers are human and lie
The fine print of the IC engine says "ISO conditions" and "new and clean" this translates as "YMMV"
Sorry about the long and rambling response its actually simpler than the water-prop case (Cos no-one has admitted to having water propellor power/revs curves)
It happens, by chance that the example I picked at random just to illustrate the principle seems to have some good combinations of power/prop
Prop APC 12x6E
Thrust 2913 gms Thats three KG of thrust
This will fly a 2.5 KG plane vertical. Forever!
The same motor is happy at smaller diameters and larger pitches - have a look at the data!
Hope the wordstorm helps a bit
Andy - please let us have a finger-count before you commit airboating