Something to keep in mind: when testing a stationary motor/prop combination, you can only find data for static thrust. Useful for you, since you're doing a VTOL aircraft, but remember that as soon as the prop starts moving through the air the thrust it produces will drop off and the power required for a given RPM will diminish.
Related to static-thrust is stall-thrust. If the prop has a pitch steep enough relative to the rpm, the prop blades can stall and will generate a lot of drag (high amp draw) and significantly less thrust than a lower-pitched or slower turning prop. Once the aircraft gets to a certain airspeed the blades will un-stall and generate better thrust numbers and draw less amperage. This may have some relation to why the 1900kv motor produced less thrust than the 1800kv in testing.
I don't know the formulae for determining the speed at which a prop un-stalls, but eCalc and various other prop calculators will generate those numbers for a given setup; so there is a mathematical way of determining it.
I think the reason for the poor-looking 2808 motor performance is that the small, high speed prop produces less static thrust for a given power( P=TV, + friction, drag) and that it is probably less efficient than a larger prop spinning slower. The 65% rpm range on the motor seems to be quite efficient.
Regarding using high-pitch props to get the pitch speed to go 200 + mph, the only cure for that is a variable pitch prop.
Otherwise, you just have to put up with poor low-speed thrust.
<edit>
A sign of a prop stall? no obvious sign-loss of thrust compared with less pitch setting-failure to take off, with a full sized aircraft with pitch control.-been doing some google lookups!
A pylon racer at 30,000 rpm with 6 inch pitch doesn't seem to stall the prop.
I see you can get up to 14 inches pitch, on APC.
I suppose this is handy for a large scale model warbird, which would be limited to under 10,000 rpm with a 250cc single motor?
In theory those could do 18,000 rpm, too, but that would be a racy 2-stroke with a pipe- not a model airplane motor.
If they use a 24 inch propeller, they want to keep it well under about 11,000 rpm.
(speed of sound at the tips).
To get to 200 mph they wold need 3x the pitch of the pylon racer, or 18 inches?
(pitch speed of 230 mph)
Do model aircraft props even come in that pitch? - No-one trying to make those big models fly fast?
The larger pitch numbers APC show are probably mixed units-inches diameter, and mm pitch.
Those WW2 fighters with 13 foot constant speed props that go over 450 mph must get up to some huge pitches at speed?
Maximum prop speed = 1500 rpm.
Prop plane speed seems to be ultimately limited to 550 mph-the extreme pitch needed must be inefficient, plus
prop spinning speed adds to aircraft speed, and hits the speed of sound, then prop efficiency really drops off.
Supersonic props don't seem to work well, even if they are thin and curved. The sonic transition zone on the prop probably causes huge drag.... One guy was building a speed plane with motor direct drive, but he gave up.-possibly couldn't get flight approval??
Also his mate that he wanted to fly it got killed in an air crash. They do seem to have a few horrible crashes with unlimited pylon racing!
https://www.popularmechanics.com/flight/how-to/g631/4-amazing-diy-planes-and-how-to-build-your-own/
David Rose:
