Graupner 14" prop reviews?

[DucktileMedia]

Seems everyone, including myself, are very happy with the 11x5's. But I never hear of anyone running the 14" props which do come in a CC and CCW pair. I would think their 14" would be more comparable to a standard 12" since E-Props tend to have very little surface area. I know a pitch of 8 is pretty steep but just curious of the heli setups people have that use these.

http://www.v-eastonline.com/products/GRAUPNER-E%2dPROP-14"X8"-LH.html

 

[jes1111]

14x8 is way too high a pitch ratio for hovering - they will exhibit "pitch stalling" - too high an angle of attack for the airflow over them.

 

[DucktileMedia]

They sell them on Kopterworx site so i figured someone was using them. But that was what I thought the issue was. Sounds like multis like the smaller pitch so they dont respond so aggressively to rpm change as well.

 

[jes1111]

Yep - multis like low pitch props because it's the swept diameter that produces the hover lift, not the pitch per se. The pitch (a.k.a. angle of attack) compensates for high speed inflow of air, like on a fixed-wing aircraft that's travelling at high speed. High pitch props on a multi will actually respond slower to demands for increased rpm since they have greater drag (which is also why they'll pull more amps).

 

[ddmt]

This user @rcg is using graupner 14x8 with pancake type motors, he seems to be happy with the setup.

 

[jes1111]

I'm quoting the physics, not my own experience - and the physics is clear and indisputable. They'll fly, of course - the lift is proportional to the diameter, not the pitch. The consequence of blade stall (which will only happen near the root where the pitch is highest) will be reduced lift, i.e. 14" props may only produce the lift of, say, 12" props. But in terms of blade drag you'll be getting the full 14"-worth, so the overall efficiency will be very poor.

I'm not having a go at you, ddmt - but there is a strong tendency in this hobby for people to take the fact that one or two people do something and say it's okay/correct as endorsement for that "something" over and above the physics ;-)

 

[mailman35]

i like the sound they make

 

[ddmt]

I'm quoting the physics, not my own experience - and the physics is clear and indisputable. They'll fly, of course - the lift is proportional to the diameter, not the pitch. The consequence of blade stall (which will only happen near the root where the pitch is highest) will be reduced lift, i.e. 14" props may only produce the lift of, say, 12" props. But in terms of blade drag you'll be getting the full 14"-worth, so the overall efficiency will be very poor.

I'm not having a go at you, ddmt - but there is a strong tendency in this hobby for people to take the fact that one or two people do something and say it's okay/correct as endorsement for that "something" over and above the physics ;-)

Nah, no hard feeling. I'm kinda "let's see what other people are using or testing and try to replicate myself" person. I never trust blindly what people are saying on web forums.