RC Airplane question.

[Doozie870]

Converted to a higher rpm set up on my trainer plane, and even though the 13x8 prop is now spinning about 2k faster the thrust is the same?

[ghostofpf1]

That doesn't sound right...
Are you using some sort of thrust measuring device ??
Ghost

[Doozie870]

I have the plane hooked to the wall with a digital fish scale lol. Cant seem to get above 4lbs 10oz this occurs at 1/2 throttle, after that it the rpms increase but the thrust remains the same, its almost like the prop loses its bite?

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[Dr. Jet]

Sounds like you are stalling the prop. Don't worry about the thrust numbers, they don't really mean that much in the "Big Picture". Go out and fly it and see if there is a difference.

What kind of prop is it? Wood? APC? APC Electric?

[ghostofpf1]

Yeah..that fish scale probably couldn't tell the difference of just 2000 rpm anyway. Like Dr.Jet said the proof is in the flying.
have fun
Ghost

[Doozie870]

They are apc electric props, I made some good progress today jumped to a 15x8 and the thrust went up to 7lbs 8oz. this involved bending the main gear down and extending the front gear with a coupler to get it to clear but the amps are still pretty reasonable 41 at full. thanks for the help.

[Bill-SOCAL]

I've been flying power planes of one type or another for nearly 42 years now. In all that time you are the first person I have ever come across that tried to gauge prop performance by using static thrust. For a prop driven plane it is sort of meaningless since the prop unloads in the air and the numbers you got on the ground are literally lost in the breeze!!

As has been said, do it the old fashioned way. Change the prop, go fly, see what it does. Kind of like what you do with a boat as well.