guys,
What is needed for a pusher configuration?

Is it only the prop that needs to change or even the motor/esc need to be different?

The reason I am asking is because I was under the impression that only the prop needs to be changed. I bought a Master Airscrew pusher prop, but no matter which direction I mount, it seems to be pulling and not pushing.....

clarification required

Pankaj

Typically, just flip any 2 of the 3 wires between the ESC and the brushless motor, and that should reverse the direction of rotation of the motor and solve your issue.

Ha ha!! Anwar bhai... Even I wonder why they brand pusher props separately. Thanks they don't fool us with a 'Pusher Motors'

Go ahead Pankaj sir, you already must be having so many props. Which plan by the way ?

Just like to add, you can also Flip the Prop as well, for efficiency , the leading edge which used to cut the air in the puller config should cut air in pusher config too.. just do static experiment with Watt meter and thrust bench(or even hand would be enough). You can clearly hear a totally different sound when the (intended) trailing edge cuts the air.

Thanks Anwar,
I interchanged red and black wires and now the pusher works.

Ujjwaana, let me first try out a pusher setup and then I shall post what I did
Pankaj

Pankaj sir, as its just matter of Prop flip, and even a static test would do, please reconsider my advice of flipping the prop instead of the motor wires. I found the prop flip more efficient than motor one since it more adheres to the aerodynamic design of the props.

Wishing you all the best

Ujjwal - I am confused.  Even if you flip a prop (by 180 degrees), a "tractor" prop will push air in the same direction and continue to be a tractor prop, right ?

Yup, anwar is right. Prop is symmetrical. Nothing happens if prop is flipped. It works same on both sides. Only the rotation of the motor does the thing from puller to pusher.

i

Quote from: merog on May 10, 2010, 07:59:57 AM
Nothing happens if prop is flipped. It works same on both sides. Only the rotation of the motor does the thing from puller to pusher.

No. prop is designed to give thrust only in one direction, means it  will not work same in both directions, reversing the motor direction will change only push or pull configuration (flipping of prop is also needed) but cannot be used by only reversing the prop. reversing will give you thrust but with very less efficiency and will be able to blow away small pieces of paper only. only flipping of prop will not give you proper result. Try out...

So Ujjwal's point is that one should reverse the prop along with changing the rotation of the motor, if they want to use a normal prop in a pusher config.

All,
I had this prop designated as a pusher. When I had first connected the motor, it seemed to act as a tractor. The thrust was very weak, but still it was 'pulling' and not 'pushing'. Again, I had tried flipping the prop, but the result was the same. It is only after I interchanged the wires as per Anwar's suggestion that actually the motor is building up a decent thrust and is 'pushing'

Pankaj

the thump rule i follow is:
1. The marking on the prop ( letters 8X4 etc.) always faces the front of the plane.
2. Now connect/ reverse the three motor wires so that the air is pushed back.

ashta

  i too had a similar situation when bulilding my multilplex funjet recently, but the manual clearly says that connect the propellor in the normal direction and change the wires b/w esc and motor for pushing, as ashta said

Quote from: sandeepm on May 10, 2010, 09:52:21 AM
No. prop is designed to give thrust only in one direction, means it  will not work same in both directions, reversing the motor direction will change only push or pull configuration (flipping of prop is also needed) but cannot be used by only reversing the prop. reversing will give you thrust but with very less efficiency and will be able to blow away small pieces of paper only. only flipping of prop will not give you proper result. Try out...

Am sorry, I tried very long back when I was studying the props and the thrusts... etc. The thing of the interchanging the leads to change the rotation of the motor resulted the wind blow to opposite direction as well as with the same and equal thrust, no loss of the pull or push.

And I experimented with the APC and SF too. Always we need to put the letters written side to front, that mean against the face of the motor. The motor rotation determines the direction of the thrust (and wind blow).

Any way the point is straight forward I think, without any confusion. The specially designated props - I dont know about them.

Sorry for comming in late. Yes, both Ashta and Sandeep sir are right - I meant 'just not wires' you need to flip the prop too.
I learnt it hard way in the fields when there were many advices poring in from fellow flyers. I was not getting the right thrust and flipping the prop worked the charm. I flipped the wires so many times that I forgot the real orientation. Please pardon me.

Real confusing..... If all the above is true, then what is so different in a Pusher prop?

Pusher props have its place where the direction of rotation is important. In IC engines you cannot change the direction and need a pusher prop when used in deltas and such. Though brushless motors can change direction, they are still uses for electric pusher props. Examples - some electric pattern planes use contra rotating props so that they don't have to mount with an offset. Another is quadrotor.

Quote from: PankajC on May 11, 2010, 10:04:26 AM
Real confusing..... If all the above is true, then what is so different in a Pusher prop?

In my opinion, there is no difference in pusher prop...

I agree with what merog said. this can happen if one make a hand made prop out of a thin metal sheet, without any profile, means simple folding the tin sheet in the form of a prop. in this case only reversing the direct will only change pull of push configuration, no need to flip the prop. but in our r/c case where we can see a profile in prop. we have to flip the prop along with reversing the direction of motor.

Sandeep has a point. Most viable props are like  Wing's Aero-foil themselves. the leading edge is thicker and trailing edge thinner, with semi/under chamber planforms. Thus, if the trailing edge cuts the air first, whole aerodynamics changes too, leading to very poor thrust. Thin props without any airofoil shape are exception.

Tipping on Ashta saying I am confused (indeed), I gave a second thought what goes in when we move to pusher config:

Problem: I have to reverse the motor orientation without changing the Air flow direction

1. The prop would remain facing the same direction as it should be in puller config (so now the motor shaft enters the prop from opposite direction as from before) due to aerodynamics of the prop.

2. Even though the motor (not wires) has been flipped 180* (motor front facin back now), the shaft should be rotating in the same direction as before - the rotation should be reveresed, thus flip the wires.

So : 1. flip the prop. 2. flip the motors any two wires

Notwithstanding the flexibility of BL Motors, Rajesh sir (Rotorzone) is correct too as we cannot change the direction of glow/IC engine shaft rotation. So, we need to have a prop whose aerodynamics are such that it pushes air on clock wise rotation.  The  answer is, change the pitch direction of the prop (the leading edge now facing towards motor instead of away for it as in normal props).

Synopses
1. On EP motors, we don't need specialized  pusher props as we can simply flip the wires and change the rotation diection.
2. We have to use specialized pusher props for IC engines as we cant change the rotation direction.

There is enough evidence that people are successfully (and efficiently) using same prop for pusher config on  Electric motor by flipping props and wires.

Best example to understand the prop and motor things in details....buy a VPP (Variable pitch prop) setup and check yourself....you will understand things and will be clear like a air.



i havent see the VPP but i can guess that VPP prop are different then ours (like heli)

Sandeep