HobbyKing.com New Products Flash Sale
Closed Thread
Thread Tools
Old Jul 25, 2012, 01:16 PM
Registered User
United States, NY, Syracuse
Joined Jun 2012
28 Posts
Discussion
Dumb pusher prop question

I have been building f22 jets and the pans call for a pusher motor/prop. Instead, I have been installing a standard motor and standard prop with the motor facing forward (tracker). I see that they sell pusher motors and pusher props. Someone told me that you can use a standard motor and put a standard prop on backwards to make a pusher. Is this true?
kc2pxp is offline Find More Posts by kc2pxp
Sign up now
to remove ads between posts
Old Jul 25, 2012, 01:32 PM
Registered User
tacx's Avatar
United States, MI, Macomb
Joined Apr 2009
2,554 Posts
No, That does not work because when you put a regular prop on backwards the angle and direction of the pitch of the blades is the same.

A regular prop will fly a plane if installed backwards but it won't be as efficient because the profile of the props blades is different from one side to the other.

A pusher prop is actually the same as a regular prop except for the fact that the blades pitch in the opposite direction.

There is no "standard" motors. Brushless or brushed motors can run both ways.

When talking electric setups you do not need a pusher prop. No matter which way you face the motor you can use a standard prop and always face it forward. To make the prop run in the correct direction you only need to connect the motor so it runs in the correct direction

Pusher props are mainly used in glow engine setups where you cannot reverse the engine. For example, in an air boat, or a water plane that has the engine facing the rear.
tacx is offline Find More Posts by tacx
Old Jul 25, 2012, 01:35 PM
Shelter Kitty "Orange Death"
bartricky's Avatar
United States, FL, Monroe
Joined Jan 2008
3,163 Posts
Quote:
Originally Posted by kc2pxp View Post
Someone told me that you can use a standard motor and put a standard prop on backwards to make a pusher. Is this true?
True. Std. for electric motors as you can reverse the rotation.
bartricky is offline Find More Posts by bartricky
Old Jul 25, 2012, 01:36 PM
Suspended Account
United States, VA, Ashburn
Joined Apr 2012
2,784 Posts
Not sure I understand what the guy above me is saying lol, but all you do is reverse the prop and switch two wires from the ESC to the motor.
RCAddict16 is offline Find More Posts by RCAddict16
Old Jul 25, 2012, 01:52 PM
Shelter Kitty "Orange Death"
bartricky's Avatar
United States, FL, Monroe
Joined Jan 2008
3,163 Posts
Quote:
Originally Posted by RCAddict16 View Post
Not sure I understand what the guy above me is saying lol, but all you do is reverse the prop and switch two wires from the ESC to the motor.
As long as the motor is turning CW looking from the rear and the prop is facing forward.

Pusher props are from glow engines that only turn one direction.
bartricky is offline Find More Posts by bartricky
Old Jul 25, 2012, 02:02 PM
AndyKunz's Avatar
Illinois
Joined Sep 2001
23,380 Posts
Quote:
Originally Posted by tacx View Post
There is no "standard" motors. Brushless or brushed motors can run both ways.
With many brushed motors there very definitely is a preferred direction of rotation.

The timing advance is done by the commutator and endbell. Rotating the endbell causes advanced/retarded timing, which affects RPM, no-load current, and the whole power curve. A motor configured for good power in one direction will have very poor performance (often resulting in a meltdown) when power is reversed.

A brushed motor with 0 degrees of advance will run (equally poorly) in both directions.

A BL motor OTOH can run in either direction because the timing is performed in the ESC.

Andy
AndyKunz is offline Find More Posts by AndyKunz
Site Sponsor
Old Jul 25, 2012, 02:12 PM
Registered User
builderdude's Avatar
United States, TX
Joined Jun 2011
2,646 Posts
You can indeed wire the motor to run backwards. However, you lose a great deal of efficiency with the prop. If you look at the prop closely, it has an airfoil. I wouldn't want to run one backwards against the airfoil. You can do it, but with all the pusher props available, why would you want to?

I've done a number of pusher planes. Well, 3 to be exact. Just wire the motor up like you normally would and buy a pusher prop. If the prop arc is a concern with ground clearance, you can even get 3-bladed pusher props, which is what I use. They work great.

Look for Master Airscrew to find a wide selection of pusher props. Several stores online carry them.
builderdude is offline Find More Posts by builderdude
Old Jul 25, 2012, 02:50 PM
Retired in NC
Rich in ILM's Avatar
USA, NC, Wilmington
Joined Sep 2010
2,066 Posts
Quote:
Originally Posted by kc2pxp View Post
I have been building f22 jets and the pans call for a pusher motor/prop. Instead, I have been installing a standard motor and standard prop with the motor facing forward (tracker). I see that they sell pusher motors and pusher props. Someone told me that you can use a standard motor and put a standard prop on backwards to make a pusher. Is this true?

I am going to try to simplify this as there seems to be conflicting information.
A brushless motor can run in either rotation by switching 2 of the 3 wires. From the back of the plane looking at the shaft... Have the motor turn clockwise if you want to use a standard prop. Have the motor turn counterclockwise if you want to use a "pusher" prop.
In each case the lettering on the prop must face IN THE DIRECTION OF FLIGHT. In other words in this case the prop must face towards the motor which is opposite of the way it faces when the motor is on front of the plane. But in both cases the lettering is facing the direction of flight. Props, like wings, attack the air thick to thin.
Rich in ILM is online now Find More Posts by Rich in ILM
Old Jul 25, 2012, 03:19 PM
Expo/DualRates = Lack of Skill
typeRA's Avatar
San Diego, CA
Joined Mar 2009
789 Posts
Pusher props are a byproduct of glow engine models. Most types of glow engine can only run in one direction, so to use one in a pusher configuration, you'd need a reverse pitch propeller.

Standard propellers are designed to rotate clockwise (when viewed from the rear). Pusher propellers designed to rotate counter-clockwise. They are essentially mirror images of each other.
typeRA is online now Find More Posts by typeRA
Old Jul 25, 2012, 03:42 PM
Wake up, feel pulse, be happy!
C₄H₁₀'s Avatar
United States, AK, Fairbanks
Joined Aug 2009
12,406 Posts
So if I want my plane to fly backwards, I install a pusher prop backwards and leave motor rotation clockwise

I've seen and heard whole lot of misinformation on the subject of "pusher" props. For brushless motors, I vote that we all just call them "reverse-pitch" or "reverse-rotation" props.

The only foolproof way to know (if you're new to the art of prop-whispering) is to look at the plane head-on and check to see that you're looking at the convex side of the prop blade.

It amazes me how many people are unfamiliar with the term "convex".
C₄H₁₀ is offline Find More Posts by C₄H₁₀
Old Jul 25, 2012, 04:36 PM
Old age is not for sissies
Azarr's Avatar
Dayton Intl, Ohio, United States
Joined Jan 2000
7,833 Posts
A lot of confusion comes from the fact that if the motor is turning in the correct direction the prop will blow air in the correct direction no matter which way it's installed. It's an old free flight trick to reduce power significantly for flight testing.

If you need to see this yourself, it's a simple experiment. Take the plane you've been flying forever and turn the prop around and see what happens.

The beauty of electric motors is that you can take advantage of this. For example, a lot of the guys flying electric control line run their tractor positioned motors in CCW with a pusher prop. It changes the direction of torque to pull the plane to the outside of the circle rather than inside.

As Butane indicated, the convex (curved) side of the blade always faces the direction of flight, whether it's a tractor or reverse pitch (pusher) prop, just the motor rotation direction changes.

The advent of quads and other multi-rotors has spawned a whole new batch of reverse pitch (pusher) props.

Azarr
Azarr is offline Find More Posts by Azarr
Old Jul 25, 2012, 06:08 PM
I fly 3-C Crash,Crunch,Crumble
Mr. foambuilder's Avatar
USA, NM, Clovis
Joined Feb 2010
1,072 Posts
Quote:
Originally Posted by Azarr View Post
A lot of confusion comes from the fact that if the motor is turning in the correct direction the prop will blow air in the correct direction no matter which way it's installed. It's an old free flight trick to reduce power significantly for flight testing.

If you need to see this yourself, it's a simple experiment. Take the plane you've been flying forever and turn the prop around and see what happens.

The beauty of electric motors is that you can take advantage of this. For example, a lot of the guys flying electric control line run their tractor positioned motors in CCW with a pusher prop. It changes the direction of torque to pull the plane to the outside of the circle rather than inside.

As Butane indicated, the convex (curved) side of the blade always faces the direction of flight, whether it's a tractor or reverse pitch (pusher) prop, just the motor rotation direction changes.

The advent of quads and other multi-rotors has spawned a whole new batch of reverse pitch (pusher) props.

Azarr
^+1 There is at least one person on here that knows what is going on. I am appalled at times as to how much incorrectr information is given here on these threads. Thanks Azarr Roy
Mr. foambuilder is offline Find More Posts by Mr. foambuilder
Old Jul 25, 2012, 06:24 PM
Registered User
builderdude's Avatar
United States, TX
Joined Jun 2011
2,646 Posts
One thing no one is listening to is the fact that by driving a tractor prop backwards, you've also got the airfoil backwards, which is inefficient.

If that's okay with everyone on this thread, then go for it and be happy...
builderdude is offline Find More Posts by builderdude
Old Jul 25, 2012, 06:50 PM
Registered User
ggcrandall1's Avatar
USA, GA, Marietta
Joined Aug 2005
5,624 Posts
Quote:
Originally Posted by builderdude View Post
One thing no one is listening to is the fact that by driving a tractor prop backwards, you've also got the airfoil backwards, which is inefficient.

If that's okay with everyone on this thread, then go for it and be happy...
No one is suggesting you run a "tractor" prop backwards. Regardless of the position of the motor the "face" of the prop always faces the front of the plane and the rotation of the prop will always be the same as viewed from the front of the plane. The "face " of a prop is the convex side of the prop blades and generally has the numbers identifying the diameter and pitch of the prop.

BTW technically there are no tractor or pusher props. They are right hand turn or left hand turn. Example on the P-38 they used a right hand turn prop on one side and a left hand turn prop on the other. Both props were on the front of the motor booms. So how could you identify one as a tractor prop and the other as a pusher?

Glen
ggcrandall1 is offline Find More Posts by ggcrandall1
Old Jul 25, 2012, 07:22 PM
Old age is not for sissies
Azarr's Avatar
Dayton Intl, Ohio, United States
Joined Jan 2000
7,833 Posts
+1, Glen is just absolutely correct. The "pusher" terminology came about as someone else mentioned because of glow and gas motors. The planes with motors in the rear were termed "pushers" and because most gas/glow motors are not capable of running in reverse, the props became designated as "pushers" to differentiate them from conventional right hand props.

With the advent of electric flight, this no longer was an issue, however, convention dies hard and we're basically stuck with the "pusher" nomenclature.

builderdude: as Glen said, no one is suggesting that the motor be run with the prop on backwards. however, when moving a motor from the tractor position to the pusher position, you do have to reverse the motor direction with a right hand prop. Because you've re-oriented the motor with the shaft facing rearward. The prop still faces the direction of flight and turns in the same direction. On the same aircraft, if you're using a left hand (pusher) prop you would not change the motor direction and the prop still faces the direction of flight.

This does get confusing, another thing I see often that adds to the confusion is that people talk about putting the prop on "backwards" on a pusher plane when what they really should say is to put the prop on facing the direction of flight. The fact that the convex side is now facing towards the motor instead of away from it has no bearing since we can simply change the motor rotation.

Azarr
Azarr is offline Find More Posts by Azarr
Closed Thread


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Dumb newbie question s4n1ty Flying Wings 4 Apr 27, 2012 12:20 AM
Discussion Newbie dumb ass question scottieusa Batteries and Chargers 6 Mar 13, 2012 06:52 AM
Discussion dumb question from a sailplane guy David Forbes Micro Ready-to-Fly 4 Mar 06, 2012 08:56 PM
Help! Dumb prop adapter / prop question nyc863 Electric Plane Talk 3 May 31, 2010 05:07 PM
Discussion I have a dumb question about pushers... jbarr2000 Foamies (Scratchbuilt) 6 Sep 05, 2008 10:14 AM