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pusher vs puller prop for single motor planes

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Old 08-01-2011, 04:17 PM
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M9cat
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Default pusher vs puller prop for single motor planes

So I just bought some pusher props for my Super Cubs, (single motors)..I didnt know that they were counter rotating props so i just switched the red/blue wires from my motor to esc...How well or will the plane even fly right? It seems to be working just kinda scared to put into the air..

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Old 08-01-2011, 07:42 PM
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Default RE: pusher vs puller prop for single motor planes

It depends on how it is designed. Many full scale aircraft have left handed props. Most models have the motor set for right thrust to counter the torque effects of the motor and prop. If this model has that built in then a left handed prop will make it worse. But you can fix it by adding spacers on the right side to get it to have the same amount of left thrust. The only other difference is instead of right rudder on take-off you will need left rudder.
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Old 08-01-2011, 09:48 PM
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Default RE: pusher vs puller prop for single motor planes



Well the props were for my Hobbyzone SuperCub LP with a 480brushless,and the other is a FlyZone Select PiperSuper Cub with a.10motor,,and yes i tried theprop out onthesupercublp first andit worked fine,no pull to either side,but aslightbit,isnt the fastest prop for the plane but it worked fine.. 10x6 masterairscrew works the best for that setupI found so far..any other advice will be much appreciated..
FYIim only 2 months new to RC flying...

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Old 08-02-2011, 08:11 AM
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Default RE: pusher vs puller prop for single motor planes

Save the props for a pusher and buy new props.

As indicated the thrust line is set for a normal tractor prop. You are introducing some mild inefficiencies using a pusher prop on that plane.
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Old 08-02-2011, 10:20 AM
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Default RE: pusher vs puller prop for single motor planes

Quote:
ORIGINAL: M9cat
I didnt know that they were "counter rotating props" so i just switched the red/blue wires from my motor to esc...How well or will the plane even fly right?
A true electric pusher prop is a left-handed prop designed for normal clockwise rotation. In order to get the same efficiency using it as a puller prop you need to BOTH reverse the motors direction to CCW as well as flip the prop around on the motor shaft. "Counter rotating props" refers to a twin engine plane in which one puller/tractor prop is rotating CW and the other puller/tractor prop is rotating CCW. The two puller/tractor props are a mirror image of each other.

Originally props were designed to run counter-clockwise, viewing from the front of the ENGINE or MOTOR. This is because, until recently, model aircrafts were primarily powered by Internal Combustion engines with Counter-Clockwise(CCW) rotation. So in order to use gas IC CCW engines for pusher setup, special "Pusher props" are commercially manufactured with negative pitched(left-handed) prop blades, as compared to a conventional(right-handed) tractor prop blade. If you put both of them face-to-face to compare, the props are an identical mirror image of each other. In other words if you put your pusher prop in front of a mirror the image you see in the mirror is now a puller prop configuration.

A tractor prop on a gas IC engine turning CCW could also be considered a tractor prop on an electric motor rotating CW, but ONLY if the prop is flipped around on the motor shaft. In other words one is referred to as a left-handed prop and the other as a right-handed prop, Some twin engine planes use counter-rotating props both of which are a tractor or puller. One is a left-handed prop and the other a right-handed prop. So, it depends on the normal rotation of the power plant for its compatible prop as to whether it is called right-handed. A right-handed prop on an IC gas engine with normal CCW rotation, and a right-handed prop on an electric motor with normal CW rotation are actually a mirror image of each other. Yet they are both called a puller, tractor or right-handed because of the power plant's designed rotation for spinning the prop.

Since the last decade, electric models started to become very popular and one so-called advantage of them over IC engines is that they can be wired to rotate either clockwise or counter clockwise. This will also allow a conventional tractor prop to be setup for pusher configuration, by BOTH flipping the puller prop the other way around and now reversing the motor to a CCW rotation. So, you can turn a puller prop into a pusher prop and vica versa by BOTH flipping the prop the other way around and reversing the motors rotation.

Besides reversing the motor from CW to CCW you also need to flip the prop around to turn a pusher prop into a puller prop. A pusher prop is a mirror image of a puller/tractor prop. However, what is more important is using the recommended propeller design that is most efficient for your plane as well as your flying style (from slow flyer to glider to sport, racing or aerobatic).
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Old 08-02-2011, 10:59 AM
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Default RE: pusher vs puller prop for single motor planes

Thank you all for the info...much appreciated...changing my props to standard pullers/tractors. and yes it didnt seem to make the plane fly right or have the "pull" it needed lol..
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Old 08-02-2011, 01:04 PM
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Default RE: pusher vs puller prop for single motor planes

Yes! That’s your ONLY solution because as with the SuperCup and other HZ planes they use push-on props, so the props can’t be flipped on the shaft.

As you've used the prop’s leading edge of your pusher prop with reversed rotation now becomes the trailing edge and the trailing edge of the prop is now the leading edge. Although, it doesn’t look much different on these thin plastic push-on props the efficiency of the prop is still reduced. A more dramatic comparison in reduced efficiency might be like Michael Phelps swimming with his hands reversed with thumbs now facing outward and little finger toward the inside of his body. His hands can still be cupped, but each swimming stroke is now less efficient.

These thin inexpensive plastic push-on props by HZ are overall(various flying patterns) the most efficient prop for using on the stock SuperCub setup. You could experiment with a little spinner and other more expensive props, but eventually realize that these inexpensive thin blade push-on props designed for the SuperCub and other HZ planes still give the best all around performance.

As far as which pitch should be called right-handed and which one left-handed depends on your perspective. From the perspective of the pilot in an IC CCW plane the prop is right-handed from his perspective sitting in the cabin behind the prop looking at its rotation in front of him. Well, you say, "Why then don't they refer to the engine as CW instead of CCW?" My guess is that originally you had someone stand in front of the plane to grab hold of the propeller and give it a spin to get the motor started. From that vantage point the prop is being spun CCW. However, seated in the plane the pilot sees the prop rotating right-handed or CW. From the perspective of a parkflyer standing in front of his model plane with a CW electric power plant the prop is rotating right-handed. All HZ pusher planes still use the motor wired for CW rotation. This CW pusher rationale is determined by viewing the prop's rotation from behind the model plane. In either case (electric puller CW or electric pusher CW) the pilot is viewing the prop's rotation when looking at the prop/motor with its shaft end being closet to him (puller viewed from in front of the plane and pusher viewed from behind the plane.)
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Old 08-02-2011, 04:04 PM
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Default RE: pusher vs puller prop for single motor planes

I just now noticed that apparently both the Super Cub DSM and LP use a 9x6 prop with mounting hole accessible from both sides (see HZ link and pic below) ... http://secure.hobbyzone.com/search/HBZ1002.html

Therefore, you could use a pusher prop on the LP if it is comparable in specs to the stock 9x6 by BOTH flipping the prop and reversing the motor's rotation. It may be worth a try for your own learning experience to note the difference in traction.

When converting a pusher prop to puller prop any lettering on the prop or the molded stamped diameter x pitch will now be facing outward indicating that you have flipped the prop on the shaft besides reversing the motor's rotation.

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Old 08-02-2011, 10:25 PM
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Default RE: pusher vs puller prop for single motor planes


Quote:
ORIGINAL: opjose

Save the props for a pusher and buy new props.

As indicated the thrust line is set for a normal tractor prop. You are introducing some mild inefficiencies using a pusher prop on that plane.

What are the inefficiencies? Electric motors can easily be reversed, as the OP noted, to allow for either a clockwise or counterclockwise prop. I doubt the OP meant counter-rotating, but rather "reversed pitch" or "pusher" for conventional motor direction. The only inefficiency would be running a prop in the correct rotation, but installed backwards - it still produces thrust in the correct direction - but inefficiently. In other words, running a prop in the wrong rotation direction would push the plane in the wrong direction, whether the prop was on correctly, or on backwards.

It sounds like the prop was simply not a good diameter/pitch for the motor.

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Old 08-03-2011, 03:54 AM
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Default RE: pusher vs puller prop for single motor planes

Interesting thread.

Some years ago, I was at my local field with a friend. At the time, he was flying a .40 sized sport plane with a 46 IC engine. He had installed a new, differenty type of propellor. On his first flight he noted that the airplane seemed slightly slower, and there was a strange "whistle" that wasn't there before. He kept that prop on the airplane for the next couple of months, figuring that the whistle was normal, as we didn't observe any damage to the prop, and it was well balanced.
It wasn't for quite some time that he realized that he had mounted it backwards, I.E. with the trailing edge of the prop pointing foward. It worked, but after installing it correctly the plane picked up speed and was less sluggish. So they will work backwards, just not quite as well.
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Old 08-03-2011, 08:18 AM
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Default RE: pusher vs puller prop for single motor planes


Quote:
ORIGINAL: Bozarth

What are the inefficiencies? Electric motors can easily be reversed, as the OP noted, to allow for either a clockwise or counterclockwise prop. I doubt the OP meant counter-rotating, but rather ''reversed pitch'' or ''pusher'' for conventional motor direction. The only inefficiency would be running a prop in the correct rotation, but installed backwards - it still produces thrust in the correct direction - but inefficiently. In other words, running a prop in the wrong rotation direction would push the plane in the wrong direction, whether the prop was on correctly, or on backwards.


Kurt
The plane is designed with a slight right thrust built into the motor mount though he does not see it, it's there.

In order to run a pusher prop he must mount the prop in a tractor configuration and reverse the motor direction.

That causes the plane to increase the amount of left yaw, which he will compensate for via rudder trim.

The additional rudder trim required to straighten out the flight of the plane adds drag and reduces ( by a small factor hence the "mild" ) the efficiency of his whole setup.

Better to save the inexpensive prop and just use what the plane was designed for.


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Old 08-03-2011, 09:27 AM
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Default RE: pusher vs puller prop for single motor planes

I would agree with your point about the thrust angle - I was addressing the prop. Thanks

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Old 08-03-2011, 11:41 AM
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Default RE: pusher vs puller prop for single motor planes

There's another issue that hasn't been pointed out yet.

Brushless motors can run equally well in either direction.

However, some DC brushed motors often can NOT. There is usually a built-in timing adavance in the way the magnets and brushes and so on are built that makes the motor run better in one direction than the other.

Sure, the motor will run backwards, but it won't produce as much power and will draw more current in the process. It does vary a lot with the motor, and there ARE brushed motors timed for equal running in both directions. So, if you want to run a DC motor backwards from the designed direction, you should do a bit of research or comparitive testing on the bench to make sure the motor wants to do backwards well.
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Old 08-03-2011, 12:10 PM
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Default RE: pusher vs puller prop for single motor planes

Quote:
ORIGINAL: Montague
There's another issue that hasn't been pointed out yet. Brushless motors can run equally well in either direction.
However, some DC brushed motors often can NOT.
Good Point, however ("i just switched the red/blue wires from my motor to esc") wouldn't the stock brushed 480 have red/black wires).

So, all of my foregoing talk that I've spent an hour preparing/editing about an assumed stock setup still has some relevance. Now can understand better that's why he's possibly experimenting with another prop that will provide better performance if it's a brushless setup in his SC. What doesn't make sense is why he didn't buy a tractor/puller prop instead of a pusher when there are so many electric tractor/puller designs from which to choose for trying out on a brushless setup. And why he is bothering having to drill out the center shaft hole on the prop when you can both buy the proper size spinner or proper hole dia. prop. (However, I remember all the mistakes I made during my learning curve that made it harder on me than necessary instead of easier ... live and learn). Any way the following is what I prepared before seeing your recent post.

Here’s a quote from the following APC link: http://www.apcprop.com/v/html/Pusher.html

“The APC line of electric pusher propellers is designed for counter clockwise (CCW) rotating tractor applications. These propellers are intended for use on airplanes with twin tractor electric motors where a CCW rotating propeller may be desirable. These propellers can also be used in a true pusher application by mounting with the ‘APC’ lettering facing towards the front of the aircraft.”

That’s why they are called a ‘pusher’ because when mounted on a rear motor pusher aircraft the lettering is correctly facing inward (unseen) toward the motor housing or “towards the front of the aircraft” when the motor is now rotating CW when viewed from behind the plane. However, when used for CCW tractor application the prop is flipped with the ‘APC’ lettering now facing away from the motor. So, when used as a tractor application it is possible to paint over or otherwise remove the lettering if the pilot thinks others will think he has the prop mounted backwards. If you don’t flip the prop on the motor shaft when converting a CW pusher to a CCW tractor the prop will be spinning with the trailing edge now being the leading edge resulting in poorer performance.

Assuming both the leading edge and trailing edge of the pusher propeller he was trying was an identical mirror image of each other(which is highly unlikely) then it wouldn’t be necessary to flip the prop on the shaft. You would only need to change the motor’s rotation when converting such a prop of identical symmetry from a pusher to a tractor/puller. However, a poorer difference in his SC flying performance may still be noticeable even if the prop had perfect symmetry so it didn’t need to be flipped. The reason being that the pusher prop he was trying may not be as efficient a design for his SC as the thin blade stock prop specifically designed for a SC DSM or LP.

Quote:
ORIGINAL: opjose
As indicated the thrust line is set for a normal tractor prop. You are introducing some mild inefficiencies using a pusher prop on that plane.
Because the motor’s rotation is reversed from CW to CCW, the affected motor torque to the planes central axis is reversed. In order to reestablish the correct the thrust angle it would need to be a mirror image or in other words any slant or shiming toward one side from center axis would now need to be reverse shimmed the same amount off center axis toward the other side.

The bottomline is to use the recommended stock propeller unless you have modified the SC with a different power plant that may now require a different propeller to achieve maximum performance.
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Old 08-03-2011, 12:19 PM
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Default RE: pusher vs puller prop for single motor planes

Hmm, you're right, I parsed red/blue as red/black as there were only 2 wires to the motor which would mean brushed.

But if there were 3 wires, and two were swapped, then it's brushless and that's how you reverse it, and what I wrote doesn't apply. Now I'm confused about what is going on, but that's ok, it doesn't matter if I'm confused.

The thrustline issues were well covered already, but those would be my next concern with reversing the motor. And just shimming the motor might not work, since some models have the back of the motor offset to the side to make the prop end up in the center of the cowl. In those cases, you'd have to move the motor to the other side of the firewall center line and then shim to get the prop back to the center of the fuse (and through the cowl if there's a cowl).
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Old 08-03-2011, 12:32 PM
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Default RE: pusher vs puller prop for single motor planes


Quote:
ORIGINAL: Montague
Hmm, you're right, I parsed red/blue as red/black as there were only 2 wires to the motor which would mean brushed.
You may want to reread the first part of my post as it is still relevant (see other edited intro ... making it harder on oneself than necessary).
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Old 08-04-2011, 05:43 AM
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Default RE: pusher vs puller prop for single motor planes

Quote:
ORIGINAL: Montague
Now I'm confused about what is going on, but that's ok, it doesn't matter if I'm confused.
You are not alone ... So here's what I think is causing the right-handed(puller) vs. left-handed(pusher) confusion. The SC 480 brushed is gear driven so there are two possibilities. ONE: If the motor is wired for CW rotation then the prop is spinning CCW meaning the stock prop is actually a left-handed prop (pusher designed for puller application). TWO: If the brushed 480 is wired for CCW rotation then the prop is spinning CW and the stock prop is a right-handed prop (tractor/puller).

When converting the SC to brushless you could use an inrunner and say with gear reduction or an outrunner with direct drive. Depending on which way you go you can still use a right-handed prop or Tractor/puller prop as you either rotate the gear reduction inrunner CCW so the prop is spinning CW or you rotate the direct drive outrunner CW so the prop is spinning CW.

Reading through the thread again M9cat says ...

"Well the props were for my Hobbyzone SuperCub LP with a 480brushless,and the other is a FlyZone Select Piper Super Cub with a .10motor,,and yes i tried the prop out on the supercub lp first and it worked fine,no pull to either side,but a slightbit,isnt the fastest prop for the plane but it worked fine.. 10x6 masterairscrew works the best for that setup I found so far..any other advice will be much appreciated.."

So, it sounds like he may be using a 480 b/less inrunner with the same gear reduction setup. That means that if the inrunner is rotating CW then the prop would be spinning CCW meaning you would need to use a left-handed (pusher) prop for tractor/puller application. On the other hand(right-handed) he now knows he can reverse the rotation of the inrunner to CCW so the gear driven prop spins CW and now he has many options for trying out other right-handed, tractor/puller props to his hearts content.
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