Counter rotating or not
03-16-2019, 08:15 AM
#1
Thread Starter
Counter rotating or not
I'm building an OV-10 electric and don't know if I should use counter rotating motors or not. First of all will a brushless motor run backwards as well as forward (same power)? I know if you reverse two of the three wires it will run the other way. Counter rotating; I've saw were some people say it doesn't make much difference. What do you think??? I'm new to twins and have plans for more.
Skyhawk
Sandusky, OH
Skyhawk
Sandusky, OH
03-17-2019, 05:15 AM
#3
Thread Starter
I know some of the motors, to reverse the motor, the shaft needs to slide through the motor and come out the other side. Doesn't make sense to me.
What's a good source of electric props?
Skyhawk
What's a good source of electric props?
Skyhawk
Last edited by Skyhawk940; 03-17-2019 at 05:31 AM.
03-17-2019, 01:07 PM
#5
The only time I've seen this required is when the X mount needed to be on the front with the motor recessed into the fuselage or firewall as opposed to having the mount on the back of the motor. Not to reverse the rotation, again, there is no reverse rotation on a brushless motor, its merely a factor of how you have to mount it and what prop you're using, if you need to spin it the other way, as you already said, you reverse two wires.
03-19-2019, 07:00 AM
#6
Banned
First, whose kit/plans are those?
Second, memory doesn't allow me to provide details but, do some research on the Lockheed P-38. It started with the props spinning the same direction. Then they reversed one. Then they reversed the direction of both. Which way they settled on I don't know (but you could probably figure it out from a picture. But I know running them opposite does improve things. And one combo is better than the other.
Also, I've been told that for electric you pick your prop first. Determine the speed range of the model to get max prop RPM. Then find a motor capable of spinning that prop at that RPM. And nothing says you can't use a prop for a nitro motor on an electric.
Second, memory doesn't allow me to provide details but, do some research on the Lockheed P-38. It started with the props spinning the same direction. Then they reversed one. Then they reversed the direction of both. Which way they settled on I don't know (but you could probably figure it out from a picture. But I know running them opposite does improve things. And one combo is better than the other.
Also, I've been told that for electric you pick your prop first. Determine the speed range of the model to get max prop RPM. Then find a motor capable of spinning that prop at that RPM. And nothing says you can't use a prop for a nitro motor on an electric.
Last edited by Appowner; 03-19-2019 at 07:03 AM.
03-19-2019, 08:06 AM
#7
The electrics can be a bit confusing. We all got accustomed to glow engine displacement and the very narrow range of props they are able to use for a certain displacement. Current brushless electrics are far more flexible. First thing is that the motor does not care which direction it is spinning. Back in the days of brushed motors, the timing of the motor was determined with the contact location of the brushes on the armature. With brushless motors the timing is purely a function of the speed controller. In some cases with the larger setups the timing is user adjustable. Faster spinning inrunner motors require low timing, 0 to 5 degrees while the lower rpm outrunner motors such as what the OP has requires high timing, 20 to 25 degrees. Most of the lower cost, smaller stuff will be plug and play but you do loose a little bit of efficiency. In order to select the correct size prop you need to know the KV of the motor, what voltage you will be running, the motor diameter and the motor length. For example one of my electrics has a 63mm diameter with a 55mm length. The KV is 230 and I run a voltage of 38v. Multiplying the KV x V we get 8,740 rpm. The prop selected is a 21.5x13.5 delivering around 2,700 watts at about 65 amps. If I was to lower the voltage ( thus rpm ) I could fit a larger prop and if I upped the voltage I would have to go with a smaller prop to keep amperage draw the same. I am going to assume that the batteries selected by the OP are going to be 3S or 11.1V, knowing the diameter of the motor and the KV would allow a prop size recommendation. I suggest looking at the APC web site to select props. Robert has in the past few years introduced a number of multi Rotor prop sets in various sizes that may work very well and are quite inexpensive. They come in sets of 4 with two being CW and two CCW rotation. As far as how to set up rotation, I would do some experimenting but I suspect you will notice little or no difference. Good luck with the project, the OV-10 is one of the airplanes that I always liked, Cal Fire has a few flying close to my home often.
03-21-2019, 05:35 AM
#9
I would run them the same direction to keep it simple. After a few twins I haven’t seen any problems with this setup. The only time I would consider counter rotating props is if it was a taildragger to prevent it swinging on takeoff.
Just my opinion.
paul
MU-2
Just my opinion.
paul
MU-2
03-24-2019, 02:08 PM
#10
Banned
Why stick with the same old thing when a simple change, especially with electrics, could possibly make a noticeable performance improvement?
Time to experiment and have fun doing it I say!
Time to experiment and have fun doing it I say!
04-01-2019, 08:05 AM
#12
Banned
So I contacted some vendors and guess what? XOAR offers precision matched tractor and pusher props. Only trick is you have to special order them.
So the selection is out there but one has to step up and ASK.
So the selection is out there but one has to step up and ASK.
04-29-2019, 03:09 PM
#14
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As others said, If you can make it work, I feel it's probably worth doing. Sometimes it's difficult to find the correct props. Some planes I have had with both normal rotation were difficult to handle until the rudder became effective where as others it wasn't noticeable at all. Probably more pronounced with tail dragger such as a DC-3.
05-16-2019, 05:57 AM
#15
I know, this thread hasn't been active for over two weeks but, when I saw the reference made on the P-38, I felt I had to speak up.
When the P-38 was first designed and built, it had the same engine and gearbox mounted on both nacelles. Like most other planes, both props rotated CLOCKWISE when viewed from the cockpit. This did, however, cause handling issues due to the "swirling" wake from the props hitting the vertical tails. To eliminate the problems this caused, the left engine was given a gearbox that reversed the prop rotation to COUNTERCLOCKWISE, thus countering the effects of the right hand prop.
When the RAF saw the P-38 and what it could do, they ordered some but, unfortunately, they ordered it with the original configuration of clockwise spinning props. The handling issues quickly resurfaced and, when combined with another issue, the plane was subsequently pulled from front line service.
The other issue the RAF had with the P-38 was its high altitude performance. Since the plane used the American made Allison 1710 rather than the Rolls Merlin 1650, engine performance dropped off above 15,000 feet much more drastically than the Merlin or German engines, even with the Lightning's Turbochargers feeding the engine's single stage Superchargers. Since most of the air combat over Europe was above 15,000 feet, the RAF felt the lack of power, at altitude, was a major liability.
The USAAC, on the other hand, fell in love with the Lightning. With the counter-rotating props and extremely long range(not equaled until the Merlin powered P-51 Mustang arrived), the Lightnings were quickly thrown into the fight as bomber escorts, "Pathfinder" bombers, photo-recon and several other tasks. In the Pacific, the Japanese A6M "Zero" was the primary fighter used by the Army and Navy for the first half of WWII. Like the Lightning, it was best below 15,000 feet and long ranged. Unlike the A6M, however, the Lightning was much faster, had armor and self sealing fuel tanks, but the biggest advantage was it could return home with one engine inoperable. So effective was the Lightning, over the Pacific, that the two highest scoring American pilots flew it.
When the P-38 was first designed and built, it had the same engine and gearbox mounted on both nacelles. Like most other planes, both props rotated CLOCKWISE when viewed from the cockpit. This did, however, cause handling issues due to the "swirling" wake from the props hitting the vertical tails. To eliminate the problems this caused, the left engine was given a gearbox that reversed the prop rotation to COUNTERCLOCKWISE, thus countering the effects of the right hand prop.
When the RAF saw the P-38 and what it could do, they ordered some but, unfortunately, they ordered it with the original configuration of clockwise spinning props. The handling issues quickly resurfaced and, when combined with another issue, the plane was subsequently pulled from front line service.
The other issue the RAF had with the P-38 was its high altitude performance. Since the plane used the American made Allison 1710 rather than the Rolls Merlin 1650, engine performance dropped off above 15,000 feet much more drastically than the Merlin or German engines, even with the Lightning's Turbochargers feeding the engine's single stage Superchargers. Since most of the air combat over Europe was above 15,000 feet, the RAF felt the lack of power, at altitude, was a major liability.
The USAAC, on the other hand, fell in love with the Lightning. With the counter-rotating props and extremely long range(not equaled until the Merlin powered P-51 Mustang arrived), the Lightnings were quickly thrown into the fight as bomber escorts, "Pathfinder" bombers, photo-recon and several other tasks. In the Pacific, the Japanese A6M "Zero" was the primary fighter used by the Army and Navy for the first half of WWII. Like the Lightning, it was best below 15,000 feet and long ranged. Unlike the A6M, however, the Lightning was much faster, had armor and self sealing fuel tanks, but the biggest advantage was it could return home with one engine inoperable. So effective was the Lightning, over the Pacific, that the two highest scoring American pilots flew it.
