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Old 06-08-2012, 08:07 PM   #1
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Default WATT Meter readings ??????

I was out flying my Sbach 342 the other day and doing a flat spin well when I went to pull out at the bottom I almost went in because there was not enough power. I know part of that was my fault because I did not have any trim to keep my motor spinning a bit. I also decided to check my watts on my meter and try a second prop just to see. First prop was a APC 18X10 running 1526 WP or watt power and 39 amps then I tried a 20X6-10 wood prop (I know the number is strange but that is how it is listed) running 2284 wp and 59 amps. So is the 2284 WP my watts for rating power output or in other words the magic 150 watts per pound = a starting point for 3D planes? If so I'm running about 190 watts with this setup because my plane is about 12 lbs not sure off hand as my scale has a dead battery. I plan on uploading the vids to youtube soon. So don't forget my ? is that number my watts for adjusting the watt per pound? also do you have any prop recommendations the specs call for a 20X10

Please don't give me a link to motocalc according to that crap this plane shouldn't evev fly or not very well anyway.
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Old 06-08-2012, 09:15 PM   #2
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The numbers with the second prop look good, you should have tons of power.

If you could list your hardware and the actual model then it would let people give you much more meaningful answers.

Steve
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Old 06-09-2012, 04:41 AM   #3
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I am running a Hacker A60 -7S V2 28 Pole out runner and a Castle Creations HV 85 AMP ESC and it is all powered with 2X 5000 mah 5 cell packs for a total of 37 volts. The plane is a Pilot Rc Sbach 342 with 73 in WS and weighs in about 12 to 13 lbs.

http://www.aero-model.com/Hacker-Bru...Outrunner.aspx

http://www.castlecreations.com/produ...hv_series.html

Looks like A Main does not sell the battery anymore but it is a ProTek RC battery it does have a 45C discharge rate

http://www.chiefaircraft.com/prc-sbach25-01.html

I'm running a Spektrum radio and RX and Savox Servo's and a CC high voltage BEC. Links to vids coming tonight or early tomorrow.
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Old 06-09-2012, 04:50 AM   #4
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I would fly it with the second prop and see how you like it. 190 watts per pound should make it a great flyer.

Mike

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Old 06-09-2012, 08:23 AM   #5
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Originally Posted by haasjj View Post
I was out flying my Sbach 342 the other day and doing a flat spin well when I went to pull out at the bottom I almost went in because there was not enough power. I know part of that was my fault because I did not have any trim to keep my motor spinning a bit. I also decided to check my watts on my meter and try a second prop just to see. First prop was a APC 18X10 running 1526 WP or watt power and 39 amps then I tried a 20X6-10 wood prop (I know the number is strange but that is how it is listed) running 2284 wp and 59 amps. So is the 2284 WP my watts for rating power output or in other words the magic 150 watts per pound = a starting point for 3D planes? If so I'm running about 190 watts with this setup because my plane is about 12 lbs not sure off hand as my scale has a dead battery. I plan on uploading the vids to youtube soon. So don't forget my ? is that number my watts for adjusting the watt per pound? also do you have any prop recommendations the specs call for a 20X10

Please don't give me a link to motocalc according to that crap this plane shouldn't evev fly or not very well anyway.
Im curious about that statement in red above. Why do you feel you need to keep the motor idling? This isnt like glow. The motor will, or at least should, start up instantly and give full power within less than a second.

Is that not the case?

If the motor start up is slow, it may be you have one or more of the settings on the Castle HV controller set wrong - perhaps a delay programmed on the throttle or a slow start up, wrong timing, or?

I agree with the others, as long as everything is running at reasonable temps, go with the larger prop

I think I need a signature.
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Old 06-09-2012, 08:39 AM   #6
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Looks like a great set up. 20x10 is the correct prop for your motor and all the other hardware is well specified. it should go really well.

In the past I've sometimes struggled with exit of flat spins on some planes which turned out to be my dumb thumbs not centring the elevator. On some planes if you don't take out all the elevator input (or even reverse it) the plane will keep spinning regardless of what you do with other controls, and even if you apply power the plane will just keep spinning.

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Old 06-09-2012, 07:40 PM   #7
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Originally Posted by Larry3215 View Post
Im curious about that statement in red above. Why do you feel you need to keep the motor idling? This isnt like glow. The motor will, or at least should, start up instantly and give full power within less than a second.

Is that not the case?

If the motor start up is slow, it may be you have one or more of the settings on the Castle HV controller set wrong - perhaps a delay programmed on the throttle or a slow start up, wrong timing, or?

I agree with the others, as long as everything is running at reasonable temps, go with the larger prop
The reason for that statement is because that is what I was told by another pilot in our club with more large electric experience than me. He said I should put mt trim up about half or more to keep the motor spinning so when you need to punch it you have almost instant power, but I agree with you that the motor should be full power very quick wo the trim and this motor is.
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Old 06-09-2012, 07:49 PM   #8
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Originally Posted by JetPlaneFlyer View Post
Looks like a great set up. 20x10 is the correct prop for your motor and all the other hardware is well specified. it should go really well.

In the past I've sometimes struggled with exit of flat spins on some planes which turned out to be my dumb thumbs not centring the elevator. On some planes if you don't take out all the elevator input (or even reverse it) the plane will keep spinning regardless of what you do with other controls, and even if you apply power the plane will just keep spinning.

Steve
It might just be that I did screw up mostly because I am not use to this larger plane yet, this is my first 1/4 scale aerobatic plane and I'm still finding the differences between a 48" quick and nimble plane and this much larger and heavier plane. The reason I was thinking it might be either no trim or a prop problem was because I thought their was not enough air over the control surface to pull out of the spin, which is more or less the case but I just needed a fix with either my flying or the plane.
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Old 06-09-2012, 08:02 PM   #9
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I personally don't like using trim on the throttle because if you forget and land with the trim still on you can get into trouble VERY quickly. Somebody told my son to do that when he was learning IMAC and we almost ran into things on landing more than once.

We have never used trim on any of our 3D planes and don't use it on the IMAC planes anymore either.

A better alternative is to mix the throttle with the landing gear switch to throttle up. Then you just have to flip a switch to use.

Mike

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Old 06-09-2012, 09:34 PM   #10
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Here is the first video link if this works. The second video with the flat spin discussed above should be up later.

http://youtu.be/XRWMhGeNBrY


YouTube Video
ERROR: If you can see this, then YouTube is down or you don't have Flash installed.
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Old 06-09-2012, 09:39 PM   #11
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The link didnt work.. When you insert a Youtube video dont use the complete Youtube URL address, just use the identification code part, something like: T1BnKKlx-ZE

Steve
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Old 06-09-2012, 09:52 PM   #12
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Link works now. Thanks JetPlaneFlyer just took me a bit to get what you meant but it is truly working now.
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Old 06-10-2012, 01:46 AM   #13
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Originally Posted by haasjj View Post
The reason for that statement is because that is what I was told by another pilot in our club with more large electric experience than me. He said I should put mt trim up about half or more to keep the motor spinning so when you need to punch it you have almost instant power, but I agree with you that the motor should be full power very quick wo the trim and this motor is.
That is usually not an issue, since the prop is usually windmilling even with the transmitter throttle at full off. I've got a hand full of Hacker motors, including three A50's an A60-16M and an A60-5. Never had a problem with instant response when slamming the throttle to full power from full off.

ESC's are both 80 Amp Castle Creations HV units running on a 12S2P or 10S2P A123 battery packs.

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Old 06-10-2012, 05:22 AM   #14
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Originally Posted by kyleservicetech View Post
That is usually not an issue, since the prop is usually windmilling even with the transmitter throttle at full off. I've got a hand full of Hacker motors, including three A50's an A60-16M and an A60-5. Never had a problem with instant response when slamming the throttle to full power from full off.

ESC's are both 80 Amp Castle Creations HV units running on a 12S2P or 10S2P A123 battery packs.

I see what you are saying and if you check out the vid it does have good power I just wasn't sure what to think when the plane didn't come out of the spin as fast as I thought it should have. I was going by a little guessing and a little of what someone told me but I think he was off in his thinking.

Thanks for all the comments but I still want to make sure of one thing. When I read the watts on my watt meter that is the number I use to get the watts per pound correct
Then I should use that to find the most efficient prop correct
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Old 06-10-2012, 05:23 PM   #15
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Originally Posted by haasjj View Post
I see what you are saying and if you check out the vid it does have good power I just wasn't sure what to think when the plane didn't come out of the spin as fast as I thought it should have. I was going by a little guessing and a little of what someone told me but I think he was off in his thinking.

Thanks for all the comments but I still want to make sure of one thing. When I read the watts on my watt meter that is the number I use to get the watts per pound correct
Then I should use that to find the most efficient prop correct
Yup, that would be whats used for the watts per pound.

However, if you're doing 3D, you're likely more worried about "Pulling Power", and being able to fly vertical with authority when needed. So, just find the best propeller for your needs, and make danged certain to not run your motor/esc/battery pack over their maximum ratings. Which is where the wattmeter comes in to play.

My guess is for 3D, you need a larger diameter propeller with lower pitch. But still need enough pitch to fly the model in level flight. This is where those programs such as www.motocalc.com might save you a few $$$$ in buying an assortment of propellers.

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Old 06-10-2012, 05:44 PM   #16
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Baseline for 3D is props with a pitch/diameter ratio of 1/2 . So you are spot on with your 20x10 prop.

Less pitch and you tend to find yourself lacking in speed which is not good higher energy 3D stuff like tumbling and pop tops and the like. Also very low pitch tends to be inefficient and can seriously reduce your flight time.
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Old 06-11-2012, 01:00 AM   #17
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Thanks again for your input. If I try a 22in prop what do you think a good one would be? I was thinking a 22X6 but that might not be enough pitch. By the way here is the other vid with the bad flat spin exit that is about 4 mins in if you want to skip ahead.


YouTube Video
ERROR: If you can see this, then YouTube is down or you don't have Flash installed.
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Old 06-11-2012, 03:07 AM   #18
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LOL! You sure cut that spin close When you powered up, you didnt go to full power immediately. You hit full power about the same time you hit the ground

You were pretty darn low when you started the pull out too. I dont think there is a problem with the power system.

On the prop - I would stick with a 22x10 or 12. Like JetPlaneFlyer said, too low a pitch wont work as well.

I think I need a signature.
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Old 06-11-2012, 10:54 AM   #19
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[QUOTE=haasjj;872412]then I tried a 20X6-10 wood prop (I know the number is strange but that is how it is listed)


FWIW, props with two hyphenated numbers after the diameter are progressive pitch, in this case 6" progressing to 10" at the tip.

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Old 06-11-2012, 06:39 PM   #20
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[QUOTE=Azarr;872783]
Originally Posted by haasjj View Post
then I tried a 20X6-10 wood prop (I know the number is strange but that is how it is listed)


FWIW, props with two hyphenated numbers after the diameter are progressive pitch, in this case 6" progressing to 10" at the tip.

Azarr
I kinda figured that but since almost all props are progressive is why I thought the number was strange.
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Old 06-11-2012, 07:23 PM   #21
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[QUOTE=haasjj;872825]
Originally Posted by Azarr View Post

I kinda figured that but since almost all props are progressive is why I thought the number was strange.

Actually most props have pretty much the same pitch root to tip. Remember the pitch isn't the angle of the blade but is the amount that the blade would move forward if it were screwing through a solid substance, like a bolt screwing through a nut.
The inner part has a steeper angle because it doesn't travel as far per revolution so it needs a steeper angle to move forward by the same amount as the tip.

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Old 06-12-2012, 02:16 AM   #22
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Originally Posted by Larry3215 View Post
LOL! You sure cut that spin close When you powered up, you didnt go to full power immediately. You hit full power about the same time you hit the ground

You were pretty darn low when you started the pull out too. I dont think there is a problem with the power system.

On the prop - I would stick with a 22x10 or 12. Like JetPlaneFlyer said, too low a pitch wont work as well.
I just watched the vid again and I hit full throttle before or about the time I was coming out of the spin and then cut throttle when I knew I was going to ditch and just land.
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Old 06-12-2012, 02:18 AM   #23
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[QUOTE=JetPlaneFlyer;872836]
Originally Posted by haasjj View Post


Actually most props have pretty much the same pitch root to tip. Remember the pitch isn't the angle of the blade but is the amount that the blade would move forward if it were screwing through a solid substance, like a bolt screwing through a nut.
The inner part has a steeper angle because it doesn't travel as far per revolution so it needs a steeper angle to move forward by the same amount as the tip.

Steve
So what is a progressive prop then and why does mine read the way it does? It is a zinger prop.
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Old 06-12-2012, 02:33 AM   #24
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Just a little advice. Zinger props are absolute crap. High amps, less power and thrust. A bad combo. You really should look at APC-e or Xoar props.

I think you will be much happier.

Mike
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Old 06-12-2012, 06:22 AM   #25
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Originally Posted by rcers View Post
Just a little advice. Zinger props are absolute crap. High amps, less power and thrust. A bad combo. You really should look at APC-e or Xoar props.

I think you will be much happier.

Mike
Yeah I've heard that several times now, so I have a bit of buyers regret. I was using an apc prop in the vid's above just the wrong size. I will be buying a Xoar prop they even make some nice 3 blade props which would be scale for this plane, just not sure if it would work. If not they're electric line is very nice, once I found out that they make props for civilian airplanes I kinda figured they know what they're doing.
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