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Old 12-05-2014, 09:34 PM   #1
walter3
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Default power system for 1978 duallist opinions?

i have a 10lb. auw 1978 pica duallist with power 32 770 kv motors with 75 amp esc on 4s 3600 batts. how many watts do i need to fly this well. i have multiple props, some standard some counter rotate. i have a watt meter. im getting around 110 watt per lb on one set and 160 watt per lb on another. will these both work? the 110 happen to be counter rotate, the other standard. both well under the amps for the esc even at wot. thoughts? thanks for the imput. walt


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Old 12-05-2014, 10:45 PM   #2
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Sounds like adequate power with either setup to fly safely. Whether you need 160 W/lb will depend on what kind of flying you like to do and the airframe itself. You may prefer less power with longer flight times.

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Old 12-06-2014, 01:14 AM   #3
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That is a nice looking plane!

I totally missed that you were using different props thought you meant one motor pulling 110 watts the other 160 watts. My bad for over looking this in your post.
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Old 12-06-2014, 02:10 AM   #4
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110 watts/lb will almost do the current AMA Sportsman sequence. 150 watts/lb will do intermediate and maybe advanced.

That is if the props are correct for the plane. You can put excessively small dia +high pitch high rpm setup on and go nowhere at all, or excessively large dia low pitch and be able to hover like a heli but never have airspeed to fly on the wing...

Watts are not the only thing to look at.

When doing glow-e conversions I generally look to turn slightly lower rpm with 1 inch more dia and 1 inch more pitch or move from 2 blade to 3 blade with 1 inch more pitch. Its a good cross check to see if you picked the right system.
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Old 12-06-2014, 03:04 AM   #5
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Originally Posted by walter3 View Post
i have a 10lb. auw 1978 pica duallist with power 32 770 kv motors with 75 amp esc on 4s 3600 batts. how many watts do i need to fly this well. i have multiple props, some standard some counter rotate. i have a watt meter. im getting around 110 watt per lb on one set and 160 watt per lb on another. will these both work? the 110 happen to be counter rotate, the other standard. both well under the amps for the esc even at wot. thoughts? thanks for the imput. walt
Assuming proper propeller diameter, pitch and RPM, that 160 Watts per pound should just about fly your model straight up.

But with the wrong (way way wrong) diameter, pitch, and RPM, your model might not even get off the ground Like an 6 inch prop turning at 20K RPM.

With a model of this size, a proper propeller would be somewhere around a 14-16 inches in diameter, about 8 or 10 pitch, and around 8000 RPM. More or less.

Can you provide your prop diameter/pitch/RPM? Along with that, the models wingspan, wing area along with the weight. That would really help on checking out your setup.

What kind of reverse props do you have? I've got one of the TwinStars, and am trying to find a 10X7 reverse pitch prop. Seems no one makes them.

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Old 12-06-2014, 05:46 AM   #6
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thanks for the responses. this plane has limited ground clearance. i am using 3 blade props all 10 inch with about 1.25 clearance from tip to ground. kinda tight. my pitch is around 8 i think on the props pulling 160 watt per lb. 7 pitch on the 110 watt per pound. this plane has a 66 inch wingspan. the 160 watt props are durafly paddle shape blades quite fat at the tip and swing standard rotation. the others are counter rotate thinner master air screws. 10 lb. plane. not sure of rpm. fairly thick wings. huge horizontal stabilizer as well.


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Old 12-06-2014, 06:12 AM   #7
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The 160 watt props sound in keeping with the change from 2 blade to 3 blade when compared to the props expected when the plane is flown using glow. should do fine.
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Old 12-06-2014, 06:13 AM   #8
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Originally Posted by walter3 View Post
thanks for the responses. this plane has limited ground clearance. i am using 3 blade props all 10 inch with about 1.25 clearance from tip to ground. kinda tight. my pitch is around 8 i think on the props pulling 160 watt per lb. 7 pitch on the 110 watt per pound. this plane has a 66 inch wingspan. the 160 watt props are durafly paddle shape blades quite fat at the tip and swing standard rotation. the others are counter rotate thinner master air screws. 10 lb. plane. not sure of rpm. fairly thick wings. huge horizontal stabilizer as well.
I just ran the numbers on your 4S LiPo pack and model in www.motocalc.com. Motocalc predicts a total of around 43 Amps and 600 Watts for each of your motors, a safe value for the motors them selves. Predicted RPM is around 9500 for a 10X8 prop. Motocalc suggests that a 10X6 prop would not be enough pitch to fly your model safely.

This winds up as 110 Watts per pound, not a really high number with a 10 inch diameter prop, so use reasonable caution on the maiden flights.

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Old 12-07-2014, 08:02 AM   #9
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i think i should use caution if going with the master air screw 10x7 props with just 110 watts per lb. however i was thinking the counter rotation would add some extra insurance as far as ease of flight and trim possibly. the standard rotation have more pull at 160 watts per lb and i have heard by many this plane does not need counter props to fly great. torn as to which i should use on maiden. wish i could find the counter rotate 3 blades in a 10x8 prop. it seems elusive. i wish i was not getting both opinions about the need for counter props on this model. i sure hope its not needed because i really don't want to fly her under powered. once i get her maiden in the books, successfully, ill feel better about testing out all my prop options a bit more. Walt.

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Old 12-07-2014, 08:25 AM   #10
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2 issues with not counter-rotating:

1) torque turn effect, especially if applying high power at low speed.
Can be dealt with by good throttle management.

2) single engine out one side will be worse than the other.
Generally best immediate response to loss of one is kill power and treat it initially as a dead-stick.
Slowly apply power and find out where the plane has best control for making a landing if you don't think you can just glide it back to the runway.
Do not turn toward the dead-stick side if you can avoid it. The working motor will try to pull the nose around and point the plane at the dirt.

E-twins can have single-engine out for a few causes. Eliminate one by connecting ESCs in parallel to one main battery pack, or paralleling the 2 power systems' packs with a jumper.
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Old 12-07-2014, 04:12 PM   #11
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i have heard that as well, however, 98% of those i have questioned who have flown this particular plane all say she fly's great on standard rotation and there is no need for counter rotate props. that said i would feel better with the counter as one less thing to worry about. trying to figure the better of the two options.... lower power counter rotate props or more powerful standard rotation. i am proficient with the slow smooth application of power so was hoping that would help me out. as long as the 110watt per lb. will be enough i am tempted to go counter for maiden and try 160 watt/lb.standard later on. thoughts?

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Old 12-07-2014, 08:16 PM   #12
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You can compensate for both of the negative issues with the thrust line. If the kit specifies normal rotation on both props and the thrust lines are set by the kit specs then you can expect that the thrust lines are

1) Not 0-0 (0 up and down and 0 right/left offset)
2) Not the both pointed outboard the same amount. (All twins really should have thrust lines pointed away from center a little as this minimizes effect of single engine out.)

There are twins that have very little issue with loss of one due to the thrust line setting.
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Old 12-07-2014, 10:50 PM   #13
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this has down thrust built in very easy to see but less obvious is the sideways thrust angles. the wing and nacelles were constructed before i got the kit so i can only assume the original builder was following the standard build directions as best i could see. i have heard the long nacelles also help with the flight qualities of a dead engine situation. there is a great video of a guy flying this plane and has 2 separate single engine deadsicks on camera and just flys it in like its no big deal. all captured on camera. he may also be a great pilot but does not seem like a panicked situation in the least. i still would rather fly her counter on maiden and hope that 110watts/lb. will do the job so i can get a sense of what 160watt/lb might provide. accident can always happen but i have yet to have a electric powered plane stop working in flight. i try to use high rated components and dont push there abilities as well as incorporate some back ups if i can. if anyone can tell me where to get a good 10x8 3 blade in standard and counter rotate i would be thrilled! thanks for all the great information. i really appreciate all the valuable info. i want her maiden to be a great experience. Walt.

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Old 12-08-2014, 12:07 AM   #14
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A plane will fly on 30 to 50 watts/lb.... if you have the right prop. It has to provide the thrust and pitch speed needed. The Piper J3 Cub OEM version of appx 1936 had about 35 watts/lb at rated max load.

75 watts/lb is marginally capable of looping from level flight. This is also close to the power:weight of competition Pattern Aerobatic models of the 1970's.

100 watts/lb can do reasonably well for general sport flying but its not going to make a big round loop as seen in modern Pattern aerobatics.

150 watts/lb gives the capability to maintain airspeed in extended vertical climb and potential to not drop airspeed doing rolls in the vertical. This is now considered minimal for anything past Sportsman Pattern.

200 watts/lb is needed for doing low level hovers with ability to accelerate vertically, directly into other "3D" aerobatic maneuvers.


All of these assume good match of prop to aircraft and flying style desired.
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Old 12-08-2014, 04:39 AM   #15
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that is comforting. appreciate it. i am only looking for spirited general sport flying. i would rather throttle back and get longer flight times to be honest. i have zero interest in any 3d type flying and get the biggest thrill from high speed low level passes now and again. thank you for all the information. your comments are the reason i highly prize forums of this type. much appreciated. i just installed my scorpion back up guard. works fantastic! 25$ for insurance on this pretty girl is worth it. not much weight at all. if i fry a esc i still want full flight surface control. very cool devise. hope i never use it.

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Old 12-08-2014, 07:16 PM   #16
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Wow, that is one nice plane!
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Old 12-08-2014, 11:02 PM   #17
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thank you! that's why im asking lots of questions and want a safe maiden. i will cry like a child if i crash this plane by not making the right call. Walt.

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Old 12-08-2014, 11:24 PM   #18
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I would aim for 150w/lb myself. I built a P47 awhile back, and it was sitting at around 100w/lb. with the front cut out, it turned into a parachute, and couldn't get past stall really. If it were 150w/lb, it would hav done better. 100w/lb will work for a plane that achieves lift easily, or is aerodynamic, but most warbirds aren't designed to float around like a slow stick. Best bet is to give it enough that could allow it to fly non-scale, like vertical flight. You can always throttle back.
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Old 12-09-2014, 01:03 AM   #19
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i totally agree! however this is way more aerodynamic than a p-47. i have one as well that i love. my 110 watts/lb setup happens to be counter rotate so i thought it might be extra safety with that. my 160 watt/lb setup is standard rotation. that's the only reason i am entertaining the lower watt set up at all. trust i want max thrust for sure! Walt

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Old 12-09-2014, 01:43 AM   #20
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Originally Posted by walter3 View Post
i totally agree! however this is way more aerodynamic than a p-47. i have one as well that i love. my 110 watts/lb setup happens to be counter rotate so i thought it might be extra safety with that. my 160 watt/lb setup is standard rotation. that's the only reason i am entertaining the lower watt set up at all. trust i want max thrust for sure! Walt
What are you using for the counter rotating props at 110 Watts per Pound?

I'm looking for a pair of 10X7 electric props, one forward, one reversed.

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Old 12-09-2014, 04:52 AM   #21
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"master air screw" 10x7 3 blade are giving me 110watts/lb. with 4s batts. durafly 10x7-8 are giving me 160watts/lb. the master air screw are counter rotate the others are not.

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Old 12-09-2014, 05:58 AM   #22
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Yes your model is undoubtedly more aerodynamic. Can you get counter rotating 10x8x3 or something? I've never really looked into anything but 2 blades, as they don't have a performance gain like a full scale would, such that a 4 blade should get double the thrust, but it doesn't. 110 will work perfectly fine though. As for non-counter rotating, you aren't dealing with a gasser, and one motor cutting out is unlikely. You will see some torque, but I can't see it being more than a single prop plane.
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Old 12-09-2014, 06:15 AM   #23
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http://www.hobbylinc.com/htm/mas/masma1070t.htm

http://www.hobbylinc.com/htm/mas/masma1070tp.htm
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Old 12-09-2014, 07:05 AM   #24
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That is one beautiful plane you have there. I have not flown one electric yet, but I have flown it on glow with 2 K&B 40's and a 9X7 prop. That's the rear exhaust model, not the regular engine. It flew fantastic and I NEVER had a problem with an engine out. I have turned BOTH ways with a dead engine and it has never bitten me. You just have to remember to keep your airspeed up a little. It also helps to keep that rudder in while flying on one engine too.

It's a fantastic flying plane and should be great on 160 watts per pound. I would fly that first and worry about throttling back if you need to for top speed. I would also fly half the flight time with the batteries you are using for that first flight just to make sure everything is alright before getting carried away. It will also give you the ability to make more then one approach if you need to. If you haven't flown this plane before, then I would take it easy at first just to get used to flying it. Once you do, your gonna LOVE it.

The worst engine to loose is the left, so you may want to be a little careful if you ever loose that one. I have lost both engines (not at the same time) and it always came home in one piece with no problems, so don't worry about loosing a motor. Even if you do, it still flies fantastic.

After I finish the two gliders I have going now, I am going to build one and see if I can still fly one like I used to. I have been without one for to long and I always loved that plane. I should have ordered two of them instead of just one. Then I would have had a spare when I needed it. As it was, the kit was no more when I needed that second one. I have the plans now and can build from that and will hopefully have one ready for next summer.
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Old 12-09-2014, 02:06 PM   #25
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thanks for the comments. was your plane flying on standard rotation props? Walt p.s. thepiper92 -those are the ones i got. i cant find that setup in a 8 pitch. if you do please let me know. thanks a lot. p.s. i just received some 3 blade 10x7 standard rotation emp props. they are supposed to be good quality ones. will test later with watt meter to see what i get. look fatter than mas ones and have a nice looking blade shape. look efficient. report to follow after balancing and testing with watt meter. Walt.

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