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Old 05-10-2014, 08:28 AM   #1
thepiper92
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Default Using Motocalc

So I was playing around with Motocalc, came to around 17oz for empty weight of the P47. I don't have a scale that can measure it properly, but I took the max of what the plane likely would be (24 oz) and subtracted the weight of the battery, motor and esc. No specs on area of wing, but it is somewhere around 300sq in I gather (the Mini Switch is around 170, and the the P47 has a larger span and clearly a larger area distance from the leading to trailing edge. Putting it at 250 changes results very little. I found the specs for the motor, an RCtimer 2830/11 1000kV, including resistance, weight. I also found the specs for the battery, although under cell weight, I gather the program asks for individual cell, so I divided the weight by 3 for the battery. The results that I got were stall speed until 18mph, level flight at clopt=0.53 25mph (whatever that means), 29mph level flight at Cl=0.4 and a max airspeed of 44mph. Now, my specs are obviously not accurate completely. I know how to find the wing area, but it isn't that far off. As for weight, that may make a difference, but I'm thinking of the answer to my question: Does the front end of the P47 really suck the plane back that much, or am I running much too heavy (not sure what it would be other than 2 retracts, and a bit of extra sheeting on the wings). These results are a 10x6 prop. All going up to a 10x8 prop does is increase the top speed to 53mph, would this have helped me quite a bit you think? I would have achieved the 10x6 max airspeed at 75% throttle according to this. Now here is what I am confused about, an 11x8 prop has nothing different than a 10x8 prop...what does that mean? I really want to get down to figuring this prop stuff out, I am tired of crashing because of screw ups on my part of installing the wrong props. My own flying mistakes, that is fine, but not mistakes before I fly.
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Old 05-10-2014, 08:50 AM   #2
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Hi How many lipo cells are you using, that 2830-11 can use 2 to 4 lipo cells, if your using a 3 cell lipo, then the 10x6 might be to big of a prop, the 10x6 IMHO should be used with a 2 cell lipo, with a 3 cell lipo, you should use about a 9x5 or 8x6 prop, and with a 4 cell lipo use a 8x4 prop, check your amp draw with a wattmeter to be on the safe side.

http://www.rctimer.com/product_121.html

Model: 2830-11
Motor size: Ф28*30mm
Shaft size: Ф3.17*45mm
Weight: 52g
KV(rpm/v): 1000
Max Power: 210W
Battery: 2-4Li-Po
Prop: 10x7/8x4
Ri(M Ω): 0.127
ESC: 30A


Look at the 2830-11 prop specs at Heads up RC, they will get you very very close with your motor

http://www.headsuphobby.com/Firepowe...otor-E-630.htm

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Old 05-10-2014, 08:57 AM   #3
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if unsure about a prop size for a motor, look at the motors at heads up RC, look at a motor thats the same size or close to your size motor and KV, I have had to do this myself to avoid screwing up too

http://www.headsuphobby.com/Firepowe...otor-E-630.htm

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Old 05-10-2014, 09:17 AM   #4
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It is a 3s. 10x6 essentially leaves the plane at barely above stall at full throttle, and it was suggested that a higher pitch 10x8, or going up to a 11x8 would be better. Is the only way to do this by going lower kv, or a physically larger motor? Would 9x5 not give worse performance? It's one of those things I can't grasp get, how does a larger prop increase performance if you are technically slowing the rpm down with more stress on the motor?
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Old 05-10-2014, 10:39 AM   #5
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As has been said a few times.. You need a wattmeter so you can see what's going on and if the current motor is operating at it's limit, if the battery is performing ok etc etc. Actually weighing the model would be good too rather than just making numbers up.

Otherwise it's all guesswork.

But on the face of it the motor may already be over-propped and you are still short of power. If so that means you need a larger motor with greater watt rating.
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Old 05-10-2014, 02:11 PM   #6
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Given the setup you've described, you should be fine. Thrust and wing loading are OK. I too would recommend you start with a smaller prop like a 9x6.

I've found that motocalc tends to overestimate the power needs of a model. If motocalc says a setup is marginal, it's usually really OK. Better than underestimating your power needs.

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Old 05-10-2014, 04:02 PM   #7
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Well with a 10x6, it was marginal, considering I turned the wing into dust because I could barely get past stall. Wouldn't a 9x6 give me less power? Now let's say I can go to a same sized motor, but less kv so that a 10x8 would work. This is the same sized motor, same power, just lower kv so it doesn't get overstressed. Would that lower kv motor give me more speed than a 10x6 on my 1000kv rctimer motor. Btw, the motor does handle 10x6, it does not get too hot, so I am good, though I will be getting a wattmeter. I also don't want to go to a smaller prop, for a couple reasons. One, the plane would look odd with smaller, and two, the front end of the P47 is massive, and if I get much smaller ill be spinning the prop to cool the motor, nothing more. Also, the results are okay in motocalc, but clearly that front end must make the plane like a flying wall, for my UMX SBach goes faster, meaning its hovering around the stall no doubt.
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Old 05-11-2014, 02:26 AM   #8
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If you have described everything accurately, you are at almost 100W/lb and around 100% thrust to weight. You should be good. Not 3d levels of power by not marginal either. What size battery are you using? You should be pulling around 18A

I have a pair of these in my He-219 and found that a 9x6 APC prop was best in that application.

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Old 05-11-2014, 02:41 AM   #9
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I thinking the massive wall of a cowl is holding it back, it's a large cowl, and traps air. Can't think of other factors.
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Old 05-11-2014, 04:05 AM   #10
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Originally Posted by thepiper92 View Post
I thinking the massive wall of a cowl is holding it back, it's a large cowl, and traps air. Can't think of other factors.
The outer third of the propeller diameter provides most of the thrust on the prop. So, that prop should be something like double the diameter of the cowl.

And, as you indicate, a big diameter cowl is an air brake. I had a model like that awhile back. It helped a little bit to fill in the open hole with some real thin balsa sheeting painted black.

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Old 05-11-2014, 05:05 AM   #11
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I have cut out a large area in the cowl for air, as well as made exhaust in the the fuse. I better the diameter of the prop would be better at 11. What do specs show for 11x6-11x8 on your hacker. Its nice to get a ballpark of the motor sized needed.
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Old 05-11-2014, 05:43 AM   #12
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Originally Posted by thepiper92 View Post
I have cut out a large area in the cowl for air, as well as made exhaust in the the fuse. I better the diameter of the prop would be better at 11. What do specs show for 11x6-11x8 on your hacker. Its nice to get a ballpark of the motor sized needed.
That Hacker A30-12XL motor is rated for 60 Amps, with a 650 watt rating.

Motocalc predicts it will turn an 11-6 prop at 9500 RPM, pulling 33 Amps out of a 4S LiPo battery. For that, you'd need a LiPo on the order of 2200 - 3000 Mah.

Prop blast is 55 MPH, rate of climb is WOW, and flying time will be on the order 4 minutes at full wide open throttle. Flying speed is around 54 MPH, stalling is around 19 MPH. It will be pulling about 33 Amps, at 470 Watts. wing loading is a very light 18 ounces per square foot.

I think that would be a very good match that will impress anyone that sees it fly. Just make certain your model is strong enough to handle that sort of power up front.

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Old 05-11-2014, 05:56 AM   #13
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3000 is too much weight for the plane, it's rated at 1300, a 3000 would make it ridiculously nose heavy where the battery sits. The specs you are giving are similar to what my 60 inch wingspan Hurricane will be using. I'm hoping for max 300 watts, maybe a tad bigger of a motor. The plane was designed for 370-400 size. The weight I have in it can't be that much; 17 oz is the max weight I would think it to be, it could be lighter.
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Old 05-11-2014, 07:57 AM   #14
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Okay, so how about this motor: http://www.hobbyking.com/hobbyking/s...er_1020kv.html

Typed it into motocalc, with the specs from the site, and using a 10x8

These are the specs I typed in:

Motor:

Constant: 1020kv
No-load: 1.1 amps
Resistance: 0.06 ohms
weight: 2.86 oz

Battery
1300 3s
Impedance: 0.0257 ohms
Cell weight: 1.36oz

ESC: Hobbywing 40a

Resistance: 0.006 ohms (the resistance of whatever esc it selected before, can't find the actual info)
Weight: 1.34oz

Prop: I just selected what was available for generic, and changed pitch to 8, but the two constants probably aren't correct, and I can't find MAS in the system, other than geared.

Results are
19mph stall, 25 mph opt, 29 mph level and a top speed of 58mph. I have trouble understanding what the other info means, such as efficiency and what it is actually doing, but it seems temps are around 70F, or at least I think that is what the temps are showing. Does that seem like a good motor?
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Old 05-11-2014, 10:03 AM   #15
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Please show your P47 plane, mfg, etc, from what I can see so far, is that your lipo is to small at only 1300mah, that will get drained down real fast and not give very much power with a 2830-1000kv motor turning a large 10" prop,

The Firepower 450 Sport is especially well suited for medium to large parkflyers that require the use of a 9 or 10 inch prop. This motor would be a good choice for planes like the Multiplex Gemini, E-flite Taylorcraft 450, Seagull EP Extra 300, GWS Formosa II, E-flite Mini Pulse, Filton Extra 260 mini, E-flite P-47 and many, many others.


this 450 motor from HEADS UP RC will produce 37oz of thrust with a 10x6 prop. Here is where using Thrust is the Easiest way to find a power system,

http://www.headsuphobby.com/Firepowe...otor-E-650.htm



a 1800mah 50C lipo will be better to use with props over 8" with the 2830-1000kv motor and with the HURC 450 Motor


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Old 05-11-2014, 10:16 AM   #16
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Chellie,

This plane is based on a rubber power 'stick and tissue' design. It's meant to be lightweight and slow flying so piling in a big heavy battery is unlikely to be the answer. the lightweight structure probably couldn't take it for starters.

Bottom line is we need some facts.

Thepiper92,
What is the ACTUAL watts that the motor is pulling and what is the ACTUAL weight and wing area of the model?.. give some factual data to work on.

We could speculate forever based on made up numbers, but that wont get to an answer as to what's really wrong with the plane.
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Old 05-11-2014, 10:26 AM   #17
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Originally Posted by JetPlaneFlyer View Post
Chellie,

This plane is based on a rubber power 'stick and tissue' design. It's meant to be lightweight and slow flying so piling in a big heavy battery is unlikely to be the answer. the lightweight structure probably couldn't take it for starters.

Bottom line is we need some facts.

Thepiper92,
What is the ACTUAL watts that the motor is pulling and what is the ACTUAL weight and wing area of the model?.. give some factual data to work on.

We could speculate forever based on made up numbers, but that wont get to an answer as to what's really wrong with the plane.
Your right, I kind of figured he might have the E Flite p-47, yes we need more facts

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Old 05-11-2014, 10:36 AM   #18
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Originally Posted by CHELLIE View Post
Hi How many lipo cells are you using, that 2830-11 can use 2 to 4 lipo cells, if your using a 3 cell lipo, then the 10x6 might be to big of a prop, the 10x6 IMHO should be used with a 2 cell lipo, with a 3 cell lipo, you should use about a 9x5 or 8x6 prop, and with a 4 cell lipo use a 8x4 prop, check your amp draw with a wattmeter to be on the safe side.

http://www.rctimer.com/product_121.html

Model: 2830-11
Motor size: Ф28*30mm
Shaft size: Ф3.17*45mm
Weight: 52g
KV(rpm/v): 1000
Max Power: 210W
Battery: 2-4Li-Po
Prop: 10x7/8x4
Ri(M Ω): 0.127
ESC: 30A


Look at the 2830-11 prop specs at Heads up RC, they will get you very very close with your motor

http://www.headsuphobby.com/Firepowe...otor-E-630.htm

RC Timer are usually very good at specs ... when they say a prop size - you can believe it.

The specs on that motor .. Model: 2830-11 are good and I use that motor and it's higher KV cousin ... watch my Badius Aerobatic machine ...

In the RC Timer specs ... when you see

Battery: 2-4Li-Po
Prop: 10x7/8x4

The two prop sizes are those recc'd for the two LiPo sizes given .. ie 10x7 for the 2S ... 8x4 for the 4S ...
For a 3S - just pick a prop that falls in between those two .. ie a 9 x 5.5 ... I would go for a 9x6 ..

OK - weigh scales ... local Kitchen / Cookery Shop / Supermarket ... I use a 10kg Digital Scale ... and for finer range .. 2kg Digital scale.

You should find above for less than $10 a throw !

For prop thrust use ... I use a hanging Fisherman's digital scale ... ebay have them for about $3 - 5 ...

Nigel

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Old 05-11-2014, 11:06 AM   #19
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The fisherman's digital hanging scale is perfect for weighing small to medium models too. But if you don't have one as Nigel says, kitchen scales will do the job.
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Old 05-11-2014, 12:19 PM   #20
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Originally Posted by JetPlaneFlyer View Post
The fisherman's digital hanging scale is perfect for weighing small to medium models too. But if you don't have one as Nigel says, kitchen scales will do the job.






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Old 05-11-2014, 04:22 PM   #21
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Originally Posted by JetPlaneFlyer View Post
Chellie,

This plane is based on a rubber power 'stick and tissue' design. It's meant to be lightweight and slow flying so piling in a big heavy battery is unlikely to be the answer. the lightweight structure probably couldn't take it for starters.

Bottom line is we need some facts.

Thepiper92,
What is the ACTUAL watts that the motor is pulling and what is the ACTUAL weight and wing area of the model?.. give some factual data to work on.

We could speculate forever based on made up numbers, but that wont get to an answer as to what's really wrong with the plane.
I haven't been able to pick up a wattmeter, or scale. The wing is destroyed anyway. So I can't weigh it accurately. Is there any quick way to find area instead of taking the a square wing shape and subtracting the square inches until it meets the wing shape? Sorry I can't be of more help, I am short on stuff I should have, and the plane is largely in pieces.

I was hoping everything related to this would move to this thread, which is why I made it, but some info I found in another thread is that the prop may be too close to the large cowl. And air is having difficultly going over. As for the battery, it was rated for 1300 3s. Literally all I have done to the plane different from the plan is add sheeting on the top of wing, servoless retracts and two servos for ailerons. Again, sorry I can't be of my help for the specs currently.
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Old 05-11-2014, 04:44 PM   #22
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Originally Posted by thepiper92 View Post
I haven't been able to pick up a wattmeter, or scale. The wing is destroyed anyway. So I can't weigh it accurately. Is there any quick way to find area instead of taking the a square wing shape and subtracting the square inches until it meets the wing shape? Sorry I can't be of more help, I am short on stuff I should have, and the plane is largely in pieces.
There are plenty of online CoG calculators and ones to download ... these with a few measurements thrown will give you wing area ...

I was hoping everything related to this would move to this thread, which is why I made it, but some info I found in another thread is that the prop may be too close to the large cowl. And air is having difficultly going over. As for the battery, it was rated for 1300 3s. Literally all I have done to the plane different from the plan is add sheeting on the top of wing, servoless retracts and two servos for ailerons. Again, sorry I can't be of my help for the specs currently.
Cowl in fact affects inner section - not outer ... so if you have a large frontal area - you compensate by adding a bit to prop diameter ... but carefully as not only prop drive loads a motor - the outer part having a serious effect on motor load... but also diameter and weight ...
Prop too close to cowl ? Go have a look at a real plane and that will answer that one ...



unless the prop is literally hard up on the cowl - no.

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Old 05-11-2014, 05:00 PM   #23
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Originally Posted by solentlife View Post
There are plenty of online CoG calculators and ones to download ... these with a few measurements thrown will give you wing area ...



Cowl in fact affects inner section - not outer ... so if you have a large frontal area - you compensate by adding a bit to prop diameter ... but carefully as not only prop drive loads a motor - the outer part having a serious effect on motor load... but also diameter and weight ...
Prop too close to cowl ? Go have a look at a real plane and that will answer that one ...



unless the prop is literally hard up on the cowl - no.

Nigel
Thanks for the info. As the P47 is close to an ellipse, I get around 290.13 sq in. As the leading edge of the wing is straight, it will be a little more than this, so 300 is extremely close.
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Old 05-11-2014, 05:12 PM   #24
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Okay, I'm judging off of my Mini Switch specs. It has a slightly heavier motor in it, and I am getting a total weight of 21.9oz by adding the difference in weight of the bigger motor. Just by holding the two aircraft, the P47 is clearly lighter ( the motor is still "in" the P47 and the motor is in the Mini Switch). So the P47 must be closer to 14 oz without the electronics
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Old 05-12-2014, 04:19 AM   #25
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Okay I figured some stuff out kinda. I compared to a durafly p47. I believe it uses the same setup as my spitfire did, which is a 10x8 4 blade, which would convert roughly to a 9x6-9x7 two blade, and a 750kv motor. The durafly is 43 inch wingspan, but it's a hefty 1200g flying weight. The cowl seems a tad tapered on the durafly, but with this info, I don't think my plane has a power issue, so it's something else, something is holding the plane back.
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