Tag: diameter

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Customer asks a good prop question with implications…..

Hi Dave,

Quick question about the APC props. I note that for multi-rotor the sizes seem to be with 4.5 pitch. Is there a reason why I should not use say, 9×6 with 9x6R for multi rotor craft?

Thanks
David

Answer:
Hovering props or props that produce best thrust in static air tend to be pitched about 1/2 of diameter or less. As you add more pitch, they can fly faster, but have less bite in static air. They can actually be stalled and have less lifting force until the prop gets to moving forward. This is also why props which are the same otherwise make more noise with lots of pitch. Initially they are stalled or partially stalled. So, if you need more prop than a 9-4 to apply the power to the air you have available in your system, you go to 10-4, not a 9-6. Certainly a 9-7 would be such a bad choice as to be worthless.

All this is considering the model is essentially hovering all the time. Even forward flight isn’t quite as forward as an airplane. Other types of flying and machines can have other considerations that make higher pitch (relative to diameter) correct but this is unlikely in all multi-rotors except maybe a racer.

What we call these props is 1/2 square. Meaning pitch is about 1/2 the diameter. A pattern aircraft or war bird might use a 3/4 square (like a 10-7 or 11-8) or even a square prop (like 12-12) because hovering is not a required and speed is more desirable. These setups are poor on hole shot, but once they get moving they really go.

Dave
Hi Dave,

Quick question about the APC props. I note that for multi-rotor the sizes seem to be with 4.5 pitch. Is there a reason why I should not use say, 9×6 with 9x6R for multi rotor craft?

Thanks
David

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Understanding Wire Size

This page intended for reference purposes and will be updated from time to time.

When trying to understand wire sizes, it’s important to understand the measurement system. Not all the world uses AWG (American Wire Gauge). Most wire available for our hobby today comes in metric, some sizes are close to familiar gauge sizes, some in-between. Most high quality wire today is not sold at an exact AWG size although some is. This leads to some confusion when trying for example to purchase wire that is “about 16 gauge” (or whatever your looking for). Because in America most people are looking for a certain gauge size, we try to list on RadicalRC.com with the nearest approximation of the AWG gauge size. Many vendors claim wire offered is larger than it is in order to exaggerate the perceived value.

To figure the cross sectional area of a stranded wire, measure the diameter of an individual strand. The radius is 1/2 the diameter. If the strands are 0.08mm (typical with the high end wire we offer) then the radius is .04mm. To figure the circular area, we figure that area for a single strand. In the case of the above example, the area* is .00502654832mm^2. Multiply that by the number of strands to get the total area in square mili-meters (mm^2). For example, our Silicone Sub-C wire has 399 of these strands. Multiplying the overly long number above x 399 strands = 2.0055927796 or rounded to 4 digits after the decimal point (proper procedure) we find the area of the 60 strand wire is 2.0056mm^2. When we look down the chart in the Square mm column we see most approximates 14 gauge.

Armed with information and a metric caliper, you figure out if your being “out figured” (hustled) or not.

The following chart is general in nature. I suspect the resistance is calculated based on single strand wire. This may be different for high strand count wire and not the subject of this article.

AWG Diameter(mm) Diameter(in) Square(mm^2) Resistance
(ohm/1000m)
40 0.08 . 0.0050 3420
39 0.09 . 0.0064 2700
38 0.10 0.0040 0.0078 2190
37 0.11 0.0045 0.0095 1810
36 0.13 0.005 0.013 1300
35 0.14 0.0056 0.015 1120
34 0.16 0.0063 0.020 844
33 0.18 0.0071 0.026 676
32 0.20 0.008 0.031 547
30 0.25 0.01 0.049 351
28 0.33 0.013 0.08 232.0
27 0.36 0.014 0.096 178
26 0.41 0.016 0.13 137
25 0.45 0.018 0.16 108
24 0.51 0.02 0.20 87.5
22 0.64 0.025 0.33 51.7
20 0.81 0.032 0.50 34.1
18 1.02 0.04 0.82 21.9
16 1.29 0.051 1.3 13.0
14 1.63 0.064 2.0 8.54
13 1.80 0.072 2.6 6.76
12 2.05 0.081 3.3 5.4
10 2.59 0.10 5.26 3.4
8 3.25 0.13 8.30 2.2
6 4.115 0.17 13.30 1.5
4 5.189 0.20 21.15 0.8
2 6.543 0.26 33.62 0.5
1 7.348 0.29 42.41 0.4
0 8.252 0.33 53.49 0.31
00 (2/0) 9.266 0.37 67.43 0.25
000 (3/0) 10.40 0.41 85.01 0.2
0000 (4/0) 11.684 0.46 107.22 0.16

*Area of a circle = 3.1416 X (Radius X Radius)

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