cloud_9's blog
Understanding Drive Calc....credit to "Landru"
Discussion / Posted by cloud_9 / May 24, 2013 @ 07:19 PM / 1,558 Views / 0 Comments / Reply
A discussion of what the graph in the main window is showing, in which Landru clears up my confusion

Discussion / Posted by cloud_9 / May 24, 2013 @ 05:09 AM / 1,429 Views / 0 Comments / Reply
I know that wing loading is an important factor in the way a model flies. Does model size enter into it? Suppose I have a 36" span plane and a 72" span plane, both with wing loadings of 16 oz/sq ft. Will they have approximately the same flying characteristics? (given a similar airfoil, power / weight ratio, etc)

Griffin replies: To get a cubic wing loading of 6.5 on the smaller plane to match the larger, you would need to get the weight down to 12oz and have a wing load of 8oz. In theory, the two planes would look like they are flying at the same speed, and they would stall at a relatively similar airspeed. It's not a perfect system of course, but it is about 200 times more helpful than wingloading....

-Steve

PS, figuring cubic wing loading can be done on a calculator, but I like to cheat and use this great on-line calculator:

http://www.ef-uk.net/data/wcl.htm
Tests with Turnigy 4250 (a post from the Magister thread)
Discussion / Posted by cloud_9 / May 21, 2013 @ 10:00 PM / 1,218 Views / 0 Comments / Reply
Magister Power System Numbers for a Turnigy 4250 Brushless

http://www.hobbyking.com/hobbycity/s...idProduct=8489

Dimension: 48mm x 42mm, 68mm(with shaft)
Weight: 199g (kv1000) (not including connectors)
Diameter of shaft: 5mm
Length of front shaft: 18.7mm
Lamination thickness: .2mm
Magnet type: 45SH
Max performance
Voltage: 4S
Max current: 45~54A
Prop: 10x5~11x5.5
Thrust: 2050~2450g
For 2000-2500g 3D model airplane.
Kv (rpm/v) 1000
Weight (g) 199
Max Current (A) 54
Resistance (mh) 0
Max Voltage (V) 15
Power(W) 0
Shaft A (mm) 5
Length B (mm) 48
Diameter C (mm) 42
Can Length D (mm) 27
Total Length E (mm) 68

Prop..........Size........V.........A........W.... ..RPM.....Thrust
=============================================
Xoar..........10x5.....11.68.....36.2....424....11 220.....2lb 12oz
APC.........10x5.....11.60.....35.6....413....1119 0.....3lb
APC.......11x5.5.....11.28.....46.4....524....1026 0.. .3lb 12oz
MAS.....11x7x3.....10.85.....51.0....554.....9680. .. .4lb 2oz
APC.........12x6.....10.98.....56.7....623.....939 0.. ..4lb 6oz
Determining a Model's Power Requirements (Eflite)
Discussion / Posted by cloud_9 / May 21, 2013 @ 09:52 PM / 1,194 Views / 0 Comments / Reply
1. Power can be measured in watts. For example: 1 horsepower = 746 watts
2. You determine watts by multiplying ‘volts’ times ‘amps’. Example: 10 volts x 10 amps = 100 watts

Volts x Amps = Watts

3. You can determine the power requirements of a model based on the ‘Input Watts Per Pound’ guidelines found below, using the flying weight of the model (with battery):

• 50-70 watts per pound; Minimum level of power for decent performance, good for lightly loaded slow flyer and park flyer models
• 70-90 watts per pound; Trainer and slow flying scale models
• 90-110 watts per pound; Sport aerobatic and fast flying scale models
• 110-130 watts per pound; Advanced aerobatic and high-speed models
• 130-150 watts per pound; Lightly loaded 3D models and ducted fans
• 150-200+ watts per pound; Unlimited performance 3D and aerobatic models

NOTE: These guidelines were developed based upon the typical parameters of our E-flite motors. These guidelines may vary depending on other motors and factors such as efficiency and prop size.

4. Determine the Input Watts Per Pound required to achieve the desired level of performance:

Model: E-flite Brio 10 ARF
Estimated Flying Weight w/Battery: 2.1 lbs
Desired Level of Performance: 150-200+ watts per pound; Unlimited performance 3D and aerobatics

2.1 lbs x 150 watts per pound = 315 Input Watts of total power (minimum)
required to achieve the desired performance

5. Determine a suitable motor based on the model’s power...Continue Reading
Understanding Lipo battery voltage and capacity:
Discussion / Posted by cloud_9 / May 11, 2013 @ 11:25 AM / 2,387 Views / 9 Comments / Reply
From Everydayflier:

4.2 100%
4.1 90%
4.0 80%
3.9 70%
3.8 60%
3.7 50%
3.6 40%
3.5 30%
3.4 20%
3.3 10%
3.2 0%

From NoFlyZone's blog, numbers from IA-Flyer:

It also seems that we will maximize our Li-Po life by taking them down to no lower than 20% of their capacity. Here is the latest and greatest information I have managed to gather from extensive reading on this subject.
"Resting" Voltage per cell
4.20v = 100% of our battery's amp capacity remains.
4.03v = 76% of our battery's amp capacity remains.
3.86v = 52% of our battery's amp capacity remains. (A good voltage to store our Li-Pos at)
3.83v = 42% of our battery's amp capacity remains.
3.79v = 30% of our battery's capacity remains.
3.75v = 20% of our battery's amp capacity remains. (Where we want to take our Li-Pos to for long life)
3.70v = 11% of our battery's amp capacity remains. (Detrimental 'battery voltage dump' begins)
3.6?v = 0%
In line with the above, we do NOT want our Li-Po's resting voltage to be less than 3.75v per cell, which would mean we had used about 80% of their capacity.

Fully charged: 4.20v/cell x 3S = 12.6 volts
Storage voltage: 3.85v/cell x 3S = 11.55 volts
20% left: 3.75v/cell x 3S = 11.25 volts
CCCV Charging
Discussion / Posted by cloud_9 / May 11, 2013 @ 11:24 AM / 2,164 Views / 0 Comments / Reply
A diagram of how CCCV charging works.

# Images

Zip charging A123s with DB Terminator II
Discussion / Posted by cloud_9 / May 11, 2013 @ 11:23 AM / 1,876 Views / 0 Comments / Reply
Graph of zip charging A123 cells, using Dan Baldwin's Terminator II. At the right, voltage reaches cutoff level, connection is terminated (presumable causing voltage spike), amperage drops, final voltage at full charge.

# Images

Tip Stall and Flaperons
Discussion / Posted by cloud_9 / May 11, 2013 @ 11:20 AM / 1,854 Views / 0 Comments / Reply
Tip Stall and Flaperons
Discussion / Posted by cloud-9 / Jul 10, 2008 @ 12:05 PM / 7,900 Views / 0 Comments / Reply
Why flaperons increase the tendency to tip stalling. Comments and corrections most welcome.

Full length flaperons:

The angle of attack at the root is usually greater than at the tip, thanks to washout, even when flying level. Thus, in level flight, stall starts at the (trailing edge of the) wing root. When banked and turning, the inside wing tip travels slower than the root, the outside wingtip travels faster than the root. The inside wingtip generates less lift, since it is traveling slower. So when turning, there is a tendency for the inside wing to drop, and a tendency for the outside tip to lift, relative to flying level. This can lead to tip stall.

When flaperons are dropped, the overall angle of attack is increased, and stall tendency is increased (stall speed is decreased). The whole wing is more likely to stall. This magnifies effects of turning on lift and stall behavior of the wings tips and tip stall likelihood is increased.

Flaperons on outer wing:

When the flaperons are only on the outer part of the wing, the angle of attack of the outer part of the wing is increased (stall speed decreased) but the inner part of the wing is unaffected. Thus, when turning, the effect of this difference in stall characteristics of the inner and outer wing are added to the above-described effects, and tip stall probability is increased further.