gouda

My Feedback: (69)

Here is the start of my latest conversion project. I didn't see any threads on a similar conversion, so I though I'd start one.

I have the CG Cub noted above that is going to EP. I have both a 2828 and 4120 AXI motor available. I have been through all the motocalc work on this using both motors. What I have found is that either will work, but the 4120 gives me a bit more margin and will better allow for the addition of floats which are in the plan.
That total airframe weight as received out of the box is 76 oz. A bit heaver that I was hoping for, but still ok. I don't believe that there is much that cab be done to remove any significant amout of weight with out ripping the whole plane apart.
A couple of pics are shown below.

I have been watching Greg Covey's conversion of the Graupner Decathlon in this forum and will be following his lead in a number of areas. Thanks Greg!

This plane is larger that the Decathlon and heavier as well, which is all the more reason to go with the 4120. Also (per Motocalc) I can use a 4S pack, while the 2826 would need a 6S pack. Saving me a bit of $$.

Wingspan: 76.5" (1945mm)
Wing Area: 744 sq in (48 sq dm)
Weight: 7.5lb (3.4kg)
Length: 48" (1245mm)

I'll add updates and photos and significant steps are completed.
Any questions or comments are welcomed.

algutkin

My Feedback: (1)

gouda:

I don't want to detour from your thread on the cub conversion, however, power size seems to be a big consideration when converting a glo to electric. I too have a cub that I want to convert. With all the calclulaltion software out there, it still seems to be somewhat of a delema. Do we still just have to use the old fashioned trial and error method?

For example, at the moment I am also finishing up a conversion, a 60size high wing trainer. Total weight with motor and batteries is just under 6 lbs. I have installed a 2826/10 motor but Moto Calc is throwing me a curve. It doesn't seem to like the motor temp when a 6s2p battery setup is proposed. I noticed that this setup is also one of your choices. I'm also trying to use a 11X8 prop. Do you have any experience with the opinion section of Moto Calc, the warning that motor temp of 396 can damage the motor?

Al G.

gouda

My Feedback: (69)

No problems it's godd discussion fodder. below is the details of the out put I got from motocalc. have a look and see how it compares. Then we can look at things closer. Watch what you put for the empty weright of the plane. I used the weight off the model box at first then realized it was the finished weight.


MotOpinion - Untitled
800ft above Sea Level, 29.92inHg, 60°F

Motor: Model Motors AXI AC4120/14; 650rpm/V; 2A no-load; 0.041 Ohms.
Battery: Thunder Power TP1950; 4 series x 2 parallel cells; 1950mAh @ 3.7V; 0.015 Ohms/cell.
Speed Control: Generic Brushless ESC; 0.006 Ohms; High rate.
Drive System: Generic 12x7in Prop; 12x7 (Pconst=1.25; Tconst=0.956) direct drive.
Airframe: CG Cub ARF; 744sq.in; 107.7oz; 20.8oz/sq.ft; Cd=0.045; Cl=0.42; Clopt=0.69; Clmax=1.38.
Stats: 61 W/lb in; 51 W/lb out; 20mph stall; 29mph opt @ 66% (41:14, 88°F); 36mph level @ 81% (28:33, 95°F); 798ft/min @ 18.5°; -215ft/min @ -4.9°.

Power System Notes:

The full-throttle motor current at the best lift-to-drag ratio airspeed (27.2A) falls between the motor's maximum efficiency current (24A) and its current at theoretical maximum output (144.5A), thus making effective use of the motor.
The voltage (13.7V) exceeds 12V. Be sure the speed control is rated for at least the number of cells specified above.

Aerodynamic Notes:

The static pitch speed (53mph) is within the range of approximately 2.5 to 3 times the model's stall speed (20mph), which is considered ideal for good performance.
With a wing loading of 20.8oz/sq.ft, a model of this size will have trainer-like flying characteristics. It would make an ideal trainer, for use in calm to light wind conditions.
The static thrust (64.5oz) to weight (107.7oz) ratio is 0.6:1, which will result in short take-off runs, and no difficulty taking off from grass surfaces (assuming sufficiently large wheels).
At the best lift-to-drag ratio airspeed, the excess-thrust (35.2oz) to weight (107.7oz) ratio is 0.33:1, which will give strong climbs and rapid acceleration. This model will most likely readily loop from level flight, and have sufficient in-flight thrust for many aerobatic maneuvers.

General Notes:

This analysis is based on calculations that take motor heating effects into account.

gouda

My Feedback: (69)

Here is the 2826:

MotOpinion - Untitled
800ft above Sea Level, 29.92inHg, 60°F

Motor: Model Motors AXI AC2826/12; 730rpm/V; 1.2A no-load; 0.062 Ohms.
Battery: Thunder Power TP1950; 6 series x 2 parallel cells; 1950mAh @ 3.7V; 0.015 Ohms/cell.
Speed Control: Generic Brushless ESC; 0.006 Ohms; High rate.
Drive System: Generic 9x5in Prop; 9x5 (Pconst=1.25; Tconst=0.956) direct drive.
Airframe: CG Cub ARF; 744sq.in; 107.8oz; 20.9oz/sq.ft; Cd=0.045; Cl=0.42; Clopt=0.69; Clmax=1.38.
Stats: 72 W/lb in; 62 W/lb out; 20mph stall; 29mph opt @ 61% (56:04, 95°F); 36mph level @ 74% (38:35, 104°F); 766ft/min @ 17.7°; -215ft/min @ -4.9°.

Power System Notes:

The full-throttle motor current at the best lift-to-drag ratio airspeed (22.3A) falls between the motor's maximum efficiency current (17.8A) and its current at theoretical maximum output (132.8A), thus making effective use of the motor.
The voltage (21V) exceeds 12V. Be sure the speed control is rated for at least the number of cells specified above.

Possible Aerodynamic Problems:

The static pitch speed (66mph) is greater than 3 times the stall speed (20mph), which might make take-off or hand launching difficult, and is inefficient in flight unless very high speeds are intended.
Pitch speed can be decreased by using a lower pitched and/or larger diameter propeller, a higher gear ratio, a lower cell count, or some combination of these methods.

Aerodynamic Notes:

With a wing loading of 20.9oz/sq.ft, a model of this size will have trainer-like flying characteristics. It would make an ideal trainer, for use in calm to light wind conditions.
The static thrust (55oz) to weight (107.8oz) ratio is 0.51:1, which will result in short take-off runs, and no difficulty taking off from grass surfaces (assuming sufficiently large wheels).
At the best lift-to-drag ratio airspeed, the excess-thrust (34.1oz) to weight (107.8oz) ratio is 0.32:1, which will give strong climbs and rapid acceleration. This model will most likely readily loop from level flight, and have sufficient in-flight thrust for many aerobatic maneuvers.

General Notes:

This analysis is based on calculations that take motor heating effects into account.

algutkin

My Feedback: (1)

gouda:

My only option is the 2826/10, I have an extra. my setup is 3s4p, 6000 mah total. Flying weight is 6 lbs. I set this up to use an 11/10 apc E prop. I cut this prop down from a larger size. Just balanced the prop and ran it for a static test WOW.

According to Motocalc this plane should be able to do consecutive loops and any aerobatic maneuver. LOL. The way that I fly, the craft will do all this on it's own. I don't have time to compare every aspect of the reports, wife is yelling at me to get dressed. Howver, it seems that your setup will have lots of RPM and a smaller prop, mine, approx 8,000 RPM max and a big honkin prop.

OK, here comes the funny part. I tried all kinds of calcs first and nothing seemed to come out perfect. I put in all kinds of prop sizes, and battery combinations in order to get the opinion to come out favorable in every aspect. Well, I had no choice, the Axi 2826/10 is supposed to power a 6lb aircraft, and it was going to do it. I didn't have a 11/8 prop so I used a cut down 11/10 prop. I then static tested the setup in our living room, it's raining outside and cold in the garage. It felt good and nothing was hot. I then put my ending numbers in Moto Calc and it came out with a glowing report. Don't forget this is a 60 size high wing trainer.

The term "just do it" comes to mind. Moto calc seems to contradict itself in the reports. One paragraph says, might make take off difficult, in another part, very short take off run. This thing is going to fly great on 11.1 volts and a max of 34 amps WOT.

gouda

My Feedback: (69)

You know, I agree. I take the motocalc stuff only as a rough guideline. I try to research and find out what others have done. That seems actually to be the best bet. I went the 4120 route mostly because it's a bigger plane and I want to add floats, so pushing 7.5 Lbs is very possible. I think your work has shown what will work. Makes a great air conditor doesn't it?

mickey-gem

I have the AXI 2826/10 in a Sig Rascal 40, it weighs in at just undr 6 pounds. I believe I am running
an 11x 7 APC E prop. It pulls about 40 amps at full throttle. I am using 2 Kokam 2s 3200 Lipo's in series
for a 4s1p configuration. This set up flies this palne with much authority, super fast flyby's, knife edge,
tight loops.

I also have the AXI 2826/10 in a World Models E-3D plane 3 pounds flying weight, 3s Kokam 3200 lipo
14X7 APC E prop it pulls around 35 amps at full throttle and pulls the plane vertical very quickly.

Don't go over 4s on the 2826/10 and just prop it to pull no more than 40 amps at full throttle. This little
motor is impressive and is suitable for a wide range of airframes due to it's small size and light weight.




Kind regards,

Jesse