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Old Nov 11, 2007, 12:11 PM
White Mountains in NH
dlabrie's Avatar
In the White Mountains of NH
Joined Dec 2006
296 Posts
Quote:
Originally Posted by qban_flyer
I am using a 10X4.7SF orange GWS on two cell 2100s flying my GWS Zero, which has less wing area (204 sq. inches) and higer wing loading (9oz/sq foot) than the BB. It does a very nice job with plenty power to spare, so your BB on three cells may leave its wings behind with that much thrust!
I guess, I quite don't get it. But if I don't open it up all the way won't it be OK?

David
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Old Nov 11, 2007, 12:44 PM
Postcards From The Purple Edge
tuppertn's Avatar
United States, OK, Sand Springs
Joined May 2007
3,919 Posts
Quote:
Originally Posted by dlabrie
Kendall,

I have the DX6 radio. I am still learning to use it. I decided to do the Y on the ailerons at first then figure out how to separate them and do flaps. What do you mean by differential? I did add about 30% exponential to the ailerons. The rudder swings about 1.5" each way.
Differential allows the aileron to travel less on the downward throw than on the upward throw. The point being that the downward throw creates more drag than the upward throw. In a turn that extra drag pulls at the outside (higher) wing dragging it down again and pulling the plane toward the outside of the turn. That's adverse yaw. In extreme cases (like my BB would do) you push the stick left, the plane starts to roll left then falls back to the right.

That sounds like it should be enough rudder.
Quote:
Originally Posted by dlabrie
I put a 1047 on it and it ran up to 18 amps. I put the 1080 on and it hit 15 amp at WOT. Wouldn't an 8040 swing faster and draw more amps?
That motor is rated for a max (burst) current of 16A. They're not super high quality motors and they will burn up if you push them. Their efficiency at that current level is just over 40%. They make heat pretty quick. Personally, I don't like to push a BP21 over 13-14A.

You're right that the 8040 will swing faster, but it will actually draw less amps because the motor works a lot less to swing it, even though it swings faster. In fact, the reason it swings faster is that the motor doesn't have to work as hard. Consider that the motor's highest rpm/lowest current draw/lowest torque state is under no load (spinning WOT with no prop). It's lowest rpm/highest current draw/highest torque state is at stall. (In this case stall is where the motor is running at full power, but not spinning, so rpm equals zero. As if you were to forcibly hold the prop still and go WOT. Has nothing to do with the airplane actually stalling.) As a rule, motors draw more and more current and spin slower and slower as the prop size increases. Pitch has less of an impact than does diameter.

I'm assuming that's a 1080HD/DD, right? The 1080 draws less current than the 10x4.7SF because, even though it's a more aggressive pitch, the blades are thinner giving it less overall surface area and therefore less air resistance. If you're wattmeter tells you 15A then you should be okay. Just don't use WOT for more than 15 seconds. Your motor will get very hot. That, and the fact that by then your BB will be in the lower stratosphere.

kendall
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Last edited by tuppertn; Nov 11, 2007 at 01:02 PM.
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Old Nov 11, 2007, 01:04 PM
I'm not flying backwards!
Tony65x55's Avatar
Oshawa, Canada
Joined Sep 2004
3,753 Posts
Nice build David and good advice regarding the propeller. BP-21's WILL burn (don't ask)

Good luck on the maiden, I'm sure she'll fly fine.

Tony
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Old Nov 11, 2007, 01:11 PM
Postcards From The Purple Edge
tuppertn's Avatar
United States, OK, Sand Springs
Joined May 2007
3,919 Posts
Quote:
Originally Posted by Tony65x55
BP-21's WILL burn (don't ask)...
I think toasting a BP-21 is some sort of rite of passage. Sort of an RC bar mitzvah.
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Old Nov 11, 2007, 01:30 PM
I'm not flying backwards!
Tony65x55's Avatar
Oshawa, Canada
Joined Sep 2004
3,753 Posts
Not too many of us that sent one to that great "cooker in the sky". Of course, if your BP21 was attached to a BB, it was already closer to the "cooker in the sky" than most.

Tony
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Old Nov 11, 2007, 01:52 PM
Always Ready!
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Chicago, IL
Joined Dec 2006
5,179 Posts
Try the GWS 8040 HD prop... it's well documented that the 8x4 is the best all-around prop for this motor on a 3S lipo. Some have tried 8x6 for more speed, but it will eat up your amps and you'll burn it up at WOT. 9x5 is about the same as the 8x6 -- too much prop, too many amps -- you'll end up burning it up just to produce the same amount of thrust as the 8x4.

You can try a 9x3.8 on 3S- which has less pitch speed but turns slower due to the greater diameter... you may "barely" get a bit more thrust out of it than the 8x4... at the cost of a lot more amps, meaning shorter flight times... so it's not worth it to burn 3amps more for 1oz extra thrust... especially since you'd already be overpowered for this trainer anyway.

If you want this motor to go really, really fast, use a 7x5 or 7x6 on 3S... very fast... not ideal for a BluBaby which is designed to fly slow
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Old Nov 11, 2007, 04:55 PM
White Mountains in NH
dlabrie's Avatar
In the White Mountains of NH
Joined Dec 2006
296 Posts
Quote:
Originally Posted by warhead_71
Try the GWS 8040 HD prop... it's well documented that the 8x4 is the best all-around prop for this motor on a 3S lipo. Some have tried 8x6 for more speed, but it will eat up your amps and you'll burn it up at WOT. 9x5 is about the same as the 8x6 -- too much prop, too many amps -- you'll end up burning it up just to produce the same amount of thrust as the 8x4.

You can try a 9x3.8 on 3S- which has less pitch speed but turns slower due to the greater diameter... you may "barely" get a bit more thrust out of it than the 8x4... at the cost of a lot more amps, meaning shorter flight times... so it's not worth it to burn 3amps more for 1oz extra thrust... especially since you'd already be overpowered for this trainer anyway.

If you want this motor to go really, really fast, use a 7x5 or 7x6 on 3S... very fast... not ideal for a BluBaby which is designed to fly slow
I just ordered some 8040 props from Headsup RC. I have also ordered some 2410-09 moters from UH.

Do you have to have the ailerons pluged into separate chanels to use the differential? What should the degree or percentage difference be?

Well the wind didn't die down today Maybe tomorrow

Thanks,
David
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Old Nov 11, 2007, 04:58 PM
Micro Flyer "Q"
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United States, MD, Silver Spring
Joined Sep 2003
1,416 Posts
Quote:
Originally Posted by dlabrie
I guess, I quite don't get it. But if I don't open it up all the way won't it be OK?

David
David,

The 2408-21 is designed to operate at or around 13A max continuosly if it is to last. Anything larger than an 8X4 prop on two cells will shorten its life if not kill it outright.

The chart below was borrowed from the site of a dealer (HeadsUp RC) that sells them. I have checked some of these specs on my own and they seem to be fairly close to those posted below. HeadsUp RC also sells the 2410-09 motor.

Coloration and size are those of the seller's website.
--------------------------------------------------------------------------
Propeller data for 3 cell Lipo batteries:

GWS props fit the 3mm shaft on this motor perfectly - no adapter needed. APC and Master Airscrew props require a prop adapter or prop saver for a 3mm shaft (available in my store).

The GWS EP8040 is the most commonly used prop with this motor. It will produce about 22 ounces of thrust at 14 amps with a pitch speed of 43 mph. This motor is only rated for 13 amps, so you need to provide for plenty of airflow over the motor and use full throttle sparingly until your Lipo has discharged somewhat.

The APC 8x4E produces 22 ounces of thrust at 14 amps with a pitch speed of 39 mph. The same caution must be used as with the GWS EP8040.

I do not recommend using any other 8 inch props with this motor when using a 3-cell Lipo.

The APC 7x5E produces 20 ounces of thrust at 14 amps with a pitch speed of 54 mph. The same caution must be used as with the GWS EP8040.

The GWS EP7035 produces 16 ounces of thrust at 9 amps with a pitch speed of 47 mph.

The APC 6x5.5E produces 11 ounces of thrust at 10 amps with a pitch speed of 65 mph.

The Master Airscrew 7x4 3-blade produces 15 ounces of thrust at 12.5 amps with a pitch speed of 43 mph.

The Master Airscrew 6x4 3-blade produces 11 ounces of thrust at 9.5 amps with a pitch speed of 48 mph.



Recommended props for 2 cell Lipo batteries:

The GWS EP1060 prop produces about 15 ounces of thrust at 11.5 amps with a pitch speed of 33 mph.

The GWS EP1047 prop produces about 15 ounces of thrust at 12.5 amps with a pitch speed of 24 mph.

The APC 9x3.8SF prop produces about 16 ounces of thrust at 11.5 amps with a pitch speed of 24 mph.

The GWS EP9047 prop produces about 14 ounces of thrust at 10.5 amps with a pitch speed of 27 mph.

The GWS EP9050 prop produces about 14 ounces of thrust at 10 amps with a pitch speed of 32 mph.

The GWS EP9070 prop produces about 13 ounces of thrust at 12.5 amps with a pitch speed of 35 mph.

The GWS EP8040 prop produces about 12 ounces of thrust at 7.5 amps with a pitch speed of 32 mph.

The GWS EP8043 prop produces about 12.5 ounces of thrust at 8 amps with a pitch speed of 31 mph.

The GWS EP8060 prop produces about 13 ounces of thrust at 10 amps with a pitch speed of 39 mph.

The GWS HD8060 prop produces about 12 ounces of thrust at 9 amps with a pitch speed of 41 mph.

The above data is a result of my own testing using fully charged Lipo batteries.



2408-21 Specifications:
Weight = 1.6 ounces (46 grams)
Diameter = 1.2 inch (31mm)
Total Length = 2.4 inches (62mm)
Shaft Length = 1.2 inches (31mm)
Shaft Diameter = 3mm (GWS Props fit nicely)
Voltage = 7.2 to 12.6
KV = 1750
Current = 13 amp max.
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Old Nov 11, 2007, 05:18 PM
Always Ready!
warhead_71's Avatar
Chicago, IL
Joined Dec 2006
5,179 Posts
I didn't put any differential on my BB... and I only use one servo, mounted on top of the wing so I can easily adjust it. I don't have much adverse yaw problems. I could mix in a bit of rudder if I want coordinated turns, but totally unnecessary. I have a cub that suffers from adverse yaw, and it also has only one aileron servo, so I added mechanical differential.

Here is a good pic of how to add mechanical differential using one aileron servo:

http://www.rcgroups.com/forums/showt...678#post321678

Depending on whether the servo is mounted on top or on bottom of the wing the V-shaped servo arm will point forward or rearward... whichever way produces more up than down aileron when the servo is pushed left-right.
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Old Nov 11, 2007, 05:22 PM
Always Ready!
warhead_71's Avatar
Chicago, IL
Joined Dec 2006
5,179 Posts
Quote:
Originally Posted by qban_flyer
David,

The 2408-21 is designed to operate at or around 13A max continuosly if it is to last. Anything larger than an 8X4 prop on two cells will shorten its life if not kill it outright.
Um - you mean 8x4 on 3 cells.

On 2 cells, you can go as big as 10x6 and still be under 13 amps.
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Old Nov 11, 2007, 07:05 PM
Registered User
Joined Aug 2006
170 Posts
Successful Flight:

With the battery against the front of the nose bulkhead, the 42" BB took to the air level and true. The CG is close to .3 (maybe a little less) which is low for a KF wing, but the joy is in the flying, not the numbers.

qban joined me at the field. To be completely factual, he took the controls after I moved the battery. It is unclear whether the plane would have flown as well for me as it did for him but thems the facts.

I have a few more corrections to make. I'll add wing tips and move the motor up on its mount to improve the thrust line (more good advice from qban). This may move the CG. We'll see. Ailerons are next. Maybe a camera.

But as everyone who has built one these amazing planes, there is nothing sweeter than watching sheets of foam that have been agonized over for weeks finally get airborne.

All together now, one more time:

THANKS TONY and all of the participants on this thread You guys are awesome.

elight50 (very happy)
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Old Nov 11, 2007, 07:51 PM
I'm not flying backwards!
Tony65x55's Avatar
Oshawa, Canada
Joined Sep 2004
3,753 Posts
You're welcome Elight and congratulations on your successful maiden. Now fly the living bejeezus out of it! Get good and when all your turns, climbs and dives are instinctive, expand into ailerons and cameras and other birds and anything your heart feels like.

Tony
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Old Nov 11, 2007, 08:08 PM
Always Ready!
warhead_71's Avatar
Chicago, IL
Joined Dec 2006
5,179 Posts
congrats elight50!

I hear you on adding a camera... The new FlyCamOne V2 is due out just in time for Xmas, and my wife says I was good this year! So I need to start working on skis or floats for now, so I can fly when the snow hits

http://www.hobby-lobby.com/video-camera.htm
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Old Nov 11, 2007, 08:16 PM
Micro Flyer "Q"
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United States, MD, Silver Spring
Joined Sep 2003
1,416 Posts
Quote:
Originally Posted by warhead_71
Um - you mean 8x4 on 3 cells.

On 2 cells, you can go as big as 10x6 and still be under 13 amps.
OOOPS!

DANG! I hit the #2 key instead of #3. I was so concerned with copying and pasting the table that I didn't even preview the post.

I shall give myself 20 lashes with wet noodle to atone for my typing transgression.
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Old Nov 11, 2007, 08:21 PM
Micro Flyer "Q"
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United States, MD, Silver Spring
Joined Sep 2003
1,416 Posts
Quote:
Originally Posted by Tony65x55
You're welcome Elight and congratulations on your successful maiden. Now fly the living bejeezus out of it! Get good and when all your turns, climbs and dives are instinctive, expand into ailerons and cameras and other birds and anything your heart feels like.

Tony
HE, HE, HE!

That he was doing all morning long. He flew, and flew, and flew until the ESC's LVC kicked in.

Lovely blue flying machine on two cells swinging an 11X4.7SF propeller. Smooth as silk!
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