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Old Aug 14, 2012, 05:59 PM
Jack
USA, ME, Ellsworth
Joined May 2008
16,806 Posts
My Industrial Strength Blu Baby 33 flew at 689 grams/24.3 oz. or just over 3/4ths of a pound. That was with a KFm2 wing and a 115 gram motor. I guess I am still the record holder for a heavyweight BB33?

The 115 gram motor and 183 gram 4S A123 pack flew very well for me. That was a plane that could fly in 25 MPH of wind with not problems at all.

So if your 24 gram motor is only giving you 72 Watts of power (the 3 Watts per gram rule of thumb) the main difference is that my BBIS #2 had more like 300 Watts. And there a logic to all of this.

The light floaty BB's that fly with the 24 gram motors weigh 226 grams/8 oz. to 283 grams/10 oz. It takes 30-50 Watts to make a one pound plane fly. And that is probably "just barely" and and still air.

When I added weight and power to my BB 33's it was not in pursuit of speed it was in pursuit of lower speed power and an ability to have a plane that could fly in the conditions here. And it was also intended to survive my ineptitude as a pilot.

If you get your plane weight so that the CG is about 70 mm/2-3/4" back from the leading edge of the wing and do a test glide, you can tell if adding more power will give you a plane that will fly.

I do test glides over deep weeds (no landing gear on the plane) to soften the impact. Hold the plane shoulder high and give it a not too hard, full arm stroke, forward push. It should leave your hand level and stay that way initially. It will slowly start to one side or the other but should settle into the weeds pretty much level.

If that looks OK, give it about half throttle and try a low power test glide. That should be a longer glide and you'll have time to get the controls in hand and start correcting the drift or any climbing and diving. The goal is to have level straight ahead flight with a slow climb rate.

Set your TX up with 100% servo travel on high rates and 50% on low rates. Add 20-40% exponential if you have that to soften the response to initial stick movements by excited new pilots.

When your low power test glide turns into a flight, use full power to launch and don't add untill you need it. Try to fly without touching the throttle at all for the first few minutes. And as soon as you have control shift to low rates.

A 70 to 90 gram or so low Kv (800 or so) motor on that will give you a nice windy day plane.

Jack
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Old Aug 14, 2012, 06:09 PM
Emress
sirbow2's Avatar
United States, SD, Rapid City
Joined Nov 2011
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Quote:
My Industrial Strength Blu Baby 33 flew at 689 grams/24.3 oz. or just over 3/4ths of a pound. That was with a KFm2 wing and a 115 gram motor. I guess I am still the record holder for a heavyweight BB33?
oooh i just added some dowels for the wing rubber bands so i might have to reweigh haha.


so my plane was 3x the weight it shouldve been...oops
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Old Aug 14, 2012, 08:15 PM
Jack
USA, ME, Ellsworth
Joined May 2008
16,806 Posts
That is not always a bad thing. With weight comes some good things like stability in flight and penetration into the wind. At 24 ounces the wing loading is about 13 oz./sq.ft. and that is still light enough for a very nice flying airplane. Heck, 15 oz./sq. ft. is is consider OK for glides! The best gliders only get down to about 10 oz./sq. ft.

So don't give up on that plane, it just needs more power!

Some here lost track of the fact that the BB 33 was built as and to be an indoor flyer. We have brought it outside into the wind and made it do things that are way beyond the original concept. And that is OK, there is no holy grail here that has to be worshiped, no rules that say we have to do this or that.

Adding the down and right thrust will help your plane eventually. The first sign that you need it will be when you get it flying with enough power and the nose pitches up when you open the throttle. Put about 2-3 degrees down and 1-2 degrees of right thrust in there and it will accelerate and climb, staying level, because of the increased speed. You'll probably have an "X" type mount with the bigger motor and you can add washers between the mount and firewall to push the mount out at the top and to the right a little.

Jack
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Old Aug 14, 2012, 08:55 PM
Emress
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United States, SD, Rapid City
Joined Nov 2011
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well, i dont have any bigger motors as the only other 4 are on my quad

any motor recommendations for a bigger motor close to the Midwest USA? one of my 20-22l motors (like my qaud) with a 9x5 would give about 1020g max so that'd work. maybe a little bigger.
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Old Aug 14, 2012, 09:30 PM
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sixfins's Avatar
United States, FL, Sunrise
Joined Jul 2011
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Sirbow, like I said earlier, just more power should be all you need for this one. What do you think Jack, something in the 150-170 Watt range should work.
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Old Aug 14, 2012, 09:53 PM
Emress
sirbow2's Avatar
United States, SD, Rapid City
Joined Nov 2011
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cool. so a 20-22l with a 9x5 prop is 177.6w calculated from 11.1v
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Old Aug 14, 2012, 11:08 PM
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USA, KS, Wichita
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What's the recommended dihedral for the 33" plane?
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Old Aug 15, 2012, 12:40 AM
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Omaha Nebraska
Joined Feb 2006
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Quote:
Originally Posted by mclarkson View Post
What's the recommended dihedral for the 33" plane?
All my airplanes I use this:

R/E/T, Dihedral, no ailerons. Top wing 3-5 degree per side. Mid wing 5-7 degree per side, and Bottom wing 7-10 degree per side.

R/E/A/T, Dihedral using ailerons. Top wing 0-3 degree, Mid wing 3-5 degree per side, and Bottom Wing 5-7 degree per side.

Never failed me yet, and this is how I built my BB's. Flew great! Measurements taken from a couple books I read on model aircraft design written by engineers with many successful designs to their name!
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Old Aug 15, 2012, 06:05 AM
Jack
USA, ME, Ellsworth
Joined May 2008
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Quote:
Originally Posted by sirbow2 View Post
well, i dont have any bigger motors as the only other 4 are on my quad

any motor recommendations for a bigger motor close to the Midwest USA? one of my 20-22l motors (like my qaud) with a 9x5 would give about 1020g max so that'd work. maybe a little bigger.
If your 20-22L is this HK motor:

http://www.hobbyking.com/hobbyking/s...idProduct=4700

It will probably work. Get in the habit of looking at motor weights and you'll quickly have a better feel for the power you can expect. If you go from a 24 grams (3 x 24 = 72 Watts) to a 56 gram (3 x 56 = 168 Watts) motor you will be doubling the power potential.

The motor weight, Kv rating, and battery choice are the three things that interplay to determine prop size and power levels. If your 20-22L is the 924 Kv version you can estimate the RPM you can get out of it. The no load speed would be the Kv times the battery voltage. So a 924 Kv on a 12.4V pack gives you a 11,458 RPM no load speed.

Typical quality motors when running at their continuous power rating (one that does not eventually overheat the motor) will run at about 75% of their no load speed. So 75% of 11,485 is the propeller RPM you can reasonably expect to get out of that motor on 3S. And 11,458 x .75 = 8,953 RPM.

To see if that will work with your prop choice you can look the prop up in the data base at FlyBrushless.com. I'm not sure which prop you use but here is the info on the GWS HD 9 x 5

GWS HD 9x5 - http://www.flybrushless.com/prop/view/13

Looking at the thrust to RPM graph there, that prop will have about 800 grams of thrust at 9,000 RPM. That will put you at a 1.2:1 thrust ratio and that is way more than the minimum needed for flight. More rules of thumb of course, it is said that 0.33:1 is the minimum for stable flight, 0.5:1 is enough for sports/park flyers and basic aerobatics, and 1:1 is good for advanced aerobatics and 3D.

So all the numbers stack up to say that your plane will fly!

Jack
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Old Aug 15, 2012, 08:20 AM
Emress
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United States, SD, Rapid City
Joined Nov 2011
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Wow! thanks a ton. these few posts are pretty much a entire guide for choosing motor + prop for a plane! hopefully when i start getting use to plane stuff i can start answering posts (that's what my last 1k posts were in the multirotor forum )

question. if .33 is the bare minimum why does this motor not work? we already kow that the motor isn't powerful enough, but, 480g thrust / 688g is .69:1 ratio. why did you calc no load from 12.4? not 12.6

i think this motor maybe a wee bit too big for this plane. wouldn't want it to go tearing itself apart, no?
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Old Aug 15, 2012, 08:59 AM
Jack
USA, ME, Ellsworth
Joined May 2008
16,806 Posts
Good question.

I took the link sirbow2 posted at face value it is this motor:

HXT - 2730-1300 - http://www.flybrushless.com/motor/view/449

but looking at it closer I see this motor too:

HXT - 2730-1300 (Silver Wonder) - http://www.flybrushless.com/motor/view/63

And that shows the 9 x 5 but only on 2S. A 8 x 4 on 3S had a thrust of 399 grams though so a 9 x 5 could have have done a little better. It is a little bit too much prop for 3S that motor by the testing there but it might have been OK on his motor and that still put the thrust up at 0.58:1.

These darn rules of thumb and theoretical power systems, they can be pretty hit ofr miss sometimes.

Jack
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Old Aug 15, 2012, 09:36 AM
Emress
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United States, SD, Rapid City
Joined Nov 2011
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ok, im sure that's it. i angled the motor down and to right from the cockpit view and now it doesn't have any real stability issues, just cant fight the wind(12mph). could i throw it diagonal into the wind so it doesn't get blow backwards?

EDIT: yay! i got it up once.... and only once it was wierd; i put it up to 100% thr, gave it a nice big toss and up it went and i had control of it for about 30sec(fighting the wind the whole time) and then it got stuck in some rows of corn, but after i got it out i couldn't get it to go back up. too bad the cam wasnt on when it worked that one time

i think im just gonna get some new foam and rebuild it properly as its taken quite a beating so far :P
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Old Aug 15, 2012, 01:44 PM
Must not buy more planes!
mclarkson's Avatar
USA, KS, Wichita
Joined Jul 2010
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Quote:
Originally Posted by Freddie B View Post
All my airplanes I use this:

R/E/T, Dihedral, no ailerons. Top wing 3-5 degree per side. Mid wing 5-7 degree per side, and Bottom wing 7-10 degree per side.
Thanks. So just short of 1" to just short of 1.5", then, correct? [sin(5)*(33/2)]
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Old Aug 15, 2012, 01:47 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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Quote:
Originally Posted by sirbow2 View Post
ok, im sure that's it. i angled the motor down and to right from the cockpit view and now it doesn't have any real stability issues, just cant fight the wind(12mph). could i throw it diagonal into the wind so it doesn't get blow backwards?

EDIT: yay! i got it up once.... and only once it was wierd; i put it up to 100% thr, gave it a nice big toss and up it went and i had control of it for about 30sec(fighting the wind the whole time) and then it got stuck in some rows of corn, but after i got it out i couldn't get it to go back up. too bad the cam wasnt on when it worked that one time

i think im just gonna get some new foam and rebuild it properly as its taken quite a beating so far :P
That is a lot of wind to deal with for a maiden flight, if you can patch it up and wait for a calm day I'd think things could go a lot better.

Get it flying and then add the cam is my advice.

Jack
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Old Aug 15, 2012, 04:36 PM
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United States, AL, Northport
Joined Jun 2012
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Quote:
Originally Posted by sirbow2 View Post
ok, im sure that's it. i angled the motor down and to right from the cockpit view and now it doesn't have any real stability issues, just cant fight the wind(12mph). could i throw it diagonal into the wind so it doesn't get blow backwards?

EDIT: yay! i got it up once.... and only once it was wierd; i put it up to 100% thr, gave it a nice big toss and up it went and i had control of it for about 30sec(fighting the wind the whole time) and then it got stuck in some rows of corn, but after i got it out i couldn't get it to go back up. too bad the cam wasnt on when it worked that one time

i think im just gonna get some new foam and rebuild it properly as its taken quite a beating so far :P

If you do rebuild I suggest white Gorilla Glue and masking tape instead of hot glue. Regular Gorilla Glue is ok to use also if you can't find white, it just foams up more and takes longer to dry.
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