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1/2a line length?

Old 11-27-2008, 06:44 AM
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Default 1/2a line length?

hi all, i have just finnished building a goldberg 21.5" 1/2a mustang for my son, it has a cox049 in it, i flew a lot of control line as a kid and teen but dont remember what length the 1/2a lines were, any help would be appreciated? also are there any plans for a suitable handle that could be made out of wood? thanks Greg
Old 11-27-2008, 12:25 PM
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Default RE: 1/2a line length?

35' would be a good place to start .008 dia.
Old 11-27-2008, 05:57 PM
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Default RE: 1/2a line length?

I agree on the 35 foot length. You didn't mention what Cox engine you are using. If product engine / Sure Start, or Baby Bee 35 would do. If using a Black Widow, I would go 40. Just a personal preference.
Old 11-27-2008, 06:25 PM
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Default RE: 1/2a line length?

I also like .012" lines. they are plenty small enough and less fragile. the standard lengths for 1\2 A competition are 35'-42' length depending on the event.
Old 11-27-2008, 07:11 PM
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Default RE: 1/2a line length?

We use dacron line typically sold with a 1/2a handle at the hobby shop. Usually there is 60 to 70 feet of dacron line on the spool which will result in lines about 30 to 70 feet long. A good starting point is 30 ft, which will work well in most cases. You can adjust the line length for the plane and engine combination and resulting line tension. For a slower plane use 28 ft or so and for faster planes try 35 ft.

Kevlar fishing line works well but is expensive. Typically sold as Spyder wire at Wally World.

We fly 1/2a all summer long and rarely break a line using the dacron stuff. Not one break all last summer! It's very cheap and strong. Less than $1.00 for a spool, change it when it gets frayed or really dirty. You can buy it from Sig, Brodak, or Tower Hobbies if not available from your local hobby store. Send me a PM and I'll send you some.

Braided cable can be used but is very fragile and much more expensive. Use .008 for 1/2a. I've never tried .012 for 1/2a, I think it is way too heavy for the typical cox motor to haul around. Probably OK for a 1/2a plane with a Norvel on the snout. Norvel engines have much more power. .012 cable is usually used with planes powered with .09 to .19 size engines as I recall.

Don't spend too much time worrying about it! Get some string and have fun!
Old 11-28-2008, 01:39 AM
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Default RE: 1/2a line length?

thanks for the replies, i thought the lines would be 1/2 of what you guys are suggesting, lucky i asked or i might of ended up very dizzy. the motor is a standard cox 049 with the spring starter ( it came of a kyosho cessna foam plane from the 80s) i have run the motor up in the mustang and it has better than 1 :1 thrust. i was thinking i could use some braided fishing line as i have some 14lb on a reel. again thanks for your replies. regards Greg
i will post results of the maiden soon.
Old 11-28-2008, 11:09 AM
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Default RE: 1/2a line length?

The .012" lines will still be cleaner in the air than any dacron and spiderwire and these are also what is required for competition. In mouse racing, .012" 42' lines are required. While .008" may be preffered for performance and sport flying they are fragile and if going with braided steel lines, the beginner would be better off with the larger .012" I believe.
This is certainly something to worry about later though and I would concentrate on getting in the air. Availability of these items will be a big factor. I have always bought my lines in bulk (being a combat flyer) so I have plenty laying around.
Also remember that when you begin to do aerobatics, the longer lines actually give you more room to manuever. I would not suggest going under 35'. You lap times could be so short that you could get dizzy.
Old 11-29-2008, 04:12 AM
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Default RE: 1/2a line length?

One last question which isnt covered in the instructions, where should the c of g be? should it be on the bellcrank or forward or aft of it? thanks Greg
Old 11-29-2008, 06:02 AM
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Default RE: 1/2a line length?


ORIGINAL: Gregor32
One last question which isnt covered in the instructions, where should the c of g be? should it be on the bellcrank or forward or aft of it? thanks Greg
Greg,

On most planes it ranges from the leading edge of the wing, to 25% of the wing chord back from the LE. The further back, the less stable but more maneuverable. I can't answer for that specific plane, never built one.

George
Old 11-29-2008, 12:11 PM
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Default RE: 1/2a line length?


ORIGINAL: Gregor32

One last question which isnt covered in the instructions, where should the c of g be? should it be on the bellcrank or forward or aft of it? thanks Greg
Typically on a proven design such as one that has been kitted, the CG will fall ahead of the bellcrank mounting screw and the hole where the leadout attaches on the bellcrank.

Look on the this plane and you will see a line above the wing just ahead of the bellcrank mounting screw and the words "BALANCE LINE".
On most all C/L planes you do not want the CG to fall behind the Bellcrank mounting screw as this will have very adverse effects for controlled flight.

I hope this helps some.

Robert
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Old 11-29-2008, 02:39 PM
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Default RE: 1/2a line length?


ORIGINAL: build light


ORIGINAL: Gregor32

One last question which isnt covered in the instructions, where should the c of g be? should it be on the bellcrank or forward or aft of it? thanks Greg
Typically on a proven design such as one that has been kitted, the CG will fall ahead of the bellcrank mounting screw and the hole where the leadout attaches on the bellcrank.

Look on the this plane and you will see a line above the wing just ahead of the bellcrank mounting screw and the words "BALANCE LINE".
On most all C/L planes you do not want the CG to fall behind the Bellcrank mounting screw as this will have very adverse effects for controlled flight.

I hope this helps some.

Robert
Sorry, but this is not a good rule of thumb. The bellcrank location has nothing to do with the ballance. The airplane needs to balance at the center of pressure of the given airfoil used. the leadout needs to be slightly behind this for proper line tension.
A friend of mine designed a 1\2 A combat model with the bellcrank mounted just ahead of the stab just to prove that bellcrank location did not matter. It is the leadout location that matters.
Now, generally kits place the bellcrank near the CG so you have a straight shot to the leadout guide, but I would never calculate CG by the location of the bellcrank.
the 25%-30% rule is a safer bet for most airfoils. I would go with the 25% on a plate airfoil to start with to be safe.
Old 11-29-2008, 06:37 PM
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Default RE: 1/2a line length?

Quote by vertcal grimmace:
"Now, generally kits place the bellcrank near the CG so you have a straight shot to the leadout guide,"

This agrees with what I said in my last post. A model purposly designed with the bellcrank mounted just ahead of the stab just to prove that bellcrank location did not matter is simply to make a point and not establish a norm.
I have a plan for a halfA control line which uses no bellcrank at all. I have not built it nor do I see any reason it would not fly as designed. It too relies on the leadout position just as does your friends combat design.

Calculating a CG is as you said, "the 25%-30% rule is a safer bet for most airfoils." is quite true but I was trying to help Gregor32 with his Goldberg (kitted) 21.5" 1/2a mustang.

I did not imply my statement was to be used as a rule of thumb reference for calculating CG on any plane.

Gregor32, Please have fun with your pland and your son, That is what matters most. Try to make sure there is no wind if possible.

Robert
Old 11-29-2008, 07:17 PM
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Default RE: 1/2a line length?

I think you've pretty much got the line length covered, CG opinions can vary a bit, best to start out closer to the leading edge then work it back until becomes responsive to your liking.

some good info can be found here...

http://www.aeromaniacs.com/Benchtrim.htm

http://www.aeromaniacs.com/Tips.html

http://www.aeromaniacs.com/
Old 11-30-2008, 06:27 AM
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Default RE: 1/2a line length?

thanks again for all the info in your replies, at the moment the balance is right on the leading edge, im not sure if it should be further back as i have covered the pane with solarfilm and this may be lighter than the manufacture had designed it to be when painted. but it is intended as a beginner plane, i will fly it this week as is and see how it performs. regards Greg
Old 11-30-2008, 08:27 AM
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Default RE: 1/2a line length?

That is not a bad place to start. Nose heavy is always preferred to tail heavy when it comes to CG.
Being nose heavy, it will be less responsive to elevator inputs. Not a bad thing for first flights. You can always move the CG back little by little till it "feels" right to you. You might then move it just a bit further back to see how that feels. You might then see how well it performs and leave it there!
Just don't exceed 30% behind the leading edge. If you ever do you might find out why!

Remember just add little bits of weight to the tail to get her where you want her to balance.
This is all part of the fun of flying. So have fun you two!

Robert

Old 12-01-2008, 04:26 AM
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Default RE: 1/2a line length?

Greg,

Melbourne has some great CL clubs with some of the best & most helpful blokes in Oz. Do a google search to find the one nearest to you and fly with them.

Their collected wisdom will save you many tears.

Good luck to you and your son. Beware when the boy becomes so hooked you've got to take him flying every weekend.

Regards

Greg
Old 12-06-2008, 09:21 PM
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Default RE: 1/2a line length?

an update, we did the maiden today, the conditions were not good with a stiff breeze blowing but my son would not take no for an answer, so i had a friend help with a hand launch and all went well for the maiden i did have to watch the line tention when flying into and accross the wind, my son was next and he didnt know to step back to keep the lines tight and it nosed in on the first curcuit and broke the prop[X(] he was a bit upset but realized the wind was the problem so we will try again as soon as i get a new prop. any sugestions on what size? i think it had a 6x3 is this ok? the writing has worn off. cheers Greg
ps the line lenghth was right, thanks
Old 12-07-2008, 07:22 PM
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Default RE: 1/2a line length?

On the .049 I always like a 5x3.
Old 12-07-2008, 09:58 PM
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Default RE: 1/2a line length?

There is a Cal Smith 1/2A CL design called the 'Teenie Geenie'. It had, he said "centrifugal stability" and was balanced on the leading edge. On your usual 1/2A, leading edge to about 10% chord back is the good range. I've flown the AMA pattern with success in 1/2A stunt competitions with airplanes which balanced on the leading edge of the wing.
Old 12-08-2008, 11:23 AM
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Default RE: 1/2a line length?

Congrats on the flight! Welcome to the wonderfrul world of CL flight. Nose heavy will help in the wind along with a more rearward leadout location. This will be beneficial at this stage since you are just trying to get around the circle. When learning stunt that is when you want to move the CG back. 1\2 A's are a lot of fun but maybe you could start thinking about a .35 size profile ship. They really hang out there well and are great fun. Good luck.
Old 12-14-2008, 02:57 AM
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Default RE: 1/2a line length?

I have two Cox planes. One was delivered with a 6 x3 and one with a 5 x 3. The 6 x3 is on a very light Extra 300S and the 5 x 3 is on a larger heavier Hiper Viper, you be the judge. Either will work well. If you are going to spend a-lot of time with cox engines PM me and I'll get you two very reliable sources for engine parts, props and advice. I personally would avoid the new Sure Starts like the plague. You should also invest in a piston pin seating tool available from Davis Deisel. The performance of the .049/.051s falls off dramatically when the con rod to piston fit gets loose - and they WILL. The "new" Sure Starts need this treatment right out of the box before any fuel is put in.

Bill
Old 12-16-2008, 01:31 AM
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Default RE: 1/2a line length?

Thanks again for the replies, i could only get a MA 6x3 prop which seems to fly the plane well, we have had a very succesfull outing with my son having his first proper flights, he managed to fly a full tank of fuel a number of times on the day (he loves it) i even managed to have a go! yes i loved it to! anyway the cofg is
definatly wrong and i will be trying a more rearward position this weekend. i found that level flight requires about 10deg of up elevator and the responce is very sluggish/poor. cheers Greg
Old 12-16-2008, 10:31 AM
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Default RE: 1/2a line length?

There is a useful saying. You can move the CG back on a nose heavy airplane. You may be able to repair a tail heavy airplane.
Old 12-19-2008, 03:17 AM
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Default RE: 1/2a line length?

the responce is very sluggish/poor
Actually this sounds just about right for a first flight trainer. Move the CG back in small increments to where it does what you want, and congrats on the flight of your model.

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