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3-line control systems - 7/7/2007 7:14:15 PM   
EF


 

Posts: 238
Joined: 2/25/2005
From: HAIFA, ISRAEL
Status: offline 		I noticed this is used for CL scale models.

Questions:
1) how does it work? is the third line working against some kind of spring?
I saw the many 3-line bellcranks offered by Brodak, but could not see how they work or what the differences between them are.

2) Is a 3-line handle suitable for 2-line models too or is it better to have separate handles?

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Erez
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RE: 3-line control systems - 7/7/2007 8:05:12 PM   
smcouch77



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Joined: 10/31/2006
From: Indianapolis, IN, USA
Status: offline 		The three line system works by changing the length of the third line relative to the main lines which control the elevator. It's kind of tricky to operate. A lot of guys are going to electronic controls with servos to operate the throttle and other functions. Clancy Arnold makes units from one channel up to, I think, nine. Not very expensive and very easy to use.
You can use a three line handle for a two line plane, but they are pretty bulky.
Steve

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RE: 3-line control systems - 7/7/2007 8:22:41 PM   
EF


 

Posts: 238
Joined: 2/25/2005
From: HAIFA, ISRAEL
Status: offline 		Thanks, where can I find the Clancy Arnold system? couldn't find it, does he have web site?

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Erez

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RE: 3-line control systems - 7/7/2007 9:38:37 PM   
smcouch77



Posts: 659
Joined: 10/31/2006
From: Indianapolis, IN, USA
Status: offline 		Here's Clancy's info.

Clancy Arnold
317-387-1940
clancyarnold@juno.com

Give him a call. He's a real nice man to do business with. I have his controls in two planes and they work great.
Steve

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RE: 3-line control systems - 7/8/2007 7:25:31 AM   
cutaway


 

Posts: 339
Joined: 6/25/2007
From: Lake Worth, FL, USA
Status: offline 		A "poor man's" 3-line bellcrank can be made out of two ordinary two-line ones. Fox steel ones would be great. Aluminum Perfect's can work, but I wouldn't put a "big" plane on them...may .19-.25 max.

Keep one stock - that's the elevator, then mount that one on a second one just to the rear of the pivot by maybe 1/2" or so, and chop off the remaining part of that arm.

Now what you have is an ordinary crank that will move a bit from inboard to outboard as the throttle line is pulled, but not enough to screw around with the controls enough to be noticeable .

What needs to be done next is mount a wedge/pin/bolt into the crank mount to limit the outboard motion of the throttle crank arm because all your 2-line tension will be trying to pull towards the inboard (making the throttle crank arm swing outboard mashing ribs and such. A wedge/pin/bolt limiting its swing to maybe 30 degrees or so seems to work OK. Most throttles won't need much movement, and if you started with 3" cranks, the arm the throttle rod goes on has a lot of swing already

I've built and used a few of these and they work quite well. Not as fancy as an old Walker style with arcing grooved pivots and such but cheap, effective, and durable.

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RE: 3-line control systems - 7/8/2007 5:34:30 PM   
EF


 

Posts: 238
Joined: 2/25/2005
From: HAIFA, ISRAEL
Status: offline 		Well, from cutaway's response I understand (and correct me if I'm wrong) that while "up" and "down" work against one another, both "up and down" work together against the throttle or third line? that would explain what the third line is pulling against...

But now, going back to Brodak's large selection of 3-line bellcranks, apart form the actual size, what are the differences?
I mean - some say they are for an inverted engine and some for an upright one, but if I use a flexible throttle cable - what does it matter?
Also - some say the "up" line is the front one and not the back - what is the significance of this?
And finlly, how effective is this 3-line throttle control during taxi? (is it really possible to taxi the model around the circle reliably?)

Sorry for so many questions...but I don't know anyone who flys this type of model...

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RE: 3-line control systems - 7/8/2007 6:06:36 PM   
R8893


 

Posts: 421
Joined: 10/19/2002
From: Cincinnati, OH,
Status: online 		Cutaways description is correct. I would add one thing. The second bellcrank is mounted exactly half the distance between the bolt and the line connection. All three lines will have equal tension. It is an example of the kids on a teeter totter balance that we all did in grade school. With a single bellcrank both lines have equal tension and the full reaction force is on the pivot bolt. NOw consider adding another bell crank on the first one. Only in this case the new bell crank will have its center bolt exactly half the distance out one arm of the first bellcrank. There will be two line attached to this second bellcrank. The first bell crank is still ballanced because we have the force from two lines but the moment arm is only half. This is how a Brodak bellcrank is configured if you know how to look for it. In practice the first bellcrank is hooked to the throttle and the second one mounted to it goes to the elevator. There will be equal tension in all the lines. Working the elevator does not affect the throttle. Working the throttle will actually have a minor effect on the distance from the handle to the model. You will now rightly conclude that there is going to be some "monkey motion" at the handle to make this all simple and that is what is inside the three-line handle Brodak sells. For this system to work there must be tension in the lines. If they are slack you get no throttle or elevator response. This can be an issue when you are taxying the model. In this case the electronic systems mentioned by Steve are a real advantage. All my old carrier event models used three-line systems and I have one scale model on three-line. All the others are electronic, but I use JR radios in the Direct Servo Control mode. Another reason for not using the three-line handle for a two line model is that the three-line handle does not have any adjustment to neutralize the elevator.

EF just noticed your last post while I was slowly typing my response. The up or inverted version really doesn't matter and it relates to how the bellcrank is mounted in the model, not you engine mounting. One or the other may be easier to install in your model. I set mine so that you get full throttle when both elevation lines are pulled. With the upright bellcrank this causes the throttle link to move to the rear. This is backwards from most engine throttle arms, so you have to have a reversing bellcrank in the system someplace. Setting up a throttle linkage that moves in the proper direction and has low friction is a challenge. I have never worried about which leadout was the up vs. down line--however the really serious stunt pilots seem to think it matters. Yes a reliable taxi is possible (required in F4B competition) but see my comment about line tension above. Please ask all the questions you want and if our responses don't make sense ask us to explain again.
Chuck

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RE: 3-line control systems - 7/8/2007 6:07:28 PM   
smcouch77



Posts: 659
Joined: 10/31/2006
From: Indianapolis, IN, USA
Status: offline 		If you are using a flex cable for throttle, it shouldnt make a difference wether the engine is upright or inverted. As to the front or back line being up, it does make a difference. If the elevator control horn is above the elevator, then pulling on the rear line will make the plane dive. If it's below, it will make the plane climb. It's usually below, but you need to look at the side view of your plans and order acordingly.
Yes, you can taxi, but as you have guessed, it isn't easy. Like I said before, electric controls are much easier to use.
Don't worry about asking questions. Us old farts just love to give advice.
Steve

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RE: 3-line control systems - 7/8/2007 6:55:55 PM   
cutaway


 

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From: Lake Worth, FL, USA
Status: offline 		"both "up and down" work together against the throttle or third line?"

Yea, yanking the throttle line actually levers the "normal" elevator crank to the outboard a bit. A Walker crank scheme mitigates this, but at the expense of much greater complexity. As a practical matter, it really doesn't matter ;->

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RE: 3-line control systems - 7/8/2007 6:58:38 PM   
EF


 

Posts: 238
Joined: 2/25/2005
From: HAIFA, ISRAEL
Status: offline 		Thanks everyone, I appreciate all this wealth of information!

I have sent an e-mail to Calncy Arnold requesting some technical and commercial info.

BTW, does using his system require insulated wires and if so are they significantly thicker in diameter and does this mean they need to be shorter than when flying the same model size with "normal" lines?
It does seem that electronic control is simpler.

I used to fly stunt many years ago (mid seventies), and have concentrated since on scale RC.
I will probably first build a simple 2-line stunt model just to get back into things, but my scale interest will probably eventually lead me to scale CL models.

I have some 30-40 year old plans for 35-46 stunt models, some I have never built, and it should be very interesting to go back and build them...

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RE: 3-line control systems - 7/8/2007 9:09:12 PM   
R8893


 

Posts: 421
Joined: 10/19/2002
From: Cincinnati, OH,
Status: online 		EF,
Yes you do need insulated lines--at least one of them. I have one model, a deHavilland Hornet with both lines insulated. It seems to me that there is a lot of friction between the lines and I have trouble maintaining smooth control around neutral. I have three other models with only one line insulated--the signal. I leave the ground (earth) line uninsulated. I prefer this method. The insulated line is significantly thicker and creates more drag. Two of my models are rather heavy--close to 7 kilograms--and our rules require a line diameter of 0.027 inches of the steel cable. With insulation these lines are about 0.038 inches. The Hornet weighs about 3.5 kg and has two .30 cubic inch engines and two insulated lines this size. Because of the drag I have shortened the lines to about 55 feet. The two heavy models, a Typhoon and Henschel 129 have lines about 65 feet and only one insulated line. In flight the insulated line can be seen trailing behind the uninsulated one and this causes the controls to move off neutral. Both models use the insulated line on the "up" line and I set my handle to give about 1/8" down elevator when my hand is neutral. Here in the USA we purchase fishing line that is nylon coated to use for our flying lines.

If your radio systems have direct servo control you can easily use them in the control line model.
Chuck

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RE: 3-line control systems - 7/9/2007 4:10:19 PM   
EF


 

Posts: 238
Joined: 2/25/2005
From: HAIFA, ISRAEL
Status: offline 		R8893 this is very interesting – obviously there is no "something for nothing" – each approach (3-line vs. electronic control) has its advantages and limitations.

Is it practical, on a non-aerobatic scale model that you do not plan to loop, to use non insulated lines (both)?
In such a case using maybe a safety switch in the handle, that would only initiate the system prior to takeoff when you are holding the handle and thus ensuring no contact between the lines?
Has anyone tried this?

Also, reading what you have written about your scale models leads me to another question – what is considered a "sensible" size limit for a CL scale model?
For example – would Nick Ziroli's 101" span B-25 be practical and if so, using what engines and line lengths?
Is there some rule-of-thumb on model wingspan, weight, engine capacity, and line lengths for 2 or 3 line systems?





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RE: 3-line control systems - 7/9/2007 6:18:48 PM   
R8893


 

Posts: 421
Joined: 10/19/2002
From: Cincinnati, OH,
Status: online 		EF,
I am quite certain there must be at least one insulated line. The signal amperage is very small (this makes it possible to use the steel lines which have high resistance) and it is very easy to create a short circuit. I learned this the hard way!

Regarding the size of models. The international rules from the FAI (class F4B) allow models of a single engine plane to weigh a maximum of 6 kg. A multi engine model can be 7 kg--hence the 6.85 kg my Henschel weighs. In the USA we can go to 20 pounds, (9 kg) in our Sport Scale class. I participated in the last two World Championships and most of the models were very close to the weight limit. The top Polish competitor managed to build a Fairey Battle with a 2.3 meter span at less than 6 kilos! I sure can't build that light. I am a believer that bigger models fly better, and your question suggests that you do too. However the pull on the lines gets to where it is no longer fun to fly the models. I recently finished a Aichi D3A1 Val dive bomber from the Skyshark kit (no longer available) that I think is a good compromise of wing area, weight, line tension, flyability, and transportability. It weighs 3.4 kg, has a .60 engine, and about 0.5 sq meters of wing area. The Val is the best flying of the scale models I have. The FAI rules also have wing loading rules, but if you went over the limit the model would be so heavy it would not fly well anyhow.

The FAI rules also limit line length to 21.5 meters and our rules for other classes are 21.3 meters. Most of our flying fields are not big enough to permit longer lines.

Chuck

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RE: 3-line control systems - 7/10/2007 5:29:20 PM   
clscale-RCU


 

Posts: 426
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From: Wichita, KS, USA
Status: offline 		I also fly with electronic controls and have flown with everything but the Clancy Arnold system. I currently use the JR radios with DSC and single channel (servo driver) for my airplanes. I have a book available on these systems if you are interested. I don't like 3-line because they only work if you have line tension and can only operate 1 system.

I have currently started to fly Carrier with electronic controls

Fred Cronenwett

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RE: 3-line control systems - 7/10/2007 8:04:29 PM   
EF


 

Posts: 238
Joined: 2/25/2005
From: HAIFA, ISRAEL
Status: offline 		Would a servo tester like the one here:
http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXVK79&P=0
be suitable for operating a throttle servo for example?
Would it be installed on the handle, use one insulated line, battery in the handle, and a servo in the model?

On second thought, how do you run 3 wires through 2 lines...?

< Message edited by EF -- 7/10/2007 8:16:43 PM >

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RE: 3-line control systems - 7/10/2007 9:55:24 PM   
R8893