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Speed,Combat,Scale,Racing => Carrier => Topic started by: Dennis Toth on March 02, 2023, 07:41:58 AM
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Guys,
For ships equipped with a third line for engine throttle control that is not connected to the or secured by the bellcrank mount bolt, and not connected to any control surfaces considered a load bearing line? It seems that since its only function is to activate the carb throttle linkage it should not be subject to the pull test or size requirements? I assume the size limits are there to try and equalize the drag?
Best, DennisT
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I would say that if the two flight control lines comply with the rules the third line could be anything you want.
Here's the problem with a spring-loaded throttle:
Spring-loaded to HIGH: as the speed decreases you have a hard time overcoming the spring and getting all the way to idle.
Spring loaded to LOW: As the speed increases the drag on the speed line increases and keeps you from getting to full high speed. Also, with the plane stationary, you may not be able to pull it high speed enough to get moving.
Solving these issues by increasing or reducing spring loading generally causes a problem the other way.
That's why we use the J Roberts system or 2.4 RC.
Yes, I tried it once and didn't like it. This system appears on the plans of some early kits. I doubt that the designer actually made it work.
The J Roberts system actually does load-share properly and allows three lines of reasonable size. The stacked bellcrank system save the cost of a true J Roberts bellcrank.
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In the early days of Navy Carrier I won several contests using a spring loaded throttle system. It works with practice but the J-Roberts came out and the rest is history. Nothing like a Sterling Gaurdian with McCoy Red Head .60 on crank case pressure by Bill Johnson. It also took practice to get the metering system right. Then they started helicoptoring the planes and I never really got enough practice doing that. When I go fly my carrier planes it is stiil the old way with flaps and no sliding lead out guide. D>K
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If you look at the geometry of the J-Roberts or the Brodak 3-wire bellcrank, you'll see (after some hard thinking) that all the various lever arms are arranged so that each line carries 1/3 of the total line tension.
If you have one handy you can test this -- when you move the throttle line outward, the up and down lines pull inwards about 1/2 as much, and visa-versa.
This is necessary. Because you can't push on a rope, in order for the throttle "signal" to get transmitted to the plane via the line position, there must be tension on all the lines. For everything to work nicely, this tension needs to be evenly distributed.
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In the early days of Navy Carrier I won several contests using a spring loaded throttle system. It works with practice but the J-Roberts came out and the rest is history. Nothing like a Sterling Gaurdian with McCoy Red Head .60 on crank case pressure by Bill Johnson. It also took practice to get the metering system right. Then they started helicoptoring the planes and I never really got enough practice doing that. When I go fly my carrier planes it is stiil the old way with flaps and no sliding lead out guide. D>K
I agree that the spring CAN work if you are willing to settle for a 20-25 MPH low. But if you want to fly scale and do a dead stop and a taxi lap you will have a hard time. At this time you can still do 3-line for $100 or 2.4 RC for $60.
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I was flying at Whittier Narrows with an older experienced CL pilot with lots of flights using 3-line. He told me he was going to try the electronic controls but he was going to hate it. I told him I would buy everything from for the price he paid if he did hate it. We were flying with the servo driver single channel down the line electronic controls at the time.
After his first flight with the servo driver, he put in a normal flight. shut the motor down walked over to the three of us and asked "how do I convert those models right now". He never flew with 3-line again.
My go to system is 2.4 Ghz now since it's a wireless version of the down the line electronics we used from 1990 to 2013.
Fred
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There's a pretty broad spread of prices for radios -- which means that if you want throttle-only you can get in pretty cheap. If you want to have flaps or bomb-drop or whatever then things get more expensive or you have to get creative about how to use a cheap radio.
Tactic is a good brand for cheap-but-reliable. With the current geopolitical situation I wouldn't trust Chinese radios to be in good supply, but if you want to go really cheap check out Hobby King or other Chinese store fronts and shop by price -- don't come crying to me if China gets embargoed and you can't get parts, though.
If there's not already a thread on wiring up a plane for RC throttle control -- ask, ye shall receive.
Or go three-line and enjoy that nostalgic feeling of the throttle line catching on a weed and pulling full throttle when you're trying to taxi.
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With a basic three channel car radio you could use the throttle for throttle and the push button for the landing gear or brakes.
You can remove the spring from the steering wheel use it for flaps.
$40 radio, $4 per servo, and the battery pack is your problem. My solution is four AAA cells which come in handy as tip weight.
Or, for cost of a receiver, servo and four D-cells, you can be like me and use the push button for a self launching device.
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Dennis
The pull test in carrier includes everything connected to the handle including the safety thong. As long as the two up-down lines are the correct size for a two line control it seems to me that it would be OK to hook up the throttle line any way you want.
However with a Roberts type handle and bell crank all three lines are load bearing. That is why three lines systems can use smaller diameter lines than 2 line systems. In profile carrier for example three lines use .015 and two lines use .020.
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What John says is true.
So assuming that you are flying profile carrier you would need two .021" plus one .012" to do what you propose. A serious competitor would not use a setup that puts him at a disadvantage vs the other two systems.
So if you have the Up/Down handle in your right hand and the gas pedal in your left, the throttle pull will reduce the tension on the flight controls. How much is a matter of finesse.
The one time I messed with this idea resulted in a delima of strong or weak throttle spring. A weak spring allows line drag to move the throttle. A strong spring take too much pull off the up/down bellcrank.
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All three lines on the J Roberts system are load bearing. At the King Orange years ago I injured a spectator when the Throttle Line in the Handle failed . After the High Speed portion flying my Class 1 Skyraider the line throttle went to Full Throttle , after the engine finally quit (Almost Dizzy Pilot) I started yelling for the spectators to watch out and to get back from the circle. As the airplane slowed the line splayed out making the circle much larger eventually hitting someone while tearing off his glasses and cutting his face. DNF in Class 1 , First in Class 2 with 133 mph and a good slow with landing (Before Line Sliders)