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All Forums >> RC Airplanes >> 3D Flying! >> electronic weight jack
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electronic weight jack - 2/22/2002 7:48:40 PM   
stevezero



Posts: 813
Joined: 12/18/2001
From: Greensboro, NC, USA
Status: offline 		Has anyone thought or tried using a sailboat winch servo (three full revolutions on the head, end point to end point), with a cable and pulley system, to have an adjustable weight jack? You could put 1-3 oz of weight on the cable, have a pulley near the tail, and use the landing gear channel and atv to move your cg from precision and somewhat stable location, to " holy cow did you see that ", and then back to stable for landing. Wingspan99 and I have been talking about how to work this out, and it would definately be easier on a larger scale plane for many reasons. Access to the tail of the fuse is easier, the plane could handle the extra weight of the servo/pulley head, cable, and pulley system. And since most large scale planes need weight in the tail to balance, they could handle the extra and not see a degradation in performance. You could take a 2 oz weight, inline on the cable, and move it back upwards of 4-6 inches, depending on your pulley/head arrangement, which would alter your balance significantly. On a 15-20 lb plane, it wouldnt notice the overall weight increase, but it sure would boost performance, and sanity on landings.

They use weight jacks on race cars to alter thier balance during the race, why cant we do the same?

Feel free to give some input, positive, negative, or otherwise.

Steve
       Post #: 1

electronic weight jack - 2/22/2002 11:48:37 PM   
Cody-RCU



Posts: 395
Joined: 1/12/2002
From: Plaistow, NH, USA
Status: offline 		I don't know of anyone who has tried it, but I know it is illegal in IMAC contests.

(in reply to stevezero)
       Post #: 2

electronic weight jack - 2/22/2002 11:54:07 PM   
Phil Cole



Posts: 755
Joined: 1/27/2002
From: Redwood City, CA, USA
Status: offline 		I remember thinking it would be a good idea, but it wasn't an original thought on my part.

I read about in the TOC rule that specifically bans moveable CGs (and timed snap switches and a bunch of other stuff).

(in reply to stevezero)
       Post #: 3

A different twist - 2/23/2002 7:12:25 AM   
aerobat66-RCU



Posts: 131
Joined: 12/2/2001
From: Acworth, GA, USA
Status: offline 		A guy in my club was talking about the same idea. Then I thought: What about using water? Have 2 small fuel tanks strategically placed fore / aft, an electric fuel pump and a mini servo to operate the pump switch to fill / drain. Just pump water from one tank to another to adjust the C.G. Connect the vent from one tank to the other, and you have a closed system, and the air has somewhere to go when the water moves. Note the time it takes to transfer the water, and you would know when to turn the pump off. Power the pump with a second battery, or better yet, find one that takes AA cells in the pump. That way, if the pump locks up or something fails, you don't drain your radio battery.

Not necessarilly better than your idea, but something to think about.

John

(in reply to stevezero)
       Post #: 4

electronic weight jack - 2/23/2002 7:59:37 AM   
OnTheEdge



Posts: 1170
Joined: 1/14/2002
From: Drums, PA, USA
Status: offline 		I was discussing this once with a guy who used to build planes for a former TOC pilot. While he never tried this he said if you remove one of the wires from the pot on the servo (which one I don't know) the servo will turn indefinately. What he said to do is use a long piece of threaded rod attached to the output shaft of the servo, then put a micro switch on each end of the rod so that the balast weight hits the switch at the ends of rod, thus stopping the servo. How it's actually wired I don't know but it seems like it could work. I always thought to avoid adding extra weight, why not just use the Rx battery(s). Just make sure there is enough extra extention so the wires don't pull the connectors apart when the batteries are traveling down the worm gear (boy wouldn't that suck). In theory it seems like it could work but not sure in practicality.

_____________________________

Avoid zen aerobatics...when the ground........and the plane.......become as one.

(in reply to stevezero)
       Post #: 5

electronic weight jack - 2/24/2002 6:25:09 AM   
Diablo-RCU


 

Posts: 3208
Joined: 12/19/2001
From: Hammond, IN, USA
Status: offline 		Just keep in mind what would happen if your weight shifting device failed, you know Murphy's law. I can just see the water pumper crapping out. Sounds like the submarine that couldn't blow it's ballast tanks, so it kept sinking until it imploded. Make sure you have a video camera for the first flight.

(in reply to stevezero)
       Post #: 6

electronic weight jack - 2/24/2002 7:36:51 AM   
stevezero



Posts: 813
Joined: 12/18/2001
From: Greensboro, NC, USA
Status: offline 		How true Diablo. We keep joking that we need to just set up the camera on the tripod and let it run whenever we fly. I hear you can win 10,000 on Americas Funniest Home Videos for footage like that. Should almost cover the cost of a 50% plane smacking, right?

Actually, we were talking about this at work(have to do something productive there, right?). It would not be for competitive purposes, unless you call having the flight with the highest P-factor(pucker, that is). As for the Murphy's Law comment made earlier, we were talking about a not so radical CG change, could still be landable even with a servo failure (albeit with some extra speed and some down elevator)

(in reply to stevezero)
       Post #: 7

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