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Pre stretching cable/ Prop differences

Old 02-26-2002, 03:13 PM
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Blackie
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Default Pre stretching cable/ Prop differences

I have my cables hanging with a rough 10 pound weights on the other end. How long should I leave these up before I take them down.

I was wondering if there was a web site that offers a chart or diagram as to the diameter and pitch differences.

I am accustomed to boat props somewhat but have no idea about plane props.

Thanks
Blackie
Old 02-26-2002, 07:09 PM
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Default Pre stretching cable/ Prop differences

Elaborate Please
Old 02-26-2002, 07:13 PM
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KingAirJockey
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Default Pre stretching cable/ Prop differences

huh?
Old 02-26-2002, 11:16 PM
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Blackie
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Default Pre stretching cable/ Prop differences

Not clear enough? sorry I will try and be a bit more clear.


A pull-pull cable system over time will stretch in the plane, I was told to hang them up and place a 10 pound weight on one end for a given time before installing in the plane to pre-stretch the cable. The time given I am not sure of.

On the prop issue, I am familiar with boat props but not plane props.

ie: A 19 pitch boat prop offers low end torque but takes away from top end speed. A 21 pitch boat prop offers low torque out of the hole but give more top end speed.

I was just curious to know how a plane prop works dia/pitch etc....

Thanks
Blackie
Old 02-27-2002, 12:07 AM
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Hanger Rat
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Default Pre stretching cable/ Prop differences

I think someone was putting you on. A pull pull cable will not lengthen or shorten merely by moving an elevator. the only thing that alters the length is summer heat and winter cold. When you set up your pull pull you must put an adjustable clevis at one end of each cable and check and adjust the tension at the start of every flight day. Plane props work the same as ship props, only one turns in the air the other turns in water and the pitch determins how far forward you move at each revolution.
Old 02-27-2002, 01:09 AM
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Ed Smith
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Default Pre stretching cable/ Prop differences

Do you hang your cables from skyhooks hammered in with a left handed hammer?

Ed S
Old 02-27-2002, 02:40 AM
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Blackie
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Default Pre stretching cable/ Prop differences

Ed thats so old is that your best? Tell you what, why don't you go ask your mommy for a better one.
Old 02-27-2002, 05:38 AM
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Default Pre stretching cable/ Prop differences

Oh now THAT was FUNNY!

Blackie, what airplane and what engine?
Old 02-27-2002, 11:39 AM
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Blackie
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Default Pre stretching cable/ Prop differences

Jazzy thanks for asking

I am almost finished with my AW 540 T 90 size edge. I am powering it with a saito 100.

Keep in mind ( you may have read in previous post ) that I am only 9 months into the hobby and some of the members think I am moving to fast. I believe if I tame it down a bit I should be ok.

Thanks
Blackie
Old 02-27-2002, 11:40 AM
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Ed Smith
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Default Pre stretching cable/ Prop differences

Blackie,

I am an old guy, what do you expect. My Mommy died a while ago

Ed S
Old 02-27-2002, 08:09 PM
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Rodney
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Default Pre stretching cable/ Prop differences

I don't know what kind of cable you are using but I have used nylon coated braided steel fishing line for years--all the way from 30 pound test to 120 pound test and it does not stretch. I don't even notice a change with extreem temperature changes. I have also used 50 lb. test nylon leader on both elevator and rudder on a quarter scale Cub with no evidence of stretch over a two year period. I was always leary of the nylon leader material so watched it closely for any ill effects and found none.
Old 02-28-2002, 02:36 AM
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Default Pre stretching cable/ Prop differences

Blackie,
I don't have a Saito 100 but, I would probably start with a 15X6. I'd also be thinking about a 15X8 and a 16X6.
Do you have the desrtuctions for the engine? They will give you a range of props this engine can handle. Just remember, the bigger the prop, (diameter), the harder it is to spin it. That is where pitch comes into play.

9 months into the hobby and you're about to fly an Edge? What else have you flown that would bring you up to this level?

That bit about pre-stretching cables... certainly was amusing. Did someone really tell you to do that?
Ed was just joking with you. We in this hobby like to have fun. Giving and taking jibes is something we all do at one time or another. Some more than others. Try to relax and have some fun with it.

Jeff
Old 02-28-2002, 04:05 AM
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Blackie
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Default Pre stretching cable/ Prop differences

Aside the trainer (avistar) I also have a WM super stunts 60 which flies like a big kite and an H9 Aristi, the edge makes my forth.

The cable thing I have heard more then once from club members and not all at the same time nor from the same members. And yes one of out most experienced pilots told me to hang the weights. There is another member that flies the big birds told me to use kevlar that it won't stretch over time. As a matter of fact I have had to go in and re-tighten my cables on the pull-pull system on my super stunts 60 *shrugs*

Getting back to the remark Ed made, since I don't know him and I certainly can't see his expression's maybe a smily face or a just kidding would have serviced. All that aside sorry to hear your mother's passing Ed
Old 02-28-2002, 04:15 AM
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Default Pre stretching cable/ Prop differences

Blackie there is absolutely no sense in hanging weights on your cables. Think about it, if these cables stretched with a 20lb weight or whatever what do you think it would be like to fight a couple of hundred pounds of swordfish with the same cable?
Old 02-28-2002, 02:47 PM
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Steve Campbell2
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Default Pre stretching cable/ Prop differences

Good point, Hanger Rat; IF the cables were of the same constitution as fishing leaders, whatever.

This intrigues me. While I'm certainly not new to the hobby, I AM new to big planes; just started assembling a H9 1/4 scale CAP. I've used plenty of closed-loop control systems on helicopters, but all with pushrods and ball links.

This kit comes with a cable pull-pull for the rudder; a first for me. The airplane will weigh around 13 pounds, and no doubt there will be a lot of stress on those cables. We know for a fact that metal has a certain degree of elasticity; usually more in shear than compression/tension, but it's there nonetheless. The question is, will it stretch enough to be noticeable?

Blackie's last post regarding his airplane would seem to indicate that it does.

I would be interested to hear any other thoughts on this.

Steve
Old 02-28-2002, 07:07 PM
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Default Pre stretching cable/ Prop differences

Steve, believe me your pull pull rudder cables (maybe 3 ft long ) will not stretch enough to need one click of rudder adjustment on your tx. These cables do get sloppy sometimes but its for reasons other than stretch. And what about the other side of the puzzle? If, and I say if, you can stretch this cable what happens later? Does it at some time revert to it's old length and shorten?

Remember when duck fly upside down he have quack up.
Old 02-28-2002, 07:53 PM
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Default Pre stretching cable/ Prop differences

Originally posted by Hanger Rat
If, and I say if, you can stretch this cable what happens later? Does it at some time revert to it's old length and shorten?

Provided that the material is only being deformed in the elastic range then yes.
Old 06-02-2002, 09:26 AM
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Default Still stretching

Please explain to me why my pull-pull cables keep coming loose over time?

If the cables are not stretching then whats going on? please tell me. I have two planes that are giving me this problem.

When I tighten them I am making sure to remove the clevis from the eyes so the cable does not twist back.

Thanks
Randy
Old 06-02-2002, 11:58 AM
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Default Pre stretching cable/ Prop differences

I was under the same impression concerning the pull pull cables. I believe I read it on the DP site but don't hold me to that. Their explanation was not that the braided cable would stretch but that it would relax, when under pressure with all of the engine vibration, to its full length. This would require re adjustment after your first few tanks of fuel only and gave the impression that it would not be an ongoing problem.

Jeff

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Old 06-03-2002, 03:37 AM
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Ted Farmin
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Default Pre stretching cable/ Prop differences

I don't think cables stretch. Has the Golden gate bridge started to
sag? I would look for slack coming from your servo moving as the
rubber gommets settle into the mounting screws or nylon horns
flexing or horns compressing into wood or crimpeded clamps slipping on cable or as happened to me allthread horn on rudder
bending. Study the hole system carefully and I think you will solve
your problem.
Old 06-04-2002, 02:42 AM
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Ted Farmin
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Default Pre stretching cable/ Prop differences

Blackie, as a experienced pattern and Imac flyer and with your
9 months experience I would recommend that you have an experienced aerobatic flyer get on a trainer box with you for about 12 flights when you fly the 540. Also as a full scale flight instructor there is no need to crash any airplane and a little dull instrction never hurt anyone.
Old 06-04-2002, 09:48 AM
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Blackie
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Default Pre stretching cable/ Prop differences

Ted, actually I have had it up a good several times now and had only one incident which was this past week end. Lucky enough I did what I was told to do and that was neutralize the controls and power out of the tip stall. While coming out of a knife at only two mistakes maybe two and a half high it tipped out from under me and tumbled twice before I was able to gain control, the area where it tipped was just over our tree line and the plane barely did fly out of the trees. That was a wake up call, as far as normal flight the plane flies like a glider with an engine.

As far as just following the pattern the plane flies very easy and the next time I decide to practice any type of 3D I will make sure it has plenty of hight for me to recover.

As far as your recommendation I will take it into consideration especially when I am trying to do 3D stuff.

I do have an little H9 Aresti that I can knife and other things with very well so I believe I will just stick with it when I try to learn the 3D stuff and just fly the Edge in the pattern until ready.

Randy
Old 06-04-2002, 04:37 PM
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Default Pre stretching cable/ Prop differences

Ted is correct, these cables do not stretch; I have two planes well over 5 years old and still flying with cable on elevator and rudder and they have required no adjustments in that time. These are big birds, 17 pounds or more with lots of use.
Old 06-04-2002, 07:05 PM
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Default Pre stretching cable/ Prop differences

personally I think what happens is that when you crimp the wire when new there is allways a tiny loop in the line around the crimp that under stress pulls thru until it tightens completely around the crimp tube, that and the plastic parts (horns etc) will wear just a bit
with time, also if you adjust the tightness on one end and the cable turns (not just the clevis) with vibration it will work it's way back out because you have induced a twist in the line

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