View Full Version : Wing joiner rod.

04-18-2006, 03:01 AM
I recently picked up a Kyosho Soarus II sailplane on eBay. This plane has a 75", two piece wing. The wings attach to the fuselage by way of a steel joiner rod. I had one of these planes a while back and I know from experience that the steel joiner rod will bend. Can I replace the steel rod with a carbon fiber rod?

What I'm thinking about doing is to strip the covering off the underside of the wing, adding a full length strip of carbon fiber tape to the spar and then recovering the wing. Replacing the steel joiner rod with a section of carbon fiber rod of the same diameter would be the other mod I'd like to do. I'm thinking the carbon rod would be both stiffer and lighter. So, can I do the carbon for steel swap and if so do I use solid carbon or carbon tube?

04-18-2006, 08:37 AM
Yes you could replace steel rod with carbon But,and its a big but,when overstressed,carbon will break,whereas steel will bend. Stick to steel!
If your going to dismantle the wing,it may best to replace the existig steel rod with the next size up.

04-18-2006, 12:25 PM
So, can I do the carbon for steel swap and if so do I use solid carbon or carbon tube?

A tube is stronger than a rod. Didn't believe it myself and can't remember where I read it that convinced me otherwise.

I have no way to convince you other than I said so.:D


04-19-2006, 11:30 AM
Thanks for the help! I appreciate the advice.

04-23-2006, 04:25 PM
This may be a bit late ,but i'm not too sure that a tube is stronger than a rod.Weight for weight it will be (larger diameter than an equivalent rod) but dia for dia it will be weaker.I've tried to find a reference for this ,but with no luck.Does anyone out there know the definite answer?its an interesting point.

04-25-2006, 05:59 AM
Hi George(Warden)
Sorry I didn't get to say good bye at the float fly but my wife was having eye problems with the wind and we didn't stay long. I believe you were getting ready to fly when we left.
With your flying skills I wouldn't hesitate to use a carbon fibre rod. You will save a lot of weight as well. I just finisher doing a new TWINSTAR II. It has nothing but a carbon fibre tube as a joiner. As soon as I get a couple of prop adaptors I'll maiden the thing. I dont like the push on props they recomend you use.
I'll be looking forwaed to your next visit to the area. I'll order some better weather.

Fly safely


05-04-2006, 01:31 PM
Yeah, bill, thanks for the tour. I appreciate all the info. Sorry to hear about your wife.....it was a tad windy on that day. I know I've never flown off water when it was that windy before. My 69" Porterfield collegiate handled the wind fairly well but the little Soarstar had problems. Takeoffs and landings with the soarstar were no problem but taxiing the little plane just didn't work. As soon as I turned the plane so that I was dealing with a crosswind the plane would flip over. I had lots of fun and I'm planning on coming back in September.

Thanks again to all for the info on the joiner rod issue. I'm still not sure which way I'm going to go but I recently equipped the plane with lipo batteries so weight really isn't an issue. With that in mind, I may just stick with the steel rod.

05-05-2006, 02:24 AM
From my experience building an Astroflight 70 from the 1985 plans, stay with steel! I wanted to split the wing to make it easier to transport in the cab of my pickup truck, so used heavy wall tubing and a carbon fiber rod. Winds picked it up on the maiden flight and snapped the rod. It fluttered down from about 50ft. Amazingly enough, it didn't hurt anything. The helicopter-like motion going down cushioned the sudden stop at ground level! Could not get 1/2 of the broken rod out from the heavy wall aluminum tubing. Dulled up three drill bits getting most of it ground out. Put in 1/8in brass tubing with music wire inside that and joined the wing halves permanently with 30 min epoxy and Sig fiberglass cloth. Winds had calmed down a bit, so gave it another try. Over 40min in the air and only 1/2 the charge drained from the LiPoly! I love this plane! Specs are: 70in Wingspan, AUW including batt: 23oz. Wing loading of about 6oz sq ft. Power is an Eflite Park 400 outrunner, CC25 ESC, 3s1p 2100ma Lipoly, FMA direct dual conversion receiver and two eflite S-75 servos. I extended the nose two inches to compensate for the difference in weight between the Astroflight 05 and the outrunner. White monokote on the fuse, red and yellow transparent monokote on the "feathers". Can't afford the folder prop and spinner yet, so will use the 10x7 eflite with a prop saver.

06-12-2006, 08:12 PM
Google "DixiePins" They are hardened mold ejector pins, and they come in all kinds of decimal sizes.

06-13-2006, 01:36 PM
A tube is stronger than a rod. Didn't believe it myself and can't remember where I read it that convinced me otherwise.

More surface to take the stress?

06-14-2006, 02:28 AM
Somehow, I think that there is a part of the phrase missing in "a tube is stronger than a rod", ie, POUND FOR POUND, a tube etc. Structures are fickle about what is stronger. In my experience, I have found that a square tube is "stronger" than a round tube, but only in the direction of the widest section, ie, if you use a square tube on a 45deg angle to expected stress, it will be nearly unbreakable. Many years ago, I went through the agony of setting up a sailplane that way, and never bent or broke anything... as far as the joiner was concderned. You only have to watch me fly to guess about the demise of the model...

07-26-2006, 03:51 AM
In the great "TUBE versus ROD" debate, let me toss in my two cents worth - consider if you had a large prybar constructed from a solid steel rod, and another made from a tube of the same alloy and in the same outside diameter and 1/16 inch wall thickness. Somebody do the math and compute the area of a one inch rod compared to the tube (the empty space in the middle of the tube is air, which adds NO tensile or compressive strength so it doesn't count).

Most of the stresses are carried on the outermost part of the rod, so a tube may have a great percentage of the strength of the rod. But, considering that failures I have seen in tubing often result from wall failure allowing the tube to buckle and "hinge" so that there is an abrupt and acute bend at the failure point, I believe the material in the center of that rod is also very important. Not that a rod won't bend, but it may bend a lot more than the tube before it completely fails. Consider also that tensile and compressive forces are specified in some form of force per area (like pounds per square inch).The only way a tube could have the same area to absorb the stresses of tension and compression as a solid rod of the same diameter would be if the tube had a really small hole through the center leaving very thick walls. Which would, pretty much, make it also a solid rod now wouldn't it?

07-26-2006, 11:17 PM
Myself being a structural engineer, Intruderdave is on the right track. For a given weight per linear foot, a hollow tube (circular or square) will be stronger than a solid one. The next step is optimizing the O.D. and the wall thickness considering local buckling or simple bending failure, etc, which is way beyond my scope of expertise. I just pick standard sections from the design manual, I am not a engineering research type of guy. An example of this is how modern bicycle frames are made from very large diameter, thin wall aluminum tubes.

07-27-2006, 02:51 AM
I'm not a structural engineer, but I did stay at a Holidy Inn expr... (you get the idea)

07-27-2006, 12:46 PM
Hmmm, bicycle frames AND beer cans????:)

From what I've read here, I'll go with the stock steel. I am going to strip off the bottom covering but that's as far as I'm going. I could go with a carbon tube but then I'd have to install larger sockets in each half of the wing to accomodate a larger joiner rod. I don't wanna go there!

Thanks for the help!