Attention Genie Builders...Help!!

[ScottLister]

Hey Guys, I built up the carbon spar for Harley's easy LT/S as per the script and when I checked it out this morning I found a bow in the spar :eek: The bow is about 3/16 to 1/4 inch at the center where the bolt hold down is. The bow is such that it will give the wings anhedral. I have weighted the spar down again hoping it might straighten out but I really have my doubts about it. Do you think when the 1/16 balsa is bagged on if it is weighted well and is flat and straight the balsa will hold it straight or should I order more spars and start over? Any Ideas and help would be great.

Thanks
Scott

[mhodgson]

Never built a genie but have used similar construction style and had the same problem once.

I found I could unwind the Kevlar thread (I had only tacked it into place at the time) split the spar down the middle of the balsa web and rejoin it straight, then rebind. It will end up a little heavier but that is far better a bent one. Even if you have already epoxied the thread on it is worth splitting the spar or else start again.

Personally I would not force a bent spar in (unless I wanted it bent of course) as it may cause warps and uneven bends as it tries to return to it's original shape.

[ScottLister]

The spar hasn't been wrapped yet, do you think the wrap will pull some of the warp out?

Scott

[harleym]

Hey Guys, I built up the carbon spar for Harley's easy LT/S as per the script and when I checked it out this morning I found a bow in the spar :eek: The bow is about 3/16 to 1/4 inch at the center where the bolt hold down is. The bow is such that it will give the wings anhedral. I have weighted the spar down again hoping it might straighten out but I really have my doubts about it. Do you think when the 1/16 balsa is bagged on if it is weighted well and is flat and straight the balsa will hold it straight or should I order more spars and start over? Any Ideas and help would be great.

Thanks
Scott
Scott. . .the "script" gives specific directions to get a straight spar. Namely, when adding the 2nd spar, you need to work on a flat plane surface and with the spar system upright, weight it down on top while the epoxy cures.

Consider this: Eyeball along the bottom of the assembly to see if one or both sides are bowed, or if the apparent anhedral is due to a bend at the center. If one side is relatively straight, you may only need to straighten the other side. Work gently from the blade box toward the bolt holddown, to progressively break/loosen the top spar from the blade box and the vertical webs. Once you get it off the blade box, you can just slit through the foam webs with a thin, unbacked razor saw, etc. If the bottom spar will then touch the work surface by applying gentle pressure, simply smear epoxy where loosened and weight the assembly down on a flat plane surface. If necessary, do the other side, too. When straight, wrap with the thread. Latest File 3 at http://genie.rchomepage.com/ shows a setup to quickly do the wrapping. Let me know how this works out for you.

[mhodgson]

The spar hasn't been wrapped yet, do you think the wrap will pull some of the warp out?

Scott

The spar is essentially a lamination, carbon-balsa-carbon. The lamination is what is keeping it bent
If you split it straight down the middle, between the carbon caps, and then glue it back together (straight) again, working on a flat surface, they should come out straight. I am assuming you used prelaminated carbon strip. In which case it will happily take up the new straight line, as that was the way it was laminated.

You can then bind and you will never know the difference apart from a little extra weight.

You may need a hard balsa strip laid in to keep the spar height, particularly if you split it with a saw, due to the width of the saw blade.

Martin H

[gklimber]

Do what Harley says. All is not lost. Rarely is all lost with this ship.

jer

[lincoln]

Hey Guys, I built up the carbon spar for Harley's easy LT/S as per the script and when I checked it out this morning I found a bow in the spar :eek: The bow is about 3/16 to 1/4 inch at the center where the bolt hold down is. The bow is such that it will give the wings anhedral. I have weighted the spar down again hoping it might straighten out but I really have my doubts about it. Do you think when the 1/16 balsa is bagged on if it is weighted well and is flat and straight the balsa will hold it straight or should I order more spars and start over? Any Ideas and help would be great.

Thanks
Scott
Get it straight. If the epoxy has not been curing all that long, you might figure out how to jig up the spar absolutely straight, and then put it in the car in the sun for a few hours on a hot day. (you want something like 140F to 160F with the normal sort of epoxy, I think) That may fix it. If not, I guess you need to split it like everyone says.

[ScottLister]

Thanks Lincoln, I am trying to get it done in time for the soar in. I plan on cutting it today and trying to get it straight. I can't imagine why it came out bent. I laid it up just like the instructions said. I have a large granite bench top from the science rooms at school which is absolutely flat and level. I weighted everything down flat and left it for 36 hrs. Oh well, let's just hope the saying "the third time is a charm" doesn't apply here!!!!!

Scott

[Nico Peursum]

I plan on cutting it today and trying to get it straight. I can't imagine why it came out bent.
Oh well, let's just hope the saying "the third time is a charm" doesn't apply here!!!!!
Scott

Did you manage to save your spar?

[ScottLister]

I haven't had a chance to get to it yet. I have been sidetracked with the holidays. I would like to get to it tomorrow or wednesday.

Scott

[ScottLister]

Well I finally got back to the genie spar yesterday. I followed Harley's advice just as he stated in his earlier post and the spar now straight as an arrow and wrapped. I didn't have kevlar thread or kevlar tow, so I used 55lb. test spectra line(braided) instead. I have used this on other spars and have never had a problem. Today I plan to make more progress on the wing.


Scott

[gklimber]

Harley IS da man.

jer

[ScottLister]

Agreed!!!!!!

Scott

[harleym]

Hey you guys. . . you give me too much credit.

It's just a case of having made more blunders over a longer time than all the rest of you put together, that qualifies me as an "experienced" builder.

Thing is, I forget things and must remember to read the pertinent text when I go to do something. When I have just learned something new that works, I try to promptly head from the workbench to the computer to incorporate it in the text, while it is really fresh in my mind. You see. . .I suffer from that age-related "CRS" syndrome which means I better do it quickly before the thought evaporates. Just wait. . .you'll see.

It's a standard joke between me and my older friends when asked about recalling something, to respond "No, that's happened too recently for me to remember".

However, I am very good at words to songs from my high school days, even if I have not heard a song since before WW2.

Yes, to keep from "painting myself into a corner" I, too, follow my own written instructions. When I screw up yet another time, it is usually the result of my not rembering to follow my own "script".