I need some advice on making a structural repair to my Citabria. It had an accident in 1978 and the right gear had to be reattached. The tubing was replaced where the U-bolt goes through the fuselage. That same repair is now needing to be redone as the tube has compresed where the nuts go on the U-bolt and the aft U-bolt pass through is cracked. I noticed this while taxing and applying the brake and saw the tire move aft about an inch on the right side and none on the left. This damage has been there for some time as I can tell by the patterns and smoking from the metal movement. What I would like to know is how far down should I tear the airplane? At a minimum I will have to remove the boot cowl, open up some fabric and take out the front floor boards and remove the right gear leg but, what I am concerned about is the rest of the weight of the aircraft on that cluster of tubing after the broken area is cut out. Will I need to remove the wings, etc...? Thoughts??
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Cracked tubing
- Thread starter tex289
- Start date
David Johnson
New member
You probably don't want to hear this, to do it correctly is a lot of work. I would contact the factory to see if they can put it back in the original jig and do the tubing repairs for you. If you don't have a jig with all the gear bolt attach points you are asking for trouble. The problem is the fuselage will have to be taken most of the way down. I am working on a fuselage jig for the 7 series, but it is a several year project at the rate I am going. It would be nice to know you would not have to go thru this again and it was fixed for good. Hope it works out for you, David Johnson
Paul Agaliotis
New member
I,ve repaired a half dozen Citabria,s with this same damage. It is fairly common on the higher time airframes. You will need to pull the wings and engine for proper access. If you are careful you can grind and cut to allow the saddle to slide off the lower longeron on the aft side. If the airplane was not used very long with the cracked gear box, you can get by with replacing the 3 square tubes. Check the vertical tube at the front door frame area for cracking on the left side and the same tube on the right. I replace the forward piece of lower longeron from the gearbox to the engine mount.
We now install a strap plate to the outside of the gearbox saddle for added support.
Just some food for thought. Some of these airplanes I have worked on since new and until we started using the new bolts and bars I never had this style of failure. Of course we did have few U bolts crack but thats why you pre-flight.
Paul
We now install a strap plate to the outside of the gearbox saddle for added support.
Just some food for thought. Some of these airplanes I have worked on since new and until we started using the new bolts and bars I never had this style of failure. Of course we did have few U bolts crack but thats why you pre-flight.
Paul
Thanks for both of your input, total time on this airframe is 1400, but the right gear leg was knocked off in 78' when the aircraft was 2 years old. the U-bolt has 3-4 washers on it and the tubing is compressed from repeated torqings at annuals. the left side looks fine and all other tubes in this area seem fine as well. the square tubing is cracked at the aft pass through for the u-bolt. I have decided to remove the wings to make this repair and to get it into my welders shop. Paul what is the necessity in removing the engine?
Paul Agaliotis
New member
Tex,
When the lower longeron is removed there is no support for the engine weight. This allows the the weight to push that corner up and aft.
Paul
When the lower longeron is removed there is no support for the engine weight. This allows the the weight to push that corner up and aft.
Paul
Paul can I contact you off the forum to discuss this further? Also I am planning on using the plates/bolts instead of the U-bolt arrangement, has your experience been negative with this replacement? My plane is not used hard ie.. rough strips or as a trainer, I fly from pavement and grass equally but all the grass strips are pretty smooth, and I run stock size tires with wheel pants. I'm no stranger to this type of repair as we've done it on Stearmans, Air Tractors etc..., but this plane is my pride and joy so I want it done as right as I can without tearing it down for a full on resto. Thanks again for all your insight.
Tommy Eskind
teskind77@sbcglobal.net
Tommy Eskind
teskind77@sbcglobal.net
Paul Agaliotis
New member
I would love to hear from you Tommy. The best way is to call my office number 650 634-6373 from 2pm to 9pm Pacific time.
On the U bolts. I dont have any data other than we never failed the fuselage in this manner until we made the change. Then in the course of 3 years we had 6 identical failures. Now bear in mind all of the Citabrias are 10,000 hr airframes so fatigue could be a factor. I think the bolts and bar transfer the load to the fuselage completely while the U bolt would offer some flexibility. Hence the cracked U bolts. The damage doesn,t seem to be from landing loads. The cracks appear to be caused by hard brake use, due to the cracks generaly starting at the aft hole.
Now all of this information is nothing more than field observations. I have no engineering or scientific facts to back this up, nor due I care to collect them. Somebody with a sliderule and pocket protector can do that.
Paul
On the U bolts. I dont have any data other than we never failed the fuselage in this manner until we made the change. Then in the course of 3 years we had 6 identical failures. Now bear in mind all of the Citabrias are 10,000 hr airframes so fatigue could be a factor. I think the bolts and bar transfer the load to the fuselage completely while the U bolt would offer some flexibility. Hence the cracked U bolts. The damage doesn,t seem to be from landing loads. The cracks appear to be caused by hard brake use, due to the cracks generaly starting at the aft hole.
Now all of this information is nothing more than field observations. I have no engineering or scientific facts to back this up, nor due I care to collect them. Somebody with a sliderule and pocket protector can do that.
Paul