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Bent Frame

Posted By:
Michael Haun
3
Posts
0
#1 Posted: 4/27/2011 13:37:09

Is there anyone who can give me some help with bent frame. It was changed from someone awhile ago and frend of mine put it down to hard and bent the frame ,and when they took a look at what was all bent they found these cracks in the frame. I`m living in Germany in the near from Augsburg ,so dont laugh at my kindergarten English. Take a look at the pic`s It`s an Ultimate 10 dash 200



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Gary Skeens
6
Posts
0
#2 Posted: 5/4/2011 17:32:21

Hi, Michael

Don't worry about your English, it's better than some who grew up in our schools! As to your frame problems, that's a different matter. If it were my airframe, I would start by removing any members that are bent more than a few degrees as they will be nearly impossible to pull back into their original shape and will be weakened. This will probably involve making some kind of clamping jig to hold the frame in the desired shape as cutting the bent members will relive the strain they are currently putting on the frame and mis-shaping it..

The cracks scare me a little. Were they caused by the mishandling of your friend? If so they are probably limited to the immediate damaged area. I would sand blast away any paint or powder coating before attempting a repair in order to make sure the cracks have not traveled into the tubes proper. If the crack is limited to the weld, I would gind it out and reweld it. If the tube is cracked I would replace it. There are probably those who would repair cracked or bent tubes, but in my mind tubing is not that expensive and I would rather have the peace of mind. Obviously, I would carefully inspect the rest of the airframe for further cracks to make sure you don't have a more sreious problem than butter-fingered freinds.

Good luck,

Gary



Mike Huffman
Homebuilder or Craftsman
11
Posts
4
#3 Posted: 5/6/2011 09:03:35

I mostly agree with Gary Skeens, having repaired steel tube fuselages that were bent much worse than this.  I'm not sure you would have to jig the fuselage in this case--based on the photos, it seems the damage is pretty well isolated to the left landing gear attach area. 

The first step, as Gary says, is to remove the paint or powder coat all around the affected area.  If it is paint, the easiest method may depend on the capabilities you have.  Sandblasting is good, but a good chemical paint stripper may be the easiest.

Next, I would cut out the two vertical pieces of tubing that are buckled in compression.  It may also be necessary to cut out the diagonal brace in that bay, but I would try to avoid that, since the diagonal establishes the location of the bottom engine mount at the firewall.

If it were me, I would want to avoid having to rebuild the lower longeron, the rudder pedal attach area, and the steel plate reinforcements.  Therefore, my approach would be to try and straighten the lower longeron. 

I would use a portable hydraulic frame straightening tool such as those sometimes used in automobile frame straightening--in the U.S. the most common brand name is Port-A-Power--you can look it up on the Internet to see what it looks like.

My suggestion would be to first  temporarily grind and reweld the crack on the longeron at the firewall.

You would attach spacer blocks (perhaps 50 mm thick or so) underneath the longeron at the firewall and at the forward lower wing spar attach point.  Then you would attach a strong steel bar across the two spacers, spanning the length of the damaged longeron area.  (Better yet, weld the spacer blocks to the bar to make it easier to handle.)  The steel bar would then provide a strong surface to pull against using the Port-A-Power.   I would suggest using a steel block against the top of the longeron at the bend to distribute the Port-A-Power force so as not to distort the longeron.

You will need to use lots of heat on the lower longeron, the steel reinforcing plates, and other associated structure during the straightening operation.  I would want to have at least three people present--two people using oxy-acetylene torches with large heating tips (we in the U.S. call them "rosebud" tips) and the third person operating the Port-A-Power.  You would need to get the entire area (including the entire length of the longeron, the steel reinforcing plates, and the rudder pedal attach crossmember) up to a dull cherry red before attempting to pull the lower longeron back straight.

Once straight, I would perform a dye penetrant inspection of the entire area, looking for cracks.  If none were found, the next step would be to replace the vertical members that were previously cut out.

Last, I would reinforce the repaired lower longeron crack at the firewall by forming and welding a "finger patch" over the cracked area, extending upward onto the vertical member and aft along the top of the longeron.  FAA Advisory Circular AC43.13-1B (available on the FAA website) has details of finger patches.

If this method does not work, the only recourse would be to cut out the lower longeron in that bay and rebuild all the associated structure.  Here again, AC43.13-1B has information on how to do so.

I hope this helps!



G. Michael Huffman SportAviationSpecialties dot com 904-206-0522
Michael Haun
3
Posts
0
#4 Posted: 5/11/2011 14:11:26

Thanks  for the info, don`t have a lot of time now, will write more over the weekend and let you know what I`m up to. And I`ll post some pic`s.



Gary Skeens
6
Posts
0
#5 Posted: 5/11/2011 20:31:16

Michael,

Mike's tips sounded pretty good, I didn't want to be more specific on what I could make out from the pictures. You might get the DVD's on chromoly airframe construction from TM Technologies. You can find them at www.tinmantech.com



Michael Haun
3
Posts
0
#6 Posted: 5/26/2011 12:13:48

OK  ,everybody                                                                                                                                                                                                                                        I´ve got some time now to write about what I`m up to . There are a lot of extra pipe`s on this frame that don`t belong here. If you look at the first pic they are markt with a red line , these I`m going to cut out , and the pipes that are markt with a purple line, I`m going to cut at the line and put in new one`s.                                                                                        

                 I can`t sandblast the frame don`t have one and I`ve found out you can take the powderpaint off, (I don`t know what that`s called in englisch) but anyway if you take a hot air gun and heat it up a little you can scratch it off the pipe pretty good.

                 The reason I`ve decided to cut it all out is that the crack in the pipes went all the way into the motormount and there was know way of being shure it was safe to weld it up ,because when you look at the 2 pic that shows what I cut out ,you can see all of what some madman welded into this frame . who ever it was chanded the landing gear from the motormount to the front of the frame. I`m going to change that back to original plans.

                 In the next pic I grinded the old pipe and the weld away, and put in a new pipe.Then put in the front a new one and now I`m waiting for my pipe order to get here, so that I can get going .

                 Oh and by the way thanks for the info on the adress of the FAA. thats how I`m welding everything up.This you can see in the last pic`s .As soon as I get this side done up Í`ll post some more pic`s .



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