Straightening out the fuselage

So there I was... ready to start tracing the fuselage floor... when I placed the foam on top of my fuselage and realized there was a hiccup! My F22 bulkhead was at an angle (left side was 1 inch farther aft than the right).

How could this have happened?! When dealing with a hiccup (and if you are involved with a project of this scale, trust me... you WILL have hiccups), I take the following approach:

1. Identify the problem

2. Find the root cause of the problem. I do this by calling it a night, removing myself from the situation and coming up with different scenarios as to what may have caused it. I then come back the next day and test my hypothesis - you need a way to verify that what you think is causing the problem is in fact the REAL root cause of the problem.

3. After identifying the root cause, come up with a plan (or many). Mentally go over the pros and cons of each and choose the path you think is most likely to succeed.

4. Take action! Apply the plan - don't be lazy here. If it costs a little more (time or money), remember that this will show in the end result - so do it right! Take the time to implement your plan wisely.

That being said - here is how I approached this particular hiccup:

After a lot of head scratching, I realized in order to find the root cause of the angled F22 bulkhead, I needed a way to physically measure it. To do this, I drew a straight line down my level workbench - representing the fuselage center line. I then drew perpendicular lines representing all bulkhead fuselage stations. By placing the fuselage on top of my workbench, I could now physically see (and measure) what was off. It was clear that the left fuselage sidewall was 1 inch ahead of the right fuselage side wall - the root cause was now identified.

The plan - so now I had to come up with a plan that would fix this issue. I decided that the best plan of action was to turn my workbench into a temporary jig. I did this by constructing positioning bars (made out of 2x4s) and screwing them onto my workbench (making sure they aligned with the F22 line I had previously drawn onto my table). On the aft side, I constructed an adjustable positioning bar (again, made out of 2x4s and two bolts) that would allow me to slowly sandwich the fuselage and hence force it onto the forward stops - straightening everything out.

Here is the overall picture - notice the fuselage is upside down on my workbench (never mind the fuselage floor against the back wall). Notice the stoppers (made out of 2x4s) on the left (the forward fuselage) and the adjustable positioning bar on the right (the aft fuselage).

A close up showing the forward 'L' shaped stoppers. They were screwed onto my workbench for a firm hold.

Notice how the left side of the F22 is 1 inch aft of where it should be, while the right side is up against the stop. (This picture was taken prior to 'sandwiching' the fuselage into place).

A close up of the aft adjustable positioning bar (again, BEFORE tightening it down). Notice how the left side of the firewall is up against the positioning bar - proving that the left fuselage side was 1 inch aft with respect to the right side fuselage wall.

Another close up showing the aft adjustable positioning bar setup.

 Notice the bolts holding the positioning bar - I now had a way to tighten the bolts, which would clamp the entire fuselage into proper position.

 A top view showing how the bulkheads too were not aligned, due to the left fuse being skewed 1 inch aft from the right side fuse wall.

 It was now time to sandwich the fuselage into its square position... cross your fingers!!

 Notice the wrench on the right side... I slowly turned it, forcing the fuselage into place.

 Taaaaaaaaaa-daaaaaaaaaaaaa! Magic! The left side fuselage wall now perfectly square with the right!

Forward fuselage section squared... check!

Aft fuselage section squared... check!

Instrument panel squared... check! (I purposely made the lines on my workbench a bit away from the actual bulkhead so that I had room to check for squareness.)

Front seat bulkhead squared... check!

Lower longerons still level... check!

 F22 bulkhead still level... check!

Done right? NOPE!! Not yet!! But Ary, what is it NOW?! Well looking down along the longerons, I could tell I missed one thing... I didn't bother to CENTER the bulkheads. This meant that the left longeron curve was not a perfect mirror image of the right longeron curve. No worries... this was a 'simple' fix.

I started out by measuring the center line of each individual bulkhead and marking it. I then placed a string from the F22 center to the firewall center. I now had a visual aid to see which bulkhead was off center (wherever a tick mark was offset from the string).

I then made this contraption out of 2x4s to force the bulkheads into their proper center line position.

Fine tuning took a bit of work... but in the end, ALL bulkheads were aligned with the center line!

Instrument panel tick mark aligned... check!

Front seat tick mark aligned... check!

Rear seat tick mark aligned... check!

Hard to see in this picture, but the line was tied such that it was with the firewall center line tick mark.

Firewall center line aligned with the fuselage center line along my workbench... check!

 I kept fine tuning and tweaking these clamps to get the left longeron curvature to match the right longeron curve for a perfect mirror image.

Again, fine tuning and tweaking these clamps to get the left longeron curvature to match the right longeron curve for a perfect mirror image.

When all was said and done, this put a 2-week dent into my schedule, but in the end - I feel it was required and time well spent. I now have a straight, well aligned fuselage and feel confident to start work on the fuselage floor. Hopefully, the fuselage will remain squared and level after the fuselage floor is bonded into place and the jigs are removed once cured.



Anonymous said...

Thank you for creating such a thorough journal of your build experience. Seeing it up close and in detail like this is inspiring!

Did you consult with other builders before you set about straightening out the fuselage?

Also, where are you located?


Ary said...

Thank you for your comment!

I consult with other builders all the time - but I'm extremely cautious about whose advice I take. I have a degree in aerospace engineering so I approach most problems analytically.

For this particular 'fix', my main concerns were: 1) was the floor going to hold the fuselage in place after it was bonded on, and 2) would forcing it into place introduce unwanted stress on the already bonded bulkheads.

Looking at the amount of surface area that the floor bonds onto the lower longerons, I was convinced the floor could withstand the shear loads without a problem.

As for the induced stress seen by the already bonded bulkheads - I'm planning on post-curing the entire fuselage when finished, so any induced stress will be alleviated then.

I'm in northern California. Where are you located? Are you in the middle of a build or thinking about getting started?

Thanks again for your comment!

Feel free to contact me via email: thelongezbuild (at gmail dot com)