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Rob's REBVAIR Project
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Date: 8-3-2017
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Number of Hours: 20.00
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Manual Reference:
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Brief Description: Steel Drag strut fabrication
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Having damaged one of the MAM-supplied drag struts in attempting to fit it to the aircraft, I decided to bite the bullet and fabricate 4130 steel drag struts (following examples on Murphybuilders). Being custom fabricated out of steel meant they would not only fit perfectly, but also support a person's weight to assist in getting into the plane. 99% of builders don't have these steel struts and probably stand on the tire when they need help getting in. Since I'm adding wheel fairings, the tire wont' be accessible. Also, sharp eyes will note that all this fabrication work is further complicated by the use of the Mohr landing gear fittings. They are more robust than simply putting a bolt through a tube, and have brass bushings that can be replaced. They did however, require additional thickness tubing to be added to the drag strut design.
Image 1. I was initially very concerned about heat warpage. For example, adding the center perpendicular tube resulted in a significant bend in the drag strut. But this was easily corrected by heating the joint to red hot and gentling easing things back into place. In fact, heating up joints while the strut was bolted into position allowed the strut to find it's "comfort zone", and took out any stress in the system. I know the welds aren't pretty, but they did penetrate I can assure you.
As always, I had to deviated from the very well drawn plans. In this case the suggested footpeg gusset presented a flat plate into the windstream with a downward angle. I know the effect is small, but with all the effort I'm putting into getting this streamlined, it felt wrong to weld on this additonal piece of drag that actually decreased lift.
As you can see in Image 2, I fabricated a bracket to accept a 1/4" bolt to attach a footpeg of my eventual design. The bolt is close to the tubing intersection, and a bushing sits between two gussets making this a very robust attach point.
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