Thursday, June 16, 2022

Lid Operation on the Airplane Hauler...

 The design of the lid mechanism took a bit of experimentation...but that's how projects sometimes go :-)  Once the camper was gutted, I installed a set of heavy barn door hinges on the back side, and lift handles on the access side of the trailer. The lid weighs about 74 lbs, and I measured about 37 lbs at the lift handles required to move it. That doesn't sound like much, but to grab 37lbs at mid-chest high and push  it up to about 7 ft, while trying to put lid support poles in place at the far corners was more than I anticipated. A project within a project begins...

LID SUPPORT POLES - I fabricated lid support poles and floor mounted retaining pockets, and hinged them in the corners of the lid. Once the lid was lifted, they would "kinda" fall in place and could be secured with a pin. When it was time to lower the lid, things got fun. I would go to the corners and lift the poles, freeing them from their "pockets", and the lid would immediately start a hurry. That wasn't gonna work. I realized I needed to install a set of gas struts to help manage that. 

GAS STRUTS - The gas struts was another interesting part of this. Forces required to open and/or assist the lid movement are amplified greatly as you measure closer and closer to the hinge line. Long struts aren't cheap, and the stronger they are, the more the strut compression force is converted to side / hinge loads when the lid is in a lowered condition. This little all aluminum frame wasn't designed for that, and took a bit of experimentation. I finally settled on a pair of struts that would help lift the lid, slow the descent of the lid, and not have such tremendous side loads when not deployed. I also had to design a vertical member to transfer the lid load to the floor and not bend that little aluminum rail the strut was connected to. OK, that problem was solved...

LID POLE RETRACTION - Lifting the lid was now a cinch, getting it back down and closed was the next problem. The lid poles, even when freed from their retaining pockets, was a fight to get them out of the way. I'd have to go from side to side, moving each one closer to the hinge line, lowering the lid....bit by bit. Not gonna work. 

1- I tried several low hanging bungee cables to pull the bottom of the poles to the opposite wall once free, but they would never pull far enough (due to elasticity), or the poles would get snagged on fasteners on the floor along the way, etc. I shaved the bottom of the poles at an angle to help with sliding. That helped, but wasn't the fix.

2- Plan B...I rigged a cord system that started at the lift handles,  traveled around the perimeter of the lid, down into the lower section at the hinge line, and back to the lift poles. I would lift the lid a little to free the poles from their retaining pockets, then pull the cords to retract the poles. Those poles are long, and by the time I found the best attachment point to get the ratio so the stroke of my arm would retract them, they were heavy. This system would work, but was going to require a number of pulleys to minimize friction in all of the corners. I may experiment with this more later, but for now, I wanted something simple.

3- Plan C, back to bungees. After pondering it a bit, I realized I needed to pull from a different angle and location, something that would require a minimum of motion, and a short bungee. Also, something that would keep cables and things out of the way for easier end loading of the trailer. Using vice grips attached to a rail inside of the lid, and a number of ties straps on the poles for attachment point, I was able to optimize the location of these two points. A fastener was installed in the lid as a "hook point", bungees were attached to the lift poles, and it worked relatively well. 

PARTIAL LID OPENING - After playing with it a bit, I found it helped to have the door open & step deployed. It was also needed to attach and release the bungees (seen in the video). A small intermediate support was fabricated to facilitate this.  

WIND CONTROL - We've all been at the flying site when rogue winds would roll through and have canopies flying, trailer doors swinging, and airplanes making unintended flights across the pits. I had this fear of wind grabbing the top and ripping it off of the trailer, so I rigged a simple pinning mechanism to hold the lid poles into their floor mounted retaining pockets. Between that and the gas struts, I _hope_ this will be adequate :-)

CLEARANCE - Once all this was worked out, more or less, I had to clear a path for the poles to swing back and forth during deployment and retraction. This wasn't too hard, but just took a little planning on the interior layout. The video below shows how this redneck lid management system works :-)