Viper MkII Landing Gear

I’m working on the undercarriage now that the main fuselage is almost done and is in need of support instead of umpteen saw-horses. Lots of geometry here.

My intent is to build the outer fascia in plywood box-sections to get the shape and size right, based on original concept drawings. I can then place steel square hollow sections, (SHS), inside and weld a solid frame within.  The landing gear will not articulate, but rather be solid pieces that are placed under the Viper during assembly and bolted into the frame underneath.

I have a fair bit of structure experience, but as I am not an engineer, I am going for absolute overkill on this. I’d rather spend extra dollars on heavier material for support, than have any doubt about it’s ability to support the ship and a live load of one person. Law-suits are way more expensive.

Here’s a screen video of the front catapult engaging and thrusting a Viper out of the Galactica’s port side launch tube.

 

Working on the front skid first, I’ve welded doubled SHS inside the foot, with a rigid strut of doubled SHS at 15 degrees, as per specs of the original build. Once I’m happy that the whole leg inside is rigid and strong, I will fix the cladding to it and clean it up.

Adding the articulated leg-brace behind was a simple matter of getting creative with whatever I had in the shed. Leftover round offcuts from the ammo turning and some PVC pipe, with a bit of plywood and silver paint.

Rear landing gear x 2

The rear landing legs are interesting because there is a fifteen degree angle leaning forward and in from the ground up. I’ve sent a diagram around the engineering circles to get some indication of how strong my legs will be – how much weight they can support. My general attitude towards this sort of thing is to OVER-ENGINEER to the max, so that there is absolutely no doubt whatsoever, that the legs can support the weight of the viper and a pilot.

Being that the Viper itself is made of thin plywood and polystrene foam, covered in fibreglass, the finished aircraft will be quite light. The heaviest part of the entire ship is the cockpit and pilot. The steel frame inside each modular section is light, but strong. Each module, (besides the cockpit) is light enough that I can lift it, but the size of each module makes them cumbersome to gain leverage on, even though they are light.

All that stated, I have worked out that each leg is capable of supporting the entire ship’s weight on it’s own and then some, but it then becomes a matter of sharing the load between the three and finding the balance point. I understand that it may work out back heavy, in which case a little ballast in the nose should fix that.

The diagram below was for working out worst case at one metre. In truth, the strut will be shorter than this and also have further reinforcing spars welded to it, so it will much be stronger than the answers provided to me. There is plenty of room within the fascia cladding to add whatever I need to get the job done.

The back legs are confusing to translate from the technical drawings to reality, but I’m getting there.  The difficulty is that there are so many weird angles to get right. Hardly a plumb aspect to it and few 90 degree angles. At one stage, idiot stupid me made both cowlings the same instead of mirror image! GAAAHH!!!!

I would have a much easier time of it if I could afford decent quality wood and a big variety of thicknesses to choose from. Unfortunately, a lot of the wood is second hand, poor quality and I have to do it in layers. Lots of layers means lots of cleaning up to get them all the same. Freehand with a jigsaw is hard to keep accurate to the drawn lines, so finishing off with a flap disk then hand-sanding to make it all look like one piece once it’s painted. A little bit of putty goes a long way, but paint hides all manner of sin.

There are some details in the leg cowlings to build.

 

Thanks to a new social media friend named Sean, who kindly provided a long off-cut of rubber mat to simulate the texture of the technical drawings. It is easy to cut and trim using a knife and after some contact adhesive applied, it locks down nice and flat.

More detail. Hydraulic line simulation using plastic coat hangers heated and bent to shape.

Replacing the catapult linkage. I’ve kicked and broken the plywood one twice now, so it’s time to replace it with 10mm plate steel and steel tube. Strong enough to sling-shot a Viper out of a launch tube!

I found a work lamp close enough in appearance and size to use for the front landing gear landing light.

29 September 2018

Fitting the undercarriage.

I really want to make this safe around people. My plan today was to get all three legs attached and supporting the spacecraft, but it took all day to do just one and get it right. The craft modules are light, (except the cockpit), but I am well aware of accumulative weight and the effects of cantilevering over a support.

Over-engineering is the way for me, so lots of steel. I had engineering friends calculate the failure points for me and then I added extra strength to have absolutely no doubt.

I found a 10mm height difference on the horizontal centre line from front to rear over eight metres. I’ll fix it in time.

 

 

13 October 2018

Memoirs of a Viper builder…

Every fortnight I have a Saturday to work on the Viper. I often get overly ambitious as to what I think I am going to get achieved with that one day and am often left disappointed and discouraged. Today was no exception. This time, i deliberately set my sights a little lower and vowed that I would only work on the rear legs of the undercarriage and get them DONE! Long after dark, I was still going and had to shut down the grinders, drills and welder for the sake of sleeping babies and the spirit of being a good neighbour.

I got one leg on and the other leg half done. Lots of false-starts, standing and staring, contemplating and planning before a single piece of steel was cut. The tricky part was to avoid getting too elaborate with the way it fits together. Keeping it simple and basic is actually quite hard, but I got there in the end. When I take this thing to events and shows, I don’t want to be spending half a day assembling it. At the most I’d like to get it down to an hour, to an hour and a half.

After curfew, I shut the shed door and did some quiet drilling on the press and prepared the steel for tomorrow’s cutting if I get a chance.

 

 

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