It's not that the springs are too weak -- it's that your force vectors are wrong. As the undercarriage leg moves up it effectively gains leverage over the spring because you're creating a longer lever and thus the spring has less effect. What we used to do was put a spring *between* the axles (ie: directly from wheel to wheel) and then add another spring in the centre to pull the middle of the spring slightly closer to the bottom of the fuselage (so as to provide clearance for the mainspring when operating over long grass. This works *really* well -- unless you are trying to operate from a surface where half a wheel's ground-clearance isn't enough.
That seems like the fastest / easiest way, plus he can still adjust 3-way tension with the cable & crimp method he was describing. Might even be the lightest way.
hmm... unless there is a solid connection in the center though, simply connecting the wheels to each other leaves the fuselage free to flop over to one side. Would that center spring you mention be under very tight tension, or at least very short? I'm starting to think I'll just make a rigid center triangle from that aluminium.
That seems the logical way to go next; it requires the least work from where you are now. The ground clearance is the downside though. I have watched the video where the original undercarriage broke a number of times, and I think that the longer grass where you actually touched down contributed to the failure.
That'll be 5000 series aluminium which is optimised for low corrosion rather than strength or ductility (high manganese from memory). It is easy to machine and weld but not as strong as other alloys such as 2000 (high copper), 6000 (high silicon) or 7000 (zinc) series. It'll probably suffice for your needs though.
Yep, I would definitely make a triangle in the center. You have this nice aluminium, its gonna be perfect for it. This way You can make tension cables shorter and more wide angles for better force vectoring. And what comes after it You dont have to use stronger springs.
Hey mate :) I use the same geometry as you mention is commonly used. I however do not use springs on my old Bush Decathlon, but fat shock absorbers from a monster truck. They are mounted from the point on the spring steel struts where they meet the wheels, to the point where the wing struts meet the fuselage. The geometry is good, the shocks are light plastic but very capable, as the springsteel axle/wheel struts take a lot of the strain. The plane is a heavy 1.8kg. Ive had some serious bastard landings on farm tracks here, and never had a breakage yet. Shocks!! :)
I think you should try hocking the two sides of the "springs+cable" on the carbon legs. This way the springs would be almost "level" but you could mess with the distances to get what you want. I Don't know if my idea is very clear, but I will reply to and comments and try my best to help you. I have been watching your videos for a while and learnt a lot too so Thanks for your good job.
3 strip of door skin with carbon sandwich between abs in the outside wrapping the door skins.... bent around my 25 gal air compressor tank then tied in place with cordage makes very nice gear..... Also can use fiberglass and I have even used drywall fiberglass tape..... Use bungee chords duplicate piper cub exactly
Very interesting and nice to follow your project. I am no expert or engineer or anything like that but you know what I would like to see? Instead of these skinny, thin hard looking wheels, some nice fat puffy soft wheels. I just think it would make the landings much easier on the structure of the entire aircraft. Anyway, looking forward to the maiden flight and of course, Happy Flying.
I was looking at these a while ago, for size and looks they would be perfect but look at the price. Plus they weigh 455g each, while mine weigh 300g for both. www.topmodel.fr/en/product-detail-6408-airtop-balloon-wheel-z180-mm-pair
Hi Chris. I would copy the tried and tested method with the solid centre spring mount. It will give a more stable result. I would also consider fitting something to stop the end of the carbon tube from being damaged, where you are using it as an angle stop. Maybe a rubber pad or preferably something that contacts one of the mounting brackets before the carbon tube. It looked great in the air on the maiden flight.
Yep. When you drill alumunium, it just oddly satisfying. I use (leftover) 1100 type of alumunium for my camera mount where i put on my quadcopter. Easy to work with
Lowering the mounting point for those springs on the struts will help with your current setup. The triangle in the middle would definitely help. Just a different idea if you want to maintain maximum ground clearance... Maybe an axial type spring like you may find on a screen door or a light gate would work ? Many are adjustable to the amount of tourque you wish to have and they mount right in the corner of the hinge so there is no obstruction of ground clearance.
It seems that you could take the springs and cables out and just put in struts that run from around the axles up to a central attach point on the bottom of the fuselage to replace them. It doesn't look like you need the shock absorbing benefit of springs, and struts would keep the wheels aligned how you want them. 1/4"-20 all thread (metric equivalent), 4 nuts and 4 clevis ends and you're in business. You can whip up the attach brackets needed from what you have leaning up against the wall. The brackets that attach to the fuselage could be a 1 piece part, with holes at each end to pin the clevises to, and the screws that attach the part to the fuselage running through the center of it. For a decent aluminum to use in the future, 6061-T6 would work well for you. It's very common, easy to machine and it's weldable. If you are running CNC machines to cut parts from metal, I can't imagine an easier material to work. You need to have the speeds and feeds correct, and the right cutters, cutting direction, depth of cut and coolant, but that issue is the same no matter what metal you are working with. If you have to do radical bending, might have to switch to a different kind of aluminum (1000 series likely), but for everything else you are doing, the 6061 should be fine. Heating the stuff for bending is not necessary unless you are drop forging or something, and could cause some serious problems with strength of you went much over 300F. For simple bends, the grain direction doesn't matter much either, so you can just ignore it. The difference in strength would only matter if you were trying to absolutely minimize weight, and had done all the flight loads studies and stress analysis that goes along with it. This reference gives some basic details about properties of the various alloys. www.clintonaluminum.com/best-aluminum-alloys-for-machining/
You need 3d printer. Some of those minor issues you coyld resolve easily. Like to make a cap with exact angle to lay on end of carbon tubing reducing preasure by distibuting it evenly over end cap.
It's all about the angles as most have said below. Instead of using straight springs what about trying some RC coil over shock absorbers, maybe cut down on any tendency for the plane to "spring" back into the air after a heavy landing.
Have you looked at the shock and springs used for RC cars? They may work better and the shocks would dampen them. I can tell you on many older full scale aircraft budgie cords are used.
It's nearly there! :). Move the wheel spring mounts right down to near the wheel axle. Yep in the centre a triangular mount point, but it doesn't have to be solid.. the two downward sides of the triangle can be just solid braces/linkages - attached to the top of the opposite landing gear. The two linkages join together in the centre, giving you the fixed mounting point you want for the springs. Exactly like cub style models. I'd copy the HK tundra landing gear. Better yet, see that the Avios grand Trundra uses rubber bands instead of springs. In your case though you could use bungee cord.. you can multi wrap it to fine tune the tension. Camping stores have that cloth covered bungee cord as used in dome tent poles, there's a few sizes. Put the spring part up near the triangle mount point, with linkage then from the spring down to the wheel mount - to get the springs away from ground debris. See the tundra here: hobbyking.com/en_us/durafly-tundra-1300mm-51-sports-model-w-flaps-pnf-upgrade-version.html You can see the landing gear close up in their attached video under the files tab on that page. Cheers.
In addition it would be possible to move the anchor point of the spring a bit down on the opposite leg, that would give it more leverage. I believe that this would still be better than having on spring between the wheels, because with layout I described, when you have force on one leg, much less force is applied to the other leg (because of different leverages), which is important due to how the leg is stopped from going too far in. P.S. I really like how this project is concluding.
I found a scrap piece of aluminum laminated to plexiglass in the trash pile after a gas station remodeling...4' x 12'. :-P I have enough to make strong landing gears to last me 2 life time... It's little bit heavier.....it's just 3mm plexiglass sandwich between 2 -ea 2 mm aluminum. It'll still flex ( give)..but you gatta kind of work it...to bend it. :-P . I also found different type of plexiglass or telfon material.. In other words....The plexiglass isnt going to SPLIT like wood. It'll still flex.The laminated plexiglass between the aluminum is COOL.. I can BEND IT..becuase plexiglass by itself isnt easy to bend. :-P I also found a roll of thin stylrene..It;s the same thickness as poster board/cards but it's PLASTIC :-P ..it was actaullly the old sign's art work... If there;s an electronic manufacturing near you....go ask them for old semiconducter storage/shipping tubeit;s harder plastic and also the way they're designed...they wont bend too easy ( to protect thousands of dallor worth of chips in a dozen tubes.lol) It's light but just as strong as those piece of wood you're using.... My plant use to Throw those out.....daily.
its a tough call, you gotta have some amount of suspension but how much?, the triangle part seems inevitable with both springs attached at the peak, (upside down peak),, are there no options for softer tyres and skid shoes i reckon would have saved the original design, only really broke because the carbon dug in when the wheel was gone, anyway its great fun to watch,
5:04... that finish is called "brushed aluminum" 17:02... There is a logical reason the cub landing gear is set up that way... and it works. Why waste time to reinvent the wheel. Look at the length of the springs on the Cub and how long they will stretch at maximum deflection. The attaching pivot point (opposite the wheels) is much better placed when in full deflection.
as a beginner the most difficult part for me to get right was the landing gear..... who knew the damn thing always kept breaking, sometimes even before takeoff!
You need a rubber bands between the axles but why all the complications just for wheels use two layers of your alloy fixed together like normal model wheel frame simple and poor the money into some Bush cub style wheels , we make them out of cheep jandles glued together and sanded to shape a hundred mills round and 30 wide last for years died black good luck
One spring between the two struts tying both wheel assemblies together? If you look at full size example you gave the two assemblies are tied together at that central point. Yours are completely independent
Your first and last sentences seem contradictory :) Unless I'm missing something the middle section in the full size is rigid, so there is no difference between connecting to that central point, and connecting to the opposite side of the fuselage (other than the angles I described, and the load being shared across two points instead of one). In any case you didn't mention how the outcome would differ, if that's what you were saying...
@@iforce2d the first part was a suggestion to easily test something else. Put a single spring between both assemblies the forces acting on both with counteract and I think it will work better than a spring on each independently. My second half of the comment was referring to the stresses in the full size version being shared in the same way. Although it's a solid brace it's two triangles on opposing sides of the central point.
@@iforce2d "so there is no difference between connecting to that central point, and connecting to the opposite side of the fuselage" It's something about the lateral centre.. terminating both springs at the lateral centre line I think maximizes the self leveling ability of the two springs as they work together. In Cad you can connect up lines to represent the linkages and then move the assembly to see the effect. I don't know if you've tried that. Works great when designing FPV camera mount positioning. p.s. FreeCAD is highly recommended and especially for Linux.
You might want to have a look at this paper on fixed leading edge slats, I found it interesting. naca.central.cranfield.ac.uk/reports/1933/naca-report-407.pdf
Use rubber bands. Cheap, tuneable, easy to replace and a natural rising rate. Steel springs are almost always linear rate. Hardware store springs are rubbish. Poor materials and poorly heat treated
One thing that might be handy to make (if you want to bend some more aluminium/metal): ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-Ggy1DHwAh_0.html
