Supermotive

Regarding springs,my choice would be acme aero springs but my budget (read wife) says no way. I am experimenting with eurethane pucks with some success. 2 kg weight saving,no chance of bottoming out and a degree of rebound damping.some more hard testing is required but results are favourable.

Dusty, would you please share details about your plane and the pucks you chose and you testing results (or opinions)

The pucks are definitely firmer than the springs., which I believe is a good thing as my spring setup had been bottoming out.

This is the top of the rod that goes out to the wheel. The bolt was partial chopped through from the hammering. I fly off field a lot and on some pretty rough hillsides.

I have tried different urethane shore hardness. Currently the red (90) is the best. I tried a 75, which was too soft and sagged. 

The next step is to machine the pucks to have grooves around them, or vertically drill them. Like a pistol magazine. Urethane can't be though of as a spring as it doesn't compress.

Think more like water where it just displaces and absorbs energy in the process. 

The piece of wire is my high tech device for measuring suspension travel. This is from a normal landing, so there is plenty of travel, but I would like more.

 

If rebuilding a suspension I would use 5 or 6 pucks to effectively change the rate. My weight saving calculation was out a little, approximately 1.4kg weight saving. 

We get the urethane here from an industrial supplier as a one piece tube. We freeze it,and part it off in a lathe. This is extremely cheap so not a huge cost for experimenting.

I have a wee way to go, but even at this stage I see a huge improvement over the die spring. 

I will post updates as I go, but am pretty busy with work at the moment, and rebuilding another kitfox.

 

 

 

 

I've been thinking about making new struts for my gear and using snowmobile springs and then saw this. My setup currently would use bungees. Here in the USA, Mcmaster Carr has the 90A durometer tubes for sale, here are some links:

https://www.mcmaster.com/87235K58 6" long tube 2" OD, 1" ID 90A durometer

https://www.mcmaster.com/87235K32 Same thing but 36" long and much better price per inch.

I may have to give this a go.

 

I have often wondered why nobody has criss-crossed the space below the fuselage with slightly longitudinally offset gear legs, then use the kind of vertical spring-shock arrangement above the wheels.  The Just Aircraft SuperStol gear pivots about the centerline keel.  Criss-crossing the lower fuselage give even better geometry, with shallower angles, and hence even less squat as the gear compresses.  It puts more stuff out in the propwash, though.  Still, this concentrates virtually all the gear's force at the shock/spring attachment.

I have had several landing gear failures since going to the spring "bush gear". I have been researching the subject and have noted quite a few similar failures of that type gear, all in about the same location and of the same nature, Inward bending of the forward strut leg. I have been reluctant to re enforce that leg for fear of promoting a more serious failure elsewhere. The gear is a Chinese copy of the gear used by Piper from the 1930s onward but the Piper gear does not seem to suffer the same failure. Today I made a cardboard model of the gear geometry and I believe I have located the problem. The bottom anchor bolt for the spring leg on the "bush gear" is fastened to a metal plate welded between the front leg and the axle. When the spring strut is fully extended and bottoms out, or the spring becomes coil bound, that point then becomes a rigid fulcrum with the axle as a lever. The upward motion or the axle is then translated into an inward rotary motion on the front gear leg. The failure always seems to occur at the point halfway between the axle and the fuselage, which makes sense. I have never bent a rear strut, nor the spring strut, always the front one.

Looking at photographs and real life examples of Piper, Hatz, and Pietenpol gear shows that the anchor point on those gear is at the inboard end of the axle. My model shows a significant difference in the movement of the middle of the forward gear leg when the anchor point is moved to the end of the axle. As a matter of fact, the farther inboard the pivot is, the lesser the rotary movement at the front gear leg center.

I have yet to figure a force analysis on the gear, but I think i am onto something. I'll post more as I find more.

On a positive note, my welding is getting better.

Bob McCaa

 

All of the "bush gear" I have seen has a straight pull from the axle point through the vee to the upper mount.  By lowering the intersection of the Vee like you see on the piper gear you will better distribute the forces.  This along with changing the springs to ones with more travel before they bind is the key to an easy fix.  The gear I now have on my plane had been bent more than once and was bent when I got it.  I straightened the tube and lengthened the slots as well as changing out the springs.  Since that time I have flown the plane a a weight much greater than the published numbers and have dropped it in pretty hard with no ill effects.

The gear legs that I have were custom built, but if one would supply me with measurements on the gear they have I can mock it up and make replacement vee and struts that would take care of the issues without having to completely swap the gear legs.  Would be a quick matter of lifting the plane, pull a few bolts, pop the new struts and vee in and lower it back down. 

 

Regarding springs,my choice would be acme aero springs but my budget (read wife) says no way. I am experimenting with eurethane pucks with some success. 2 kg weight saving,no chance of bottoming out and a degree of rebound damping.some more hard testing is required but results are favourable.

Just thought I would put in my 2 bits. I built a Bush gear for my Mod 1 Kitfox. I used die springs in a housing similar to the bearhawk gear. Designed it to take 3 G's before spring would go solid. I did a very poor landing. The gear held up fine but the fuselage failed. I don't believe the springs went solid because the safety cable cable ties were unbroken. I have considered building new tension members with bungees. I believe an Aluminum Spring Gear or bungees are the more forgiving as they provide the most flex (not including the new Highlander gas strut gear). Here is a link to the drop test video I did on my gear; http://www.youtube.com/watch?v=fvQtKQ5gHVY

Dave  

Well I decided to go to cabane gear on the Avid+ and move the bungee gear that is on it now to the Mini+.  I had a few days off over the holiday so was able to get it all fab'd and tacked up.  Now I just need to coax Leni into welding it.  (I'm hoping he has forgotten about the pain of the Mini+ fuselage weld by now).  Leni, I promise that this is all new 4130 so should be much easier to weld...

My plan is to go with the Acme Aero shocks if I can get them to configure them for my geometry and GW.  I left an email with them but have not received a response or talked to them yet.

The bungee gear I have on the Avid+ is 5.5" taller than the Airdale extended gear.  I was able to modify the jig I had built for that gear and made this gear 8.5" taller than the Airdade extended gear. 

I know there has been a lot of discussion about the best geometry for the cabane type gear and since It seems the cub gear is pretty well proven, I decided to match the cub gear relatively close.  The tubes are a little different though, I used 1 1/8" X .049 for the main tubes and 7/8"  X .049 for the cabane.  I also have the third mount point forward of the stock mounts on the Avid to give it more strength and a wider V for the leg.  This gear is probably overkill and a lot heavier than needed for normal situations but I tend to land in some places that can be rough and I don't want to break it in the middle of nowhere.

Anyway, here are the pics.

nice progress. Thanks for sharing!

Would you like to share some more info regarding your landing gear, like width and especially tube dimensions front and rear legs...

most of the tubing is .049, 1 1/4 inch for the front leg and 1 inch on the rear.  The legs are about 33 inches long and center to center on the tires is about 82 inches. Keep in mind this is hillbilly engineered...

Thank you Ken for the input and yeah I would love to pop over to your strip when the weather improves, could you email me your phone number to airbornetroubadour@protonmail.com

Troy has trouble keeping up with me, he likes to cruise at 60 mph @ 5000 and I'm doing about 75 mph at that so I have to slow down for him. We flew a loose formation with a phantom and it was hard work for me. On the way back from out day out at Rougham I lost them owing to a later take off slot. But I arrived over 10 mins ahead of them both at my eco cruise!

I know what you mean with the LAA it's sad how the organisation set up to promote light aircraft flying is sometimes a major obsticle to flying as well.

I would like to do the mod that you have done to the tail feathers on your Avid as I have a covered round rudder in the Hangar. The extra weight i could carry would be handy for another crew member.

I have emailed you with my phone number. Skiing this week, when I get home I’ll see if I have the tail plane mod. details. Is yours a Speedwing Aerobat? Needs to be for the mod. to get you 1020lbs max weight.

Ken

Jabiru sold them, I don't know if they still do but I would nut be surprised if they do, they fit the plenums.

Down in wasilla workin on the wings, 3days in on reassemblie and lookin good. 

I had thought about building a fairing that would completely enclose the cabane.  It would attach to the belly of the plane like a belly pod.  Most likely out of fiberglass.  I think it would cut down on a bunch of drag, and the area behind the cabana could maybe become a baggage area if built right.  JImChuk

I have this if its any help. 

Today's efforts.  Hope I didn't forget anything....JImChuk