Bringing a Kitfox 1 back to life

213 posts in this topic

Posted

Making some progress on the gear. I’ve spent much more time looking at it and researching than I have actually working on it. Another hour in the morning and I’ll be done with the V. Next, on to the shock struts, then I’ll perform the surgery on the back legs. I’ll have to be a little creative to make it clear the lift strut bolt, but I can make it work. A few observations. The cabane gear is, by function, a falling rate suspension. That is, the spring will affect the pull of the gear less as it travels farther upward. This is because the gear legs will move up more than they move out, the more they travel upward, from 45 to 90 degrees, but the shock struts are counteracting the outward movement. At less than 45 degrees, the tires will move outwards more more than upwards. Lowering the center of the V will help counteract that falling rate effect. I decided to use bungees for my gear. I went with the two bungees of the lighter J3 Cub, which might still be on the stiff side for this, but they’re readily available. For the cost of buying the gear, I got all the materials to build it, the J3 legs with 1-1/4” axles, plus a set of Goodyear 26x11-4 Airwheels on the old 4” wheels with expander brakes, and a few sets of McCauley 6” wheels and brakes. The guy I got the Airwheels from, pointed out that the little wheels and drum brakes are actually lighter than the Cleveland wheels and brakes that many people have switched to. They do look good on it, too. 

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Posted

Dressing it up with a bow tie bracket. 

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Posted

Nothing to it, right? My plan is to put a couple gussets on the cabane V attach brackets, then I’ll be done with that. I stuck the bushings in the shock struts and used them to locate the gear temporarily. I’ll cut them apart and make the bungee mounts later. I got the left hind quarter tacked in place. That was fairly straight forward. The old J3 legs I got, had 1-1/8 rear legs that had been spliced with 1-1/4.  I cut it off at the weld and sleeved it again with 1-1/4, cheating the angle to make it slightly wider to line up with the Kitfox mounts. I could have fit the cabane V mount inside the landing gear mount bracket, but the bolt has better shear strength if the gear is tight to the brackets, so I put the cabane mount on the outside, and I’ll lengthen the bushings to fit the mounts. The hardest part is taking off the mill slag without a sand blaster. I have over an hour at the bench grinder, taking it off with the wire wheel. 98163785-5B6A-437E-9DD2-6A0D715F612B.thu

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Posted

Looks like an excellent job to me!  Is there going to be any damping effect?  Like a added shock to absorb the sudden retraction?

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Posted

I’m considering using small shock absorbers. It would be nice to have some damping. My shock struts are 30-3/4 center to center, which makes some Cub setups a bolt on affair. I saw one pair of used ones for $1,700, which is more than my entire suspension. There’s a Super Cub gear, complete with dampers and bungees, for $800 on Craigslist. I’ve been looking at mountain bike and mini bike shocks. I could make that work. I need 3” of shock travel to allow 6” of vertical travel of the wheels. 

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Posted (edited)

I’m considering using small shock absorbers. It would be nice to have some damping. My shock struts are 30-3/4 center to center, which makes some Cub setups a bolt on affair. I saw one pair of used ones for $1,700, which is more than my entire suspension. There’s a Super Cub gear, complete with dampers and bungees, for $800 on Craigslist. I’ve been looking at mountain bike and mini bike shocks. I could make that work. I need 3” of shock travel to allow 6” of vertical travel of the wheels. 

I have no doubt you will come up with a solution. Have you checked out ATV shocks? Mine has a single shock on the rear with almost 5" travel and is adjustable for firmness. Would be nice to be able to use something available on the local market.

Edited by Allen Sutphin

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Posted

Do you have a picture of how the shock is mounted on your suspension? I’ve been considering different ways of mounting a shock. I could go without it, but I’d like the damper if I can find a reasonable way to do it. 

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Posted

Do you have a picture of how the shock is mounted on your suspension? I’ve been considering different ways of mounting a shock. I could go without it, but I’d like the damper if I can find a reasonable way to do it. 

I have the standard gear on mine. I was talking about the shock on my ATV. I like the Cub/Piper type gear arrangement with the shock in the middle. I am looking around for a J-3 type gear.

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Posted

Do you have a picture of how the shock is mounted on your suspension? I’ve been considering different ways of mounting a shock. I could go without it, but I’d like the damper if I can find a reasonable way to do it. 

I have the standard gear on mine. I was talking about the shock on my ATV. I like the Cub/Piper type gear arrangement with the shock in the middle. I am looking around for a J-3 type gear.

I was chatting with Randy Moore in TN last night.  A few on the board have purchased his Hatz style gear which uses compression springs "in the middle". I have not heard any complaints of his builds.

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Posted

I would guess about every style of gear has its pro's and con's. Randy's gear is probably the cheapest price of the ones that are available ready made. Until I know better, I'll stick with what I got for now. Adding weight is my biggest issue.

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Posted (edited)

Allonsye,  

his gear is built ok, and strong, very light weight, and good guy to deal with, and $1350 with shipping, ready to bolt on, so i got one set from him, paid in full, he built it to my specs, then sent it ground shipping to me in Ak that takes 17+days, i paid $150 for priority 3-5 day shipping i thought,??  anyways all the center V bolts holes where all crooked/off by half a bolt hole, and the left gearleg was 5/8" shorter than the right,  the springs r suppose to b 6" long so there is preload and the ones in the setup where 5" long so just the plane sitting empty the springs where colapsed 3/4", so had to send it back to him so he could build me a whole new set again.  He said he has no idea how that happened, Now im waiting again for the new second set, hate to say that about that, but it is true, started all this on august 11th and i have pic.  Sorry for that bad news. 

Edited by Buckchop

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Posted

If the left leg was shorter than the right, it must have been built for a West Virginia plane! LOL!

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Posted

Or a NASCAR track. 

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Posted

It took me all day to finish one A arm, after I already had the leg amputated and the new one tacked in place. There was a lot of on and off to check the fit, and I spent a lot of time scratching away at the rear leg to make clearance for the lift strut bolt. I finally cut out a 7/8” wide rectangle, ground it down a ways, and welded in a piece of .050”. I’ll strap the back of it, too, to reinforce that weak point. It’s right where it goes from the sleeved part, to the thinner walled, smaller diameter, original leg. These original J3 legs were 1-1/4” front and 1-1/8” rear. The back was .049” thickness, and I couldn’t check the front. Both had been repaired, with an inner sleeve in the front, and an outer on the rear. I made my new hind leg with .058” 1-1/4. I’m trying to keep it light, but I’m still leaning toward over-building it. If starting from scratch, I’d use the lighter stuff. .058” fits snugly over the next 1/8” size down. I used 3/4” .049” for the cross bar at the top of the A-arm. The V is .058”. The other leg should go quicker.

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Posted

That modification took me from 0” to 7” of vertical wheel travel before the leg hits the bolt. I’d get a little more if I flipped the bolt over.

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Posted

Sorry it didn’t work out right the first time with your gear, Buckchop. It sounds like Randy is a good guy, so I’m sure he’ll get it squared away. 3/4” ride-in with an empty plane seems like the springs are light. With 5” of spring, and geometry similar to mine, you’ll have about 10” of upward wheel travel. I was figuring on 6”. I think the bungees safely stretch to double their length, so I could probably have more. I’d say there would be bigger problems at play if I’m landing where I need more than 6” of suspension travel. Motocross bikes have 10”-12”. I was waiting to see your post when you got it going, then I saw the J3 gear for sale and decided to give it a shot, myself. I’ve read most, if not all, of the the posts about wide gear. Springs will be cheaper than bungees. Four new bungees ran me $200. Ow. That was half as much as the 4130 steel for the whole gear assembly, with lots left over. I don’t think there’s much difference between a spring bottoming out versus the bungee suspension bottoming out against a limit cable or shock. There just needs to be enough resistance, and travel, in the first place. And try not to drop the plane like a bag of bricks. I like the wider A-arms that I have. They give the plane more leverage to not get twisted up. My biggest concern with the whole project is the weight. I know it will be a bit heavier, at least a few pounds. I’d like to get a pair of smaller, lighter, more manageable tires.

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Posted

Just about got my bungee struts done. I got half the stop plates ground to shape, then had to come in and warm up. It currently has 8” of vertical wheel travel, with the slightest bit of positive camber, and 3.5” of strut extension. I’m tempted to give it just a little more camber. If I increase the camber slightly, and flip the strut bolts, I’d probably see 10” of travel. The bungees I bought are the 1080 HD CW, rated at 900 lb. I’m going to try them on and see if it has any spring. The regular 1080, rated at 750 lb. is probably more appropriate. As I understand it, the rating is the straight pull strength, so doubling it over, like on a Cub, or as I plan to do, would double it. So, 3,600 pounds per side, with two bungees doubled over. Because of the mechanical advantage of the suspension,  that would equal 3,150 lb. (7,200 x .4375). At 3 G’s, my 850 gross plane would push down 2,550. With the regular 1080 bungees, the theoretical pull is 2,650. That sounds like the right number. 1080 CW. 

I used 3/4 and 5/8 .058 for my bungee struts. I welded in 1/2” (3/8” i.d.) tubing for the bushings. The short end, I plug welded the 5/8 inside the 3/4, so the seam would be smooth where the pieces meet, not welded. The inner extends 10” inside the lower, leaving over 6” inside to hold the angle and guide it back in straight, when it’s fully extended. I might weld a plug in and make a rubber stop, so it doesn’t slam steel to steel when it’s pulled to the stop. 

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Posted

Sorry it didn’t work out right the first time with your gear, Buckchop. It sounds like Randy is a good guy, so I’m sure he’ll get it squared away. 3/4” ride-in with an empty plane seems like the springs are light. With 5” of spring, and geometry similar to mine, you’ll have about 10” of upward wheel travel. I was figuring on 6”. I think the bungees safely stretch to double their length, so I could probably have more. I’d say there would be bigger problems at play if I’m landing where I need more than 6” of suspension travel. Motocross bikes have 10”-12”. I was waiting to see your post when you got it going, then I saw the J3 gear for sale and decided to give it a shot, myself. I’ve read most, if not all, of the the posts about wide gear. Springs will be cheaper than bungees. Four new bungees ran me $200. Ow. That was half as much as the 4130 steel for the whole gear assembly, with lots left over. I don’t think there’s much difference between a spring bottoming out versus the bungee suspension bottoming out against a limit cable or shock. There just needs to be enough resistance, and travel, in the first place. And try not to drop the plane like a bag of bricks. I like the wider A-arms that I have. They give the plane more leverage to not get twisted up. My biggest concern with the whole project is the weight. I know it will be a bit heavier, at least a few pounds. I’d like to get a pair of smaller, lighter, more manageable tires.

using the die springs that he uses your looking at less than 2" of compression before the springs go metal to metal.  That is my main argument with the die springs that these guys are selling with "bush gear".  The ones that were on the gear I got had 1.57" of compression before they were sacked out.  And the guy was pissed that he bent the bird and gear legs on a pretty "normal" landing.

If we are working on a budget, either the skidoo center shock spring I have used or bungees are the only way to go.  If money is not an object, then go full blown with the shock set up and hope they don't ever leak on ya.

For me, "bush gear" means keeping it simple and functional like you have done with yours!  I would love to come see your project one day soon.

:BC:

 

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Posted

I’m not quite satisfied with the bungee struts. I want to sleeve the lower strut where the bungees attach. I’ll try to get some 7/8 tomorrow, and redo them. I was thinking about how much pull there is going to be on those nubs, and how it would give, if it did. I think what would happen is that it would kink the lower bungee strut tube, pinching it tight onto the inner guide rod. Putting a doubling sleeve on it would make it a lot stronger and less likely that could ever happen. 

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Posted

I would put a diamond shaped reinforcing plate on the ears as well.  That's a lot of tension on the welds and I would be afraid of cracking at the toe of the weld.  

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Posted

I do have to agree with simple simple simple, i also love the bungiees more, Dont matter if on the gear legs, or for the tension on ur skis.  

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I was overthinking things, putting a doubler on the shock strut. I got a chance to look at some J3 and J5 struts at Stoddard’s, today. They are straight 3/4 with ears welded just like mine, sliding in a 7/8 section, with a slot and bolt through it. Mine, I made with 5/8 inside 3/4, which would have been fine. The ears were all 3/4 on 3/4. I was pretty much right on with my initial design. It looked much like High Country’s shock strut with his Ridge Runner gear. I have some 1080 bungees on the way. I didn’t get the cold weather ones, just because I didn’t want to special order them. The 1080 and 1280 are the same pull weight, but with different diameters; 5/8 and 3/4, respectively. I’ll hold on to those 1080 hd cw sets, until I have a chance to try these out. They also had a set of Pacer hydrasorbs for $300, with bungees, but I passed on them.

The brakes aren’t anything I want them to be, but I’m going to give them another chance. Too much travel and not enough brake. I looked at the Grove 4” disc conversions, which are probably the best way to go, but expensive. I have the McCauley wheels and brakes, but I’d need the 1-1/4 - 1-1/2 axles adapters and some tires and tubes. Heavier, but less expensive. It looks to me like these drums and shoes are just worn, meaning more travel is needed. It’s possible the Matco MC5 master cylinders I have don’t have the volume needed to expand the tubes. I’ll finish and cover the gear, and if the old tricks don’t work on the brakes, I’ll go to plan B. 

On a side note, Airframes Alaska massively expanded their place since last spring. Definitely worth checking out if you’re in Anchorage. They had a tenant in the back half, and now the whole building is theirs. Pretty cool, if you’re into that kind of thing. 0A7B1FA8-6DAB-4166-BA96-55379D252644.thu

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I never liked drum brakes anyway. It would have been easy to use them, and I liked the 4” wheel and 26” tire combination, but the brakes just aren’t working. The masters don’t have enough volume to fill the tubes and push the pads out. It strokes out. Grove said they don’t have the disc conversion in stock. 6-8 week lead time. So, I’m going with the McCrackleys. I’ll need the axle adapter and a set of tires, but I can get those. McCauley had serious problems with cracking and broken bolts. Since this is an experimental, I can drill and through bolt them, so it’s not a problem. Got epoxy on the gear legs. Looking good. 

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Posted

I could have had it up in the air, already. I better have it done this week. I’ve been realizing just how much time and money I’ve sunk into this. Just fly it, already. 

The bungees got sent on a world tour, courtesy of the USPS. I hope they do end up here.

I got a good deal on some 8.00 x 6 tires and tubes. Now I just need axle adapters to fit the 1-1/2 bearings to my 1-1/4 axles. Got the gear mounted, but no bungees. 

I like the idea of the wide gear, but I could have been flying it instead of blowing more money on it, if I stuck with the stock gear. Wider really is better, right? It’s 70” between the torque plates.

 

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Posted

Do you have a picture of how the shock is mounted on your suspension? I’ve been considering different ways of mounting a shock. I could go without it, but I’d like the damper if I can find a reasonable way to do it. 

I have the standard gear on mine. I was talking about the shock on my ATV. I like the Cub/Piper type gear arrangement with the shock in the middle. I am looking around for a J-3 type gear.

I was chatting with Randy Moore in TN last night.  A few on the board have purchased his Hatz style gear which uses compression springs "in the middle". I have not heard any complaints of his builds.

Nice, nice and nice I think you will be very happy that you spent the extra time and money.  Looks like you have a lot of travel And you will be happy with the wide spread at the fuselage much stronger mounting point.

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