New legs for the Avid

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Posted

A month or so ago, I picked up a High wing cabane gear that was made for a Kitfox 3.  I was going to put it on the Avid MK IV.  Turns out the Avid is 1/2" wider than the Kitfox where the cabane goes, so I had Lowell make me a cabane to fit the Avid.  Started the install today.  Always takes longer than I think, but should be done by tomorrow evening when it's supposed to be clear, calm and cool.  We have a frost warning for tonight... Good thing I'm done painting fabric.  JImChuk

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Posted

Nice! Could you take a close up photo of the front attachment points? Does the cabane « V » sit outside or inside the attachment points on the frame?

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Posted

They sit outside the landing gear mounting points on the fuselage.  JImChuk

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Posted (edited)

I now have several hours on this gear on my Mark IV, Lowell had to modify the cabane 7/8" wider for my Avid. It is fantastic, the aircraft is so stable on landing it is a whole different experience. For those who want, I have an analysis of the landing strength which says this gear is good for about 12 feet per second, and about 4 g's on landing before those yellow springs bottom. This makes the gear stronger than any Cessna.

Lowell was a pleasure to work with, and the gear was half the price of a Grove gear.

Fred, here is a detail of the cabane forward attach point, which runs to the outside of the fuselage ears.

cabane detail.jpg

Edited by nlappos
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Posted

I now have several hours on this gear on my Mark IV, Lowell had to modify the cabane 7/8" wider for my Avid. It is fantastic, the aircraft is so stable on landing it is a whole different experience. For those who want, I have an analysis of the landing strength which says this gear is good for about 12 feet per second, and about 4 g's on landing before those yellow springs bottom. This makes the gear stronger than any Cessna.

Lowell was a pleasure to work with, and the gear was half the price of a Grove gear.

Fred, here is a detail of the cabane forward attach point, which runs to the outside of the fuselage ears.

 

That's a nice setup! Those springs look stiff...what is the rate? Have you calculated your total wheel travel? spring travel?

Brooks

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Posted

Looks great Jim!

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Posted

This is the Highwing LLC gear, made by Lowell Fitt. The springs are stiff - 1450 lbs per inch. In a max landing the gear moves up 4" and out 4" assuming no tire flattening (which would be at least 3" more, I think) as the spring closes its 1.78" compression. If the spring was softer, the gear is worse, since the spring will bottom earlier at less force.The gear is good for 12 feet per second sink rate, and about 4 g's when the spring is completely compressed. See below for the geometry.

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Posted

The math looks pretty good and I am sure that the engineering on the Tacoma Narrows Bridge looked good also.  After two failures I can attest that there are flaws in the design of this style of gear but if you grease it on every time they will last you a life time.  If mine were the only failures my experience could be discounted but ther have been others.  The wider stance does make the plane handle much better.

I sure can agree the doing business with Highwing LLC was right on the money and I would do business with them again but not to purchase that gear. 

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Posted

Well I got the gear mounted today.  Sure was a pain in the neck getting the fairings on though.  Lots of holes that all have to line up.  I enlarged the holes on the second side, and it went much better.  I was done about 10 minutes after it was to late to fly.  I did taxi up and down the strip once, and it seems the bumps are smoothed out considerable compared to my bungee gear.  Maybe tomorrow it will get tested out.  Paul, did your gear have the cross piece at the top of the V of the cabane?  I think that helps to resist the inward and downward pull on the cabane.  The Kitfox cabane didn't have it, so I think that was an improvement after some failures.  I'm also tempted to tie the center to the seat truss.  I figure if it can't go down, it can't pull the sides of the fuselage in.  My seat truss is also reinforced with .040" steel plate.  Any comments or thoughts are welcome.  I don't want to be welding on this fuselage any time soon.  (or ever)  JImChuk

Next step is to work on the brakes.  

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Posted (edited)

My cabine did have the cross member, I suggest adding a king post at the center of the crossmember going to the low point of the cabine to help strengthen the cabine.  Maybe attaching the cabine to the truss would help, but I just don't know.  I do know that part of the failure mode is the cross member is deflected downward as the sides of a he fuselage are pulled inward  maybe the problem is that the fuselage just isn't stout enough for this style of gear.

my new gear has Roberts Rage struts, the cabine also has X bracing in addition to the cross member.  The front mount was built heavier with additional holes to mount the cabine. The downside is that it is not a simple bolt on application and requires new mount fabrication.  I also built the gear legs wider to attach to the rear gear mount at the strut attach point. I see that Kitfox has also went to a wide stance on their gear legs.  The center attach point for the standard gear is a weak point.  One thing that I would change is the angle of the gear legs are to steep as are the gear legs on the so called Bush Gear design.  If you think of that gear as a Sunday flier gear not as a Backcountry airstrip gear it is probably very serviceable for the average pilot.  I do know that I was not descending at anywhere near500 feet per minute when the gear/fuselage failure happened

Jim i also reinforced the seat truss on the first rebuild and that has worked good. 

Here is a link to photo of what my gear looks like now.

Edited by wypaul
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Posted (edited)

The pic link doesn't work. My bad...

Do you have a picture of the damaged gear and fuselage?

Thanks, Brooks

Edited by MnAvidFlyer

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Posted (edited)

If you touch/click on the banner "new Tall gear " it does work.  

Edited by wypaul
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Posted

Yes Paul, it would be interesting to see how the fuselage was bent.  PM if you don't want it anywhere else, and I'll delete it after taking a peek.  I got to fly my plane today for a while.  Seems to me the new gear is way more stable then the old standard bungee gear was.  Bumps seem to be smoothed out on the strip a fair amount as well.  I did tackle the brakes (or lack there of) today, and had some success with that.   I moved the mastercylinders 1" closer to the pedals by drilling new holes in the arm that's welded onto the toe brake pedal.  I was surprised I could move the cylinders that much, but they kind of go under the rudder pedal for the most part.  I would say the brakes are a huge improvement.  Not going to stand it on it's nose or hold the mighty Jabiru back at full throttle, but much much better then they were.  I did put a bevel on the front and back of the yoke the arm bolts to so when the arm pivots down, it doesn't hit on the back of the slot in the yoke.  Hope that makes sense....   JImChuk

PS  when I came back after supper, I had a little friend waiting to see me.  Rode up on the 4 wheeler, and she stayed.  When I walked up to the plane, she came closer.  If you can zoom in, you will see her bottom jaw it off set from the top one.  She was a fawn last winter and was the smallest one around.  Looks like she is in poor shape now for it being the end of summer.  Suppose she has a hard time eating with those teeth not lining up.  Surprised the wolves we have running around haven't picked her off.  I had two timber wolves on the strip a couple of weeks ago.  

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Posted

Jim

 

I have the cabane gear on my MK4 and love the extra 10" width.

I also faired the springs with some aluminum fairings just in keeping with my efforts to reduce drag at everywhere possible. I even put fairings on the flat plate where the leg struts meet in the middle.

This is not a great shot, but you can see the fairings I am referring to.

The one in the middle was made by using two chrome spinners front and back. This helped eliminate about 24" of flat plane on the gear.

John M

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Posted

If you can get close ups of your gear fairing, that would be nice John.,  I wonder what would the effect be if enclosed the entire cabane.  2 pieces of aluminum with a bend in the middle would do it plus maybe some support depending on how thin the aluminum was.  Could maybe double as a small storage compartment....  A Champ or Chief has similar structure to the cabane, and it's all covered.  It doesn't stick down quite as far though.  I did notice today that the prop hub was about 1 1/2" lower than it used to be with the MK IV bungee gear.  Used the same tires.  JImChuk

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Posted

Another way of streamlining is to add a cargo pod. There is no noticeable speed drop with the pod on or off. The aircraft does feel smoother in flight with it on. There must be a lot of turbulance

 

 

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Posted

I got looking at a fairing for the cabane, and if it was 7" down at the lowest point, it would cover the cabane.  1 1/2" at the edges where the cabane bolts to the fuselage, maybe 16" forward to a point in the front, and 24" toward the back.  Actually if you follow the angle the fuselage bottom is to the bottom of the cabane, and then angle up toward the fuselage in front of the cabane it would blend in fairly well maybe.  Perhaps I will play with that.  Look at the picture of my Avid from the side, and maybe you can see what I was trying to say.  Fit some doors into it, and it would be a cargo pod as well.   JImChuk

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Posted

Jim:

My cabane gear is completely faired including the springs and the mid junction plate, as I mentioned. I'll get a better photo today and post it.

I also have gap seal tape at the elevator and rudder gaps. All struts, wings and horizontal are faired. And as I mentioned before, I have installed wing strut cuffs.

My cruise is 90-95 MPH TAS at lower altitudes and 100-105 up above 10,000 MSL. This is at 2900 RPM with my Jabiru 2200.

John M

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Posted

Let's see if I can attach the photo of my bush gear fairings.

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Posted

John,  put a little propeller on the front, and they will think you have a wind generator there.:).  You gave me some more ideas.…  JImChuk

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Posted (edited)

Probably going to change the subject back to my gear legs, and maybe should start a new thread about it instead, but I got my new brake pedals on and up to the point of being able to test them to see if they were an improvement.  Here are some pictures of what I did.  I took the rubber boots off the master cylinders, and was able to get them under the pedals.  That allowed me to reposition the arms coming off the brake pedals and getting better leverage.  The boots are to keep dirt out of the cylinders and for that 'm going to put a thin piece of aluminum on the top oft the cylinder, and tape it on with electrical tape that folds over onto the aluminum and also sticks to the sides of the cylinder.  Don't gain any height that way, and the bottom of the rudder pedal clears the top of the cylinder.   I bolted things together, cause I wasn't sure how it all would work, and even if it was welded up, I would still use a couple of bolts to hold the sides together, at least on one side.  I can bend one side out enough to get it onto the rudder pedal tube so it's simpler to make.  How did they work you say?  Well I was never able to lock the tires on anything before, maybe on glare ice, but maybe not even then.  A week ago, before I moved the cylinders forward on the original pedals, I could hardly hold it at 1200 RPM on the Jabiru.  After I moved the cylinders in on the top, it would hold up to about 1900.  Today I could hold it to right at 2600.  Was able to hold the brakes and lift the tail off the ground with the throttle.  Never could come close to that before.  It's still a work in progress, they are a good bit better on the left wheel than the right, and that can start a swerve if you are getting on both brakes fairly hard.  I changed the brake pads on the right wheel when I installed the gear, I'll put new ones on the left side also and see if that has anything to do with it.  If I make another set of pedals, they will be a little bit different, maybe more welding and less bolts, but I think the concept works.  JImChuk

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Edited by 1avidflyer
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Posted

This is what Brett did for me. I added the block to keep my toes off of the brake.

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Posted

Bandit,  how well do your brakes work?  Also, what make and model are your master cylinders.  JImChuk

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Posted

Looks a lot like what I did, except I changed to an external reservoir and the shortest cylinders matco makes (4g or 4h), and made the cylinder connection right above the pivot point.  It gave me the 2.5x mechanical advantage Matco recommends, and went from barely able to hold the plane at idle (with the 'intensifier' kit in the old 5 cylinders), to holding it at full throtttle.  Avid Model C, 582, original Peery prop

Mark

 

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