109jb

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Everything posted by 109jb



  1. 109jb added a post in a topic New Rotax 670 Install   

    While it is true that ethanol based fuel is recommended by Rotax over Avgas, don't forget that fuel system compatibility may be a more influencing concern for what fuel to use. There are many cases of folks with older fiberglass fuel tanks reporting that their tanks and/or the tank coatings were not compatible with the ethanol based fuels, leading to fuel system contamination. I have an older Kitfox IV (912 powered) that has the Kreem lined tanks and just sold an older Kitfox IV (582 powered) that also had the Kreem lined tanks.  I am leary of  using any fuel with ethanol for the reasons stated above. On my project airplane I am contemplating cutting the tanks open, removing the Kreem liner, and re-coating with a know ethanol safe liner so that I can use auto gas with ethanol. In my particular case, non-ethanol based auto gas is not readily available to me, so going that route would be very problematic. If I do reline the tanks then I would opt  for auto gas with or without ethanol, but it would probably be ethanol based due to availability. On the 582 powered airplane I ran Avgas with decalin lead scavenging additive. On that airplane the plugs stayed clean and I didn't notice any excessive buildup of deposits when borescoping, but I didn't own/run that airplane very long, so don't have a long track record with the Avgas/Decalin fuel. Just food for thought.
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  2. 109jb added a post in a topic Another Kitfox IV rebuild project   

    So for the bungees I haven't settled on a diameter or number of wraps. What I can say is that on my particular design the bungees will need to provide about 1.58 times the force of the original bungee setup to provide the same amount of "cushion". I plan to figure out the amount of stretch the original bungees had and then tailor the new bungees to provide the same amount of force. This is based on the geometry of the gear as shown in this drawing.
     
     

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  3. 109jb added a post in a topic Another Kitfox IV rebuild project   

    Thanks Jim. Run of the mill polyethylene it is.
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  4. 109jb added a post in a topic Another Kitfox IV rebuild project   

    Have a question. For the rudder cables there is a section next to the seat that has a 5/16" O.D. plastic guide tube that gets inserted into short pieces of 3/8" x 0.035 tube at either end. These pieces are about a foot long or so. Is that tubing something special or just run of the mill polyethylene tubing from the hardware store?
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  5. 109jb added a post in a topic Another Kitfox IV rebuild project   

    So per my other thread, I made a set of cabane landing gear for my Kitfox 4  project. For design, I made my own decision on width and height, but I didn't re-invent the wheel and did a lot of internet searching for tube sizes. It came down to a combination of looking at other airplane designs, other kitfox landing gear designs, etc. It was a lot of internet sleuthing. To save someone else from having to go down the same road, I decided to make a pdf showing how I built my gear. It was built in place on my fuselage, and I don't know how close it would be on other Kitfoxes. I've attached that pdf here. I had a chance to get a better picture of the gear with the airplane outside showing how the gear came out. Since these pictures were taken I have decided to make a couple changes, namely, I am going to add a tube between the front and rear legs about half way down, and I am going to change the lower shock strut mount. The current arrangement was chosen so that I could use the the wheel penetration skis I have. I put the skis on and realized that I could just extend the axle a bit farther inboard, through the inboard mount of the ski and put a yoke on the bottom end of the shock tube. This should alleviate some of the bending moment in the gear leg during landing.
     


    Cabane Landing Gear for Kitfox 4.pdf
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  6. 109jb added a post in a topic Fuselage landing loads (Kitfox IV) and cabane gear   

    I decided on that attachment to keep the axle geometry stock so I can still use the wheel penetration skis I have. It was a hard decision and I am aware that the cub style bungee mount at the axle takes some of the bending moment out of the gear. I may see what I can do to accommodate both the cub style axle mount while keeping the ski mounting. The front leg on this gear is 1-1/4" x 0.058" wall so even with the current placement will take a very hard landing to bend.
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  7. 109jb added a post in a topic Fuselage landing loads (Kitfox IV) and cabane gear   

    So I got it welded up. Seems like it is going to work well. The height and width came out very close to plan. A lot was done in place on the fuselage so it is definitely a one-off.

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  8. 109jb added a post in a topic Kitfox 4 rebuild   

    Use a DPDT switch like this

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  9. 109jb added a post in a topic Oratex 6000 on a PA12   

    Looks like you are priming as you go. Are you mixing epoxy primer and using a gun, or just using a rattle can? Just trying to figure how I'm going to do inevitable touch ups for added stuff.
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  10. 109jb added a post in a topic Fuselage landing loads (Kitfox IV) and cabane gear   

    Yeah. I'm mainly looking for improved handling and to get everything gear related on the outside of the airplane because I plan to eventually get an amphibious set of floats. The stock bungees would be a pain to deal with for seasonal gear to amphib and back changes.  Also gets rid of the hole in the bottom of the fuselage.  If I can land in a bit more rugged terrain that's OK too but wasn't a priority. 
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  11. 109jb added a post in a topic Fuselage landing loads (Kitfox IV) and cabane gear   

    Oh.  I forgot to mention that the other night I found a vendor selling gear doing just what I'm describing. It is the Shock Monster gear for the Kitfox IV. You can see a picture at this link https://store.tk1racing.com/ProductDetails.asp?ProductCode=80-2761  I can't afford $2200, so the couple hundred bucks spent on tubing will have to do.
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  12. 109jb added a post in a topic Fuselage landing loads (Kitfox IV) and cabane gear   

    On another note I haven't decided how I am going to go for the shock struts.  I'm considering using bungees instead of springs like Joey Myers on the facebook group does. The bars in his setup are both aligned  unlike the cub type gear that has them at 90 degrees and uses shock rings. For now I'll probably just use some conduit and make solid links so i can move it around.

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  13. 109jb added a post in a topic Fuselage landing loads (Kitfox IV) and cabane gear   

    I think this is what you are asking for. 
    Here is a drawing from the front. The red is the load at the wheels. The green is members in compression, Blue is members in tension. The purple is the resultant load on the part of the cabane where the shock struts mount (shock/springs/bungees not drawn).  This load is the one that would try to pull the points in the yellow circles together, but the added horizontal member will prevent the yellow circles from coming together.
    The drawing were made in Autocad, and then the arrows added using just Microsoft Paint.
     
     
     
     

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  14. 109jb added a post in a topic Fuselage landing loads (Kitfox IV) and cabane gear   

    So I went ahead and started on the new gear today. Got the legs on and they swing free. Still have to cut off the front tubes and put on the axle mounts. I will be using the 3/4" axles like the stock gear and the 8" Douglas wheels. Hopefully the Nanco N800 will become available again.

     


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  15. 109jb added a post in a topic Fuselage landing loads (Kitfox IV) and cabane gear   

    Thanks Jim, but I disagree. My cabane will have a tube under the fuselage between the mounts on either side of the fuselage. That will form a triangle and the cross tube will be in pure compression. this will take most of the inward load you are describing and the fuselage won't really see it.
    Of course. It has to if the door sill is bent. 
    I have looked at many here and on other websites. The seat truss bending I have seen is either secondary to the door sill bending, or the result of hitting the limit cable on the gear.
    As I see it, the stock design puts the door sill in bending, and due to the bungee arrangement also puts the seat truss in bending. Both the door sill and the seat truss are short in height and made from light tubing and it is not hard to see that a hard landing could easily overstress these lightweight short trusses. Using the forward mount takes all of the bending out of the door sill truss, and using a cabane takes all of the bending off of the seat truss. The lateral tube on the cabane will prevent any sort of twisting due to the mount pivot being hung below the longeron.
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  16. 109jb added a post in a topic Fuselage landing loads (Kitfox IV) and cabane gear   

    I don't get this statement. The front mount is at the door post and is far stronger than the 6" tall door sill. How do you figure that it is a "position of less strength"?
    The loads are eventually reacted at the door posts regardless of where the actual mounts are. The difference is that the stock mount position requires the door sill truss to take the load in bending and transfer that bending load to the fore and aft ends of the door sill truss and into the door posts. Using the forward mount puts it into the forward door post much more directly.
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  17. 109jb added a post in a topic Fuselage landing loads (Kitfox IV) and cabane gear   

    Actually, thinking about  it more, the moments with the stock gear will be resolved wit an upward vertical force at the forward mount and a downward force at the rear mount. In other words, the rear gear tube will be in tension and the forward gear tube will be in compression. This is even worse for bending in the  sill area.
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  18. 109jb added a topic in Avidfoxflyers General Hangar   

    Fuselage landing loads (Kitfox IV) and cabane gear
    I have been working on my Kitfox IV project and am getting to the point where I will be making my cabane style gear. First of all, it will be about 2 inches taller and 84" wide to the outside of the wheels. I've been reading up on the reinforcement people have done to the fuselage. Most have added shear plates between the tubes. I don't really like that solution for several engineering reasons so I set about to do a bit of loads analysis. No numbers, but ....
    In the first picture is the stock gear as mounted on the airplane. A hard landing (AKA dropping it in) will create primarily a vertical load if the brakes aren't applied. You can see that with the gear about 4 inches ahead of the front mount that the vertical load is resolved by 2 vertical loads and moments about the attach points. Since the forward mount point is in the middle of the door sill it puts a bending moment into the sill and if hard enough bends the door sill truss as we have all seen. The "fix most have used is to do the shear webs. they probably help a little, but shear webs only work in the tension direction so won't help with crushing  of the vertical tube above the front mount, and the original diagonal tubes are already oriented to take the load in tension. Bottom line is that the web will make the sill more resistant to bending, but the benefit in my opinion is minimal.
    Now a tube on the other hand can take tension or compression, so adding opposite direction diagonals like the green lines in the second picture would do a few things. First, they would create an additional load path to the front and rear ends of the truss, getting the load directly into the meat of the fuselage structure. Second, the added diagonals will also make the entire sill area more resistant to bending. Third, instead of the one vertical tube at the forward mount taking all of the vertical load, there are two more load paths, alleviating some of the load on the vertical member. 
    Going further, many of the aftermarket gear mount to the stock  locations, so any problems with the main gear are still there. I started looking at the mounts on the side of the fuselage and at least my airplane has the float mounts, including one forward of the stock mount at the next tube cluster forward. In the third picture I've sketched up a gear that mounts at the stock rear mount and that forward float mount. Using these 2 mounts puts the load directly into the fuselage at the forward and rear ends of the door opening, thereby taking all of the bending load out of the door sill. It also puts the landing load vector between the mounts instead of cantilevered forward of both mounts. This should help the front gear tube loads.
    Finally, I took modified an orthographic projection of the airplane to show the stock gear and a cabane gear using the float mount. Personally I think the gear using the forward float mount looks better. so that is what I'm going to do. 




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  19. 109jb added a post in a topic Nanco N800 tires   

    Gear works has no stock. I don't think their system checks to see if something is in stock. I called and the guy had to physically check stock and call me back.
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  20. 109jb added a post in a topic Nanco N800 tires   

    Also. If anyone happens to have a Nanco N800 tire that is not mounted could you weigh it so I can compare weights to alternate tires in case I have to go that way?
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  21. 109jb added a post in a topic Nanco N800 tires   

    do you have a link? This is the only one I could find and I don't see any online ordering there.  https://www.tireco.com/
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  22. 109jb added a post in a topic Nanco N800 tires   

    Called tireco and they said they don't sell to individuals, but they checked stock anyway and said they don't have them in stock. That is what I'm finding everywhere.
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  23. 109jb added a post in a topic Nanco N800 tires   

    I bought a set about 6 months ago for $90 a pair but now can't find any anywhere.
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  24. 109jb added a topic in Avidfoxflyers General Hangar   

    Nanco N800 tires
    For my project airplane I'm planning to use the Nanco N800 21x12-8 tires but have not had any luck finding any in stock anywhere. Does anyone have a place I can get a pair?  Or a cost effective alternative that will fit the 8" ATV rims that came with the  Kitfox 4's?
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  25. 109jb added a post in a topic 582 replacement.   

    On the video he says weight is without exhaust, coolant and the brushless outrunner.
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