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About motortommy

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  1. motortommy added a post in a topic Fuselage landing loads (Kitfox IV) and cabane gear   

    …after some more research, I understood that with fuselage both leveled and loaded a slight positive camber of 1-2deg is desired while the wheels should be straight or show minimum toe-out. Not decided, if I will go with welded axle tube or adapt a bolt on axle like Grove which would be much easier to adjust via shims…
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  2. motortommy added a post in a topic Fuselage landing loads (Kitfox IV) and cabane gear   

    …so besides the easier fairing issue wrapped bungees also maybe offer more range for adjustment. I really like to build a cub style landing gear as it should be a proven design and knowledge is spread open. What I´m not fully aware of is the correct strength/tension of the bungee setup. To clarify my question I spared no effort and created this high end drawing

    Most airborne cabane gear looks like #2, means there is some ´sag´ when unloaded. Maybe intention is to offer some kind of progression as load builds up? How to find good setup? Do you agree that plane on the ground should more look like #1 (straight) than #3 (empty weight already compressed the gear). Adjustment depends on strut travel, no. of wraps, bungee strength and –preload…

    Hope you get my point...
    (could explain better in native language)
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  3. motortommy added a post in a topic wing spars for Europe   

    ....glad it worked out well for you!
    Please share some pics/insight of your wing rebuild (if you like)
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  4. motortommy added a post in a topic Fuselage landing loads (Kitfox IV) and cabane gear   

    so what‘s the reason that cub design attaches the bungees 90 deg. bar to bar? Is it because the use of bungee rings? Aligned it would be much easier to create some kind of fairing...
    Any ideas?
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  5. motortommy added a post in a topic wing spars for Europe   

    Yes that`s also my thinking. I´d love to buy from the factory (spar $195) but packing & freight add another $1420 Plus the risk that something stupid could happen during the long journey...
    @Manu: Thanks! will check ULM Tech   
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  6. motortommy added a post in a topic wing spars for Europe   

    might be an option, but to be honest I like to go `genuine factory` with my rebuild. I have already a sleeve I want to get rid of...
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  7. motortommy added a post in a topic wing spars for Europe   

    Hi Skelly,
    I´m in need of only one for a mk4, means without extruded stiffener...
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  8. motortommy added a topic in Avid and Kitfox parts Suppliers   

    wing spars for Europe
    as I´m probably in need for a new Kitfox IV spar, I contacted the factory. While pricing for the spar itself would be quite reasonable, transportation costs are infernal.
    So meanwhile I found a mill located in Germany producing following spec.
    2,5"x.065 162"
    EN AW-6061-T6 seamless drawn
    EN 573-3, EN 754-1, 2+7
    EN 10204/3.1
    Where`s the beef? Minumum slot they produce would be 7 pcs. Price would be around EUR 300,- per spar.
    Please PM, if you`re located within Europe and interested.
    • 10 replies
  9. motortommy added a post in a topic New wingtips...   

    So was it worth the effort? Yes and No!

    For the spent money (materials, tools, …) I could have bought likely a set of factory tips, including horrific transatlantic shipping cost. Further it took me roughly 3 months (sure not fulltime) from scratch to finished part, but:

    -        my wingtips were in desolate condition, badly repaired and way too heavy (left 2.3kgs/right 2.7kgs)

    -        even the modern style tips I borrowed still weighed 1.5/1.7kgs

    -        my new parts weigh 1.5 per set, means only by replacing the tips I saved 3.5kgs including preferred new look for free!  

    -        I wanted to try, if I´m still able and willing to work with fiberglass (after having 25years break) as my planning is to touch seatpan, cowling, wingtanks, panel,… as well

    Finally after tearing the whole plane down for months finding more and more issues I didn`t like, it was mentally important to create something gaining strength to proceed with the project. These wingtips were the first new homemade parts I made for my plane…

    OMG it´s difficult to express…hope you get my point.

    Thanks for reading!
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  10. motortommy added a post in a topic New wingtips...   

    vacuum process was successful! 
    honeycomb bonds perfect w/o bubbles or unglued spots. Next was some grinding to get a nice fit and smooth transitions...

    ...test fitting the molds together to check fot both clearance an space for glue. The honeycomb offers a nice surface for a strong bond.

    Then again into the vacuum bag after the inner top layer was applied. coffeetime!

    Now the sandwich is ready, including both inner and outer layers enclosing the honeycomb. Cutting protrusions and preparing for bonding. 

    Finally the halves were glued together using additional 1" reinforcing tape covering seam and edges. Now it`s getting hot! Both wingtips, still in their molds went into a heated box for tempering the epoxy resin for about 8 hours @ 75 deg. C.
    Exciting moment. Final demolding! No trouble, no damage! YES!!!  

    Even slightly better than calculated. Final part is 730grams means 1.6lbs?! Further only 40grams variation between left and right part. That is marginal for homemade handcrafted production

    Finished part, ready for paint preparation

    End of story 
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  11. motortommy added a post in a topic New wingtips...   


    So after cleaning the molds were polished and coated carefully several times using release agent. Finally first parts were made. I decided to go with a sandwich construction consisting of only 3 very thin layers of fiberglass enclosing an aramide honeycomb core. Each wingtip is made up of two halves which were glued together later using a reinforcement tape.

     Some may ask why no carbon fiber?
    I wanted to have both lightweight but also robust wingtips. To achieve this with pure carbon layup, more layers soaking lots of resin (=weight) would be needed. Pricy and IMHO no advantage here.

     Further, I wanted to try a sandwich construction using vacuum technique anyway in view of future components like cowling, seatpan, etc., I`m planning to do. 

    All four waxed molds have gelcoat and first layer of 80gram on - let it set.

     If proceed w/o wait following vacuum pressing would cause imprint on top surface… 

    Next is matching/cutting the honeycomb core. Nice material easy to work with, though expensive. The uncovered area will later touch the aluminum stripe attached to the outer rib.


    Honeycomb is glued in a wet bed of an underneath additional 80gram layer. Covered by perforated film (blue) absorber fleece (white) and a peel ply stripe. Afterwards the package was carefully put into a poly bag. A vacuum pump will soak excess resin through the foil into the absorber. Less resin means less weight!


    Pump is working at least until resin has set (better 5h). Check for leaks!

    Time for beer or coffee!

    To be continued…
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  12. motortommy added a post in a topic Another Kitfox IV rebuild project   

    John. Thanks! I immediate saved your .pdf via Facebook. I also spent nights studying cub-style landing gear. As both commercial options (groove and cabane gear) are out of scope, I probably also will end up making my own...Thanks again for your time creating the file.
    Question regarding the bungee. Is your planing to go with the wraps? What about using fabricated rings? Both options: How to determine correct force/tension?
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  13. motortommy added a post in a topic New wingtips...   


    See how the black resin molding compound faded more and more as the fiberglass layup builds. I decided to make a strong mold which also can handle tempering. Maybe overkill, but I need to make at least 2 sets

    Exciting moment. Will the top half release? Original part unscathed? As with 2-piece molds it is better not to demold until finish both halves, I could not withstand to ckeck. If something would have gone wrong only one surface would be damaged…

    As everything turned out as expected, I continued. Lower half (removed parting) and certainly opposite wingtip.

    Almost ready. Some trimming and bolts to secure alignment added. No need for ground board anymore...

    Finished mold righthand, white is original wingtip (still with insert)

    stains are residues of release agent, I forgot to remove before photoshoot

    Next. Let`s make parts…

    To be continued…
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  14. motortommy added a topic in Technical tasks   

    New wingtips...
    my original Kitfox droop style tips were repaired already several times and therefore way too heavy. Further I like the look of the more modern ones. So it was very welcome to get a set borrowed by a buddy for creating a mold. Due to great stiffness to weight ratio I decided to use a honeycomb sandwich construction (for the first time).

    The better the master form the better the mold the better the final produced part. So it was nice that I was allowed to repair, sand, paint and finally polish the samples.
    Next step was to fix the quite flexible part safely for further handling onto a wooden board (by the way the borrowed parts belonged to a plane in service so any damage or drilling should be avoided)


    As a 2-piece mold was necessary it was kind of tricky to arrange a ´parting plane` where the mold later splits

    after some trimming the small left gap was sealed with modeling compound.
    Cleaning/waxing - ready to cast the top half!
    to be continued...
    • 8 replies
  15. motortommy added a post in a topic case of disaster or to live one`s dream   

    Jim. I followed your rebuild closely. Lots of valuable input there. Thanks!
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