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  1. #1
    grosbeak's Avatar
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    Hobbistar 60 - Bolt-on wing conversion

    My Hobbistar trainer's stock method of securing the wing is rubber bands over dowels.



    Not much else is stock about this plane, though... the wing has been rebuilt, a lot of the covering has been changed, it's been converted to a tail dragger and at the time of this writing I've just finished installing a DLE 20 2-stroke gaser in place of the original glow engine. So it's high time I converted the wing to bolt on.

    I've spent a lot of time thinking about this mod and I've asked a lot of questions. I've settled on a 4-bolt approach using 1/4-20 nylon bolts. The front bolts will go straight down through the thickest part of the wing while the rear bolts will go through a stock reinforcement near the trailing edge of the wing. Here's a rough diagram - not to scale.



    The bolts will thread into tapped holes in 1/2" plywood mounts. The mounts will be removable for access to the plethora of stuff packed into the fuselage.
    MAAC 83386
    Stetson Flyers, Ottawa
    G-RSBK

  2. #2
    grosbeak's Avatar
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    Someone gave me the idea of lining the wing holes with a sleeve to prevent the wing from being crushed when the bolts are tightened. I went to Home Depot and challenged a rep in the Tool section to help me find something suitable. Our search led us to another rep in the plumbing section and the perfect solution.






    Yep, that's right. A toilet supply tube. A 1/4-20 nylon bolt fits perfectly.




    I plan to mount the sleeves flush with the upper and lower wing surfaces. The top of the mounts are flush with the wing saddle so the sleeves should come into direct contact with the mounts.
    MAAC 83386
    Stetson Flyers, Ottawa
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  3. #3
    grosbeak's Avatar
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    I was skeptical of the strength that half an inch of tapped plywood and a nylon bolt could provide. Never having tapped wood before, I tried it on a scrap piece, hardening the threads with thin CA before threading in the bolt.




    I made it tight. REAL tight, to the point I thought the threads would strip or the head of the bolt would break. Neither happened, and I was convinced.

    MAAC 83386
    Stetson Flyers, Ottawa
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  4. #4
    grosbeak's Avatar
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    There was a little housekeeping to do on the wing. First step was to cut off the control rods that were the attachment point for the stock single servo.






    Next was the replacement of the wing strap screws. I hate, hate, HATE cheap Phillips screws so I cut down some #4 button head hex screws. Pictured are a POS stock screw, a 3/4" #4 button head hex screw, and the same type of screw cut, tapered and paired with a 4-40 washer.




    Much better.

    MAAC 83386
    Stetson Flyers, Ottawa
    G-RSBK

  5. #5
    grosbeak's Avatar
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    Here are the wing mounts, test-fitted inside the fuselage.




    I started by aligning the top of the rear mount flush with the top of the wing saddle and clamping it in place. I used a pin vise to drill through the fuselage into the mount (see the red arrows).




    I'll be attaching them through the fuse with two 3/4" #6 screws on each side.
    MAAC 83386
    Stetson Flyers, Ottawa
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  6. #6
    hookedonrc's Avatar
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    I am onboard again...subscribing.
    Will add something clever and witty if I ever come up with something.

  7. #7

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    When I converted the wing on my Avistar to a bolt on, I cut it in half and made a new center rib out of ply with a tongue on the front. Added some hardwood in the front of the saddle for the tongue to fit into and more at the back for the bolts. I also removed all the dihedral too.

    I wish I hadn't removed the aileron torque rods though as it would be easy to cut the stock ailerons and mod them for flaps. i had already put two servos in the wings for the ailerons anyway.

    Still need to cover the wing and install engine/radio , etc. Trying to decide if I want to make a cowl for the engine like the RCM article for the Tiger. http://www.rcmplans.com/issues/reque...-092000-1.html

    Bill S.
    Last edited by Twin_Flyer; 12-19-2013 at 07:20 PM.
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  8. #8
    grosbeak's Avatar
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    Quote Originally Posted by hookedonrc View Post
    I am onboard again...subscribing.
    Good to have you back again!

    Quote Originally Posted by Twin_Flyer View Post
    When I converted the wing on my Avistar to a bolt on, I cut it in half and made a new center rib out of ply with a tongue on the front. Added some hardwood in the front of the saddle for the tongue to fit into and more at the back for the bolts. I also removed all the dihedral too.

    I wish I hadn't removed the aileron torque rods though as it would be easy to cut the stock ailerons and mod them for flaps. i had already put two servos in the wings for the ailerons anyway.

    Still need to cover the wing and install engine/radio , etc. Trying to decide if I want to make a cowl for the engine like the RCM article for the Tiger. http://www.rcmplans.com/issues/reque...-092000-1.html

    Bill S.
    Good ideas, Bill... I want to keep the dihedral for stability and I don't want to put any more work into this than I have to.
    MAAC 83386
    Stetson Flyers, Ottawa
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  9. #9
    grosbeak's Avatar
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    Both mounts installed.







    Ground the control rods down further and marked the working area on the bottom surface near the trailing edge.







    Rear bolt holes are drilled into the wing.







    I'm going to hold off on the front ones while I reconsider the position of the bolts and the mount.
    MAAC 83386
    Stetson Flyers, Ottawa
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  10. #10

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    Count me in! I've been reading your DLE 20 thread and it looks great. I agree your front wing mount does look far back. I've been wanting to do this mod for awhile on mine, and can't wait to see what you come up with and how it performs. Keep up the good work!

  11. #11

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    I converted mine 10 years ago. Hate the rubber bands. Mine is still flying and working great. Did mine similar but a little different. Let me know, I can post pictures if your interested.

    Terry

  12. #12
    grosbeak's Avatar
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    Quote Originally Posted by kfla View Post
    Count me in! I've been reading your DLE 20 thread and it looks great. I agree your front wing mount does look far back. I've been wanting to do this mod for awhile on mine, and can't wait to see what you come up with and how it performs. Keep up the good work!
    Thanks for the props!

    I can't wait to see what I come up with too!

    Quote Originally Posted by tlj125 View Post
    I converted mine 10 years ago. Hate the rubber bands. Mine is still flying and working great. Did mine similar but a little different. Let me know, I can post pictures if your interested.

    Terry
    Yes please, Terry - pictures would be appreciated.
    MAAC 83386
    Stetson Flyers, Ottawa
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  13. #13
    hookedonrc's Avatar
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    Just brainstorming here...and this may be crazy. So...I went and looked at the photos on the DLE 20 thread. Build a strong bulkhead just above the fuel tank where the wing front meets the fuse. (This will take some good measuring. Anyway, on to my idea. Instead of putting the dowels in the wing, mount them facing to the rear in the new bulkhead, but lower than the wing surface as it cross the fuse. OK so now you have 2 dowels facing the rear. Build a cross bulkhead on the wing.... the bulkhead extending above the wing surface. Then drill 2 holes through the new bulkhead that the dowels will slide into. Can be drilled ahead of time....
    So to install the wing, you place it rearward of the dowels, line up the two holes and slide it forward until the holes on the rear of the wing match the holes in the rear attachment block. Put in the rear bolts and you are good to go.
    Hope that is not too confusing or making it too complicated.

    Found a picture that I can refer to as an example. In the picture, the balance blocks of the Cessna would be turned 90 degrees, and under the wing inside the fuse. They extend beyond the lower part of the wing so you can slide them in. If in the right place, the bulkhead on the wing with the holes pushes up right against the new bulkhead above the fuel tank and the rear bolts go right where they are now.

    Click image for larger version. 

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    Last edited by hookedonrc; 12-20-2013 at 12:46 PM.
    Will add something clever and witty if I ever come up with something.

  14. #14
    grosbeak's Avatar
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    Quote Originally Posted by hookedonrc View Post
    Just brainstorming here...and this may be crazy. So...I went and looked at the photos on the DLE 20 thread. Build a strong bulkhead just above the fuel tank where the wing front meets the fuse. (This will take some good measuring. Anyway, on to my idea. Instead of putting the dowels in the wing, mount them facing to the rear in the new bulkhead, but lower than the wing surface as it cross the fuse. OK so now you have 2 dowels facing the rear. Build a cross bulkhead on the wing.... the bulkhead extending above the wing surface. Then drill 2 holes through the new bulkhead that the dowels will slide into. Can be drilled ahead of time....
    So to install the wing, you place it rearward of the dowels, line up the two holes and slide it forward until the holes on the rear of the wing match the holes in the rear attachment block. Put in the rear bolts and you are good to go.
    Hope that is not too confusing or making it too complicated.

    Found a picture that I can refer to as an example. In the picture, the balance blocks of the Cessna would be turned 90 degrees, and under the wing inside the fuse. They extend beyond the lower part of the wing so you can slide them in. If in the right place, the bulkhead on the wing with the holes pushes up right against the new bulkhead above the fuel tank and the rear bolts go right where they are now.

    Click image for larger version. 

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    I think I understand... My main concern is space under the wing - there's a gas tank there now. And it's certainly more involved than what I have planned... but something to consider!
    MAAC 83386
    Stetson Flyers, Ottawa
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  15. #15
    hookedonrc's Avatar
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    True about the gas tank, but if it doesn't come to the top of the bulkhead and sits below it like the picture on the DLE thread it might. I will leave it to you since you can sit and stare at it and I can't.
    Will add something clever and witty if I ever come up with something.

  16. #16

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    My version

    Here are a few pics that show how I did mine.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  17. #17
    grosbeak's Avatar
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    Quote Originally Posted by hookedonrc View Post
    True about the gas tank, but if it doesn't come to the top of the bulkhead and sits below it like the picture on the DLE thread it might. I will leave it to you since you can sit and stare at it and I can't.
    You're right about the fuel tank - there's plenty of space above the tank. I won't rule out the dowel idea but it's still more complicated than I want at this point.

    Quote Originally Posted by tlj125 View Post
    Here are a few pics that show how I did mine.
    Excellent - I see you mounted the front bolts near where I was planning to... tell me, did those bolts hold up well in that position? Did either one ever break because of the wing pulling against it in flight?
    MAAC 83386
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  18. #18

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    Wing bolts don't have to be nylon. Use aluminum or steel bolts if your gut tells you the nylon might fail. In a mishap the nylon bolt sheering isn't going to save you from damage anyway. I redid my Hobbistar 60 several years ago and never could come up with a clean easy bolt on conversion and ended up staying with rubber bands (YUK). I didn't think there was enough meat (strong wood) in the upper windshield area to use dowels and I wasn't willing to reconfigure the fuselage to do it. It's not an easy plane to do that to. Maybe the two bolts back near the c/g like you were thinking and tlj125 showed in his photos PLUS a horizontal tab sticking out forward under the L.E. and into a slot made under the windshield area would provide an attachment at the front and rear of the wing that you would have faith in. Make the tab out of 1" aluminum strap material or hardwood. (and dump the nylon bolts too)

  19. #19

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    Quote Originally Posted by grosbeak View Post
    You're right about the fuel tank - there's plenty of space above the tank. I won't rule out the dowel idea but it's still more complicated than I want at this point.



    Excellent - I see you mounted the front bolts near where I was planning to... tell me, did those bolts hold up well in that position? Did either one ever break because of the wing pulling against it in flight?
    I have flown this plane year after year for over a decade and have never broken a wing screw or mount. Flown off grass, tarmac, water, and snow with no issues. Recently recovered the fuse with monocote. Still have to do the wing. One of my longest lived planes. Its the energizer bunny of the fleet. Good luck with yours.

    Terry

  20. #20
    hookedonrc's Avatar
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    If you have the room, I like tlj's idea better, and it is simpler. Only thing left is to figure out the way to strengthen the mount points on the wing.
    Will add something clever and witty if I ever come up with something.

  21. #21
    grosbeak's Avatar
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    Quote Originally Posted by 52larry52 View Post
    Wing bolts don't have to be nylon. Use aluminum or steel bolts if your gut tells you the nylon might fail. In a mishap the nylon bolt sheering isn't going to save you from damage anyway.
    I have to disagree with you on that score - last year I cartwheeled my Pulse 125 on landing and besides the prop the only damage was to the wing bolts, which sheared exactly as designed.

    Quote Originally Posted by tlj125 View Post
    I have flown this plane year after year for over a decade and have never broken a wing screw or mount. Flown off grass, tarmac, water, and snow with no issues. Recently recovered the fuse with monocote. Still have to do the wing. One of my longest lived planes. Its the energizer bunny of the fleet. Good luck with yours.

    Terry
    Great news - and I see you used Nylon bolts. Thank you!

    Quote Originally Posted by hookedonrc View Post
    If you have the room, I like tlj's idea better, and it is simpler. Only thing left is to figure out the way to strengthen the mount points on the wing.
    I do too... especially since my plan is so close to his!

    At the back the wood is extra thick, so with the anti-crush sleeves it'll be fine. At the front I will also use the anti-crush sleeves, plus a thin sheet of plywood - I'm thinking 1/16", covered in white - between the holes and the bolts.
    MAAC 83386
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  22. #22
    grosbeak's Avatar
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    While I was thinking about where to put my forward wing bolts, I checked the length of the bolt against the thickness of the wing at my first chosen position.





    Nope, that's not going to work! I didn't find any 1/4"-20 nylon bolts longer than 2-1/2". Ergo, the location of the forward bolts has to change... so I put the dowels back in the fuselage, banded the wing on and marked holes in my new location.







    Holes drilled.







    Anti crush sleeves epoxied in. They will be cut flush to the surface of the wing.


    MAAC 83386
    Stetson Flyers, Ottawa
    G-RSBK

  23. #23
    grosbeak's Avatar
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    While I was at it I put the rear ones in.







    I wrapped up the evening's work by blackening the wing mount screws and washers with a Sharpie.







    That's better.


    MAAC 83386
    Stetson Flyers, Ottawa
    G-RSBK

  24. #24

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    grosbeak,
    What do you use to print the labels on the plane (under the switch above) ?

    Bill S.
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  25. #25
    grosbeak's Avatar
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    Quote Originally Posted by Twin_Flyer View Post
    grosbeak,
    What do you use to print the labels on the plane (under the switch above) ?

    Bill S.
    I have a Dymo handheld electronic label maker - it uses the D1 cartridges. I bought a black-on-clear cartridge for these labels.

    I have used inkjet water transfer decals in the past with success.
    MAAC 83386
    Stetson Flyers, Ottawa
    G-RSBK


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