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Freewing Mig-29 Drag Chute Modification

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  • Freewing Mig-29 Drag Chute Modification

    This thread is intended to assist with the modification of the Freewing Mig-29 to add a drag chute if desired. It is a mod which will require skill with 3D printed parts and the ability to cut into the foam of your plane. It is not the easiest mod to do so if you question your abilities, it would be best to just pass on this one or find someone skilled enough and willing to do the work.

    IMPORTANT!!! Before proceeding, be aware that in order to install this mod there is a carbon fiber alignment spar located between the two nacelles that you must cut through. It is not a structural member but if to are at all concerned about the strength of the stab mounts on this plane possibly being weakened as a result then do not attempt this mod. I have flown mine and it works fine but it is your call.

    I cannot control what people will print with, the outcome or performance of individual mods so I assume no liability expressed or implied beyond this point. I will tell you what I did and what worked for me.

    First a bit of background. After collaborating with Paul Helms (Helmsman52 here on HobbySquawk) on a drag chute mod for the Freewing F-4 Phantom, we decided to have a go at a chute mod for the Mig-29 as well. For those who don't know, Paul has become a master at making chutes for various aircraft including larger scale turbines. With this project I wanted to make the release mechanism predominantly 3D printed to make it easier for people to get without having to come to me for it. I have my own projects to work on so time is limited to make short kits like I have been doing for the F-4. While Paul was busy making me two different prototype chutes to test, I set myself to designing the release mechanism in Fusion 360.

    Based on my experience with the F-4 I wanted this one to be simple and easy to make. I also wanted it to not be complicated by the need for a release mechanism choosing instead to rely on the shock cord snapping in the event of an accidental release during flight. My initial mechanism met these requirements so I installed it in my plane. After receiving the chutes from Paul it was apparent that the deluxe chute would prove to be too bulky to fit in the chute tube and that the economy version fit fine. I proceeded with testing and discovered an issue we did not anticipate. Deployment was uneventful, the problem was that while trying to taxi back, the chute acted like a thrust reverse which stopped the plane dead in it's tracks. It was literally as though it had brakes applied. Throttling up only caused the shock cord to fail. Paul and I tried everything we could think of to no avail.

    The full size aircraft will drop their chutes at the end of the runway after landing so we felt our only option was to have the ability to do the same which meant adding a release capability and a significant redesign of the mechanism. Not what I wanted to do but after further thought I felt I had a solution that did not require an additional servo and was easy to re-attach the chute after each release. Arguably it was more scale too.

    What follows is a description of the 3D printed components that make up the mechanism, additional parts you will need to complete it, recommend tools and some pics of preparing the plane for the install.

  • #2
    Files are at thingiverse.com/thing:4724667

    Here are the parts as printed. They were printed on my Ender 3 Pro with Polymaker Polylite ASA filament. My slicer is Simplify 3D. The only part that requires supports is the Main Body (the big white part). Other filaments can be used but I just don't know how it would turn out with something like PLA for instance as I print almost exclusively with ASA now.

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    Other things you will need to complete the assembly are shown below:

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    They are as follows:
    • Some kind of strong thin cord
    • 1 spring - Hillman #543018
    • 2 - 2mm x 1mm rare earth magnets
    • 1 - 130mm long piece of 4mm carbon fiber tube
    • 1 - 130mm long piece of 6mm carbon fiber tube
    • 1 - GH-S37D servo and it's hardware
    • 1 - foam donut. I used some of a blue camping pad. It is closed cell and about 1/2" thick.
    • 1 small piece of piano wire or equivalent. A pin would work. (Not shown)
    • 1 servo extension about 36" long. (Not shown)
    Some tools that will be needed.

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    In addition you will likely need some 220 grit sandpaper, a razor saw and some FoamTac glue.

    Construction of mechanism

    Let me start by saying that there will likely be the need to sand or trim some of the 3D parts to allow them to fit together and move properly. Dry fit everything together first before applying any adhesive!!! Particular care must be taken to make sure that the triggers work smoothly, especially the trigger to jettison the chute. Sand and trim accordingly where any binding occurs that inhibits free movement of the triggers. Although technically not necessary, I did add a small rubber band around the forward end of the main body to help ensure that the triggers returned to their original positions.

    Once you have the additional items you will need to assemble the mechanism, start with the plunger and insert the 6mm carbon fiber tube until it is flush with the face of the piston and glue it in place with some thin CA.

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    Next, insert the release catch into the 4mm CF tube and CA it in place.

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    Now, take your thin cord and pass it up through the cord anchor, over the cross member, back down through the anchor and secure it with a knot. A small drop of CA on the knot will help it to not come untied. When done, insert the anchor into the open end of the 4mm tube and CA it in place. Leave about a foot of cord. It will be cut shorter later.

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    Then glue the foam donut to the end of the chute tube using something like FoamTac. Make sure the hole in the donut is big enough to accept the tapered shoulder of the chute trigger plate.

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    Next, slide the spring over the 6mm CF tube, insert the piston assy into the chute tube aligning the 6mm CF tube with the hole in the front end of the tube. Insert the 6mm CF tube into the chute trigger plate taper shoulder side first until it is flush on the forward face of the plate, then secure it with thin CA. The piston assy is now complete.

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    The main body will be next. This is the part that will need the most attention, teimming and sanding. Once the support structures have been removed you will clearly see the dezign intent. The critical things to make sure of are that the triggers are free to move. The chute trigger is easier to do than the jettison trigger. I used a length of sandpaper to get in between the catch block and support beam until it moved freely. It needs to be tested with the 4mm CF tube and release catch inserted into the block. You will likely need to do some minor trimming with an Xacto blade to permit the catch to easily insert into the block and actually seat into the lip of the catch. This is critical to the function of the jettison feature so take your time and only remove small amounts of material as needed and again ensure there is no binding. Testing the fit of this will require that the chute tube is inserted into the main body and that the piston is in the cocked and ready to fire position. You must also make sure that the 4mm CF tube and catch assy slides easily inside the 6mm CF tube of the piston assy. I think you get the idea by now. Just do your best to make sure the jettison tube is easy to slide into place and the catch block slides sideways to allow the catch to seat and the catch block to return to its original position. You also do not want it to take a lot of force against the catch block to release the jettison tube. It is basically just like one of those toy dart guns.

    Now it is time to install the servo and horns. This is where it gets tricky. I ended up using a long and a short horn and turned the short horn over on top of the long horn. This way I was able to position the short horn to delay pushing on the jettison trigger block. I added some FoamTac to help glue the short horn in place and secured it all with the screw provided with the servo.

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    I set the servo on a three position switch. First position - ready to deploy, second position - deploy chute, third position - jettison chute. Just make sure you set the servo throws through your transmitter and receiver and position the horns accordingly until you achieve the proper functions. When you are satisfied that everything is working properly with minimal if any binding the next thing to do is to tie a loop in the anchor cord just past the end of the chute tube. Do this when it is in the cocked and ready position. I also added a small split ring I found in the fishing tackle section of a local department store which gave me something to eventually attach the chute to.

    The last thing to do is assemble and secure the hatch and hatch ring. The hatch is held shut with two small 2mm diameter x 1mm thick magnets. You will need to clean material out of the magnet pockets in both the hatch and ring to allow the magnets to seat flush. Glue the magnets in place with CA. Sand the hinge faces if necessary until the hatch and ring fit together without any binding. Now, using the small hinge pin location marks on the hatch ring, drill them both for the hinge pin you have selected. The hinge pin should be just long enough to barely extend past the outside edges of the hatch ring hinge forks. Secure the pin on each end with a small spot of medium or thick CA and make sure the hatch moves freely. Make sure the hinge is positioned on the bottom of the chute tube and that the hatch fits flush on the end of the tube then secure it with some thin CA.

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    Position the hinge like this.

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    The mechanism assembly is now complete and ready to be installed. The final piece of this system is the chute and I highly recommend the chutes from Paul for their fit, appearance and quality.

    Installation

    Again I want to emphasize the need to plug the mechanism servo into your receiver and set your throws to achieve proper function before ever gluing the mechanism in place. The first position of a three position switch should eject the chute and the next position should release the chute. It is much easier to make any adjustments while the mechanism is still loose. To make the cuts in the foam I used a utility knife. The kind with the long blade you can snap off. Measure from the base of the chute hatch (blue line) 275mm and place a mark in the center bottom section of the fuselage between the nacelles.

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    When I initially installed the mechanism on my plane I cut the whole back end of the fuselage at the panel line between the nacelles and then carefully bored a hole in the foam for the chute tube to fit but the foam ends up being very thin and it is not easy to bore straight. Therefore, I highly recommend removing the whole chute tube section (in red) instead and then filling/blending it back with some light weight spackle instead.

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    At the panel line you will discover the carbon fiber alignment spar so just cut all the way through the foam and up to the spar wide enough to receive the chute tube. Next, cut the foam between the nacelles on the other side of the CF spar about 40mm wide up to the 275mm mark you made earlier. A rib of foam exists in the center of the fuselage between the nacelles so do your best to separate the rectangular plate from it trying to leave some of the rib intact to later secure the tapered tabs on the mechanism main body to. All I can tell you is that if I can do it, you can too.

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    Next, using a razor saw, cut through the CF spar making sure that the gap is just wide enough to accept the chute tube. You should have something similar to the photo above when done. It is very easy to now pull the servo extension into the radio compartment with a wire.

    Again, I highly recommend hooking the mechanism to your receiver and setting all of your throws before finally glueing the mechanism in place with FoamTac. Fire it multiple times to make sure it works as intended. To wrap this up here is a video showing the operation and packing of the chute. I hope that it helps clarify any questions you may have had to this point.



    This completes my explanation of how to build and operate this mod for the Mig-29. My intentions have been to provide all of the information you would need to successfully complete this mod in your own plane while keeping me from having to do it for you. I have no intentions of making these for people as I have enough of my own projects to do. Best wishes to your success.

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    • #3
      Bump, I am officially done with the updates to this thread. Happy landings.

      Comment


      • #4
        Thank you for sharing, much appreciated

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