Firefox Mig 31

Discussion in 'Scratchbuilding!' started by jibracer13, Jul 12, 2016.

  1. I have 2 of those , slightly different when I bought mine. 4000kv on 3S and was suppose to have around 450g thrust, I was lucky if I got 250. They of course don't sell that motor anymore so I will wait to see how yours perform, that is with 4S and 3300kv ;)
     
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  2. @EricR Hey Eric I built a bracket for my thrust stand to hold the edf's, remember mine is 4000kv and suppose to be 3S but I tested it both ways.

    On 3S 15.66oz Thrust or 430g, 305 watts and 26A .

    Of course that is the initial burst and it dropped off from there pretty quick, I ran twin edf's but all the extra weight I was under the 1-1 ratio.

    On 4S 24.0 oz Thrust or 670g , 660 watts and 43A.

    Batteries were 2200 40C 3S and 4S with a 50A HK esc.

    So if yours are somewhat close on the 4S you could have a fighting chance. I did run mine quite long on 4S the motor was getting warm to slightly hot , maybe with 2 smaller 4S batteries (lighter) I might give these guys a go again. :)

    Cheers
    Jeff
     
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  3. Flybyknight22

    Flybyknight22 Top Gun

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    Way to go on that bracket Wild!

    I like the sound of the EDF and they have a certain cool/wow factor to them that's also nice.

    In my testing of EDFs I have been disappointed in the amount of thrust they produce compared to standard outrunners so I have so far stayed away from them in these parkjets.

    Hope you have better luck.
     
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  4. I hear you, my 1st one is a poor feeling but now that I have gone beyond the manufactures specs it looks like it might work. ;)
     
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  5. Agent_J

    Agent_J Cadet

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    I'm glad I'm not the only one who had issues with the original Firefox plans. My solution (after four previous attempts to build it by the plans) was to turn it into a true pusher plane, with a Super Mega Jet on the back. Once I get some more test flights in and make sure that I haven't missed something stupid, I plan on posting a step by step build. Right now I need to glue it back together after misjudging the CG on the first flight, and an absolutely hideous toss that caused it to flip over and break both rudders and a wingtip on the last. In between though, I had three smooth flights, so it's looking good.
     

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  6. JettaManDan

    JettaManDan Administrator

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    interested to see your results. Mine is a wall hanger now...it looks amazing..just didn't fly well lol
     
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  7. Agent_J

    Agent_J Cadet

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    This is a quick video of the pusher conversion. I kept it unlisted on YouTube so it wouldn't cause a bunch of people to start bugging Dave and company about the plane. They were kind enough to let JettaManDan post the plans, and I don't want to cause aggravation.

    The first video I took showed about three seconds of the plane spiraling almost completely out of control. The second showed empty sky 95% of the time. This one had a few decent scenes of the plane, which is why I edited and uploaded it. Please pay no attention to me talking to myself.

     
  8. Flybyknight22

    Flybyknight22 Top Gun

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    Agent_J,

    Flight looked pretty decent to me, not bad at all.

    How do you think it handled from launch to landing?
     
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  9. Agent_J

    Agent_J Cadet

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    Flybyknight22, it flew pretty smooth. I've only had it in the air for less than ten minutes, so it's still getting trimmed out and I'm still trying to learn how I need to fly it. The biggest change from the earlier stick motor mount is the ease of launch. Without the extra foam behind the motor, the plane has a lot more usable thrust. Before, I would go to toss it, and would have to hope that it would gain enough speed to start getting lift before it would smack into the ground. At least so far, I'll give it full throttle and toss it, and it's nowhere near as anxious as it used to be.

    As far as the flying itself, I just did some circuits of the field - back and forth with simple turns. The only acrobatics I tried were one barrel roll, which felt pretty crisp, and one loop, which was really tough to pull off with the original motor mount design. The landings were okay, but I came down a little too hard and cracked the nose (more than it was already) so I need to work on that. It's patched up and I'm waiting for the next somewhat calm day to try it some more. I'm planning on taking some video from a distance when I launch it to see what works and what doesn't, since I can't really judge what I'm doing in that moment.

    And please enjoy the picture of the repair job that I started at the field with some scrap foam from another damaged plane and finished after I got home. It doesn't look great, but it'll hold together, and that's most important right now.
     

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  10. Flybyknight22

    Flybyknight22 Top Gun

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    AJ,

    Nice job getting it to fly.

    Good to see the Mig-31 in the air, well done!

    Maybe with a few tweaks here and there like a mid-engine prop-slot and a few other mods the Fire Fox might be an EXCELLANT all around flyer.
     
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  11. Agent_J

    Agent_J Cadet

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    When I'm flying, I try to remember three rules. In no particular order, "Check everything" "Altitude is your friend" and "Don't push your luck". In two flights I managed to break each of these rules, which resulted in the carnage you see here. However, I managed to get six test flights in before the Firefox turned into a lawn dart, and I'm very pleased with the results. Launching was easy - hold the plane at about a 45 degree angle, give it full power and a firm toss and it's airborne. On low rates it flies smooth, and on high rates it does loops and roles easily. Landings are also easier because I can bring the plane in on a more traditional approach, whereas the original version had a tendency to just sort of belly flop as it slowed down.

    The problem came on flight six near the end when I was too low to the ground and trying something stupid (two rules broken), and both rudders and the left wing broke. It only took about ten minutes to patch it up with spare foam and white duct tape, but I missed that a servo had come unglued (the third rule broken). The resulting flight was almost completely out of control because of my stupidity and the plane ended up going straight down into the dirt, burying the nose all the way up to the canards. I'm working on the post mortem to see if there are any more modifications I want to make, but it's looking very good to me as is.

    If nothing else, this experience has taught me to bring scrap foam and a glue gun to the field when I'm testing a plane. If I hadn't missed the servo coming loose, I might still be beating that plane up in the name of my fellow RC aviators. But it's still progress.
     

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  12. EricR

    EricR Ace Pilot

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    Thanks for sharing your experience and Lessons Learned. Been there myself. I hope to build it someday.
     
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  13. Flybyknight22

    Flybyknight22 Top Gun

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    Aaaaaay Jaaaaaaaay!

    Say it ain't So! :)

    Love your NTSB report on the Mig-31, thank you for sharing your experiences with it and the pics.

    The photo you took of the crash is, well,...

    SPECTACULAR!!!!

    IMG_2388.JPG
     
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  14. Agent_J

    Agent_J Cadet

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    Flybyknight22, I'm glad you enjoyed the picture. Even with going straight in like it did, there was not much damage to the rear of the plane. I took a red Sharpie and traced all the cracks before I did the final disposal, and was pleasantly surprised by how intact it still was. If not for the fact that I wanted to build the next version, I might have just put together a new nose and tried to patch it.

    I have the parts laid out for my second prototype on two sheets of Model Plane Foam. I only started experimenting with MPF a couple of weeks ago, but I have a feeling it's the frontrunner to take over for Depron, so that's what I want to use for any build pictures and instructions.
     

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  15. Flybyknight22

    Flybyknight22 Top Gun

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    AJ,

    Sorry about the crash but if you gotta crash why not do it with gusto! Yours was a crowd pleaser! :)

    I love what you are doing with this old set of plans and especially your willingness to share the journey with us.

    I wish I had the time to play with it but not going to happen anytime soon if ever for me. There's just too much on my plate these days.

    MPF has been around for awhile and I use it almost exclusively as depron is almost impossible to get for me.

    Always interested to see your progress with the Mig-31.
     
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  16. Agent_J

    Agent_J Cadet

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    It's been a while, but I have an update on prototype 2. After building it, I decided to do a quick paint job on it using Testor Gloss Black spray paint, Icy Blue Lacquer for the cockpit, and some pinstriping just because. I just covered the very bottom of the plane with clear tape so I wouldn't have to wait for paint to dry before putting it on the shelf and also to help with orientation. Then it was just waiting for a calm day for testing. Now, I could say that I got through that day without a crash, but that would be a lie. I could say that it didn't involve prototype 2, but that would also be a lie. I could further say that the crash was not serious, and I would finally be telling the truth. This time, the problem wasn't something stupid I did - I lost radio control of the plane and got it back maybe 10-20 feet from the ground. Just enough to get it level before it hit. The biggest damage was some bending on the wingtips (fixed with carbon rods and epoxy), one small part that needed re-glued and some minor cosmetic dings.

    I think many of you will agree that there are few surprises better than going to a plane that has hit the dirt and finding it still intact. After a thorough check, including the servos, twice, I tossed it up and flew out the rest of the battery. Then a couple more flights with no issues despite the minor damage.

    Tonight, I took it up to a local park so I could start to get out of the testing phase and just fly it. It was a little windier than I would have liked, and with it being cloudy, I had a harder time keeping orientation. Long story short, I took my eyes off the plane for a moment, looked back just as a gust of wind caught it, and it ended up corkscrewing down to the ground. As I walked up to the plane, I was already dubbing it "Excalibur" because it hit the ground at a shallow angle and stuck. This time, the very tip of the nose was messed up, the motor mount broke off, and there was some flexing where the fuselage met the main body of the plane. I was smiling on the way home because I knew that it was going to be a relatively easy fix. It took about a half hour to repair, and doesn't look showroom new anymore, but it should fly. On this version, I had put carbon fiber rods down both sides of the nose, and had reinforced all the leading edges with the "Light Weight Structural Reinforcement for RCPlanes" tip from FatherAndSons. I believe that is what saved the plane to fly another day.

    I know I said that I would post my changes, and I still plan to do that. However, I'm kind of obsessive-compulsive when writing things like that, so please be patient with me. I want to make sure that I explain things clearly so you won't run into the same issues I did.

    Hope you're all having a great start to the summer!
     

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  17. Flybyknight22

    Flybyknight22 Top Gun

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    Your blacked out Fire Fox looks PIMP!
     
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  18. Sidewayskiwi

    Sidewayskiwi Ace Pilot

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    Please ignore my email asking for these plans -- lol
     
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  19. Sidewayskiwi

    Sidewayskiwi Ace Pilot

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    How on earth does double step KF's work??
     
  20. Sidewayskiwi

    Sidewayskiwi Ace Pilot

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    Can anyone give me an idea on wingspan and length ?
     
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