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Dec 05, 2018, 05:39 PM
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GWRIGHT's Avatar
Discussion

Jetfire 20


Andy Kunz recently reworked the old Airtronics Jetfire 20 plans , lightening and modernizing and I received a set of the laser parts last weekend so I thought I'd post a pic. I didn't think to take pictures throughout the process,.. but I only spent about 4~5 hours in the shop last sunday, so it's basically only one building session to this point. I have some balsa blocks ordered to carve/sand the wingtips and hatch, plus the fairing on top of the wing. I wanted a nosedragger for a change, and don't have any nosegear in the workshop, so have some of those on order too from a couple brands to see what's going to work the best. A little slower than my normal building of a model, but hopefully I'll get it to a "ready to cover" point this weekend. i think Andy did a good job modernizing the structure. I remember seeing either 3.5 or 3.75 lbs on the kit box, and this looks like it's going to be a pound or so lighter. with the equipment I have planned. yes, the ailerons are past the last rib in the pic and no that's not a mistake. There are wingtips that need to go on the end
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Dec 06, 2018, 12:22 AM
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J Bergsmith's Avatar
Nice, the Jetfire’s were nice flying airplanes. Airtronics kits were awesome quality!
Dec 06, 2018, 09:11 AM
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GWRIGHT's Avatar
I'm looking forward to getting this in the air. I got impatient waiting on the big balsa blocks to arrive for wingtips and hatch so I cut a bunch of 1/4" thick sheet into rib blanks and laminated together this morning with titebond. they'll be cured when i get home and i can carve/sand when I get some time. In the picture is a shade under 10 ounces and the servos/rx/esc/motor/battery that's going in it total 16.11 ounces. goal was 2.5 lbs, or 40 ounces. Covering should add 3.5, then there are wheels/pushrods/linkages, so i'm optimistic i'll be well under the 40 ounce target, which would be a pound lighter than the airtronics kit. May have a chance to hit 2~2.25 lbs which would be awesome. I know this power system is OK for 3D'ing a 40 ounce plane, or taking it to over 70mph with a different prop, so it should be "adequately" powered. I want this to fly like an old-style sport plane but a bit more power, so I'll probably prop down and detune it to get longer flights. It's the same little 71 gram motor used on the craz-E-wing with an 8X10, Mini uproar with a 10X5, other projects with props from 8X4 up to 12X4, and even flew the original slowride for the first year using a really thin carbon 13X4. i love that little $20 motor because of the versatility, and I'm sure I'll find the optimum prop to power the jetfire appropriately.
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Dec 06, 2018, 03:16 PM
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My short kit from Andy got here this morning. Like you it looks like I'll have to do some laminating for the cowl, wing tips and hatch. LHS didn't have squat for balsa thicker than 1/4" other than a 1x1x36" piece. Not what I wanted but I grabbed it anyway at almost $9.00. A nice slab of 1/2"x4" balsa would have made things so much easier. They had NO music wire and I grabbed the last bag of hinges. I asked the kid at the counter why they don't restock this stuff and his reply was that nobody builds anymore. Well I DO! Looks like after the first of the year I'll be online ordering balsa restock for my personal LHS! I easily have 3 times the Dubro stock that they do. It's depressing....

I've only been able to pull the sheets out of the box so far. Looks amazing for such a small parts count for a plane this size. Andy did a great job of consolidating and "adding lightness" in his rendering of this bird.

I won't pollute your thread with my build. Because of so many distractions right now it'll be hit or miss for me getting work completed. I'll try to shoot and save pictures but won't post progress until I'm close to completion. Looking at the kit this won't take long if I can just get everyone to leave me alone for a while....

Joe
Dec 06, 2018, 04:35 PM
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GWRIGHT's Avatar
A couple little observations. I don't like putting strings in the wing when I build it to pull servo cables through, so I cut a hole in the inner W4 next to the front servo rail in each wing panel. I cut a piece of paper and rolled it up into a tube, then placed between the ribs. This way I have a tunnel on ea side for the servo wires. You can see the paper tubes in the picture. when you roll the tubes, tape them with scotch.
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Dec 06, 2018, 04:38 PM
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Also,.. the center wing sheeting is 3/32, not 1/16. I used 1/16 on the first side then wondered why the spar/turbulator spar and trailing edge sheet weren't flush. After a few choice words as to what an idiot I was, I searched for 1/32 sheet, of which I had none. I cut another layer of sheeting from 1/16 and sanded it down to 1/32 before laminating on top. No harm except a couple more grams of glue, but man what an idiot i am sometimes.
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Dec 06, 2018, 05:17 PM
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Thanks for those heads up Gary. I did a tiled print of the plans and trying to get it all pieced together. Keeping the grandson from grabbing the sheets is taking more time than getting it taped together.

I haven't even started the build yet but will look at the ribs. I have a bunch of 1/2" rocket tube that I normally use for servo/motor wires. A gram or two heavier than paper but my hands are so messed up I can never roll the paper good enough to work.

I have some of the old Goldberg 1/8" nose gears that I snagged on eBay a while back. Last one will be going on the JetFire. I'm pretty sure I have the spec dural gear somewhere but will probably bend my own from 1/8" music wire.

Looking forward to your final AUW. I have several Scorpion motors that I'd like to use. If you end up at the 2-2.5 pounds that you think you will I can plan to go really conservative then. No need to equip for 500 watts. I plan on 3S only as I don't have any 4S packs. With that fat wing we won't get 90 mph speeds from it so might as well power for thrust instead. I plan to add my EagleTree system for airspeed at least. I need to keep my eyes open for the GPS expander for cheap...

Joe
Dec 06, 2018, 05:59 PM
Sagitta Fanboy
Looking great!

Andy hooked me up with one too, so I'm looking forward to its arrival.
Dec 06, 2018, 06:43 PM
AndyKunz's Avatar
Instead of building the one I cut for myself I modified the CAD to make a UMX sized one for 2S 180 motors. I gave one of those to Michael and the other sits waiting for me to catch up. Michael also got a 50% Marks Wanderer. All I need is time.

I look forward to seeing what each of the builders does on these.

Andy
Dec 06, 2018, 07:32 PM
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Quote:
Originally Posted by AndyKunz
Instead of building the one I cut for myself I modified the CAD to make a UMX sized one for 2S 180 motors. I gave one of those to Michael and the other sits waiting for me to catch up. Michael also got a 50% Marks Wanderer. All I need is time.

I look forward to seeing what each of the builders does on these.

Andy
Andy,

Don't tell me this! I have a complete 2S UMX AS3X package from a Pitts S1. A tiny Jetfire would be beyond cool! Gotta get this one done first....

Joe
Dec 06, 2018, 09:16 PM
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I got the .pdf plan file printed out in tile form. Got tired of fighting with my grandson over the pages and threatened to throw all of his XBox games in the garbage disposal if he didn't leave me to get this finished. It worked! I'm the original BAD grandpa.

I hope to get started on the JetFire build early tomorrow. I also have to build and setup the 3D printer that just arrived for my daughter. (I know NOTHING about 3D printers!) I'll be going back and forth between the two. Hoping for success with at least one of the projects.

Joe
Dec 07, 2018, 04:45 PM
'Douglas' to his friends.
Quote:
Originally Posted by turbojoe
...I hope to get started on the JetFire build early tomorrow. I also have to build and setup the 3D printer that just arrived for my daughter. (I know NOTHING about 3D printers!) I'll be going back and forth between the two. Hoping for success with at least one of the projects...
Careful with that, Joe. If you're half as fuddy-duddy as I, you'll end up with a 3D-Fire and a Jet-Printer..!
Dec 08, 2018, 08:24 AM
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I've had precious little time to work on my build and it looks like I may have even less in the next week or two. I'm up early to try to make any progress I can before I get pulled away again.

I started with the fuse. I've managed to do the few laminations and done a trial assembly. I found the proper dural main gear and got it and the mount plate drilled out and T-nuts installed. The formers are glued in but I'll need to pull F1 back off and do some brain storming for my motor choice. The lower portion of the former has to share real estate with the motor box and the nose gear mount. I'll have to decide which motor and motor box I will use and how much will have to be cut from the box to clear the nose gear. It shouldn't be a big deal after I decide which motor and motor box I end up with.

I'm also thinking I might build the cowl separate and magnet mount it to F1 for easier access to the motor area. Again, everything hinges on my motor choice. I may set the fuse aside until I hear what your AUW is Gary. That'll give me a better idea of how physically large of a motor is really needed. I don't have any 4S packs so I'll be setting this up for 3S. Makes the motor choice even more critical. Why do I always make thing so hard for myself?

Aside from problems I've created for myself everything looks and fits together so well you can trial assemble most of the fuse without using glue. Very nicely designed and cut.

Joe
Dec 08, 2018, 08:30 AM
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Quote:
Originally Posted by Dad3353
Careful with that, Joe. If you're half as fuddy-duddy as I, you'll end up with a 3D-Fire and a Jet-Printer..!
That's what I'm afraid of. Her 3D printer is still sitting on the table packed in the box. It has been opened but nothing removed yet. I told her she may not be seeing it in one piece until after the first of the year. Gives her some time to start learning CAD anyway so she can start creating the designs she wants to print.

Joe
Dec 08, 2018, 08:58 AM
AndyKunz's Avatar
Joe,

You might want to trim the corners on top of the two formers so you can put triangle stock on the top like on the bottom.

You can mount the motor on the back side of F1 if it makes things easier for you.

Andy


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