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Scratch and Kit Built Aircraft Discuss and share your scratch built or kit built aircraft as well as building techniques, methods, mediums and resources.

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View Poll Results: Which version is your favorite?
F-16 6 54.55%
T-38 5 45.45%
Voters: 11. You may not vote on this poll

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Old 02-24-2016, 01:45 PM   #1
Bald Paul
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Default Mini Kobra project

Next CAD project - a 36" wingspan, electric power version of the Sig Kobra.

I'm still looking over the plans (Thank you, tobydogs, for the plan set!) and making mental notes of how things will fit at 80% of the original size, how to re-design the fuselage top, etc.

One of the things I have to decide on is which configuration to build - the F-16 tail, or the T-38 tail?

Like my Tigercub project (39.5" span electric version of the Tiger 2), I'll be sharing CAD files and plans in case anyone wants to build one of their own. But, I'm only going to design the pieces for one configuration, so please, vote for your favorite!


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File Type: jpg T38.jpg (17.9 KB, 261 views)
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Old 02-24-2016, 01:52 PM   #2
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F-16 for looks...

T-38 for better rudder effectiveness.

************

I also like to carve sort of Horner style drooped wingtips.

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Old 02-24-2016, 01:54 PM   #3
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Originally Posted by fhhuber View Post
F-16 for looks...

T-38 for better rudder effectiveness.
You're not helping.
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Old 02-24-2016, 02:08 PM   #4
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The vast majority of Kobra, Kougar, King Kobra models built in the 1970's and 1980's used the T-38 tail. It was very rare to see the F-16 style.
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Old 02-25-2016, 02:59 AM   #5
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A 36" version would be amazing. I built a Kobra back in the 80's and only flew it once before someone made me an offer I couldn't refuse. I built and own the original prototype of the Mountain Models idea of what an updated, laser cut version of the Kobra should be. I still have a NIB Kobra kit. A "park sized" version would be a must have. Gotta have one. Watching the thread with eager anticipation.......

Joe

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Old 02-25-2016, 04:10 PM   #6
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I'm partial to the F-16 look as well.... Who needs a rudder anyway. Just bank and yank!

Steve

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Old 02-25-2016, 07:12 PM   #7
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I like the T-38 better. For my taste the F-16 one looks like it's trying too hard to 'play jets'. It doesn't really suit a plane with a prop on the front to my eye, but each to their own.
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Old 02-25-2016, 10:27 PM   #8
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I prefer the F-16 look and would just spend the 10 minutes to cut my own if you went with the T-38. Not a big deal. I've got plenty of wood.

Joe

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Old 02-25-2016, 11:00 PM   #9
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Originally Posted by Turbojoe View Post
I prefer the F-16 look and would just spend the 10 minutes to cut my own if you went with the T-38. Not a big deal. I've got plenty of wood.

Joe
Well, it really isn't much work in CAD to design both versions. I would just do a "F16 cut file" and a "T38 cut file" to have the short kits laser cut.

This one may take awhile. I'm convincing myself to design this one in 3D, vs. the 2D CAD I've been using. So, there's going to be some time teaching myself a whole new set of commands to mess up.
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Old 02-25-2016, 11:30 PM   #10
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Heck, I can't draw 1D or even stick people for that matter.

Joe

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Old 02-26-2016, 04:04 PM   #11
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Default Initial thoughts

I had the original plans copied and shrunk to 80% of original size. This gives me approximately a 36" wingspan, and a fuselage of 28" (not counting the spinner or rudder).

Definitely enough room inside for servos, radio, battery compartment, etc. I have a new canopy that looks very close to the resized plans. The turtledeck (plastic on the original) may have to be re-shaped a bit to fit the canopy, but the overall looks of the plane won't really be affected.

Still a lot of design notes to make, including deciding on a power package, before the actual CAD work begins. But, it looks promising!
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Old 02-27-2016, 12:52 AM   #12
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At this size you'll probably end up with AUW of what, 20-24 oz. at most? Plan for 200+ watts. We can always throttle back.

I love the Mountain Models Firestorm iteration of the Kobra but please stay true to the original design on this one. It's just GOTTA have trike gear!

Joe

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Old 02-27-2016, 01:03 AM   #13
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Originally Posted by Bald Paul View Post
Well, it really isn't much work in CAD to design both versions. I would just do a "F16 cut file" and a "T38 cut file" to have the short kits laser cut.

This one may take awhile. I'm convincing myself to design this one in 3D, vs. the 2D CAD I've been using. So, there's going to be some time teaching myself a whole new set of commands to mess up.

Your retired you have all the time to learn a new set of commands.

I went with the T38 tail for what it's worth. Looking forward to watching your progress on this one. I have the Kougar in electric love the trike landing gear. You have flown off of that club field it is why I am partial to the landing gear. Tough to nose over.
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Old 02-27-2016, 01:22 AM   #14
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Originally Posted by Turbojoe View Post
At this size you'll probably end up with AUW of what, 20-24 oz. at most? Plan for 200+ watts. We can always throttle back.

I love the Mountain Models Firestorm iteration of the Kobra but please stay true to the original design on this one. It's just GOTTA have trike gear!

Joe
Originally Posted by gramps2361 View Post
Your retired you have all the time to learn a new set of commands.

I went with the T38 tail for what it's worth. Looking forward to watching your progress on this one. I have the Kougar in electric love the trike landing gear. You have flown off of that club field it is why I am partial to the landing gear. Tough to nose over.
After flying the Tigercub with the trike gear, I'm convinced it's the only way to go for small planes on grass.
That BMJR Spacewalker I built was great, but no matter how smoothly I touched down with it, the gear would always get sucked into the turf and over it would go.
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Old 02-27-2016, 03:30 AM   #15
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trike gear looks great, i am using a 10x7 e apc prop and a 35-48-1100 kv turnigy sk series motor with 80 amp esc. the batteries i use in it is the same in the tower hobbies uproar. 2 4cell 2200mah 20c batteries run parallel. vertical lift in the uproar with a 12x6 prop.

the trike gear always had me mowing the grass on takeoff...lol,when i would put it back on the table after a flight,grass was stuck all over the kobra. it's one reason i never really flew the kobra much. this is also why i love building but have to many hanger queens hanging around.

narrow is the place to land...wide is the space to crash....choose the narrow way!
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Old 03-01-2016, 04:44 PM   #16
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Default A slight delay - and the demise of the Tigercub

There may be a slight postponement of the design of the Mini Kobra. The Tigercub prototype met an untimely end this morning. I'd like to blame some radio glitch, or a mechanical issue, or a lightning strike but this one gets chalked up to pure pilot error.

Making a low, inverted pass over the field. Went to pull up, and just plain forgot that when inverted, DOWN = UP. Whoops. Wing bolts did their job - the wing is fine. Fuselage is gone back to the wing dowel bulkhead. The battery hatch cover popped off, so that survived. Luckily, I have all my CAD files (we can rebuild it, we have the technology!) and it doesn't appear that the motor or any of the electronics suffered any damage other than a broken prop.
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Old 03-08-2016, 08:17 PM   #17
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Since I have to rebuild the Tigercub fuselage, I made a few improvements in the battery hatch access which required a redesign of the hatch cover, fuselage sides, and fuselage doublers, and an additional hatch doubler/retainer. I guess it's Tigercub V2.

Anyway, when laying out the cut sheets for the laser cutter, it was evident that a lot of wood would be wasted. Soooooo, I did another re-design. Quick one in 2D CAD, with constant chord wing, reduced in size and converted to electric, based on the RCM Advanced Trainer plan (attached).

Don't worry, the Mini Kobra is still in the works, but after my 'dumb thumbs' incident with the Tigercub, I thought a slightly more docile ship might be a good idea.

Any interest on a build thread for this one?


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Old 04-04-2016, 01:48 PM   #18
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Tigercub fuselage is done. The improvements to the battery hatch cover give more room to stuff wires in without physically enlarging the battery tray area. I'll have to update the CAD files accordingly.

When I laid out the cut files for the parts, I added the parts for my version of the RCM Advanced Trainer in a smaller, electric powered size to the laser cut order.

Mini Kobra project is still in the works (still working on the new 3D CAD program) but the build of the "First MATE" (the first Mini Advanced Trainer Electric) will commence shortly.
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Old 04-06-2016, 08:12 PM   #19
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Foam wings http://www.eurekaaircraft.com/foamwings/index.html If you do get a plan figured out for the Kobra i would enjoy building a smaller electric one some day . i built a 40 size nitro one long ago and destroyed it in combat ,lol joe
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Old 04-26-2016, 02:02 PM   #20
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Haven't really updated this thread for awhile. The RCM Advanced Trainer version (renamed the First MATE - Mini Advanced Trainer Electric) is coming along nicely. Didn't really do a build thread on this one.


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Old 04-27-2016, 12:12 PM   #21
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sweet!
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Old 04-29-2016, 01:44 PM   #22
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I think I may have ADD. The Mini Kobra may be dead. Since it's a re-scale of an existing design, and I already did the Tigercub (resized Tiger 2) I felt it was sort of a 'been there, done that' project. The First MATE is still under construction, but I decided to attempt a "scale" project. How about a kit of a kit?

The Zenith CH701 home built caught my eye. Pretty much a box fuselage, STOL wing with fixed leading edge slats, and flaps. Fuselage is super roomy. I have some decent 3-views and dimensions. Some challenges in design (I'm trying to figure out how they mount the wing on that thing!) and, of course, I'm still dealing with the learning curve of a new 3D CAD program, searching through the 840 pages of user guide.


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Old 04-29-2016, 10:52 PM   #23
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Originally Posted by Bald Paul View Post
I think I may have ADD. The Mini Kobra may be dead. Since it's a re-scale of an existing design, and I already did the Tigercub (resized Tiger 2) I felt it was sort of a 'been there, done that' project. The First MATE is still under construction, but I decided to attempt a "scale" project. How about a kit of a kit?

The Zenith CH701 home built caught my eye. Pretty much a box fuselage, STOL wing with fixed leading edge slats, and flaps. Fuselage is super roomy. I have some decent 3-views and dimensions. Some challenges in design (I'm trying to figure out how they mount the wing on that thing!) and, of course, I'm still dealing with the learning curve of a new 3D CAD program, searching through the 840 pages of user guide.
Love that plane, there's one parked at an airstrip not far from the field I fly at. I won a raffle to fly in this plane, a Cessna 172, or an RV8...I did the RV8, but this looked fun too.
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