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My very first scratch build and design - the JSF F-35

Old 08-01-2008, 12:29 PM
  #1  
IFlite
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Default My very first scratch build and design - the JSF F-35

Hi guys, I've just joined this forum, and thought I should share my latest project, -my first ever scratch-build. The design is my own, I've simply drawn inspiration from pictures on the web of the JSF F-35.

I've been flying electric aircrafts for a couple of years, and thought it would be great to design and scratch-build my own. This plane was originally meant as merely a prototype, but i decided to put a motor and electronics in it and see how it flies. The next version of the plane will be made of EPP, but since EPP isn't available here (Norway), I've ordered it from the US, and the shipping takes a while. Therefore, this prototype is made from Depron, which is kinda nice, but a bit brittle and will easily break as I'm sure you all know. At least Depron is readily available and cheap here in Norway.

Except for my F-27c Stryker, I've never had a jet-fighter-like plane before, so I decided to try to copy the JSF F-35. I really like it's shape, looks kinda sexy. I measured all the angles and surfaces of the plane's profile, and cut it out from Depron. Then I glued a 4mm carbon fiber tube down the middle from its tail to its nose.
Then I cut out the vertical ribs, and glued them to the fuselage profile (I'll call it the wing from here on, allthoug It's makes out the main fuselage). I had to bend the Depron quite a lot when doing this, and the Depron would just bearly bend this much without breaking. I actually think this was an ok approach, and it gave the wing a nice, curved look. For my EPP version, this will be a lot easier to do, due to the EPP's flexibility.
Next I glued a 4mm cf tube across the wing, providing stiffness to the main wings. I cut out the tail fins from Depron as well (All parts of the plane is depron, either 3mm or 6mm), and cut out two slits in the wing and glued them to it on the underside, supported by small Depron-triangles, ensuring they would stay in an 90 deg. angle to the curved wing.
With the wing and tail fins in place, the underside of the plane was completed by creating a curved surface to go on the nose's underside, and straight surfaces covering the three exposed sides of the wing ribs. The rib closest to the plane's nose would resemble the plane's air intake. I stiffened the bottom of the air intake with a 3mm cf tube aswell. Finally, I carved out a solid nose tip for the plane, from something resembling EPP. I'm not sure what it actually was, -It came with some product packaging of some sort, which I had kept in case times like these. As you can see it's bright white, and should be spray painted I guess, for the esthetics.

At this point, my prototype was mostly done, because my original intent was not to make this one fly, but to test out my build process ideas. All in all, I would say most things worked out ok, and while it could be prettier, I think I'll follow this build process for my next version aswell. I'll go for a deeper, more curved underside for the nose though, on the next version, because I think the whole nose looks a litle "flat". Ofcourse I admit that much could be done to make the model look more like the real F-35, but this is my first ever scratch-build, and I wanted something simple.
However, I now had a complete plane and a lot of electric hardware from old planes laying around, and with the EPP still not arrived, I decided to try to get this plane to fly. After browsing through some wattflyer-projects, I decided to go for a mid-mounted motor with the propeller spinning through a slit in the wing. I made a motor mount from a ice lolly stick reinforced with glue (acryle-something, flash I believe it's called, green tube), and glued the whole thing to the latter wing rib. I cut pieces of the main wing for ailerons (elevons), and glued the two servos (Dynam) to the wing with a piece of 6mm Depron between the servo and the wing (in case I want to remove the servos without damaging the thin 3mm Depron wing. The ESC, reveiver and battery was mounted to the wing's underside with sticky velcro. A slofly 9*5 propeller was mounted to the motor.
Now, these electrical components were all taken from an old Dynam Extra 330L, except for the receiver, which is a Spectrum DSM2 2.4 GHz AR6100 receiver. I have one of these in all my planes now, and I'm really happy with them. Anyways, I'm unsure of the specs on the rest of the gear, maybe one of you guys can help me out here. I don't even know the size and specs of the motor, but it's roughly the same size as my EFlite 450, but a bit longer. The ESC is actually hard-wired to the motor, so there's no connectors between the two. I guess it's around 25 amps or something, but that's just a guess. Maybe one of you guys have had a plane like this and knows the specs?
The elevons were attached to the wing with small, lightweight plastic hinges, and I used a couple of Parkzone elevon pushrods (as used on the Stryker), as I really like that their lenght can easily be adjusted. As you've noticed, I only have elevons on my plane, and I use controller mixing for the elevator/aileron actions. I like the idea of keeping it simple, and this also requires one (or two) less servos and keeps the weight down.

Finally, everything was ready for her maiden flight! I got a buddy of mine to help me, because with no landing gear and mid-mounted motor, this plane was difficult to launch with two free hands, and impossible to launch alone. I guess I'll mount landing gear on my next version. We went to an area with some tall grass (for hard landings... ), and got ready to fly. I'd just taken a wild shot at the center of gravity, and figured we'd have to experiment a litle to get it right. And that turned out to be correct. The expermentation that is :-). On the first flight, she stalled right away, and kind of just hovered hanging by the propeller. I moved the battery a bit forward, but the second flight was still not good. She stalled easily, and was difficult to turn and control. The third flight was better, and for the fourth flight, I changed from my lightweight 11.1v 800mAh lipo (allready in it's maximum forward position), to my heavier 1250mAh battery. This battery, all the way to the front by the air intakes, did the trick. She flew great, did ok turns, and she actually flew quite fast, even on 1/3 throttle. I did a couple of laps around the field (trying to stay above the tall grass...) and she was a beauty. This was truely a wonderful moment, seeing my own baby flying . It really made all the effort worth it. (Allthough, it's been quite pleasent to build this bird aswell).

As this is my very first project, it's probably got tons of room for improvements. I'd be happy to get feedback from you guys, and incorporate them in my next version.
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Old 08-07-2008, 08:26 AM
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Default My EPP and EDF has arrived!

Finnally, both the EDF-unit and my EPP arrived yesterday! This means I can finally start creating the next version of my scratch-built F-35. However, I'm not sure the EDF motor is big enough for the job though. It's a 55mm edf with 6 blades and a C-20 motor. The spec says it will generate 480 grams of thrust, and since my plane's flying weight will be around 300 grams, I figured it should do. Any views on this? I've never had an EDF before, so I really don't know.

Please reply if you have any experience with EDFs.
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Last edited by IFlite; 08-07-2008 at 08:31 AM. Reason: typo
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Old 08-08-2008, 11:35 AM
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Default Slowly taking shape...

progressing...
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Old 08-08-2008, 11:48 AM
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I have no edf experience so I can't be much help there but it looks good.
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Old 08-08-2008, 11:53 AM
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Default Hover

Hey. Is that a Bravo Model. Probably no VSTOL in your future. Nice plane man.

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Old 08-08-2008, 12:18 PM
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Default Vstol

Thanks Cheech . I think VSTOL will be hard to do, but it would be really cool though . Especially since the F-35B comes with it. I've seen some VSTOL EDFs on youtube, but I guess that's quite an undertaking

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Old 08-08-2008, 03:20 PM
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Default Edf vstol

Check this one out: [media]http://www.youtube.com/watch?v=hhgtMFX3ATo[/media]

nice huh
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Old 08-08-2008, 05:09 PM
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Well, you could make it VSTOL without too much work. Place the plane on the ground, give a tiny bit of throttle, enough to make some noise. With one hand, slowly lift the plane off the ground to the desired height. Now give it full throttle and toss the jet forward. For vertical landing (the hard part), do a slow fly-by or harrier, and catch the jet in the air with your hand. Reduce throttle, then slowly lower the jet and place it on the ground. There you go, VTOL capabilities!

btw, nice looking jet. Looking forward to the finished product.
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Old 08-08-2008, 05:48 PM
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Nice looking builds you have going there IFlite, very nice.
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Old 08-11-2008, 07:08 AM
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Default Nearing completion

Thanks firemanbill and aero_K.

It's almost finished now, well, finished enough for its maiden flight anyways! I'm hoping for some nice weather this afternoon, I can't wait to test it Also, because it's made out of EPP, it should be almost indestructable, which is a cool feature

I'll keep you updated on how she flies.
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Old 08-12-2008, 09:49 AM
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Default Insuffiscient power...

Oh no! :/ My EDF unit seems not to be powerful enough for the job. Darn. I did the maiden flight yesterday, and she would barely stay airborn at level flight, and would descend just by turning slightly.

This was a setback, and a bit strange, as the edf with the brushless C-20 motor is reported to genereate 480 grams of thrust. However, while I havn't yet measured it, the EDF doesn't even generate 300 grams of thrust.

So, there are three options, - buy a bigger EDF, mount a second EDF in parallel, or go with the tried and tested mid-mounted motor as in the prototype. The latter is at least a tried and tested approach....But I really wanted to try EDF on this one. Any tips, anyone?

Regards,

Last edited by IFlite; 08-12-2008 at 12:05 PM.
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Old 08-14-2008, 12:19 AM
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I have not had good luck with EDF either.
I think they suck, and blow.

Seems that everything has to be setup perfectly in order to acheive rated values, and when you approach those setups, weight always suffers. I not sure how people make EDFs happen (at least from scratch). The best I could do was ok performance, with a 6 min flight. Not really acceptable to me.
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Old 08-14-2008, 09:52 AM
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Default Back to mid-mounted motor

Thanks TVCasualty, good to hear I'm not the only one with EDF-problems

I removed the EDF, and put in the brushless motor and a 9cm propellar instead, at least I know this works. I cut a slit in the top wing as I did with the prototype, and it flew nicely. Well actually, it flew ok, and I experienced a strange wobble-effect at low speeds. The plane would start to oscillate from side to side, and this wouldn't stop before I gave more throttle. Anyone experienced this strange effect before?

Also, i notice that the plane drops quite a lot when I do turns, which I have to correct for with the elevators (elevons actually). Ofcourse all planes do this to some extent, but this was much more noticable on this plane than on any other planes I've flown. I guess this is a result of the design and shape of the plane, and it probably doesn't help that the wings are flat (desk profile), and don't generate much lift.

Anyways, here's the lastes pics of the bird. I'm working on the nose now, and I'll post some more pics soon.

Happy flying everybody!
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Old 08-15-2008, 09:45 AM
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Default Finished!

With the nose and landing gear in place, I guess it's finished. Whohey!
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