Kfx 201 - RC Groups
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Dec 28, 2017, 02:01 AM
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elmagnificado's Avatar
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Kfx 201


After many a moon, I finally had time to sketch up another on my to do list. Modeled this one off a Deviant Art find I think called the KFX 201. I think I'm gonna go with all working control surfaces, including canards... you know..... just because. 1-servo canards, 1-servo ailerons, and 2 servos for elevons. I can't decide is I only want pivoting elevons on the side or include some surface in the prop wash for thrust vectoring.

It's mostly an experiment so just going with $tree FB and hot glue, but I wanted it bigger than most of my park flyers so It'll have a 40" wing wing span and a 7" prop on a cheap 2200kv ebay motor and 40A esc. I have tons of these motors and esc's so not worried about burning them out. We'll see which burns out first.

I might post build pics, but definitely will post maiden video.

Edit. Added (very) rough plans. I might not get to this build for a couple weeks so if anyone wants to take a crack at it, be my guest.
Last edited by elmagnificado; Dec 29, 2017 at 02:31 PM.
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Dec 28, 2017, 07:56 AM
Laughs at un-boxing videos...
basicguy's Avatar
My last 2212 2200kv motor held up to a 7x6 prop at 34 amps for some time in the summer on the nose of a plane powered at 3s. I faired the motor in a bit and it didn't last one more flight.
Dec 28, 2017, 11:02 AM
Registered User
looking forward to build pics.
Why not try pink foam as material?
Good luck with the Project.

// Mats W
Dec 28, 2017, 02:02 PM
Slopeosapien
jonesymj's Avatar
That looks awesome!

I'd definitely build that!
Dec 28, 2017, 03:29 PM
flyin' fool
goldguy's Avatar
Get it ready the Jan.1st fly-in. Lots of time!
Dec 29, 2017, 03:27 AM
Registered User
elmagnificado's Avatar
Quote:
Originally Posted by Mats W
looking forward to build pics.
Why not try pink foam as material?
Good luck with the Project.

// Mats W
Got tons of $tree FB I gotta use up before the wife decides to "clean" out the garage.
Dec 29, 2017, 07:52 AM
I Look, Listen, and Learn
Timbo383's Avatar
Using dtf will be perfect for this plane due to the flexibility of it, you should get some nice smooth curves and bends to match the original plane lines.
Just one suggestion. Before you spend alot of time on the functional canards....which I do understand the "just because aspect"....I think they might not work too well. I'm not an expert at anything, just general knowledge, but I believe being so close to the cg they would act more like air brakes or flaps. Also being so close to the main wings the air flow would be disruptive the the lift of the main wings. Like I said, I'm not sure, I'm just making suggestions before you do the extra work and add extra weight that's not usable.
Dec 29, 2017, 09:22 AM
Registered User
Yep, unless the move-able canards are controlled by a properly programmed flight controller they'll almost certainly do more harm than good most of the time. Keeping them fixed will be reasonably beneficial for most of the flight envelope - acting more like strakes (or Leading Edge Root Extension, LERX). Lots of posts about this topic with the details - if interested, do a search.
Of course, canards that are much further ahead of the main wing are a totally different story.
Dec 29, 2017, 02:05 PM
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elmagnificado's Avatar
Quote:
Originally Posted by Timbo383
Using dtf will be perfect for this plane due to the flexibility of it, you should get some nice smooth curves and bends to match the original plane lines.
Just one suggestion. Before you spend alot of time on the functional canards....which I do understand the "just because aspect"....I think they might not work too well. I'm not an expert at anything, just general knowledge, but I believe being so close to the cg they would act more like air brakes or flaps. Also being so close to the main wings the air flow would be disruptive the the lift of the main wings. Like I said, I'm not sure, I'm just making suggestions before you do the extra work and add extra weight that's not usable.
Yeah, I was playing around with how "scale" I wanted the curves on top while trying to keep it a simple build. I kept running into aesthetic issues with the motor placement breaking up the curves too much, so I scrapped any curves behind the motor mount. I also needed something to mount the motor onto so I raised the fuse a bit near the motor to create a small vertical surface to mount the motor. I widened the fuse top next to the motor mount to blend more into the wing plate.

Regarding the canards, my intent was more for reversing them (pointing down/forward) similar to an SU 37 to get more air flow over the wing in high alpha. I've had decent luck with canards in a few of my last canard jet designs. I know they may not be very effective to supplement elevators in a loop due to being close to the CG, but I'll just lower the throws or turn them off altogether in that mode .

Also added some color (sort of). I have a bunch of black and white DTF and don't really have time (patience) to paint so just use what I got to make it look kind of cool. You'll see a lot of this black and white motif on my other builds.
Last edited by elmagnificado; Dec 29, 2017 at 02:46 PM.
Dec 31, 2017, 12:11 AM
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elmagnificado's Avatar
This might be a topic for a different discussion thread, but I had an idea that might be a little out there.

I know there are a couple thread discussions about successful ducted prop designs, not EDF's, but actual foam/formed ducts around a standard prop. What if you take this concept but tilt the prop angle relative to the duct tube to get a flatter/elliptical duct tube that could be more scale looking for a sci-fi jet. See attached concept sketches. The sketches show a fairly extreme angle, but this can be adjusted. I'm not sure what the fluid dynamics are or if this would have a huge negative impact on thrust, but it's worth a few bench tests to see what happens.

I'll post some results if/when I get around to it. Holiday vacation is coming to an end and probably won't have time to tinker with this idea for a couple weeks. Wouldn't mind some input from any fluid dynamics guys (or gals) out there.
Last edited by elmagnificado; Dec 31, 2017 at 12:36 AM.
Dec 31, 2017, 07:53 AM
I Look, Listen, and Learn
Timbo383's Avatar
Like the idea and concept, don't think it will be too efficient tho, but hey for a little bit of time and practicaly no cost it's worth a try just to see. If I get some time later I may give it a try, you got me curious.
Dec 31, 2017, 09:53 AM
Registered User
Yes, turning the thrust results in loss of thrust. In the drawing shown, the turn is very dramatic, so I'm guessing much thrust would be lost, but with today's huge thrust-to-weight ratios in RC you could get away with it - with the right motor/prop.
Jan 08, 2018, 12:32 AM
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elmagnificado's Avatar

bench test for flattened duct


Finally got around to testing out the angled ducted prop idea. I used an old 2200kv ebay motor with a 3-blade 6x4 prop similar to the sketches. I don't have a sophisticated thrust test rig, so I just tape it my scale to get an "idea" of what kind of thrust I can get.

Control: I tested just the prop and motor by itself and was getting around 790-800 g max thrust.
Test setup 1: After I built the set up shows in the pics, I only got around 300g max thrust. Over 60% reduction in thrust. (damn you nuteman! )

There are plenty of improvements that can be made to increase efficiency. Here are just a few running through my head as I was testing it:
1. the shape of the inlet duct can be more aerodynamic like a real EDF
2. much tighter tolerances around the duct and fan blade (I had trouble centering everything with my quick and dirty setup. I had about 1/4" on one side and had to trim a bit of foam on the other to keep from scraping ).
3. adjusting the angle of the prop with a larger elliptical cross-section while still achieving a somewhat slim profile.

Test setup 2: I will adjust the prop angle and tolerances on the next setup.

I am willing to take a hit on thrust if I can at least get a plane to fly with it, but it might not be the overwhelming success I was hoping for. I'm envisioning slapping this thing on a flying wing or a simple delta just as a proof of concept.... then back to the original build in the OP....
Jan 08, 2018, 01:40 AM
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elmagnificado's Avatar
Ok, real quick sketch of the delta I'll use for the ducted prop idea. Hopefully enough wing area at 30" WS to be floaty enough to fly. I'll just velcro the guts on top.

THEN, back back to the OP plan..... promise.
Jan 08, 2018, 05:32 AM
I Look, Listen, and Learn
Timbo383's Avatar
That looks pretty, only problem I see is grass and dirt getting into the duct on landings.


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