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Jan 21, 2016, 10:51 PM
Learning to build planes.
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Big Stable KFm3 Delta [build info & video]


This is a delta that is nice to fly :-) I find it very relaxing because it is not hard to control. I can flight it for 40 minutes with 2x3s-2200mAh batteries, if there is not a lot of wind and I fly it very slow (A bit below 50% throttle).

Big slow delta with KF-m 3 airfoil (3 min 46 sec)


I ended up building this plane while learning how to build a Big Slow Delta, so there is some resemblance to the 40" BSD: I use the same dimensions and also the surfaces that extend below the wind. I have learned a lot in the process.
  • Root chord 83cm (32.68"). Wingspan 102cm (40.16"). COG is 40 cm from the tip.
  • AUW is about 870 grams with two 3s 2200mAh LiPo batteries.
  • SunnySky X2212-9 1400kv Brushless Motor
  • 8x4.5 propeller
  • 30A ESC
  • TGY-S306G-HV servos (I'm getting some jitter, I'll try another brand)

It is important that the motor does not vibrate. I used two carbon rods to avoid vibrations. We tried to suppress vibrations in the blue twin (see image below) with a different motor mount but it didn't work and the plane was almost impossible to flight.

It is built with Model Plane Foam and EPS. It can carry a bit of payload, it glides a bit and it can land with some speed.

It doesn't have a lot of reinforcements but I have been able to repair a lot of crashes, until it doesn't make sense to repair any more. I glued it with Gorilla glue and it helped with the weight: it doesn’t have a lot of hot glue.

I think the design can be improved, but it is already fun the way it is. I hope we can find improvements on this thread. I will build another one right away and share the progress on the new build. Tips are welcome :-)

Now I am wondering:
  • How to add more strength without adding a lot of weight? (KFm3 is helping with strength).
  • What do the surfaces below the wing do exactly? (I mean aerodynamics, they help with landings and to protect the propeller).
  • What is the best way to use KFm3 airfoil (and other airfoils) with this delta?

There are no plans yet, but I hope the images below are useful (everything is in centimetres).

Thanks to people on rcgroups for the help, to @sr71fan for making the B.S.D. design, to @tucanae47 who started helping me build new deltas, and to @cterraza who usually helps me with electronics.
Last edited by nelsoneci; Jan 22, 2016 at 09:38 PM. Reason: Mostly formatting. Add sr71fan to credits.
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Jan 21, 2016, 10:53 PM
Learning to build planes.
nelsoneci's Avatar

Plans?


[Reserved for plans]
Jan 21, 2016, 10:59 PM
Registered User
I loved it XD
Jan 22, 2016, 12:16 AM
skumgummi dave
Good job!

Dave-
Jan 22, 2016, 08:19 AM
Registered User
Dickeroo's Avatar
Nelson ...

You've done an excellent job with this build.

~ Dick
Feb 01, 2016, 02:44 AM
Learning to build planes.
nelsoneci's Avatar

Build starts!


First, I draw the delta over the model plane foam. This time I'm cutting 1cm from the aileron height, moving the area of the control surfaces from 15.5% to 13.8%. I'm trying to reduce aileron vibration by giving less area to the the control surfaces. I've read digital servos vibrate more than the analog servos.

Then there is a closeup of where the central stabilizer goes. It is used to help hold the motor mount as well.

And then the delta is cut. I use a bit of tape to hold the tip and then I'll tape it and glue it with gorilla glue.

Next step: Cut the EPS layers for the airfoil. I hope to do this tomorrow.

ATM I'm cutting by hand. I think I wouldn't like to use Inkscape. I'm learning openscad with the lasercut library. But I'm not there yet, attaching the first baby steps Parametric design seems very fun.
Feb 04, 2016, 02:05 PM
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KFm9 for the delta wing


I liked how this delta (J-43) flights with KFm9 so I'm trying it with the new big delta. I got thinner EPS (10mm).

Two weeks ago I built a smaller version with the same proportions and no motor and then I tried a simple elastic launcher. Wingspan = 70cm (27.5 inches), AUW = 260 grams. After trimming we launched it harder and it went straight up! Like an arrow and I had to land it fast because we were trying it in a small street... I hope to maiden it in a field in two days. I would like to add a small motor And perhaps experiment with high-mounted prop.

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Back to the build. I drew the second KFm step over the EPS.

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I cut it and added a wood spar. It is located between the EPS and the Model Plane Foam. The wing is more rigid this way, it's the first time I put a spar in this location.

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Then the other KFm steps. I used about 35%, 50% and 75% for the steps. The bay is a bit bigger in this test. There is a small mistake, the last step is bigger in the right, I corrected it after gluing.

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I let the gorilla glue dry overnight.

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Then I cut the leading edge at 45°. I used hot wire, mostly because I wanted to test this method. I needed a bit more heat but I think it was easier than using a knife. The result is better than the previous one I cut.

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Then I sanded the EPS and smoothed the leading edge.

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Then I added a bit of tape to the leading edge. I didn't add a lot of gorilla glue there so the tape is useful there.

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Next steps: Build skids and vertical stabilizer, install electronics.
Last edited by nelsoneci; Feb 04, 2016 at 03:03 PM.
Feb 16, 2016, 11:42 PM
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Stable Flight with CC3D Revo Flight Controller + Camera


Hi there! Long update.

I got a CC3D Revo Flight controller. I crashed the first delta I built a few times because I didn't know how to tune the controller. I taped/glued what was left of it without a lot of hope and a friend helped me set up and tune the controller. It flew well! I was about to recycle the parts from it while it was still alive :-)

Because of the crashes it was more flexible, so I put a carbon rod near the elevons. It (originally) has two more in the skids.

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Here is what the original wing looks like now, with the tray open on purpose. And a closeup of the CC3D board (not pretty).

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The delta is not hard to fly, but adding stabilization makes it into a more gentle delta. Here is an example. I got overexcited and sent my phone for a ride :-) So there is a nice take from above of the hand launch and the landing.

Stable Flight - Big Stable KFm-3 Delta (0 min 47 sec)


Then we put a camera on the wing. The friend who helped me set-up the controller does FPV and I think he managed to get me into that addiction. I'll try to get something affordable for FPV when I finish documenting the build. This is the first time I put a camera on a plane.

Highlights: 1:25: flying fast, 2:40: reckless pilot is chasing me with his small FPV quad, 4:05: too close to that tree, 5:13: Landing.

Trying a camera and CC3D stabilization - Big Stable KFm3 Delta (5 min 34 sec)


At 4:30 the wing was vibrating a lot at full throttle and I noticed that the wind was blowing strong, this is taken from the video (it's in the middle at about 4:48):

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Here is a nice crash, I tried to do a roll without turning off the flight controller and it didn't work. Nothing happened to the wing! Other than getting dust on it.

Crash with Big Stable KFM-3 delta, with no damage. (0 min 24 sec)


I'll continue documenting the build soon! I am still learning OpenScad and I think that I will be able to generate the plans. The nice thing is that it will be easier to generate plans for different wingspans, propellers and slot locations. The file that will generate the plans is here (work in progress, I'm getting some help here as well).
Last edited by nelsoneci; Feb 17, 2016 at 07:29 AM.
Feb 23, 2016, 01:20 AM
Learning to build planes.
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KFm9 delta / First version of the plans


We finished the build of the KFm9 delta. A new one because we wanted to test the first version of the plans. The maiden flight went well! The day was a bit dark so I edited the video to leave the parts than can be seen better.

Big Stable KFm-9 Delta - Maiden flight (1 min 28 sec)


It flew well. I forgot to balance well in the roll axis so when unpowered it tried to go to a side. We only did one flight.

Each vertical stabilizer has an area of 3.5% of the wing area. With more area they looked too big. My guess is that the surfaces below the wing count for vertical stabilization so the stabilizers above the wing do not have to be big. Just guess work from what I have read... What do you think? I've read there is a formula for this.

The change in elevon length from 9cm to 8cm made it a bit harder to do loops, but I think I like it this way.

I am attaching the first version of the plans. This version still needs a bit of cutting, but it saves a lot of time if you laser cut the 4 skids (each skid is made of 2 glued pieces). And you get more precision. No plans yet for the EPS KFm steps but I think the instructions above can help with this and the wing to help you draw the steps. What I do is that I use the wing to help me draw the biggest KFm step, and then I use that step to help me draw the smaller one, and then once more and I have all the steps I need. Camilo with the pieces after we cut them:

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Next steps:
  • Update the plans so that you do not need to cut the holes where the skid tabs go. Same for the elevons.
  • Build a smaller version to see how it flights 70cm/28in of wingspan.
  • Build another one for me since I gave this one to the pilot of the video. First time I make a plane for somebody else.
  • Build plans for the KFm steps.

And that's it for now.
Last edited by nelsoneci; Feb 23, 2016 at 01:35 AM.
Feb 23, 2016, 09:28 AM
Registered User
Dickeroo's Avatar
Nelson....

Very nice flight. That Delta looks great in the air. A very smooth line of flight. Terrific design.
Mar 01, 2016, 12:44 AM
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Glide test of not-so-stable kfm9 delta


Quote:
Originally Posted by Dickeroo
Nelson....
Very nice flight. That Delta looks great in the air. A very smooth line of flight. Terrific design.
Thanks for the encouraging message :-)

I finished the build I started cutting by hand, this time trying to hide the cables. With a different motor configuration.

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Here is a glide test, at the beginning of this video.

Big no-so-stable KFm-9 delta (2 min 17 sec)


This version is less stable and it could be because of three things (I think).
  1. Vertical stabilizers are too small (it's more stable when flying inverted).
  2. Weight closer to the CoG and then the back is less heavy.
  3. Pushrods too long make the elevons flexible.

The good thing about (2) is that rolls are easier, that can be seen in the video.

It was fun to fly in moderate winds and I'm learning to use the wind to get lift. I spent about 3 minutes flying with 35% of throttle by using the wind. In this flight I managed to stay in the air for 23 minutes and 40 seconds with a single 2200mAh battery (Lipo saver was set to 3.6v and I linked right after the alarm went on).

I'm not sure what I'll try next. I want a stable delta to keep, one like the one I built before this one. And I would also like to try symmetric air-foils.

I'm also wondering... If I wanted to add a bit of wing area, how would be a good way to do it? The restriction that I have is that it needs to fit into a small car. I like this shape but I don't know what the implications are:

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BTW, I'll test an EDF motor that needs a 50A ESC. I'm not sure of what to do with it :-) It would be nice to test it with a symmetric airfoil such as KFm-6. This one won't be slow... But I won't try this that soon.
Apr 24, 2016, 05:07 PM
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Big motor, too much torque


Hello there! A few updates.

Quote:
Originally Posted by nelsoneci

This version is less stable and it could be because of three things (I think).
  1. Vertical stabilizers are too small (it's more stable when flying inverted).
  2. Weight closer to the CoG and then the back is less heavy.
  3. Pushrods too long make the elevons flexible.
The issue with the unstable delta was the third, the pushrods were too long and then they became too flexible. I used small carbon fiber tubes (black thing around the wires) and this solved the issue, I have a stable delta now! I also did hide the servos.
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Now, I'd like to share a picture of a delta decorated by its owner (not me):

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I tried a bigger motor, the motor of the PKZ T-28 trojan. The thrust was great but I couldn't counter the torque. I think I needed more thrust angle, the T-28 has a lot of thrust angle. But I'm not sure I'll try this motor again. What do you think?

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I think the next test will be to increase a bit the tip chord to compensate for the area that will be lost, and try two motors that rotate in opposite directions. Both of them with prop-in-slot. Hoping to avoid the effect of motor torque.

Tips are welcome, as always!
Apr 25, 2016, 04:21 AM
Registered User
Making larger elevons and trimming appropriately should be able to counter the torque. It will also lead to the benefit of needing less control surface displacement for a given response rate, and better control in extreme high alpha maneuvers. Just make sure your servos are strong enough.
Apr 25, 2016, 04:28 AM
Registered User
Oh, and your elevons should extend inboard all the way to the center so that you get as much prop wash as possible over them.
Apr 25, 2016, 06:18 AM
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Quote:
Originally Posted by nuteman
Making larger elevons and trimming appropriately should be able to counter the torque. It will also lead to the benefit of needing less control surface displacement for a given response rate, and better control in extreme high alpha maneuvers. Just make sure your servos are strong enough.
I should try this. In one test I could make it go straight with elevon trimming but I didn't have room for turns, it would only turn in one way.


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