Big Stable KFm3 Delta [build info & video] - Page 2 - RC Groups
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May 02, 2016, 12:54 AM
Learning to build planes.
nelsoneci's Avatar

Full-span elevon


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 tried with full span elevons. With a plane that I was about to discard. The delta can turn, but this is too way too hard to control and it tends to go to the right. Do you know of a thread (or post) about a big motor in prop-in-slot configuration?

I'm not sure I want to pursue this direction but I'd like to see what others have done. The nice thing if this works is that one could keep the plane in the air for more time with the same batteries because the motor wouldn't need a lot of throttle.
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May 02, 2016, 02:09 AM
Registered User
Quote:
Originally Posted by nelsoneci
I tried with full span elevons. With a plane that I was about to discard. The delta can turn, but this is too way too hard to control and it tends to go to the right. Do you know of a thread (or post) about a big motor in prop-in-slot configuration?

I'm not sure I want to pursue this direction but I'd like to see what others have done. The nice thing if this works is that one could keep the plane in the air for more time with the same batteries because the motor wouldn't need a lot of throttle.
Hi Nelson,

So you've overcome the first problem (inability to turn) - good job!
Now, the tendency to the right can be solved with trim to the left.
Regarding the "too hard to control" issue: Don't forget that if you make elevon chord and/or length larger you're increasing maneuverability, but also decreasing the feeling of "stability" when those surfaces move. This can be resolved by adjusting control throw mechanically (or with expo in the transmitter) and moving CG slightly forward. Personally, I just adjust my control inputs to be less aggressive at mid/high speed - then I can use full deflection at very slow speed to achieve really high alpha - you get used to the new behavior.

The Firefly design on this site has been built with some pretty large prop-in-slot arrangements (do a search here), but here's a plane I did that is essentially the same idea and it has a 10 inch prop in it (the turbulence that day was wicked). The slot wasn't cut wide enough at that time, so it was pretty noisy - after widening the slot it was much quieter. In the landing, note how slow the plane can be flown:

Flight of Vectored Thrust Delta with takeoff landing (1 min 40 sec)


In this one, I use the same motor/prop, but the prop is well behind the wing so it has lots less interference and noise:

Launch, Loop, Land 80 inch span flying wing, constant chord (0 min 39 sec)
May 02, 2016, 08:18 AM
i can't learn fast enough
Hi Nuteman.
Do you have plans for the 80 incher. I really like that wing style, and would like to try my hand at one.
Thanks
Terry
May 02, 2016, 08:31 AM
Registered User
Quote:
Originally Posted by Terry Glenn
Hi Nuteman.
Do you have plans for the 80 incher. I really like that wing style, and would like to try my hand at one.
Thanks
Terry
No plans, but the essential specs are in post 5 of this thread: https://www.rcgroups.com/forums/show....php?t=2404275

The thread also has some other useful info based on questions from others.
May 02, 2016, 09:11 AM
i can't learn fast enough
Thanks much.
Did you make the fuse, just big enough to hold the ele stuff?
Do you have a layout for the wing shape, the numbers mean nothing to this beginner, hehehehe.
Thanks
Terry
May 02, 2016, 09:23 AM
Learning to build planes.
nelsoneci's Avatar
Quote:
Originally Posted by nuteman
Hi Nelson,

So you've overcome the first problem (inability to turn) - good job!
Now, the tendency to the right can be solved with trim to the left.
Regarding the "too hard to control" issue: Don't forget that if you make elevon chord and/or length larger you're increasing maneuverability, but also decreasing the feeling of "stability" when those surfaces move. This can be resolved by adjusting control throw mechanically (or with expo in the transmitter) and moving CG slightly forward. Personally, I just adjust my control inputs to be less aggressive at mid/high speed - then I can use full deflection at very slow speed to achieve really high alpha - you get used to the new behavior.

The Firefly design on this site has been built with some pretty large prop-in-slot arrangements (do a search here), but here's a plane I did that is essentially the same idea and it has a 10 inch prop in it (the turbulence that day was wicked).
@nuteman: Thanks for the prop-in-slot example and for the videos. The plane was rather unpredictable, it is the weirdest thing I've flown so far (with a tendency to go to the right). I've countered torque with trimming before but this was different. Perhaps the thrust angle was not enough, adding a picture.

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FYI this is the motor have been experimenting with: http://www.horizonhobby.com/product/...-960kv-pkz4416
May 02, 2016, 09:41 AM
Registered User
Quote:
Originally Posted by nelsoneci
@nuteman: Thanks for the prop-in-slot example and for the videos. The plane was rather unpredictable, it is the weirdest thing I've flown so far (with a tendency to go to the right). I've countered torque with trimming before but this was different. Perhaps the thrust angle was not enough, adding a picture.

Attachment 8954100


FYI this is the motor have been experimenting with: http://www.horizonhobby.com/product/...-960kv-pkz4416
Hi Nelson,

I don't think your thrust angle is going to make a huge difference either way. For that specific issue, you're primarily dealing with rotational torque about the long axis, so getting the trim right is the first step. After that, there might be other issues.
Without seeing a flight video and/or getting precise specs for your plane I can only recommend some of the "typical" things to check/change/experiment with:
1. CG - Needless to say, this is absolutely critical. 9 times out of 10 when a wing finally flies right its because the builder finally got CG right. Very "touchy" behavior is very often mostly because of a too rearward CG.
2. Yaw stability - Vertical fins that are on the small side resulting in very marginal yaw stability can make the plane touchy. I notice yours are very short. Double their height (not width - we want them behind the CG) as a start and gradually cut them down, if needed.
May 02, 2016, 09:46 AM
Registered User
Quote:
Originally Posted by Terry Glenn
Thanks much.
Did you make the fuse, just big enough to hold the ele stuff?
Do you have a layout for the wing shape, the numbers mean nothing to this beginner, hehehehe.
Thanks
Terry
Yes, the fuse is just a very short pod for the electrics and the back acts as the motor mount.

The specs I gave for dimensions of the planform itself are stated in the only way I know how to - Is there a specific part you have a question about?
If so, it's probably better to post it on that thread...
May 04, 2016, 09:58 AM
Learning to build planes.
nelsoneci's Avatar
Quote:
Originally Posted by nuteman
Hi Nelson,


1. CG - Needless to say, this is absolutely critical. 9 times out of 10 when a wing finally flies right its because the builder finally got CG right. Very "touchy" behavior is very often mostly because of a too rearward CG.
Hi @nuteman. Thanks for the tips.

The CG is OK, as the experimental plane has the same dimensions as others I've built and we know where the CG should be, but...

Quote:
2. Yaw stability - Vertical fins that are on the small side resulting in very marginal yaw stability can make the plane touchy. I notice yours are very short. Double their height (not width - we want them behind the CG) as a start and gradually cut them down, if needed.
The fins are indeed small. I thought that the skids act as fins that are below the delta wing, but maybe this is not the case. So I should try increasing fin size. Having more torque challenges the original design.

The easiest for me would be to increase the twin fins because I can laser cut. Here is what it would look with each fin having about 6% of the wing area.

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I could also try adding back the single vertical stabilizer that the Big Slow Delta has and make it a BSD with KFm profile. The motor is now way back to allow for bigger batteries in the front so this would change the BSD but not too much.

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So, I think I have two pending tests:
  1. Increase fin size.
  2. Use two motors (less KV) and have them spin in different directions.

And at the same time be happy and keep using the motor that works :-) What I am doing now is that when I go to the flying field I take with me a delta that works and a experimental one.
Last edited by nelsoneci; May 04, 2016 at 09:59 AM. Reason: Say thanks.
May 04, 2016, 12:40 PM
Registered User
Quote:
Originally Posted by nelsoneci
Hi @nuteman. Thanks for the tips.

The CG is OK, as the experimental plane has the same dimensions as others I've built and we know where the CG should be...
Nelson,

I didn't get into detail about the CG. To state it more clearly: Any time a plane is touchy for whatever reason (in your case, the increased torque due to larger prop/motor), the very first thing to try is to move CG forward and see if things improve. The reason: Forward CG increases stability of the plane as a whole - and as a result of that all three axes are more stable, typically.

It's also the easiest thing to try, so why not?
May 04, 2016, 12:43 PM
Learning to build planes.
nelsoneci's Avatar
Quote:
Originally Posted by nuteman
Nelson,

I didn't get into detail about the CG. To state it more clearly: Any time a plane is touchy for whatever reason (in your case, the increased torque due to larger prop/motor), the very first thing to try is to move CG forward and see if things improve. The reason: Forward CG increases stability of the plane as a whole - and as a result of that all three axes are more stable, typically.

It's also the easiest thing to try, so why not?
Got it. Thanks.


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