Saturday, October 31, 2015

DIY Canard Airframe 04

Woot! First time out with the laser cutter. Unfortunately, the holes that I meant for the bracing to go through were too small for the piece of wood meant to go through it... looks like I'm going to have to make another trip down. If not, it was a very successful run.


I spoke to hastly. The holes were too small, because the entire object was printed at about 88.8% of full scale! Darn it. I was wondering why the battery fit so snugly when I had planned for lots of space. Only then did I measure it, and realized that there was a size discrepancy.

If so, then the weight for the full fuselage will far surpass my original design estimates, and if I continue down this path, will have an airframe with much higher wing loading.

I need to think how to proceed. Very likely I will just proceed, as I do hope to learn more about creating a canard.

The original idea behind the wood frame, is to have a strong underlying structure, as the foam weakens significantly with holes cut into it.

Let us ponder.

Edit 2:
Didn't want to make a new post. I stuck the whole thing together with Titebond III .As I didn't have any clamps, I just relied on the thick rubber bands used to hold down the wing to hold the pieces together.

Titebond is a pleasure to work with, while the working time _could_ be longer, it was good enough for the few pieces I had to cludge together. In addition, it clean up with water! Some people have mentioned that it doesn't sand as well as Titebond III, but I don't think I will need to sand much as it just wipes away with a damp paper towel. And it washes off in the toilet, easy!

The strength of the glue is extremely impressive. I did some test with some waste plywood pieces and the glue of the veneers gave way before the glue bond. That's extremely impressive. The assembled fuselage otoh feels extremely rigid, and that's before I even put in my extra bracing.

I think I will just go ahead with the build. My motor is theoretically able to give about 600g of thrust with an APC 8x4E prop, and if the aircraft comes in about 800g, the thrust to weight ration _should_ be fine.

In the unlikely event that I would need more thrust, swapping to a 9x3.8SF will give over 800g of thrust, at the expense of flight time. In my limited experience so far, all my designs have take off at perhaps 60-70% on the throttle, and I can usually fly around half throttle, so it's very likely I will have enough thrust on just the 8x4E.

Quite excited to see how this build goes, but I am also very tired as I could not sleep well last night, kept waking up ever so often. Argh.

Friday, October 30, 2015

DIY Canard Airframe 03

Laser cutting this design tomorrow :3

After some thought, I decided to just do the whole fuselage. Alot of the material will be removed anyways, and the estimated weight is about 130g? I've added lots of structure at the points between the 3 "pods" that should be rather strong.

The DTF will then be more of a protective surface and less a structural thing. Which is good, as I really have my doubts of the longevity of the fuselage once holes are cut for equipment.

Securing the battery down is another story that I'll think about later :)

Wednesday, October 28, 2015

Google Cardboard & Unity

Eh, got bored waiting my turn for the laser cutter. Only can get time on it on Friday. Sooooo bored!

Monday, October 26, 2015

DIY Canard Airframe 02

I was introduced to last week, and it's very eye opening to see how much can be done inside a browser! I'm really not sure how heavy they will weigh, and I haven't yet figured out how much offset I need to give the pieces to accommodate the laser's kerf.
I'll stew on this for a day or two, then hopefully I'll have some laser cut pieces later this week.

In other news, I have also been experimenting at making a strong fuselage out of DTF (Dollar Tree Foam/Readiboard). While Experimental Airlines has a great way of making a strong fuselage, I do not have the space nor tools to do what he does, so I've been trying out various ways to get a strong fuselage.

It seems like without cutting a hole in the fuselage (for putting in batteries etc), I could get a very very strong tube by leaving the paper on, and constructing a tube similar to the way Flitetest does their swappable power pods.

However, once a hole is cut, the structure weakens immensely, and you can see that it won't take torsional stress very well. For a canard planform that relies on a strong section connecting the front and back, I thought this would be a major weakpoint, something I had to figure out.

Experimental airlines deals with it using additional pieces of DTF to strengthen the walls, in additin to some bracing to keep the tube square, and this appears to work well. I tried this, and it didn't seem all that strong, when I realized... perhaps I was using the wrong kind of glue?

Being the need for strength, I pulled out Foam Tac as it's been very strong so far for bonding many many materials, and I really like that it's rather flexible after it's dried. It was this flexibility that I was concerned with, and did a quick test, gluing two pieces of DTF using Foam Tac and Gorilla Glue.

Gorilla Glue was the clear winner in this case, the material broke first before the joint - heck the joint is still there and everything around it is all broken up from my attempts to pull (shear) them apart.

Foam tac unfortunately didn't work as well in this test case; I pulled it apart really easily.

This further reinforces the need to test various adhesives in various contexts. Hot glue, for example, I haven't used much as it's so heavy, but perhaps it may prove to be an even stronger joint.

In addition, with wood-wood adhesive joints, there is still one glue type designed purely for wood that I haven't tested: Titebond III. This is supposed to be *the* ultimate wood-wood adhesive. Have to test this shortly.

Saturday, October 24, 2015

DIY Canard Airframe 01

After much calculating over the evenings this week, I decided to go back to my roots and build something simple. I really wanted to build a twin boom pusher airframe, but it seems like my ideas were very heavy and not good for flight.

I then watched some flite test and experimental airlines to get some ideas, and the Ansley Peace Drone came up, and I thought hey, why not, let's build something similar.

To keep things more on the lighter side of the spectrum, I'm going for a fuselage mainly made up of DTF (Dollar Tree Foam/Readiboard) , with plywood used to build sections that need to be rigid. For example, the motor mount.

VR Take 2 - it works!

So after returning the previous headset I got from amazon, I was still curious about bluetooth controllers for gaming, so read up around reviews and found this particular one that garnered good praise in its "Red Samurai" guise, as marketed by gamestop. Thankfully, it's a generic controller produced by Lemon, aka the S600. Browsed, and came across it under the Vigica brand, and decided to go for it.

It also came bundled with a vr headset for a few dollars more, so I thought, why not. Now when I first put this headset on, it worked pretty good! As good as the sunnypeak I tried, or even better, as I felt the rectangular screen was closer. For some reason, I took the phone out of its protective casing when testing. I then put it back into the protective casing before slotting it into the headset, and.... it made the experience very, very blurry. Seems like 1-2mm of distance between the screen and eyes is a BIG thing for VR this close.

The bluetooth controller also paired with little drama, though it's rather annoying to have to disable it as it appears to be a keyboard to the OS, thus the virtual on-screen keyboard does not show up. I haven't yet found any games I want to play with yet, but a gamepad testing app showed that all the buttons were working, which is well and good :)

Tuesday, October 20, 2015

VR - maybe not for me

Bought a pair of "3D VR Glasses" - basically a plastic version of google cardboard to give it a go. I've always regarded VR to be a gimmick - back in the 90s, I tried some "VR" googles for flight simulators and while it was cool, I really did not think it added anything. Of course, back in the day we were limited to low quality graphics and, IIRC, no head tracking. Tempered by my past experience, I never really got into the VR craze.

Skip forward to today, I gave it a go, but I think it's not for me. First, I think the glasses are probably not paired well to my vision. The image is only somewhat in focus, and I think it's the reason why I'm getting a mild headache.

The headtracking works great, if there's drift, I don't think its an issue at all.

My main issue is the apps for VR, while quite immersive, are just not my cup of tea at all. I think that for maximum use of VR, a dedicated game controller would be required. My version of google cardboard didn't have the magnetic button, so I have to use the included bluetooth controller. Which, unfortunately I can't seem to make it work in gamepad mode, only mouse mode (which works great!)

Probably gonna sell it soon. Urgh, have this pulsing headache on my temples. Graaah.


So I tried my friend's SunnyPeak VR Headset, and it works great! It came with resin lenses, and had the ability to change the interocular distance, and I had a much better time. The pictures were sharp, and I did not get any headaches. Seems like if you're nearsighted, not all work the same?

Saturday, October 17, 2015

RC Annular Wing

Getting back to this build! Finally decided to build it with rudder and elevator, instead of just rudder alone as I was planning to.

I've also no idea how things would work, I'm just going to use what I've learnt from building the 3 previous aircraft.

The only thing I know is where the approximate CG for this wing is, so I'm keeping the rear end as light as possible and keeping the weight up front. Hopefully it will all work out!

Monday, October 12, 2015

Kfm3 flying wing post-mortem

Maiden'd the Kfm3 flying wing this evening, and while it does fly, I really don't like the handling characteristics. It's rather pitch sensitive (expected) but for some reason it does not turn as well as I hope. It rolls well enough, but doesn't track as well as my Kfm4 wing. I wonder if it's because of the vertical stabilizers....

In addition, it has difficulty penetrating the wind. Even at full throttle it appears to move rather slowly. But more importantly, it's handling characteristics in a crosswind are rather poor. For some reason the Kfm4 wing dealt with it better. Maybe the wind was much stronger today.

Finally, the stick mount is just not working for this design. In order to have the thrust line aligned with the middle of the wing, the motor actually juts out under the wing. I've made a foam block to shield it, but hard landings can bend the mount.

In any case, I think I'm done with this experiment, and going to use what I've learnt so far to build another design. This one will be a swept wing with a pod, and the wing sweep will be a bit more than my first wing in order to make balancing the CG easier.

Sunday, October 11, 2015

Kfm3 Flying Wing Build Log 05

I was surprised when I received a small parcel today, containing the Cobra motor I ordered from the US last weekend. It's a Cobra 2204/58 1080Kv motor. This motor weighs almost half the weight of the Emax I was using, so I decided to rebuild a new, lighter weight pod. In doing so, the AUW of the wing is now 346 grams!!!

One advantage of having a pod (or fuselage) is that adjusting the CG should be much easier now - all I need to do is slide the battery forward and back, and use some foam spacers to take up the space.

On the flip side, there are now far more things to go wrong, and the wiring is more complicated. For example, the pod is attached to the wing with rubber bands. I've never crashed this airframe before, so I'm not sure how well it would take damage.

If the motor pod _does_ get destroyed though, it won't take too long to rebuild. In fact, I will probably have to create a new one when if I decide to put a camera and fpv gear on it.
The previous pod had the thrust line running more or less directly through the middle of the wing. In a sudden burst of randomness, I decided.... hey, let's try it with a high thrust line. And then I attached the motor with the mount flipped up.
 I can't wait to test her out on her maiden flight Sunday evening!

Saturday, October 10, 2015

Kfm3 Flying Wing Build Log 04

 Eh, didn't update the blog as I was struggling to figure out how to attach the pod to the wing.
I'd experimented with several ways of folding the tube after watching various vids only, and decided that I do not have the tools to do it, and came up with a sort of kludge solution that I _think_ kinda works.
So in the end, it started with the motor mount. It's basically a square basswood section sandwiched between two thin slices of basswood, with balsa filling in the gaps. I'm not sure how durable this will be, but it appears to be quite firm. Zipties are threaded through the wood section into the tube.

BBQ skewers are then pierced through and supported by hot glue from the outside. While this actually holds the wing very well - I'm rather surprised by how tight the wing is joined - I fear any crash will simply force the skewers backwards, tearing up the pod.

I'm also not exactly sure how I'm going to mount the electronics inside the pod, or how to strap the battery in. Oh well, I'll figure it out. This is what makes it fun anyways!

Thursday, October 08, 2015

Kfm3 Flying Wing Build Log 03

 Got the flying side of the wing taped, and the leading edge taped with heavier duty gorilla duct tape.
Folding the wing was much more difficult than I thought. I didn't have enough heavy objects to put pressure on the wing, so I placed what I had in the middle, and held down the left and right sides manually with pieces of unused foam.

Also, I got the pod built. It's slightly warped, and I'll probably cut off the warped area.
I've removed the electronics from the Kfm4 wing in preparation to fit them in tomorrow!

Wednesday, October 07, 2015

Kfm3 Flying Wing Build Log 02

I found some 5mm square basswood pieces, as well as some 3/16in wood dowels (about 5mm). The basswood was not as long as I hoped, while the dowels were longer than the span of the wing. I decided to take the longer dowels (I think they are pine) and fit them into the wing. The pine isn't as stiff as the basswood though, and I hope that for this small wing, it will be enough.

Tomorrow I'll be taping up the opposite side of the wing before I form the leading edge, and the pod has also been cut out from another sheet of DTF and ready for taping and forming too!

Tuesday, October 06, 2015

Kfm3 Flying Wing Build Log 01

So I need a new airframe. Spent some time ogling the beautiful projects on rcgroups, realize that I do not have the tools to get such cool builds going, and just decided to randomly design something.

After some thought, I've decided to build the following
- Kfm3 airfoil with 4:1 aspect ratio.
- A pod or fuselage of sorts below that will hold most of the electronics.

Easy yes?!

I quickly did some calculations on the flying wing calculator, and the CG is about... 4cm from the leading edge. I'm not sure what this plane is going to look like... but man, I gotta have some weight up front!

The Kfm3 airfoil is selected based on its heavy lift capabilities, as well as for ease of build. As the wing design I'm going with is totally rectangular, it is extremely easy to measure and cut out. Also, the ability to put in several spars (thinking of just 2 spars, really) to stiffen things up is really enticing.

Right now, I have a 9.5mmx9.5mm basswood stick, which I think may be too thick. So, I'm going to Michaels tomorrow to see if they have a 5mm square basswood stick, if not I'll just wing it and use the 9.5mm. It should prove superbly strong. I'll also have to be careful how to mount the servos, as I want them near the spar to properly support the wing and not allow the wing to lose its stiffness.

The pod below is not properly thought out yet, but it's going to be based on the pods seen on Experimental Airlines. Mine though, will be much smaller with a 4cm inner diameter - the widest thing I'm fitting into the wing is the battery, which is about 37mm wide. I was considering designing it to fit a gopro, but I'm not ready to send up a few hundred bucks into the air, experimental design or not!

Now in a previous post, I mentioned I wanted to have the motor up high, so as not to strike the ground. This may not be the best of ideas as the motor needs to go rather high, or, I need some long landing gear.

Given I'm not in the landing gear fan club thanks to the weight, and that I do not have a proper "runway" to take off from, I think I'm scraping that idea, but am very interested to try out how folding props work, so I'll go with that instead. Perhaps I'll have skids of sorts under the wing? No idea yet. Or, I could just have extra tall winglets that extend below the wing. I need to remind myself that the winglets need to be behind the CG for them to work properly.

Interesting interesting!

Monday, October 05, 2015

Kfm4 Flying Wing Post Mortem

Yesterday, I took the wing out for a flight in the evening, but it barely flew for 5 seconds before the motor cut, and I had to do a deadstick landing for real. When I arrived at the wing, the ESC was beeping the overcurrent tones, and the motor was just jittering back and forth very strongly when throttle was applied.

The motor was also nigh impossible to turn, even with the connections to the esc removed. A short while after, it started to free up, but it made clicky noises, and would sometimes just jam up for no reason. Seems like it threw a magnet :(

Having no spare motor, the only other choice was to take the CF2812 1534Kv motor from my Teksumo. Same motor mount, but it should have less torque and much higher rpm! I didn't change the prop and the wing flew fine, just much faster! I also could not fly as slow compared to the1200Kv motor, wonder why? Maybe the torque is not as good at the lower rpms but comes in at higher rpms? No idea....

Anyways, I took her out for a spin this evening, and she flew totally swell, as in the video below:
 Also compiled a selection of crashes :P

Unfortunately, this is the last time I will be flying her. It seems like the mods I made to hold the battery, as well as the holes used to hold down the servos have a very detrimental effect on the airframe, and the cumulative crashes cause the front section to fold up, as well as the left wing to fold up along the weaker portion by the servo mount.

She still flies, but tends to tip to one side, as I think the damaged section of wing, which actually bends upward, may be causing a dihedral effect. There are also other issues with the wing. While the front leading edge of the wing has 3 layers of DTF, the trailing wing section only has one section, and in reality is very weak. The 1 layer wing has detached around the motor mount, and I _think_ this changed the sound of the prop, perhaps because the air entering the prop now becomes even more turbulent?

I think if I were to remake this wing, I would make the following changes:
- More sweep to move the CG back. Balancing this wing has been difficult.
- A lighter motor - both for ease of balancing the cg. I also don't need the speed... for now.
- A carbon fiber spar, that would help the area weakened by the servo.
- Consider switching the elevons from foam to balsa (maaaaybe?) may improve handling if there is less flex.
- Perhaps 2 pieces of DTF minimum would help longevity.
- Figure out a way to allow thrust angles to be set easily! Ripping out the motor mount is a really bad idea.
- Colours or something to differentiate from top/bottom! There were several times I've lost orientation, not fun!

My next design will have the following requirements:
- Ease of building: Probably going with a plank wing and Kfm3 airfoil
- Prop safety: Prop will be high and not impact ground. (What about folding prop?)
- Minimum parasitic drag on wing
- Battery to be mounted below wing - perhaps the lower CG will give some amount of self-leveling, and not weaken the wing.
- Carry a mobius-type camera
- Carry a fpv camera
- Possibly have a tail section? vtail or elevator/rudder.

Good luck, me!

Saturday, October 03, 2015

Kfm4 Flying Wing Mods 2 Test Flight

Unfortunately, I had the camera angled too low, so out of 20 mins of footage, I had maybe... 20 seconds of aircraft, mainly in crashes XD

If not, the mods went very well, it was actually much easier to fly, I actually ran both batteries! That, is a win in my opinion. I first flew with the new thrust angle, which now had very benign behaviors in flight.

However, it still felt rather twitchy, so after I flew the first pack for about 10 mins, I added 14g of weight to the nose, and switched over to a new battery. She now flies with authority on the sticks! Much so that I tried some full throttle overflights as well as loops, and she handled it without any issues.

Loops perform very well with this wing, previously on my Nutball, it was nigh impossible to recover from a loop for some reason. This wing just pulls out of it easily. I also tried going vertical, then purposely stalled her while vertical. Once she nosed over, a little throttle brought her back into full control. I like this wing!!!

The main thing now is pitch sensitivity. She is *really* sensitive to the elevator input. I checked the transmitter when I got back, seems like the travel was set to 90%, while the aileron input only at 85%. Oops.

Roll on the other hand was great. Nothing like those crazy aerobatic planes you see, but perfect for newbies like me. 

Finally, battery life. My battery pack flew for about 10minutes. After the flight, the charger only put back 380mah back into the 1000mah battery (!!!!) This means, flight times of 15 minutes will be easily achieved, or, I can have the wing carry some heavier gear with no issues.

Really small motor!

Damn this thing is tiny! It's going to be used to convert my annular wing glider into an r/c aircraft. I hope I know what I'm doing!!!
Couldn't figure out how to press the prop into the motor, so I used a drill bit to enlarge the hole, then superglued the prop onto the motor.
The weight of the various components is 16g. The thrust of this motor/prop combo is supposed to be around 44g, so I have very little leeway if I want to get 1:1 thrust/weight ratio.

Here's a short video of it spooling up to 50% throttle, as well as how I wired it up.