Kfm4 Flying Wing Mods 1 Test Flight

The mods have made the wing much better. She still pitches up on throttle, but it's not as bad as the maiden flight. The elevon throws on the other hand seem to work very well, no issues there. Gonna figure out if I want to simply add down thrust, which appears to be the solution for wings I've seen, or to adjust the thrust line to give it a more pitch down moment of rotation.

Kfm4 Flying Wing Mods 1

Based on the results of yesterday's maiden flight, I've adjusted the motor mount to give more or less a zero thrust angle, and also setup the servo horns so that they give much, much more throw.

Evidently, I did it the wrong way round, resulting in the *least* amount of throw possible! The new setup gives as much throw as possible without binding. There is a fair bit of difficulty in getting the pushrods to be exactly correct, and after snapping many pieces of 1.3mm piano wire from attempts at bending/straighten/bend - I gave up, and used a cut down piece of bbq skewer to join the two control rods using CA, and then shrink wrapped on top of it. It appears very strong, and I hope it does not give in a crash.

The battery is also now mounted flush into the body, with a thin piece of ply to support it, and hold the velcro strap in place. The unfortunate result of this modification, is that the wing now flexes a fair bit more.

I also placed the battery further back, partly for structural reasons, and partly because I want to have space for the FPV gear. In order to balance it, I needed to put in 21g of weight up front.

Which brings me to this! This package arrived from banggood today. I just checked, this purchase was made on the 13th of August, so this took over 6 weeks to get here! Not a good idea if you are in a rush :)

The contents are very well protected by this rubber-like material. I did a quick test, and it works with the fpv screen I bought previously, so yay! I doubt I will fly it any time soon, as I want to get confident flying the wings before I do any fpv flights.

Kfm4 Flying Wing Maiden Flight

I think the basic planform is fine, it's just the finer details that need to be tweaked. The thrust angle is probably the main thing, I'm going to remove it totally before I fly it again. The elevons also have very little command of the airframe, and I'm not sure if it's because the wing is flying slowly and thus the control surfaces do not provide much force, or its because I need much more throw.

The other thing I'm going to modify before the next flight is the battery - I'd velcro'd it onto the wing, but it came off in one off the flights. I'm going to embed the battery into the airframe like my Teksumo to be held down with a velcro loop, that will keep things tidier, and probably less drag too!

Kfm4 Flying Wing Build Log 08

She's all done and ready for her maiden! Still have to figure out a name for her :)

For the ESC, I was waiting for a delivery from overseas, but as I had a full weekend free, decided get this aircraft complete this weekend and bought an ESC from the lhs instead of waiting.

Originally I wanted to get a 20A ESC, but I did a quick static thrust test this morning using the heavier-duty electronics on my Teksumo, and I was getting an average of ~10A with the Emax CF2822 1200Kv motor. Armed with this knowledge, I had two options at the LHS, a Hitec 20A ESC or the Castle Creations Talon 15.

I've been quite curious about Castle Creations products, and the ESC weighed only 7-ish grams, and has a 50% buffer for the current draw, so decided to go ahead with it.

Testing the static thrust on the CF2822 with the following props give me the following results:

• 7x3.8SFW / 9.91A / 570g ~ 59g/A
• 7x5E / 9.05A / 480g ~ 53g/A
• 8x3.8SF / 12.3A / 690g ~ 56g/A
• 8x4E / 10.6A / 590g ~ 55g/A

Looks like I'll be going with the 7x3.8SFW for the maiden. The 7x5E prop is possibly stalled, and work better only in the air. But we'll see :)

Kfm4 Flying Wing Build Log 07

Almost there! Got the control horns into the elevons, and glued on the winglets as well.  The wing now weighs in at a beefy 317g, and this weight will only rise once I add in the pushrods and electronics.

The only big thing now is to fashion a motor mount :)

Kfm4 Flying Wing Build Log 06

Spent last night and tonight taping up the wing with packing tape, and the leading edge with some super heavy duty gorilla duct tape. Without the tape, the wing weighs 56 grams. After adding on the elevons and adding in on the packing tape, it now weighs 103 grams!!!!

In addition, I've tried gliding the wing, and it is very slightly tail heavy. Adding in a 3 gram weight (2 x 10 cent coins) and the plane glides forward slight nose heavy. Checking the CG, it is at the 35% of the way along the chord. That's way behind what's the supposed CG, but I'll run with it and see what happens :)

It seems like the elevons are considered part of the wing area, and they were not included in the CG calculations. Adding them in, it seems the CG of the wing is actually at 25%, so yay!

Added in the servo as well!

Kfm4 Flying Wing Build Log 05

According to the CG Calculator for my wing, for a 20% CG position, it's 11.8mm from the leading edge of the wing. Unfortunately, this requires a fairly heavy weight up front in order to balance the motor and prop! I knew there had to be a reason why the popular wings tended to be more swept back! The more swept back the wing, the easier it is to get the CG right as it is moved further away from the leading edge.

Several solutions, apart from adding weight, present themselves. A light motor would help alot, and I'll probably even drop the prop down to a 7in, no idea if it'll save weight at all. I tried putting my 3s 2200mah battery up front, that balances it up well enough, but is over double the weight of my 1000mah battery, so, not particularly ideal either.

I've also tried putting a 40A esc up front by the battery, and that helps too, but it's overkill as the motor is theoretically rated for up to 14A. In the end, I'm sure it will be a combination of all the above to get the wing just right.

Testing the CG at the 25% position _somewhat_ works. I'll cross that bridge once my esc arrives.

Ah, the things we learn :)

I've also quickly fashioned a pair of winglets. It seems like in some flying wings, it's possible to get yaw stability by adding in drag on the leading edge by chopping the corner off the leading edge. While this is a cool idea, I decided to go with the winglets instead as adding in random things I hardly know about is not a very good idea. Heck, I have no idea how to design this wing, just going by seat of the pants intuition here.

Other things I've prepped include the control horns for the elevons. After I've had control horns fly off in flight on my previous aircraft, I've decided to play it safe and use a proper dubro control horn. To spread the weight of the control horn onto the elevon better, I've cut small plywood sheets and foam-tac'd them on.

I'll need to figure out the servos as well!

Kfm4 Flying Wing Build Log 04

Added in the elevons :3 I must say I quite uncertain how to attach them - should I use some kind of hinge (I bought du-bro hinges)? In the end I decided to KISS and attach them using hinge tape - aka 3m blenderm.

I've also sanded down the leading edges to more of a "regular airfoil" kind of shape... only to realize, how was I to do it on the other side? I should have just left it. Oh well, we'll see what happens :)

Next up I could probably tape down the elevons with some new 3m tape I've got - 3m Storage Packing Tape. It's supposed to have a stronger Acrylic adhesive, and unlike the generic packing tape I got from the post office, it's thinner and amazing goop actually sticks to it very, very well - as well as foam tac.

The next step is to fit the servosin!

Kfm4 Flying Wing Build Log 03

The main wing itself had the leading edge sanded down. It seems like the Readiboard is very easy to sand, though the Gorilla glue wedged between the layers does make it more challenging. I'm not entirely sure of the blunt leading edge of the airfoil. Most people who do the bent kfm4 airfoil definitely have a much more aerodynamic leading edge. I'll see what I can read up on this online and decided if I want to go further.

The motor chosen for this wing is the Emax CF2822, 1200Kv motor, and I've got a medley of props to try out, but decided to go with the APC 8x3.8SF for a start as I am not looking for speed. That said, I hope the prop is fast enough to take us beyond stall speed......

For the motor area, I've added on another piece of foam to reinforce it. Hopefully this will work!

Right now, it's weighing in at 56g, without the elevons. Everything I've got piled on takes it to about 300g. This will probably go up again once I've added in some packing tape to firm things up! The main component I'm missing is really the ESC, hopefully it arrives this week!

Kfm4 Flying Wing Build Log 02

 I've got the main parts of the wing glued together with Gorilla Glue.

Next I have to shape the leading edge. The wing flexs quite strongly though, I'm hoping once I apply a layer of packing tape, it would help.

Kfm4 Flying Wing Build Log 01

Something that I'm working on, a blunt-nose flying wing that will utilize the Kfm4 airfoil. I originally got a rough idea from a flying wing that I know works - the Teksumo - then I plugged values into this Flying Wing CG Calculator to give it the width of a DTF board, lesser sweep, and a blunt nose.

After that, I brought the design into Houdini, and adjusted the rear end of the wing to have the motor fitted more forward into the wing in the hopes this will help balance the CG easier. Also, I widened the rear in order to accommodate up to 8 inch props.

PID Controller experiment

Something I've been very curious about, so decided to extend the pitch/roll estimation code I'd wrote to drive a stablized servo. Seems to work pretty alright. When I twist the platform rapidly, it does overshoot a little before it stabilizes, and I think, apart from the PID code itself, could also be something to do with the settings of the accelerometer/gyro.

Annular Wing Glider

Got a quick video of the annular wing in flight :) I've ordered some micro components in the hopes that I can make it fly :)

It flies!

Or rather, it glides! After observing that the wing would spin along its longer axis, I thought about putting in a "fuselage" up front to balance the upward moment.

Before I put the fuselage on though, I noticed the wing, depending on which side I threw it, would pitch upwards, while the other side would pitch downwards.

I thought that if the wing pitches up, the fuselage up front would serve to balance against this upward pitching.

And I was right! I taped a strip of foam board up front, and upon throwing the wing, it flew upwards, before falling on its butt. This meant* that the weight was too heavy behind, so I taped on a small piece of plywood to the bottom (see the two tiny pieces of tape sticking out from the fuselage).

After adjusting the plywood weight forward and back, I managed to get it so that it would fly straight before it lost lift and crashed! Wooo!

With this, I am very confident I will be able to get it flying with a motor. I'm probably going to make it a very simple airplane controlled only with a rudder and throttle.

Some notes:
- "Aspect ratio" of the wing before it is rolled up is 5.6; 50.8cm x 9cm.
- The center of gravity is roughly 10mm from the leading edge of the wing.

*this is based on what I've read about aeronautics online; do not take this for science or fact as I do not have proper training.

Annular wing

I read about annular wings today, and on a whim, decided to just make one from the leftover from from the previous build. Apart from plain old curiosity, I'm using this to test some 30 minute gorilla glue.

Interestingly, when I tossed this into the air, it goes forward for a few feet, before tumbling into a spin along its longer axis (wanted to make a circle, but didn't realize how much strength the packing tape would make the joint flat.).

I'll probably get around to building a rudder of sorts and a "fuselage" that leads the wing. See if I can make it glide. Should be fun :)

Nutball RET Build 05

Finally completed the Nutball build! I'm calling her Cat Scratch :)

Right now, she's balanced at maybe 26-28% behind the leading edge of the airfoil. Seems to be fine?

One of the things I decided about the build was to use only hot glue for all the parts. Hot glue unfortunately, appears to weigh a ton! While I estimated Cat Scratch to come in just below 200 grams, she now weights in at 217 grams!

Upcycled some plastic from a plastic box to make the control horns. They were rather flimsy, so I put in a short stick of basswood to accompany it.

She flew really well, and I hope to get a video tomorrow :)

Nutball RET Build 04

Got most of the build complete! What's left is the control rods for the elevator and rudder, which I hope to get tomorrow.

In the end, I decided to have a thin basswood spar along the entire length of the wing to take on the thrust generated. Apart from the motor, which is properly bolted down with loctite, the rest of the parts are held down by hot glue, tape or velcro.

Can't wait to maiden her tomorrow!

Nutball RET Build 03

Spent the evening just soldering all the connectors together. I've estimated weight of the nutball to be about 200g in total. Hopefully, that will be good enough for the thrust provided!

Nutball RET Build 02

Forming up the wing dihedrals and elevators this evening. A shallow cut and it some hot glue to fill in the gap. I'm quite surprised at how fast and strong hot glue is. I don't think I've had a glue gun before.

The elevator is also cut out, and shaped so that it will be able to rotate properly.

Will have to wait for the weekend to get the tiny things I don't want to fabricate or don't have, like control horns and piano wire.

Lemon RX finally arrived!

The Lemon RX finally arrived, it's almost 4 weeks! Very surprised at how lightweight is is though, with the satellite receiver it's only 9 grams!

It bound with my DX6 without any dramas, and works, but no way to tell if the range is as good as the spektrum original until I do a range check.

Nutball RET Build

I'm building a Nutball RET (Rudder, Elevator, Throttle) flyer, according to this page at rcgroups. I think most people use EPP foam, unfortunately that stuff is not easy to source in Canada. The main issue is shipping cost - the foam is very affordable, but to ship something that large, no matter how light, costs a fair bit!

Many have gone the route with the foam boards from Dollar Tree, aka DTF.

Each sheet is about 115g in weight, with both sides of the paper backing. I'm very much tempted to leave them on to support the very thin foam, but the paper is not actually glued to the foam, and pulls away easily with a fingernail.

I've quickly marked out the circle with my uber high tech marking tools, as well as the lines for the wing dihedral and elevator.

If this works well, I will want to convert it to elevons like my Teksumo, so I can practice with this and not the Tek, as the small park near my place is just too small for the Tek.

Teksumo Redeux II

I had a successful flight! I was thinking about it last night, then I realized, that I forgot to put any reflex into the elevons! At the same time, I swapped in the 7x5E for a 8x4E and the launch went as well as any other teksumo launch on youtube :)

I'm thinking that the 2812 1534Kv motor is very likely over propped with the 8x4E - it's suggested a 7x6 prop at max. So... probably have to see if I can be bothered to put the 1130Kv Sk3 motor in.. the one that I was fooling around with.  To err on the side of safety, I am more inclined to purchase a "fresh" motor.

Probably will have to do some calculations to see if I can get her to fly a slow-fly prop, that would require a really slow motor, not sure if there are any that can do the job with 3S.

I will shelf her for the time being, as I think I want to gain some proficiency with LOS flights at speed. With the Radian and Vapor, they are so easy to fly, as well as self leveling. The Tek flies at a whole another speed level, and the reaction time needed is magnitudes higher.

As such, I've decided to build a smaller aircraft, the Nutball :)

Teksumo Redeux

After some thinking, I'm probably going to rebuild the Tek as a lighter aircraft - the 606g weight is probably the reason why she needs to fly fast.  The batteries are the heaviest thing on the aircraft, taking up a 3rd of the weight. Servo wires and stuff also do not help, so if I make it into a pure LOS aircraft, I should be able to make it fly at a much slower clip. Here goes!

Teksumo Build Log 11

Completed the aircraft today! To keep the wiring neat, I've used my soldering iron to cut grooves in the wing, and stuffed the wires into them.

It only occurred to me after the fact, that I should have run the wiring _below_ the aircraft. Oh well... I'll keep that in mind next time.

And... here it is with the extra weights added to the right wing, and all the components taped down.

I went for a maiden flight this evening, and I think that... I shouldn't have gone for a heavy weight Teksumo for a start - at 606g flying weight, she flies, but only at a good fast clip. Attempting to fly at half throttle simply results in a nosedive into the ground >.>

One of these nosedives broke my motor mount. Graah. Shouldn't be too much trouble to fix. Still, I think I'm just going to fix this, and call it a day because the aircraft travels *really* fast, way faster than I can control.

I still want to fly FPV one day, but not a good idea to start with an aircraft that needs to travel so fast. As such, I'm calling it a day, and going to look into scratch building lower speed foamies, before I step up to the fast stuff :)

Teksumo Build Log 10

I finally decided to place the receiver on the very left side of the wing, however this requires the servos to run rather long wires across the wing, which probably add a fair bit of weight. On the flip side, the fpv transmitter can be put in the other wing, so they won't be too close together, and will balance each other out. First, I thought I'd just desolder the servo connections and extend the leads directly from the servo.

Unfortunately, it is nigh impossible to get the control board out to desolder :( So, the next better option is to just use extension leads.

I also took the opportunity to check out the gears on the front of the servo. Interestingly, for a servo marketed as a metal gear servo, there is a nylon gear in there. Let's see how it goes.

The extension leads I'm using are re-purposed cables used for connecting microcontrollers. The connectors do not fit properly into the receiver, and I had to sand down the plastic to fit. Otherwise, it works.

I've cut grooves to put the servo leads through.

And here's the Teksumo after much more additions. The winglets and motor mount have been glued on, and following an article from flitetest, applied Amazing Goop to the leading edge of the wing.

For the big wires from the speed controller, I've held them down using cable ties threaded between the wing. However, I cut small strips of plywood to strengthen the areas where the cable ties are, in the hope that the plywood will resist the cable ties from "biting" through the foam.

Right now, the Teksumo weights in at 528g, and I am still missing stuff like the velcro to hold the battery down, as well as some duct tape to cover parts up open areas like the receiver section on the left wing. I would think with the cameras on board, it will be close to 700g? Darn it.

Anyways, if all goes well, I hope to maiden this baby tomorrow!

Teksumo Build Log 09

I've been waiting for my receiver from Lemon RX for over 3 weeks now, and with the weather cooling down, I really want to get this completed and flying asap. I decided to just buy the Spektrum AR400 to save time. 4 channels, with diversity, and weighs in at 6 grams. With this, I started testing out the servos and motors, all of which went very well.

With the motor now definitely working, work could proceed to shorten the shaft of the motor. Wrapped the whole thing up with a used plastic bag, leaving only a hole for the shaft to poke through. Layers of duct tape were used to make sure no metal shavings would get stuck on the magnet whilst the shaft was being shortened. 

Things went well, and I also went to RP Electronics to pick up a set of M3 screws/nuts/washers to attach the motor's mount to the teksumo's motor mount.

Next up, now that I actually have the control in hand, was to see which props were usable.

Since I have a 2nd motor, I zip-tied the spare's motor mount to a piece of plywood, and duct-taped the thing down to my scales. Time to see if the watt mater owns its keep!

I only have 3 props that fit this prop adaptor, all from APC: 7x5E, 8x4E and 8x3.8SF.

The slow fly prop is not designed to spin that fast, so I did not dare take it up beyond a few amps of testing. The 8x4 prop appears to give slightly better thrust for the same amp draw, so I'm not sure which one to choose... .

On the motor's can, the recommended sizes are from 5 to 7 inch. I choose this motor because of this post from Crash Test Hobbies. Evidently, someone read the wrong prop pitch and got 7x5s instead of 7x6.

I'm only needing to connect the electronics, strap them down, attach the winglets and I'm ready to fly! I just keep waffling on where I should put the receiver etc. Her weight right now in the photo, is about 495g. Almost there! ARGH!