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My KFM Wing Build

jross

Active member
#21
Took it out today. Realized after I'd duffed it a few times, I had forgotten to install winglets. May have been part of my problem. I launched the plane and it consistently went into a nose up attitude, rolled left and went in nose first. Same behavior with no reflex and 2 mm of reflex. Played with CG a bit but it didn't seem to make much difference. Throttle was about half on an F pack. I don't have any 1300 mah batteries with the right connectors so had to use a 900 and an extra 500 to balance things out.

I struggled with finding real estate to mount electronics, ESC and RX in particular. Had so much extra wire laying around, I wondered if that could have been part of the cause. Had trouble buttoning electronics up tight. I can see how building custom looms for wings could be helpful. No extra wire to deal with. So she's back on the bench tonight and I'm wondering what I did wrong. Wondering about thrust angle and whether I messed that up or perhaps the firewall is pointing slightly to one side.
 

Paracodespoder

Well-known member
#22
Oh No! I maidened my KF wing today as well! Built it last night, put the electronics in today, and maidened it. Mine has a 20 inch wingspan and runs off of an extra 1106 I had laying around, maiden was line of sight, and second flight was fpv, this little kf wing has no issues with wind and flies great 👍! KF wings are super easy to build and fly great.
 

jross

Active member
#23
... maiden was line of sight, and second flight was fpv, this little kf wing has no issues with wind and flies great 👍! KF wings are super easy to build and fly great.
Uggghhh! Now I feel like a moron. My wing jinx continues. At least this one didn't break in half after 10 crashes.

What did you glue up your wing with?
 

Paracodespoder

Well-known member
#24
Just hot glue (y), I removed the paper between the two layers and used a couple beads of hot glue, I used a strip of duct tape on the leading edge, I advise you do the same. I crashed into a tree and all the damage done was a twig stuck in the leading edge, no damage done. hoping to fly again tomorrow, probably won't get to due to winter storms :(, oh well.
 

jross

Active member
#25
Think I'll rebuild with hot glue. The warp on this wing from using white glue means if it does fly, it won't be easy to trim out. At times it's been symmetrical but it isn't now. Round two.
 

Hai-Lee

Old and Bold RC PILOT
Mentor
#26
Think I'll rebuild with hot glue. The warp on this wing from using white glue means if it does fly, it won't be easy to trim out. At times it's been symmetrical but it isn't now. Round two.
I have used a wide variety of glues over the years and all work quite well!
The best results from the polyester glues, (gorilla) and the PVA glue if you allow it to properly dry under the weights holding it flat in the press.

If the hot glue works for you by all means use it but the polyester glue has always given the best results for first attempt and the PVA has always given the most economic results, (least cost), even though the time to dry can be painful even with the ambient temps here!

Do not give up as the reward is MORE than worth it!

Have fun!
 

jross

Active member
#27
Do not give up as the reward is MORE than worth it!
Giving up isn't in my nature but definitely feeling like a moron. Beautiful sunny day today. Taking the TT and Explorer out to enjoy it. New KFM is on the table tonight. Decided it's not getting any prettying up until it flies. No need to doll it up if it doesn't fly. Give her a good blast of Scotch Guard, (waterproofing) some tape on the leading edge and bottom and up she goes.
 

jross

Active member
#28
Total rebuild went well. Used hot glue for foam and epoxy for firewall. Foam isn't nearly as well bonded together but still firmly glued. Decided if I was going to spend the time to build, may as well throw some tape on everything. Wing came out nice and true this time. Remembered the winglets. So much for not dolling it up.

20190113_125255[1].jpg

This thing definitely takes a beating. Probably duffed it 40 times at least. Many cartwheels. Hit a tree. Twice. Many snow darts. Got more exercise walking to pick up the plane than I did cross country skiing today. But persistence paid off. My wing jinx is broken! Flew four 900 mah batteries and didn't kill the plane! Amazing. It was a messy affair but I did it. My shoulders were in knots after I was done.

Plane wanted to climb hard under throttle and in general. Set my reflex at 2.5 mm and guessing I could dial that down a bit but not sure. CG was bang on and very slightly nose heavy. Went with about 20 cms of throw in either direction and 35% expo, which I'd never used before. That was an education in itself getting used to the soft stick in the center. The plane was pretty squirrely. No way I could do a fast pass on this plane right now. Not sure how low I'll have to set dual rates for that but I need to get it flying straight and level first. There was a fair bit of wind which made it all but impossible for a newbie like me to trim it at all. Couldn't take my finger off the stick to hit the trim switch if I'd tried. Intentional landings went well. I dead sticked them all and was able to flare for nice landings. It glided better than I expected and didn't fall from the sky like a rock when power was cut.

I flew a frickin' wing! Need some dialing in but the jinx is off. When I said I'd broken every wing I'd ever flown, I wasn't kidding. No other wing I've flown took this kind of beating and still flew. Not even close.

Thanks for your encouragement, @Hai-Lee, and everyone else who provided advice or answered questions.

Bungee launcher is definitely next.
 

Hai-Lee

Old and Bold RC PILOT
Mentor
#29
Total rebuild went well. Used hot glue for foam and epoxy for firewall. Foam isn't nearly as well bonded together but still firmly glued. Decided if I was going to spend the time to build, may as well throw some tape on everything. Wing came out nice and true this time. Remembered the winglets. So much for not dolling it up.

View attachment 121983

This thing definitely takes a beating. Probably duffed it 40 times at least. Many cartwheels. Hit a tree. Twice. Many snow darts. Got more exercise walking to pick up the plane than I did cross country skiing today. But persistence paid off. My wing jinx is broken! Flew four 900 mah batteries and didn't kill the plane! Amazing. It was a messy affair but I did it. My shoulders were in knots after I was done.

Plane wanted to climb hard under throttle and in general. Set my reflex at 2.5 mm and guessing I could dial that down a bit but not sure. CG was bang on and very slightly nose heavy. Went with about 20 cms of throw in either direction and 35% expo, which I'd never used before. That was an education in itself getting used to the soft stick in the center. The plane was pretty squirrely. No way I could do a fast pass on this plane right now. Not sure how low I'll have to set dual rates for that but I need to get it flying straight and level first. There was a fair bit of wind which made it all but impossible for a newbie like me to trim it at all. Couldn't take my finger off the stick to hit the trim switch if I'd tried. Intentional landings went well. I dead sticked them all and was able to flare for nice landings. It glided better than I expected and didn't fall from the sky like a rock when power was cut.

I flew a frickin' wing! Need some dialing in but the jinx is off. When I said I'd broken every wing I'd ever flown, I wasn't kidding. No other wing I've flown took this kind of beating and still flew. Not even close.

Thanks for your encouragement, @Hai-Lee, and everyone else who provided advice or answered questions.

Bungee launcher is definitely next.
Congratulations! You will be moving up to the Arrow or spear in no time now!

As for the setting of the CG and the reflex the CG is judged by gliding with full up elevator. (Do it at height!). If the wing slows down and staggers from side to side and then drops a wing the CG is too far aft! If whilst gliding with full up elevator it slows and then bounces the nose up and down repeatedly it is too nose heavy. Ideally at full up elevator in a glide it should just remain level and sink to the ground in a steep but controlled glide!

After the CG is set you set the reflex for level flight at about half throttle. If the wing still noses up or down when throttle is opened up then add a shim or two to the motor to adjust the thrust angle a little BUT do this after everything else is set because once setup properly the motor thrust angle is not as sensitive!

Believe it or not I am in the middle of building another 4 to order! (One to be a more visible best for a person who easily loses orientation at distance, (a false fuselage and maybe a centreline fin are in order!

Well done and welcome to the wing flying fraternity!

Have fun!
 

jross

Active member
#30
Thanks! I have a spear built but did a really nice job and don't want to destroy it quite yet. Planning on flying this KFM wing until I become more proficient. Will play with reflex and CG when I get some calm flying in. From what you've said above, looks like I need to set my CG forward. It would climb, stall and then drop a wing. Got so excited I bought two Zephyr IIs from a buddy who was more or less giving them away fully equipped including FPV gear on both ships. I can see how buying gently used gear from keeners who lost interest is not a bad way to go.

With the bungee launcher, how do you set tension? Do you weigh the plane and then use the equivalent of a fish scale on the end of the bungee to match the weight of the plane? That part has me confused. I'm sure once dialed in, hand launching this plane will be easier but my launches were very inconsistent.
 
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Hai-Lee

Old and Bold RC PILOT
Mentor
#31
With the bungee launcher, how do you set tension? Do you weigh the plane and then use the equivalent of a fish scale on the end of the bungee to match the weight of the plane? That part has me confused. I'm sure once dialed in, hand launching this plane will be easier but my launches were very inconsistent.
I spent ages looking for a fishing scale and just gave up! I normally tension it by walking away from the release with the end of the cord in my hand until I think it has enough pull for what I want. I do tend to have more tension than required but then the planes are quite light and so even if the pull is 10 times the weight it does not really matter.

Just make sure that the hook on the plane is 40% of the way from the CG point to the nose of the plane and on the underside. It will launch very well and with a little height even without applying any elevator. DO NOT apply throttle until the bungee has completely detached from the plane and is clear of the propeller. So normally launch a little fast a little glide and then give it hell!

If launching an EDF you can apply full throttle immediately after the bungee is released.

You do not need a ramp though a ramp does give a neater launch and no dirt of grass stains until landing!

If your launches are barely getting the plane flying add more tension and for bigger and heavier planes a longer bungee with an increase in tension give s great results, (weights around 5 - 10 KG).

Have fun!
 

Hai-Lee

Old and Bold RC PILOT
Mentor
#33
Fishing store. Checked the other day. Had 4 types. Analogue or digital. Cheap or expensive.
If you wish to quantify the force then cheap is good enough. As for me a guesstimate is more than adequate! Besides I like watching the bird head skywards at a higher speed than its VNE:whistle:. It is your choice but you should make the decision for a scale after the bungee is built and even perhaps after the first couple of launches, (especially since the KFM wing can take a licking and keep on kicking).

Have fun!
 

jross

Active member
#34
After shot of said beaten bird. Only thing I lost was one of the nickels I was using to adjust CG. Nose was slightly rounded. This thing hit hard several times. Hit the butt of a tree almost two feet around. Was upset with the tree so I hit it again. Still amazed this not only survived, but looks none the worse for wear. Light enough and strong enough it just bounces off things. And out of 40 crashes, no busted props. When I first flew the Tiny Trainer, I busted at least one prop every time out although I'm getting better at managing the throttle when when impact is imminent. Cut the power. We're goin' down.

Once I master this plane, I'll move to an FT wing. The twin FT sea builds appeal to me too with differential thrust and all. At this point I have one motor appropriate for this plane and one 12 amp ESC I share with my Tiny Trainer. ESC in my A pack failed. Money doesn't grow on trees. The airframes are cheap. It's all the other bits that add up.

Two more questions, @Hai-Lee. I set the CG at 16 cms back from the nose as suggested. What's the range you've seen on that measurement? Do I move the CG forward a cm or 5 mm? I know it's something I'll need to play with but I'm greener than green. The FT builds are pretty specific about CG and control surface deflection. Hasn't failed me yet. This plane is somewhat new to me in that respect. I'm learning a lot because of that.

Second question. Hope I'm not wearing you out! If I can balance this with a 2200 3S, will it fly? Hurtin' for batteries in the middle of what I have. I have 900s or 2200s. I have 92% less wing than your build plans to fit a 30 inch piece of foam board so there's that too.

20190113_161843[1].jpg
 

Hai-Lee

Old and Bold RC PILOT
Mentor
#35
After shot of said beaten bird. Only thing I lost was one of the nickels I was using to adjust CG. Nose was slightly rounded. This thing hit hard several times. Hit the butt of a tree almost two feet around. Was upset with the tree so I hit it again. Still amazed this not only survived, but looks none the worse for wear. Light enough and strong enough it just bounces off things. And out of 40 crashes, no busted props. When I first flew the Tiny Trainer, I busted at least one prop every time out although I'm getting better at managing the throttle when when impact is imminent. Cut the power. We're goin' down.

Once I master this plane, I'll move to an FT wing. The twin FT sea builds appeal to me too with differential thrust and all. At this point I have one motor appropriate for this plane and one 12 amp ESC I share with my Tiny Trainer. ESC in my A pack failed. Money doesn't grow on trees. The airframes are cheap. It's all the other bits that add up.

Two more questions, @Hai-Lee. I set the CG at 16 cms back from the nose as suggested. What's the range you've seen on that measurement? Do I move the CG forward a cm or 5 mm? I know it's something I'll need to play with but I'm greener than green. The FT builds are pretty specific about CG and control surface deflection. Hasn't failed me yet. This plane is somewhat new to me in that respect. I'm learning a lot because of that.

Second question. Hope I'm not wearing you out! If I can balance this with a 2200 3S, will it fly? Hurtin' for batteries in the middle of what I have. I have 900s or 2200s. I have 92% less wing than your build plans to fit a 30 inch piece of foam board so there's that too.

View attachment 121996
The cg on the plans is almost exactly correct! some minor build variations can occur, ( a minor curl or the like as well as some drag differences due to the open nature of the equipment mounting), so do the full up elevator glide test and it will tell you exactly where the cg works best on your version. Normally exact cg within 1 or 2 mm of plan point. On the full size version the CG point is 160mm from the point of the nose. As yours is scaled down I would also scale the CG point down to 147.2mm unless you only reduced the wingspan and kept the wing length as standard.

As for battery some here are flown using 2200 3s and one using an 1800 4S. The general battery recommendation is for a 1300 3S.

Am currently working on a further strengthening to improve crash resistance further after one was flown at high speed into a barbed wire fence and it was ripped apart along the centre line, the prop and motor mount also hit the wire as the wing broke and the motor mount area was ripped off and danced the prop along one of the wings before the motor disconnected itself.

Have done the basic work on 4 new strengthened models and the fitout starts today.

Sorry for my lack of earlier response but the internet connection has been down for the last day and a half!

Have fun!
 

jross

Active member
#36
As yours is scaled down I would also scale the CG point down to 147.2mm unless you only reduced the wingspan and kept the wing length as standard.
Dooohhh! Can't believe I missed that. Bet it flies way better with the CG moved forward over a cm. I made a parallel adapter so I can run 900 and 500 mah batteries together. That also made it much easier to balance the plane. Looking forward to the next flight. It should be much improved, I hope. Thanks for reminding me I'd scaled down the plane! Newbie mistake.
 

Hai-Lee

Old and Bold RC PILOT
Mentor
#37
Dooohhh! Can't believe I missed that. Bet it flies way better with the CG moved forward over a cm. I made a parallel adapter so I can run 900 and 500 mah batteries together. That also made it much easier to balance the plane. Looking forward to the next flight. It should be much improved, I hope. Thanks for reminding me I'd scaled down the plane! Newbie mistake.
You should be able to fly it on just the 900 with perhaps a little added nose weight if you cannot get the battery forward enough.

I normally mount the battery sideways across the nose and it doesn't' seem to effect the aerodynamics at all!

It should fly a lot better with less weight and the balance set properly! (Shows how it can even fly even if very tail or nose heavy, with a bit of effort of course). You'll be a wing ace in no time!

Have fun!
 

jross

Active member
#38
You should be able to fly it on just the 900 with perhaps a little added nose weight if you cannot get the battery forward enough.
I added weight with only the 900 at the very front mounted sideways and it took so much I figured why not add some weight that does something, like a 500 mah battery. Balance worked out perfect with some room to move forward or aft if necessary. Trying to figure out how to weasel out of work for a couple hours tomorrow...
 

jross

Active member
#39
Finally got it out again today. Changed the CG. I had issues getting it more than 5 feet off the ground. Think I need to increase my throws beyond 20 mm as it wouldn't climb with full up elevons. I tried for a half hour and switched to the Explorer which flew better than ever before. Nice not to get completely shut down. Getting dark just as I started having fun. Time for some lights me thinks.
 

Hai-Lee

Old and Bold RC PILOT
Mentor
#40
Take the CG back towards the original position that you were using and do the balance test as set out above in post #29. I do the balance test with EVERY wing I build and fly. Nothing better than getting it properly balanced and setup!

After doing the balance then do the reflex and it should all be well!

Have fun!