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Z Bend vs. FT Linkage Stopper

jross

Active member
#21
The Mini Arrow is getting dual Z bends. Can't wait to crash that baby!
Success! I crashed the heck out of it. Didn't skewer the motor pod and on the last crash, it moved forward and the prop did some chopping. Flew way nicer once I remembered to add expo. Problem now is, I can't get enough up trim to get the reflex I need for level flight. Wants to nosedive with full radio trim when I go neutral on the stick. With a linkage stopper, I could fix that quickly. Thinking about a little kink in the control rods to bring the elevons up and get zero trim on the radio so I have some wiggle room. Will something like that work, @Headbang?

Not sure why I need so much more reflex than the plan calls for. These wings are tricky to set up, it seems.
 
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Headbang

Well-known member
#22
I would say you are running nose heavy. Or, if there is a big difference between full throttle and low throttle, then it could be the angle of the motor. Instead of adjusting linkages, try moving the battery back a little. Other option is to adjust sub trim. Not regular trim. Sub trim will be somewhere in servo setup on most radios. On spectrum it is under servo setup, then select over from travel to sub trim. Same place you do reversing. I've had a chance to fly a few ft designs that need reflex, they all only need 5mm. Bottom of control surface lines up with top of wing.
 

jross

Active member
#23
I would say you are running nose heavy. Or, if there is a big difference between full throttle and low throttle, then it could be the angle of the motor. Instead of adjusting linkages, try moving the battery back a little. Other option is to adjust sub trim. Not regular trim. Sub trim will be somewhere in servo setup on most radios. On spectrum it is under servo setup, then select over from travel to sub trim. Same place you do reversing. I've had a chance to fly a few ft designs that need reflex, they all only need 5mm. Bottom of control surface lines up with top of wing.
Which is weird. I'm already tail heavy according to the CG posted with the build video. But it's entirely possible. Gonna slide the battery back and give that a whirl. I use a Taranis so I'll need to figure out sub trim on OpenTX.
 

Headbang

Well-known member
#25
Brilliant. Learn something new every day. Pretty easy on a Taranis. My Z bends might survive!
Sub trim was the reason I suggested z bends. Back in the old days using my FM airtronics systems, we did not have any sort of anything! You had to adjust linkages, use mechanical mixing (christy mixer of you were rich). I think there was a dip switch for reversing. These days we have it so easy, might as well use what we have!

Glad I could help!
 

makattack

Winter is coming
Moderator
Mentor
#26
Success! I crashed the heck out of it. Didn't skewer the motor pod and on the last crash, it moved forward and the prop did some chopping. Flew way nicer once I remembered to add expo. Problem now is, I can't get enough up trim to get the reflex I need for level flight. Wants to nosedive with full radio trim when I go neutral on the stick. With a linkage stopper, I could fix that quickly. Thinking about a little kink in the control rods to bring the elevons up and get zero trim on the radio so I have some wiggle room. Will something like that work, @Headbang?

Not sure why I need so much more reflex than the plan calls for. These wings are tricky to set up, it seems.
When using z-bends, on both ends, yes, I always add a "V" bend (usually in an accessible place, which on the Arrow is pretty much anywhere) so that I can mechanically trim it out. Even when it's trimmed for the maiden, I find that with wear and tear / age, they need to be readjusted eventually.

Wings can be tricky to setup / fly simply because they are so pitch sensitive. That said, they are my favorite flying setup.
 

jross

Active member
#28
When using z-bends, on both ends, yes, I always add a "V" bend
Makes sense and really simple. I like simple. Are there issues with the V bend collapsing or extending? What's the biggest plane you've used it on? How tall do you make the V bend?
 

evranch

Active member
#29
I've never used the linkage stoppers, I personally prefer the metal clevis ended rods. No need to apply torque with a screwdriver to your servo arms, and they will never slip. I had to make do with dual Z-bends on my last build since I ran out of clevis rods. I also ran out of plastic control horns and had to make the plywood ones - on a cold day it was a good project for me and my daughter to cut out and build all the little bits for a plane from scratch.

I found with the plywood horns at least you can slit out the horn and slide it forward or back, then glue it back into place and fill the slot. Foam is super forgiving of this sort of stuff! I used the little marking flags for my control rods in this build, and they are too hard of steel to bend while installed without trashing everything.

Taranis subtrims are brilliant, fly the plane, trim for level flight and then select trim->subtrim on the outputs page... and done!
 

makattack

Winter is coming
Moderator
Mentor
#30
Makes sense and really simple. I like simple. Are there issues with the V bend collapsing or extending? What's the biggest plane you've used it on? How tall do you make the V bend?
Most of the planes I build are FT style or similar park flyer sized. The biggest one that uses this technique is probably a FT Blunt Nose Versa Wing. Using push rods that are typical of the FT builds, I've never had a problem with the V bends collapsing, but as with any material, things don't always stay static and require adjustments. It really works out because generally speaking, it's the foam that changes more than the pushrod shape, and when the foam changes (e.g. the control surfaces go up or down based on age/temps, etc) I can just bend in or out the V bend to adjust for that stuff.

I would say my V bends are between a half inch to almost one inch in size, mostly depending on how long the whole push rod is. The longer or thicker my push rod material is, the bigger my V and vice-versa.
 

jross

Active member
#31
I would say you are running nose heavy.
Bingo! Slid the 900 back a 3/16ths and it flew well. Might need to go back a shade more but not much. Really windy so impossible to trim it or relax but I did set up sub trims. These little wings are a gas. Rockets but able to surf the wind too. The Arrow got tossed around like a ping pong ball. Good practice.
 

Bricks

Well-known member
#32
Only bad thing with using sub-trim is your servos will not move equally in each direction from the transmitter stick. You will have more movement on the control surface versus the other. Ailerons one side will go up farther or down then the other. Always better to adjust mechanical to correct flight tendencies.
 

Headbang

Well-known member
#33
Only bad thing with using sub-trim is your servos will not move equally in each direction from the transmitter stick. You will have more movement on the control surface versus the other. Ailerons one side will go up farther or down then the other. Always better to adjust mechanical to correct flight tendencies.
I agree!
For the application we are using it for, it is just fine. On my larger 3D planes I use dog bones mainly with ball joints, easy to adjust! On my speed planes I use L bends with a nylon keeper on the servo, and ball joints or metal clevises on the surface horn, easy to adjust as well. On FT planes I just get it super close on the z bends, few clicks of subtrim does not mean much on these. Linkages get easier and more expensive as soon as you start using 2mm rods or larger.
 

mayan

Well-known member
#34
I also like linkage stoppers one the servo side and z bends on the control horn side. I haven't had a linkage stopper fail even when the bolt came off the stopper stayed in place. However agree with the rest that say that sometimes its just a pain in the rear to put them in the servo arm, and fasten them on the push rod. I will defaintly check out the square ones, didn't know they existed.

Another option that interests me is the V bends makattack mentioned here. Seems like this would be a great solution for me.
For that reason I tend to use z-bends, and I don't really worry about the accuracy of them because I make sure I have enough wire to put in one "V" bend along it for adjusting / fine-tuning / trimming the control surface.
@makattack do you maybe have a picture of this to share so I can see how you do them?
 

Bricks

Well-known member
#35
.

Another option that interests me is the V bends makattack mentioned here. Seems like this would be a great solution for me.

@makattack do you maybe have a picture of this to share so I can see how you do them?
Pretty simple looks like this --------V----- it is just your pushrod with a V or U shape in it so you can open or close the V to adjust your linkage put it in an accessible place.
 

sprzout

Knower of useless information
Mentor
#36
I have not gotten any for some time now, I usually get them from eBay.

For me a good stopper needs three things, a push on washer, a square body & an Allen wrench tightener. A Philipps head tightener is the worst.
Agreed on the Allen/hex head set screws. I bought a screwdriver style wrench to get in and tighten mine down (I've been able to get them tighter with that method because it NEVER seems to fail that the longer arm of the allen wrench hits the side of the plane, or the linkage, or it's uncomfortable for me to try to tighten it down in some way), and it's DONE, locked in.

I've never had a linkage stopper fail, like some have complained of, but I have had it be loose before I did my maiden preflight checks, which just means I didn't tighten it down properly from adjusting deflection or something. Not a biggie; that's where you want to find out before you put it u in the air, and a dab of low hold Loctite does WONDERS on keeping the set screw locked in.
 

makattack

Winter is coming
Moderator
Mentor
#37
Yep, pretty much as @Bricks drew it with ascii characters... I use a V shape because it's easier to bend with needle nose pliers vs making a smooth "U" shape. Here's my "terrible artist's rendition" :
zvbends.png
 

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makattack

Winter is coming
Moderator
Mentor
#39
The V shape can be anywhere so long as it accessable?
Yes. Although, with thicker push rods, you may find it harder to get the leverage to bend them near the ends if just using needle nose pliers. May need a vice or a beefier pair of pliers for thicker rods.
 

slipshift

Active member
#40
I've been using a small vice-grips, it holds well and won't pinch fingers if it slips. The vice-grips also work well for straightening music wire for linkages. Coiled wire is a WHOLE lot cheaper than straight wire.

Jim