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FT Mini Arrow 05/12/2019

KJ4DCE

New member
#1
Test Flight #1: I add ¾ throttle and hand launch the Arrow. Right a way I hear the sound of the prop hitting something. I cut the throttle and it noses into the ground. Not much damage up front, but the back is chewed up a little bit. The engine mount had pushed forward causing the prop to come in contact with the back. I hadn’t put skewers through the engine mount because I thought the friction fit would be fine. I didn’t bring any skewers with me, so I found a stick on the ground, cut a point on it, passed it through the engine mount, and trimmed the extra off.

Test Flight #2: I add ¾ throttle and hand launch the Arrow. It pitched nose down very quickly, but was able to pull the nose up and start to climb. I had the CG right on the marks from the plans with just a touch nose heavy. But I used all my trim adjustment and the nose still wanted the drop. I had set the elevens according to the glide with the plans also.

But I was flying. I turned down wind and pulled the throttle back to 1/3. It was twitchy, but flying level.

I barely move the stick to make a right turn, not too bad, nice and smooth. Coming back into the wind, I add a little more throttle, everything is good.

Setup to make a left turn, not bad again.

I flew around getting more comfort and realizing that my time flying the FT Tiny Trainer was time well spent. I didn’t feel overwhelmed by the Arrow like I thought I would. But I certainly had to “fly” the Arrow much more than the Tiny Trainer.

Ok, let’s put the spurs to her. WOW…that little A Pack motor really screams. I pull back the throttle and turn into the wind. Full throttle, what wind. WOW, this is awesome.

Feeling brave, let’s go for a loop. Well that was easy.

Try a slow pass. That’s amazing.

Never done a barrel roll, let me get up some speed and altitude. That was easy too. WOW. This is fun. Couple more.

Hang on a minute….it’s flying different, very wobbly and not responding to inputs well. I cut the throttle and do my best to glide it down. After a long walk to get the Arrow, I find that the top part of the wing had separated from the fuselage. This was why it was wobbly.
Oh well, nothing a little hot glue can’t fix.

Questions:
  • What did I do wrong setup the CG?
  • Was me having the “fly” the Arrow more so than the mostly “hand off” way I flew the Tiny Trainer common?
  • Are there ways to strengthen the joint between the top part of the wing and the fuselage?
 
#2
1. You probably made a simple error at some point, I can't identify where, but I would try putting it on a piece of wood so you can accurately balance it about the points. Or the error was systematic and the holes were placed wrong, in which case you should check how far back from the front the CG should be.
2. 4 channel aircraft always need corrections. This is especially true for the arrow, as it is really light and gets pushed around by the wind a lot.
3. What I would recommend is to use fiber tape and wrap over the top of the plane with CA on it. You could also stick a small piece of birch or balsa through the center pod and glue it down. I made a thread a while ago called "modifications i have made to various FT designs" that should have more info on arrow reinforcements. Also, for the power pod you should put a glue ring around the holes so that the skewer doesn't dig into the foam. Hope this helps!
 

FoamyDM

Building Fool-Flying Noob
#3
The CG on the plans is good - my experience.
With the nose down issue - did you put enough reflex (a base elevator up deflection)? also do you have the thrust angle correct? these would create a small moment rotating the nose down.

The fiber tape on top and bottom are important to keeping the wings together.

Good Luck. The FT-arrow is one of my favorites to keep in the car for fun flying. sounds like you are on the road.
 

CarolineTyler

Well-known member
#4
Some pictures of my Mini-Arrow
The CofG I have marked with two spots of hot glue on the bottom, makes for easy checking...
IMG_20190513_181931298.jpg
The reflex I have for level flight...
IMG_20190513_182035462.jpg
And the tiny modification I made, two little strips of foam board to stop the wing collapsing next to the middle "fuselage"
IMG_20190513_182003044.jpg

Hope this helps!!
 

KJ4DCE

New member
#5
Thank you for the tips CarolineTyler. Definitely will try the strips and the glue on the CG points.

FoamyDM, the picture of the reflex CarolineTyler posted looks very much like the way mine are set. Does that look right?

How do I check the thrust angle?
 

FoamyDM

Building Fool-Flying Noob
#7
Yup. The reflex to be in-line with the bottom plate if not a *little* up.

It's built into this wing section used on the Prandlt-D (note the right-most upturn) MainWingSection.PNG

Thrust angle... t-square at the fire wall? (don't have a good method.)
 

CarolineTyler

Well-known member
#13
on the Arrow I use .8mm piano wire - If you use think wire like that then make sure you put in the wire guides made of a small cable tie Josh details in the build video - they work a treat.
 
#14
If it was coming unglued, you might have not gotten it together quickly enough while the glue was still hot. I started out with the cheapo $5 glue gun I had in my garage, and a lot of my earlier planes came apart on me like that. I didn't get the wings glued and pressed fast enough and half the glue wouldn't stick. It would make that sticky noise if you squeezed them. At some point I upgraded to an 80w Adtech glue gun and that fixed the problem. I eventually got the 200W version as a gift. That one even handled large builds like the Sea Duck with ease. I think the 80W one is ~$25, totally worth it.

If the foam was de-laminating, that is sort of inevitable. Every crash will work it apart a little bit more. Glue it back together and it will be even stronger.

Hah! Mine is starting to look a bit like that. The Arrow glides so nicely that it's irresistible to play catch with. Toss it, give it a little burst of power to turn around, glide, catch, repeat. After a hundred times the foam on the nose really turns to mush. Hah!
 

Keno

Active member
#15
Interesting what you can do with FT Arrow. We use them in combat so we beefed them up. Enlarged the fuselage to 2" X 1- 5/8" OD to accommodate FT Swappable Power Pod firewall. move the hatch to mount motor and/or change it. Rap the fuselage in fiber reinforce packing tape round its sides and firewall don't use anymore than necessary (weight). The larger size fuselage allows the use of a larger battery, ESC and receiver. We found wing breakage so we added packing tape across its span at the CG area and a small piece on the bottom of the motor area. Like speed, a 2206 2300KV will move it along. Just some ideas but I guess it could be considered as overkill by some, anyway it works for us.
 

jross

Active member
#18
My Arrow did the same the other day. Top of wing let loose on one side. Hot glued it and worked fine until a gust disoriented me and I slammed into the ground last night. Glue joint I repaired held. Fuselage bottom on one side broke loose. Wings were floppy. My solution in photos below. See how it goes. Feels nice and rigid. Like @FoamyDM, I keep meaning to rebuild but other things take priority. If I can patch it up for another day, all is good.

The Arrow is so fun to fly. My first wing. Finally feeling confident enough to put electronics in the Spear I built months back. At some point this summer, I'm hoping to put the Zephyr II on 6S I bought this winter into the air. Couldn't resist buying it complete for $200 even though I knew it would take me a bit to earn the chops to fly it.

10 inch tongue depressor on the bottom. Cut away tape and paper to get a good bond to foam. Tape over top.

20190514_121840.jpg

Barbecue skewer stuck though the fuselage flush with top of wing. Liberal amounts of glue and tape over top.

20190514_121832.jpg

Took 20 minutes instead of a total rebuild. The F Pack can easily handle the added weight. Batteries charging now. Hoping to pop a couple off on the road this afternoon.
 
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Keno

Active member
#19
[QUOTE="jross, post: 474855.[/QUOTE]

Jross, I had this problem also, good comments and ideas here. What I do to prevent this from happening is use White Gorilla glue on the edges of the spars when folding the wing over and the clamp the wing down. If you are using FT's WRFB you might think about scoring the areas that are to meet when gluing, Gorilla glue or Hot Glue. A lot of times I will actually remove the paper. On DTFB the paper can actually separate from its foam and failure. Oh well for what it worth, Happy flying
 

jross

Active member
#20
The CofG I have marked with two spots of hot glue on the bottom, makes for easy checking...
Stole that one today rebuilding my Arrow. I'd covered my old CG holes with a tongue depressor and had to do something. So easy and very tactile. Like a tiny Hershey's Kiss made out of hot glue. Tricky but doable.

I'd been wanting to use those sewing pins with the plastic ball on the head but can't seem to find any. Think maybe my Mom bought everything local and is hoarding. Quilters are like that.
 
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