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FT Delta twitchy and unstable - is that normal?

#1
Hey guys, since I destroyed my FT Flyer the other day I decided to bite the bullet and have another go with my Delta, and while I didn't think the conditions were too windy (15km/h gusting to 25, or 9-15mph) I found it quite difficult at times to keep a stable attitude during a turn and found myself suddenly inverted several times. The good news is I was able to recover most of the time, and the prop saver actually did it's job for a change.

I suppose my questions are, were the conditions to blame or is there something else going on that I should be investigating, and are there any modifications I can make to reduce the tendency to suddenly go inverted? The only mechanical concern I have is a bit of slop in the control rods which results in about 5mm of play at the trailing edge of the elevons, but I would have thought that if it was a problem it would be unstable all the time. (but I acknowledge that it isn't a good thing)

My control throws are less than recommended, I had low rate on and I have been tinkering with my Tx settings to further reduce the roll rate to make it more controllable. Most of the time it's actually quite docile even without expo since my cheap transmitter doesn't have it. As this is only my second plane and I've only been flying since last September, I don't necessarily know what "normal" behavior is for this style and size of plane.
 

Craftydan

Hostage Taker of Quads
Staff member
Moderator
Mentor
#2
From your symptoms (most of the time it's docile, but every once in a while it goes nuts . . . on a gusty day), I'd say it's the wind. In wind the delta is going to be bouncy . . . not becasue of your rates but becasue it's far too light to put up with that bully pushing it around (the wind, not you).

In these conditions a self stablizing airframe like the flyer will help, but the delta is a second-stage trainer -- it's designed without the roll stabilization in the dihedral to teach you to manually keep the wings level. Where the flyer will resist a brief gust and flatten back out when it's gone, the delta will flip and you've got to correct for it manually.

There are mods you can do . . . but they would defeat the purpose of the delta. You will need to learn to keep the wings level without help, especially in the wind. That skill is key to moving on to more complex models.
 

Ace2317

Senior Member
#3
I second Crafty Dan on this. It sounds like wind to me. I had a Delta (my first build) that I had the throws waaaaaaaaayyyyyyy too high for and it was difficult to control at best on a calm day so if it's usually stable, it's probably the wind.

It sounds blunt to say "you'll get used to it," but it's somewhat true. I've known some excellent pilots who are terrified to fly in a gentle breeze. It's better just to get used to how it flies in wind and be able to handle it. Otherwise, (especially if you live in a place like me) get a simulator because you'll be sitting inside about 300 days of the year waiting for that perfect day. Haha.

Another option is to look into something with gyros. My first bank and yank was a UMX Spitfire with AS3X and it made it much easier getting used to flying in wind.
 
#4
Thanks for the replies... I wasn't sure if it's normal for the delta to behave like that but I'm still learning a lot of things, including what to consider "too windy". I do have a bit of a reckless streak though :black_eyed:

It sounds blunt to say "you'll get used to it," but it's somewhat true.
I can see the truth in that.
 
#6
Thanks for the tip but I've already discovered that - I moved the CG about 1/2" forward from the plans and that solved my attempted maiden's pitch instability, but it seems a bit unstable in the roll axis.

If I get bored I might try adding some ballast to the wingtips to increase the moment of inertia a bit, but as I'm using slightly heavier Aussie foamboard (470g/m2 vs 300 for the dollar tree stuff) and a 48g motor, I'm probably already pushing the weight a bit. Might be an interesting experiment though. AUW is 390g.