Estes Sky Dart II Trimming for vertical flight

[DirkTheDaring]

Has anyone had any luck getting the Sky Dart II to fly more or less straight up? The glide is great, but I can't get the darn thing to go up, instead it flies off to one direction or another. Having thus crashed it any number of times, I have experimented with more weight, less weight, moving the weight around, different length body tubes (in front of the wings).

Looking at the videos, I think most of the time it heads, how to say this, to the direction opposite of the body tube, e.g. as if the elevator was in the up position. (I hope that makes sense.) I've tried to make the elevator as level as possible, but with the body tube in the way I can't really make the elevator go negative.

Any suggestions on how to adjust this? I'm not sure if these means more nose weight, less, or doing some modification to get the elevator to go negative, or what?

Video here: And this was one of it's better flights!

Thank you.

 

[caveduck]

Moving elevator boost gliders are always troublesome. There is nearly always going to be some pitch up moment even with the elevator incidence at zero; slight negative incidence for boost is usually needed. If you can’t move the elevator far enough, you can warp some negative incidence into the elevator and then compensate with additional positive movement for glide.

No realistic amount of nose weight will help that much.

Intentionally adding some roll (use rudder incidence to induce a barrel roll on boost) will also help a lot by averaging out the pitch error.

 

[DirkTheDaring]

Moving elevator boost gliders are always troublesome. There is nearly always going to be some pitch up moment even with the elevator incidence at zero; slight negative incidence for boost is usually needed. If you can’t move the elevator far enough, you can warp some negative incidence into the elevator and then compensate with additional positive movement for glide.

No realistic amount of nose weight will help that much.

Intentionally adding some roll (use rudder incidence to induce a barrel roll on boost) will also help a lot by averaging out the pitch error.

Thank you, that helps.

 

[tab28682]

One thing I tried on mine that worked was to add some small balsa trim tabs to the bottom of the elevons to overcome the slight nose up tendancy. This solves the issue of not having enough down trim due to the body tube being in the way. Mine only needed a tiny bit of down trim to boost straight.

East to correct the glide after adding the down trim tabs by cranking in a little more up elevator.

 

[DirkTheDaring]

Great idea, thank you!

 

[GlenP]

Hard to tell the wind conditions from the video, not sure if there was camera shake or wind shake even before lift off. This one will definitely weathervane to the extreme, wind seems to be likely as that turned abruptly right off the rod. Best for no-wind launch conditions, or rotate the wings 90-deg so they are more parallel to the wind direction. Then the rudder will start a barrel roll, but should at least start the climb a little better off the pad while accelerating.

 

[DirkTheDaring]

An awesome flight of the Sky Dart.



Finally got a great (and I mean great!) flight out of my dart. Modified it so that it gets down elevator on launch. Reduced internal weight. Rebuilt it many times from various crashes. And, importantly, launched it with a C6-0 booster engine. No delay means it switches into glide mode earlier, so it’s higher up and has more time to start the glide.

It still turned horizontal while under thrust. I don’t know why it does so.

Sorry about the poor video. It’s awfully hard to track and very hard to see on the screen.

Thanks for all your help!

 

[Gunstar]

I'm building one right now. My guess is that the off-center weight of the wings and tail fin are what make it flip over on accent.
I'm thinking of replacing the half-tube air intakes with full tubes to act as fin tubes. Does that sound like a good idea?

 

[GlenP]

I'm building one right now. My guess is that the off-center weight of the wings and tail fin are what make it flip over on accent.
I'm thinking of replacing the half-tube air intakes with full tubes to act as fin tubes. Does that sound like a good idea?

The kit comes with one single tube that is split into the two halves for those simulated air intakes. But, sure, you could cut the length of that tube in half instead and use them as tube fins. I would place them roughly in the middle of the original location to maintain c.g. of the stock kit. Those can be used for placing small amounts of clay to balance the glider. You can even chamfer cut the ends to give a similar intake appearance.

 

[Gunstar]

The kit comes with one single tube that is split into the two halves for those simulated air intakes. But, sure, you could cut the length of that tube in half instead and use them as tube fins. I would place them roughly in the middle of the original location to maintain c.g. of the stock kit. Those can be used for placing small amounts of clay to balance the glider. You can even chamfer cut the ends to give a similar intake appearance.

I was thinking more of keeping the tube the same length, just use the tube from the kit on one side and another tube same size and length on the other side. This is more about getting it to fly straight up under power than looks. If it doesn't help that I might as well build it stock.

 

[GlenP]

I was thinking more of keeping the tube the same length, just use the tube from the kit on one side and another tube same size and length on the other side. This is more about getting it to fly straight up under power than looks. If it doesn't help that I might as well build it stock.

Not sure if there is a general rule of thumb for the ratio of the length of a tube fin to the diameter. If you use a too long tube, then friction in the long tube will restrict airflow and it won’t be as effective of a fin. That full length tube might be okay as a tube fin, but just looks too long. You can breathe through a short snorkel, but probably not through a 100’ hose, for an extreme example. I am sure it would work as you intend and that is a good idea to increase the directional stability. The dia is plenty large enough.

 

[DirkTheDaring]

Fwiw I had my worst flight ever yesterday. Went horizontal, hit a tree, shredded a wing, and somehow the inner booster tube disappeared even though it couldn’t have gone far. You may be advised to ignore any advice I have ever given. While I will repair this, I’m gonna look for another kit to buy and do a clean build.