Hi-Start launch problems with BoT and Discus 3-meter

[rogerflies]

Problem #1:
My friend was launching his Bird of Time yesterday on a hi-start. It went up straight for about 100 feet, then it turned hard to the right and started flying in a tight spiral until it hit the ground. He said he was unable to get it to come out of the spiral.

He's launched the plane many times with no problems, and it has been launched successfully with my winch, too. The radio was on and it was working before and after the crash.

Any idea what went wrong? I'm have almost no experience with hi-starts.

Problem #2:
Same friend has a Discus 3-meter scale ship. When launching with a hi-start, the nose pitches up violently just after the plane is released, then immediately noses over and starts a normal climb. Thankfully, it doesn't fall off to the side. We tried it once with the winch, and it did the same thing.

Once it's up, it flies a little fast, but otherwise it's fine. Weight (about 65 ounces) seems about right for the size.

Any idea what's going on? I have no experience with scale sailplanes or T-tails, and I've never seen this happen with any other planes.

Roger

[becsta]

For problem 1, two possibilities springs to mind:

a) Not enough tension on launch. Because there's no winch, with "infinite" energy available to the glider, you need to tension the histart until you can hardly hold it. The energy in the line will diminish with time until it's expended (usually when you ping off at the top), or the plane overflies the line. If she's still pointing skywards when the tension drops off, she's gonna stall.

When you launch the plane, do you just let it go, or do you throw it? You have to throw it to get it to fly before it leaves your hand - don't just let it go...

b) There was enough tension to start off with, she launched, but overrotates, stalls, drops a wing, and bye-bye plane. My F3J Icon will do this sometimes - she rotates to vertical pretty much straight away (this is on the winch), starts tracking skyward, but gets to a spot where she just won't climb higher, but gets twitchy. In this case, she's over-rotated, and I have to give a blip of down elevator to get her to continue the climb. Maybe this is what your friend experienced - the glider overrotated, and essentially stalled.

When a glider stalls, and it's still on the line, it's gonna get nasty...

Problem #2. Maybe the towhook is too far back?

[davidjensen]

You may need a little down elevator for the launch. The ship may be nose heavy and has some up elevator to componsate. When th ship is vertical on tow the CG is irrelevant and it only sees the up elevator.

[aeajr]

You describe a stall. Either the hi-start was not strong enough, the angle was too steep, the throw was not strong enough.

Is this the hi-start he normally uses? You said it went straght up for 100 feet then turned to the side. That's normally a stall.

Was there a breeze?

Does he pull up elevator on launch?

Were any changes made to the plane since the last flying session.

[Libelle201B]

Sure sounds like a stall to me, without enough tension on the histart. Is your histart rubber up to the task? It's better to have a strong histart in my opinion. Tow hook location is also very important. Never start with the tow hook at the cg or behind it. Be conservitive and start at 1/4" or more ahead of the cg until you know how the plane handles on the launch. If everything is ok, you can move the hook back in small increments to get a steeper climb. If you are flying scale type sailplanes, make sure the histart rubber is up to the task. :)

[kenb]

For the scale, that behavior is common as the tow hook on the bottom has more leverage than on a TD design, especially if you get in the air before "flight speed" is obtained. if you ROG its a bit better than a "soft" throw, a tow bridle and hooks under the wing really helps tame the launch.
Ken

[Guz]

Try looking at the tow hook. Not sure if it's adjustable on BoT, but if it is, it may have moved back to behind the CG.

[rogerflies]

Thanks for the inputs. I'll pass along the info.

Roger

[Robglover]

Check the wings for warps as well. You may want to add some wash out to the BOT.

[rogerflies]

I got an update from my friend.

The BoT misadventure has been traced to the Tx being set on the "other" plane. Oops.

We plan to try the scale glider next time with max tension on the hi-start or winch and a flat launch. Both my winch launch and his hi-start launch were upward. Now we know that's not the way to launch it.

Roger

[Captain Canardly]

Is there a chance you are on FM channel 44 with a channel 4 TV in the neighborhood?? that combo hates us!
Johnny