Launching Trouble

[Stu]

For some strange reason I seem to have a major problem launching S8D models. So far I have built two models and they have both crashed on launch.

All the videos that I have seen on the internet show the models accelerate very quickly up the rails but mine, using competition D motors, just seem to stagger up the rails -fall backwards and crash.

The first model weighed 200gms and the second 220 gms.

Any help or advice anyone can offer would be greatly appreciated before I crash a third model.

Thank you in advance.

Stu

[slogfilet]

Which exact motor are you using? A "competition" motor may have very low average thrust, and might not be enough to get a nearly 8oz model up in the air.

I'm not familiar with an S8D (but be VERY careful searching them out in Google) so I could be off base.


EDIT: I realized this was posted in the Glider section after I responded... an area where I have no experience. Sorry bout that. Best of luck!

[Stu]

The motors are Quest and Delta D4 and 5

[plano-doug]

EDIT: I realized this was posted in the Glider section after I responded... an area where I have no experience. Sorry bout that. Best of luck!OK, now we're getting somewhere. I didn't catch it either, and " S8D" didn't strike any nerves.

But I know gliders are susceptible to binding on the rod. Any cross wind tends to torque the airframe such that the launch lug is forced askew of the launch rod. It takes much thrust to overcome the drag caused by this. So the complaint that the gliders "stagger up the rails" now makes sense.

In fact, most if not all the rocket motor's impulse can be spent climbing the rod such that little is left when it gets to the top.

There are several things one can do to handle this. First, wait for the winds to calm. Next, move the glider up the rod (rail) so that it has less distance to traverse before it clears. Try to position the pad and rail such that any crosswinds have minimal effect.

If you are launching with the rod angled, gravity can also case the lug to bind. Try to prop the glider in such as way as to counter the effect of gravity on its tail.

The ultimate launch guide for this may be the glider equivalent of the launch tower. I've seen cases where fliers placed several launch rods parallel with the glider wings and airframe centered in the cluster of rods. The simple way to do this is to stick the rods into the soil. The glider is placed between the rods and the launch lug is not used, so there is much less chance of binding.

HTH.

Doug

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