Some Glider Questions

[awseiger]

At the first MMMSC launch I attended, a few people had some rocket boosted gliders. I usually tend to go for rockets that go really fast and really high, but something about the idea of the main flight event being recovery instead of boost seemed fun.

As of now, I am planning a "delta" rocket using a BT-70 tube, and a MMT that rear-ejects and pops up little ailerons to make the rocket fly like a plane. Someday I want to add some RC to the general idea with an extra long-burn motor I can air-start (Apogee Medalist). But that's a little bit in the future.

Regardless, I still wonder... How exactly does one check the "rocket" stability of their glider? I can make a glider no problem, but I want to be sure that it also works as a rocket. I can't see how the cardboard cutout method (My usual CP "calc") would work for a glider that is not uniformly finned. My simulation software can't handle something like this, and swinging it around my head with a string attached to the CG always ends up acting like a rocket slingshot...

Thanks for the help!

[jadebox]

The cut-out method for estimating the Center of Pressure should work. Just make a silhouette from the front and another one from the side and ensure that the CG during boost is in front of the CP that you estimate each both views.

-- Roger

[kjohnson]

You may find that you need to extend the motor mount forward to the base of the nose cone and add some weight to the front of that tube. That way you get the noseweight you need for rocket boost, but it ejects with the motor pod so your glider is lighter.

What you are describing is very close to the old Estes Skydart model. Take a look at the instructions here to get an idea of what you need to do.
http://www.spacemodeling.org/JimZ/k-57.htm

kj

[awseiger]

Ahhhh that was the key I was looking for. Makes complete sense! I definitely wouldn't have done that if you hadn't said anything.

Just started building this today. The wing is cut and curing in its slightly up-bent position. I may start a build thread...

[Rocketbuilder]

Ahhhh that was the key I was looking for. Makes complete sense! I definitely wouldn't have done that if you hadn't said anything.

Just started building this today. The wing is cut and curing in its slightly up-bent position. I may start a build thread...

Please do. (With lots of pictures...)

[kjohnson]

Or a least some photos of the finished glider.

kj