Open Rocket - Basic questions I can't find an answer for

I recently downloaded OR and have been playing with it for a few days now. I've created what appears to me to be a reasonable model of Estes' Eggscaliber, albeit with a standard nose cone (tangent ogive) rather than the egg carrying nose.

Question 1 - Stability
I have one on line source that states that the CG should be at least one half of the max body diameter forward of the CP. I have several successful simulated flights with a smaller stability factor. Is there a generally accepted rule of thumb for this?

Question 2 - Speed at recovery deployment
Does anyone know what the number is that OR uses to determine if it issues a warning? Again is there a generally accepted "do not exceed" speed?

Question 3 - Speed at landing
This is kind of an addition. Is there a general limit for landing speed?

Thanks for any help you can offer.

Diggr

#1 - I have no idea what your source is, but the accepted standard for stability is one full BT width forward.

I can't answer nos. 2 or 3, but for #3, you could experiment by gradually increasing your main chute size until you get no warning, and then see at what descent rate the warning goes away.

Thank you John! I've since managed to find a source that would suggest that the CG should be 1 to 1.5 BT dia. forward of the CP. Apparently it has to do with lack of stability early on and excessive weather cocking if too much above 1.5 caliber. I'm more than willing to accept those numbers as goals of design.

I'm still in an information gathering phase at this point in time. Part of that "gathering" is to try and get a feel for how OR evaluates a design. To paraphrase, if you will permit, how does Mister OR think?

Time for lunch!

Diggr

speed of deployment and speed of landing depend on many factors:

For Deployment
What materials? - cardboard, fiberglass, carbon fiber? I assume you have used cardboard.
How long and strong a shock cord? - longer will allow for a higher speed. The main concerns are getting a zipper (the shock cord tears through the body tube) and stripping the chute (tear the lines off). Have you done anything to reinforce the body tube edge (soak it with CA)?
What size chute (or are you using a streamer)? Standard Estes plastic or a nylon chute. The plastic chute will strip easier than a sewn nylon chute. And a bigger chute can create a larger shock when opening.

For landing
What are you landing on? Hard concrete or soft grass?
Again, what materials - balsa, bass wood, fiber glass?
And reinforcement? - paper the fins, soaked in CA? Are they TTW mounted?
Fin shape - will they hit the ground first or will the body tube? - Basically, what part of the rocket will hit first and take the beating?

For cardboard body/balsa fins I would try to get a landing speed less than 15fps. If actually carrying an egg you may want even lower....

There is a special rule for short fat rockets and stability, typically they will show stability margins of less than .5 yet are completely stable. A general rule of thumb for landing speed is 20fps adjusted for rocket construction and landing conditions. Drogues sized that give velocities over 50fps when the main opens causes a high deploymeny speed warning, or if the deployment is early or late if using motor eject.

Diggr said:

I have several successful simulated flights with a smaller stability factor.

Click to expand...

Set the wind speed higher and you will see the effects of stability margin more. You need very little margin for a simulation with low wind, gusts, no rod whip, misalignments, or other disturbances, but reality is not so perfect.

Thanks to all for the responses. They give me the information I was looking for. Additional reading has given me both additional information and pointed to sources for additional information. So I'm good for now, but I'll probably be back for additional pointers.

Ya'll take care.

Diggr