Minimum Diameter and Rear Motor Ejection

[Normzilla]

I'm picking up this little guy to eventually run 29mm H motors. https://www.madcowrocketry.com/mongoose-29/

Anyone have any experience with this kit? I am considering a rear motor ejection for it but I don't want to reinvent the wheel if others have already succeeded with this kit.

Thanks
Nathan

 

[blackjack2564]

Yeuuup....I built the first one and did instructional manual, back in 2009. Before MadCow.

There was no small Mongoose then, it was called a BlackHawk, as were all the versions smaller than 54mm. [24-29-38] They came with everything, special glue, shock cord, chutes & first kit with fin guides standard!

Wildman sold the small ones called BlackHawks and Curtiss sold the 54-75-98 called Mongoose.

Since then the original conical "molded" NC's have been replaced with spiral wound fiberglass Von Karmon's

Here is original build thread with ton's of building info along with link's in it to some of the coolest build threads ever posted on the Forum..

https://www.rocketryforum.com/showthread.php?2627-BlackHawk-Carbon-29mm-Min-Diam-build

Only real difference is the new nose cone with bulk plate, no need to glue shock cord into cone. several pages in...you'll find the coupler/shock-cord attachment. This was a major event build and everyone was chiming in with new methods and helpful hints, truly "epic"...LOL

There is no need for rear ejection other than being a "novelty". Close to a thousand of these things were sold and are still flying in normal deployment configuration. [many, many many of them lost, due to speeds and altitude achieved with just G motors]

Your nutz if you fly without a tracker on anything over a small F motor. Kiss it good bye!

Have fun building, its a fantastic little kit you will have a blast flying.

 

[Reinhard]

I've played with similar rear ejection ideas in the past, but haven't tried it yet.

One thing to consider, is the proper amount of BP. If the motor volume is bigger than the volume of the parachute compartment, interesting things can happen during ejection. If the BP charge doesn't generate enough gas to completely displace the volume occupied by the motor, the motor might get "sucked back in" before it completely clears the body tube. Inertia may overcome this and the quality of the seal will have an effect too. I'm aware of one non-nominal flight where this effect might explain what had happened. The problem can be counteracted by using more BP. More BP will result in higher peak pressures unless slower BP is used. The deployment can get rather energetic, not only because of the larger charge but also because of the longer "barrel". Mathematically speaking: W = F * s

In a nutshell: Carefully ground test it multiple times with the biggest motor casing you want to fly. Start with small charges. Don't forget to plug the motors ejection hole, if present.

Reinhard

 

[dhbarr]

One thing to note for minimum diameter in this size is that many CTI cases have a forward bulge where the casing was rolled. They also makes a tailcone closure, which you'll presumably want if you go that way.

If you don't want a tower or lugs, Mayhem flyaways via AMWPROX.

 

[Normzilla]

Very good to know. Thanks all for the replies.