I have built my first HPR rocket. I haven't certified yet. I am going to try in April. I am most likely going to go with basic motor ejection. I do have a flight computer but I do not want to complicate things for my first flight.
My question is what options are there for parachute ejection... With a motor charge the blast direction is towards the nose cone, pushing out the piston or wadding, blowing the nose cone/payload off and the parachute. What if you put the charge in the bottom of the payload section pointing down into a "charge capture tube" (for lack of the right word). This would certainly blow the nose cone/payload section off the rocket but would the nose cone/payload pull the parachute out?
There are other combinations of this but I am curious if this method would even work.
I put the charge in the bottom of the payload facing up.
the payload section is a closed breach smooth bore cannon, made of kraft tubing. that makes it an antique cannon by AFT specs even.
the chute is covered totaly in a LOC Nomex Blank and is the cannon wading in fact. It is packed on top of the charge.
the shock cord is put on top of the nomex and the ccone then just fits on.
the chute cannon charge then pushes the nomex out the tube like the Black Powder Cannon it is.
I use PalmerCo chrages, and blow it out or blow it up ;-)
the charges are made of kraft paper with the Oxral match hot glued in the bottom. BP is added till the tube is almost full , then dog barf added to fill, masking tape for closure.
The reason the ejection charge in motors faces that direction is because that is the only reasonable direction for it to face. To manufacture a motor tube differently would add significant cost.
The direction of the ejection charge in motors does not cause deployment to occur. Deployment occurs because of a sudden increase in air pressure, which acts equally in all directions in the tube. The nose cone is not really popped off. The nose cone and rocket are pushed apart. Action-Reaction.
The direction of the charge is inconsequential for pressurizing the tube. When the pressure exceeds the retention force holding the nose cone and fuselage together, the cone and fuselage will part ways. When a piston or sabot is not used, you hope that the nose cone is moving away from the rest of the rocket with sufficient force to pull the parachute out. Rarely does the air pressure push the parachute out. Sometimes a parachute fits loosely enough that it will fall out of the tube.
When a piston or sabot is used the device shoves the parachute out. This is usually much better than hoping it gets pulled out by the nose cone. The piston/sabot also protects the parachute from the ejection charge. Nylon doesn't mix well with fire and heat.
All of the statements made above assume that the ejection charge is not a tightly directed charge. If you create a nicely directed charge, and if the charge is large enough, you have duplicated what happens in a gun, and it can blast a hole through the fuselage, parachute, etc. I've seen that happen a couple of times.
If you examine the C02 deployment devices you will find that the CO2 is not directed at the nose cone.
You really want the charge so that it blows EVERTHING out. Do not depend on the nose cone ejection pulling the rest of the recovery system from the tube.
Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!
It's hard to resist when you have a big mouth AHole like JI and his small band of followers.
DOT (to JI) - how many people does your company employ? JI - Less than two. rmr (to JI) - how many followers do you have? JI - Less that it used to be. rmr - how many is that? JI - Thousands used to attend my launches. rmr - That's nice. How many followers do you have? JI - fewer than the number of fingers that a weasel has. rmr - how many fingers does a weasel have? JI - it depends on weather you are referring to the South American weasel or the North American West Coast Weasel. rmr - THe North American West Coast Weasel. JI - The ones that attended my launches 20 years ago had thousands of fingers. Now, because TRA illegally decertified my backdated motors, they only have three. rmr - so you are saying that you have less that three followers? JI - No I never said that.
As a follow up... I have a PML Ariel. I am going to use the motor charge for ejection on its first few flights but it would be nice to use my computer to control the ejection charge. At some point I want to go dual deployment.
1) Putting the charge at the bottom of the booster is not going to work with the PML piston system (I have already been told to ditch it), but even without the piston system, if the computer is in the payload bay then I need long wires (longer than my tubular nylon strap) between the computer and the charge? Is that right? They show a picture of that in my Perfectflite manual.
2) Is it possible (or suggested) to use the current payload section of the Ariel to hold the electronics and main chute and charge in a dual deployment setup? From what I have seen it looks like dual deployment is done with a coupler section but then it looks like the charges are pointing in the "wrong" direction. That is you are relying on the force of the coupler separating from the booster to pull out the drogue.
Yea, the Coverdale launch crapped our today because of the weather. I had nothing better to do this afternoon, so I made a two grain 98 mm L and a three grain 98 mm M.
On the JI FAQ:
RMR - JI, what have you done for the hobby lately?? JI - Don't change the subject -- stay on topic..
I was thinking of coming down. When I woke up and saw the weather, I thought maybe next time. Still have that hand problem so, I don;t know when I'll fly again.
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