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denverdoc
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I'm trying to put together a proposal for a small amatuer rocket flight, and could use some assistance. This is not a terrorist strike aimed at your backyard, but flown under the auspices of the Triopli Rocket Association that provides safety guidelines and insurance to members in good standing.
See: http://www.tripoli.org/
My question has to do with the stresses between an external airframe and one or more enclosed motors that are attached to the skin of the airframe. Generally the configuration consists of an inner cylinder which is glovefit sized for the motor that is then glued into centering rings. In turn these annuli are glued to the inside of the airframe at varius stations.
This particular configuration is a bit different. But I believe the same principles apply.
The stresses would seem to vary. At full ignition, there would be a strong axial shear component equal to the thrust of the motor trying to tear loose and leave the airframe behind. Now my question is assuming that the airframe gets dragged along for the ride, is there any change in the net forces.
For one the drag of the vehicle is not felt by the motor(s) directly. This would then add to the shear forces exerted on the adhesive or mechanical attachments to the motor?
OTOH the airframe is developing velocity and so its inertia is helping to relieve the stress--I think but am not sure whether "jerk" is operative here--in other words--hit the motor with a sledge hammer, the shear forces are peak, but once it all starts to move, the same relative force is not as apt to tear things loose.
When the motor burns out, then another development: the drag forces become paramount on the af, while the inertia of the motor is unabated.
So another jerk?
Clearly my thinking on the subject is muddled, and any help is appreciated.
See: http://www.tripoli.org/
My question has to do with the stresses between an external airframe and one or more enclosed motors that are attached to the skin of the airframe. Generally the configuration consists of an inner cylinder which is glovefit sized for the motor that is then glued into centering rings. In turn these annuli are glued to the inside of the airframe at varius stations.
This particular configuration is a bit different. But I believe the same principles apply.
The stresses would seem to vary. At full ignition, there would be a strong axial shear component equal to the thrust of the motor trying to tear loose and leave the airframe behind. Now my question is assuming that the airframe gets dragged along for the ride, is there any change in the net forces.
For one the drag of the vehicle is not felt by the motor(s) directly. This would then add to the shear forces exerted on the adhesive or mechanical attachments to the motor?
OTOH the airframe is developing velocity and so its inertia is helping to relieve the stress--I think but am not sure whether "jerk" is operative here--in other words--hit the motor with a sledge hammer, the shear forces are peak, but once it all starts to move, the same relative force is not as apt to tear things loose.
When the motor burns out, then another development: the drag forces become paramount on the af, while the inertia of the motor is unabated.
So another jerk?
Clearly my thinking on the subject is muddled, and any help is appreciated.