The main concern with the proposed design was potentially
yielding the rocket motor ring. To determine whether or not this
could occur during operation, an analysis was performed using
FEA calculations on Solidworks, as seen in Figure 7. With the
proposed solution, the design is expected to maintain a factor of
safety far greater than the desired 3.0 with respect to yielding the
motor ring. [2].
The team also needed to determine the torque necessary to apply
and test the adhesion of the standoffs using a power screw. From
equations (1) and (2), the torque to raise and lower was
approximated to be .313 and .176 lbf-ft respectively [3].
(1)
(2)
The entirety of the design displayed in Figure 8 was
manufactured in the 98C machine shop. The majority of the
device was created by the capstone team using the mills and
lathe machines available to students. Some parts that required
complex geometry, such as the motor clamp pieces, required the
machine shop managers to create using the CNC. The bulk of the
design was constructed of Aluminum 6061 with a stainless steel
lead screw, brass nut and aluminum screws/bolts.
Northrop Grumman Standoff Bonding Device
Department of Mechanical Engineering, Northern Arizona University, Flagstaff, AZ 86011
Brandon Bass, Tyler Hans, Sage Lawrence, Elaine Reyes, Dakota Saska
Rocket motor integration activities at Northrop
Grumman field sites bond standoffs (threaded
mounting devices that are used to mount avionic
electrical components) using long sure adhesives to
rocket motor domes of various geometry. The
standoffs are held by metal brackets, which are
taped to the motor dome for up to 72 hours to allow
for curing of the adhesive. This method is unreliable
and fails roughly 5 percent of the time resulting in
either the brackets slipping or falling off the motor
domes. An increase in man hours is incurred when
the taping method fails; this costs time and money
when installing these standoffs. For this reason,
Northrop Grumman’s Flight Systems Group has
requested for our team to design, analyze, and build
a prototype universal dome standoff bonding tool
that can be mounted to the attach rings of several
variations of rocket motors that will hold standoff
brackets in place while the adhesive cures.
Abstract Conclusion
The goal of the Northrop Grumman standoff project was to design, analyze,
and build a prototype articulating bonding tool. The team was able to
complete all these goals before spring break, although some improvements
to the design would have been made if more time was available. Due to the
limitations imparted by COVID-19, the team was unable to complete the
testing of the device to the desired standard. Based on initial testing before
spring break and analyses performed by the team through the school year,
the device is expected to perform all design activities with a minimum factor
of safety of 3.
References
[1] Propulsion Products Catalog, Northrop Grumman, Falls Church, VA,
June 2018
[2] “Aluminum Alloys - Mechanical Properties,” The Engineering Toolbox,
2008. [Online]. Available:
https://www.engineeringtoolbox.com/properties-aluminum-pipe-
d_1340.html. [Accessed: 18-Oct-2019]
[3] R. G. Budynas and J. K. Nisbett, Shigley's Mechanical Engineering
Design, New York: McGraw-Hill, 2011.
Acknowledgements
Dr. Sarah Oman, Daniel Johnson, 98C Machine Shop, Perry Woods, Tyler
Trebilcock and Derek, and Northrop Grumman
Design Requirements and
Approach
SubassembliesSub
Analysis and FabricationThe mounting arm is required to:
- Support brackets bonded 4-36 inches inboard
from the motor ring
- Have 6 degrees of freedom
- Be ESD (electrostatic discharge) compliant
- Perform a pull test of 50 lbs at 45 deg. of freedom
- Maximum deflection of .1” for rail design
- Be adaptable to several mounting bracket
templates
- Hold a bracket to up to 10 lbs
- Lock in place and apply a force of 20 lbs
- Have a Factor of Safety of 3.0 based on
maximum expected loads
- Be easily manipulated by hand
- Allow the use of multiple mounting arms at a time
- Be mountable to several rocket motors
Figure 1 displays one of the rockets that the
standoff bonding tool will be designed for.
Pictured left are four of the five
main subassemblies for the final
design. Clamp to Motor Ring
(Fig. 2), Angling Mechanism
(Fig. 3), Rail System (Fig. 4),
Rail Rart (Fig. 5). The final
subassembly which holds the
standoff templates directly was
not finished before the impact of
Covid-19 reached campus. This
final assembly can be seen in
the finalized CAD image in
Figure 6. This assembly would
be fully adjustable to adhere to
the many template dimensions.
It would have another angling
mechanism to match the face of
the motor dome as normal as
possible to ensure proper
adhesion of the standoffs.
Figure 2. Motor Ring Clamp Figure 3. Angling Mechanism
Figure 4. Rail System Figure 5. Rail Cart
Figure 8. Final Product
Figure 6 Final CAD Model
Figure 7. Ring Moment FEA
Figure 1. Castor 50XL [1]