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(vNARCON 2025) This project investigated parachute performance for precision duration models such as ARC (TARC) and S2/P. Significant findings included:
Reducing the shroud line length can increase the descent rate of a parachute. However, the change is gradual. A shroud line length reduction of 50% or greater may be needed to make a significant change in the descent rate.
If a parachute doesn't initially have a spill hole, cutting a spill hole, even as large as 15% (by area), is ineffective for increasing the descent rate.
If a parachute already has a spill hole, increasing the size of the spill hole will gradually increase the descent rate. However, this effect limited by how large the spill hole can be before it affects the opening reliability of the chute.
Parachutes with spill holes appear to have greater stability during descent. Flight tests and analysis suggests that increasing the spill hole size beyond ~10% (by area) doesn't provide much additional stability.
Model rocket motors can have thrust misalignment sufficient to produce off-vertical trajectories. The cause of thrust misalignment is not understood. Some potential workarounds are presented including making the models long (large pitch moment of inertia) with high static stability margin (2 calibers or greater).
(NARAM-63) This project investigated thrust misalignment (off-axis thrust) in model rocket motors. Significant findings included:
Photos and videos showed that some flights had misalignment between the vehicle centerline and the motor's exhaust vector. Misalignment was typically 1.5-2° but was occasionally larger, up to 3.5°.
At the 2022 TARC Finals, 30% of flights had pitch rotation greater than 5°, in a few cases exceeding 30°.
3-axis static testing showed that model rocket motors produce various levels of lateral thrust. For "C" through "E" motors, the lateral thrust was typically small (less than 1 N). Some "F" motors also had small lateral thrust. However, some "F" motors had larger lateral thrust, sometimes exceeding 4 N.
Data from many sources (TARC practice/qualification flights, TARC Finals, static test data, sport and contest flights) indicated that thrust misalignment did not appear to be attributed to specific motor types, thrust levels, propellant types, or motor manufacturers.
Model rocket motors can have thrust misalignment sufficient to produce off-vertical trajectories. The cause of thrust misalignment is not understood. Some potential workarounds are presented including making the models long (large pitch moment of inertia) with high static stability margin (2 calibers or greater).
(NARAM-62) Modern piston launchers using long (34" or greater) piston tubes can reach velocities of 15 20 meters/second (33 45 MPH). Large impact loads occur when the high velocity piston tube 1) hits the fixed stop in a fixed head piston launcher; or 2) picks up the floating head of a floating head piston launcher. This project investigated the structural dynamics of piston launchers. Analysis showed that large impact loads initially occur near the piston tube/support tube interface and then propagate through the structure as an impact wave.
Significant findings include:
A modern high velocity fixed head piston launcher has a high probability of structural failure using stock paper body tubes. Structural reinforcing options include thick wall tubes, double-wall tubes, tape covering, and other methods.
Loads in a floating head piston launcher are ~50% lower than a fixed head piston launcher but are still significant.
The piston head in a floating head piston launcher should be as light as possible. Avoid using heavy piston heads such as metal parts or empty motor casings.
The mass of the rocket has no significant effect on piston impact loads.
A new concept called a compound piston launcher was developed for FAI competition. A compound piston launcher uses an internal tube to replace the floating head and keep the moving piston tube attached to the launcher.
(NARAM-61) Rail launchers are often used for launching large model rockets. The mechanics of rail launchers are straightforward. However, the loads and dynamics of rail launchers are not well established. Issues of interest include optimum location of rail guides and the loads between the rocket and rail launcher during launch
(NARAM-60) The objective of this project was to identify or develop an igniter for reliable ignition of clusters of black powder motors (essentially, a replacement for the out-of-production Q2G2 igniter). A variety of commercially available igniters were initially considered, but none were ideal for cluster ignition. A series of custom igniters were built and tested. All used a nichrome bridge wire and a pyrogen. A variety of wire gages (diameters), coil design, and pyrogen dips were tried. Sixty-one (61) tests were performed including igniter-only tests, ground tests of clusters, and flight tests. The best igniter used 36 AWG nichrome bridgewire, pyrogen made from nitrocellulose and black powder, and 26 AWG “shooter wire” for long leads. Good power supply was achieved using a 3-cell LiPo battery with high burst discharge current capability.
(NARAM-59) The objectives of this project were to measure accelerations during piston phase of flight and to compare flight results to analysis predictions. The project successfully achieved both objectives. The project focused on the Estes A3T and A10T motors and 13 mm diameter pistons. An altimeter/accelerometer was used to measure axial accelerations during flight. Analysis results were calculated using an updated version of the Piston Launcher Performance Program (PLPP) originally developed by Geoff Landis.
(NARCON 2017) This project had two objectives: 1) measure accelerations during piston phase of flight; and 2) compare flight results to analysis predictions. The project successfully achieved both objectives.
The analysis results were very sensitive to the representation of the thrust-time curve during the piston phase of flight. Using high resolution data from new static testing, the analysis results for vehicle accelerations and velocities had very good agreement to flight data. This showed that the piston launcher theory was accurate for size of piston launcher, motor, and model examined in this project.
(NARAM-58) Flight and wind tunnel testing was performed to investigate streamer performance. The flight testing used a carrier rocket to loft streamers to apogee and then deploy the streamers. Some flights were made with a single streamer, while other flights were made with multiple streamers in the single flight. Each streamer was attached to an altimeter so that the sink rate could be directly measured during the entire descent.
The flight testing produced some interesting results. However, the results had significant scatter. Flight testing introduced uncontrolled environmental variables (such as wind and thermals) that made interpretation of results difficult.
To provide better control of the conditions for streamer testing, a wind tunnel was designed and constructed. The tunnel was oriented in the vertical direction in order to best simulate the descent of a streamer model. The tunnel was designed to investigate the velocity range of interest for competition streamer duration models (1-4 m/sec).
Initial qualitative testing was performed for four streamer configurations. Materials included Mylar, micafilm, and a party banner. Several folding techniques were examined including “Z” accordion folds, scorpion folds, and “heat sink” folds. Results indicated that, at very low speed (1.3 m/sec), a 1 mil Mylar streamer with scorpion folds was superior to Mylar and micafilm streamers with accordion folds.
(NARAM-57) Analysis was performed to predict the performance of helicopter duration models with different blade angles and airfoils. The analysis results indicated that performance may be improved using 1) two-segment blades with different angles for the inboard and outboard sections; and 2) thin cambered airfoils.
Flight test models were constructed to measure descent rates during flight. The models were an internal rotor design and were sized to be similar to “S9A” models flown in international competition. A new hub-and-arm design, manufactured using 3D printing, was used to precisely mount the blades.
Limited flight testing was performed to attempt to measure the steady state descent rates of helicopter duration models. The data is preliminary at this point. Additional flight testing would be useful.
(NARAM-56) This report describes the development of a computer program for developing optimum designs for SuperRoc altitude models. The program includes three features: 1) calculate SuperRoc failure velocity using FlexRoc method; 2) altitude trajectory simulation similar to Rocksim and OpenRocket; and 3) optimization using maximum gradient method. The program takes an initial starting design and adjusts the design variables (body tube length, wall thickness, fin span) to achieve the maximum SuperRoc score. Specific case studies were analyzed for D SuperRoc Altitude (an event flown at NARAM-56). Flight tests were performed to verify the analysis results.
(NARAM-55) This report describes the mechanics of flop wing deployment and how to achieve greater deployment moment for better reliability. Deployment moment is driven by the offset between the tension device (rubber bands, etc.) and the flop wing hinge axis. When using thin rubber bands, the initial moment to start the flop wing deployment is nearly zero, leading to deployment failure and unreliability. Methods to increase the initial deployment including using thicker elastic (bungee cord), lever arms, and a new "clip" concept. An alternate approach is to use rotary springs to guarantee that sufficient moment is available. Static testing of several flop wing deployment methods was performed to verify analysis results.
(NARAM-54) This report describes a method for simulating the performance of Helicopter Duration (HD) models. An Excel spreadsheet is used to perform a transient analysis to simulate the spin-up and steady state portions of HD descent. The spreadsheet has several assumptions and limitations, but results seem reasonable and have moderately good agreement to a sample model. The spreadsheet was used to perform sensitivity studies of blade angle (for a flat blade) and the optimum curvature for a curved blade.
(NARAM-53) This report describes a modal approach for calculating the divergence/failure velocity of a SuperRoc vehicle. The approach was applied to a variety of kits, plans, and competition models for SuperRoc models. In every case, the modal approach predicted the correct results. Models predicted to fail actually failed during flight, while models predicted to be stable had flown successfully.
(NARAM-52) Describes techniques to use NASTRAN to perform aeroelastic transient simulation of SuperRoc flights. Also discusses using Excel spreadsheet to perform static aeroelastic assessment.
(NARAM-50) Includes graphs for predicting flutter speeds of selected fin sizes. Also includes material testing and properties for 1/64, 1/32, and 1/16 plywood.
(NARAM-18) Investigated the effect of vibration, shock, and temperature cycling on the failure rate (cato's) of D12 engines. Showed that low level vibration (normal handling) and shock (dropping an engine) did not damage D12 engines. Showed that high temperature cycling (5 deg F to 175 deg F) caused nearly 100% cato's.
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