Date: 10-14-2023
Time: 1 pm - 3:45 pm
Aerodynamics
Questions:
- On slide 4, are the numbers profile drag?
- What is the assumed angle of attack for the fin drag?
- Is the 5 degree angle of attack used for flutter calculations as well?
- Why do the trailing edges have phenolic?
- Would carbon fiber not be ok in these temperature ranges?
- How do we plan to model the erosion of the leading edges vs time? How will that affect the flight?
- Where does the temperature on the trailing edge come from?
- What epoxy are we using?
- Is vacuum bagging still going to be a thing?
- How are we heating the fin can?
- Has the camera housing been modeled with the vehicle sims?
- Nose cone design????????????
- When in flight are those fin lift & drag loads from a couple slides ago from? Confusing sentence but did you assume 5/15/whatever degree angle of attack at Max-Q or something
- Have calculations on the profile drag been done to ensure the drag separation?
-Are the 5 plies just to make the fin continous with the phenolic?
-What will the upward facing aeroshells look like?
-For simulations, are mach numbers calculated basedon decreasing air pressure or sea level?
-What finish was used in the sims?
-Do simulations take into account grain geometry?
Comments:
- One piece of advice is idk which method you used in rasaero. There is the barrowman and the rogers modified barrowman method. This second one gives the best results so you can knock your safety factor down for temperature if u need.
- Can sanding carbon fiber edges to get a point instead of using phenolic (esp for trailing edges)
- G410? or something for epoxy
- Make sure the weaving of the carbon fiber alternates between 0 and 45 degrees to maximize tensile strength
- RAS Aero has a protuberance feature, but he doesn't know if it works
Avionics
Questions:
- Raven and DENNIS aren't technically redundant because they are on the same power system?
- Do we plan to duplex (send and get data at the same time) using bluetooth?
- What boards duplex?
- How are we solving the GPS at altitude problem?
- Are we using tilt lockout?
- Are there plans to do thermal management on the pad if we have to leave it htere fore a long time?
- Is there any reason to not run the Raven on it's own power system? If we lose the power board we only have one board for recovery?
- Are there any secondary retention mechanisms for power connections?
- What is the data transmission rate? [kb/s]
- What testing is being done for pyro boards specifically?
- How are you going to confirm that the parachutes will light if they are being fired by DENNIS? (she doesn't trust)
- Which flight computers are actually flying in command on each stage?
- Does DENNIS have a mach lockout? Has it been tested at high machs?
- Any use of a Kalman filter with IMU, GPS, etc to gather accurate performance data?
Comments:
- make avionics system fully redundant. have raven on a completely separate board
Solid Propulsion
Questions:
- If the motor burns for 9 seconds but we reach 150k ft is that a failure? Recommend more quantifiable requirements that define failure (not "ish")
- What is the strength of 6061-T6 at temperature? Was it taken into account here? Do the margins get bad at worst case tolerances? (apparently at temp the yield stress is 35k psi)
- is there going to be FEA for the cases? Are strength margins all based on hand calcs?
- have the calculations on stress been done for the forward closure lip/FRR lip?
- Is the case going to fly at 1200 psi and proofed at 1800 psi? It sounds like we are double counting FoS for parts (ie the calcs are at 1800 and then we add another FoS on top of that)
- Are the o rings 200 or 300 series? The larger the o rings, the more tolerance we can handle
- Are we calculating the throat based on 1200 psi or lower?
- Is the booster nozzle optimized for sea level or some other altitude?
- Interested in learning more about nozzle geometry design (is ok with calcs + openMotor)
- Is the liner a single piece?
- How reproducible is the propellant? Does it pour correctly? Are you getting good density?
- What is the rationale for mixing three different grains?
- How produce the mandrels?
- What was with the taper between the forward closure and the FRR?
- Why is there the lip for the fiberglass?
- If the liner/casing tolerances stack up is worse case, how to we plan to address this? If there is interference between the two or having a gap between the two? Do we have a lathe large enough to turn down the id/od to get them to fit properly?
- Asked about why were mentioning both 1800 psi and 1200 psi for the booster? Confused if the 1800 was just for the margin of safety
- Does the 20,000 ft altitude come from sims?
- Have we done worst case scenario calculations with the tolerances for hoops stress?
- any reason for UNC threads vs UNF?
- What is the grain geometry for the HEI?
- Why is there the o ring groove between the bolts?
- How are we going to manufacture the dowel holes? (SHOULD NOT MATCH DRILL BECUASE THE TOLERANCES NEED TO BE REALLY GOOD, OTHERWISE ROLL COUPLED INSTABILITY)
Comments:
- faster burn at higher pressure happens with all propellants. Second comment on selecting for quantitative data
- Use A basis material properties, not the first thing that comes up when you google it. There will be different specs and drawn lengths which will affect the strength
- Have a dedicated slide to summarize margins for each part that shows they are positive
- concern about how thicc the o rings look compared to the grooves
- good job :)
- Concern about designing nozzle for sea level
- Worried about 1200 psi for the max pressure. Says that he and andrew generally aim for 700 - 800 psi
- worried about our characterization of Blue Voltage
- likes the thrust curve :)
- wants a top level interface slide
- increase the amount of phenolic, worried about sharp edges in the nozzle
- blue voltage has lower c* than angry goat, thinks that the propellant characteristics page isn't telling us much directly useful information
- confused about why using two different propellants
- "CMS stuff is going to cost like 3 million dollars"
- has something to turn down ODs
- doesn't like the order of CDR, thinks that we should have started with AeroD/an overview of the rocket so that there was the systems engineering. Didn't like any justification that was "that's what other spaceshot teams have done" thinks exec should have presented stuff about the mission first
- In general the booster looks good. Do the edits that Sam suggested with putting o rings between the grains if they are uninhibited
- You can get generally better preload for a given torque value when using UNF. Using ox compatible lubricant (tribolube) will prevent seizing, therefore lowering the number of bolts needed (and therefore mass)
- Include bolt calcs for every bolted joint along with the margin calcs. Include preload, separation margin and (if applicable) strength margin
- The nozzle geometry does not look like 15 degree half angle
- make sure preload is taken into account with bolt strength especially with flange joints
- Thinks 200 psi seems really low
- If you dislike the chamber pressure just decrease the throat area
- Parametric studies over a design space would be helpful
- why not 3" diameter but longer??
- like the dowel idea for staging but those holes will potentially create gaps in the heat sink aluminum nozzle possibly causing a burn through. Also, I am still very skeptical of y’all using angry goat still. That propellant was made very hastily in a short amount of time with the minimum amount of data needed to characterize, and predictions will be u reliable at higher pressures. I suggest you either try to use blue voltage for both or recharacterize angry goat
Structures
Questions:
- How did we know ASIT wasn't going to work? Is there data behind this or story or calcs?
- Don't we only need one pin to stop rotation? Why 4?
- Did you do calcs for the eye-bolt? Is there a secondary retention mechanism?
- Does the anti-rotation rod interfere with anything?
- Have there been axial calcs to confirm the bottom bolts on slide 19 won't just rip out? (Concerned about them not having a lot clearance)
- Will the capsule holding the black powder be sealed so proper ignition occurs?
- Are the parachutes reefed?
- What are the initial velocity inputs for the shock calcs?
- What are the plans to improve the reliability of the tender descenders?
- Are there any ground testing planned for any of these systems?
- Is there a mass margin generated from our motor performance? When we weigh all of the parts will we know whether we break that margin?
- Why do you have a factor of safety for the bulkhead? It won't be bearing load
- Did the lead engineer design the board layout or was it avoinics?
- Any concern with RF signals with all of the metal hardware?
- Can you explain how decreasing the length fo the rocket overall leads to a reduction in roll instability? (gil answered and said stability >3 bad)
-Where did the 460lb load on piston mount come from?
Comments:
- May be a good idea to tape the dowel pins slightly. There could be a situation where the friction from wanting to rotate prevents separation
- when showing FEA, show supports and loads set up
- FoS should be set by us. Then margin yield and margin ult: MSy = yield strength/(FoS_yield*analyzed stress) - 1. Above 0 is good, below 0 is bad. FoS will be different for yield and ultimate
- include color bar in FEA
- Scale for FEA. Need boundary conditions. Need constraints
- reiterating that FoS is set by us and the margin is the result
- "Jorian have you gotten accelerometer data from other flights to ground vibe environments"
- On the roll-coupled instability & length convo - as I remember it static stability margin & longitudinal mass moment of inertia influence this a lot (especially at resonance roll rate). This article has some good info, I think there are more that I'm looking for and will send after review. http://www.ninfinger.org/rockets/ModelRocketry/Model_Rocketry_v01n05_03-69.pdf
https://www.ninfinger.org/rockets/ModelRocketry/IndexToVolume1.html