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10-14-2022
Almost finalized the spreadsheet just waiting on last lengths to be put in by roman now which changes a few CG values
Realizing won’t account for CG changing due to min/max mass scenarios. Determined this should be fine for this cycle.
Created list of what we want to simulate, and excel to track data
Decided to use RSE files from previous simulations (early KOTS 2023 simulations) as new ones were not created for this yet. Trying 100% thrust, 120% and 150% as decided by Joel and Aaron.
01-28-2023
Just realized I haven’t put updates here in forever.
We finished cycle 1 essentially on estimated schedule and published the mini report.
The cycle 2 data took a little bit longer to gather and be confident in because of a lack of work over the holidays and also due to wanting to be very confident in this data but unfortunately a lot of designs on the rocket are not yet at a place where they can give us good estimations. Also the SF got delayed a week until today.
One unfortunate part of this is that the 3d printed metal fill bulkhead design needed to be sent away for printing in January around the 24th. For this they needed fairly good loading calculations so we decided to add a cycle 1.5. This used the data currently gathered alongside some rough estimations of: engine data, airframe weight sections and other sections in general. This was then simulated with two types of fins (clipped delta and trapezoid) based on research about what was the best shapes. This generally showed that clipped delta was better for apogee and also that the fin size of last years rocket is actually a good estimation of what we will need this year. This is new information as previously it was thought it would be able to be smaller than last year. However I think due to a length reduction and possibly other factors the inherent stability of the rocket has decreased. We are currently planning on completing cycle 2 around mid February according to the plan laid out in this document https://docs.google.com/document/d/1JNvpdeczEOeFuUGfQ1QNFMN_b9wIcHwRmjX0BIFrfug/edit#.
A weather review of New Mexico conditions was also completed to analyze the conditions we are using in our simulations and for further use as to weather variation in stability. This is located https://docs.google.com/spreadsheets/d/16RH75F2kThyLBTv0jcvQgWOC8h9-sMPgf0onBELOxmY/edit#gid=0
Sensitivity analysis was done on various nosecone and boattail shapes to determine if they need to be taken into consideration at this point. Neither significantly changed stability. Nosecone shape can be improved by changing to a power series with 1/2 shape parameter. This would improve apogee by around 400ft however this is most likely not going to be done as remaking nosecone moulds is prohibitive in both team member time and manufacturing time. The boattail various shapes had very little effect on flight with a perfectly square extension of the rocket reducing apogee by around 300ft and various curvatures not making a large impact.
A big drop in stability was noticed around the end of the engine burn which makes our lowest stability at a very different time than previously. The cause of this difference is mostly unknown.
02-10-2022
Currently sizing fins and thought I would jot down some notes:
We discovered we had positioned the RSE file wrong in OpenRocket. There is conversations in slack about this but essentially the RSE file has a value called “len“ which is the distance from the top of the potential fuel volume (tip of the rounded bulkhead) to the end of the fuel grain. This is the distance that OR considers the RSE. Therefore we can align the RSE using the internal top of the fuel bulkhead (farthest fore point on rocket that Nitrous could reach essentially). Decided to set this location as 1 inch fore of the front plane of the Feedsystem section. Pending future analysis by Aaron. This is good for stability as mass shifts forward compared to what we previously thought.
Found an error in the cycle 2 spreadsheet where we completely missed a bodytube section weight. This highlights the importance of verification and idiot checks.
Determined that boattail length does not need to be decided at this point as it does not affect fin sizing too much but that tapered diameter would be 5.5in in our sims (based on rough guess by Aaron) and length in sims will be same as last year at 4.2 inches to simply things.
Had conversations about launch rail length this year summarized by the following:
stability is lowest throughout the flight immediately off the launch rail
We are currently sizing fins to be as small as possible while having enough stability as this will reduce drag and increase apogee.
The longer the launch rail the more stability we have off the rail as we will be going faster when we depart and this effect is noticeable
We are in a place still where we still want a wee bit more apogee to be where we want to be.
Therefore 40ft should be the launch rail length again this year if it can be done
Launch rail length calculation:
rail length is 40ft.
When first rail button leaves tower it is considered to have left the tower in the DTEG.
First rail button is roughly at the fore plane of Feedsystem section 66.39in from nosecone tip. rounding to 66in, rocket is 174in long so 174-66=108in have to be subtracted from the rail length.
40ft = 480in-108in = effective rail length of 372in
This is the value inputted into openrocket
Discovered some problems with RASAero summarized below:
Roman, Ryan and I just had some conversations about an issue we just noticed. Unfortunately we didn't notice how impactful this would be until now but essentially RASAero is not letting us input:
how the engine mass changes over time (instead assuming it linearly decreases),
how the engine CG changes through the burn (instead assuming it stays still we think)
the engine CG in relation to the rest of the rocket (although we have a weird lead on that from a forum that says the engine CG is set to half the engine length which we could mess with).
Due to this RASAero is not giving us stability values that make sense. Because the engine is a large portion of the rocket mass this is not really something that is easy to guess at or apply a conversion factor to so excepting a major breakthrough we will not be using RASAero for fin sizing which is happening this weekend