- Nov 22, 2020
- Reaction score
- New Mexico
I agree, I did that analysis mainly as a sanity check and out of curiosity for what the approximate difference would be.I'd just conservatively ignore the effect of the fillet. The tool has several other conservative simplifying assumptions baked in, so taken as a whole, if you can get critical numbers higher than your expected speeds I think you're good to go.
It’s more common to talk about bevel angle than length. Back in the day, Dynacom used 10° which is a good balance between performance and ease of machining. The Princeston SpaceShot used a 5° bevel on the sustainer fins. Their technical documentation is worth a read—what you’re trying to accomplish is more in line with their work than typical level 3 projects.What do most people use for the length of their bevels for high performance fins?
I have been looking for a paper like this for a while, thank you. Using degrees as opposed to length makes sense, shows how much machining experience I have… Have you done the beveling yourself for your projects? I was told that MacPerformance Rocketry is a good option for beveling.It’s more common to talk about bevel angle than length. Back in the day, Dynacom used 10° which is a good balance between performance and ease of machining. The Princeston SpaceShot used a 5° bevel on the sustainer fins. Their technical documentation is worth a read—what you’re trying to accomplish is more in line with their work than typical level 3 projects.
Agreed. I am no stranger to wood working but a router is something I am still very cautious with. Yes it is in a table mount but 2 hp is going to win the fight with your flinger for sure...If you haven't used these before, be careful, they will bevel a finger far faster than fiberglass.
This is probably the simplest tool for the job. The only reason I don't have one is the need for a router table and the room to keep it.
I agree, this mock up is with a 5" sled but I am not sure if that will be the finished length. Just got the Eagle CO2 in the mail and the updated CAD shows better clearance for the components so I think it is definitely a workable concept. This is also modeled with the 35 gram CO2 cartridges which is what I expect to need based on 3x #6 shear pins. RASAero says ~200# peak drag and conservatively assuming all of that will be acting to cause separation. Once I get some more data on internal volume after the hardware arrives I will test the 35g CO2 with the shear pins.I would extend that sled and/or rotate the tracker to get the GPS and RF antennas completely clear of the CO2 cylinders. You want to keep them away from any adjacent metal, if possible... since the allthread runs through the length of the NC, the best you can do is to have the GPS antenna point away from it, and live with the (hopefully) minor effect on your RF signal from the allthread.
Funny you should mention that. I have a 1/4x20 titanium all thread from McMaster Carr that threads into my nose cone tip. It is 36" so I will cut it to final length eventually but it is half the weight of the steel all thread. I have their titanium nuts and washers as well.Have you considered using a titanium bike spoke for the metal tie? Very light, around 280kg breaking load, and the lower conductivity would help around your antenna.
What's the breaking strain on that?
Minor diameter of 1/4"-20 is 0.207".
That checks, been a while since I used those mech terms... Given a very conservative max NC weight of 5 pounds that would be >300G of acceleration needed to shear the rod which would seem more than sufficient. I agree with the bending considerations but I hope the bulkhead in the FWD section of the NC will help with that. Rocksim shows a descent rate of about 130 fps with the drogue. I would plan to use a forged eyebolt on the end of the rod and have a "locking" mechanism on the end of the rod. Probably either a cotter pin or a tab I can fold over to absolutely minimize the chance the bolt could unscrew. Some loctite couldn't hurt either.Minor diameter of 1/4"-20 is 0.207".
Area = pi * r^2, so .034 sqin.
Area * tensile = 1683 lbs.
That's ultimate tensile strength, so what load does it break at.
Yield strength (where it takes a permanent set) is 40 ksi, so 1346 lbs.
Edit - there's a crapton of assumptions on that. The math is based around a smooth tensile bar the diameter of the minor diameter of the thread...so, not sure how that changes things. Also assumes a straight pull, any sort of bending on it throws the calcs out the window.
That makes sense, I have always used SF 1.5 for manned aircraft design and I think 1.15 minimum makes sense for a project like this.For most aerospace structures, you size to criteria of something like:
So for a 1683lb Ultimate capability, you would have a max allowable load of 1122 lb, if you're using conventional aerospace structures analysis methods.
- No detrimental deformation (yield) at 115% of Design Limit Load (let's call that your operating load here)
- Safety Factor = 1.5 at Ultimate Load (civil engineering applications like factories may have SF=3 or 5, if lifting loads are applied)
- For a threaded rod or bolt, you would also check shear strength of the threads. McMaster doesn't publish that for the threaded rod but you can google it
Do you have a reference that documents this somewhere? I'm woefully ignorant of RF interference characteristics, except for the gross generalizations like don't put an antenna inside a carbon shell, and such.The only reason I prefer Ti in something like this is it's lower interference compared to Al with electronics.
Fair enough, when I bought the rod it was for a previous build that would have used 2 all threads in a more traditional AvBay setup and so I wasn't as concerned with the strength and more with the weight and trying something new. Given I may need ballast anyway I may just use a cheaper steel rod...The 1.15 criteria would apply to the Yield strength, which actually gives you a higher load than Ftu/1.5. You'd size to the lesser of the two, which in this case is the ultimate strength.
Different materials have different ratios between yield and ultimate strength but for heat treated materials it's generally going to be around that 1.5 relationship.
That McMaster Ti rod is commercially pure, very soft, so yield and ultimate are very close together. It needs to be alloyed to get real strength. As it is, it's marginally better than the shittiest aluminum, which makes me question why you're spending the money on it if your goal is simply reduce weight in the nose. Use an appropriately sized aluminum rod for 1/10 the cost and 2/3 the weight.