Fin fillets came out ok'ish with 5min epoxy.
[...]
I'm looking forward to trying out the fixit epoxy clay with the next one - I'm hoping the longer working time and the ability to use isopropyl alcohol on a finger to smooth and shape will help, followed by CWF ad sanding...
So, how did it fly?
a
I suggest a test flight with a lower impulse motor to see if the tracker performs adequately before punching it to out of sight land. The seconds you wait to reacquire the signal after the button is pushed become agonizing. Kurt
Well - ASPIRA-I flew today. Kind of.
[...]So I built my f39-9 and re-padded it.
It went like a scalded cat.
GPS signal was good. We lost site of it but that wasn’t surprising.
Wandered around the coords for a bit and just couldn’t find my rocket. Then it dawned on me and I started looking for a nose cone instead of a rocket. Sure enough, I found the NC with the gps, LiPO and A3, but no rocket.
A quick examination and I discovered the vitamin tube I used to extend the NC: I put the shock cord either side of the mold pour spot, which is the weakest part of the tube - lesson learned - fill the base with epoxy next time.
Altimeter data View attachment 331048
So with Aspera-I MIA, I guess we start the final design and build for Aspera-II - going higher and faster but with a disposable motor this time. Build will take the old NC extension design and strengthen the attachment point.
My thoughts so far are to lengthen the vitamin tube by 10mm and fill the bottom 8mm of the canister with epoxy.
I’ll drill holes through canister and epoxy this time for shock cord attachment. I’m wondering if this will be sufficient.
Thats a shame. For the next build there is a note in some Apogee documents that suggest you only need 3 fins not 4 for stability. That will help reduce drag a fair bit.
I've been working on a scratch built 29mm design similar to the aspire in open rocket, and found I was getting better performance by adding nose weight and reducing fin size. Drag seems to be a lot more critical than minor changes in mass when trying for supersonic.
Just to make sure we understand the failure point: your nose-cone shoulder extension, in the form of vitamin tube, failed by way of ...
... either that tube disintegrated at the point of shock cord attachment ...
... or was it that the shock cord did not epoxy to the tube properly and peeled off?
Either way, I would avoid using the same materials (fragile or epoxy unfriendly vitamin tube) in the second rocket!
How did that compare to your sims?
If the sims are off/too optimistic, by how much?
If your goal was to go supersonic, as the thread subject indicates, will you achieve your goal, net of the real world adjustments?
Personally, I don't care about speed targets, but if that's your goal, you may want to make sure you are on track to achieve it!
If you are not making it, your only recourse may be to cut the weight.
Are you sure the vitamin tube will not crack and disintegrate at the point beyond which it is filled with epoxy?
It failed you once before, why rely on it again?
I would shop for the target diameter fiberglass, phenolic, or cardboard tube, in that order of preference/strength.
Good luck!
a
Looking at the A3 data, it appears that there is a large G load shortly before it hits the ground.
Perhaps, and this is just a thought, at apogee the ejection charge G load was enough to crack the mount but not separate the nose cone yet. Then the parachute didn't open until it was near the ground, where the jolt of it opening finished separating the nose cone and fell free.
If that's more or less what happened, then the rest of the rocket would be nearby though.
I think the data supports the hypothesis - if we look at the last 5secs of the data in more detail:
View attachment 331202
I think the 12G load at 46.8sec could be the chute finally opening (it was only a small 6" estes plastic") at an altitude of 11m... If you look at the Gforce data after, there is a 5G spike that could be impact of the NC, followed by a reading where the GForce drops below 1 (NC going weightless as it reached it's "bounce apogee") then it lands and settles to 1G resting on the ground....
The only part I don't get is, if the NC only separated 11m of the ground, : WHERE THE HELL WAS MY ROCKET?!?!
;^)
Interesting - the more I look at that A3 data, the more I think the NC didn't separate till the VERY end...
A 65g nose cone took 45 seconds to land from an altitude of 700m... descending at ~20m/s...
That't the same speed as this rocket coming down on a streamer...
By a few online calculators, a 65g nose cone should fall from 700m in 11 sec... Flight profile shows it took 45 secs to land:
View attachment 331187
How did you determine that the 65g nose cone should have an average terminal velocity of ~60 m/s? What is the CdA? Are you sure the nose will fall ballistic, or maybe it will be unstable and tumble?
It is a good question: A little intuition and some assumption.. I can't see this particular nose cone tumbling, certainly not for 45secs... It is of course possible, but for my money, for the NC to tumble at the same speed as an the airframe was simmed to on a streamer, I would be surprised...
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