My L3 Project...A 7.5" LOC Goblin...AMA

[DAllen]

So the rocket is done...the TAPs are happy with everything. Just trying to figure out when and where to launch this bad boy. What can I say? I am a 'Round Earth Shill.'

 

[Theory]

cool deal, and first things first. that sticker on the fin is AWESOME! going to need to find me one.

any additional details on the build?

what are you looking to fly it on?

 

[DAllen]

cool deal, and first things first. that sticker on the fin is AWESOME! going to need to find me one.

Found it on Redbubble. It looks great but the quality is a little iffy. I got 3 of them just in case and they were cheap. When I went to peel off the backer tape (or whatever you call it) the decal itself started to separate. Once I finally did get the good one on it looks pretty good.

Can't seem to find the one I originally bought now but there are a lot of iterations of this theme:

https://www.redbubble.com/shop/?query=not flat we checked decal&ref=search_box
I'll do some more digging and see if I can find the original

any additional details on the build?

Lots of details lol. Anything specific you want to see?

Some highlights:

- Used mostly wood glue other than RocketPoxy for the fillets only because I wanted giant fillets.
- Moved the e-bay from the coupler to the TOP of the coupler to make room for longer motors.
- Everything else is pretty much stock
- RRC2+ and RRC3 alts
- Shear pinning both upper and lower recovery with 4ea 4-40 nylon screws
- Ended up buying the 54mm, 75mm and 98mm adapters to go with it

what are you looking to fly it on?

AT M1297. Should hit somewhere between 5 and 6k.

 

[Nytrunner]

Moved the e-bay from the coupler to the TOP of the coupler to make room for longer motors.

Nice! I plan to do the same thing in my eventual L3 for the same reason. (6XL grain cases are stupid long)

 

[Rocketjunkie]

I built a 7.5" Goblin in 2010. Originally Blue Tube main body and PML internals. I put the main in the nose cone so I could fit a 98/15360 in it. https://www.rocketryforum.com/threads/almost-a-goblin.8709/
Here's the flights:
Alt Motor Date Location
Blue Tube body, weight 24 Lb. prepped but no motor.
2633 K700 (54/2560) 5-15-10 Orangeburg, SC
3504 L800 (75/3500 EX) 5-16-10 Orangeburg, SC
6350 M1350WW (75-6000) 6-12-10 Orangeburg, SC Onboard video
3714 L935 (54/6GXL) 7-3-10 Penn Yan, NY
5448 L1100 (75-4800 ex) 7-5-10 Penn Yan, NY
6403 M1500 (75-6000 ex) 7-11-10 Orangeburg, SC Onboard Video
5309 L952 (98/5120) 9-5-10 Orangeburg, SC
7803 M1100 (98/7680 ex) 9-6-10 Orangeburg, SC Main at apogee, 18" zipper onboard video
13004 N800 (98/15360 ex) 4-8-11 Price, MD Past trees, 6" zipper, tracker required
2085 K375NW (54/2560) 7-3-11 Orangeburg, SC
3551 L935 (54-6GXL) 10-2-11 Orangeburg, SC
2346 K1275 (54/2560) 6-10-12 Orangeburg, SC
4815 L1300R (98/5120) 10-13-12 Orangeburg, SC Zipper
7758 M1100 (98/7680) 12-9-12 Orangeburg, SC Cracked fin broke off during boost
0 L1500 (55-30 75-4G) 6-1-13 Pittsburgh, PA CATO on pad, destroyed
Rebuilt with G12 main body, otherwise same as before. Weight 32 Lb. prepped less motor.
3023 L935 (54-6GXL) 1-9-16 Rembert, SC G10 main body, rest same as first Goblin
3956 L1390 (75/3840) 5-15-16 Rembert, SC
4323 L1300 (98/5120) 9-4-16 Rembert, SC
4569 L2500 (98/5120) 5-7-17 Rembert, SC
8782 M750 (98/10240 moon) 4-28-18 Bayboro, NC
4150 L750 (75-6000 ex) 9-2-18 Rembert, SC No deployments, destroyed, power failed just b4 apogee
Rebuilt same as previous one.
3887 L750 (75-6000 ex) 5-26-19 Rembert, SC GF

 

[PromptSupercritical]

Hmmm...thought it would be bigger. That is so cool!
Good luck with the maiden. I'm starting in on my first L1 project - Mini Magg 5.5.
These large diameter rockets are the best. And the fin sticker...awesome...

 

[DAllen]

I built a 7.5" Goblin in 2010. Originally Blue Tube main body and PML internals. I put the main in the nose cone so I could fit a 98/15360 in it.

You know, I've watched all of your Youtube videos prior to buying this kit just to get an idea of how its going to fly. You have some great footage. I mean...I assume this is yours?

 

[Rocketjunkie]

You know, I've watched all of your Youtube videos prior to buying this kit just to get an idea of how its going to fly. You have some great footage. I mean...I assume this is yours?

Yes, it's mine. There are a couple videos of other Goblins, the owner is mentioned in the description.

 

[Hangfire]

That launch sound is perfect, I might use that as a ringtone.

 

[DAllen]

As of right now...I might be going to MMWP for my L3 flight. Looks like I should be able to make that work with my TAPs.

 

[DAllen]

Can you say fin flutter? I CAN!!

 

[Nytrunner]

Oh no, Im real sorry to see that Dave.

What's the autopsy turned up.?

 

[mbeels]

Oh crap. Do you think it will be repairable for a second attempt?

 

[DAllen]

Everything other than the fin can survived. I will rebuild it. Already have a new fin can on the way.

Next iteration is definitely going to involve fiberglass.

 

[Bat-mite]

Very unfortunate, but that was some incredible video footage. Best wishes on your next attempt!

 

[Speaknoevil]

Yep, those squarish, extended fins are a suspectable profile. Sorry that it happened. I did see the whole flight and expected flutter, but was hard to discern at what was probably 3500 ft and 400 mph. Great you caught it on video. You'll get it next time!

 

[Mugs914]

Yipes, that was sumthin' else... Sorry to see that Dave.

Any idea when you'll get to try again?

 

[FredA]

Curious -- what did you TAP's say????

 

[mbeels]

Any idea of how fast you were going when it hit?

 

[DAllen]

Any idea of how fast you were going when it hit?

Tough to say exactly. I haven't taken the time to get the RRC3 out to see what it says. Maybe I'll do that tomorrow but after looking at the sim and the video I'd guess it was somewhere north of 500mph.

 

[DAllen]

Curious -- what did you TAP's say????

I believe their phrasing was something along the lines of "that sucks."

 

[John Cummings]

I believe their phrasing was something along the lines of "that sucks."

Was Tim your TAP? That sure sounds like Tim....

 

[Speaknoevil]

Was Tim your TAP? That sure sounds like Tim....

Yikes. Don't like where this is headed

 

[John Cummings]

Yikes. Don't like where this is headed

Twas a joke....If you know Tim that’s probably the first thing he’d say.
Tim’s a great guy and has forgotten more stuff about rocketry than many of us will know. I was at MMWP this weekend btw and saw Dave’s flight. That does suck...but is all part of it. I’m sure you’ll get it next time Dave!

 

[ChicagoDave]

Can you say fin flutter? I CAN!!

You know, on Saturday I saw another Goblin suffer a Fin Removing Incident at MMWP. Either MMWP doesn't like Goblins or that fin design is susceptible to flutter. Or both.

 

[HVArcas]

Nice! I plan to do the same thing in my eventual L3 for the same reason. (6XL grain cases are stupid long)

Where Is an NY resident flying a 6XL L3 project...

 

[FredA]

I believe their phrasing was something along the lines of "that sucks."

like Goblins or that fin design is susceptible to flutter.

Did you TAPs (plural) talk to you about flutter??? If not, why not?
"That sucks" is rather late and poor feedback....

 

[Rocketjunkie]

My 7.5" has 3/8" plywood fins and I've never had problems except 1 flight where the fin was already cracked from landing on pavement. Flown on K through long burn N motors.

 

[dhbarr]

Wow!

 

[tsmith1315]

Nice build, I hate to see that happen. Does it seem that all 4 fins were affected the same way?