3" Tailcone Aerodynamics Research Rocket

[watheyak]

To me, conventional DD is the antithesis of the KISS principle. Familiar yes, simple no. You have two completely separate sets of recovery hardware, two airframe breaks, and an av-bay doing double duty as a major structural component. You're doubling all the failure points. Every time I fly one of my older conventional DD rockets I can't help but think I've over-worked the plumbing. Too much voodoo. Though, if you're flying a large cardboard and plywood rocket it's probably an acceptable option.

For anything higher performance, or where space is limited, I really think DD from a single tube with the use of cable cutters, ARRDs and the like are ideal from a reliability/repeat-ability standpoint. Elegantly simple, fewer moving parts. The cable cutter may have a bit of a learning curve. It's important to have it set up and stress relieved properly. But once that's done, there's just not a lot that can keep it from doing it's job. As CarVac said, "Simple components that interconnect in a simple manner". I like that.

Scott w
TRA 7726
KF7EIV

 

[Chrisn]

However, I plan to never once use conventional dual deploy on one of my own rockets. In my opinion, it's boring and suboptimal for performance, and there are more elegant solutions with equivalent reliability.

Wow -- If I was your prof and I read this, I would fail you for sure....you botched the experiment because you didn't want to use a tried and true, but "boring," configuration....

Your experiment wasn't about optimal performance, but performance variations...
Epic fail, IMHO

And the method he used was not tried and trued? Carlo had commented that he has used the cable cutter successfully, and that he has not done dual deploy with a different method.

AFAIK the experiment isn't over yet, and there is no data. I wouldn't be calling it botched

Chris

 

[FredA]

.... two airframe breaks, and an av-bay doing double duty as a major structural component. You're doubling all the failure points.

If these are failure modes in YOUR rocket with a [small] L-motor, then I suggest you re-take Airframe-101.
These are not real failure modes for YOUR experiment.

You lost focus and went nutty on the airframe.
You could literally buy any 4" FG kit, build it stock in a day (stock except the tailcone) and be flying tomorrow.
No tip-to-tip needed for L motors...

Nuff said...
Hope you'll find a way to get some data you can share.

 

[Reinhard]

.... two airframe breaks, and an av-bay doing double duty as a major structural component. You're doubling all the failure points.

If these are failure modes in YOUR rocket with a [small] L-motor, then I suggest you re-take Airframe-101.
These are not real failure modes for YOUR experiment.

You lost focus and went nutty on the airframe.
You could literally buy any 4" FG kit, build it stock in a day (stock except the tailcone) and be flying tomorrow.
No tip-to-tip needed for L motors...

Nuff said...
Hope you'll find a way to get some data you can share.

I seem to remember that the goal of the project was to gather data over a range that includes rather high Mach numbers on a limited budget. So there was was an incentive for optimization in this regard.

Reinhard

 

[GDJ]

.... two airframe breaks, and an av-bay doing double duty as a major structural component. You're doubling all the failure points.

If these are failure modes in YOUR rocket with a [small] L-motor, then I suggest you re-take Airframe-101.
These are not real failure modes for YOUR experiment.

You lost focus and went nutty on the airframe.
You could literally buy any 4" FG kit, build it stock in a day (stock except the tailcone) and be flying tomorrow.
No tip-to-tip needed for L motors...

Nuff said...
Hope you'll find a way to get some data you can share.

Well show us how to build it then.

 

[CarVac]

Well show us how to build it then.

Making sure you get to at least Mach 1.6, and achieve a 1.35:1 diameter ratio tailcone with a 15-degree half-angle, on a budget. I would love to be shown up.

 

[GDJ]

Making sure you get to at least Mach 1.6, and achieve a 1.35:1 diameter ratio tailcone with a 15-degree half-angle, on a budget. I would love to be shown up.

I'll be honest with you CarVac: I would love like heck to try this out. It's a cool experiment that only I can do on OpenRocket.

However, FredA really seems to have a knowledge that we lack. I think it's a perfect opportunity for him to show us that he has "The Right Stuff" in this matter.

 

[CCotner]

Wow -- If I was your prof and I read this, I would fail you for sure....you botched the experiment because you didn't want to use a tried and true, but "boring," configuration....

Your experiment wasn't about optimal performance, but performance variations...
Epic fail, IMHO

.... two airframe breaks, and an av-bay doing double duty as a major structural component. You're doubling all the failure points.

If these are failure modes in YOUR rocket with a [small] L-motor, then I suggest you re-take Airframe-101.
These are not real failure modes for YOUR experiment.

You lost focus and went nutty on the airframe.
You could literally buy any 4" FG kit, build it stock in a day (stock except the tailcone) and be flying tomorrow.
No tip-to-tip needed for L motors...

Nuff said...
Hope you'll find a way to get some data you can share.

Look, I don't know what stick you sat on, but give the man a break.

It is unfortunate that the cable cutter systems didn't work. It is especially unusual given that, as I'm sure you noticed, the designer of the device himself is also trying to understand the failure.

I'd like to see you design a rocket that you can make that can fit a 30 degree tailcone of significant length and spend non-trivial (2-seconds plus) above mach 1.6, that can be built by complete rocketry newbies in their spare time (most of the team on this project were freshmen), that could be flown 3-4 times per day by experienced flyers, and that has room for a sizeable (2" OD by ~14" long) electronics bay, that flies on a small desert lakebed (can't be allowed to drift, can't be allowed to land quickly). Was CarVac's design the best possible given restrictions? I don't think so (it could have been lighter, wildman FWFG is heavy stuff), but it's the best we could do in the given restrictions.

Ante up a better design and lay off the personal attacks, on us and on others.

 

[watheyak]

Fred's a little angry about something. And he's a TAP???

Btw, is there an Airframe 101 class? Sounds fun. sign me up!

Scott w
TRA 7726

 

[GDJ]

Btw, is there an Airframe 101 class? Sounds fun. sign me up!

Perhaps FredA runs it.

 

[CarVac]

Fred's a little angry about something. And he's a TAP???

Btw, is there an Airframe 101 class? Sounds fun. sign me up!

Scott w
TRA 7726

Perhaps FredA runs it.

I'd say Jim Jarvis runs it.

 

[watheyak]

I'd say Jim Jarvis runs it.

I'd pay a lot to take that class...

 

[CCotner]

I'd pay a lot to take that class...

Haha, me too!

If, you know, I had any, but that's a different problem.

 

[GDJ]

Haha, me too!

If, you know, I had any, but that's a different problem.

AYE! I would....but plane tickets are a pretty penny.

 

[WoShuGui]

It most definitely separated at apogee. The cable cutter's cable was ripped by the deployment shock.

I found the rocket on the ground, with a rolled-up parachute next to it, shroud lines extended.


IMG_5008-output by CarVac, on Flickr

I have had it take as long as 15 anxious seconds for the burrito bundle to unwrap with the Archetype setup. Is it possible the chute remained covered in the protector, maybe even with the cable still tied, all the way down and the whole thing came apart on impact? It looks like the nomex blanket isn't attached. Seems more plausible than an exposed chute bundle staying closed.

 

[dixontj93060]

I had a canopy not inflate at MWP (not from cable cutter set up, just normal Nomex burrito). It was my fault--"launch fever" and I didn't take the time to disassemble, shake the chute out, apply baby powder, etc. I had prepped it three days before and was running behind prepping some other rockets. On descent the main was fully exposed but never opened. When I got to the recovery area, the chute was stuck together kinda like a crushed plastic grocery bag. So a question, was the chute freshly prepared and packed before the flight above, or had it been prepped and then sat for a while? As in my case, that could be an issue.

 

[CarVac]

I had a canopy not inflate at MWP (not from cable cutter set up, just normal Nomex burrito). It was my fault--"launch fever" and I didn't take the time to disassemble, shake the chute out, apply baby powder, etc. I had prepped it three days before and was running behind prepping some other rockets. On descent the main was fully exposed but never opened. When I got to the recovery area, the chute was stuck together kinda like a crushed plastic grocery bag. So a question, was the chute freshly prepared and packed before the flight above, or had it been prepped and then sat for a while? As in my case, that could be an issue.

Usually I try not to prep that far in advance.

It had been completely free up until 15 minutes prior to the flight. As soon as I pulled on the shroud lines as it sat on the ground, it unfurled perfectly.

 

[rocketgeek101]

What type of chute is that? From the pic It looks a little plasticy. Also, did the aluminium tip snap off? how did you have the tip attached to the nose?

Thanks.

 

[patelldp]

These days you can do "traditional Dual Deploy" using the filament wound nosecones. Both Gary T. and Jim H. have shown some picture of how they intend to do it. This would GREATLY minimize the rocket length while also providing a little more assurance for those concerned with the cable cutters.

 

[CarVac]

What type of chute is that? From the pic It looks a little plasticy. Also, did the aluminium tip snap off? how did you have the tip attached to the nose?

Thanks.

These days you can do "traditional Dual Deploy" using the filament wound nosecones. Both Gary T. and Jim H. have shown some picture of how they intend to do it. This would GREATLY minimize the rocket length while also providing a little more assurance for those concerned with the cable cutters.

It was a 60" Fruity Chute elliptical; the first flight was on a 60" Spherachute, which is actually a good deal smaller, but which we had neglected to bring to Black Rock.

The nose tip snapped off because it was only attached to allthread and the tip doesn't have a shoulder: the allthread rod bent on landing.

I suppose a slightly more-traditional dual-deploy could be done using the FW nosecones, by breaking in the middle (descending drogueless) and then popping the nose off for the main event, however that would have meant I couldn't use the CF tube since that would have blocked GPS reception and radio contact with the BRB GPS.

 

[patelldp]

I suppose a slightly more-traditional dual-deploy could be done using the FW nosecones, by breaking in the middle (descending drogueless) and then popping the nose off for the main event, however that would have meant I couldn't use the CF tube since that would have blocked GPS reception and radio contact with the BRB GPS.

Only half of the bay would have been in the CF. The other half would be in the FG nosecone. While on the pad your signal may be hampered some, but once it deployed at apogee it would have been in the open. I doubt you'd lose lock due to CF being on the ground side of the bay, not the sky side.

 

[troj]

I have had it take as long as 15 anxious seconds for the burrito bundle to unwrap with the Archetype setup. Is it possible the chute remained covered in the protector, maybe even with the cable still tied, all the way down and the whole thing came apart on impact? It looks like the nomex blanket isn't attached. Seems more plausible than an exposed chute bundle staying closed.

Drogueless, or with a drogue?

A small drogue, placed properly, should prevent that 15 second issue as it will also work as a pilot, pulling the "burrito" apart. When going drogueless, all bets are off and you're relying on the airstream to do it for you.

-Kevin

 

[CarVac]

Drogueless, or with a drogue?

A small drogue, placed properly, should prevent that 15 second issue as it will also work as a pilot, pulling the "burrito" apart. When going drogueless, all bets are off and you're relying on the airstream to do it for you.

-Kevin

Where would you put a drogue, so that it would both act as a pilot and not pull the burrito apart?

 

[troj]

Where would you put a drogue, so that it would both act as a pilot and not pull the burrito apart?

Perhaps put a loop midway down from the drogue and run the cable tie through that, then attach the Nomex blanket a bit down from that.

It may take some trial and error to figure out exactly how to do it, but as folks have already demonstrated, purely relying on the airstream to open the burrito in time is asking for problems (and is a safety issue).

-Kevin

 

[dixontj93060]

Perhaps put a loop midway down from the drogue and run the cable tie through that, then attach the Nomex blanket a bit down from that.

It may take some trial and error to figure out exactly how to do it, but as folks have already demonstrated, purely relying on the airstream to open the burrito in time is asking for problems (and is a safety issue).

-Kevin

Another thing that helps, at least in separating the Nomex protector from the parachute, is to place a loop and attach the protector a few feet down/away from the chute attach. As the shock cord extends there is some pull to help separate the two. I have started to do this versus tying the protector to the parachute/shock cord attach point.

 

[FredA]

OK -- Perhaps I came across a little to harshly....sorry.
Just that I see this all to often -- an experiment gets ruined by lack of focus on what's being tested and how to design the experiment to eliminate other distractions.
Too many projects needlessly push the envelope in multiple areas for unknown reasons....over complicating the design....impacting the results.
This project looked like it fits that category.

Sure -- nice to have data to mach 1.8, but really, mach 1.6 data is better than no data....
Focus on the experiment and not "state of the art everywhere" - what's really necessary.

This data could already be in the can....but instead we have a cable-cutter debate.

I'll shut up for now -- best of luck continuing the experiment -- would like to see the data.

 

[WoShuGui]

Drogueless, or with a drogue?

A small drogue, placed properly, should prevent that 15 second issue as it will also work as a pilot, pulling the "burrito" apart. When going drogueless, all bets are off and you're relying on the airstream to do it for you.

-Kevin

Perhaps put a loop midway down from the drogue and run the cable tie through that, then attach the Nomex blanket a bit down from that.

It may take some trial and error to figure out exactly how to do it, but as folks have already demonstrated, purely relying on the airstream to open the burrito in time is asking for problems (and is a safety issue).

-Kevin

Another thing that helps, at least in separating the Nomex protector from the parachute, is to place a loop and attach the protector a few feet down/away from the chute attach. As the shock cord extends there is some pull to help separate the two. I have started to do this versus tying the protector to the parachute/shock cord attach point.

Some really good thoughts... the trade-off seems to be between isolating the burrito from separation/descent shocks and having some pilot to open the bundle after cable cut. My Archetype setup has evolved to the following...
View attachment 155794

The drogue is optional to keep heavy nose cones above the booster (risk main tangle with drogue or booster; your choice). To isolate the cable tie and strain relieved wire, the shock cord is looped through the nose cone and then to the burrito. My results without this isolation have been poor... broken wire (even with good strain relief) and/or broken cable tie at separation.

The setup is still missing the pilot; hence the 15 seconds (or more) of terror. Troj has my next iteration... a tiny drogue or short streamer pilot that tugs on a corner of the protector after the cable tie is cut.

Wish we could make CC DD more reliable, it really has advantages.

 

[BLKKROW]

This is really just an idea that came to me while reading this thread. First of all, please understand I have not used a CC but plan on using them for future flights.

Thinking about the drogue chute idea, can you not calculate how much the drogue will pull on the bundle and make sure the cable tie can hold the bundle together while the drogue is in use.

If this is a far out idea then please ignore me.

 

[FredA]

If you use these at least do NOT depend on ordinary "shooters wire" to withstand the beating of a burrito in the wind.
Solid copper fails quickly due to work hardening with repeated bending...and has crap ability to withstand tension.

Use a stranded wire made to flex.

 

[WoShuGui]

If you use these at least do NOT depend on ordinary "shooters wire" to withstand the beating of a burrito in the wind.
Solid copper fails quickly due to work hardening with repeated bending...and has crap ability to withstand tension.

Use a stranded wire made to flex.

Good point. I have been using scavenged igniter wire which is not only single strand, but also pre-hardened... two strikes. Haven't flown over 5,000' with it, so exposure time isn't as bad; but unused stranded wire is definitely better. One thing I do that helps, is to coil the wire at the flex points to reduce stress. Grouch has a picture in post #327 of https://www.rocketryforum.com/showthread.php?37812-Archetype-Rocketry-Presents/page11&highlight=archetype showing the idea; although I would coil all the way from the bulkhead to the burrito.