AeroTech Open Thread

[Neutronium95]

The minimum payload size and mass requirements, combined with the 10,000 foot altitude requirement tend to force college teams into building L or M powered rockets. I'm not sure how I feel about that to be honest.

 

[OverTheTop]

The minimum payload size and mass requirements, combined with the 10,000 foot altitude requirement tend to force college teams into building L or M powered rockets. I'm not sure how I feel about that to be honest.

I was unsure of this myself, but as a mentor of a university team I find it actually seems to work reasonably well. I suppose we need to factor in the variability of the teams and also the individuals within the teams, so there will be variation both on the micro and macro scales. I am lucky enough to mentor a team that does very well and just needs a gentle nudge in the right direction to do great engineering. I am very lucky in this regard. Their engineering skills make me look good .

I do know of other teams that were not so safety oriented and for this, and other reasons, earned themselves a bad name. A little guidance and mentorship goes a long way to making a good solid engineering team.

 

[cautery]

It's been a long while since I've done any real web dev, but if it's just the index.html page source you need you can use the wayback machine, https://web.archive.org/web/20210330124213/http://www.aerotech-rocketry.com/
When that loads just right click and view source in chrome and you should get something resembling index.html, the links and image url's will all be messed up due to the archive location vs. the real.

THIS!!! I've had SEVERAL clients for whom I "saved their bacon" using the WayBack Machine!
In my last two decades, I started a policy of keeping FULL BACKUPS of ALL my clients data for them. This, too, has saved a number of my clients untold thousands of dollars in lost data, history, and recreation/dev time. In fact, it became a REQUIREMENT for me to take on a new client at a certain point.

 

[Sooner Boomer]

I'm going to post this here because we plan on using Aerotech motors, but it would apply regardless of mfgr (even EX). The question is: how accurate are the published thrust curves. I'm looking at the "jitter" or "noise" in the curves. Is this an artifact or are there actually inconsistancies in the otherwise smooth thurst? We're looking at a boosted dart project, and the concern is that a "hickup" in the thrust can cause the dart to prematurely uncouple from the booster.

 

[dhbarr]

I'm going to post this here because we plan on using Aerotech motors, but it would apply regardless of mfgr (even EX). The question is: how accurate are the published thrust curves. I'm looking at the "jitter" or "noise" in the curves. Is this an artifact or are there actually inconsistancies in the otherwise smooth thurst? We're looking at a boosted dart project, and the concern is that a "hickup" in the thrust can cause the dart to prematurely uncouple from the booster.

There's various vibrations. Some of them match up with a sampling cycle, high or low. The area under the curve is reasonably accurate within tolerance. One can guarantee that, for instance, spitting a liner or chunk of propellant will surely jiggle.

That said, unless the booster is dramatically unaerodynamic you should basically be toggling between much-thrust and mucher-thrust.

 

[Sooner Boomer]

Here's an example: L1300R

That's a ~125 lb/ft "chuff" there at the beginning. Then there's a ~20 lb/ft "dip" at the end.

OK - this particular example is from Thrustcurve. Is it accurate, does it represent the actual output?
I'm not trying to say anything bad. I just want to know how accurate the published data is. The other options are test flights w/o seperable payload, or burning one on a test stand.

 

[Theory]

bet that is quite close to accurate.

would not at all be concerned about the early dip. if you look at the time, that dip accounts for about a 1/10 of a second. would not be noticeable in hobby rocketry. The dip at the end is similar, given the amount of aerodynamic drag and other forces at play, this will also be far from noticeable.

also worth noting is the degree to which all motors are allowed to deviate from the certified spec. no two are going to be exactly alike, and some may differ by several percentage points.

 

[DAllen]

I have a USLI team in need of 4ea L2200's and have heard through the grapevine that there are some long lead times for orders with AT. Can someone verify what that lead time is? If it's too long we're either going to need to go with CTI or try to find vendors who already have these motors in stock. I am aware that AT is doing a special run of some 3 grain L motors for USLI teams but my team would really like to use the L2200 instead. Just need some help on sourcing motors and possible alternatives here in case these lead times are untenable...

 

[Theory]

I have a USLI team in need of 4ea L2200's and have heard through the grapevine that there are some long lead times for orders with AT. Can someone verify what that lead time is? If it's too long we're either going to need to go with CTI or try to find vendors who already have these motors in stock. I am aware that AT is doing a special run of some 3 grain L motors for USLI teams but my team would really like to use the L2200 instead. Just need some help on sourcing motors and possible alternatives here in case these lead times are untenable...

Have you contacted your local vendor or AT directly? Likely your best bet for a purchase like that.

 

[DAllen]

Have you contacted your local vendor or AT directly? Likely your best bet for a purchase like that.

Yes. I've talked to 2 different dealers about this order and both told me the lead times were "long" so I' just trying to nail down something a little more specific.

 

[COrocket]

Yes. I've talked to 2 different dealers about this order and both told me the lead times were "long" so I' just trying to nail down something a little more specific.

I just did an Aerotech propellant preorder with Balsa Machining, and their best estimate is 8-10 weeks between dealer order and shipment from Aerotech, so figure another week or two for the dealer to receive for pickup, or then add another shipping time if they need send it to you. It does look like they have L2200s in stock for regular price if you need one sooner than that though.

 

[DAllen]

Well that was quick…I think we have that little issue solved

 

[mikec]

We're looking at a boosted dart project, and the concern is that a "hickup" in the thrust can cause the dart to prematurely uncouple from the booster.

Stuff happens regardless of the published thrust curves. If you want 100% assurance, don't rely on drag separation but use shear pins and a separation charge at detected burnout.

That said, a hiccup large enough to cause separation seems unlikely to me.

 

[boatgeek]

We're looking at a boosted dart project, and the concern is that a "hickup" in the thrust can cause the dart to prematurely uncouple from the booster.

One way to address that concern is to plot the expected booster drag (and maybe weight*) on top of the motor thrust curve. There won't really be much if any drag at that first hiccup, so I wouldn't expect that there would be a negative force at the ISC. The second dropoff in thrust at 3.2s kind of depends on the drag profile. It still seems unlikely that this would cause drag separation, but stranger things have happened (see some of Jim Jarvis' flights).

* It would probably be easiest to do this as a free body diagram on the top of the booster so you can see if the net force on the ISC is positive (booster pushing the dart) or negative (booster falling away). It would take some thinking on how to handle the weight and drag of the dart, though.

 

[Sooner Boomer]

Can anyone tell me the maximum OD of 29mm and 38mm engine nozzles? I'm looking at replacing the individual clips that hold the motor in, with a single washer. I need to make sure the center hole is big enough in the washer I have (not worth excessive grinding, the clips work fine).

 

[Steve Shannon]

Can anyone tell me the maximum OD of 29mm and 38mm engine nozzles? I'm looking at replacing the individual clips that hold the motor in, with a single washer. I need to make sure the center hole is big enough in the washer I have (not worth excessive grinding, the clips work fine).

Why not just make the center hole ID the same size as the ID of the motor casing? The nozzle OD is limited to that. That’s pretty much what aero pack retainers do.

 

[Maxwelljets]

Can anyone tell me the maximum OD of 29mm and 38mm engine nozzles? I'm looking at replacing the individual clips that hold the motor in, with a single washer. I need to make sure the center hole is big enough in the washer I have (not worth excessive grinding, the clips work fine).

Here's the dimensioned drawing for the largest nozzle Aerotech uses for 38 and 29mm motors.

 

[Sooner Boomer]

Here's the dimensioned drawing for the largest nozzle Aerotech uses for 38 and 29mm motors.

Thanks! I've never see that dwg!

 

[Sooner Boomer]

Why not just make the center hole ID the same size as the ID of the motor casing? The nozzle OD is limited to that. That’s pretty much what aero pack retainers do.

There's no "make". Either the extant washer fits or the idea doesn't work.

 

[Steve Shannon]

There's no "make". Either the extant washer fits or the idea doesn't work.

There are washers available from companies that have a very wide range of inner and outer diameters. Substitute the work “buy” for “make” in my original question.

https://www.bokers.com/washers/?gcl...cgGGmIqJ6zyQaOqNxKakeWUnUyPh0RskaAlVOEALw_wcB

 

[Sooner Boomer]

There are washers available from companies that have a very wide range of inner and outer diameters. Substitute the work “buy” for “make” in my original question.

https://www.bokers.com/washers/?gcl...cgGGmIqJ6zyQaOqNxKakeWUnUyPh0RskaAlVOEALw_wcB

Thanks. I think the one I have will work. Just for fun, I grabbed my dial calipers to measure. Wow, those are heavy! I'm so used to digital, plastic micrometers that the weight of "real" machinery was surprising.

 

[Rocketjunkie]

https://www.bokers.com/washers/?gcl...cgGGmIqJ6zyQaOqNxKakeWUnUyPh0RskaAlVOEALw_wcB

I have a custom run of 38 mm fiber washers from them. They have a 7/8" ID for use with offset core motors like my I85 Still have about 1500 if you need some.

 

[ihbarddx]

I'm going to post this here because we plan on using Aerotech motors, but it would apply regardless of mfgr (even EX). The question is: how accurate are the published thrust curves. I'm looking at the "jitter" or "noise" in the curves. Is this an artifact or are there actually inconsistancies in the otherwise smooth thurst? We're looking at a boosted dart project, and the concern is that a "hickup" in the thrust can cause the dart to prematurely uncouple from the booster.

A boosted dart strategy works by imparting great speed to a body (the dart) with a high ballistic coefficient. As such, it works best for the shortest-burning motors in an impulse range. With a sufficiently short burning time, and competently executed ignition techniques, hiccups shouldn’t be a problem. (Worry a little more about thrust curves that tail off slowly.)

To answer your specific question, rocket motors are neither perfect nor are they perfectly reproducible. Measurements aren’t perfect either. Like… Welcome to the third rock.

 

[DeltaVee]

The AeroTech website URL has been redirected to the AeroTech Store site until we can sort out the issues. Unfortunately the hosting company overwrote the index.html page with the “under construction” page, and we are trying to figure out how to re-create it. The rest of the site is still there. We apologize for the inconvenience and hope to restore the website soon.

Most of the URLs I've bookmarked (eg. http://www.aerotech-rocketry.com/customersite/resource_library/ etc) now return " 404 not found." These were working fine a few days ago... This is a bummer.

 

[cautery]

Most of the URLs I've bookmarked (eg. http://www.aerotech-rocketry.com/customersite/resource_library/ etc) now return " 404 not found." This is a bummer.

The /customersite/*.* was working just a couple of days ago.

I take it as a possible sign that someone is actively trying to de-"Charlie Foxtrot" the website.
I surely hope they don't get convinced they have to pay to fix this problem OR to re-create all that content.
@AeroTech.... I am pulling for y'all! I'd fly out or remote in and fix it for y'all if I wasn't retired.


You could always go to the WayBack machine in the meantime.

 

[Handeman]

Most of the URLs I've bookmarked (eg. http://www.aerotech-rocketry.com/customersite/resource_library/ etc) now return " 404 not found." These were working fine a few days ago... This is a bummer.

I'm getting a 403 Forbidden error. Like you have to be logged into the site, not that they are not there.

 

[bad_idea]

As has been said, the Wayback Machine is your friend. Many companies deliberately opt out of Wayback; it's good for both Aerotech and the community that Aerotech did not.

 

[Ben Murdock]

Anyone happen to have downloaded a recent copy of the Aerotech Master Motor Matrix before the Aerotech website went down? It is usually found here, I should have downloaded it instead of always relying on the web version: http://www.aerotech-rocketry.com/up...wormOLO0QJaCaozGMWamFgwUOATzuCGeluPzuE0otBUSg.

Thanks in Advance!

 

[GlueckAuf]

Anyone happen to have downloaded a recent copy of the Aerotech Master Motor Matrix before the Aerotech website went down? It is usually found here, I should have downloaded it instead of always relying on the web version: http://www.aerotech-rocketry.com/uploads/711b2f97-fd38-44c3-bc2f-b9646d776a44_AeroTech Master Motor Matrix 6-10-20.pdf?fbclid=IwAR2JZBoaftKoqPwormOLO0QJaCaozGMWamFgwUOATzuCGeluPzuE0otBUSg.

Thanks in Advance!

Here's one I pulled off of the 'net a couple of weeks ago. Dated June 2020, whether or not it's the latest one, I can't be certain.

 

[Sooner Boomer]

Here's one dated 4/21/21