Aerotech Delays

[n3tjm]

I heard it said, Aerotech has three Delays

S = Shred
M = Maybe
L = Lawn Dart

Today I flew a D15-L

Brand spankin new Estes Outlander (~$30 kit), upgraded to 24mm mount because I did not want the rocket to hit the ground before the chute deploys. I decided to use a D15-4T for its first flight.

Maybe Aerotech meant that the ejection occurs 4 seconds after it hits the ground? Cause that is what happened. The D15 ignites instantly, the Outlander shoots off the pad straight and true, climbs up to apogee. a four second delay would of been perfect. Starts coming back down. A seven second delay may of popped the chute in time. But no. impact. spectacular as bits of silver paper from the "tanks" fly in all direction. smoking. About four seconds after impact the ejection goes off. I needed a bag to collect the pieces.

After the hassles with Aerotech warrenty with my last two Aerotech motor failures/Issues (G71's and G53's), I honestly don't think its worth contacting them. They made it clear that they will not honor their motors purchased over a year ago and without receipt (and as a response, I don't stock up on Aerotech motors like I used to, I only buy what I know I am flying during the next few launches, and I encorage everyone to do the same). This is the last load of D15's which was purchased in 2007 and of course since it was purchase onsite vendor, there was no receipt...

Tonight I was going write a thread about my outlander. Guess I did but not with the tone I would like...

 

[Donaldsrockets]

Ouch!!!

I hope you can somehow repair that.

Maybe Papa Elf will send another one.

 

[stickershock23]

Dude, that stinks, That rocket is such a time consuming expensive rocket to build to destroy it like that. (very cool rocket though)

I wish we could get them to understand our frustrations! Seems like AT wants to keep coming out with new stuff, but wont look into the problems with what is out there.

It really stinks that when you go to push the button, in stead of looking forward to a cool/fun flight, not only do you have to worry about what you did. but now you have to worry about the motor too. will it cato? will the delay work. is my rocket going to be destroyed? Isn't there enough for us to worry about already?

 

[n3tjm]

Seems like AT wants to keep coming out with new stuff, but wont look into the problems with what is out there.

Exactly. I felt like posting that at one of garys Aerotech Announcement threads where someone posted how cool that he was introducing new stuff. I didn't, was not my thread and felt it inapropriate to attack someone else's thread.

It really stinks that when you go to push the button, in stead of looking forward to a cool/fun flight, not only do you have to worry about what you did. but now you have to worry about the motor too. will it cato? will the delay work. is my rocket going to be destroyed? Isn't there enough for us to worry about already?

Hit the nail right on the spot. I think exactly that. I wish there was Pro18's and Pro24s, probably will never happen and I understand why CTI would not make those.

 

[tibadoe]

Sorry to see the aftermath.....hope you can fix it.

 

[Jeroen_at_CTI]

I wish there was Pro18's and Pro24s, probably will never happen and I understand why CTI would not make those.

Be careful what you wish for...
Jeroen

 

[r1dermon]

ouch, wow i've never had that long of a delay by mistake...usually i scuff it with a razor before install just in-case...

btw, can't wait to try those CTI pro29s. and i agree, 24mm CTI would be baaaaad.

 

[stickershock23]

Be careful what you wish for...
Jeroen

Jeroen, I have lots of wishes. can the CTI fairy help out LOL

NT3jm, Don't ever hide what you have to say. Just because some people frown upon talking "bad" about something. If there is a problem it needs to be brought up. think of all the other rocketeers that read these forums, hear only the good stuff, then go on that bad info. CRASH!! and their hard work is destroyed too. If your new at this hobby that can be pretty devastating.

My personal opinion. people may not like what I have to say. but I hope at least a few of them listen to it and learn from my mistakes, or bad choices. I don't want to hurt anyone, I want them to know what really happens. Maybe save them a Crashed rocket or at least a headache.

Gary R, did you hear that. I tried to tell you this when I worked for you. We don't need tons of new stuff. we need stuff that works right all the time. Do that and way more people will be happy!

 

[Bobj]

I'm new here so I don't want start off on the wrong foot...

Let me say this, there are many things about this hobby that I find very cool. Eratic delay grains are not one of them.

I my short time in the hobby I have had many more flights go a little (or more than a little) wrong due to erratic delay grain performance than I have had flights go right.

Our on-site guru's seems to blame every type of delay anomoly on getting even a tiny spec of grease on the grain. Not sure what they would say if I pointed out that the instructions call for the front delay grain spacer to be filled with grease when using a plugged front closure.

I know, using a plugged front closure technically turns the delay grain into a tracking grain. The grease remains. The grain burns.

Delay grain issues are the one thing that pushed me into electronic ejection so soon.

 

[DAllen]

Be careful what you wish for...
Jeroen

I almost wet myself when I heard that. :y:

-Dave

 

[The EGE]

The only AT motors I have ever had a problem with are D15s. Of 2 D15-4s, one had a 7-second delay (which nearly destroyed my Deltie Thunder) and one at least 5.

I have had 2 D21 (-4 and -7), 3 E18-4, 1 E15-4, 1 F12-3, 1 F23-4, 1 G78-7, and 1 H128-M, all with delays accurate to under a second.

I think the D15 is just cursed. Or perhaps it's that the D15 fuel grain is so short, and so the igniter is almost 1.5" away from the delay grain (because you're supposed to tape over the end of the grain). That means that the delay grain will not be ignited by the igniter, and instead by the fuel grain istelf, which may take a while - perhaps a second, or more, thus leading to a longer delay time.

I suspect the same problem may exist for 29mm E loads, since they only fill up a third of the casing. Anyone got evidence of that?

 

[ben_ullman]

The only AT motors I have ever had a problem with are D15s. Of 2 D15-4s, one had a 7-second delay (which nearly destroyed my Deltie Thunder) and one at least 5.

I have had 2 D21 (-4 and -7), 3 E18-4, 1 E15-4, 1 F12-3, 1 F23-4, 1 G78-7, and 1 H128-M, all with delays accurate to under a second.

I think the D15 is just cursed. Or perhaps it's that the D15 fuel grain is so short, and so the igniter is almost 1.5" away from the delay grain (because you're supposed to tape over the end of the grain). That means that the delay grain will not be ignited by the igniter, and instead by the fuel grain istelf, which may take a while - perhaps a second, or more, thus leading to a longer delay time.

I suspect the same problem may exist for 29mm E loads, since they only fill up a third of the casing. Anyone got evidence of that?

I don't fly AT much anymore but that would probably be the case.

Ben

 

[n3tjm]

I would love to see Pro18's and Pro24's. =) It would be nice to be able to buy 18mm and 24mm composites from a company other than Aerotech whom pretty much states that their motors will fail one way or another a year after you buy them. I need to look it up, but does Aerotech's warranty cover delay time issues? They should. CTI does on a case to case basis.

[rant]
Just got started using pro29's this year (so far only got the 4g case and flown a H170) but have replaced all my Aerotech 38 and 54mm stuff with AMW and CTI stuff (Dont have CTI in 54 yet). Biggest issues I have is it is harder to get CTI stuff. Not that many vendors carry their motors, and the ones that do don't seem to offer much of a discount or are vendors that I avoid unless I have no choice to buy from. AMW loads was easy for me to get back when they were in NH, and I have placed once large order with Paul early last year to stock up on Pro38 loads and an AMW 54mm J load. Pauls gone, but Robert DeHate is running that show now. A trip to Salem, MA is not practical for me to do when I want loads, but he does come to some of the CMASS launches so I have access to loads then. And sometimes he hands me loads to sell for him, which I have quickly sold. If I had the money, I would stock up on Pro29 and 38 stuff to sell at CMASS launches too because every single launch since the last one Robert has been able to get to people have asked me if I had any to sell.
[/rant]

 

[MarkH]

Sorry to hear about the badluck delays.

I've probably flown about 40 AT loads (D-H) in the last 1.5 years and have only had late delays on two E16-4 loads which were more like a 7 sec delay both times. I flew 2 D15 4s, a g71-7, and 3 G53-7s in the last year all with accurate delays.

 

[NjCo]

My personal opinion. people may not like what I have to say. but I hope at least a few of them listen to it and learn from my mistakes, or bad choices. I don't want to hurt anyone, I want them to know what really happens. Maybe save them a Crashed rocket or at least a headache.

And keep it up too. We are certainly listening. After all isn't that one of the big reasons for a forum? We learn things from others that maybe we wouldn't have figured out on our own. I've been around the block a few times so to speak so I'm able to offer my share of advice and knowledge but so far my experience has only been with low power rockets. There isn't a week that goes by when I don't pick up some little tidbit from someone here though and in the end that's why I keep coming back. One of these days I'll break into mid power rockets and this is just the type of advice I'm looking for. Anything that lets me build better, fly safer and recover the rocket I've put hours of time into in one piece and able to fly again is what I'm after. Bring it on cause I'm all ears!

 

[Pat_B]

Can't remember the exact reload I used but I had an excessively long delay that destroyed my Executioneer a few months ago. It was also embarrassing because it was in front of a group of scouts for a demo launch. Made us look pretty stupid actually.

We built new demo rockets based upon designs that fly on BP motors and clusters so that we can have reliable flights- best decision we've ever made to avoid the embarrassment of hoping the delay is what it says it is.

There's a reason that the AT motors have a reputation for flaky delays and that's because it's true.

 

[stickershock23]

Can't remember the exact reload I used but I had an excessively long delay that destroyed my Executioneer a few months ago. It was also embarrassing because it was in front of a group of scouts for a demo launch. Made us look pretty stupid actually.

We built new demo rockets based upon designs that fly on BP motors and clusters so that we can have reliable flights- best decision we've ever made to avoid the embarrassment of hoping the delay is what it says it is.

There's a reason that the AT motors have a reputation for flaky delays and that's because it's true.

That always stinks when a bunch of prospective new rocketeers are watching and you have a failure.

Now if we could only get Aerotech to realize that. I think they are spending to much time trying to make NEW stuff to care about what we really need. Poor customer relations....

 

[Garoq]

Earl Nightingale once said something like this:

Great attitude=great results
Mediocre attitude=mediocre results
Poor attitude=poor results

Static test of a production D15-4T taken out of inventory:

[YOUTUBE]kh1OAqbywj4[/YOUTUBE]

Karl must've had a great attitude.

 

[Garoq]

BTW Karl tested the other two reloads in the pack, one was 4.3 seconds and the other was 4.5 seconds.

 

[Pat_B]

So my Executioneer's nose cone that was in a hundred pieces in the mud must have had a bad attitude? Aerotech's Hot Rockets

 

[stickershock23]

So my Executioneer's nose cone that was in a hundred pieces in the mud must have had a bad attitude? Aerotech's Hot Rockets

No before every Aerotech launch you must get on the ground fold your legs up and repeat ofter me..

"ooooohhm oooohhmm goood rocket motor, I love you soooo much... i am so happy to fly you"

Did you listen in the video posted. I swear i heard "much better that time" in the background. much better than what? maybe ones that the delays wern't right. or Karl's attitude?

I'm screwed. if good attitude means a good launch, Every rocket I fly is going to crash or worse.

 

[daveyfire]

BTW Karl tested the other two reloads in the pack, one was 4.3 seconds and the other was 4.5 seconds.

I've always wondered about the accuracy of the pyro delays in the "internally spaced" motors like the D15T and E16W, due to the possible pressure variations in the long tailoff from the really short c-slot grain and the large empty internal case volume. (Train of thought: slag deposition in the small nozzle throat during the burn leads to slightly different end throat diameter, combining with regressive thrust curve and isentropic blowdown at thrust termination to lead to slightly unpredictable pressure variations during delay burn. I'm probably overthinking this, since variations have been observed both in slagging and non-slagging propellant types.)

Still, I'm consistently amazed that pyro delays come out even this close. I think perhaps the flight profiles which these motors see (lifting larger and/or draggier model rockets to low altitudes on smaller fields) exacerbates the problem a bit; things happen closer to the ground, thus leaving a little less room for error

(For the record, I've never been victim of a "bonus delay" and I've flown more 24/40s and 29/40-120s than I can count... so at least 20 )

 

[sylvie369]

I can't wait 'til you guys see the back cover of this month's Sport Rocketry.

 

[Garoq]

For the record, I've never been victim of a "bonus delay" and I've flown more 24/40s and 29/40-120s than I can count... so at least 20

Interesting...you must have a great attitude!!

 

[Garoq]

I can't wait 'til you guys see the back cover of this month's Sport Rocketry.

Glad you like it.

 

[daveyfire]

Interesting...you must have a great attitude!!

I do what I can! :cyclops:

(and I'm disappointed at the moment that I don't get SpRocketry anymore... you guys should post an archive of ads to the resources section of the AT website, some of them are pretty entertaining!)

 

[stickershock23]

I've always wondered about the accuracy of the pyro delays in the "internally spaced" motors like the D15T and E16W, due to the possible pressure variations in the long tailoff from the really short c-slot grain and the large empty internal case volume. (Train of thought: slag deposition in the small nozzle throat during the burn leads to slightly different end throat diameter, combining with regressive thrust curve and isentropic blowdown at thrust termination to lead to slightly unpredictable pressure variations during delay burn. I'm probably overthinking this, since variations have been observed both in slagging and non-slagging propellant types.)

Still, I'm consistently amazed that pyro delays come out even this close. I think perhaps the flight profiles which these motors see (lifting larger and/or draggier model rockets to low altitudes on smaller fields) exacerbates the problem a bit; things happen closer to the ground, thus leaving a little less room for error
(For the record, I've never been victim of a "bonus delay" and I've flown more 24/40s and 29/40-120s than I can count... so at least 20 )

These are great theories, and probably true. I expect delays to vary by 2 or 3 seconds. the ones I hate are the ones that go 3 to 5 seconds or even more off what they are supposed to.

I have flown tons of them myself and fired more than I can count. and talked to dozens of people that have had "bad/bonus delays" I have seen MANY that were way off.
(remember I used to do all of AT's warranty work [also remember I am now in no way affiliated with them, so this is my opinions not AT's])

Maybe since we know they are not correct all of the time. NAR/TRA should stop certifying delay times. then there is no worry as to right or wrong. you get what you get. it might be what it says it might not. In other words. tell people delays are not an exact science, Motor manufacturers try their best to make them what they say, but there is just NO WAY to make them perfect. If you decide to use them its at your own risk.

 

[Garoq]

I do what I can! :cyclops:

(and I'm disappointed at the moment that I don't get SpRocketry anymore... you guys should post an archive of ads to the resources section of the AT website, some of them are pretty entertaining!)

That's a great idea...and to kick it off, here's the one we're talking about:

 

[sylvie369]

Glad you like it.

I do. I think "we do these things because they're hard" is one of the all-time great quotes, and I wrote a column a few years ago (in Extreme Rocketry) praising the fact that rocketry provides "opportunity for failure". If it's easy, where is the sense of accomplishment?

Of course that means I thought that the "who can put together a reload fastest" stuff was pretty silly.

Anyway, I love the ad. I laughed my aft closure off when I saw it.

 

[Pat_B]

The bonus delay problem especially affects models that are flown to a lower altitude (obviously). I think the problem is less of a concern with the larger motors where a bonus delay isn't going to result in a crash. Furthermore, the high powered rockets are built more robust to be able to handle these sorts of problems; maybe with a short zipper.

But I've learned my lesson with using reloads on larger mid-powered rockets that were designed for lower altitude flights (such as doing demo flights in a constrained area). Simply not enough margin for error on the delay-- a few seconds or so longer makes a big difference and there are more reliable solutions in the BP market.