Aerotech Motors and Incorrect Delays

Aerotech Motors and Incorrect Delays

Post by Chris McKerna » Sat, 07 Sep 1996 04:00:00



Hello,

Is there anyway to accurately determine the delay on a Aerotech motor?

The feedback I'm always rec'ving is that the delays are way way off.

Any help on properly estimating (or preferably calculating) the delays
would be appreciated.

Thanx,

Chris

 
 
 

Aerotech Motors and Incorrect Delays

Post by Karl von Jen » Sat, 07 Sep 1996 04:00:00



Quote:

>Hello,

>Is there anyway to accurately determine the delay on a Aerotech motor?

>The feedback I'm always rec'ving is that the delays are way way off.

>Any help on properly estimating (or preferably calculating) the delays
>would be appreciated.

>Thanx,

>Chris

Motor delays are "allowed" a certain variance, and usually they'll err on
the side of a longer delay than a shorter one. There's no way to tell by
looking whether it will delay longer than it's rating, you have to roll
the dice. Or you can go to an electronic ejection (via ALTS2 controller),
but these also have their failures.

I usually err on the short side myself. My rockets are fairly rugged so
if it ejects just before apogee, that's better than halfway to the ground
IMHO.

Good luck, not that my advice should help...

Karl

 
 
 

Aerotech Motors and Incorrect Delays

Post by Mike Krug » Sat, 07 Sep 1996 04:00:00



Quote:

> Hello,

> Is there anyway to accurately determine the delay on a Aerotech
> motor?

> The feedback I'm always rec'ving is that the delays are way way off.

> Any help on properly estimating (or preferably calculating) the
> delays
> would be appreciated.

> Thanx,

> Chris

OK, this gets a little complecated,

First take the time, in seconds, of the delay and multiply by the
Hubble constant divided by 56 miles per second per degree Celcius.

Take that number and invert it.  Then take the reciprocal.

Square this result and multiply by the diameter of the delay, not
the casing, and subtract the lot number of the reload, coverted in
decimal.

This result will give the root-mean-square of the standard deviation
of the percent error of the delay.

This gives and answer in mmHg * sec * m * Hz / ft*lb / N^2
Which of course simplifies down to sec

Got it?  :)

mike

 
 
 

Aerotech Motors and Incorrect Delays

Post by C. James Co » Sat, 07 Sep 1996 04:00:00


Delays on motors certified by the NAR must comply with a standard
that says they must be within 20% or 1 second, whichever is greater.

Full motor data, with listings of the designations vs. actual tested
values are available from NARTS (NAR Technical Service).  I believe
the product is "EDS - 1".  See the NARTS catalog off the NAR web page
at http://www.nar.org

Good luck,
-J

 
 
 

Aerotech Motors and Incorrect Delays

Post by Konrad Hambri » Sun, 08 Sep 1996 04:00:00



Quote:

>Hello,

>Is there anyway to accurately determine the delay on a Aerotech motor?

>The feedback I'm always rec'ving is that the delays are way way off.

Chris --

All in all, I have had pretty good luck with the delays
as long as motor ignition was nominal.

I have had two ejaculation charges 'go off' real early on
F25-6's where I was trying out a Hot ignitor that was just
about too large to force into the nozzle -- I think I cracked
the delay coulmn by overpressuring the combustion chamber.

I have had a couple Black Jack's go off a little early when
the motor chuffed -- this I attributed to delay column
ignition before the motor caught fire ( of course the 2-H97's,
2-H73's and 1-H112 where I experienced blown nozzles had real
long delays -- they still havn't fired ;-)

I had a scary F50-6 flite last weekend in a 25 oz dry-mass
rocket where the delay was actually 9 sec -- mislabeled motor ??

I zippered my Astrobee last spring when I brain farted and
used an H180-Long when I meant to fly an H180-Medium
( 14 secs instead of 10 secs ):

Other than that, I have had great luck with AT 18,24,29,38
and 54 mm motors.  

Just be sure to use a hot ignition system and stuff the
ignitor all the way up the chamber ... feel for the delay
grain with the ignitor.  IMO not all, but most delay problems
are op-err and not a product QC problem.

Quote:
>Any help on properly estimating (or preferably calculating) the delays
>would be appreciated.

To estimate delay times for rockets with various motors,
go get a ( free ;-) copy of Larry Curcio's DigiTrak from:

   ftp://sunsite.unc.edu:/pub/archives/rec.models.rockets/DIGITRAK/

The program includes source code for compiling and playing with
and there is a dtfordos.zip -- ready to run DOS code.  I think
there is even a MAC version ( Larry ? )

There are several sim programs on sunsite but Larry's is the most
versatile -- it predicts, optomized mass and does temp***back-
tracking.

Virtual rocketry -- it's cheaper but not nearly as thrilling ;-)

-- kjh
--
------------------------------------------------------------

310 Third Ave - Suite C21    |  work:   (619) 585 8611     |
Chula Vista, CA  91910       |  home:   (619) 423-4451     |

 
 
 

Aerotech Motors and Incorrect Delays

Post by Duane » Mon, 09 Sep 1996 04:00:00


Konrad Hambrick wrote

< Snip>

I have had two ejaculation charges 'go off' real early. . .

< Snip>

Well now, I knew flying rockets was exciting but is it that exciting? ; )

Duane

 
 
 

Aerotech Motors and Incorrect Delays

Post by Konrad Hambri » Mon, 09 Sep 1996 04:00:00



Quote:

>Konrad Hambrick wrote

>< Snip>

>I have had two ejaculation charges 'go off' real early. . .

>< Snip>

>Well now, I knew flying rockets was exciting but is it that exciting? ; )

Blowing the cork early, while embarrasing, is always exciting ;-)

-- kjh
--
------------------------------------------------------------

310 Third Ave - Suite C21    |  work:   (619) 585 8611     |
Chula Vista, CA  91910       |  home:   (619) 423-4451     |

 
 
 

Aerotech Motors and Incorrect Delays

Post by Bob Kapl » Wed, 11 Sep 1996 04:00:00


Quote:

> Is there anyway to accurately determine the delay on a Aerotech motor?

Fire it on a test stand and measure it with a stop watch?

        Bob Kaplow      NAR # 18L       TRA # "Abort, Retry, Fail?"

 
 
 

Aerotech Motors and Incorrect Delays

Post by Rckt J » Wed, 11 Sep 1996 04:00:00


All this griping is well and fine, but how many of you have reported the
failures?

There's even a MESS form on the NAR web page: www.nar.org

-J

 
 
 

Aerotech Motors and Incorrect Delays

Post by Douglas Caske » Wed, 11 Sep 1996 04:00:00




Quote:
>Is there anyway to accurately determine the delay on a Aerotech
>motor?

 Not unless you live in Las Vegas. <g>

Quote:
>The feedback I'm always rec'ving is that the delays are way way
>off.

 I wouldn't say they are "way way" off. I don't know if I'd even go
as far as saying they are way off, except for a few cases here &
there where one might explain the delays being of on reloads due to
the (improper?) motor assembly. For example.. I recently witnessed
a case where the flyer most unknownly swapped a 7sec delay from 1
kit with a 4 sec from another. In this case 3 secs was way off as
the rocket lawn darted. Yes there are a few motors where the delay
may be off by some factor, but I'd say it's usually consistant for
a given motor. In any case where I see most delay inconsistantcies
being a problem is with the blackjack motors. They're a problem not
only because the delays tend to be longer than given, but because
the flyer has underestimated the altitude or the rocket
weathercocks, both of which give the "perception" the delay was
"way way" too long as the rocket crashes before ejection.

Quote:
>Any help on properly estimating (or preferably calculating) the
>delays would be appreciated.

 Fly, Fly, Fly, and fly some more. The more you fly the more you
get to know how each motor/delay/rocket combo performs which will
help you to better achieve success in the future.
 Doug Caskey

http://members.gnn.com/RocketWeb/RocketWeb.htm
 
 
 

Aerotech Motors and Incorrect Delays

Post by Jerry Irvi » Thu, 12 Sep 1996 04:00:00



Quote:

> All in all, I have had pretty good luck with the delays
> as long as motor ignition was nominal.
> I have had two ejaculation charges 'go off' real early on
> F25-6's where I was trying out a Hot ignitor that was just
> about too large to force into the nozzle -- I think I cracked
> the delay coulmn by overpressuring the combustion chamber.

VERY unlikely.  Because:  why then did you NOT crack propellant too?
QC

Quote:

> I have had a couple Black Jack's go off a little early when
> the motor chuffed -- this I attributed to delay column
> ignition before the motor caught fire ( of course the 2-H97's,
> 2-H73's and 1-H112 where I experienced blown nozzles had real
> long delays -- they still havn't fired ;-)

QC

Quote:

> I had a scary F50-6 flite last weekend in a 25 oz dry-mass
> rocket where the delay was actually 9 sec -- mislabeled motor ??

Common AT mistake.
QC

Quote:

> I zippered my Astrobee last spring when I brain farted and
> used an H180-Long when I meant to fly an H180-Medium
> ( 14 secs instead of 10 secs ):

Op Err

Quote:
> Other than that, I have had great luck with AT 18,24,29,38
> and 54 mm motors.  

> Just be sure to use a hot ignition system and stuff the
> ignitor all the way up the chamber ... feel for the delay
> grain with the ignitor.  IMO not all, but most delay problems
> are op-err and not a product QC problem.

3 of 4 (types of) failures were QC, therefore I disagree with your summary
statement.

Quote:
> -- kjh

Jerry

--

Box 1242, Claremont, CA 91711 USA
Opinion, the whole thing.

 
 
 

Aerotech Motors and Incorrect Delays

Post by David Beav » Fri, 13 Sep 1996 04:00:00


Quote:


>> Is there anyway to accurately determine the delay on a Aerotech motor?

>Fire it on a test stand and measure it with a stop watch?

I simply don't let the delay train and ejection charge anywhere near the motor
anymore - I've found altimeter based ejection to be MUCH more reliable. I made
the switch after a premature ejection at LDRS last year (my Quantum Leap on a
long burn 54 MM motor popped the chute at about 100 feet and proceeded to loop
the loop over the crowd for the rest of the three seconds or so of boost, then
rained bits down all over the pad area....). Altimeters aren't that expensive
when you compare them to a destroyed rocket, they seem to work pretty much
every time. And, once you've got 'em working, doing two stage recovery isn't
at all difficult......

.............dave

....dave (Not a spokesman for) Microsoft Corp.