T-engine Staging (Was: Beginner's Mistake...)

T-engine Staging (Was: Beginner's Mistake...)

Post by Geoff Chest » Tue, 19 Sep 1995 04:00:00



Hi, All!


Quote:
> I built my first 2-stage rocket, an Estes Mini-Cobra.
> First flight on a A10-0T and A3-4T (I think -- whatever the recommended
> engines were, sort-of) ended in a "prang".

|stuff deleted|

I built one of these recently and had a similar experience last weekend
in Manassas.  I used an A10-0T and a 1/2A3-4T combo. They were taped
together snugly, etc. so they *should* have worked...but I wound up with
a bent bird after the upper stage failed to air-start.  I subsequently
repaired the U/S and fired it successfully using the same motor that
didn't light in flight.

One of the other participants mentioned that the A10-0T is known for this
problem, and that due to the grain structure by the time the motor burns
out there's not enough forward pressure to send burning propellant into
the nozzle of the upper stage motor. I dunno...the booster stage seperated
with an audible "Pop". He offered me the use of an A3-0T which isn't
made anymore. I declined as I decided one prang was enough for a day...

Frankly I think in retrospect that the failure was benevolent in my case.
The booster took the rocket up a couple hundred feet, and had the 2nd
stage lit I would have had to kiss the bird goodbye! On the 2 subsequent
flights on the 1/2A single motor the lil' *** went nearly outta sight!

Anybody know why Estes doesn't offer the A3-0T anymore? It sounds like
this was a much more "reliable" booster motor. I'd love to fly the Mini-
Cobra as a 2-stage, but I don't want to try it on an A10 anymore....

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T-engine Staging (Was: Beginner's Mistake...)

Post by The Silent Observ » Tue, 19 Sep 1995 04:00:00




Quote:

>I built one of these recently and had a similar experience last weekend
>in Manassas.  I used an A10-0T and a 1/2A3-4T combo. They were taped
>together snugly, etc. so they *should* have worked...but I wound up
with
>a bent bird after the upper stage failed to air-start.  I subsequently
>repaired the U/S and fired it successfully using the same motor that
>didn't light in flight.

>One of the other participants mentioned that the A10-0T is known for
this
>problem, and that due to the grain structure by the time the motor
burns
>out there's not enough forward pressure to send burning propellant into
>the nozzle of the upper stage motor. I dunno...the booster stage
seperated
>with an audible "Pop". He offered me the use of an A3-0T which isn't
>made anymore. I declined as I decided one prang was enough for a day...

I might mention that I saw (a couple months ago) a bird CHAD-staged as a
Quote:
>three< stage with these motors -- A10/A10/A3, and all motors ignited --

there was also a three-stage with actual fins that did the "burn the
booster" mini-engine trick, but again, the uppers all ignited.  I think
the problem is just that occasionally, the hot particles that do the
work don't go in the hole!

Quote:
>Frankly I think in retrospect that the failure was benevolent in my
case.
>The booster took the rocket up a couple hundred feet, and had the 2nd
>stage lit I would have had to kiss the bird goodbye! On the 2
subsequent
>flights on the 1/2A single motor the lil' *** went nearly outta
sight!

Yep.  If you get a two or three stage mini bird, especially
minimum-diameter as most such are, to stage correctly, you likely won't
see the ejection.  One suggestion: don't even >think< about putting a
parachute in one of these; use streamers only, and smallish ones at
that.  They come down much closer to the pad that way...

Quote:
>Anybody know why Estes doesn't offer the A3-0T anymore? It sounds like
>this was a much more "reliable" booster motor. I'd love to fly the
Mini-
>Cobra as a 2-stage, but I don't want to try it on an A10 anymore....

My understanding is that there was some concern over the low thrust
lifting the weight of a two or three stage bird, getting it up to speed
before if leaves the rod; higher thrust is needed for this, and the A10
is the only port-burner in the mini line.  These engines are just too
small for higher thrust in end-burners.

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T-engine Staging (Was: Beginner's Mistake...)

Post by Jonathan Sivie » Thu, 21 Sep 1995 04:00:00



Quote:
>This is strange. I have yet to have an A3-4T light from the booster in one
>attempted flight and two bench-tests. I have not yet had a failure of the
>1/2A3-4T to light from the booster, however! This is also in one flight and
>two bench tests. Would you like to trade your A3's that work for my 1/2A3's?

   Have these been different A3-4T's, or trying to get the same one to light
in multiple attempts?  It does happen occasionally that there will be a thin
layer of clay (from the nozzle) covering the propellant and thus it won't
light no matter what you do, but another motor from the same batch will work
fine.  It can also happen that when an ignitor burns, but fails to light the
motor because it wasn't in contact with the propellant, that a thin layer of
carbon will be deposited on the propellant and keep it froms being ignited
by futher attempts.  Both of these problems can many times be corrected by
using a sharp pointed tool (pin, knife, etc.) to scrape the insulating layer
off.  In order for an upper stage motor to light it has to be held together
with the booster stage for just the right amount of time.  Long enough for the
burn-through particles to get into the nozzle and ignite the motor, but not
so long that it interferes with the burning of the upper stage.  Getting this
correct amount of time can be something of an art.

Jonathan

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T-engine Staging (Was: Beginner's Mistake...)

Post by Rob Maste » Fri, 22 Sep 1995 04:00:00



Quote:
>Hi, All!

>> I built my first 2-stage rocket, an Estes Mini-Cobra.
>> First flight on a A10-0T and A3-4T (I think -- whatever the recommended
>> engines were, sort-of) ended in a "prang".
>|stuff deleted|
>I built one of these recently and had a similar experience last weekend
>in Manassas.  I used an A10-0T and a 1/2A3-4T combo. They were taped
>together snugly, etc. so they *should* have worked...but I wound up with
>a bent bird after the upper stage failed to air-start.  I subsequently
>repaired the U/S and fired it successfully using the same motor that
>didn't light in flight.

<Snip>

As an aside, and for a bit of fun, try the ultimate CHAD stage -

An A10T-0 -> A8-5 (or whatever)

On a SuperNova (empty payload) you get staging at about 50'. Great fun, and
you get to really see what it's all about.

How? Real easy...Take your sustainer, and fit it as normal. Now take your
booster, and just press it in to the base of the sustainer... Done!

--

Then someone said to me "It's fabulous you're still around today, you've both
made such a little go a very long way". - Pet Shop Boys

 
 
 

T-engine Staging (Was: Beginner's Mistake...)

Post by C. D. Tavar » Sat, 23 Sep 1995 04:00:00


Quote:

> As an aside, and for a bit of fun, try the ultimate CHAD stage -

> An A10T-0 -> A8-5 (or whatever)

> On a SuperNova (empty payload) you get staging at about 50'. Great fun, and
> you get to really see what it's all about.

Um... I still remember the Spirit of NOVAAR at the Michigan NARAM --
D13-kaboom to A10-0 CHAD to F100.  Scary.
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T-engine Staging (Was: Beginner's Mistake...)

Post by kaplo.. » Sat, 23 Sep 1995 04:00:00



Quote:
> Um... I still remember the Spirit of NOVAAR at the Michigan NARAM --
> D13-kaboom to A10-0 CHAD to F100.  Scary.

There was NO Michigan NARAM, it was all just a very bad dream :-(


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        Apollo 13? Hell, I haven't even seen 1 thru 12 yet!

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T-engine Staging (Was: Beginner's Mistake...)

Post by Adrian Hu » Thu, 28 Sep 1995 04:00:00



Quote:
>Geoff Chester writes:

>>> First flight of mini-cobra on an A10-0T and A3-4T ended in a "prang".

>>I built one of these recently and had a similar experience last weekend
>>in Manassas.  I used an A10-0T and a 1/2A3-4T combo. They were taped
>>together snugly, etc. so they *should* have worked...but I wound up with
>>a bent bird after the upper stage failed to air-start.

>Hi, it's me again. I'm (sort of) glad to hear that I'm not alone in having
>problems with these mini engines and staging.

>This is strange. I have yet to have an A3-4T light from the booster in one
>attempted flight and two bench-tests. I have not yet had a failure of the
>1/2A3-4T to light from the booster, however! This is also in one flight and
>two bench tests. Would you like to trade your A3's that work for my 1/2A3's?

I'll trade your 1/2A3-4T's for my 1/2A3-2T's. :-)  I've also had problems
with double-staging my Mini-Cobra.  The very first time I tried it, all
by myself, I taped a 1/2A3-2T to a A10-0T and it worked perfectly.  The
second time I tried it was at a public display; the upper stage, a 1/2A3-2T
from the same pack as the first one, failed to ignite and the whole thing
came down at great speed.  The body tube was bent and slightly torn, but I
managed to get it into a flyable condition with some sticky tape.  Then I
tried to launch it again and it did the same thing.  Suspecting that there
may be something wrong with the 1/2A3-2T engine, I launched it single-stage
using the same engine by itself, and it flew nicely (especially considering
its body tube is now double-wrapped with sticky tape :-).  The Cobra is now
a veteran of two lawn-darts. :-)

Quote:
>I tried the bird on the same engine combo you used and mine *did* go out of
>sight! Upper stage exit stage left.   :^(

Now you know why I was using a 1/2A3-2T for the upper stage. :-)

Quote:
>            I'm wondering if it might have had an ejection failure? That
>little streamer always seemed just shy of getting hung up on the shock-cord
>mount. The motor shouldn't have ejected, as it was a *snug* fit.

I have often found that the streamer ejects but doesn't unroll.  You have
to roll it *tight* to get it into a BT-5, and once it is rolled up that
tight, it likes to stay that way.  Mine does, anyway.

Quote:
>Anyway, I'm now thinking about what to build to replace it. Maybe
>motor-ejection and tumble recovery, like the Mosquito, only in a longer
>rocket? Would streamerless recovery work, just popping the nosecone off?

It would probably work as well as your Mini-Cobra. :-)  Personally, I'd
recommend something a little bigger, e.g. a Wizard - my other small
rocket.  That is also quite a veteran now because it's usually the first
thing I fly, to see if the wind is doing anything odd a couple of hundred
feet up.  I've made an adaptor using a spent standard engine casing so I
can use mini-engines in the Wizard and it flies nicely on an A10-3T.

--
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T-engine Staging (Was: Beginner's Mistake...)

Post by C. D. Tavar » Sat, 30 Sep 1995 04:00:00


Quote:

> >Um... I still remember the Spirit of NOVAAR at the Michigan NARAM --
> >D13-kaboom to A10-0 CHAD to F100.  Scary.
> Uhhmmm, but how was the F100 ignited? And did it work? _And_ what did
> the rest of it look like?

A 14-year-old epoxied the A10 into the F100's nozzle... crooked.

It worked, if you didn't mind the 360 degree vertical loop it took right
after the F100 ignited.
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