Or at least I am sure they are questions that have been answered many times
and possibly in many ways before, it's just that I'm having a little trouble
finding the answers at the moment...

Since my first (and so far only) model bit the dust the other week, I have
decided to reincarnate the salvagable parts (fins, nose, motor mount) into
some new tubes.  But to be a bit more interesting about it (and since it was
apparently a model of a multistage vehicle and had two sets of fins anyway)
I thought I would turn it into a two-stage model.

First I was going to light the upper stage electronically.  I couldn't quite
work out where I was going to put the electronics.  I'd built a payload bay
for an altimeter I'd had for a present, and I'd thought of packing it in
there.  Then I was a bit confused about how to reliably run wires between
two parts of the rocket designed to separate.  I read about a bit, and
discovered that the gubbins is most often located in the void between the
motor tube and the main body.  That space in my model is tiny, 24mm motor -
BT60 body tube, so I can't do that.  So I've gone over to a design that
lights the upper stage using the ejection charge of the booster.  Today's
design has the motor tub in the booster stage extended forward so it slots
over the protruding end of the motor in the upper stage.  (Just thinking
about that, I'll have to add a slot to accommodate the engine hook).  I've
done it that way for two reasons: first to try to get as much of the stuff
to hit the back of the upper stage motor as possible; and second to try to
protect the recovery device (probably a streamer) from the ejection charge
and from the initial exhaust of the sustainer motor; and third (three
reasons) because I know no better.

Question 1:  Is that protection likely to be enough, or will I have to
shield the streamer some other how as well?
Question 1b:  In knowing no better, have I missed a problem with doing it
this way?

At the moment I'm half convinced that lighting the sustainer motor limits me
to BP motors for the upper stage.  For now, that's not so much of a big
deal, but I just know that later on I'm going to want to send the model as
high as I possibly can.

Question 2:  Is it possible to light composite motors using some chemical
means from the ejection charge of another motor?  E.g. can I light a fuse
either with an ejection charge, or off the top of a delay element which has
enough oomph to light a composite motor (e.g. Aerotech AP) if I stuff the
other end up into the motor core?

The next problem is that my simulations show that in all but the stillest
conditions a BP motor for the booster doesn't get it flying quickly enough
soon enough for it to fly reliably straight up, so I'd probably want to use
a composite motor for the booster from day one.  The only trouble is, I
can't get motors with zero delay to light up the upper stage.  The motors I
have used (F24W-7 & F24W-4) in flying the model before C-day have delay
elements which differ in length.  I suppose I can take one of those, e.g.
the 4s element, and shorten it further, e.g. with a flat bottomed drill bit,
to get the delay I want (as close to zero as possible without going
negative).

Question 3a:  I am asking to go up in flames by drilling out the delay
element material?  (I suspect not, since I have seen other references to it
but no details).  What do I need to be careful with?  Should I limit myself
to doing it by hand to restrict the cutter speed?
Question 3b:  The difference in length between a 7s delay element and a 4s
delay element is about 2.3mm.  Does that mean if I take another 2.3mm off
the 4s element I end up with a 1s element?  (The elements are much thicker
than 0.75mm/s burn rate would suggest, but I think the part that burns while
the motor is lit probably burns much faster than the rest).  Or are the two
elements likely to be of a different composition?

That'll do for now.

Thanks for all the helpful answers (I hope).

Neil

Question 2: Is it possible to light composite motors using some chemical
means from the ejection charge of another motor? E.g. can I light a fuse
either with an ejection charge, or off the top of a delay element which has
enough oomph to light a composite motor (e.g. Aerotech AP) if I stuff the
other end up into the motor core?

The next problem is that my simulations show that in all but the stillest
conditions a BP motor for the booster doesn't get it flying quickly enough
soon enough for it to fly reliably straight up, so I'd probably want to use
a composite motor for the booster from day one. The only trouble is, I
can't get motors with zero delay to light up the upper stage. The motors I
have used (F24W-7 & F24W-4) in flying the model before C-day have delay
elements which differ in length. I suppose I can take one of those, e.g.
the 4s element, and shorten it further, e.g. with a flat bottomed drill bit,
to get the delay I want (as close to zero as possible without going
negative).

Question 3a: I am asking to go up in flames by drilling out the delay
element material? (I suspect not, since I have seen other references to it
but no details). What do I need to be careful with? Should I limit myself
to doing it by hand to restrict the cutter speed?
Question 3b: The difference in length between a 7s delay element and a 4s
delay element is about 2.3mm. Does that mean if I take another 2.3mm off
the 4s element I end up with a 1s element? (The elements are much thicker
than 0.75mm/s burn rate would suggest, but I think the part that burns while
the motor is lit probably burns much faster than the rest). Or are the two
elements likely to be of a different composition?

I suggest you go along to a club flight if there is one near you. All
knowledge will then be yours.

Failing that there is a lot more traffic on the UKRA public forum for
which you can ask for a guest login without being a member.

Failing that, you can gap stage BP motors up to 8" or so, above which you
can use quickmatch. However, if your booster is only a bit longer than the
motor, it's quite routine to expect it to light the sustainer and to use
'tumble recovery', i.e. no recovery at all.

Complete details are on the Aerotech website.

Suggestion: Cluster two or three BP booster motors around the central
booster, each in its own pod. Light all on the ground. Boosters in
their pods will eject, booster in the middle will light the upper
stage.

"spacecadet" <nospam at (no spam) spacecadet.com> wrote in message
news:4JmdnQNabpSUQEDXnZ2dnUVZ8gOdnZ2d at (no spam) bt.com...
I suggest you go along to a club flight if there is one near you. All
knowledge will then be yours.

I had been down to a couple (it was certainly the easiest way to get to
a big enough, open enough field to fly without having to cross
everything that it all wasn't going to end up stuck up a tree
somewhere. I missed the last couple for various reasons, only some of
which were not having a model to fly with anymore, and now there are no
more (at least in that group) for some time, it seems. I'm sure I'll be
there again.

Failing that there is a lot more traffic on the UKRA public forum for
which you can ask for a guest login without being a member.

From ukra.org.uk, how do I find the forum? I've spent a little while
shuffling around the website and not found my way to it.

If you email the webmaster you will get a reply but give them a chance