NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/rec/models/rockets/3349

Text File | 1992-12-22 | 3.5 KB | 70 lines

Newsgroups: rec.models.rockets
Path: sparky!uunet!gatech!destroyer!med.umich.edu!umich.edu
From: [e-mail]  (Roger Wilfong)
Subject: Re: Other reloadables besides Aerotech? (Re: Info. about solid rocket-
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Date: Mon, 21 Dec 1992 22:14:00 GMT

In Article <[e-mail]> "[e-mail] (Iskandar Taib)" says:
> In article <[e-mail]> [e-mail] (Paul Campbell) writes:
> >In article <[e-mail]> [e-mail] writes:
>
> >>My only beef, because, I would like to fly altitude is the
> >>short burn times on all the ISP motors. This is a lousy
> >>thrust program if you are going for height, the v**2
> >>drag kills you at low altitudes.
>
> >I think that this is part of 'reloadable' technology - in order to keep
> >the casing temp. down they have to burn fast. An end-burning reload
> >would get really hot down the bottom and the case might deform before
> >it burned out, the motor mount might catch fire too.
>
> What about the Phoenix RMS loads? If I'm not mistaken these are F12 and
> G12s. The burn times are supposedly 4 and 8 seconds respectively. The
> pictures in Model Builder magazine show a reload pellet with a groove
> cut along a radius - from the center to the circumference. Doesn't sound
> like an end-burner to me....
>
> How does the delay and ejection charge fit on the RMS motors? (The
> Phoenix motor doesn't have one of course...)
>

I suspect that the truth lies somewhere between these two.

1)  In the Aerotech RMS motors, the part of the case that gets the hottest
  is around the delay element.  You don't notice it on the 24mm and 29mm
  motors because this portion of the motor is smaller in diameter.  On the
  18mm, this portion is just the same diameter as the rest of the motor.  On
  the 18mm motor, this portion gets hot enough to char a motor tube while
  the rest of the motor tube is unaffected.

  This same condition exists for the 13mm and 18mm disposables.  Since the
  disposables got through S&T, the maximum temp must be acceptable.  I
  suspect that this condition also holds for the ISP motors - but I have too
  little experience with them to say.


2)  The 32mm Phoenix motor uses end burn grains in the F and G range.  The
  slot refered to above is about 3/16-1/4" wide (and deep) and serves two
  functions; first, it provides a place to put the ignitor, and second it
  provides the starting spike in the thrust curve that gets the plane
  moving.

3)  Since the Phoenix motor is only F and G rated, it is probably dealing
  with lower pressures than a high power motor.  A reload with a time/thrust
  profile of an I-65 might very well heat the case to an unacceptable
  temperature.  Although I suspect not - if pheonolic can stand up to the
  pressure and temperature, the aluminum casing should also.  What may be
  required is a thicker cardboard insulator tube.
Any one know if Aerotech/ISP has investigated this?

If and when reloads come back, I'd sure like to see some longer burn times.
High thrust motors are great for lofting real payloads, but if you're just
lofting air in a sport model, the long burn times are more pleasing (and
I-65's are out of my budget range for a single, non-payload sport flight).