Launch Rod Velocity

[DeeKaej]

Is there a calculation for the required launch rod velocity which is needed to
get a stable start condition?
Greetings from Germany
Carpe Diem

[Yves Lacombe]

On 29 Nov 1997 14:38:38 GMT, dee...@aol.com (DeeKaej) wrote:
>Is there a calculation for the required launch rod velocity which is needed to
>get a stable start condition?

Well -- if you take a program like WinRasp to do your sims, most
people aim for 30 fps (feet per second) off the rod, which is around
9 m/sec in metric. This assumes a meter long rod. If you double
the length of the launch rod, you're giving yourself a bigger margin
of safety. :-)

--
Yves || http://www.game-master.com/yves || Prez of the A3MAQ

[Ed]

DeeKaej wrote:
>
> Is there a calculation for the required launch rod velocity which is needed to
> get a stable start condition?

> Greetings from Germany
> Carpe Diem

For stable flight, make sure CG is forward of CP. You may also, consider
some fins. I have heard of some excellent flights using Estes rockets as
boosters. For technical expertise here, contact Rich Burch, "Master of
the 1/8" Rod Launch". Sorry Rich, couldn't resist.
....Ed

[mah...@wtco.net]

Okay but if I want the slowest most "realistic" launch what is the
minimum I can get away with in a fixed fin non-gyro stabilized rocket?

Koen

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[Yves Lacombe]

On Sun, 30 Nov 1997 09:21:22 -0600, mah...@wtco.net wrote:
>Okay but if I want the slowest most "realistic" launch what is the
>minimum I can get away with in a fixed fin non-gyro stabilized rocket?

Some people have gone as low as 20 fps with no wind whatsoever. If
you want a slow liftoff, better use a long launch rod or better yet, a
very stiff launch rail or a tower launcher. I'd rather have safe and
moderately fast to slow, impressive and dangerous any day.

--
Yves || http://www.game-master.com/yves || A3MAQ Prez
CAR#S255, A3MAQ#SQ026, NAR member, TRA Pending. L1 cert.

[LarryC]

The short answer is "Yes." You can mathematically figure the launch rod
speed required for a stable flight on a calm day.

Once again... the speed at which a rocket is aerodynamically stable depends
on the rocket, but in all decent rockets, that speed is very small. You can
toss a rocket onto your living room couch and expect it to follow its nose.
That is not the greatest importance of a launch rod (despite the level II
exam). You want good launch rod speed to reduce gravity turning in the
early stages of flight. The angle wrt the horizontal reduces continuously
during the flight, and an early quick reduction flattens the trajectory
very radically - a prang may even result.

To figure the correct speed, try an off-vertical simulator. Use a realistic
launch rod length, and a launch angle that you expect to use. (You may want
to vary this angle a bit to check sensitivity. For example, if you specify a
vertical launch, you will erroneously discover that rod speed is irrelevant.)
Observe the trajectory with different motors, and choose acceptable ones.
Note the speed if you wish.

Regards
-Larry (When the wind blows, all bets are off) C.