Estes D's

Estes D's

Post by DABH » Fri, 27 Oct 1995 04:00:00



The assumption is made (by Estes) that with the delay, the MAX LIFTOFF
WEIGHT would be less, due to the longer delay, and resultant ballistic
trajectory could be avoided.

In other words, if you used a model that needed just the 3-second delay to
 eject at apogee, then a 5-second delay would probably strip the chute,
and  quite possibly, a 7-second delay would "lawn-dart" into the ground,
destroying the rocket (just before the "POP!" of ejection.. ;^ ). The
booster has a higher rating because it has NO delay and thus is moving
much faster (greater momemtum) at staging. Recovery is not considered for
the -0 booster engine.

So what you are seeing is cautionary overkill by Estes. Use your own good
judgement.

David.
David A. Butcher
Sr. Global VSAT Support Engineer

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Estes D's

Post by The Silent Observ » Fri, 27 Oct 1995 04:00:00



Quote:

>Hi all,

>Could someone please tell me why the Estes D motors have
>different Max Lift Weights but all have the same total
>impulse, max thrust and propellant weight.

>Yea ok, so the D12-7 has 3.1grams of delay as against the
>0grams in a D12-0 but surely this cannot cause the D12-0
>to be able to lift 169.8grams more than the D12-7.

>If one accepts that the D12-0 is "more powerful" than the
>D12-7 ...... would this equate into more altitude, greater
>launch acceleration, or what .... and how?

The max liftoff weights are related to the expected flight
characteristics relative to the delay.  Let's say you have a model
that's light enough to fly on a D12-7 -- it'll be under the max liftoff
weight for that motor, if 7 is anything close to the right delay.

Thus, in order to have ejection somewhere near apogee (and there's a
little assumption about drag built into this, but it's a pretty safe
one), a D12-3 can fly a heavier model than a D12-5, which can still fly
a heavier model than a D12-7 -- and the assumption is that you'll stage
a D12-0 to another motor, and again select the delay to fit, but you can
fly an >awfully< heavy or draggy model on a D12-0/D12-3 stage combo...

So the difference in max liftoff weights is more to do with burnout
velocity and coast time, than with max thrust.  A single D12 could lift
a model very close to a pound and still have the peak thrust to
stabilize it on launch -- but you'd need a pretty short delay with a
single motor, single stage model that heavy.  OTOH, if you stage that
D12-0 to a D12-3, a one-pound model will get reasonable height and eject
fairly close to apogee.

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Estes D's

Post by Gran » Fri, 27 Oct 1995 04:00:00


Hi all,

Could someone please tell me why the Estes D motors have
different Max Lift Weights but all have the same total
impulse, max thrust and propellant weight.

Yea ok, so the D12-7 has 3.1grams of delay as against the
0grams in a D12-0 but surely this cannot cause the D12-0
to be able to lift 169.8grams more than the D12-7.

If one accepts that the D12-0 is "more powerful" than the
D12-7 ...... would this equate into more altitude, greater
launch acceleration, or what .... and how?

Yours in confusion
Grant

 
 
 

Estes D's

Post by Helen Rapo » Sun, 29 Oct 1995 04:00:00


Quote:

>Hi all,

>Could someone please tell me why the Estes D motors have
>different Max Lift Weights but all have the same total
>impulse, max thrust and propellant weight.

>Yea ok, so the D12-7 has 3.1grams of delay as against the
>0grams in a D12-0 but surely this cannot cause the D12-0
>to be able to lift 169.8grams more than the D12-7.

>If one accepts that the D12-0 is "more powerful" than the
>D12-7 ...... would this equate into more altitude, greater
>launch acceleration, or what .... and how?

**************
It's not the weight of the delay that is the issue but rather
it's the delay itself that is the issue.

Maybe an example might shed some light here.  Lets suppose
you have two rockets, with the same weight which happens
to be around the max liftoff weight of a D12-3.  One
rocket is powered by a D12-3 and the other a D12-7.

You launch both at the same time.  Both reach the same
height when the one with the D12-3 ejects its nose (and
it's parachute), while the one with the D12-7 continues
down (it's coasting) and eject's it recovery system
4 seconds (+-15%) later.  Be it on the ground or a
just a few feet above it might be debatable but you will
end up with a rocket that would need repair work.

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