The FailSafe Options
Almost everyone who’s had enough electronic-deployment flights has had a flight end badly
because of a drogue deployment failure. Some common failures are:
• Motor eject charge fires late, or doesn’t fire at all
• Drogue gets stuck in the body tube
• Jammed AV bay coupler
• Insufficient pyro charge to separate the payload bay
• Shear pins a little bit too strong and the payload bay doesn’t separate
• Shorted or bad ematch doesn’t fire
• Just plain bad luck or you’re cursed by the rocket gods
All of these have the same effect… your rocket starts free-falling from apogee and ends up
picking up a lot of speed. Sometimes your Main chute will fire at the preset altitude, but this can
be a double-edged sword: the high-speed chute deployment can tear up the chute, possibly
zipper the body tube as the force of the deploying chute jerks against the shock cord, or it can
tear the shock cord right out of the mount if it’s glued in. All of these result in damage to your
rocket, ranging from minor to catastrophic depending on how lucky you are.
FailSafe helps prevent this from happening by firing the Main chute if you exceed a specified
velocity for a specified amount of time after nose-over. For example, if you expect your drogue
chute to slow the rocket to 70 ft/sec you might set FailSafe to detect a fall of 100 ft/sec for over
one second. In the event that your Drogue fails, the Main will fire at some point much closer to
apogee, at a velocity that is much less likely to cause catastrophic damage to your rocket. Yes,
your rocket is going to drift a lot more than it would with a successful dual-deploy, and it may
even sustain some damage during the higher-than-normal main chute deployment, but at least
you’ll get it back to figure out what happened, instead of having to get out the shovel and dig it
out of the dirt, or spend an hour looking for the parts that scattered about when the Main
deployed at 400 ft/sec. at 500’ AGL.
Failsafe Veloc.: OFF, 50 to 200 fps by 25 fps (default OFF)
Failsafe Time ms: 500 to 3000 ms. by 250 ms. default (1000)
We recommend 125 ft/sec for 1000 ms (one second) as a good starting point. Most rockets will
hit this threshold 4-5 seconds after apogee, unless it’s a very light rocket. If you’re flying
drogueless you can expect the rocket to fall somewhat faster, so you may want to turn up the
velocity threshold a bit, because you don’t want FailSafe to fire the Main if you’re intentionally
coming down “hot”. You can estimate how fast a drogueless rocket is going to fall by using
RocSim or OpenRocket and simulating a drogue chute with the same area as the cross-sectional
area of the rocket. In fact, we recommend that you sim ALL HPR flights… it’s easy and fun too.
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