Delay time preference, early or late?

[John Taylor]

I have a rocket that sims to a 6 second delay time.
I have one motor with a 4 second delay and one with an 8 second delay.
I haven't flown a rocket with more than a second or so off the simulation time.
Need advice
1) Prefer 2 seconds early
2) Prefer 2 seconds late
3) Or dont fly it
Thank you everyone!
John

 

[SolarYellow]

Electronic deployment or JLCR.

 

[John Taylor]

Electronic deployment or JLCR.

JLCR

 

[Daddyisabar]

Early or late are both unacceptable. Only perfection at Apogee is required. Find a way to make it perfect. Learn the ways of the Jedi!

 

[John Taylor]

Early or late are both unacceptable. Only perfection at Apogee is required. Find a way to make it perfect. Learn the ways of the Jedi!

I understand perfect is at apogee when the model is moving slowest. I sim all flights to get the proper delay time.
One thing, motor manufactures are allowed variances of 2 seconds on tgeir delay times.
Other factors can affect the burning of the delay element.
This is one model I haven't been able to find a perfect fit with the timing correct.
I was just asking if you had the choice would you prefer early or late.
Thank you

 

[Daddyisabar]

No preference. Both can result in really bad outcomes. Both can result in no damage at all. You must consider all the variables at that specific launch. Rocket characteristics, weather characteristics, all add up to a complicated scenario where you can not make a hasty generalization before hand based solely on delay time.

 

[SolarYellow]

Build a matrix of sims. Try different wind conditions, etc. Most of the things that can be less than ideal will make the rocket go not as high and want a shorter delay than a still-air optimum. You're less likely to have zipper trouble using a JLCR, so maybe you want to have it fly past apogee before hanging out the bundled laundry. Look at your speed at ejection under the range of scenarios. Maybe add some drag to the rocket to slow it down so it's closer to wanting the shorter delay. Lots of options.

In a theoretically simple scenario of still air, it shouldn't matter whether you're early or late by the same amount, the airspeed should be just about the same. And excess airspeed at ejection is what causes trouble. If it was all the same, I'd prefer to fly over the top. But it never is all the same in the real world.

 

[rcktnut]

I always go late if necessary, never had a problem. I always figured it has to stop first then start to pick up speed again. Like mentioned the outcome depends on a lot of other factors.

 

[tsmith1315]

With those times, I assume you’re talking low power.

I’d opt for 2 seconds late.

As a 70’s kid, I usually tried for a late ejection to minimize drift. I bought the long delay version every time. Not anymore, but my experience says neither is a deal breaker.

 

[Buckeye]

I prefer 2 seconds early, because the altitude is usually a little less than the simulation due to wind, drag, etc.

 

[kjhambrick]

I don't know !

What motor are you talking about and how high will your rocket fly ?

Either way, assuming velocity is zero at apogee, a free falling body in a vacuum will be going 64 ft/sec at -/+ 2-secs, before and after apogee.

Reality bites ... your rocket won't get to velocity = zero unless it flies perfectly vertically ( and with our prarie winds, it probably won't in Texas )

So ... if I was unable to adjust the delay or fly electronic deployment, I might be inclined to go 2-sec early ...

It 'feels' like if you eject 2-sec early, the lower booster section might be less apt to fly thru the chute as it deploys because the ejection charge will tend to accelerate the nose and laundry and decelerate the fin can which is already decelerating due to the gravity field on the way up -vs- accelerating on the way down ??? maybe ??? I don't know !!!

Good Luck !

-- kjh( why do I stick my neck out on Qs like these )

 

[Daddyisabar]

The hardest choice is don't fly at all. That takes the wisdom and patience of a Jedi. As a youngling level flyer I simply ask myself "What would Master Yoda do?"

 

[RokitFlyr]

Late, to actually answer the question.

 

[Rocketclar]

Electronic deployment is the way to go. There are a number of small, inexpensive altimeters for this. If it's an AT reload or DMS, you can "trim" adjust the delay with the delay tool. Either too long or too short could result in a zippered AF. Best to find an appropriate motor for the rocket with the delay time close to what you simmed or adjust the delay.

 

[Art Upton]

He is not Popin' a chute at the top. He is using a JLCR, so even if late or early it's not going to shred a chute, it will be like a small drogue or drogue less with the JLCR having the chute wrapped up.

Make sure the JLCR has a good grip on that chute roll so it does not slip out early before the JLCR opens up.

 

[Sandy H.]

*In my opinion* I'd prefer a little late. I'm sure there are valid arguments for a little early or 'perfect' but if you asked the question you actually did ask, I would say late and possibly a reefed parachute or similar.

My opinion only.

 

[neil_w]

I always get annoyed when my sim lands right in between the available delays like that, but that's the price for flying motors with fixed delays. It's not much of an issue when it's +- 1 second, but +- 2 seconds starts to get real.

But if you're flying with a JLCR it's less critical. I'd go late.

 

[Hobie1dog]

*In my opinion* I'd prefer a little late. I'm sure there are valid arguments for a little early or 'perfect' but if you asked the question you actually did ask, I would say late and possibly a reefed parachute or similar.

My opinion only.

+1 agree totally

 

[Voyager1]

I would use the motor with the delay that has the lowest velocity at ejection. Failing that, I would probably use the +2 seconds delay after apogee.
Alternatively, you could adjust the rocket mass to better suit one of the motors ejection delay.

 

[BobP]

I'd go for 'late.' You might look at the motor cert letter - that might show you a few tenths more detail re: plausible delay times

 

[ReynoldsSlumber]

Prefer late just for the satisfaction of seeing the rocket fly through the trajectory's peak. No premature eject-ulation.

 

[sriegel]

One concern with late is if you weathercock, you'll come over apogee earlier than expected and with excess speed. You'll be that much faster when it does eject.

I often find my sims are optimistic to final altitude so a touch early is often my choice.

I personally would go early if I had no other choice to get closer to optimum.

 

[troj]

I'd rather short, because then the rocket is slowing down instead of accelerating.

-Kevin

 

[Sandy H.]

One concern with late is if you weathercock, you'll come over apogee earlier than expected and with excess speed. You'll be that much faster when it does eject.

I often find my sims are optimistic to final altitude so a touch early is often my choice.

I personally would go early if I had no other choice to get closer to optimum.

Good point! I feel like I see more zippers on early ejection, but that is just my impression, not a fact for sure. Maybe early with rubber bands, tape or other methods to slow the shock cord down would be the right call.

 

[JoePfeiffer]

Because of drag, a rocket that ejects a second early is going faster than one that ejects a second late. So prefer late.

Actually prefer electronic deployment...

 

[Buckeye]

Because of drag, a rocket that ejects a second early is going faster than one that ejects a second late. So prefer late.

Drag works in both directions, so I can't get my head around this at the moment. However, the simulations will pick up this speed difference. 32 ft/s vs. 33 ft/s is pretty inconsequential, though.

Another vote for early, because when delays go wrong, they are usually "bonus delays."

 

[Rocketjunkie]

Windy day, go early. Calm day, go to the long side. However, I use dual deploy on all HPR and limit motor size on windy days.