HPR Sim Questions

[1Matthew]

Hi all! Back in December 2023 I got my L1 on a Binder Design Excel 54 mm version. I meticulously designed the rocket on Open Rocket yet still am having some issues. I am trying to match my sim down to the actual launch I had back in December and make it so that the rocket’s delay is actually proper this time.

Back in December; the rocket zippered as a result of a long delay. In my sim, it seemed like 7-8 sec delay would be optimal. However, when launched the rocket seemed to reach apogee around 4-5 seconds. This launch used an H100, with a 54-38 mm adapter.

I will attach a video of the launch from December as well as a photo of it on the pad to give you some idea of the length of this rail guide which it launched off of. I hope to launch this rocket again at FAR, but would not like to make the same mistake

I have changed my sim to accommodate for the short rail guide, yet I am still coming up with the same issue on the delay and apogee height. I’ll attach the OR File as well.

 

[1Matthew]

Here is the OR File

 

[mtnmanak]

Try changing all the finishes on all your external parts to "Unfinished" and see if that gets your sim closer to reality.

 

[OverTheTop]

I would suggest going to electronic deployment so the motor delay becomes a "don't care". Once you go that way you will like it.

 

[1Matthew]

Try changing all the finishes on all your external parts to "Unfinished" and see if that gets your sim closer to reality.

I changed all my parts to unfinished, and brought down my projected height closer to the number I remember it reading at my L1 launch, yet my delay is still not optimal. If you look at the video, the apogee of the rocket seemed to be around 4 to 5 seconds, yet the sim shows it should be around 7.5

 

[1Matthew]

I would suggest going to electronic deployment so the motor delay becomes a "don't care". Once you go that way you will like it.

This might be the solution. Would this entail buying a chute release and not having a delay, instead using e matches?

 

[OverTheTop]

Hi Matthew. A chute release won't get you to where you need to be. The chute still needs to be deployed first when using the JLCR. Altimeters like the Blue Raven, any of the Eggtimer Rocketry products, or others are used with eMatches and charges to get the chute out.

Correct, you then don't need motor delays or motor ejection.

 

[1Matthew]

Hi Matthew. A chute release won't get you to where you need to be. The chute still needs to be deployed first when using the JLCR. Altimeters like the Blue Raven, any of the Eggtimer Rocketry products, or others are used with eMatches and charges to get the chute out.

Correct, you then don't need motor delays or motor ejection.

Could you take a motor with a delay and just drill the whole delay out?

 

[1Matthew]

Could you take a motor with a delay and just drill the whole delay out?

I would not be able to do electronic deployment until next year, as I still have Junior Level 1 Certification, which is why I would like to get my simulation as close as possible. Definitely will use Electronic Charges for the future when I turn 18.

 

[OverTheTop]

Could you take a motor with a delay and just drill the whole delay out?

The delays are usually left in the motor, and undrilled for maximum delay. The BP for ejection is removed from the front of the motor.

Sounds like you need to get your delays worked out in the simulator for the JrL1. Also keep in mind that most times, on an untested simulation (see my signature quote below ) generally shows higher altitude than reality. That translates into longer predicted times. Once the simulation loop is closed with real flight data you will get closer results in the future.

 

[waltr]

I used the timer in the video to time Apogee & when ejection fired.
Launch at 17s
Apogee at 24s - Delay about 7seconds from launch but motor burn is 2.5s so needed about a 4.5sec delay from burn-out.. This is not what the Sims says...

Your ejection happened at 32s in the video, 15 seconds after Launch. This is way too long and possible simply an extra long delay (bonus delay). Since the longest delay available is 14sec did you actually adjust the delay with the Tool?
What delay time did the motor come with?

What was the Altitude obtained?

Rail guide length rarely effects Altitude or delay time if launch is near vertical. We set rail length to determine if Speed off the Rail is high enough for the rocket to be stable and going fast enough not to have any wind have much effect (wind cooking).

 

[1Matthew]

I used the timer in the video to time Apogee & when ejection fired.
Launch at 17s
Apogee at 24s - Delay about 7seconds from launch but motor burn is 2.5s so needed about a 4.5sec delay from burn-out.. This is not what the Sims says...

Your ejection happened at 32s in the video, 15 seconds after Launch. This is way too long and possible simply an extra long delay (bonus delay). Since the longest delay available is 14sec did you actually adjust the delay with the Tool?
What delay time did the motor come with?

What was the Altitude obtained?

Rail guide length rarely effects Altitude or delay time if launch is near vertical. We set rail length to determine if Speed off the Rail is high enough for the rocket to be stable and going fast enough not to have any wind have much effect (wind cooking).

Altitude was 1400 feet, I instructed my NAR mentor to drill the delay to 7 seconds, as I don’t believe I am allowed to handle the motor for Junior Level 1 Certification. Delay did not pop open at 7 seconds and it seemed the apogee was way before the intended ejection charge. This is what I do not understand. How can I get the sim to show optimal delay similar to the actual flight, the apogee in the simulation is very close to what I remember it being in person, yet the optimal delay information is off. I witnessed the delay being drilled as well.

 

[Neutronium95]

Have you weighed the finished rocket, in the flight configuration? That seemed like a pretty sluggish takeoff, although the sims do show a pretty low TWR. The surface finish is not enough to explain the discrepancy. With the mirror finish set for all, it has an optimum delay of 7.9s on the H100, and when set to the roughest possible, it has an optimum delay of 7.05s.

Better luck next time. I would suggest using a higher thrust motor. The H100 gives a pretty low twr, and the rails at ROC are pretty short, leading to marginal rail exit speeds. The H283 has about the same impulse but would get it off the rail much faster.

 

[OverTheTop]

If the delay went long, did you happen to get any grease on the end facing the fuel grains? The grease gets in the way of the delay grain igniting.

 

[Neutronium95]

If the delay went long, did you happen to get any grease on the end facing the fuel grains? The grease gets in the way of the delay grain igniting.

The H100 is a single use motor, so that's not an issue. Since it was a junior cert, the delay adjustment should have been done by the adult mentor.

 

[waltr]

The sim shows apogee at around 1400 feet and a 7sec delay.

If the rocket does NOT go straight up then it will not reach the predicted altitude and apogee will happen sooner.

The video showed the ejection firing at 15s after lift-off. This is no where near the 7sec the delay was set to..... Something else is wrong.
Guessing---- Either the delay was not drilled or the wrong delay element was built into that motor.

What was the 'un-drilled' delay time of the motor you bought?

I do agree an H100 is not the best for speed off the rail. The H283 is a better choice for an L1 cert.

 

[Tractionengines]

The H100 is a single use motor, so that's not an issue. Since it was a junior cert, the delay adjustment should have been done by the adult mentor.

Is there a chance the mentor is used to RMS motors, and didn't realize the DMS motors take a different delay drilling tool? If they used the wrong tool the delay time would be wrong.

 

[1Matthew]

Have you weighed the finished rocket, in the flight configuration? That seemed like a pretty sluggish takeoff, although the sims do show a pretty low TWR. The surface finish is not enough to explain the discrepancy. With the mirror finish set for all, it has an optimum delay of 7.9s on the H100, and when set to the roughest possible, it has an optimum delay of 7.05s.

Better luck next time. I would suggest using a higher thrust motor. The H100 gives a pretty low twr, and the rails at ROC are pretty short, leading to marginal rail exit speeds. The H283 has about the same impulse but would get it off the rail much faster.

Yes the weight of the rocket in the sim is the same as my actual rocket, I overrided it through the sustainer.

 

[1Matthew]

The sim shows apogee at around 1400 feet and a 7sec delay.

If the rocket does NOT go straight up then it will not reach the predicted altitude and apogee will happen sooner.

The video showed the ejection firing at 15s after lift-off. This is no where near the 7sec the delay was set to..... Something else is wrong.
Guessing---- Either the delay was not drilled or the wrong delay element was built into that motor.

What was the 'un-drilled' delay time of the motor you bought?

I do agree an H100 is not the best for speed off the rail. The H283 is a better choice for an L1 cert.

Both the sim and in person resulted in an apogee at 1400 feet. If something is very off in my simulation I would like to fix it so my delays are drilled accurately for next time. That’s why I’m hesitant to try another motor if I cannot even get the motor that I launched to sim right. I have a suspicion that the drilling of the delay must have been done improperly, but I am not sure.

 

[JoePfeiffer]

Something went wrong with the delay -- that was nowhere near a 7 second delay; as others have pointed out, it almost looked as if the delay hadn't been drilled at all and was still 14 seconds. Assuming the motor otherwise behaved to spec, I don't have an answer as to why the sim was so far off. I wonder if the motor underperformed? Though even if it matched the thrustcurve data it's only 43fps off the rail, which is pretty slow.

 

[1Matthew]

If I were able to relaunch this rocket in the same conditions, on the same motor, would a delay of 7 seconds be optimal? It seems like apogee happened much sooner.

 

[1Matthew]

Something went wrong with the delay -- that was nowhere near a 7 second delay; as others have pointed out, it almost looked as if the delay hadn't been drilled at all and was still 14 seconds. Assuming the motor otherwise behaved to spec, I don't have an answer as to why the sim was so far off. I wonder if the motor underperformed? Though even if it matched the thrustcurve data it's only 43fps off the rail, which is pretty slow.

My group which all were certifying used the same batch of motors as well, a couple seemed to pop very late, yet my launch had the latest of the ejection charges. Maybe bad batch of motors?

 

[JoePfeiffer]

If I were able to relaunch this rocket in the same conditions, on the same motor, would a delay of 7 seconds be optimal? It seems like apogee happened much sooner.

Good question -- if that motor underperformed, then an H100 that performed to spec might really need a 7 second delay. But if the H100 you had was already performing to spec, then 7 seconds would be too long. I would rather have a delay that was two seconds too long than one that was two seconds too short...

But I wouldn't launch that rocket on that motor in the first place. I want a minimum of 50fps off the rail, and that motor doesn't do that. I'm guessing that's why you had that big wiggle right at launch.

 

[Kane]

Am I missing something? Was the video footage sped up? I timed out the delay from ignition. Seemed pretty close to 7 seconds. The issue to me seems to be that the motor either underperformed and/or there is another flight variable at play. The coefficient of drag can have a not insignificant impact on a flight profile. I use RockSim, but I always find that I have to "tune" my coefficient of drag over the course of a few flights. Did the rocket ride up and down the rail easily when it was loaded? That could be another factor. Also, drilling.out delay grains is not the most precise or accurate procedure. I don't think it's outside the realm of possibility that some combination of a slightly "draggier" real world rocket than the sim, a sticky rail, some lag in the delay grains, or a low-performing motor could have yielded those results.
If you use the same motor again, I would recommend looking at your rocket Cd and adjust to something closer to what you observed. I would also shorten the delay a little for the next flight and consider some anti-zippering strategies like a foam ball tied to the shock cord where it exits the airframe.

 

[JoePfeiffer]

Am I missing something? Was the video footage sped up? I timed out the delay from ignition. Seemed pretty close to 7 seconds. The issue to me seems to be that the motor either underperformed and/or there is another flight variable at play. The coefficient of drag can have a not insignificant impact on a flight profile. I use RockSim, but I always find that I have to "tune" my coefficient of drag over the course of a few flights. Did the rocket ride up and down the rail easily when it was loaded? That could be another factor. Also, drilling.out delay grains is not the most precise or accurate procedure. I don't think it's outside the realm of possibility that some combination of a slightly "draggier" real world rocket than the sim, a sticky rail, some lag in the delay grains, or a low-performing motor could have yielded those results.
If you use the same motor again, I would recommend looking at your rocket Cd and adjust to something closer to what you observed. I would also shorten the delay a little for the next flight and consider some anti-zippering strategies like a foam ball tied to the shock cord where it exits the airframe.

The movie viewer I'm using right now only has timestamps to the nearest second. Looking at the timestamps:
Motor ignition at 17 seconds
Motor burnout a little before 20 seconds
Recovery deployment at 31 seconds
So that's an 11-12 second delay.

 

[Buckeye]

The coefficient of drag can have a not insignificant impact on a flight profile.

Don't think CD is an issue as noted here:

The surface finish is not enough to explain the discrepancy. With the mirror finish set for all, it has an optimum delay of 7.9s on the H100, and when set to the roughest possible, it has an optimum delay of 7.05s.

Bad delay element, bad drilling, and/or bad thrust are the likely culprits.

 

[Tractionengines]

The movie viewer I'm using right now only has timestamps to the nearest second. Looking at the timestamps:
Motor ignition at 17 seconds
Motor burnout a little before 20 seconds
Recovery deployment at 31 seconds
So that's an 11-12 second delay.

My movie viewer/editor is also showing just shy of 12 seconds timestamps from motor burnout to ejection charge smoke "puff".

I also show a 2.3 second burn time; and 6.4 sec coast to apogee.

I think the delay was just wrong.

While 43ft/sec is a little slow off the rail, it's a "normal" rocket design and in low winds, should be OK. I would refly it with the same motor, but make sure delay is drilled to 6-7 seconds, with the right tool. (Note 6 is the minimum allowed.)

 

[1Matthew]

Thank you all for the help! All of your comments have really narrowed down my search to find this perfect delay and re-instill confidence in this rocket.

 

[waltr]

Yes, this is a tough one to figure out. My guess is that the delay was NOT drilled and went to the full 14 seconds.

I and others have had delays too long (more common) or too short. Neither are nice.
There is a +-20% or +-2second tolerance in the Spec for delays. But sometimes the actual delay is way different. For small rockets (under 4-5 oz) it is not too bad but the larger (heaver) the rocket, more damage can occur.

 

[Spacedog49Krell]

The only issue I find is your delay went 12 seconds instead of 7 seconds. Your sim data and delay times are within expected tolerances for your atmospheric and wind settings. Was the temperature really 49°F at Lucerne at launch? This is where flight computer data is critical, actual pressure and temperature, in determining fault issues.

The H100 appears to be under powered, T/W, for your vehicle. I would suggest using either an H219T or H283ST for a higher off the rail velocity.