Beginner Questions on HPR Motors and Motor Selection

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TheNewGuy

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Hello everyone,
I am an Electrical Engineering student who started getting into rocketry last year, and I am absolutely addicted. I've been trying to learn as much as I can from wherever I can, and I am really enjoying it.

I built my first rocket a couple months ago, which is an LOC Hi-Tech I purchased on Apogee Components. I got Level-1 certified by flying it on an Aerotech H123W-14, and I can't wait to fly my rocket again. I have a lot of questions though, and I was hoping you guys could help answer them for me. I'm confused on the motor selection process:

1.) Simulations
Apogee Components has on their website the RockSim file for the Hi-Tech, and when I run simulations on it, I can't seem to get the same numbers for altitude that they list on their website. For example:
According to Apogee Components they say that it should reach a maximum altitude of 3,266 feet (Link here), but when I run RockSim it gives me 1,100 feet. I've tried different motors, and I always get drastically lower numbers in the simulations than what's listed. Is there something I'm doing wrong?

2.) Choosing Delay
After running the simulation, the software suggests an "optimal delay" to use with the motor. On the Aerotech H123W and various other motors, it suggests a delay of 1 second. Does that mean, using the delay drilling tool, I keep drilling until I'm down to 1 second? Also, does the delay burn immediately after the rocket is launched or after the propellant grain finishes burning?

3.) Level-2 Flight on the Hi-Tech
On the on Apogee's website, they say that for a level-2 flight you should use a slow burning J motor (specifically the J90). If you want to use a quick burning J, they suggest laying fiberglass the body and fins. I notice that the J90 isn't sold anymore, are there alternatives to the J90 or should I just go ahead and fiberglass the rocket when I want to do Level-2?

4.) Endburn-Style Forward Closure
For the Aerotech I49 and I59, they require a different forward closure than regular reloads. From what I understand, this forward closure doesn't have the small hole at the top that is usually where the black powder gets ignited. How does the black powder get ignited for these motors? Electronics only?

Thank you in advance for any help, and sorry for the barrage of questions in my first post.

Regards,
TNG
 

BDB

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I don't know much about RockSim, but I get 2489' when I used OpenRocket to simulate the RockSim file from the Apogee website using a H123. The delay time may be making the difference for you. For my first sim, I forgot to to optomize the delay, so it was set to zero, and the altitude was nearly half. It looks to me like the optimal delay is 8.2 sec. (No way to drill it that precisely.) That said, no delay maniupulation is going to get this thing to break 3k ft on a H123.

For the L2 flight, you probably just want a low thrust J motor. (Not a J600 like I'm planning.) Since this isn't a huge heavy rocket, you don't need that much initial thrust. If you were to use a high thrust motor without reinforcing the fins, you might rip them off.

Edit: I just simmed the J270 in your rocket and it predicts 4571' and Mach 1.0. I don't have any experience with this kit, but it looks to me like you probably want to glass the fins.
 
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Kallahan11

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Hello everyone,


4.) Endburn-Style Forward Closure
For the Aerotech I49 and I59, they require a different forward closure than regular reloads. From what I understand, this forward closure doesn't have the small hole at the top that is usually where the black powder gets ignited. How does the black powder get ignited for these motors? Electronics only?

Thank you in advance for any help, and sorry for the barrage of questions in my first post.

Regards,
TNG
You might see this called a plugged forward closure, some really slow burning or really fast burning propellants and snuff out the delay making motor ejection to unreliable. For these motors you need electronic deployment.
 

DavidMcCann

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typically, you shouldn't drill a delay to less than 4 seconds. Any shorter and between not being thick enough, and delay inaccuracies you risk it blowing out during boost. Also. if you're getting an optimal delay of one second, something is off in the sim, or it's a poor motor choice for the rocket (thrust to weight way too low)
 

MCriscione

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This may be a stupid answer to #1, but make sure that you're units are feet and not meters. I don't know what the default in RockSim is, perhaps this is the issue?
 

Zeus-cat

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I agree with BDB, it sounds like something is wrong with your simulation. Try running the rocket on Thrustcurve. This is a very simple, but good simulation program. All you need is motor mount diameter and length of the mount, diameter of the rocket and weight of the rocket without the motor. It will return a bunch of info on motors you could use.
 

billdz

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"On the on Apogee's website, they say that for a level-2 flight you should use a slow burning J motor (specifically the J90). If you want to use a quick burning J, they suggest laying fiberglass the body and fins. I notice that the J90 isn't sold anymore, are there alternatives to the J90 or should I just go ahead and fiberglass the rocket when I want to do Level-2?"

The J90 is still sold, check some other vendors. Best alternative would be a J180, which may be better anyway if you only have the standard forward closure. The J90 requires the extended forward closure.
 

Bat-mite

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RockSim and Openrocket use the selected "finish" to set the Cd and thus determine the max altitude. Rocket vendors will want you to know that if you can get a perfect, smooth finish, you could, on a good, windless day in perfect conditions, get to a much higher altitude than any of us can reasonably expect. Apogee is good about answering calls; might be worth asking them how they come up with their number.
 

Nytrunner

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1.) Simulations
Apogee Components has on their website the RockSim file for the Hi-Tech, and when I run simulations on it, I can't seem to get the same numbers for altitude that they list on their website. For example:
According to Apogee Components they say that it should reach a maximum altitude of 3,266 feet (Link here), but when I run RockSim it gives me 1,100 feet. I've tried different motors, and I always get drastically lower numbers in the simulations than what's listed. Is there something I'm doing wrong?

2.) Choosing Delay
After running the simulation, the software suggests an "optimal delay" to use with the motor. On the Aerotech H123W and various other motors, it suggests a delay of 1 second. Does that mean, using the delay drilling tool, I keep drilling until I'm down to 1 second? Also, does the delay burn immediately after the rocket is launched or after the propellant grain finishes burning?

3.) Level-2 Flight on the Hi-Tech
On the on Apogee's website, they say that for a level-2 flight you should use a slow burning J motor (specifically the J90). If you want to use a quick burning J, they suggest laying fiberglass the body and fins. I notice that the J90 isn't sold anymore, are there alternatives to the J90 or should I just go ahead and fiberglass the rocket when I want to do Level-2?

4.) Endburn-Style Forward Closure
For the Aerotech I49 and I59, they require a different forward closure than regular reloads. From what I understand, this forward closure doesn't have the small hole at the top that is usually where the black powder gets ignited. How does the black powder get ignited for these motors? Electronics only?

Thank you in advance for any help, and sorry for the barrage of questions in my first post.
Welcome to the forum, prepare for multiple suggestions and conflicting opinions!

1) Did you make sure that your rocket's dry weight (without motor) was the weight in the simulation? If you left the Apogee file alone, its weight may not match how you built your rocket. When doing a simulation, always adjust the design weight so that it matches the finished rocket (paint, epoxy, and hardware adds up sneakily)

2) This makes me think something about the mass of the rocket is off. Its predicting very short flight time which may discount MCrisione's hypothesis. The Hi-tech should be a lightweight rocket that flies quite high on H's. (admittedly, apogee's simulations may be optimistically lightweight.) What IS your built weight without motor and casing? (By the way, casing weight is included in Rocksim motor weight for reloadables, so don't add it in separately)
As for delays, they burn quickly as soon as motor initiation begins, then at burnout, they burn slower at a general rate of 1/32" per second. (endburners are an exception to the "ignite immediately")


Have you heard of the free program OpenRocket? It's very capable as well.

3) You've already flown an H123, so you could try looking for a J with similar average and peak thrust (look at the thrust curves on Thrustcurve.com or Wildman's online store). That way you won't get up to crazy speeds and may not require composite reinforcement. (Plus, look at other vendors besides apogee. You may find better selection of motors and prices)

4) As mentioned previously, electronics are the only way to go here. You could do altimeter deployment using BP charges, (or there's CO2 systems if they'll it in your rocket).


Good luck on your L2! Or try building a different rocket and have fun with that one for awhile! There's a lot of excitement to be had at the F-I motor range that doesn't break the bank as fast as L2 flying
 

TheNewGuy

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Thank you everyone for the replies!

You guys were right, I had a setting wrong in RockSim. Once I changed the ejection delay from '0' to "ALL" I was getting numbers almost twice that of before. Even after these changes, I'm still not getting the altitudes reported on Apogee's website. I think I might call Apogee and ask, like Bat-mite suggested.

"On the on Apogee's website, they say that for a level-2 flight you should use a slow burning J motor (specifically the J90). If you want to use a quick burning J, they suggest laying fiberglass the body and fins. I notice that the J90 isn't sold anymore, are there alternatives to the J90 or should I just go ahead and fiberglass the rocket when I want to do Level-2?"

The J90 is still sold, check some other vendors. Best alternative would be a J180, which may be better anyway if you only have the standard forward closure. The J90 requires the extended forward closure.
I just realized, the reason why I couldn't find the J90 is because I'm looking in only 38mm motors. The Hi-Tech comes with a 38mm motor mount, both the J90 and J180 are 54mm according to the documentation on Aerotech's website:
(AeroTech Master Motor Matrix) (PDF Warning)

You might see this called a plugged forward closure, some really slow burning or really fast burning propellants and snuff out the delay making motor ejection to unreliable. For these motors you need electronic deployment.
...4) As mentioned previously, electronics are the only way to go here. You could do altimeter deployment using BP charges, (or there's CO2 systems if they'll it in your rocket)...
I had a feeling this was this was the case and was not sure. The videos online I've watched of long burn motors look really cool, I want to try to fly them in the future.

Welcome to the forum, prepare for multiple suggestions and conflicting opinions!


1) Did you make sure that your rocket's dry weight (without motor) was the weight in the simulation? If you left the Apogee file alone, its weight may not match how you built your rocket. When doing a simulation, always adjust the design weight so that it matches the finished rocket (paint, epoxy, and hardware adds up sneakily)
Thank you for the long reply! I have a rough estimate on the rocket's weight, but not an exact number. I think I'm going to look at getting one of those cheap pocket scales so that I can get a more accurate simulation like you're saying.


2) This makes me think something about the mass of the rocket is off. Its predicting very short flight time which may discount MCrisione's hypothesis. The Hi-tech should be a lightweight rocket that flies quite high on H's. (admittedly, apogee's simulations may be optimistically lightweight.) What IS your built weight without motor and casing? (By the way, casing weight is included in Rocksim motor weight for reloadables, so don't add it in separately)
As for delays, they burn quickly as soon as motor initiation begins, then at burnout, they burn slower at a general rate of 1/32" per second. (endburners are an exception to the "ignite immediately")
Just to check my understanding, if the package says the delay is 14 seconds, that's 14 second after the motor get's ignited. Right?


Have you heard of the free program OpenRocket? It's very capable as well.
I'll download it now!


3) You've already flown an H123, so you could try looking for a J with similar average and peak thrust (look at the thrust curves on Thrustcurve.com or Wildman's online store). That way you won't get up to crazy speeds and may not require composite reinforcement. (Plus, look at other vendors besides apogee. You may find better selection of motors and prices)


4) As mentioned previously, electronics are the only way to go here. You could do altimeter deployment using BP charges, (or there's CO2 systems if they'll it in your rocket).

Good luck on your L2! Or try building a different rocket and have fun with that one for awhile! There's a lot of excitement to be had at the F-I motor range that doesn't break the bank as fast as L2 flying
I love the Hi-Tech for how light it is, which is why I'm reluctant to add weight to it through fiberglass. The motor mount and my reload hardware are all 38 mm which means I need to find a 38mm J that has low peak thrust. If I have to fiberglass the body and fins I guess I will. I went with 38mm reload hardware, because I liked how it has a wide a range of motors to choose from like you mentioned.
 

dmo

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4.) Endburn-Style Forward Closure
For the Aerotech I49 and I59, they require a different forward closure than regular reloads. From what I understand, this forward closure doesn't have the small hole at the top that is usually where the black powder gets ignited. How does the black powder get ignited for these motors? Electronics only?

Aerotech has three basic types of forward closure styles.

The normal and extended closures have both a delay well and ejection charge port.

The plugged closure has the delay well but not the ejection charge port. With these, you still get the tracking smoke from the delay grain, but you have to use electronics for ejection.

The end burner plugged closures (used for the I49 and I59) do not have either. The end burner motors do not come with a delay grain, so they need the solid plug. If you use one of these motors and need an ejection charge, you will need electronics.

Strange that Tim would recommend a J90 for this rocket. That is a 54mm motor and wouldn't fit. CTI does have a J94 in 38mm
 

dhbarr

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Just to check my understanding, if the package says the delay is 14 seconds, that's 14 second after the motor get's ignited. Right?
Not quite. It's -approximately- 14s after burnout.

The delay grain is a cylinder that burns from the bottom end at a faster rate while the motor is pressurized / boosting.

After burnout / while coasting, the delay grain continues burning from the bottom, but at a slower rate ( typical formulations are 1/32" per sec ).

If you want a shorter delay, you drill a hole in the delay to let the fire get to the ejection charge a few 32nds ( seconds ) sooner.
 

billdz

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"Strange that Tim would recommend a J90 for this rocket. That is a 54mm motor and wouldn't fit."

Tim did indeed mess up, they probably cut and pasted from the description of a rocket with a 54mm motor mount:

"This kit has a 38mm motor mount, so it can do a level 2 certification. I recommend using a J90 for level 2 because it has a slow, 7.9 second burn time. Do not try to use a fast burning level 2 motor in this kit, unless you fiberglass the body and fins."
https://www.apogeerockets.com/Rocket_Kits/Skill_Level_3_Kits/Hi-Tech

J270 appears to be the best Aerotech choice, although the CTI J94 would be better.
 

billdz

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@TheNewGuy - if your simulation says the optimum delay is just one second, there must be something wrong. I'd guess ten seconds or more with a J motor on the Hi-Tech.
 

Handeman

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Congrats on the L1 and welcome to rocketry!

From your description I take it you flew none or very few MPR rockets and have no experience beyond your Hi-Tech. Nothing wrong with that, but I would highly suggest you get plenty of flights on the Hi-Tech before you decide on a L2 attempt. The Hi-Tech is not a L2 rocket, it's a L1 rocket that can take a baby J motor. The problem you will have is when you put that baby J motor in there is the near mach speed and almost 6000 ft altitude. Motor ejection at 6000 ft usually isn't a good idea on most fields, especially in the eastern part of the country.

As you fly more H motors and move up to I motors you will start getting a feel for "flying the field" where you do most of you flying. That is something you pretty much only learn from experience.

My advice would be to fly and enjoy the Hi-Tech and when you decide to get the L2, then make a decision on whether a 6000 ft motor eject flight will work, or if you want to build a bigger 54mm or 75mm MMT rocket that can fly J K & L motors instead of just baby Js like the Hi-Tech. I suspect you'll want the bigger rocket.

Good Luck
 
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