Accidentally Blurring the MPR/HPR Line

[samb]

I don’t have too much to add about changing anything. But the current rules are laid out as simply as they can be, IMO, in the document SecondRow attached to post #14 here.

 

[smstachwick]

I don’t have too much to add about changing anything. But the current rules are laid out as simply as they an be, IMO, in the document SecondRow attached to post #14 here.

Good thing to attach to your range box if you’re flying complex configurations or >E power.

 

[OverTheTop]

I was a 4H member more than a little while ago. I really liked it.

Down here it is called Young Farmers. I was a member for a number of years quite a while ago too. Fun times.

 

[rcktnut]

Back to OP's problem. Let's say the Zephyr weighs 48.0 oz. w/o motor. Using the G-78 (4.4 oz.) total weight comes to 52.4oz.

Based on the original wording:

Apogee Zephyr on a G78
Based on what I can find online this would have weighed 48.4 oz plus paint and dog barf. I think we probably hit 53 oz with this one.

it seems like the 48.4 oz weight included the motor; is that right? With a limit of 52.9 oz, you'd have needed 4.5 oz of paint and dog barf to go over the line. I'd bet you squeaked under, but I sure wouldn't bet much.

Anyway, if you did go over, it was an honest mistake and water under the bridge. Don't sweat it.

Obviously I understand regulations exist for a reason and they should be followed, but it does seem like there's some room for a motivated individual or group to clarify and simplify the regulations.

I doubt that. There are HPR motors and there are HPR flights. Well, no, actually it's all about HPR flights, and one criterion for that is the use of motors with certain characteristics, which we call HPR motors for convenience. "HPR motors" are defined by four clear lines: total impulse, propellant mass, average thrust, and sparks. HPR flights are defined by greater impulse, thrust, and propellant mass limits that only come into play when clusters or staging are involved; the presence of an "HPR motor"; and lift-off weight. Assuming that there is a good reason for each of those requirements, I don't think there's any room to state the rules more simply than the clear and unambiguous way they are already stated. Any attempt to cover every edge case would make the rules more complicate, not less.

An attempt to eliminate the edge cases would have to make the rules too restrictive, since they would have to one limit or another value very low in order to assure that other unsafe stuff can't occur. You could, for example, reduce it to "An HPR is any rocket launching with total impulse higher than 120 Ns or any sparky motor." That would, by force, also eliminate single motor impulse, total propellant mass, and average thrust greater than what's currently allowed, since you really can't exceed any of those without going over 120 Ns. But it would also eliminate many cases that are and should be MPR today.

Even if that rocket needs to be flying under HPR rules no need to have a HPR cert when using a MPR motor in it.

What does that mean, it flies "under HPR rules" but you don't need a cert. "You need a cert" is the essence of HPR rules.

G motors above 80Ns average thrust could be sold to members of NAR, Tripoli...

NAR or Tripoli membership is proof of nothing except having paid NAR or Tripoli dues.

Mixing up the weight of a rocket with motor total impulse and motor average impulse, means sometimes they are MPR and other times they turn into HPR all what makes it confusing.

All it means is that in some edge cases, what's typically and conveniently called an "MPR motor" can power an HPR flight. Again, there are parties that ought to do a better job of communicating that, but I don't see why it's basically confusing.

It is just my opinion that a G impulse should be a G period and be able to fly as a MPR and not be called a HPR motor also under certain circumstances. Sparky G's, G's with 80+Ns average thrust, and G's in a rocket that weighs over 53oz. are all considered HPR. = BS.

It only looks like BS if you think it's all about the motor, and all about the letter. But it's really all about the flight. H motors and up are called "HPR motors" because if you use one it's certain that you're doing an HPR flight; not using one doesn't mean you're not doing an HPR flight.

-- Joe
NAR #92184
When you judge someone, remember this: how they treat others is the only thing that matters.

The regs/ codes are what they are. I would like to know how weight got involved with determining what is a MPR and HPR Flight It isn't about KE or altitude. I simmed a Zephyr with a G-78 making total weight at 53.9 oz.= 190ft/sec to 595ft. KE=2,567J Thats a HPR Flight according to what Simon says. I simmed an Aerotech Arreaux with a G-80 total weight 16.5 oz. = 770ft/sec to 3095ft. KE=12,882J. This is a MPR Flight according to what Simon says. I don't care what anybody says Simon is F'ed up. The one and only reason weight is involved is because Simon says so. No reasoning behind it what-so-ever, nothing to do with safety. It is BS
Having to cert L1 to fly a MPR motor is BS no matter what the weight of the rocket/ flight /whatever. Exceptions can be made.

 

[Steve Shannon]

The regs/ codes are what they are. I would like to know how weight got involved with determining what is a MPR and HPR Flight It isn't about KE or altitude. I simmed a Zephyr with a G-78 making total weight at 53.9 oz.= 190ft/sec to 595ft. KE=2,567J Thats a HPR Flight according to what Simon says. I simmed an Aerotech Arreaux with a G-80 total weight 16.5 oz. = 770ft/sec to 3095ft. KE=12,882J. This is a MPR Flight according to what Simon says. I don't care what anybody says Simon is F'ed up. The one and only reason weight is involved is because Simon says so. No reasoning behind it what-so-ever, nothing to do with safety. It is BS
Having to cert L1 to fly a MPR motor is BS no matter what the weight of the rocket/ flight /whatever. Exceptions can be made.

I don’t know the history of how weight became a determining factor, but if you calculate the terminal velocities and kinetic energy of two rockets which are identical except for weight during ballistic (no ejection) descent. You may see a situation where weight makes a difference.

 

[OzHybrid]

Based on the original wording:

it seems like the 48.4 oz weight included the motor; is that right? With a limit of 52.9 oz, you'd have needed 4.5 oz of paint and dog barf to go over the line. I'd bet you squeaked under, but I sure wouldn't bet much.

Anyway, if you did go over, it was an honest mistake and water under the bridge. Don't sweat it.


I doubt that. There are HPR motors and there are HPR flights. Well, no, actually it's all about HPR flights, and one criterion for that is the use of motors with certain characteristics, which we call HPR motors for convenience. "HPR motors" are defined by four clear lines: total impulse, propellant mass, average thrust, and sparks. HPR flights are defined by greater impulse, thrust, and propellant mass limits that only come into play when clusters or staging are involved; the presence of an "HPR motor"; and lift-off weight. Assuming that there is a good reason for each of those requirements, I don't think there's any room to state the rules more simply than the clear and unambiguous way they are already stated. Any attempt to cover every edge case would make the rules more complicate, not less.

An attempt to eliminate the edge cases would have to make the rules too restrictive, since they would have to one limit or another value very low in order to assure that other unsafe stuff can't occur. You could, for example, reduce it to "An HPR is any rocket launching with total impulse higher than 120 Ns or any sparky motor." That would, by force, also eliminate single motor impulse, total propellant mass, and average thrust greater than what's currently allowed, since you really can't exceed any of those without going over 120 Ns. But it would also eliminate many cases that are and should be MPR today.


What does that mean, it flies "under HPR rules" but you don't need a cert. "You need a cert" is the essence of HPR rules.

NAR or Tripoli membership is proof of nothing except having paid NAR or Tripoli dues.

All it means is that in some edge cases, what's typically and conveniently called an "MPR motor" can power an HPR flight. Again, there are parties that ought to do a better job of communicating that, but I don't see why it's basically confusing.

It only looks like BS if you think it's all about the motor, and all about the letter. But it's really all about the flight. H motors and up are called "HPR motors" because if you use one it's certain that you're doing an HPR flight; not using one doesn't mean you're not doing an HPR flight.

And Hybrids.

 

[rcktnut]

I don’t know the history of how weight became a determining factor, but if you calculate the terminal velocities and kinetic energy of two rockets which are identical except for weight during ballistic (no ejection) descent. You may see a situation where weight makes a difference.

I agree but the results of being hit by one weighing 53oz. or 63 oz. would the same. I wouldn't want to be hit by a LPR flight weighing 4 oz. or any one for that matter. Having a HPR cert isn't going to stop a ballistic recovery. Through out the history of model rockets the safety codes have done an excellent job of protecting us and property from ballistic recoveries. As far as I know, no aircraft have ever been hit by a model rocket.
I never thought of this situation before, makes no difference to me, but after seeing OP's post started wondering why weight is a determining factor in what a MPR or HPR flight is. I figured KE could be about the only reason other than just because Simon says so. KE seems not to be the reason.

 

[samb]

The last major revision of the relevant NFPA codes (2012 ish) and by extension the NAR and Tripoli safety codes actually simplified things somewhat in adopting the FAA line between Class 1 and Class 2 amateur rockets (125 grams propellent weight and 1500 grams total rocket weight). The Pyrotechnic Committee of NFPA includes many well known names in our little hobby community but a quick check found no Simons.

 

[rcktnut]

Sorry, forgot to introduce Simon. Simon is our alphabet agencies regulating our hobby. Now lets get on to discussing why shipping 1 motor containing 35 grams of propellant needs to be HAZMAT and why a 25 lb. box of motors with <30 grams of propellent each can be shipped non HAZMAT On the other hand lets not!!!

 

[Steve Shannon]

Do the math. Even if it wasn’t the way the limit was developed, 1500 grams is a reasonable limit to ensure that a rocket of the highest weight (1500 grams) can still have a 5:1 thrust to weight when using an 80 Newton motor, which is the highest thrust motor allowed in model rockets.

 

[jqavins]

The regs/ codes are what they are. I would like to know how weight got involved with determining what is a MPR and HPR Flight It isn't about KE or altitude. I simmed a Zephyr with a G-78 making total weight at 53.9 oz.= 190ft/sec to 595ft. KE=2,567J Thats a HPR Flight according to what Simon says. I simmed an Aerotech Arreaux with a G-80 total weight 16.5 oz. = 770ft/sec to 3095ft. KE=12,882J. This is a MPR Flight according to what Simon says. I don't care what anybody says Simon is F'ed up. The one and only reason weight is involved is because Simon says so. No reasoning behind it what-so-ever, nothing to do with safety. It is BS
Having to cert L1 to fly a MPR motor is BS no matter what the weight of the rocket/ flight /whatever. Exceptions can be made.

1. Are those speeds maximum or terminal velocity in the event of a deployment failure. The greater the mass, in general, the greater the hazard when (not if) an object falls from great height.
2. More detailed regulations, such as limiting either maximum or terminal E_K, would make the rules more complicated to comply with, not less. So a method and a number are chosen that will enable the simplest and most accurate compliance with the greatest level of safety in the greatest number of cases.
3. An allowance for exceptions requires the use of judgement. Allowance for the use of judgement inevitably leads to errors in judgement. That's why regulations exist in the first place. So no, you write the regulations the best you can, and there are no exceptions.

I don’t know the history of how weight became a determining factor, but if you calculate the terminal velocities and kinetic energy of two rockets which are identical except for weight during ballistic (no ejection) descent. You may see a situation where weight makes a difference.

I figured KE could be about the only reason other than just because Simon says so. KE seems not to be the reason.

Calculate the momentum at terminal velocity as well. The energy and the momentum both matter. A one pound object travelling at 100 ft/s has the same energy as a four pound object at 50 ft/s, but I'd rather be hit by the lighter one (even thought they would both suck a lot).

And again, the 1500 gram line is not supposed to mean 1499 grams is safe and 1501 is not. It's about a 1400 gram rocket being reasonably expected to be enough less dangerous than a 1600 gram rocket can reasonably be expected to be with all other flight parameters in the ballpark that can likewise be reasonably expected with each mass. And also again, it's not about the motor, it's about the flight; the very notion of "an MPR motor in an HPR flight" is flawed. It's a motor that can be used in an MPR flight being used, this time, in an HPR flight.

But, enough of that. I don't expect we'll come to any agreement, and it's not worth arguing about. The last word is yours if you'd like to have it.

Now lets get on to discussing why shipping 1 motor containing 35 grams of propellant needs to be HAZMAT and why a 25 lb. box of motors with <30 grams of propellent each can be shipped non HAZMAT On the other hand lets not!!!

Ah, now there you have an excellent point. FAR, NFPA, and FAA rules are OK as is (IMO) but the DoT rules are messed up. But yeah, let's not.

 

[jqavins]

Do the math. Even if it wasn’t the way the limit was developed, 1500 grams is a reasonable limit to ensure that a rocket of the highest weight (1500 grams) can still have a 5:1 thrust to weight when using an 80 Newton motor, which is the highest thrust motor allowed in model rockets.

Hmm, I didn't think of that angle. 80 N thrust would allow for 16 N weight, which means about 1.6 kg. And the limit of 1.5 kg leaves a bit of margin. Excellent!

 

[Alan15578]

Down here it is called Young Farmers. I was a member for a number of years quite a while ago too. Fun times.

I vaguely recall Future Farmers of America, but that may have been a local high school club, and not the 4H, in any event they should be playing with drones, not rockets. 4H does quite well with rockets.

 

[rcktnut]

Do the math. Even if it wasn’t the way the limit was developed, 1500 grams is a reasonable limit to ensure that a rocket of the highest weight (1500 grams) can still have a 5:1 thrust to weight when using an 80 Newton motor, which is the highest thrust motor allowed in model rockets.

I can't agree more but it is a rule of thumb and not in the safety codes. Lots of variables that can either increase or decrease that ratio needed for a safe flight. I did do the math and stated this in my post #26: What is now considered a G MPR motor is not going to be able to safely fly much more weight than that anyway. This was in response to flying a G in a 53 oz. rocket.

But, enough of that. I don't expect we'll come to any agreement, and it's not worth arguing about. The last word is yours if you'd like to have it.

I totally agree, I don't think it's really an argument though, just a healthy discussion. What it all boils down to for me is the fact that to be 100% legit OP needs to cert level 1 in order to fly his rocket if it was over 53oz. I just don't see a need for that if using a MPR motor. It would be nice to hear from OP what the actual weight was. I'd bet is was under by a little bit. All done!!

 

[smstachwick]

I’m skeptical that the 1.5 kilogram limit came from thrust-to-weight concerns, although it is convenient that it lines up so nicely. Given that rockets exceeding this limit require an FAA waiver as well, I’m willing to bet that this was a simple, easy-to-remember number that coincided roughly with a mass that could safely be considered an upper limit for a safe resolution of a collision with with a manned aircraft rated for bird strikes.

The FAA criteria specifically lays out a 1.8 kilogram (4-pound) mass as the standard for large Part 25 aircraft certification, basically your Learjets up to your A380s, so that appears to circumstantially support that.

I’m not super attached to this take so I’m open to different interpretations, corrections, or other insights.

 

[tsmith1315]

What it all boils down to for me is the fact that to be 100% legit OP needs to cert level 1 in order to fly his rocket if it was over 53oz. I just don't see a need for that if using a MPR motor.

Even more importantly, what it boils down to is the FAA requires a COA and a NOTAM in order to fly it legally on any motor that will get it off the ground.

Given that rockets exceeding this limit require an FAA waiver as well,

Right.

 

[OzHybrid]

There has to be a line in the sand. The line is between model rocket and rocket. Weight and rocket motor performance and use of metal in construction being prohibited for for a model rocket. Some rockets at the upper end are going to get close to the limits.
Take it as a challange of your rocket building ability to make your flight comply with the rules. 6.5" dia 4ft long, 1200gm with a G64 loaded. Made my own tube as nothing came close commercially. It's quite doable

 

[John Kemker]

I don’t know the history of how weight became a determining factor, but if you calculate the terminal velocities and kinetic energy of two rockets which are identical except for weight during ballistic (no ejection) descent. You may see a situation where weight makes a difference.

If I recall correctly, the original NFPA code for model rockets had a total mass (weight) limit, as well as a propellant mass limit. Rockets that massed over the limit were not considered "model" rockets.

 

[OzHybrid]

The rules for model rockets are a mixture of what's allowed in them and what's automatically classified as HPR. If it's classified as HPR it cannot by definition be a model rocket. So over 80 N of thrust in a single motor or over 125gm propellant total or a sparkie, hybrid or experimental. Are all HPR so cannot be a model rocket.
A Model rocket must be less than 1500gm and has construction material restrictions. The motor is not considered to be part of the construction of the model rocket so a reloadable Aerotech aluminium case would be compliant. A model rocket must be constructed from paper,cardboard, wood or plastic. ( so aluminium fins would be prohibited)
The rules are in NFPA1122 current version is 2018 for model rockets and NFPA1127-2018 for High Power. All of the rocketry codes reference these docs. Including the Australian codes.
Lastly... the propellant mass for a G used to be 62.5gm. This meant you could do a 2xG launch and know that you were within model rocket limits. The max propellant for a G can now be up to 125gm. This has allowed some new motors to be developed, but has blurred things slightly too. So careful not to exceed the propellant limit with a 2xG flight.
I'm sure someone will shoot me down in flames for something I've missed so refer to the NFPA standards.

 

[jqavins]

I vaguely recall Future Farmers of America, but that may have been a local high school club...

Not unless you went to high school in South Brunswick, New Jersey.

 

[jqavins]

I totally agree, I don't think it's really an argument though, just a healthy discussion.

(I'm prone to occasionally getting caught up in a disagreement until a discussion becomes an argument, and I know I'm not unique in that. I felt like this was starting to head that way.)

 

[Steve Shannon]

If I recall correctly, the original NFPA code for model rockets had a total mass (weight) limit, as well as a propellant mass limit. Rockets that massed over the limit were not considered "model" rockets.

All of the versions of NFPA along with all of the justifications for changes are available on the page for the specific NFPA code.
I do remember when the FAA distinguished between model rockets (up to 16 oz.), large model rockets (over 16 oz up to 3.3 lbs/1500 grams), and above. Large model rockets had some specific requirements, such as notifications to airports etc. that no longer exist.
In my opinion the FAA made things much cleaner when they adopted their current three classes. It’s not perfect; nothing ever is, but the FAA has proven itself very good to work with. Rocketry regulations are much easier to follow than the more recently adopted drone regulations.

 

[thecapotc]

I can't agree more but it is a rule of thumb and not in the safety codes. Lots of variables that can either increase or decrease that ratio needed for a safe flight. I did do the math and stated this in my post #26: What is now considered a G MPR motor is not going to be able to safely fly much more weight than that anyway. This was in response to flying a G in a 53 oz. rocket.

I totally agree, I don't think it's really an argument though, just a healthy discussion. What it all boils down to for me is the fact that to be 100% legit OP needs to cert level 1 in order to fly his rocket if it was over 53oz. I just don't see a need for that if using a MPR motor. It would be nice to hear from OP what the actual weight was. I'd bet is was under by a little bit. All done!!

The rocket is currently with the club's biggest sponsor, but I was able to get the weight of the rocket from them.

It is currently sitting with no dog barf, but all recovery equipment and the motor casing still mounted. That weight is 1386.3 grams.

Assuming based on the data available from the Apogee page where I purchased the motor for the club I can add an additional 59.7 g for the propellant weight so now up to 1446 g.

Don't recall the exact amount of the dog barf, but a 4" diameter cylinder 3" thick gives a volume of .02 ft^3, and using my google skills blown in cellulose insulation stolen from a club members attic weighs 2 lb/ft^3 so add about 18 g for the dog barf. Playing it safe since kids loaded it under supervision and we are now at 1471 g.

With a guesstimate of an additional 25 g for the non-case / non-propellant weight (not sure if the delay and ejection charges count as propellant mass) of the motor and we made it home safely by 4 grams.

Far too close for comfort now that I know the rules.

 

[dhbarr]

In my opinion the FAA made things much cleaner when they adopted their current three classes. It’s not perfect; nothing ever is, but the FAA has proven itself very good to work with. Rocketry regulations are much easier to follow than the more recently adopted drone regulations.

In my opinion, it is because our community has historically been much more deliberate about self-regulating that we didn't get caught up in the drones-for-christmas overreaction.

 

[tsmith1315]

With a guesstimate of an additional 25 g for the non-case / non-propellant weight (not sure if the delay and ejection charges count as propellant mass) of the motor

Ready to fly motor weight is available at thrustcurve.org, in Aerotech’s Motor Matrix, and in OpenRocket files.

Thrustcurve and Aerotech show 124-125g for G78 RMS, depending on delay.

 

[Steve Shannon]

The rocket is currently with the club's biggest sponsor, but I was able to get the weight of the rocket from them.

It is currently sitting with no dog barf, but all recovery equipment and the motor casing still mounted. That weight is 1386.3 grams.

Assuming based on the data available from the Apogee page where I purchased the motor for the club I can add an additional 59.7 g for the propellant weight so now up to 1446 g.

Don't recall the exact amount of the dog barf, but a 4" diameter cylinder 3" thick gives a volume of .02 ft^3, and using my google skills blown in cellulose insulation stolen from a club members attic weighs 2 lb/ft^3 so add about 18 g for the dog barf. Playing it safe since kids loaded it under supervision and we are now at 1471 g.

With a guesstimate of an additional 25 g for the non-case / non-propellant weight (not sure if the delay and ejection charges count as propellant mass) of the motor and we made it home safely by 4 grams.

Far too close for comfort now that I know the rules.

I wouldn’t worry about it too much. There’s nobody hidden behind bushes waiting to bust you for 1505 grams. Thank you for caring and doing the right thing!

 

[smstachwick]

I wouldn’t worry about it too much. There’s nobody hidden behind bushes waiting to bust you for 1505 grams. Thank you for caring and doing the right thing!

Ditto.

Also, welcome to high-power!

 

[thecapotc]

The lack of bushes at our launch site is a plus since the only thing for the rocket police to hide behind are some grass clippings in case we pick up a couple extra grams along the way.

And even though I keep telling myself I'm not really interested in going much beyond the 1996 Phoenix and Shadow BT-80 rockets I so desperately wanted as a kid I do keep hearing a little voice saying "You know a Shadow upscale to 4" would be a great rocket for an L1 cert." When I shut that one up the other one says "There's that nice 4" LOC Phoenix kit you could do an L1 on."

 

[jqavins]

Ha-hah, hooked another one! [EVIL_GRIN]

thecapotc​

THE CAPtain Of The [fire] Company?

 

[Steve Shannon]

Certification has three steps:
L1 - just another rocket.
L2 - an easy quiz followed by just another rocket.
L3 - A take home essay test and just another rocket.