Is there a maximum weight for a level 3 rocket?

Is there a maximum weight for a level 3 rocket?

Only based on the motor you use. Thrust-to-Weight ratio.

...so there is no NAR limit, as large and/or as many motors you can safely design, construct, and fly?

Read the NAR rules for level 3. It's gotta fly on a certified (commercial) motor, M through O impulse. CTI makes a 150 mm O8000, Gorilla a O4925, Aerotech a N3300 and Loki N3800.
So, if you can afford the $3100 plus the case at $4800 plus the shipping cost, you can do some easy calculations....
1750 pounds of thrust.... a 5:1 liftoff weight = 350 pounds pretty much describes it....
the N10000 will get you more weight but you loose impulse...
your mileage may vary.

...but your not limited to a single "O" (40,960) are you?

Cost no object here:wink:

jahall4 said:

...but your not limited to a single "O" (40,960) are you?

Click to expand...

Anything past 40960 N-s becomes a Class 3 rocket and the FAA process is much more involved. I'm not sure if NAR lets you fly anything like that, much less cert with it.

jahall4 said:

...but your not limited to a single "O" (40,960) are you?

Cost no object here:wink:

Click to expand...

All certification flights are limited to a single motor-no clusters or staging. It has to be a commercial certified motor, hence limited to an o motor, for a L3 cert.

Once you are L3, you can go above the o motor limit in Tripoli. This requires quite a lot of work, a lot of simulation, submit a serious write up to the TRA Class 3 committee for approval, submission to the FAA, and hopefully approval.

Please note that there are only a few launch sites that can support this type of power. For a P motor the minimum safe launch distance for a non complex flight is 2000', and for a complex is 2500'. It could be more depending on your flight profile. How many sites can support that distance?

Really was not asking about certification process. Obviously it would not make sense to use a complex rocket for cert even if it was allowed.

Interestingly the NAR safety code does specify 2000 Min Personnel distance for a complex "O" that is 500 more feet more than a non-complex "O", but of course that could cover say an N sustainer with an O booster. Anybody know?

I'll go with cbrarick's 350 lbs, thx!

Just now seeing Mark's Reply, thx, very interesting. So Tripoli picks up @ P?

What kind of project are you building or planning on building?

Nothing in particular, just trying to get an idea of the maximum recovery forces for an equipment purchase. When one starts talking about rockets of that weight, makes me question the 50x rule as 2 tons seem almost to much to believe. Surely with dual deployment that rule changes.

jahall4 said:

Just now seeing Mark's Reply, thx, very interesting. So Tripoli picks up @ P?

Click to expand...

I know Wildman just might have a single use CTI "P" in his inventory...at least he did...it's 8" in diameter so you need a big rocket...I'm thinking about it...

According to NFPA 1127 (2013) ...

4.9.1 The maximum liftoff weight of a high power rocket
shall not exceed one-third (1⁄3) of the certified average thrust
of the high power rocket motor(s) intended to be ignited at
launch.

4.9.2 A high power rocket shall be launched with any combination
of motors having 40,960 N-sec (9209 lb-sec) of total
impulse or less.

Click to expand...

So the maximum weight depends on the average thrust.

Therefore, if you were to launch a CTI 10347N10000-P Vmax with an average thrust of 10219.3 N, your maximum launch weight would be 347.36 kg (~765.8 lbs).

Math:

One-third of the average thrust of the motor is 3406.4333333 N.

1 N = 9.80665002864 kg

3406.4333333 / 9.9.80665002864 = 347.359528828393 kg

347.359528828393 kg = 765.7958 lbs

Greg

Greg:

You are right, according to the NFPA standard. However, if you fly 3:1 you'd better have calm winds.
Tim's CTI P motor isn't certified.

MickC's right the paperwork for class 3 is a lot more difficult then a level 3.

It took me 3 months to get it right and done. 540 pounds, my main recovery kevlar is 14,000 stuff.

Onebadhawk sells some real nice 7,000 pound kevlar. It would be perfect for any level 3........

To get the heaviest rocket possible, I would use a CTI O25000 for the motor. That would allow you to have a 1,860 pound rocket.

In theory yes - in reality here's what an O25000 did for a 600LB rocket. Something 3x as heavy would be 1/3 the altitude.

[video=youtube;xzcxEXHdHx0]https://www.youtube.com/watch?v=xzcxEXHdHx0[/video]

Zebedee said:

In theory yes - in reality here's what an O25000 did for a 600LB rocket. Something 3x as heavy would be 1/3 the altitude.

Click to expand...

That's an amazing video. The rocket just sort of... floated off the rail.

Zebedee said:

Something 3x as heavy would be 1/3 the altitude.

Click to expand...

It would be even worse. A simple approximation (constant T/W, no drag) can be written down as follows.

ta ... time to apogee
tb ... burn time
T/W ... thrust to weight ratio
vmax ... maximum speed
g ... standard gravity (9.81m/s^2 or 32 ft/s^2)
ha ... Apogee altitude


ta = tb * T/W

vmax = g * tb * (T/W - 1)

ha = ta * vmax / 2 = g * tb^2 * ((T/W)^2 - TW) / 2

So, if one drops the T/W from 9 to 3, the altitude gets reduced by about a factor of 12. Launching a short burning motor, like the O25000 on a T/W of 3:1, will result in an altitude of about 162ft (actually less, if drag is not neglected).
So, to make a long story short: A minimum thrust to weight ratio of 3:1 is not feasible with short burning motors in high powered rockets. If you want to get comical results, try the above formula with 38mm Warp9 motors (0.3s burn time).


If I had to guess, I'd say the maximum liftoff weight for a L3 rocket is maybe around 1000lbs, and it can be reached by clustering enough high thrust motors to max out the class 2 limit of 40.96kNs (e.g. 2x N10000 + 2x M3400). This would result in an apogee of roughly 1000ft. Depending on how fast the parachute on such a big rocket can be deployed, a few hundred additional pounds might be possible, but as the formula above shows, a modest increase in weight will result in a big loss in altitude.


Reinhard

Their website quoted 600 and something - I guess it put on a little weight during the build

Reinhard - yes I was thinking of the best case of converting X amount of chemical energy into potential energy (which is directly proportional to mass and height change)