Aerotech G-Force experiences

The first question is, how much weight are you lifting?

You might rethink the motor your planning on using...which would lead to the next question, is it built well enough to handle a larger/longer motor. H128?

If you go to Aerotech's webpage, the altitude on the rocket WITHOUT any payload is only predicted to be 640' with a G80.

If you put the data into WRASP , in a similar rocket like the LOC IV, and put the weight of 32oz for the initial weight of the rocket specified from Aerotech, along with just a 1lb payload, you have 48oz to get off the ground or 4lbs. Put that into WRASP in the LOC IV and you get 524'. Your launch rod velocity is at 27.2 ft per second, so it would be better to be safe and use a long launch rod of 5' or better. Your really pushing it for a safe flight as the minimum safe ave. thrust should be 89 newtons on a 4lb rocket (4lbs*4.45*5), and the G80 only has 77.5 newtons.

You might think about using an Aerotech H128 with a 6 second delay for a flight of around 964'

Goodluck.

-Booms

The first flight will be just the rocket itself. Second flight which might carry the Cansat itself is around the 12 to 14 ounce range.

Actually I am more worried about the likeyhood of the tube zippering after ejection or the upper body section striking the lower body section giving it's on one long (very long by my experience) shock cord and the parachute is mounted on the middle of that shock cord.

First, the longer the shock cord, the better. Second, putting the parachute at the middle of the shock cord is a mistake -- then the top half comes down and smacks the bottom half, and bangs together all the way down.

I tend to put the parachute about one-third of the distance FROM the top section -- in other words, top section, 1/3 of shock cord, parachute,

2/3 of shock cord, bottom section. This tends to keep the pieces from banging together, and allows for the bottom part (generally more robust) to touch down first.

Zippering is a problem if you don't have the right timing for the delay. If you eject at (or close to) apogee, zippering is unlikely. If you're delay is too short/long, you increase the probability of a zipper. You might want to switch to a reloadable motor, and trim the delay, if you find that the single use motors don't offer quite the delay that you need.

David Erbas-White

Parachutes shouldn't be in the middle of a shock cord. Parachutes should be

1/3 of the way down the shock cord from the top. Do that and you shouldn't have any problems with the top hitting the bottom. A 10' shock cord should suffice for keeping things apart.

If you really want to see what your rocket might do...plug the data into WRASP in a LOC IV. It's a very similar rocket even though it's shorter. The weight can be adjusted and the main similarity is the 4" dia. WRASP is free to use. You should be fine with a 4 second delay with the payload, but it could very well be too quick for the flight without the payload and cause a zipper. Best check it out in a sim. You can also try Rocksim on a free trial from Apogee if you have the patience and time to put it in.

Maybe Gary has already done so and can e-mail you the Rocksim file from Aerotech.

-Booms

What is the replacement cost of the Cansat, including time and labor? I'd strongly recommend that you make a flight with a dummy Cansat payload of the same size and weight, and resolve any issues observed, before lofting the real payload.

All good comments. I replaced the fins on mine with plywood after breaking the tips off two of them when the stuck in the dirt. Mine is far from stock. It has a 38 mm motor mount, four inch diameter ejection baffle, and instead of paint, I used Monokote for the finish. Well, the nose cone is painted. I reinforced the top of the body tube with a two inch wide strip of four ounce glass cloth applied with thin CA glue, and finished off with thick CA rubbed in with a glove covered finger. It helps prevent zippers and can hardly be seen under the Monokote.

Here's a short video on a Loki I405 motor.

Here

is Doug's "CANSAT". Although they may be using something else as that term is becoming a bit generic: like Kleenex... 8) Will

Alan Jones wrote: ...

Hi Helen,

With a 12-14 ounce CanSat stuck in it and the l/d of a G-Force, my hunch is that the G-Force will probably be more apt to turn into the wind as it lumbers up there.

Play the wind?

Best, Andy

Long time, no hear. Welcome back!

Don't forget that this rocket will need FAA notification at a minimum. if it's over 1500g not only is a waiver required, but it's subject to HPR rules including certification, even though it's only got a G motor in it.

I seem to disagree with common practice. I prefer to attach my chute direct to the nose cone / payload section, rather to the middle of the shock cord.

I don't always do it the way I outlined, sometimes I do it the way you've defined it as well. Can't really say I have a clear definition of why/when I do either way, other than by gut feel -- not something I've ever thought about, but I guess I really should...

David Erbas-White

Where is it written; rockets exceeding 1500g, using a g motor, especially a G80 Blue Thunder, require HPR certification ?? Maybe I missed it, or were you talking about motor certification???

I agree with this, I have seen to many tangled recovery's, with folks using the middle attachment, especially dual system recovery deployment.

>

Where Is The Line Between Model and High Power Rocketry?

A rocket exceeds the definition of a model rocket under NFPA 1122 and becomes a high power rocket under NFPA 1127 if it:

• Uses a motor with more than 160 Newton-seconds of total impulse (an"H" motor or larger) or multiple motors that all together exceed 320 Newton-seconds; * Uses a motor with more than 80 Newtons average thrust (see rocket motor coding); * Weighs more than 1,500 grams including motor(s); or * Includes any airframe parts of ductile metal.

Rapozo

I think you missed my point on HPR certification requirements. I do not believe an A/T G80T exceeds 160ns total or 80ns average thrust.. Therefore, no HPR certification is required to use this motor in any size rocket, (never has been to my knowledge). FAA notification; yes, but only if the total weight of the loaded rocket is at or exceeds

1500g. A 1500g or larger rocket with a A/T G80T needs a FAA notification for sure.. However, HPR certification of the individual is not a requirement.

Fred

The G-Force comes with a 18 foot shock cord, between the knots and the length of the cord that is inside of the tubes it has to be at least 16.5 feet between the two sections.

Rapozo

Hi Fred: I took a look in NFPA 1127 and any rocket that masses over 1500g at liftoff is, by NFPA 1127 definition, a high power rocket. The motor doesn't matter. And NFPA 1127 says only a certified user may launch a high power rocket. A certified user is a person recognized by a national organization to use high power motors. That means you have to have at least an L1. Therefore you must have at least an L1 to launch a rocket massing more than 1500g at liftoff regardless of motor. I haven't figured out how many MicroMaxx motors you need to cluster to get over the 125g limit to also make it a high power rocket... 8) Best wishes, Will

Since this is becoming anal retentive, why don't you verify if universities even require the HPR certification since I know they don't require them to have LEUP's to even buy M motors. They are only required to have the proper storage.

Geesh, get over it people. All they need to do is call in an FAR 101 and fly the damn thing. Give em' a break.

-Booms

Rapozo

Quite right, rockets need no certification. They do need to be passed by the RSO, even if the flyer is alone and acting as his own RSO. AR need not require use of certified motors or flyers. However, LMR is a red tape sweet spot. In this case a rocketeer (ideally an NAR or TRA member) without HPR certification or a LEUP, can purchase MR G motors containing 62.5 g. of propellant or less, and fly as many as two clustered in a rocket with a launch weight of no more than 1500 g., with simple FAA notification.

Hey Booms, Get over what?? If you don't like the topic why bother responding?? Talk about anal retentive..(:-)

Fred