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-   -   Looking for one of these engines (http://www.oldrocketforum.com/showthread.php?t=5695)

BRC 08-06-2009 04:02 PM

Looking for one of these engines
 
Aerotech G78-4G Single Use Rocket Motor or
Aerotech G80-4T Single Use Rocket Motor

If ya happen to have one laying around !!

ghrocketman 08-07-2009 08:48 AM

I do not have any of those rite now, but those are fairly common engines.
Why dont you order some through Commonwealth or another of the online vendors ??

BRC 08-07-2009 09:05 AM

I've tried the first one is not made anymore and the
second is out of stock everywear I looked. !!!

Shreadvector 08-07-2009 09:57 AM

Quote:
Originally Posted by BRC
Aerotech G78-4G Single Use Rocket Motor or
Aerotech G80-4T Single Use Rocket Motor

If ya happen to have one laying around !!


The G80-4 is no longer made for a very good reason. The current production G80 motors have 137 Newton-Seconds of total impulse. They acheived this huge increase in total power obtained by using the maximum propellant mass allowed (62.5 grams) and an extremely efficient design: nozzle expanded better than the original and operating pressure is higher thanks to a new casing design.

As a result, the maximum size Model Rocket (3.3.pounds) which is usually around 4 inches in diameter, will NEED a 7 second delay time to reach apogee. The older version of the G80 motor had a lower total impulse, so a fat and heavy rocket would require a shorter delay time since they would not fly as high or fast.

Old version: http://www.nar.org/SandT/pdf/Aerotech/G80.pdf

New/current version: http://www.nar.org/SandT/pdf/Aerotech/G80-20071207.pdf

Shreadvector 08-07-2009 10:01 AM

By the way, the new G80 is so powerful, they had to tailor the grain geometry to keep the average thrust below 80 Newtons to comply with Model Rocket Motor limits.

IIRC there are 2 segments with different geometry. Note the lower "tail" at the end of the motor burn that brings down the average.


if you have some other unusual project that really needs a 4 second delay, I suggest going with RMS where you will have a choice of motors with a 4 second delay time.

ghrocketman 08-07-2009 11:49 AM

Better yet than tailoring the grain to keep it at 80n avg. thrust or less would be to TOTALLY GET RID OF THAT REQUIREMENT for definition of a model rocket motor.
Quite frankly, now that the APCP BATFE case has been won, I'd like to see ALL consumer rocket motors through at LEAST "P" class be on the hobby shelf with NO restrictions to use or purchase other than following the proper FAA regs for flight waivers.
Yes, I'd like to see the entire cert process eliminated.

BRC 08-07-2009 02:01 PM

Quote:
Originally Posted by Shreadvector
The G80-4 is no longer made for a very good reason. The current production G80 motors have 137 Newton-Seconds of total impulse. They acheived this huge increase in total power obtained by using the maximum propellant mass allowed (62.5 grams) and an extremely efficient design: nozzle expanded better than the original and operating pressure is higher thanks to a new casing design.

As a result, the maximum size Model Rocket (3.3.pounds) which is usually around 4 inches in diameter, will NEED a 7 second delay time to reach apogee. The older version of the G80 motor had a lower total impulse, so a fat and heavy rocket would require a shorter delay time since they would not fly as high or fast.

Old version: http://www.nar.org/SandT/pdf/Aerotech/G80.pdf

New/current version: http://www.nar.org/SandT/pdf/Aerotech/G80-20071207.pdf



OK...I thought I would need the 4 second delay for my 4" Gemini Titan, but if you say the 7 sec delay will do Im on it !!!
Thanks for the insight..... :)

Shreadvector 08-07-2009 02:12 PM

Quote:
Originally Posted by BRC
OK...I thought I would need the 4 second delay for my 4" Gemini Titan, but if you say the 7 sec delay will do Im on it !!!
Thanks for the insight..... :)


Just MAKE SURE that when you buy them, they are the *NEW* G80-7 and not the old. The new packages have stickers loudly proclaiming the total-impulse. I had called Hobbylinc about that last year and they checked for me so I could get what I needed from the existing inventory.

BRC 08-07-2009 03:51 PM

Quote:
Originally Posted by Shreadvector
Just MAKE SURE that when you buy them, they are the *NEW* G80-7 and not the old. The new packages have stickers loudly proclaiming the total-impulse. I had called Hobbylinc about that last year and they checked for me so I could get what I needed from the existing inventory.


Thanks...I emailed Hobbylinc as soon as I got your last reply, but it took two days for them to respond last time as well...Thanks Again

stephen23648 08-13-2009 06:43 PM

Yes, I sent a G80-4T to NARAM for sale but I do not think it got any attention so it should still be available.


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