Single Altimeter w/main as backup?

Has anyone ever done this? My rocket should only be reaching about 1200' so DD isn't really necessary. I was thinking of firing the main out at apogee, and using the main setting on the alt as a backup at around 7-800'? Is this feasible?

Thanks
Dave

Sounds like this could be a zipper waiting to happen. I assume you're thinking of using the motor's ejection charge as your main and want the altimeter to back it up. If your rocket has 4-500 feet to fall ballistically before deployment, it will likely develop enough speed to zipper your tube. Instead, you may be better setting your altimeter to deploy at apogee and use a slightly longer motor delay as backup. That way the rocket doesn't get a full head of steam before the second charge fires.

Bryan

No motor ejection. Deployment will be from the altimeter only. The altimeter will punch the chute out at apogee. The I will set the main charge just a couple hundred feet lower as a back up.

Dave

I have a better idea

go to https://store.heavenlyhobbies.com/01-024-0001.html

That's a reasonable thing to do. You do run the risk of not having a true redundant sytem, however. If your altimeter dies, your rocket is toast. You could also set the altimeter to fire the second charge at a certain time after launch. This would prevent a failure in which the rocket does not attain the altitude you expect (say from severe weathercocking for example) and therefore would not trigger your second charge. Not sure how the Heavenly Hobbies setup would help at all, but that's alright.

Bryan

Well that's what the Internet is for, these EMRR reviews show a good idea about how the system works.....


https://www.rocketreviews.com/reviews/all/heavenly_backdraft.shtml

davalf said:

No motor ejection. Deployment will be from the altimeter only. The altimeter will punch the chute out at apogee. The I will set the main charge just a couple hundred feet lower as a back up.

Dave

Click to expand...

I'm not sure what the issue is here. What you describe will certainly work.

Why not just use the altimeter for DD?

Personally, I would just go ahead and use the DD. Even at 1,200 ft. Set the main at 400/500 and go for it. With the low altitude you will get a good look at how the drogue deploys, how it falls, whether it needs to be bigger or smaller, etc.

I've found that DD give much better deployment then trusting some delay grain to burn at the right rate. Gentler deploy at apogee and the main is done at a known and controlled speed.

Just my :2:

davalf said:

Has anyone ever done this? My rocket should only be reaching about 1200' so DD isn't really necessary. I was thinking of firing the main out at apogee, and using the main setting on the alt as a backup at around 7-800'? Is this feasible?

Thanks
Dave

Click to expand...

"My rocket should only be reaching about 1200' so DD isn't really necessary?"
No, but DD is cooler than motor ejection. I'd let the field conditions decide if I need DD or not.

"I was thinking of firing the main out at apogee, and using the main setting on the alt as a backup at around 7-800'? Is this feasible?"
What is it you are backing up?

DD is fun, and you also get deployment at apogee, not at some point that you're guessing will be near apogee. I'd set it up for full DD, and get used to flying it that way.

I've used DD on (MPR) flights that didn't even break 1000 feet.