Engine Swap

The Rocketry Forum

Help Support The Rocketry Forum:

AKPilot

Well-Known Member
Joined
Jan 5, 2009
Messages
5,347
Reaction score
0
Okay, being a newbie I've searched the forum and haven't been able to locate an answer to this . . . so any thoughts would be appreciated.

I've got several models that use C6-5 engines. While the manufacturer doesn't recommend it, is there any real harm if I put different engines in these rockets - as long as they can support the weight? Common sense tells me to go ahead. I understand the numbers, but don't understand why the manufacturers don't give a "range" of engines - most of the times they definite recommendations. For example, hypothetically, can I put a C6-3 or a B6-4 in instead of a C6-5?

The reason being, I'd simply like to experiment. Some days, depending on the weather or kids' desire, I don't need them going as high and others we'd like to push it further.

Any thoughts . . .
 

wwattles

Well-Known Member
Joined
Jan 21, 2009
Messages
2,870
Reaction score
0
The reason they recommend specific motors is to optimize 1) the performance off the pad; and 2) the delay before the ejection charge. Some models may NEED that faster burn, and whenever you play with the ejection delay, you run the risk of damaging your rocket.

From someone who knows, when they recommend a 6 second delay, don't use a 3-second delay!!!:eek:

WW
 

AKPilot

Well-Known Member
Joined
Jan 5, 2009
Messages
5,347
Reaction score
0
Okay, I've got to ask . . . what happend when you did the 3 second delay, over the 6?
 

BlueNinja

Well-Known Member
Joined
Jan 18, 2009
Messages
2,701
Reaction score
1
You will cut your airframe with teh shock cord, the airframe will be moving faster than the cord so it will "zipper". Or, if you are using estes chutes you will prolly shred those.
 

wwattles

Well-Known Member
Joined
Jan 21, 2009
Messages
2,870
Reaction score
0
It zippered AND then ripped the shock cord out. Rocket body came down hard and fast, never saw the chute/nosecone again. At least it was a cheap rocket and easy to replace!

WW
 

solrules

Well-Known Member
Joined
Dec 30, 2003
Messages
366
Reaction score
0
Don't use too long of a delay, either. I had the privilage of using one of Estes' new fangled C6-∞ motors (they are off the market now, though.)
 

North Star

Well-Known Member
Joined
Apr 14, 2009
Messages
403
Reaction score
0
Originally posted by akpilot
For example, hypothetically, can I put a C6-3 or a B6-4 in instead of a C6-5?

The reason being, I'd simply like to experiment. Some days, depending on the weather or kids' desire, I don't need them going as high and others we'd like to push it further.
The much maligned Estes kits used to (still do?) have a variety of motors suitable for each kit and usually specified a lower powered motor for the first flight so you could get an idea of how the rocket flew. I swap motors all the time in my models dependant on wind or site size.

To do this you need a basic command of rocketry so you don't interfere with the stability of the rocket (extra weight at the rear or not enough kick to produce dynamic stability) and be able to use one of the simple (free) sims for the delay time. So ,if you are new to the hobby, stick with the instructions, once you gain experience - experiment away.

There will always be some rockets that can only use one motor due to unique design features or being at the top end of the weight for a motor size (ie 18mm 24mm etc)
 

DynaSoar

Well-Known Member
Joined
Mar 15, 2004
Messages
3,022
Reaction score
0
Originally posted by akpilot
The reason being, I'd simply like to experiment. Some days, depending on the weather or kids' desire, I don't need them going as high and others we'd like to push it further.

Any thoughts . . .
Experimenting is a fine idea, and no, I'm not being sarcastic. Just understand that the rocket or chute may not survive, and that its flight might prove dangerous to anyone nearby. This may void your warranty and possibly your NAR insurance if you have it. You'll be entirely responsible for the outcome.

A B6 won't push it as high as a C6, so a shorter delay (4 seconds) is reasonable. It may not yet be stable when it leaves the rod. It may peak so low and soon that the ejection charge will go off at head height.

On a C6-3 it'll fly the same but the chute will pop while it's still travelling fast. The chute may fail, or the shock cord may rip straight down through the body tube like the peel-strip on a pack of gum. On a C6-7, same thing, but headed down (and probably not as fast).

If you can do it safely and aren't afraid of facing negative consequences, least of which is a ruined rocket, experiment away. And I'm *still* not being sarcastic. I do it often. I have a design I'm testing, and the best motors to test it aren't "legal". They're no longer certified (because they're no longer made). I'll fly it on these under appropriate conditions. By appropriate conditions I mean safety levels equivalent to a firing range because that's what it'll be.
 

AKPilot

Well-Known Member
Joined
Jan 5, 2009
Messages
5,347
Reaction score
0
Thanks to everyone for the advice . . . it was what I was looking for.

Common sense told me some things, but I would've never figured out the "zipper" effect, without going through it personally.

Thanks again . . .
 
Top