# My new project, should I do it?

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#### BruuD

##### Member
Hi there,

I'm building a rocket based on a tube of 100cm in length / 10 cm in diameter.
When it's done it will have 4 fins and use a cluster of 5 D12-3 engines to launch it.
The total weight including engines will be aprox. 600 gramms.

How is that engine configuration?
Need more power? Or maybe different engines?
I'm pretty new to rocketry and this is my biggest project so far.

BruuD

#### Fore Check

##### Well-Known Member
Just to clarify for the metric-challenged (including me)

This rocket will be about 39" long, 3.9" diameter, and weigh 21.162 oz.

Here's the Estes liftoff weight/engine chart:

Code:
           Max Lift off Weight
Engine       Ounces    Grams
------       ------    -----
D12-3         14.0      396
D12-5         10.0      283
D12-7          8.0      226
E9-4          15.0      425
E9-6          12.0      340
E9-8          10.0      283
According to this, the max liftoff weight for your cluster is 1980 grams or 70 oz. This gives you a safety rating of about 3.5, so you should be fine with your engine selection.

#### jflis

##### Well-Known Member
I agree with respect to boost, but I am concerned that the delay may be too short. 5 D12 motors will get even *that* package moving at a pretty good speed and I wonder if a D12-5 would be a better choice.

For example, our Richter Recker kit is 2.217" diameter, loaded weight is about 15.9 oz. and it uses a cluster of three D12 motors. In that vehicle, 3 seconds is *much* too short a delay and I have to use D12-5...

jim

#### powderburner

##### Well-Known Member
Welcome to TRF!

It sounds like you have a pretty ambitious project there----have you launched many clusters this big? The reason I ask is this: you may want to cut back to three 24mm motor mounts, or begin your experiments with five 18mm motor mounts.

Also, with five motors of that size, you are beginning to bump into the requirement to notify the FAA before you fly?

P.S. Does all that metric stuff mean that you are in Europe, maybe?

#### JRThro

Originally posted by powderburner
Does all that metric stuff mean that you are in Europe, maybe?
It means he's virtually anywhere but the USA, doesn't it?

##### Well-Known Member
Welcome!

OK, 5 D12's provide a combined average thrust of 60N. The weight of your rocket is about 6N. So you're looking at a thrust/weight ratio of 10:1, and that thing is going to go fast. On the other hand, it's a lot fatter than the Richter Recker, i.e. more drag, so it's going to decelerate more rapidly too.

I'd also guess that D12-5's would be better. However, I wouldn't agree with the suggestion to use either three 24mm or five 18mm mounts. Put all five 24mm mounts in. You can make 24mm - 18mm adaptors (the quick, dirty way is to knock the clay nozzles out of five used D12's). Or you can block two of the mounts and only use three live motors. And then, when you've got some idea of what the rocket will do with lower power, you can let it go on full power.

We want photos. We want launch reports.

#### JRThro

Originally posted by powderburner
Also, with five motors of that size, you are beginning to bump into the requirement to notify the FAA before you fly?
----------------------------
Here are the requirements:

For multiple motors, if the total combined impulse exceeds 320 N-s, you have to be high-power certified.

For multiple motors, if the total propellant mass exceeds 113 g, you have to notify the FAA. If it exceeds 125 g, you have to file an FAA waiver and be high-power certified.

Also, if the total rocket mass exceeds 453 g with motors loaded, you have to notify the FAA. If it exceeds 1500 g, you have to file an FAA waiver and be high-power certified.

----------------------------
Here is where his rocket fits in:

The total combined impulse of his motors is 5 * 16.84 N-s (for an Estes D12) = 84.2 N-s. No certification necessary based on this criterion.

The total propellant mass of his rocket is 5 * 21.1 g (for an Estes D12) = 105.5 g. No notification necessary based on this criterion.

The total mass of his rocket is 600 g with motors loaded. He does have to notify the FAA, based on this criterion.

#### North Star

##### Well-Known Member
Originally posted by JRThro
It means he's virtually anywhere but the USA, doesn't it?
Ahem.. there are still some of us on the fringes of Europe (floating at a discreet distance anyway) that prefer the ancient ways. Anyway- your money was metric before ours.

#### BruuD

##### Member
Thanks for all the replies!

First launch will be with D12-3 engines since I already ordered 9 of them
I think I will start with 3 onces but the motor-mount will have 5 tubes for future launches.

I never heared of the FAA
Don't know if there is a FAA in The Netherlands and if there is, I don't care.

During the construction of the rocket I will update this topic with pictures and, of course, there will be launch pictures/video's.
If the rocket is good enough I will built in my wireless cam so an on-board video will be available

Greetzz,
BruuD

#### JRThro

Originally posted by North Star
Ahem.. there are still some of us on the fringes of Europe (floating at a discreet distance anyway) that prefer the ancient ways. Anyway- your money was metric before ours.
Do you mean to tell me that the United Kingdom of Great Britain and Northern Ireland isn't entirely metric? You use feet instead of meters, miles instead of kilometers, ounces instead of grams, and pounds instead of kilograms?

#### JRThro

Originally posted by BruuD
Thanks for all the replies!

First launch will be with D12-3 engines since I already ordered 9 of them
I think I will start with 3 onces but the motor-mount will have 5 tubes for future launches.

I never heared of the FAA :d
Don't know if there is a FAA in The Netherlands and if there is, I don't care.

During the construction of the rocket I will update this topic with pictures and, of course, there will be launch pictures/video's.
If the rocket is good enough I will built in my wireless cam so an on-board video will be available :d

Greetzz,
BruuD
BruuD, I am totally unfamiliar with the regulations governing rocketry in the Netherlands. All of my comments were based on U.S. regulations.

If you don't care about the regulations in your own country, that may cause a problem for you at some point.

#### JRThro

Originally posted by BruuD
Thanks for all the replies!

First launch will be with D12-3 engines since I already ordered 9 of them
I think I will start with 3 onces but the motor-mount will have 5 tubes for future launches.

I never heared of the FAA
Don't know if there is a FAA in The Netherlands and if there is, I don't care.

During the construction of the rocket I will update this topic with pictures and, of course, there will be launch pictures/video's.
If the rocket is good enough I will built in my wireless cam so an on-board video will be available

Greetzz,
BruuD
BruuD,

Have you confirmed that your rocket will be stable with all 5 motors in it? That is, will the center of gravity (CG) be at least 10 cm in front of the center of pressure (CP)?

#### North Star

##### Well-Known Member
Originally posted by JRThro
Do you mean to tell me that the United Kingdom of Great Britain and Northern Ireland isn't entirely metric? You use feet instead of meters, miles instead of kilometers, ounces instead of grams, and pounds instead of kilograms?
Miles - certainly; Feet and inches - quite a bit ; pounds and ounces - sadly diminishing.

#### BruuD

##### Member
Originally posted by JRThro
BruuD,

Have you confirmed that your rocket will be stable with all 5 motors in it? That is, will the center of gravity (CG) be at least 10 cm in front of the center of pressure (CP)?
What's the best method to confirm this?
I usally just guess
Maybe not a good idea with a rocket of this size

#### JRThro

Originally posted by BruuD
What's the best method to confirm this?
I usally just guess
Maybe not a good idea with a rocket of this size
Yeah, maybe not.

The CG you can measure by loading up all 5 motors, the parachute, wadding, etc., so the rocket is ready to be launched. Then find the point at which the rocket will balance on a ruler, the back of a chair, or something like that.

The CP has to be calculated. What I usually use is either the free demo version of RockSim from Apogee Components (at https://www.apogeerockets.com/rocksim.asp, go to the bottom of the page and click on "Download A FREE demo version of RockSim v5"), or I use the free program called VCP, which you can get at https://myweb.cableone.net/cjcrowell/VCPMAIN.htm.

Good luck!

#### North Star

##### Well-Known Member
Originally posted by BruuD

I never heared of the FAA
Don't know if there is a FAA in The Netherlands and if there is, I don't care.
BruuD ... you might pick up some local information from here

https://www.tripoli.nl

They are a very active group and Frank (Rebel Rocketry) is a regular visitor to our big launches in UK

#### BruuD

##### Member
I have another question about the ejection charge.
Should I use only one of the 5 engine's ejection charge for ejecting the nosecone and parachute or all 5 of them?

#### dr wogz

##### Fly caster
You mean using 4 x D12-0 (booster stages) and 1 x D12-5?

Ya know, that is a good question!

I would think to use all 5. If the one with the ejection didn't fire, you're outta luck!

#### cjl

##### Well-Known Member
I would use 2 or 3 D12-5's, and the rest D-11P's. That way, there's no chance of it accidentally melting the chute or popping the nose cone when the staging charge fired (if you used D12-0's). By using 2 or 3, you are basically guaranteed that at least one will fire and give you an ejection charge, without snapping the shock cord from 5 ejection charges. Might I make a suggestion? Use 2 E mounts and launch with 2 E9-6's and 3 D11-P's.

#### Mister Rogers

##### Active Member
Originally posted by BruuD
I have another question about the ejection charge.
Should I use only one of the 5 engine's ejection charge for ejecting the nosecone and parachute or all 5 of them?
Well, that is a difficult question. If you use only one engine with an ejection charge, I would question whether it has enough force to pressurize a 10cm x 100cm space and eject the cone and chute. On the other hand, if all five have an ejection charge, there is no guarentee they will go off at exactly the same time. Delays are notoriously inaccurate. The biggest danger though would be if only some of the engines lit off in the first place because at ejection, the hot particles may ignite the TOPS of the engines that did not ignite on the ground and try to propel the rocket backwards, as well as torching the inside of the rocket.
If it were me, and I really, really wanted to cluster 5 "D" engines, then I would certainly go with one D12-5 and 4 D11-P (P is for "plugged" and will not ignite from the top). Hope that helps. Good Luck and post pictures

Forgot to add that with one D12-5, I would use a "stuffer tube" internally to reduce the volume that needed to be pressurized.

#### MetMan

##### Well-Known Member
Originally posted by BruuD
I have another question about the ejection charge.
Should I use only one of the 5 engine's ejection charge for ejecting the nosecone and parachute or all 5 of them?
Here's another thought. you could use a pair of D12-5s or however many you think will be enough to blow the nose cone and use a pair of D12-7s as well "just in case". You shouldn't need them, but it sounds cool anyway!