Need help designing a model rocket

[Art Upton]

That sounds like a good approach! Our constraints include the payload being 15 cm in diameter and the motor being about 10 cm in diameter. We'll look into what we can do to handle the thrust forces. Thank you for your response.

So in old English units, the payload is about 6" in diameter , 150mm and the motor is 4" or like our 98mm motors, yours being 100mm.

100mm diameter motors are huge even the coffee can short ones

 

[user 48716]

So in old English units, the payload is about 6" in diameter , 150mm and the motor is 4" or like our 98mm motors, yours being 100mm

Yes. Our motor's 98 mm as well, sorry about that, I just checked again.

The payload is 400 mm long, and 150 mm in diameter and the motor is 240 mm long and 98 mm in diameter (for cardboard). The motor dimensions vary depending on which material we use - PVC, aluminium or cardboard.

 

[user 48716]

they don't seem that bad (we do get that and a FAQ is a good idea), @dee can you promise not to use packing tape?

Sure! (if we get that far)

 

[Art Upton]

Yes. Our motor's 98 mm as well, sorry about that, I just checked again.

The payload is 400 mm long, and 150 mm in diameter and the motor is 240 mm long and 98 mm in diameter (for cardboard). The motor dimensions vary depending on which material we use - PVC, aluminium or cardboard.

Great, good to know, So for each type of rocket , they provide a more powerful motor.
I would ask if you can get the total impulse of the motor and the motor weight full and empty if you can.

So to us here in the States, you have a 98mm x 9.5" long motor. That would have some thrust.
We tend to call that shorter 98mm motor a "coffee can" motor due to it's looks. **

I assume you can use Plywood for fins. If not Fiberglass ?

** here is a similar motor by Aerotech 2560ns

 

[Art Upton]

Here is just the hardware on the 98mm "Coffee Can" motor

 

[Art Upton]

Another picture

 

[Art Upton]

Here is the length of the motor components, notice the case with top closure is 9.750 inches
Looking close it looks like just the case is 9.5 inches

 

[Art Upton]

CTI motors, pro 98 they are called , look like this. Sorry but their picture is so small.
The propellent grains in the 98 sizes actually can be used in either of these style cases.
They were made to be able to be used in competitor's motor hardware cases.

 

[BABAR]

That is a fault of the advisor, is it not? Unfortunately there are definitely some advisors who themselves have no experience in rocketry.

Those who can’t do, teach.

 

[WizardOfBoz]

So, give the professor who is letting his/her students do stuff that they aren't expert in some credit. One learns a lot from what the students figure out.

One comment above really scared me. It stated
"The motor dimensions vary depending on which material we use - PVC, aluminium or cardboard."

PVC is NOT a suitable material for a rocket engine burning composite (APCP) or black powder. It's not strong enough for the high pressures developed, and when it does fracture it shoots out jagged shards. Don't do this.

For perspective, one should not use PVC for pressurized air (100 psi) for the same reason (the pipes explode and send out shards). Rocket motors develop several 100 or even multiple 1000 psi combustion pressures.

 

[NTP2]

So, give the professor who is letting his/her students do stuff that they aren't expert in some credit. One learns a lot from what the students figure out.

One comment above really scared me. It stated
"The motor dimensions vary depending on which material we use - PVC, aluminium or cardboard."

PVC is NOT a suitable material for a rocket engine burning composite (APCP) or black powder. It's not strong enough for the high pressures developed, and when it does fracture it shoots out jagged shards. Don't do this.

For perspective, one should not use PVC for pressurized air (100 psi) for the same reason (the pipes explode and send out shards). Rocket motors develop several 100 or even multiple 1000 psi combustion pressures.

I don't think that's what they are talking about, the rockit body in PVC not the motor case.

 

[WizardOfBoz]

Thanks, @NTP2 I thought that this was the case, but this is reassuring. That said, and even though I like plastics, PVC would not be the material I would choose for a rocket.

There was a youtube video where a guy was building like a 4" diameter APCP rocket motor with a PVC casing. Scared the hell out of me.

 

[NTP2]

There was a youtube video where a guy was building like a 4" diameter APCP rocket motor with a PVC casing. Scared the hell out of me.

me too now!!

 

[Ronz Rocketz]

What?