Large midpower

[Nateairman]

I have scratch built a large midpower rocket. It is a cluster because I like them. 6 24mm around a central 29mm. Careful motor choice is required to keep it in the mid power range. The maiden will be on 3 f44w-8. It has simmed well and I will go back through all the details in the sim file compared to the real build.

It is under 1.5 kg and will be flown for the first time when conditions are ideal.

It will be an exciting flight!

 

[BABAR]

Cool!
how do you close off the unused motor bays so the ejection charge doesn’t turn into a sulphuric fart?

 

[Nateairman]

Cool!
how do you close off the unused motor bays so the ejection charge doesn’t turn into a sulphuric fart?

That is a good question. I plan to use blanks in the unused chambers which will be held in with the motor retainer. I have used 3d printed parts for this in the past and may do it again.

I like the method of installing plugs from the payload side but it is a long reach to get in there.

 

[Sooner Boomer]

You could use burned engines and either put some epoxy in them to seal them, or jam some tissue or paper towel in and soak with white or yellow glue. Engines make perfect plugs.

 

[Nateairman]

You could use burned engines and either put some epoxy in them to seal them, or jam some tissue or paper towel in and soak with white or yellow glue. Engines make perfect plugs.

That is a good idea. I am on a bit of a weight minimizing mission here. The parts are 8 grams each for the 24mm plug and 11 grams for the 29mm plug adding an additional 35grams to the wrong end of the rocket. I will weigh up some traditional material options tomorrow.

 

[Sooner Boomer]

Do you have engine hooks? If you're trying to save weight, you could make "engine-length" cylinders out of heavy cardboard (several wraps of manila folder might work). Glue a couple of corrugated cardboard disks (or simething else really thick but light) in for seal. Slather in glue to fireproof.

I wouldn't try to secure something like this with friction-fit tape. You might not get them back out.

 

[bad_idea]

What size body tube did you use to hold all of these motors? I've been evaluating possibilities for a ground-launched blackpowder cluster with a central motor tube to test composite airstarts (to pave the way for future staged builds), and I have mostly settled on 18 for the clustered tubes and 29 for the central airstart simply because 24 & 29 seemed - to this rocketeer who mostly builds min. di. 18 and 24mm rockets so far - to require a fantastically large body tube.

 

[heada]

Foam plugs that the top and bottom have cardboard glued to them(cut from cereal box) Very lightweight, cardboard will give flameproofing and should seal the unused MMTs

 

[Nateairman]

What size body tube did you use to hold all of these motors? I've been evaluating possibilities for a ground-launched blackpowder cluster with a central motor tube to test composite airstarts (to pave the way for future staged builds), and I have mostly settled on 18 for the clustered tubes and 29 for the central airstart simply because 24 & 29 seemed - to this rocketeer who mostly builds min. di. 18 and 24mm rockets so far - to require a fantastically large body tube.

It is 5.5 LOC tubing. If the cluster is tightened up it will fit in a much smaller tube. The potential weight savings may be enough to use a 29mm air start motor in the center. I may weigh up all the components and see if it would still be a mid power rocket.

Although black powder motors start easily I have found the performance per weight to be challenging to design large clusters around.

 

[Nateairman]

Final tally is 1,490 grams. The physical cg was slightly behind the sim cg but still over 1 caliber. Sim'd cal was 1.36 with a difference between the Cg's being about 20mm.
F44W gives plenty of velocity off the rail.
Time to set up a launch!

 

[DAllen]

This is still considered MPR?

 

[Nateairman]

This is still considered MPR?

I believe so. Please correct me if I am wrong. Less than 160Ns of impluse and under 1.5kg. That being said though, it will not be flown unless conditions and site are suitable.

 

[GalantVR41062]

Is this less then 1500grams on the launch pad? If so then yes it's a class 1 rocket according to the FAA.

https://www.nar.org/high-power-rocketry-info/understanding-faa-regulations/

 

[heada]

What is the total propellant mass? That's another FAA limit.

 

[Nateairman]

Is this less then 1500grams on the launch pad? If so then yes it's a class 1 rocket according to the FAA.

https://www.nar.org/high-power-rocketry-info/understanding-faa-regulations/

1490grams ready to fly so yes under 1500.

What is the total propellant mass? That's another FAA limit.

Total propellant mass 19.7grams per motor. 3 motors for the flight 59.1 grams. Average thrust 44Ns times 3 is 132Ns total average thrust.

Discretion is advised.

 

[Nateairman]

This last weekend was ideal at our flying field. The rocket performed extremely well. I am very happy with it. The sim'd altitude is 708' and by the look of the flight I would say it was not any higher than that.

The only mishap was my error. The chute was accidentally choked by the recovery blanket. It fell relatively slow and the field has tall grass, so the only damage was one fin which is an easy repair. I am now changing my chute protection attachment for the model and plan to fly it again soon, weather depending of course.
Photo credits to my friend Phil

 

[Bat-mite]

This last weekend was ideal at our flying field. The rocket performed extremely well. I am very happy with it. The sim'd altitude is 708' and by the look of the flight I would say it was not any higher than that.

The only mishap was my error. The chute was accidentally choked by the recovery blanket. It fell relatively slow and the field has tall grass, so the only damage was one fin which is an easy repair. I am now changing my chute protection attachment for the model and plan to fly it again soon, weather depending of course.
Photo credits to my friend Phil

Nice!

 

[Rob Campbell]

It's always good when a scratch built project performs well. Congratulations.

Rob

 

[gerbs4me]

Cool picture of the launch, gotta love scratch builts

 

[Nateairman]

Thank you everyone! I really enjoy scratch builds. Of course it helps to have some perimeters.

 

[Nateairman]

Just an update for this thread. I have the video of the launch. It is 3 cluster f44 with 3d printed plugs in the unused motor tubes. The rod was angled slightly away from out position in the event of a misfire. One rocket and a full day of RC flying. An epic day!

Video credit to my friend Phil.

 

[NoLimit]

Where did you get the launch pad for your rail? That has to be one of the cleanest looking pads I've seen.

.....nice rocket and enjoyed the video!

 

[Nateairman]

Where did you get the launch pad for your rail? That has to be one of the cleanest looking pads I've seen.

.....nice rocket and enjoyed the video!

NoLimit.

I make the pads.

They are clean and versatile.

 

[jqavins]

I only just started reading this. I was immediately struck by this:

Careful motor choice is required to keep it in the mid power range.

Do you have an engine block in that 29 mm tube? If not, you could load that center 29 mm tube with an H motor and use this rocket for an L1 cert flight. After that, there's no reason to limit yourself with such careful choices. There are lots of 29 mm H and I motors from AT and CTI.

 

[Nateairman]

I only just started reading this. I was immediately struck by thiso you have an engine block in that 29 mm tube? If not, you could load that center 29 mm tube with an H motor and use this rocket for an L1 cert flight. After that, there's no reason to limit yourself with such careful choices. There are lots of 29 mm H and I motors from AT and CTI.

No engine blocks. And yes it will fly really nicely as a L1 rocket. I just don't have the option for any high power launches here.

 

[Hobie1dog]

thanks for the video, good job on the rocket.