Derek's Level 2 Build

Discussions on mid/high powered model rockets using F powered motors and above.

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OverTheTop
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Re: Derek's Level 2 Build

Postby OverTheTop » Sun Jul 07, 2019 8:27 pm

Looks like a well thought-out design for the NC. Designing for 3D printing is a great paradigm shift and fun too!
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Re: Derek's Level 2 Build

Postby Aquaman33 » Sun Jul 07, 2019 8:56 pm

OverTheTop wrote:Looks like a well thought-out design for the NC. Designing for 3D printing is a great paradigm shift and fun too!


Thanks OTT. It has definitely been a lot of fun working on these designs.

My CAD skills are still a bit ordinary. I sometimes have ideas in my head that I can't translate into CAD designs, but I am slowly improving.

I bought some reasonable quality digital metal calipers, and they have been really useful.

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Re: Derek's Level 2 Build

Postby OverTheTop » Sun Jul 07, 2019 9:19 pm

My CAD skills are still a bit ordinary. I sometimes have ideas in my head that I can't translate into CAD designs, but I am slowly improving.

Sounds like where I am at. I drive SolidWorks like a Neanderthal I think, but a bit of head-scratching gets me where I need to go in the end :) .
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Re: Derek's Level 2 Build

Postby SpaceManMat » Mon Jul 08, 2019 9:25 am

OverTheTop wrote:
My CAD skills are still a bit ordinary. I sometimes have ideas in my head that I can't translate into CAD designs, but I am slowly improving.

Sounds like where I am at. I drive SolidWorks like a Neanderthal I think, but a bit of head-scratching gets me where I need to go in the end :) .


Arg! You guys are killing me. Need to really get into it.
QRS: 124
AMRS: 32 L2 RSO
Highest Altitude: 13,647 feet
Fastest Flight: Mach 1.55
Largest Motor: CTI 1115J530 IM
Current Project: X Wing

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Re: Derek's Level 2 Build

Postby Aquaman33 » Mon Jul 08, 2019 10:18 am

My first attempt at 3D printing the nose cone plate was not a great success. It came out shaped a bit like a taco. I believe this is to do with heat getting trapped in the part while its printing and causing it to warp.

So I upgraded the cooling fan on my printer and printed a fan duct which improves the flow of air. The blue bits are the upgrades.

Image

Second attempt and it came out almost perfectly flat.

Top side.
Image

Bottom side.
Image

Top side with everything installed (the mounting screws are installed the wrong way around in this photo :oops: )
Image

Bottom side with everything installed.
Image

Space was really at a premium. Several of the components need to be touching each other to fit and the screw holes that will be used to secure the tongue are countersunk underneath the buzzers. Don't think I could manage this level of accuracy with plywood.

And finally test fitting inside the nose cone. I'll add some washers before launch.
Image

This is a very simple location device as our club often launches near crops on a farm.

For my L1 build I used tilt switches and a single buzzer up inside the nose cone. The tilt switches kept going off during prep and it wasn't loud enough. So for this project I have gone for a timer and 2 buzzers mounted outside of the nose cone. Some rather unscientific outdoor testing suggests you will be able to hear it from about 50m away (except on windy days when you probably won't hear it at all :D ).

Once the rocket is ready for launch I will turn the rotary switch. This will start a timer and the red LED flashes to confirm the timer is running. The rocket is launched and after a pre-determined period of time the buzzers will start buzzing to help locate the rocket on the ground.

After another pre-determined period of time the buzzers switch off, but the LED continues to flash. This will conserve the batteries and make the rocket easier to locate at night. The LED is not very bright, but you can see it flashing from a reasonable distance away.

I am thinking of using a simple relay timer to make this work, but I may upgrade to a little Arduino if I work out how to do it. I am quite useless when it comes to electronics.

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Re: Derek's Level 2 Build

Postby Aquaman33 » Tue Jul 09, 2019 12:48 pm

Not a very exciting update today, but I made a tongue for my nose cone electronics.

I started by printing a full size nose cone template from OpenRocket.
Image

I then used the template to design a tongue that would fit inside the nose cone.

I cut the tongue out of 4mm balsa and laminated it with carbon and epoxy.
Image

After letting it cure for 48 hours I gave it a clear coat of epoxy to seal it.
Image

Test fitting the tongue in the bulkhead plate.
Image

Image

I am a big fan of balsa/carbon laminates. It's incredibly strong and light especially when the balsa is more than 3mm thick. The spacing between the carbon layers that you get with 3mm plus balsa adds a lot of strength.

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Re: Derek's Level 2 Build

Postby OverTheTop » Tue Jul 09, 2019 2:47 pm

That's the biggest tongue depressor I have seen!
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Re: Derek's Level 2 Build

Postby Aquaman33 » Sun Nov 03, 2019 9:11 pm

This thread (and this project) had gone a little dormant as I have been procrastinating.

The design of this rocket just wasn't doing it for me, so I decided to make some changes. It's my L2 so I want it to be right. :D

The result of lots of pondering is this:

Image

Image

The proposed changes are:
- Up size the rear body tube to 150mm diameter, with a transition down to the 100mm front end.
- Up size the motor mount to 54mm. I was reluctant to spend the money on this upgrade, but I listened to the feedback on this thread.
- Changed the fin design, so the rear edge is swept forward to reduce the chance of fin damage on landing.
- Switched from dual deploy to single deploy (from the nose cone) with motor deployment as back up.

I prefer this design because its a much more interesting rocket. The larger rear body tube adds weight and drag which reduces apogee to around 2,000 feet on most J motors. At that altitude I think I can manage without a drogue, so I can simplify the design and use single deployment. I like simple for certification flights. :)

I may invest in a chute release if I want it to come down quicker.

I plan to 3d print the transition, but (as usual) I have concerns about Z axis weakness. I obviously don’t want the rocket snapping in half, so I plan to run the 54mm motor mount tube through the transition to add strength. I may also reinforce the transition with some carbon fiber rods, or I may reinforce the cardboard mount mount tube with fiber glass.

The transition will probably be epoxied into the rear body tube. The front body tube will be secured with rivets or screws. This allows me to switch to a different front end if I want to upgrade in the future (eg. to a dual deploy front end).

OpenRocket is giving a stability caliber of approximately 1.6x for some J motors. This is a bit low for my liking, especially if I end up building the back end a little heavy. But this stability is calculated based on the diameter of the rear body tube.

Does anyone know if there are special considerations for the calculation of stability in rockets with transitions?

Can you generally get away with a lower number because the front end is thinner?

Should stability be calculated based on the average diameter?

I realise I can always add nose weight, but I don’t want to do that if it's not necessary.

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Re: Derek's Level 2 Build

Postby air.command » Tue Nov 05, 2019 6:43 pm

That's an interesting design Derek. I don't think I have seen a motor mount go through the transition, but looks good! With a draggy back end like that, will you be using shear pins on the nosecone to avoid drag separation, especially if you end up adding nose weight?
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Re: Derek's Level 2 Build

Postby Aquaman33 » Tue Nov 05, 2019 7:43 pm

air.command wrote:That's an interesting design Derek. I don't think I have seen a motor mount go through the transition, but looks good! With a draggy back end like that, will you be using shear pins on the nosecone to avoid drag separation, especially if you end up adding nose weight?


Yes, I think shear pins will be required. As you know I have experienced a bit of drag separation and the it’s not good!

My only concern regarding shear pins is that I was going to use motor ejection as my back up. I am not sure if the standard motor ejection would be powerful enough, so I may have to add a little extra black powder to the motor.....or add a second altimeter as back up.

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Re: Derek's Level 2 Build

Postby OverTheTop » Fri Nov 08, 2019 6:29 am

I use 3mm push rivets like this for my rockets:
images.jpg
images.jpg (4.91 KiB) Viewed 158 times


If you just push the outer in, and completely remove the center pin, the shear force is significantly reduced for an easier ejection.
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Re: Derek's Level 2 Build

Postby Aquaman33 » Fri Nov 08, 2019 8:06 am

OverTheTop wrote:I use 3mm push rivets like this for my rockets:
images.jpg

If you just push the outer in, and completely remove the center pin, the shear force is significantly reduced for an easier ejection.


Thanks OTC.

I have some rivets that look very similar to those, but I also have some of these sheer pins:

https://www.apogeerockets.com/Building-Supplies/Misc-Hardware/Nylon-Shear-Pins-20-pack

I will do some testing and decide which will work best.

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Re: Derek's Level 2 Build

Postby Aquaman33 » Fri Nov 08, 2019 8:07 am

Aquaman33 wrote:
OpenRocket is giving a stability caliber of approximately 1.6x for some J motors. This is a bit low for my liking, especially if I end up building the back end a little heavy. But this stability is calculated based on the diameter of the rear body tube.

Does anyone know if there are special considerations for the calculation of stability in rockets with transitions?

Can you generally get away with a lower number because the front end is thinner?

Should stability be calculated based on the average diameter?

I realise I can always add nose weight, but I don’t want to do that if it's not necessary.


Does anyone have any thoughts on my stability questions?

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Re: Derek's Level 2 Build

Postby SpaceManMat » Fri Nov 08, 2019 6:51 pm

If you want to know what diameter it’s using then look at the measurements for CG and CP, I think it will be the largest diameter.
Bigger question is what is stable for an odd shaped rocket. The caliber rule is based on an assumption that the rocket is of normal proportions, an alternative rule of thumb is 10% of rocket length.
Also, I’m not sure how fast this is going, but you might want to consider stability over the whole flight. This can be graphed
QRS: 124
AMRS: 32 L2 RSO
Highest Altitude: 13,647 feet
Fastest Flight: Mach 1.55
Largest Motor: CTI 1115J530 IM
Current Project: X Wing

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Re: Derek's Level 2 Build

Postby Aquaman33 » Mon Nov 18, 2019 3:57 pm

SpaceManMat wrote:If you want to know what diameter it’s using then look at the measurements for CG and CP, I think it will be the largest diameter.
Bigger question is what is stable for an odd shaped rocket. The caliber rule is based on an assumption that the rocket is of normal proportions, an alternative rule of thumb is 10% of rocket length.
Also, I’m not sure how fast this is going, but you might want to consider stability over the whole flight. This can be graphed


Thanks SpaceManMat.

The rocket is 166cm long.

OpenRocket is giving the following numbers:
    - CG 109cm
    - CP 139cm
    - Stability 1.98 x

139 - 109 = 30cm

30cm / 15cm (rear BT diameter) = Approx 2 x

So OpenRocket is definitely using the larger diameter to calculate stability.

If I am understanding the 10% rule correctly the CG needs to be 16.6cm ahead of the CP.
166cm (length) x 10% = 16.6cm ahead of the CP.

30cm is obviously a lot more than 16.6cm, so there is a good margin there.

Also worth noting:
    - Speed off the rail is a healthy 21 m/s
    - Thrust to weight is a healthy 11:1

So I am feeling reasonably confident. But happy to be hear other's thoughts.


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